Woody biomass estimation of Tarchonanthus camphoratus in three woodland stands at Naivasha, Kenya

Individual tree biomass equations were developed for a Tarchonanthus woodland and tested for their applicability in three woodland stands of Tarchonathus at Naivasha Kenya based on the felled tree measurements. Three homogenous woodland stands identified via the use of cluster analysis formed the basic sampling units. Forty-five Tarchonanthus camphoratus trees of varying diameter classes from 2 cm to 28 cm were selected and felled from the three stand types. Alternative relationships were analysed and the four best models are presented ( Tables 1 and 2 ). To test the accuracy of the developed models, a further fifteen trees per stand were felled and their dry weights calculated and compared with their estimated dry weights. For each model, validation was performed per stand with the aim of determining whether a particular model is applicable to a specific stand or to all stand types. The best model based on the adjusted R ², standard error of estimate and distribution of residuals is presented and compared with previously existing equations. The model uses the square root transformed form of biomass. It was concluded that the model presented here could be used to estimate tree biomass in all stands of the woodland dominated by T. camphoratus , which in many places produces nearly pure stands, excluding other woody species . The fact that the accuracy of estimation tended to vary slightly from stand to stand suggests that the model may only apply to this woodland and to any other whose structure does not differ significantly from it.  

  Table 1  Equations for estimation of standing biomass of Tarchonanthus camphoratus trees     

2.

Management impacts on vegetation dynamics of hyper‐eutrophicated fields at Berlin,Germany     

Franz Rebele 《应用植被学》2001,4(1):147-156

Abstract. This paper reports on vegetation dynamics on terrestrial, temperate grassland sites at the upper range of the productivity scale, i.e. on abandoned sewage fields (fields once used for waste water disposal) at Berlin‐Blankenfelde, Germany. I studied regeneration and the influence of different management practices (removal of top soil and mowing in late summer). Changes in species composition and cover were followed on permanent plots of 2m × 2m size through five years of vegetation development. At the outset of the experiment the abandoned fields were dominated by dense Urtica dioica /Elymus repens stands. Species richness was 7 species/ 4m², and it remained low on unmanaged plots during the time of observation (7.6 species/plot in year 5). Removal of 20 cm of top soil caused a severe decline of Urtica and a large increase in species richness (21 species in year 1 after disturbance). Mowing was slightly higher compared with unmown plots on both initially excavated and unexcavated plots. Total cover was always near 100 % (except immediately after top soil removal). Colonization of bare soil was very rapid and in late summer of the first year after disturbance cover already increased towards 100%. On all plots the vegetation was mostly dominated by perennial herbs and grasses. Winter season gaps are occupied by Galium aparine, a large‐seeded annual scrambling climber. Monocarpic perennials behaved as winter annuals in most cases. Woody species were inhibited by dense above‐ground biomass and litter cover. The paper questions whether succession on abandoned sewage fields may proceed towards a woodland stage and advises how vegetation of such hyper‐eutrophicated sites can be managed towards higher diversity.     

3.

Classification,composition, richness and diversity of British hedgerows     

D.D. French  R.P. Cummins 《应用植被学》2001,4(2):213-228

Abstract. A floristic classification of British hedgerows is constructed. Hedges (the woody, structural element) and hedge‐bottoms (the mainly herbaceous ground flora) were analysed separately because different natural and management processes were expected to affect them. The 11 hedge classes varied in size from five to over 500 plots. Over two‐thirds of all hedges were dominated by Crataegus spp. or Primus spinosa. Hedge‐bottoms were more evenly grouped into four classes whose species composition could be related to broad land use/habitat types: intensive arable, rotational/mixed farming, managed grasslands, and woodland. The woodland class was only 12% of the total, and species characteristic of true woodland habitats were uncommon even within that class, so our data do not support the hypothesis of hedgerows acting as‘woodland corridors’for plants. Richness/diversity scores differed markedly between different hedge and hedge‐bottom classes. The richest hedgerows, both in species and inferred habitats, were among the rarer types, while the most common classes (both hedge and hedge‐bottom) were consistently the poorest. Comparison of species composition and diversity in hedges and hedge‐bottoms, and associations between them, all supported the hypothesis that the relative importance of historical, management and ecological effects differed between the two parts of the hedgerow; hedges and hedge‐bottoms should be treated ecologically as largely independent units. The classifications and richness/diversity scores enable easy preliminary assessment of the conservation value of a hedgerow. They also enable individual hedgerows to be placed in a wider (national) context.     

4.

Tree species composition and diversity in Miombo woodlands between co‐managed and government‐managed regimes,Malawi     

Monica Fides Kalagho Gondwe  Coert Johannes Geldenhuys  Paxie Wanangwa Chikusie Chirwa  Emeline Sêssi Plagie Assd  Stephen Syampungani  Moses Azong Cho 《African Journal of Ecology》2021,59(1):225-240

Comparative information on the composition and diversity in tree species associations in Miombo woodland is limited. This study assessed how tree species associations across forest reserves of Miombo woodland in Malawi varied in composition and diversity concerning site factors and resource use disturbances under co‐management versus government management. Eighty nested circular plots, randomly selected in ArcGIS, were sampled to record stem diameter at breast height (DBH) of tree species: 0.04 ha for stems 5–29.9 cm DBH and 0.16 ha for stems ≥30 cm DBH. The recorded 109 tree species grouped into communities and 14 sub‐communities, using stem counts by species in TWINSPAN analysis. Sub‐divisions to level 5 showed eigenvalues ≥0.3, symbolising the stability of sub‐divisions. North/South sub‐divisions related to site factors; historical/current resource use influenced differences at levels 3–5. Species importance differed, indicating few important species in each sub‐community. Brachystegia and Julbernardia species showed importance across sub‐communities while Uapaca sansibarica in government management. Disturbances stimulated high species diversity. Recommendations include the need for a policy review towards group‐felling mature stands to stimulate regeneration and selective thinning of suppressed stems in stand development stages to maintain species diversity, productive recovery, diverse resource use value, and monitoring of harvesting impacts.     

5.

The diet of a small group of extralimital giraffe     

D. M. Parker  R. T. F. Bernard  S. A. Colvin 《African Journal of Ecology》2003,41(3):245-253

Giraffe are extralimital in the Eastern Cape Province, South Africa where recent local introductions have persisted despite limited research into their impact on the indigenous flora. The diet of 15 giraffe at the Shamwari Game Reserve was recorded by direct observation during summer (March/April) and winter (July/August) 2001, quantifying diet by frequency of occurrence (individual records scored and expressed as a percentage of the total). Preference indices were also calculated. Habitat use was measured by the number of hours giraffe fed in different habitats. The diet comprised of 14 plant species, the most important species being Rhus longispina (47.9%), Acacia karroo (25.7%) and Euclea undulata (17.6%). Importance of R. longispina, A. karroo and Tarchonanthus camphoratus fluctuated seasonally. Rhus longispina was more important in winter with a corresponding decrease in feeding on A. karroo. Tarchonanthus camphoratus was only consumed during summer. Acacia karroo thickets (previously disturbed areas) were utilized most (summer 12 h; winter 9 h), with alternative habitats utilized more often in winter than in summer. We suggest that the seasonal fluctuation in the importance of R. longispina & A. karroo reflects the deciduous nature of A. karroo.     

6.

Restoring Structure in Late-Successional Sagebrush Communities by Thinning with Tebuthiuron     

Richard A. Olson  Thomas D. Whitson 《Restoration Ecology》2002,10(1):146-155

Late successional, dense Artemisia tridentata (big sagebrush) stands restrict associated plant species production, resulting in a monotypic, shrub‐dominated community that threatens biodiversity preservation and ecosystem function. Traditional practices to control A. tridentata can severely reduce or temporarily eliminate A. tridentata and other plant species. Thinning A. tridentata with low rates of the herbicide tebuthiuron enhances herbaceous plant production, community structure, ecosystem functioning, and biodiversity. Tebuthiuron was applied at rates of 0.11–1.0 kg ai/ha to A. tridentata‐dominated plots at Ten Sleep (1979), Lander (1993), and Waltman (1993), Wyoming. Changes in A. tridentata canopy cover, associated plant species biomass, and community composition were evaluated 13 and 14 years post‐treatment at Ten Sleep, and 2 and 4 years post‐treatment at Lander and Waltman. At all sites A. tridentata canopy cover decreased proportionally with increased tebuthiuron rate. Biomass of grasses increased as shrub biomass and cover decreased with increasing tebuthiuron rate. Forb biomass varied between treatments across sample year and site. Shifts from shrub‐dominated control to grass‐dominated treatment plots were attributable to biomass differences of A. tridentata and 2–3 grass species among treatments. The number of plant species was not significantly different between treatments at any site. Similarity indexes revealed progressively greater dissimilar plant composition between the control and sequential treatment plots of increased tebuthiuron rate. Incremental rates of tebuthiuron produce gradual changes in plant species composition without reducing species richness, which may have utility in certain restoration projects.     

7.

Effects of European colonization on indigenous ecosystems: post-settlement changes in tree stand structures in Eucalyptus–Callitris woodlands in central New South Wales, Australia     

Ian D. Lunt  Nigel Jones  Peter G. Spooner  Maree Petrow 《Journal of Biogeography》2006,33(6):1102-1115

Aim There has been considerable debate about pre‐settlement stand structures in temperate woodlands in south‐eastern Australia. Traditional histories assumed massive tree losses across the region, whereas a number of recent histories propose that woodlands were originally open and trees regenerated densely after settlement. To reconcile these conflicting models, we gathered quantitative data on pre‐settlement stand structures in Eucalyptus–Callitris woodlands in central New South Wales Australia, including: (1) tree density, composition, basal area and canopy cover at the time of European settlement; and (2) post‐settlement changes in these attributes. Location Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km² in central New South Wales, Australia. Methods We recorded all evidence of pre‐settlement trees, including stumps, stags and veteran trees, from 39 relatively undisturbed 1‐ha stands within 16 State Forests evenly distributed across the region. Current trees were recorded in a nested 900 m² quadrat at each site. Allometric relationships were used to estimate girth over bark at breast height, tree basal area, and crown diameter from the girth of cut stumps. A post‐settlement disturbance index was developed to assess correlations between post‐settlement disturbance and attributes of pre‐settlement stands. Results The densities of all large trees (> 60 cm girth over bark at breast height) were significantly greater in current stands than at the time of European settlement (198 vs. 39 trees ha^?1). Pre‐settlement and current stands did not differ in basal area. However, the proportional representation of Eucalyptus and Callitris changed completely. At the time of settlement, stands were dominated by Eucalyptus (78% of basal area), whereas current stands are dominated by Callitris (74%). On average, Eucalyptus afforded 83% of crown cover at the time of settlement. Moreover, the estimated density, basal area and crown cover of Eucalyptus at the time of settlement were significantly negatively correlated with post‐settlement disturbance, which suggests that these results underestimate pre‐settlement Eucalyptus representation in the most disturbed stands. Main conclusions These results incorporate elements of traditional and recent vegetation histories. Since European settlement, State Forests have been transformed from Eucalyptus to Callitris dominance as a result of the widespread clearance of pre‐settlement Eucalyptus and dense post‐settlement recruitment of Callitris. Tree densities did increase greatly after European settlement, but most stands were much denser at the time of settlement than recent histories suggest. The original degree of dominance by Eucalyptus was unexpected, and has been consistently underestimated in the past. This study has greatly refined our understanding of post‐settlement changes in woodland stand structures, and will strengthen the foundation for management policies that incorporate historical benchmarks of landscape vegetation changes.     

8.

Vegetation-environment relations of a Middle Zambezi floodplain   总被引：2，自引：0，他引：2  

Dunham  Kevin M. 《Plant Ecology》1989,82(1):13-24

Detrended correspondence analysis was used to study the relationships between environmental factors and the species composition of vegetation on Zambezi River alluvium downstream of the Kariba hydroelectric dam. Grass, sedge and woody species were recorded in 73 stands in Mana Pools National Park, Zimbabwe. Grass and sedge species composition was related to the soil moisture regime, as indexed by soil texture and flooding frequency. The first woody plant ordination axis was related to a stand development gradient; Acacia albida was a pioneer species on lowlying sandbanks and the woody species richness of stands increased with their height above the Zambezi River. Two-way indicator species analysis identified 7 vegetation types which could be separated on the basis of their topsoil texture and flooding frequency. The types were: sandbanks; young A. albida woodland; A. albida woodland; A. albida dominated mixed woodland; mixed riverine woodland with understory; mixed riverine woodland; and grassland on clay soils.     

9.

Convergence Between Dung Beetle Assemblages of a Post-Mining Vegetational Chronosequence and Unmined Dune Forest   总被引：4，自引：0，他引：4  

Adrian L. V. Davis  Rudi J. van Aarde  Clarke H. Scholtz  Jaco H. Delport 《Restoration Ecology》2003,11(1):29-42

Abstract In Maputaland, South Africa vegetative and microclimatic changes on mined dunes drive the composition of the dung beetle fauna toward convergence with that in natural dune forest on unmined dunes. We assessed the pattern of these changes using a 23‐year vegetational chronosequence on mined dunes, which passes from grassland (approximately 1 year) to open Acacia shrubland thicket to Acacia karroo‐dominated woodland (approximately 9 years). Across this sequence, which represents successional stages in the restoration of dune forest, there was a sequential trend toward convergence in dung beetle species composition in both the entire species complement and, particularly, in shade specialist species. However, species abundance patterns showed a trend toward convergence only in early chronosequence Acacia woodland, followed by a decline in similarity between dung beetle assemblages of older Acacia woodland and unmined natural forest. This trend toward divergence was common both to the entire species complement, which includes widespread taxa, and to species endemic to Maputaland or the east coast. These trends in similarity and dissimilarity between dung beetle assemblages closely parallel the greater physiognomic and microclimatic similarity between early Acacia woodland and natural forest and the relative dissimilarity of older Acacia woodland. In conclusion, although percentage similarities between dung beetle assemblages of approximately 12‐year woodland and natural forests were comparable with those between each natural forest stand, decline in similarity in older woodland stands suggests that lasting convergence in dung beetle species abundance will only be attained once the Acacia woodland is replaced by secondary natural forest.     

10.

Long‐term effects of the abandonment of grazing on steppe‐like grasslands     

Z. Márton Enyedi  Eszter Ruprecht  Mónika Deák 《应用植被学》2008,11(1):55-62

Question: What are the consequences of grazing abandonment on the Stipa lessingiana dominated steppe‐like grasslands? What is the relative importance of management and environmental factors in causing variation in species composition and abundance in the continuously grazed and abandoned grassland stands? Location: Transylvanian Lowland, Romania. Methods: Repeated vegetation mapping of a grassland stand, where grazing was abandoned 35 years ago; re‐sampling six grassland stands surveyed 29–57 years ago. For revealing long‐term changes in species composition and rank abundance PCoA ordination was applied. The relative importance of management and environmental factors in structuring vegetation were explored by CCA ordination. Diversity, evenness and the relative number and abundance of red‐listed species were compared between managed and abandoned stands. Results: Our results pointed out that grasslands which were formerly grazed and dominated by S. lessingiana, in the long‐term absence of grazing, have been transformed into a S. pulcherrima dominated type. Management, probably by creating bare surfaces and preventing litter accumulation, had the strongest effect on the species composition and abundance in the grasslands. Abandoned grassland stands had lower diversity and evenness compared to continuously grazed stands. While at the same time, the relative number of threatened, rare species did not differ between managed and abandoned sites. Conclusion: Maintaining extensively grazed, as well as un‐managed, Stipa dominated grasslands would be important in order to create various habitat conditions for plant species, especially threatened and rare species, and promote diversity on the landscape scale.     

11.

Elephant herbivory in Majete Wildlife Reserve,Malawi     

Caroline G. Staub  Michael W. Binford  Forrest R. Stevens 《African Journal of Ecology》2013,51(4):536-543

Elephants have a major influence on vegetation structure, composition and ecosystem processes, and are primary agents of habitat change in Africa. At moderate‐to‐high population densities, elephants can damage vegetation, especially when enclosed in protected areas. This study examines the effects of elephant browsing on woody trees in Majete Wildlife Reserve (WR), south‐western Malawi. Regression analysis is used to assess the associations of six factors known to drive elephant browsing in other areas and determine which ones have the most influence on browsing at Majete WR. Twenty‐four per cent of tagged trees had been subject to elephant browsing. The model with vegetation type, stem diameter and distance from permanent water correctly predicted browsing for 80% of the observations. Elephants mostly favoured riparian woodlands, followed by Acacia‐dominated woodland and Brachystegia‐dominated woodland. Browsing occurrence was negatively related to distance from permanent water and diameter at breast height(DBH). A larger number of trees, sampled at random and covering a larger portion of the reserve would provide more reliable estimates of browsing and related factors. Knowledge of time‐ and site‐specific factors affecting elephant browsing can be used to forecast future habitat transformations and manipulate the range of the elephants within the reserve.     

12.

Changes in the ground flora in Wytham Woods,southern England from 1974 to 1991 – implications for nature conservation     

K.J. Kirby  R.C. Thomas 《植被学杂志》2000,11(6):871-880

Abstract. The ground flora (vascular plants < 2 m high, excluding trees and shrubs) was recorded in 1974 and 1991 from 163 permanent 10 m x 10 m plots arranged on a systematic grid across Wytham Woods, near Oxford (UK). The Woods cover about 320 ha, are predominantly deciduous, but of varying ages and management types. The total number of species found (173, 167 respectively), the mean richness per plot (16.7, 17.2) and the breakdown of the species list between different species types (ancient woodland indicators, other woodland species, non‐woodland species) showed no significant differences between 1974 and 1991, but mean ground cover declined from 80% to 64%. Ancient woodland indicators as a group showed less change between the years than species associated with the open glades and grassland patches in the wood. Some species increased in frequency across the woodland including Arum maculatum, Brachypodium sylvaticum, Deschampsia cespitosa and Poa trivialis; while others such as Ajugareptans, Angelica sylvestris and Circaea lutetiana declined. Mean cover of Rubus fruticosus per plot declined from 35% to 6% and of Mercurialis perennis from 32 to 24%. More species were lost from plantations than from semi‐natural stands. The results are based on only two times, so inferences on possible causes must be drawn with caution. However the results are consistent with the effects of (1) the changing conditions associated with stand growth, particularly in the plantations, and (2) an increase in browsing/grazing by deer. No evidence was found for an effect of changing soil nitrogen levels on the vegetation. Changes in the ground flora as well as the woody layers, and in managed as well as unmanaged stands should be monitored, if nature conservation objectives are to be met.     

13.

Multiple successional pathways of boreal forest stands in central Canada     

Anthony R. Taylor  Han Y. H. Chen 《Ecography》2011,34(2):208-219

Predicting forest composition change through time is a key challenge in forest management. While multiple successional pathways are theorized for boreal forests, empirical evidence is lacking, largely because succession has been inferred from chronosequence and dendrochronological methods. We tested the hypotheses that stands of compositionally similar overstory may follow multiple successional pathways depending on time since last stand‐replacing fire (TSF), edaphic conditions, and presence of intermediate disturbances. We used repeated measurements from combining sequential aerial photography and ground surveys for 361 boreal stands in central Canada. Stands were measured in 8–15 yr intervals over a ~ 60 yr period, covering a wide range of initial stand conditions. Multinomial logistic regression was used to analyze stand type transitions. With increasing TSF, stands dominated by shade‐intolerant Pinus banksiana, Populus sp., and Betula papyrifera demonstrated multiple pathways to stands dominated by shade‐tolerant Picea sp., Abies balsamea, and Thuja occidentalis. Their pathways seemed largely explained by neighborhood effects. Succession of stands dominated by shade‐tolerant species, with an exception of stands dominated by Picea sp., was not related to TSF, but rather dependent on edaphic conditions and presence of intermediate disturbances. Varying edaphic conditions caused divergent pathways with resource limited sites being dominated by nutrient‐poor tolerant species, and richer sites permitting invasion of early successional species and promoting species mixtures during succession. Intermediate disturbances promoted deciduous persistence and species diversity in A. balsamea and mixed‐conifer stands, but no evidence was detected to support “disturbance accelerated succession”. Our results demonstrate that in the prolonged absence of stand‐replacing disturbance boreal forest stands undergo multiple succession pathways. These pathways are regulated by neighborhood effects, resource availability, and presence of intermediate disturbance, but the relative importance of these regulators depends on initial stand type. The observed divergence of successional pathways supports the resource‐ratio hypothesis of plant succession.     

14.

Influence of rocky landscape features and fire regime on vegetation dynamics in Appalachian Quercus forests     

Stephen A. Signell  Marc D. Abrams 《植被学杂志》2006,17(5):675-684

Question : How do interactions between rocky landscape features and fire regime influence vegetation dynamics? Location : Continental Eastern USA. Methods : We measured vegetation, disturbance and site characteristics in 40 pairs of rocky and non‐rocky plots: 20 in recently burned stands, and 20 in stands with no evidence of recent fire (‘unburned’ stands). Two‐way analysis of variance (ANOVA) was used to assess the main and interaction effects of fire and rock cover on plant community composition. Results : In burned stands, rock cover had a strong influence on vegetation. Non‐rocky ‘matrix’ forests were dominated by Quercus, and had abundant ground cover and advance regeneration of early and mid‐successional tree species. Burned rocky patches supported greater density of fire‐sensitive species such as Acer rubrum, Sassafras albidum and Nyssa sylvatica and had little advance regeneration or ground cover. Quercus had fewer fire scars and catfaces (open, basal wounds) on rocky patches, suggesting that rocky features mitigate fire severity. In unburned stands, differences between rocky and non‐rocky patches were less distinct, with both patch types having sparse ground cover, little tree regeneration, and high understorey densities of relatively shade tolerant A. rubrum, N. sylvatica and Betula lenta. Conclusion : Under a sustained fire regime, heterogeneity in rock cover created a mosaic where fire‐adapted species such as Quercus dominate the landscape, but where fire‐sensitive species persisted in isolated pockets of lower fire severity. Without fire, species and landscape richness may decline as early‐mid successional species are replaced by more shade tolerant competitors.     

15.

Fire frequency regulates tussock grass composition,structure and resilience in endangered temperate woodlands     

SUZANNE M. PROBER  KEVIN R. THIELE  IAN D. LUNT 《Austral ecology》2007,32(7):808-824

Abstract The importance of disturbance for regulating the structure and diversity of grassy ecosystems is widely recognized, but disturbance‐mediated interactions between grassland composition and grassland resilience, and consequent implications for conservation management, are less well documented. We established replicated burning, mowing and (non‐livestock) grazing regimes in two contrasting grassy woodland remnants in south‐eastern Australia, and monitored the dynamics and resilience of the matrix‐forming tussock grasses, Poa sieberiana (Poa) and Themeda australis (Themeda), over 12 years. Introduction of frequent burning to a Poa‐dominated understorey in a rarely burnt woodland enhanced dominance by Themeda, and conversely, reduced fire frequency in a frequently burnt Themeda grassland substantially increased Poa abundance. Burning was potentially detrimental in the Poa‐dominated woodland, but sward resilience (recovery after the 2002 burn) increased as Themeda increased with repeated burning. By contrast, the Themeda grassland was resilient to 4‐ and 8‐yearly burning, but biennial burning led to poor resilience and high tussock mortality under drought conditions. Contrary to other mesic grasslands, cessation of burning had not caused sward collapse by 14 years post‐fire despite high litter accumulation, potentially due to compensatory growth of Poa, lower site productivity and drought. Biennial mowing without slash removal was similar to 4‐yearly burning in effects, while exclusion from kangaroo and rabbit grazing significantly increased sward biomass and contributed to increased Poa cover and inflorescence production. We conclude that functional complementarity associated with mixed dominants enhances resilience to variable disturbance regimes, and that below certain thresholds of abundance of each dominant, this resilience declines. Conservation management of Themeda–Poa ecosystems should thus aim to maintain an effective balance of these dominants.     

16.

Plant communities,species richness and their environmental correlates in the sandy heaths of Little Desert National Park,Victoria     

A. Hahs  N. J. Enright  I. Thomas 《Austral ecology》1999,24(3):249-257

Plant community composition and its likely environmental controls were investigated for 200 sample plots (each 100 m²) from Mediterranean-type vegetation in the Little Desert National Park, Victoria. TWINSPAN classification revealed four readily identifiable vegetation types; mallee-broombush, heathland, stringybark open woodland, and an assemblage intermediate between mallee-broombush and heathland referred to here as broom-heath. Mallee-broombush was found on Parilla Sands characterized by high Ca levels relative to heathland and stringybark open woodlands on unconsolidated Lowan Sands. The first axis of a 2 dimensional non-metric MDS ordination also divided heathlands (high axis scores) from mallee-broombush (low scores), while the second separated these vegetation types from stringybark woodlands and broom-heath. Vector-fitting revealed significant correlations between the locations of samples in ordination space and exchangeable soil Ca, soil colour, aspect and Shannon–Weiner diversity. Highest species richness/diversity was associated with the ecotonal area between Parilla and Lowan Sands (i.e. broom-heath) where a number of species characteristic of different assemblages had overlapping ranges. The fire-sensitive conifer, Callitris rhomboidea, was preferentially located in stringybark woodland and broom-heath vegetation types. Its presence was positively associated with high species richness and aspects having a southerly component. Four Callitris stands sampled for population structure were all > 40 years old and showed evidence of interfire recruitment from seeds released by old, serotinous cones. Overall, results suggest that variations in plant community composition and structure in the eastern block of the Little Desert are primarily due to variations in soil properties associated with the distribution of the two dominant substrate types, Parilla Sand and Lowan Sand. However, the interplay of topography and fire behaviour has probably been more important than substrate type in determining the distribution and population structure of longer-lived, fire-sensitive species such as Callitris rhomboidea.     

17.

Response of pine natural regeneration to small‐scale spatial variation in a managed Mediterranean mountain forest     

Ignacio Barbeito  Marie‐Josée Fortin  Fernando Montes  Isabel Cañellas 《应用植被学》2009,12(4):488-503

Questions: What influence do management practices and previous tree and shrub stand structure have on the occurrence and development of natural regeneration of Pinus sylvestris in Mediterranean mountain forests? How are the fine‐scale and environmental patterns of resources affected and what impact does this have on the distribution of the regeneration? Location: A Pinus sylvestris Mediterranean mountain forest in central Spain. Methods: Upperstory trees and regeneration (seedlings and saplings) were mapped in four 0.5‐ha plots located in two types of stand with different management intensities (even‐aged and uneven‐aged stands). Environmental variables were recorded at the nodes of a grid within the plots. The relationships between the upperstory and regeneration were evaluated by bivariate point pattern analysis; redundancy analysis ordination and variation partitioning were performed to characterize regeneration niches and the importance of the spatial component. Results: Seedlings and saplings presented a clumped structure under both types of management and their distribution was found to be related to the spatial distribution of favourable microsites. Regeneration was positively related to conditions of partial cover with high soil water content during the summer. More than half of the explained variance was spatially structured in both types of stand. This percentage was particularly high in the even‐aged stands where the pattern of regeneration was highly influenced by the gaps created by harvesting. Conclusions: The spatial distribution of the tree and shrub upperstory strongly influences regeneration patterns of P. sylvestris. Current management practices, promoting small gaps, partial canopy cover and moderate shade in even‐aged stands, or favouring tree and shrub cover in the case of uneven‐aged stands, appears to provide suitable conditions for the natural regeneration of P. sylvestris in a Mediterranean climate.     

18.

Litterfall of epiphytic macrolichens in Nothofagus forests of northern Patagonia,Argentina: Relation to stand age and precipitation     

MAYRA S. CALDIZ  J RG BRUNET 《Austral ecology》2006,31(3):301-309

Abstract: The objective of this study was to analyse how stand age and precipitation influence abundance and diversity of epiphytic macrolichens in southern beech Nothofagus forests, estimated by lichen litter sampling. Five sites of Nothofagus dombeyi (Mirbel) Oersted were selected in Nahuel Huapi National Park, Argentina. At each site, lichen fragments from the forest floor were collected at 12.5 m² plots in pairs of young and mature N. dombeyi forest. Additionally, two sites with multi‐aged subalpine Nothofagus pumilio (Poepp. et Endl.) Krasser forest were investigated in a similar manner. Average litterfall biomass per stand varied from less than 1 kg ha^?1 in a young low‐precipitation stand to a maximum of 20 kg ha^?1 in a mature high‐precipitation stand. In places with higher precipitation, litterfall biomass in N. dombeyi forest was considerably higher in old stands as compared with young ones. In places with less than 2000 mm of precipitation, differences in biomass were less pronounced. Old humid stands contained about twice as many taxa in the litter as old low‐precipitation stands and young stands in general. Mature stands in low‐precipitation sites only contained 17% of the litter biomass as compared with mature stands in high‐precipitation sites. Epiphytic lichen composition changed from predominating fruticose lichens (Usnea spp. and Protousnea spp.) in low‐precipitation stands to Pseudocyphellaria spp., Nephroma spp. and other foliose lichens, in the high‐precipitation stands. There were no clear differences in the proportion of fruticose and foliose lichens between young and old stands. Fruticose lichens dominated litter biomass in both N. pumilio sites.     

19.

Conservation management of Pinus palustris ecosystems from a landscape perspective     

L. Katherine Kirkman  Robert J. Mitchell 《应用植被学》2006,9(1):67-74

Question: Do case studies from silvicultural and restoration studies and applied conservation management in second‐growth Pinus palustris stands provide unique insights for conservation models? Methods: A review of management paradigms that conserve the high biological diversity and rare species, drawn from characteristics in both second‐growth and old‐growth stands, is presented for fire‐maintained Pinus palustris (longleaf pine) forests. Results: A common assumption that old‐growth stands provide the primary information for the development of conservation management strategies de‐emphasizes lessons learned from second‐growth and restoration studies. Primary conservation management goals for the Pinus palustris ecosystem include the perpetual regeneration of the fire‐maintained forest and conservation of the characteristically high biological diversity and rare species. Several attributes, such as a sustained population of Picoides borealis (red‐cockaded woodpecker), Aristida stricta (wiregrass)‐dominated ground cover, and undisturbed upland‐wetland ecotones, can predict a diverse and ecologically functional ecosystem. Such indicators are linked to critical structural and functional features of the system and reflect previous land management histories that suggest sustainable approaches. Conclusions: A traditional definition of ‘old‐growth’ relying on overstorey may be limited in describing important features of healthy, diverse Pinus palustris ecosystems. Some characteristics are significantly more important for maintenance of diversity than age of the trees and these features may be present in old‐ or second‐growth forests. We advocate that the management history, structural characteristics and landscape context of stands that harbour desirable conservation attributes (red‐cockaded woodpeckers, wiregrass, gopher tortoises and undisturbed upland‐wetland ecotones) can be used as indicators to identify important conservation and forest management principles.     

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Demography of the invasive shrub Scotch broom (Cytisus scoparius) at Barrington Tops,New South Wales: insights for management.     

P. O. Downey  J. M. B. Smith 《Austral ecology》2000,25(5):477-485

The exotic shrub Scotch Broom (Cytisus scoparius) has invaded large areas of eucalypt woodland at Barrington Tops, New South Wales, where it forms dense stands that have significant impacts on vegetation structure, flora and fauna. Data are presented from four 25 m² plots, which have been studied since 1985. Two plots were located in uniform broom thickets of different ages, and two were located across the margins of broom stands, which have since expanded to cover the entire plots. All broom plants in the plots (other than young seedlings, which were counted) were mapped, tagged and monitored annually. New seedlings appeared annually, but there was no relationship between their numbers (varying between years) and subsequent recruitment of older plants. The probability of seedlings reaching first flowering was less than 2%, and of surviving to mature size (>10 cm² basal area) was negligible. Seedlings mainly died through suppression (shade). Individuals less than 50 cm high were also browsed. Recruitment occurred only where light levels were high, either before closure of the broom canopy or after senescence had led to canopy opening. From approximately 12–30 years after initial invasion, broom stands underwent self‐thinning of mature plants, accelerated by collapse of plants on to each other. Recruitment of new, maturing plants, after this period produced a stand that was less dense than that found after initial invasion. Broom is creating more disturbance‐prone environments due to its impacts on other biota, likely alterations to the fire regime, and by harbouring feral pigs. Further disturbance favours broom, and elsewhere it has resulted in massive seedling regeneration. While fire or other disturbance can be used to stimulate germination, and thereby reduce a large part of the soil seed bank, denser broom infestations are likely to result unless follow‐up treatments can be applied over long time periods. A wiser management option, at least in the short term, may be avoidance of all disturbance, especially for stands of mature broom.     

Management impacts on vegetation dynamics of hyper‐eutrophicated fields at Berlin,Germany

Abstract. This paper reports on vegetation dynamics on terrestrial, temperate grassland sites at the upper range of the productivity scale, i.e. on abandoned sewage fields (fields once used for waste water disposal) at Berlin‐Blankenfelde, Germany. I studied regeneration and the influence of different management practices (removal of top soil and mowing in late summer). Changes in species composition and cover were followed on permanent plots of 2m × 2m size through five years of vegetation development. At the outset of the experiment the abandoned fields were dominated by dense Urtica dioica /Elymus repens stands. Species richness was 7 species/ 4m², and it remained low on unmanaged plots during the time of observation (7.6 species/plot in year 5). Removal of 20 cm of top soil caused a severe decline of Urtica and a large increase in species richness (21 species in year 1 after disturbance). Mowing was slightly higher compared with unmown plots on both initially excavated and unexcavated plots. Total cover was always near 100 % (except immediately after top soil removal). Colonization of bare soil was very rapid and in late summer of the first year after disturbance cover already increased towards 100%. On all plots the vegetation was mostly dominated by perennial herbs and grasses. Winter season gaps are occupied by Galium aparine, a large‐seeded annual scrambling climber. Monocarpic perennials behaved as winter annuals in most cases. Woody species were inhibited by dense above‐ground biomass and litter cover. The paper questions whether succession on abandoned sewage fields may proceed towards a woodland stage and advises how vegetation of such hyper‐eutrophicated sites can be managed towards higher diversity.     

Classification,composition, richness and diversity of British hedgerows

Abstract. A floristic classification of British hedgerows is constructed. Hedges (the woody, structural element) and hedge‐bottoms (the mainly herbaceous ground flora) were analysed separately because different natural and management processes were expected to affect them. The 11 hedge classes varied in size from five to over 500 plots. Over two‐thirds of all hedges were dominated by Crataegus spp. or Primus spinosa. Hedge‐bottoms were more evenly grouped into four classes whose species composition could be related to broad land use/habitat types: intensive arable, rotational/mixed farming, managed grasslands, and woodland. The woodland class was only 12% of the total, and species characteristic of true woodland habitats were uncommon even within that class, so our data do not support the hypothesis of hedgerows acting as‘woodland corridors’for plants. Richness/diversity scores differed markedly between different hedge and hedge‐bottom classes. The richest hedgerows, both in species and inferred habitats, were among the rarer types, while the most common classes (both hedge and hedge‐bottom) were consistently the poorest. Comparison of species composition and diversity in hedges and hedge‐bottoms, and associations between them, all supported the hypothesis that the relative importance of historical, management and ecological effects differed between the two parts of the hedgerow; hedges and hedge‐bottoms should be treated ecologically as largely independent units. The classifications and richness/diversity scores enable easy preliminary assessment of the conservation value of a hedgerow. They also enable individual hedgerows to be placed in a wider (national) context.     

Tree species composition and diversity in Miombo woodlands between co‐managed and government‐managed regimes,Malawi

Comparative information on the composition and diversity in tree species associations in Miombo woodland is limited. This study assessed how tree species associations across forest reserves of Miombo woodland in Malawi varied in composition and diversity concerning site factors and resource use disturbances under co‐management versus government management. Eighty nested circular plots, randomly selected in ArcGIS, were sampled to record stem diameter at breast height (DBH) of tree species: 0.04 ha for stems 5–29.9 cm DBH and 0.16 ha for stems ≥30 cm DBH. The recorded 109 tree species grouped into communities and 14 sub‐communities, using stem counts by species in TWINSPAN analysis. Sub‐divisions to level 5 showed eigenvalues ≥0.3, symbolising the stability of sub‐divisions. North/South sub‐divisions related to site factors; historical/current resource use influenced differences at levels 3–5. Species importance differed, indicating few important species in each sub‐community. Brachystegia and Julbernardia species showed importance across sub‐communities while Uapaca sansibarica in government management. Disturbances stimulated high species diversity. Recommendations include the need for a policy review towards group‐felling mature stands to stimulate regeneration and selective thinning of suppressed stems in stand development stages to maintain species diversity, productive recovery, diverse resource use value, and monitoring of harvesting impacts.     

The diet of a small group of extralimital giraffe

Giraffe are extralimital in the Eastern Cape Province, South Africa where recent local introductions have persisted despite limited research into their impact on the indigenous flora. The diet of 15 giraffe at the Shamwari Game Reserve was recorded by direct observation during summer (March/April) and winter (July/August) 2001, quantifying diet by frequency of occurrence (individual records scored and expressed as a percentage of the total). Preference indices were also calculated. Habitat use was measured by the number of hours giraffe fed in different habitats. The diet comprised of 14 plant species, the most important species being Rhus longispina (47.9%), Acacia karroo (25.7%) and Euclea undulata (17.6%). Importance of R. longispina, A. karroo and Tarchonanthus camphoratus fluctuated seasonally. Rhus longispina was more important in winter with a corresponding decrease in feeding on A. karroo. Tarchonanthus camphoratus was only consumed during summer. Acacia karroo thickets (previously disturbed areas) were utilized most (summer 12 h; winter 9 h), with alternative habitats utilized more often in winter than in summer. We suggest that the seasonal fluctuation in the importance of R. longispina & A. karroo reflects the deciduous nature of A. karroo.     

Restoring Structure in Late-Successional Sagebrush Communities by Thinning with Tebuthiuron

Late successional, dense Artemisia tridentata (big sagebrush) stands restrict associated plant species production, resulting in a monotypic, shrub‐dominated community that threatens biodiversity preservation and ecosystem function. Traditional practices to control A. tridentata can severely reduce or temporarily eliminate A. tridentata and other plant species. Thinning A. tridentata with low rates of the herbicide tebuthiuron enhances herbaceous plant production, community structure, ecosystem functioning, and biodiversity. Tebuthiuron was applied at rates of 0.11–1.0 kg ai/ha to A. tridentata‐dominated plots at Ten Sleep (1979), Lander (1993), and Waltman (1993), Wyoming. Changes in A. tridentata canopy cover, associated plant species biomass, and community composition were evaluated 13 and 14 years post‐treatment at Ten Sleep, and 2 and 4 years post‐treatment at Lander and Waltman. At all sites A. tridentata canopy cover decreased proportionally with increased tebuthiuron rate. Biomass of grasses increased as shrub biomass and cover decreased with increasing tebuthiuron rate. Forb biomass varied between treatments across sample year and site. Shifts from shrub‐dominated control to grass‐dominated treatment plots were attributable to biomass differences of A. tridentata and 2–3 grass species among treatments. The number of plant species was not significantly different between treatments at any site. Similarity indexes revealed progressively greater dissimilar plant composition between the control and sequential treatment plots of increased tebuthiuron rate. Incremental rates of tebuthiuron produce gradual changes in plant species composition without reducing species richness, which may have utility in certain restoration projects.     

Effects of European colonization on indigenous ecosystems: post-settlement changes in tree stand structures in Eucalyptus–Callitris woodlands in central New South Wales, Australia

Aim There has been considerable debate about pre‐settlement stand structures in temperate woodlands in south‐eastern Australia. Traditional histories assumed massive tree losses across the region, whereas a number of recent histories propose that woodlands were originally open and trees regenerated densely after settlement. To reconcile these conflicting models, we gathered quantitative data on pre‐settlement stand structures in Eucalyptus–Callitris woodlands in central New South Wales Australia, including: (1) tree density, composition, basal area and canopy cover at the time of European settlement; and (2) post‐settlement changes in these attributes. Location Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km² in central New South Wales, Australia. Methods We recorded all evidence of pre‐settlement trees, including stumps, stags and veteran trees, from 39 relatively undisturbed 1‐ha stands within 16 State Forests evenly distributed across the region. Current trees were recorded in a nested 900 m² quadrat at each site. Allometric relationships were used to estimate girth over bark at breast height, tree basal area, and crown diameter from the girth of cut stumps. A post‐settlement disturbance index was developed to assess correlations between post‐settlement disturbance and attributes of pre‐settlement stands. Results The densities of all large trees (> 60 cm girth over bark at breast height) were significantly greater in current stands than at the time of European settlement (198 vs. 39 trees ha^?1). Pre‐settlement and current stands did not differ in basal area. However, the proportional representation of Eucalyptus and Callitris changed completely. At the time of settlement, stands were dominated by Eucalyptus (78% of basal area), whereas current stands are dominated by Callitris (74%). On average, Eucalyptus afforded 83% of crown cover at the time of settlement. Moreover, the estimated density, basal area and crown cover of Eucalyptus at the time of settlement were significantly negatively correlated with post‐settlement disturbance, which suggests that these results underestimate pre‐settlement Eucalyptus representation in the most disturbed stands. Main conclusions These results incorporate elements of traditional and recent vegetation histories. Since European settlement, State Forests have been transformed from Eucalyptus to Callitris dominance as a result of the widespread clearance of pre‐settlement Eucalyptus and dense post‐settlement recruitment of Callitris. Tree densities did increase greatly after European settlement, but most stands were much denser at the time of settlement than recent histories suggest. The original degree of dominance by Eucalyptus was unexpected, and has been consistently underestimated in the past. This study has greatly refined our understanding of post‐settlement changes in woodland stand structures, and will strengthen the foundation for management policies that incorporate historical benchmarks of landscape vegetation changes.     

Vegetation-environment relations of a Middle Zambezi floodplain

Detrended correspondence analysis was used to study the relationships between environmental factors and the species composition of vegetation on Zambezi River alluvium downstream of the Kariba hydroelectric dam. Grass, sedge and woody species were recorded in 73 stands in Mana Pools National Park, Zimbabwe. Grass and sedge species composition was related to the soil moisture regime, as indexed by soil texture and flooding frequency. The first woody plant ordination axis was related to a stand development gradient; Acacia albida was a pioneer species on lowlying sandbanks and the woody species richness of stands increased with their height above the Zambezi River. Two-way indicator species analysis identified 7 vegetation types which could be separated on the basis of their topsoil texture and flooding frequency. The types were: sandbanks; young A. albida woodland; A. albida woodland; A. albida dominated mixed woodland; mixed riverine woodland with understory; mixed riverine woodland; and grassland on clay soils.     

Convergence Between Dung Beetle Assemblages of a Post-Mining Vegetational Chronosequence and Unmined Dune Forest

Abstract In Maputaland, South Africa vegetative and microclimatic changes on mined dunes drive the composition of the dung beetle fauna toward convergence with that in natural dune forest on unmined dunes. We assessed the pattern of these changes using a 23‐year vegetational chronosequence on mined dunes, which passes from grassland (approximately 1 year) to open Acacia shrubland thicket to Acacia karroo‐dominated woodland (approximately 9 years). Across this sequence, which represents successional stages in the restoration of dune forest, there was a sequential trend toward convergence in dung beetle species composition in both the entire species complement and, particularly, in shade specialist species. However, species abundance patterns showed a trend toward convergence only in early chronosequence Acacia woodland, followed by a decline in similarity between dung beetle assemblages of older Acacia woodland and unmined natural forest. This trend toward divergence was common both to the entire species complement, which includes widespread taxa, and to species endemic to Maputaland or the east coast. These trends in similarity and dissimilarity between dung beetle assemblages closely parallel the greater physiognomic and microclimatic similarity between early Acacia woodland and natural forest and the relative dissimilarity of older Acacia woodland. In conclusion, although percentage similarities between dung beetle assemblages of approximately 12‐year woodland and natural forests were comparable with those between each natural forest stand, decline in similarity in older woodland stands suggests that lasting convergence in dung beetle species abundance will only be attained once the Acacia woodland is replaced by secondary natural forest.     

Long‐term effects of the abandonment of grazing on steppe‐like grasslands

Question: What are the consequences of grazing abandonment on the Stipa lessingiana dominated steppe‐like grasslands? What is the relative importance of management and environmental factors in causing variation in species composition and abundance in the continuously grazed and abandoned grassland stands? Location: Transylvanian Lowland, Romania. Methods: Repeated vegetation mapping of a grassland stand, where grazing was abandoned 35 years ago; re‐sampling six grassland stands surveyed 29–57 years ago. For revealing long‐term changes in species composition and rank abundance PCoA ordination was applied. The relative importance of management and environmental factors in structuring vegetation were explored by CCA ordination. Diversity, evenness and the relative number and abundance of red‐listed species were compared between managed and abandoned stands. Results: Our results pointed out that grasslands which were formerly grazed and dominated by S. lessingiana, in the long‐term absence of grazing, have been transformed into a S. pulcherrima dominated type. Management, probably by creating bare surfaces and preventing litter accumulation, had the strongest effect on the species composition and abundance in the grasslands. Abandoned grassland stands had lower diversity and evenness compared to continuously grazed stands. While at the same time, the relative number of threatened, rare species did not differ between managed and abandoned sites. Conclusion: Maintaining extensively grazed, as well as un‐managed, Stipa dominated grasslands would be important in order to create various habitat conditions for plant species, especially threatened and rare species, and promote diversity on the landscape scale.     

Elephant herbivory in Majete Wildlife Reserve,Malawi

Elephants have a major influence on vegetation structure, composition and ecosystem processes, and are primary agents of habitat change in Africa. At moderate‐to‐high population densities, elephants can damage vegetation, especially when enclosed in protected areas. This study examines the effects of elephant browsing on woody trees in Majete Wildlife Reserve (WR), south‐western Malawi. Regression analysis is used to assess the associations of six factors known to drive elephant browsing in other areas and determine which ones have the most influence on browsing at Majete WR. Twenty‐four per cent of tagged trees had been subject to elephant browsing. The model with vegetation type, stem diameter and distance from permanent water correctly predicted browsing for 80% of the observations. Elephants mostly favoured riparian woodlands, followed by Acacia‐dominated woodland and Brachystegia‐dominated woodland. Browsing occurrence was negatively related to distance from permanent water and diameter at breast height(DBH). A larger number of trees, sampled at random and covering a larger portion of the reserve would provide more reliable estimates of browsing and related factors. Knowledge of time‐ and site‐specific factors affecting elephant browsing can be used to forecast future habitat transformations and manipulate the range of the elephants within the reserve.     

Changes in the ground flora in Wytham Woods,southern England from 1974 to 1991 – implications for nature conservation

Abstract. The ground flora (vascular plants < 2 m high, excluding trees and shrubs) was recorded in 1974 and 1991 from 163 permanent 10 m x 10 m plots arranged on a systematic grid across Wytham Woods, near Oxford (UK). The Woods cover about 320 ha, are predominantly deciduous, but of varying ages and management types. The total number of species found (173, 167 respectively), the mean richness per plot (16.7, 17.2) and the breakdown of the species list between different species types (ancient woodland indicators, other woodland species, non‐woodland species) showed no significant differences between 1974 and 1991, but mean ground cover declined from 80% to 64%. Ancient woodland indicators as a group showed less change between the years than species associated with the open glades and grassland patches in the wood. Some species increased in frequency across the woodland including Arum maculatum, Brachypodium sylvaticum, Deschampsia cespitosa and Poa trivialis; while others such as Ajugareptans, Angelica sylvestris and Circaea lutetiana declined. Mean cover of Rubus fruticosus per plot declined from 35% to 6% and of Mercurialis perennis from 32 to 24%. More species were lost from plantations than from semi‐natural stands. The results are based on only two times, so inferences on possible causes must be drawn with caution. However the results are consistent with the effects of (1) the changing conditions associated with stand growth, particularly in the plantations, and (2) an increase in browsing/grazing by deer. No evidence was found for an effect of changing soil nitrogen levels on the vegetation. Changes in the ground flora as well as the woody layers, and in managed as well as unmanaged stands should be monitored, if nature conservation objectives are to be met.     

Multiple successional pathways of boreal forest stands in central Canada

Predicting forest composition change through time is a key challenge in forest management. While multiple successional pathways are theorized for boreal forests, empirical evidence is lacking, largely because succession has been inferred from chronosequence and dendrochronological methods. We tested the hypotheses that stands of compositionally similar overstory may follow multiple successional pathways depending on time since last stand‐replacing fire (TSF), edaphic conditions, and presence of intermediate disturbances. We used repeated measurements from combining sequential aerial photography and ground surveys for 361 boreal stands in central Canada. Stands were measured in 8–15 yr intervals over a ~ 60 yr period, covering a wide range of initial stand conditions. Multinomial logistic regression was used to analyze stand type transitions. With increasing TSF, stands dominated by shade‐intolerant Pinus banksiana, Populus sp., and Betula papyrifera demonstrated multiple pathways to stands dominated by shade‐tolerant Picea sp., Abies balsamea, and Thuja occidentalis. Their pathways seemed largely explained by neighborhood effects. Succession of stands dominated by shade‐tolerant species, with an exception of stands dominated by Picea sp., was not related to TSF, but rather dependent on edaphic conditions and presence of intermediate disturbances. Varying edaphic conditions caused divergent pathways with resource limited sites being dominated by nutrient‐poor tolerant species, and richer sites permitting invasion of early successional species and promoting species mixtures during succession. Intermediate disturbances promoted deciduous persistence and species diversity in A. balsamea and mixed‐conifer stands, but no evidence was detected to support “disturbance accelerated succession”. Our results demonstrate that in the prolonged absence of stand‐replacing disturbance boreal forest stands undergo multiple succession pathways. These pathways are regulated by neighborhood effects, resource availability, and presence of intermediate disturbance, but the relative importance of these regulators depends on initial stand type. The observed divergence of successional pathways supports the resource‐ratio hypothesis of plant succession.     

Influence of rocky landscape features and fire regime on vegetation dynamics in Appalachian Quercus forests

Question : How do interactions between rocky landscape features and fire regime influence vegetation dynamics? Location : Continental Eastern USA. Methods : We measured vegetation, disturbance and site characteristics in 40 pairs of rocky and non‐rocky plots: 20 in recently burned stands, and 20 in stands with no evidence of recent fire (‘unburned’ stands). Two‐way analysis of variance (ANOVA) was used to assess the main and interaction effects of fire and rock cover on plant community composition. Results : In burned stands, rock cover had a strong influence on vegetation. Non‐rocky ‘matrix’ forests were dominated by Quercus, and had abundant ground cover and advance regeneration of early and mid‐successional tree species. Burned rocky patches supported greater density of fire‐sensitive species such as Acer rubrum, Sassafras albidum and Nyssa sylvatica and had little advance regeneration or ground cover. Quercus had fewer fire scars and catfaces (open, basal wounds) on rocky patches, suggesting that rocky features mitigate fire severity. In unburned stands, differences between rocky and non‐rocky patches were less distinct, with both patch types having sparse ground cover, little tree regeneration, and high understorey densities of relatively shade tolerant A. rubrum, N. sylvatica and Betula lenta. Conclusion : Under a sustained fire regime, heterogeneity in rock cover created a mosaic where fire‐adapted species such as Quercus dominate the landscape, but where fire‐sensitive species persisted in isolated pockets of lower fire severity. Without fire, species and landscape richness may decline as early‐mid successional species are replaced by more shade tolerant competitors.     

Fire frequency regulates tussock grass composition,structure and resilience in endangered temperate woodlands

Abstract The importance of disturbance for regulating the structure and diversity of grassy ecosystems is widely recognized, but disturbance‐mediated interactions between grassland composition and grassland resilience, and consequent implications for conservation management, are less well documented. We established replicated burning, mowing and (non‐livestock) grazing regimes in two contrasting grassy woodland remnants in south‐eastern Australia, and monitored the dynamics and resilience of the matrix‐forming tussock grasses, Poa sieberiana (Poa) and Themeda australis (Themeda), over 12 years. Introduction of frequent burning to a Poa‐dominated understorey in a rarely burnt woodland enhanced dominance by Themeda, and conversely, reduced fire frequency in a frequently burnt Themeda grassland substantially increased Poa abundance. Burning was potentially detrimental in the Poa‐dominated woodland, but sward resilience (recovery after the 2002 burn) increased as Themeda increased with repeated burning. By contrast, the Themeda grassland was resilient to 4‐ and 8‐yearly burning, but biennial burning led to poor resilience and high tussock mortality under drought conditions. Contrary to other mesic grasslands, cessation of burning had not caused sward collapse by 14 years post‐fire despite high litter accumulation, potentially due to compensatory growth of Poa, lower site productivity and drought. Biennial mowing without slash removal was similar to 4‐yearly burning in effects, while exclusion from kangaroo and rabbit grazing significantly increased sward biomass and contributed to increased Poa cover and inflorescence production. We conclude that functional complementarity associated with mixed dominants enhances resilience to variable disturbance regimes, and that below certain thresholds of abundance of each dominant, this resilience declines. Conservation management of Themeda–Poa ecosystems should thus aim to maintain an effective balance of these dominants.     

Plant communities,species richness and their environmental correlates in the sandy heaths of Little Desert National Park,Victoria

Plant community composition and its likely environmental controls were investigated for 200 sample plots (each 100 m²) from Mediterranean-type vegetation in the Little Desert National Park, Victoria. TWINSPAN classification revealed four readily identifiable vegetation types; mallee-broombush, heathland, stringybark open woodland, and an assemblage intermediate between mallee-broombush and heathland referred to here as broom-heath. Mallee-broombush was found on Parilla Sands characterized by high Ca levels relative to heathland and stringybark open woodlands on unconsolidated Lowan Sands. The first axis of a 2 dimensional non-metric MDS ordination also divided heathlands (high axis scores) from mallee-broombush (low scores), while the second separated these vegetation types from stringybark woodlands and broom-heath. Vector-fitting revealed significant correlations between the locations of samples in ordination space and exchangeable soil Ca, soil colour, aspect and Shannon–Weiner diversity. Highest species richness/diversity was associated with the ecotonal area between Parilla and Lowan Sands (i.e. broom-heath) where a number of species characteristic of different assemblages had overlapping ranges. The fire-sensitive conifer, Callitris rhomboidea, was preferentially located in stringybark woodland and broom-heath vegetation types. Its presence was positively associated with high species richness and aspects having a southerly component. Four Callitris stands sampled for population structure were all > 40 years old and showed evidence of interfire recruitment from seeds released by old, serotinous cones. Overall, results suggest that variations in plant community composition and structure in the eastern block of the Little Desert are primarily due to variations in soil properties associated with the distribution of the two dominant substrate types, Parilla Sand and Lowan Sand. However, the interplay of topography and fire behaviour has probably been more important than substrate type in determining the distribution and population structure of longer-lived, fire-sensitive species such as Callitris rhomboidea.     

Response of pine natural regeneration to small‐scale spatial variation in a managed Mediterranean mountain forest

Questions: What influence do management practices and previous tree and shrub stand structure have on the occurrence and development of natural regeneration of Pinus sylvestris in Mediterranean mountain forests? How are the fine‐scale and environmental patterns of resources affected and what impact does this have on the distribution of the regeneration? Location: A Pinus sylvestris Mediterranean mountain forest in central Spain. Methods: Upperstory trees and regeneration (seedlings and saplings) were mapped in four 0.5‐ha plots located in two types of stand with different management intensities (even‐aged and uneven‐aged stands). Environmental variables were recorded at the nodes of a grid within the plots. The relationships between the upperstory and regeneration were evaluated by bivariate point pattern analysis; redundancy analysis ordination and variation partitioning were performed to characterize regeneration niches and the importance of the spatial component. Results: Seedlings and saplings presented a clumped structure under both types of management and their distribution was found to be related to the spatial distribution of favourable microsites. Regeneration was positively related to conditions of partial cover with high soil water content during the summer. More than half of the explained variance was spatially structured in both types of stand. This percentage was particularly high in the even‐aged stands where the pattern of regeneration was highly influenced by the gaps created by harvesting. Conclusions: The spatial distribution of the tree and shrub upperstory strongly influences regeneration patterns of P. sylvestris. Current management practices, promoting small gaps, partial canopy cover and moderate shade in even‐aged stands, or favouring tree and shrub cover in the case of uneven‐aged stands, appears to provide suitable conditions for the natural regeneration of P. sylvestris in a Mediterranean climate.     

Litterfall of epiphytic macrolichens in Nothofagus forests of northern Patagonia,Argentina: Relation to stand age and precipitation

Abstract: The objective of this study was to analyse how stand age and precipitation influence abundance and diversity of epiphytic macrolichens in southern beech Nothofagus forests, estimated by lichen litter sampling. Five sites of Nothofagus dombeyi (Mirbel) Oersted were selected in Nahuel Huapi National Park, Argentina. At each site, lichen fragments from the forest floor were collected at 12.5 m² plots in pairs of young and mature N. dombeyi forest. Additionally, two sites with multi‐aged subalpine Nothofagus pumilio (Poepp. et Endl.) Krasser forest were investigated in a similar manner. Average litterfall biomass per stand varied from less than 1 kg ha^?1 in a young low‐precipitation stand to a maximum of 20 kg ha^?1 in a mature high‐precipitation stand. In places with higher precipitation, litterfall biomass in N. dombeyi forest was considerably higher in old stands as compared with young ones. In places with less than 2000 mm of precipitation, differences in biomass were less pronounced. Old humid stands contained about twice as many taxa in the litter as old low‐precipitation stands and young stands in general. Mature stands in low‐precipitation sites only contained 17% of the litter biomass as compared with mature stands in high‐precipitation sites. Epiphytic lichen composition changed from predominating fruticose lichens (Usnea spp. and Protousnea spp.) in low‐precipitation stands to Pseudocyphellaria spp., Nephroma spp. and other foliose lichens, in the high‐precipitation stands. There were no clear differences in the proportion of fruticose and foliose lichens between young and old stands. Fruticose lichens dominated litter biomass in both N. pumilio sites.     

Conservation management of Pinus palustris ecosystems from a landscape perspective

Question: Do case studies from silvicultural and restoration studies and applied conservation management in second‐growth Pinus palustris stands provide unique insights for conservation models? Methods: A review of management paradigms that conserve the high biological diversity and rare species, drawn from characteristics in both second‐growth and old‐growth stands, is presented for fire‐maintained Pinus palustris (longleaf pine) forests. Results: A common assumption that old‐growth stands provide the primary information for the development of conservation management strategies de‐emphasizes lessons learned from second‐growth and restoration studies. Primary conservation management goals for the Pinus palustris ecosystem include the perpetual regeneration of the fire‐maintained forest and conservation of the characteristically high biological diversity and rare species. Several attributes, such as a sustained population of Picoides borealis (red‐cockaded woodpecker), Aristida stricta (wiregrass)‐dominated ground cover, and undisturbed upland‐wetland ecotones, can predict a diverse and ecologically functional ecosystem. Such indicators are linked to critical structural and functional features of the system and reflect previous land management histories that suggest sustainable approaches. Conclusions: A traditional definition of ‘old‐growth’ relying on overstorey may be limited in describing important features of healthy, diverse Pinus palustris ecosystems. Some characteristics are significantly more important for maintenance of diversity than age of the trees and these features may be present in old‐ or second‐growth forests. We advocate that the management history, structural characteristics and landscape context of stands that harbour desirable conservation attributes (red‐cockaded woodpeckers, wiregrass, gopher tortoises and undisturbed upland‐wetland ecotones) can be used as indicators to identify important conservation and forest management principles.     

Demography of the invasive shrub Scotch broom (Cytisus scoparius) at Barrington Tops,New South Wales: insights for management.

The exotic shrub Scotch Broom (Cytisus scoparius) has invaded large areas of eucalypt woodland at Barrington Tops, New South Wales, where it forms dense stands that have significant impacts on vegetation structure, flora and fauna. Data are presented from four 25 m² plots, which have been studied since 1985. Two plots were located in uniform broom thickets of different ages, and two were located across the margins of broom stands, which have since expanded to cover the entire plots. All broom plants in the plots (other than young seedlings, which were counted) were mapped, tagged and monitored annually. New seedlings appeared annually, but there was no relationship between their numbers (varying between years) and subsequent recruitment of older plants. The probability of seedlings reaching first flowering was less than 2%, and of surviving to mature size (>10 cm² basal area) was negligible. Seedlings mainly died through suppression (shade). Individuals less than 50 cm high were also browsed. Recruitment occurred only where light levels were high, either before closure of the broom canopy or after senescence had led to canopy opening. From approximately 12–30 years after initial invasion, broom stands underwent self‐thinning of mature plants, accelerated by collapse of plants on to each other. Recruitment of new, maturing plants, after this period produced a stand that was less dense than that found after initial invasion. Broom is creating more disturbance‐prone environments due to its impacts on other biota, likely alterations to the fire regime, and by harbouring feral pigs. Further disturbance favours broom, and elsewhere it has resulted in massive seedling regeneration. While fire or other disturbance can be used to stimulate germination, and thereby reduce a large part of the soil seed bank, denser broom infestations are likely to result unless follow‐up treatments can be applied over long time periods. A wiser management option, at least in the short term, may be avoidance of all disturbance, especially for stands of mature broom.