Population dynamics of some major woody species in relation to long-term succession on the dunes of Voorne

This study is a follow-up of medium-term succession studies based on a vegetation map, scale 1:2 500, of the dunes near Oostvoorne made in 1959 and 1980. The area has a marked zonation with partly very young dunes and inner dunes at a distance of >1 200 m from the beach which are 800 yr old. The overall succession trend is a development from a largely open vegetation (resulting from overgrazing in the 19th century, which ceased 1910), to a scrub/woodland complex with locally dying off of patches of woody vegetation. To understand the processes of change, the age structure of most of the major woody species was determined.Two transects were followed in the area running from the seaward coastal ridge towards the inner dunes. 86 plots were analyzed as to represent the vegetation types distinguished in 1980. In each plot all trees and shrubs were estimated on age by means of increment boring and counting of annual rings. The abundance of seedlings and saplings (<4 yr old) of all woody species was estimated in all plots.The most important woody species are Betula (most B. pendula + some B. pubescens). Crataegus monogyna, Rhamnus catharticus, Sambucus nigra, Alnus glutinosa, Quercus robur, Salix(most S. cinerea + S. aurita and their hybrid S. multinervis). Hippophae rhamnoides, Ligustrum vulgare, and Salix repens, three important early successionals, could not be aged easily.Age distribution curves show a marked stand-still in development in the 1960s. Some species stopped rejuvenating at all. Cumulative development curves for different zones show a clear change in growth rate over the zones for Crataegus and a simultaneous rapid development for Crataegus.Two examples of species sequence within a community type are shown. An explanation of these results includes three main factors: (a) overall changes in the whole area related to disturbance and relaxation, (b) soil moisture and (c) rabbit grazing. Two main events in the development of a population are considered: germination and early development of the seedling, and untimely death of a dominant.Nomenclature follows Arnolds & van der Meijden (1976), Standaardlijst van de Nederlandse flora, 1975. Rijksherbarium, Leiden.Research on population dynamics reported on in this paper was carried out by de Cock & de Wildt as MSc students and supervised by van der Maarel, then all at the Division of Geobotany, University of Nijmegen, Nijmegen, The Netherlands. The preparation of the paper including some new observations and calculations were done by the first author in the framework of the project Population dynamics of woody species in primary successions supported by NFR, the Swedish Natural Science Research Council.     

Using plant functional types to compare vegetation structure of alien-invaded and uninvaded Acacia nilotica savannas

Four plant functional types (PFTs) were used to compare the vegetation structure of an alien-invaded Acacia nilotica savanna with one of negligible invasions. Heights, canopy covers and species richness of three native PFTs (woody plants, grasses and herbs) and one alien PFT (woody plants) were measured in 14, 1-m² quadrats sampled in a stratified-random pattern in a 400-m² plot demarcated in each savanna. In the uninvaded plot, mean heights of native PFTs were stratified. In the invaded plot, the mean height of aliens extended into the native woody stratum with the lower range of native woody PFT heights reduced to the grass stratum. Discriminant analysis of canopy covers and species richness of the four PFTs revealed significant differences in composition between plots with the alien PFT being the most important variable correlated with these differences. Univariate analysis confirmed the dominance of alien woody plants in the invaded plot but also showed significant reductions in the canopy covers and species richness of native herbs and grasses compared to those in the uninvaded plot. These results suggest that PFTs can rapidly measure small-scale, spatial differences in the physiognomy, composition and species richness of A. nilotica savannas when invaded by alien woody plants.     

A Modified-Whittaker nested vegetation sampling method

A standardized sampling technique for measuring plant diversity is needed to assist in resource inventories and for monitoring long-term trends in vascular plant species richness. The widely used Whittaker plot (Shmida 1984) collects species richness data at multiple spatial scales, using 1 m², 10 m², and 100 m² subplots within a 20 m × 50 m (1000 m²) plot, but it has three distinct design flaws involving the shape and placement of subplots. We modified and tested a comparable sampling design (Modified-Whittaker plot) that minimizes the problems encountered in the original Whittaker design, while maintaining many of its attractive attributes. We overlaid the two sampling methods in forest and prairie vegetation types in Larimer County, Colorado, USA (n=13 sites) and Wind Cave National Park, South Dakota, USA (n=19 sites) and showed that the modified design often returned significantly higher (p<0.05) species richness values in the 1 m², 10 m², and 100 m² subplots. For all plots, except seven ecotone plots, there was a significant difference (p<0.001) between the Whittaker plot and the Modified-Whittaker plot when estimating the total number of species in the 1000 m² plots based on linear regressions of the subplot data: the Whittaker plot method, on average, underestimated plant species richness by 34%. Species-area relationships, using the Modified-Whittaker design, conformed better to published semilog relationships, explaining, on average, 92% of the variation. Using the original Whittaker design, the semilog species-area relationships were not as strong, explaining only 83% of the variation, on average. The Modified-Whittaker plot design may allow for better estimates of mean species cover, analysis of plant diversity patterns at multiple spatial scales, and trend analysis from monitoring a series of strategically-placed, long-term plots.     

Small-scale spatial variation in the interactions between Prunus mahaleb and fruit-eating birds

We studied fleshy fruit consumption by birds on individualPrunus mahaleb trees in four plots in northwestern Spain.We found large variation among trees in the relative contribution of differentbird species to fruit removal. This variation, which occurred on a scale ofmeters, was correlated with the distance from the tree to nests ofPhoenicurus ochruros, a major fruit consumer, and with thekind of microhabitat surrounding each tree. In the four plots studied, treeslocated farther away from P. ochruros nests receivedrelatively fewer visits by this species, and relatively more byTurdusmerula and Sylvia atricapilla. These three mainconsumer species differed in the kinds of microhabitats (rocks, loose stones,bare or grassy soil, and woody vegetation) where they flew after visitingP. mahaleb, and thus they probably created differentpatterns of seedfall. This study adds to the evidence that environmentalfactorsextrinsic to plants, and acting at different spatial scales, greatly influencethe identity of the fruit consumers visiting individual trees. This influenceundermines the chances that fruit traits become evolutionary modified so as toattract those consumers providing the best seed dispersalservicesto the plants.     

Early post-fire vegetation regeneration in <Emphasis Type="Italic">Larix kaempferi</Emphasis> artificial forests with an undergrowth of <Emphasis Type="Italic">Sasa senanensis</Emphasis>

Post-fire vegetation regeneration was studied for a 6-year period in a 13-year-old-artificial forest consisting of Larix kaempferi with a dense undergrowth of Sasa senanensis. The study site was classified into three fire severity categories according to the degree of Sasa senanensis scorching, that is, a high-severity category, a mid-severity category, and a low-severity category. Study plots were established in areas which fitted the criteria for each category, and in nearby unburned sites. A total of 41 woody species were newly emerged during the 6-year study period in the burned and unburned plots. Only a few seedlings and resprouts emerged in the unburned plots, while many seedlings emerged in the high-severity plots from the first year after fire onward. A high-severity fire that burns the rhizomes of Sasa is necessary for the vegetation recovery by germination of seed. Whereas the establishment of seedlings was restricted to a few years after fire, the regeneration through resprouting continued into the last year of observation. The survival time of resprouts was longer than that of seedlings, and the survival time of shade-tolerant species was longer than that of shade-intolerant species. In contrast, shade-intolerant species grew more rapidly than shade-tolerant species. The plants ability to exceed the maximum height of the Sasa before the bamboo recovers can be critical to the survival of shade-intolerant species. Because resprouts have a stronger resistance to the shade of Sasa than seedlings, the resprouts of shade-tolerant species play a major role in the re-establishment of woody species after fire in sites with considerable Sasa ground-cover.     

Beyond the tropics: forest structure in a temperate forest mapped plot

Question: How do the diversity, size structure, and spatial pattern of woody species in a temperate (Mediterranean climate) forest compare to temperate and tropical forests? Location: Mixed evergreen coastal forest in the Santa Cruz Mountains, California, USA. Methods: We mapped, tagged, identified, and measured all woody stems (≥1 cm diameter) in a 6‐ha forest plot, following Center for Tropical Forest Science protocols. We compared patterns to those found in 14 tropical and 12 temperate forest plots. Results: The forest is dominated by Douglas‐fir (Pseudotsuga menziesii) and three species of Fagaceae (Quercus agrifolia, Q. parvula var. shrevei, and Lithocarpus densiflorus), and includes 31 woody species and 8180 individuals. Much of the diversity was in small‐diameter shrubs, treelets, and vines that have not been included in most other temperate forest plots because stems <5‐cm diameter had been excluded from study. The density of woody stems (1363 stems ha^?1) was lower than that in all but one tropical plot. The density of large trees (diameter ≥30 cm) and basal area were higher than in any tropical plot. Stem density and basal area were similar to most other temperate plots, but were less than in low‐diversity conifer forests. Rare species were strongly aggregated, with the degree of aggregation decreasing with abundance so that the most common species were significantly more regular than random. Conclusions: The patterns raise questions about differences in structure and dynamics between tropical and temperate forests; these need to be confirmed with additional temperate zone mapped plots that include small‐diameter individuals.     

Differences between banded thickets (tiger bush) at two sites in West Africa

Abstract. This paper deals with the influence of edaphic conditions on the spatial structure of banded thickets or tiger bush (brousse tigrée). It is based on two sites in West Africa, with similar climatic conditions but located on contrasting substrates. The spatial structure was described with standardized characteristics including thicket spacing, thicket/inter‐thicket contrast, upslope/downslope asymmetry and species zonation throughout the vegetation band. Recruitment and senescence features of woody stands were emphasized in order to understand current dynamics. Data were collected on transects oriented perpendicular to the contours and so to the thickets as well. A standardized analytical procedure was applied to data from both sites to ensure consistent and thorough delineation of thickets. The overall periodicity of thickets, the woody flora and the dominant species Combretum micranthum were similar at the two sites. However, thicket spacing, thicket/inter‐thicket contrast and upslope/downslope floristic asymmetry of the thickets were higher in the less favourable site. Also seedlings were less abundant, with a greater dependence on pre‐existing thickets. Not all banded vegetation systems show sharp contrasts and are strongly asymmetric, since such characteristics are likely to be reinforced by adverse environmental conditions. As a consequence, current dynamics may be more diverse than expected. Quantified inter‐site comparisons can greatly help to classify African banded vegetation systems and to discuss potential dynamic outcomes.     

Long-term observations of rain forest succession,tree diversity and responses to disturbance.

The relationship between succession and tropical forest diversity hasbeen much debated. A fundamental disagreement hinges on whether high localspecies richness is a transient successional property, albeit one that can bemaintained by disturbance, or is rather a property of stable late successionalcommunities. This paper addresses this controversy employing a series oflong-term permanent sample plot data spanning seven decades. W.J. Eggelingstudied the vegetation of Budongo Forest, Uganda during the 1930s and 1940s. Hedescribed a series of ten plots (1.4 and 1.86 ) as asuccessionalprogression of forest types in which tree species numbers show a unimodalrise-and-fall over time – a pattern best known from Connell'sillustration of his intermediate disturbance hypothesis. Tree communities infive of the original plots have been intermittently re-assessed over thesubsequent decades. One data-series provides observations spanning 54-yearsfromone intact undisturbed old-growth forest plot. The remaining fourplots were assessed before and after controlled disturbances (tree poisoning)executed in the late 1950s and early 1960s, and the resulting data-series spanc. 20 years of pre-disturbance and c.35 years of post-disturbance changes. Theunimodal pattern of species-richness in the original comparative plot-series isparalleled by a similar rise-and-fall in stem-densities, but rarefactionconfirms that the unimodal pattern in richness also holds for fixedstem-counts.The proportion of species occurring in both large and small stem-size-classesincreases across the series. As richness declines in later succession, lowabundance species occur predominantly in larger stem-sizes. All time-seriesshowa rise in species richness ranging from 12 to 177% (over 50–60 years). Each of thedisturbed plots ultimately reaches greater richness than was recorded anywherein Eggeling's original series. Contrary to expectation a small rise wasalso recorded in the undisturbed late successional plot (c.42 species 10 diameter ha^–1, rising to c.47). The lowestspecies density observed in the study is a 1940s record of c. 10 species 10 diameter ha^–1 in monodominantCynometra [Caesalpinoidae] forest and thehighestrecord is c. 61 recorded in 1992, in theyoungest vegetation type monitored. These observations indicate both thevolatile nature of tree-richness patterns and the limitations of simple modelsas aids to interpretation when confronted with real patterns of long-termchange.     

Population structure and spatial patterns for trees in a temperate old-growth evergreen broad-leaved forest in Japan

The population structure and spatial pattern of major tree species in a warm-temperate old-growth evergreen broad-leaved forest in the Tatera Forest Reserve of Japan were investigated. All stems 5 cm in diameter at breast height (DBH) were mapped on a 4 ha plot and analyses were made of population structure and the spatial distribution and spatial association of stems in different vertical layers for nine species. This was done in the context of scale dependency. The plot was located on a very gentle slope and 17.1% of its canopy layer was in gaps. It contained 45 woody plant species and 4570 living stems with a basal area of 63.9 m² ha^–1. Castanopsis cuspidata var. sieboldii, the most dominant species for the basal area, had the maximum DBH among the species present, fewer smaller stems and a lower coefficient of statistical skewness of the DBH distribution. The second most dominant species, Dystilium racemosum, had the highest stem density (410 ha^–1), more abundant smaller stems and a relatively higher coefficient of skewness. Most stems in different vertical layers showed a weakly aggregated distribution with loose colonies as basic units. Gap dependency for the occurrence of stems under the canopy layer was weak. Maximum slope degree of the plot also weakly affected the occurrence of stems. Spatial associations varied among intra- and interspecific cohorts in the different layers and spatial scales examined, and positive associations among cohorts were found more frequently as the scales examined became larger. This tendency suggests that key factors forming observed spatial associations might vary with the spatial scales.     

Managing open habitats by wild ungulate browsing and grazing: A case‐study in North‐Eastern Germany

Question: Can wild ungulates efficiently maintain and restore open habitats? Location: Brandenburg, NE Germany. Methods: The effect of wild ungulate grazing and browsing was studied in three successional stages: (1) Corynephorus canescens‐dominated grassland; (2) ruderal tall forb vegetation dominated by Tanacetum vulgare; and (3) Pinus sylvestris‐pioneer forest. The study was conducted over 3 yr. In each successional stage, six paired 4 m²‐monitoring plots of permanently grazed versus ungrazed plots were arranged in three random blocks. Removal of grazing was introduced de novo for the study. In each plot, percentage cover of each plant and lichen species and total cover of woody plants was recorded. Results: Wild ungulates considerably affected successional pathways and species composition in open habitats but this influence became evident in alteration of abundances of only a few species. Grazing effects differed considerably between successional stages: species richness was higher in grazed versus ungrazed ruderal and pioneer forest plots, but not in the Corynephorus sites. Herbivory affected woody plant cover only in the Pioneer forest sites. Although the study period was too short to observe drastic changes in species richness and woody plant cover, notable changes in species composition were still detected in all successional stages. Conclusion: Wild ungulate browsing is a useful tool to inhibit encroachment of woody vegetation and to conserve a species‐rich, open landscape.     

Woody vegetation spatial patterns in a semi-arid savanna of Burkina Faso,West Africa

Spatial patterns of woody individuals were studied in a semi-arid savanna of West Africa located in Burkina Faso at and around 14° 12 N and 2° 27 W. The study was based upon a 10.24 ha plot within which individuals were mapped. Spatial pattern analysis was carried out using second order characteristics of point processes as K functions and pair correlations. The overall density amounted to 298 individuals ha^-1. The most abundant species were Combretum micranthum G. Don., Grewia bicolor Juss. and Pterocarpus lucens Lepr. Anogeissus leiocarpus (D.C.) G. et Perr. was also an important constituant of this vegetation type, owing to its taller stature. Clumped spatial distributions were identified for all species except for two, for which complete spatial randomness (CSR) was found (including P. lucens, a dominant woody plant). No regular pattern was found even when tall individuals were considered alone. Aggregation dominates interspecific relationships, resulting in multispecific clumps and patches. The overall aggregation pattern was constituted by two different structures. A coarse-grain pattern of ca. 30–40 m was based on edaphic features, and expresses the contrast between sparse stands on petroferric outcrops and denser patches on less shallow soils. A finer-grain pattern made of clumps ca. 5–10 m wide, with no obvious relation to pre-existing soil heterogeneity. There was no overall pattern for saplings (between 0.5 m and 1.5 m in height) irrespective of species, and thus no obvious common facilitation factor. For species with a high recruitment level there was no significant relationship between mature adult and saplings. The only case of clumped saplings with randomly distributed adults was found in P. lucens. However, this cannot be unequivocally interpreted as density dependent regulation since the existence of such a process was not consistent with the spatial distribution of dead P. lucens individuals (victims of the last drought). The mean density around dead P. lucens was lower than around surviving ones, indicating that the last drought tended to reinforce clumping rather than promote a regular pattern of trees. Spatial pattern analysis yielded no evidence supporting a hypothesis of stand density regulation through competition between individuals. Other processes, as surface sealing of bare soils or insufficient recruitment, may play a more important role in preventing a savanna-like vegetation from turning into denser woodlands or thickets.     

Nigerian Man and Biosphere research plots in Guinea savanna: floristics and structure of the vegetation

A study was made of the vegetation of three plots used in the Nigerian Man and Biosphere Research Programme for Savanna Studies. The aim is to provide detailed information on the vegetation of the plots which may possibly contribute to an understanding of factors influencing savanna structure and relative abundances of forbs, grasses and woody species. Results show that there are differences in the species composition of the plots. There are more forb species than grass species in each plot. The woody basal areas and crown areas of the plots do not depend entirely on the density but also on the size of the woody species. There are differences in herbage yield in the plots that could be attributed to differences in soil properties, species composition and level of human and animal activities between the plots.     

Tree species composition and rain forest-environment relationships in the middle Caquetá area,Colombia, NW Amazonia

As part of an integrated forest vegetation and soil survey, tree species composition (DBH 10 cm) was recorded in 95 plots of 0.1 ha, distributed over the principal physiographic units in the middle Caquetá area, Colombian Amazonia. A total of 1077 tree species was found, classified into 271 genera and 60 families. Leguminosae and Sapotaceae show high familial importance values in all physiographic units. Lauraceae, Chrysobalanaceae, Moraceae, and Lecythidaceae are more important on well drained (flood plain or upland) soils, while Palmae, Guttiferae, Bombacaceae, and Apocynaceae are more important in swamps and on podzolised (white sand'rs) soils. Plots on well drained soils show a lower degree of dominance than plots in swamps or on podzolised (white sand) soils. The composition of the most dominant species in the plots changes continuously. Most species (59%) are only recorded in one plot. Individual plot pairs generally show a low overlap of about 2–5 tree species, resulting in Jaccard coefficients below 20%.complementary to a previous forest classification based on TWINSPAN analyses, detrended and canonical correspondence analyses were carried out, using CANOCO 3.1. Despite of a low amount of tree species variance explained (only 6.2% by the first two canonical axes), meaningful patterns of tree species composition were recognised. These are most strongly related to drainage, flooding, humus forms, and soil nutrient status. Forest types are well separated in the CCA ordination diagram. The most frequently found tree species are listed according to their preference with respect to drainage, flooding, and soil nutrient status.Tree species composition in the well drained upland forests was analysed separately. In view of the model explaining high NW Amazonian tree species diversity on the basis of dense community packing and high beta diversity along soil gradients, the canonical analysis here focused on the effect of soils. By means of partial canonical ordination it was found that patterns of tree species composition depended significantly on soil properties, even though the edaphic component explains only a small fraction of the tree species variance. The results show that the well drained uplands of the middle Caquetá area are covered by a complex of two intergrading tree species assemblages. The first assemblage (community of Goupia glabra-Clathrotropis macrocarpa) is associated to some-what less poor, clayey soils developed in Andean origin deposits or Tertiary sediments from the Pebas formation. The second assemblage (community of Swartzia schomburgkii-Clathrotropis macrocarpa) shows affinities to very poor, loamy soils developed in parent materials derived from the Guiana shield. This simple dichotomous pattern of geology, soils, and forest types is incompatible with concepts of high soil heterogeneity and associated beta diversity controlling tree species diversity in well drained uplands of NW Amazonia. The gradient length of tree species in the detrended correspondence analysis was low (3.7 SD), also suggesting a low beta diversity.     

木论喀斯特峰丛洼地森林群落空间格局及环境解释

基于广西壮族自治区木论国家级自然保护区典型峰丛洼地景观尺度内不同微生境条件和植物群落类型50个样地 (20 m × 20 m)的系统取样调查, 用二元物种指示方法(TWINSPAN)对样地内胸径(DBH) ≥ 1 cm的木本植物进行分类, 选择10个土壤环境因子和5个空间因子, 利用除趋势典范对应分析(DCCA)研究了森林群落分布的土壤环境与空间格局, 并给予定量化的合理解释。结果如下: 1) TWINSPAN将森林群落划分为11组, 在三级水平上分为4类生态群落类型。2) DCCA第一排序轴集中了排序的大部分信息, 突出反映了各森林群落所在的坡向和土壤主要养分梯度, 沿第一轴从左到右, 坡向由阴转阳, 岩石裸露率越来越高, 土壤主要养分逐渐降低, 森林群落分别出现了由原生性和耐阴性强逐步向阳性先锋树种为主的次生林和人工林变化的格局。3)因子分离分析结果表明, 土壤环境因子对森林群落分布格局的解释能力为39.16%, 其中21.02%单纯由土壤环境因子所引起, 空间因子的解释能力为31.34%, 其中13.16%独立于土壤环境的变化, 18.15%是土壤环境和空间因子相互耦合作用的结果, 不可解释部分达47.66%, 表明喀斯特峰丛洼地森林群落的物种共存受生态位分化理论和中性理论双重控制。     

Termite- and Mulch-Mediated Rehabilitation of Vegetation on Crusted Soil in West Africa

The rehabilitation of vegetation on structurally crusted soils by triggering termite activity through mulch was studied on three soil types in northern Burkina Faso, West Africa. A split-plot design was used in a fenced environment for the experiment. Insecticide (Dieldrin) was used at a rate of 500 g a.i. (active ingredient)/ha to create nontermite and termite plots. Three mulch types consisting of straw (Pennisetum pedicellatum), woody material (Pterocarpus lucens), and a composite mulch (straw and woody material) applied at a rate of 3, 6, and 4 tons/ha, respectively, were used to trigger termite activity. The grasses and woody species on the plots were surveyed. Nontermite plots responded weakly to mulch treatments, but even in the first year vegetation established on termite + mulch plots. Termite activity resulted in the increase of plant cover, plant species number, phytomass production, and rainfall use efficiency. Infiltrated water use efficiency and plant diversity were not statistically different among treatments during the first 2 years but were in the third. Woody species established only on termite plots. The three types of mulch plots showed greater vegetation development than bare plots, which remained bare throughout the experiment. Analysis of the termite and mulch interaction indicated that mulch plots without termites did not perform better than bare plots, especially in the case of woody plant regeneration. Vegetation rehabilitation was best with composite and straw mulches with termites, followed by woody mulch with termites; it was worst on bare plots.     

Structure and pattern in temperate seasonal forests

Demography, spatial pattern, and diversity of canopy and subcanopy trees, shrubs, and lianas were compared in two cool and two warm temperate North American forests, paired at 30° and 40° north latitudes. All woody stems 1 cm dbh in 16 randomly located, non-contiguous plots totalling 1 ha at each of the four sites were measured, mapped, and identified. Basal area and overall density did not differ between latitudes. Demographic and spatial analyses revealed remarkable similarity in spatial dispersion, irrespective of density or species composition. At all sites, dispersion of canopy trees was random but all understory stems were uniformly distributed relative to all canopy trees. Species diversity and vertical structure differed between the warm and cool temperate sites, especially in species composition of individual strata. Associations of understory species relative to canopy species were more random at 30° than at 40° north, where a higher degree of association between canopy and understory species' patterns, coupled with their size class distributions, suggested more lengthy regeneration cycles and an alternation of species assemblages. The forests at 30°, those subject to periodic canopy disturbance by hurricanes, had more vertical mixing of species (i.e., canopy species represented in all size classes), more tree saplings, and significantly more shrub and liana species.     

Diversity of arbuscular mycorrhizal fungi across a fragmented forest in Panama: insular spore communities differ from mainland communities

It is now understood that alterations in the species composition of soil organisms can lead to changes in aboveground communities. In this study, we assessed the importance of spatial scale and forest size on changes in arbuscular mycorrhizal fungal (AMF) spore communities by sampling AMF spores in soils of forested mainland and island sites in the vicinity of Gatun Lake, Republic of Panama. We encountered a total of 27 AMF species or morphospecies, with 17, 8, 1 and 1 from the genera Glomus, Acaulospora, Sclerosystis, and Scutellospora, respectively. At small scales (<100 m²), we found little evidence for spatial structuring of AMF communities (decay of Morisita-Horn community similarity with distance). However, at large spatial scales, we found that the AMF spore community of a mainland plot was more similar to other mainland plots several kilometers (>5) away than to nearby island plots (within 0.7 km). Likewise, most island plots were more similar to other island plots regardless of geographic separation. There was no decay in AMF species richness (number of species), or Shannon diversity (number of species and their spore numbers) either with decreasing forest-fragment size, or with decreasing plant species richness. Of the six most common species that composed almost 70% of the total spore volume, spores of Glomus tsh and G. clavisporum were more common in soils of mainland plots, while spores of Glomus small brown and Acaulospora mellea were more abundant in soils of island plots. None of these common AMF species showed significant associations with soil chemistry or plant diversity. We suggest that the convergence of common species found in AMF spore communities in soils of similar forest sizes was a result of forest fragmentation. Habitat-dependent convergence of AMF spore communities may result in differential survival of tree seedlings regenerating on islands versus mainland.     

Small mammal community ecology

Summary The abundance of food in natural 1-ha plot of shortgrass prairie was artificially manipulated by adding alfalfa pellets and whole oats on a regular schedule. The small mammal species naturally inhabiting the manipulated food plot did not respond in either their density or weight to the supplemented food. However, a new specialized seed-eating species, Dipodomys ordii, invaded the food plot and persisted in relatively high density. As a result of this colonization, species diversity was significantly higher on the food plot relative to the unmanipulated control plot. In a second experiment, application of water and nitrogen to two 1-ha plots of shortgrass prairie resulted in increased productivity. However, the increased production on this latter treatment was associated with vegetation growth and thus major changes in habitat structural characteristics relative to the control treatment. Two new species, Microtus ochrogaster and Reithrodontomys megalotis, colonized the nitrogen+water treatment, but other small mammal species resident to the shortgrass prairie largely avoided this treatment. As a result of this manipulation, species diversity was significantly lower than the species diversity on the control treatment. These two results agree with the MacArthur prediction regarding how species diversity responds to an increase in production of scarce resources without changes in other habitat variables, and to an increase in productivity associated with changes in other habitat variables.     

Tree community features of two stands of riverine forest under different flooding regimes in Southern Brazil

Two 1 ha plots of a Southern Brazilian subtropical riverine forest, subject to different frequency and duration of floods, were compared to detect the differences in physiognomic structure, tree community composition, richness and diversity. Each plot was made up of 100 contiguous 10×10 m subplots, where 3451 trees with pbh 15 cm were measured and identified. The survey observed 30 tree species, in the frequently flooded plot and 48 in the occasionally flooded plot. A detailed topographical and soil survey was carried out in both plots and indicated that the levels of organic matter and most mineral nutrients were higher in the frequently flooded stand. The forest understory was denser in the occasionally flooded stand which also showed taller emergent trees. Multivariate ordination and grouping techniques showed that the species’ abundance distribution was strongly related to the topographical variation. There was a clear pattern of species turnover according to topographic position, indicating that tree species developed different abilities to survive flooding events. As a result, the two plots also differed in their tree frequency per species regeneration, vertical distribution and dispersion groups. Both species richness and diversity decreased with increasing flood frequency, also showing a patchy distribution within both stands. At a local scale, flooding regime is regulating the spatial variation of α-diversity by forming different seral stages of predictable species composition. Compared to regularly flooded riverine and floodplain forests, riverine forests, with unpredictable flooding regimes, may show higher diversity at a local scale and more abundant opportunistic species of high environmental plasticity.     

Native woody vegetation in central Argentina: Classification of Chaco and Espinal forests

Question

What are the composition and spatial patterns of native woody plant communities in the southern Great Chaco and Espinal?

Location

Córdoba Province, central Argentina, an area of ca. 161,000 km².

Methods

We collected 351 geo‐referenced relevés representative of the geographic, topographic and ecological variation of the Chaco and Espinal woody vegetation in central Argentina. The relevés were classified into vegetation types using the hierarchical ISOPAM method. Forest and shrubland types were described on the basis of diagnostic species occurrences and their distribution in relation to environmental factors. A map of the actual vegetation derived from remote‐sensed images (Landsat) and field data was used to describe the current distribution and abundance of the different vegetation types.

Results

The classification of the 351 plots × 837 species matrix revealed two major clusters comprising seven woody vegetation types corresponding to Chaco lowland and mountain forests and shrublands, Espinal forests and edaphic vegetation. The most important gradients in woody vegetation types are related to elevation, temperature and rainfall variables.

Conclusions

Subtropical seasonally dry woody plant communities from the southern extreme of the Great Chaco and Espinal forests were described for the first time based on complete floristic data. Our results show that lowland Chaco native forests, as well as replacement communities, are still present in its southern distribution range and are well distinguishable from other vegetation types such as the Espinal and mountain forests. Overall, extensive Espinal forests have almost disappeared while Chaco vegetation is highly fragmented and degraded.