Soils and vegetation of central Australian sandridges III. Sandridge vegetation of the Simpson Desert

This is the third of a series of papers describing the soils and vegetation of the central Australian sandridges and their interrelations. It details topographic—floristic patterns on fourteen transects at seven sites in the northwest, southwest and southeast Simpson Desert. There is a consistent vegetational zonation on the main Simpson sandridges, with regional modifications due to the broad scale NW-SE floristic gradient. Closer dunes have more similar vegetation than distant ones. Swale vegetation is less consistent than sandridge vegetation and depends on soil type. Species differ greatly in their degree of restriction both topographically and geographically. Zone separation differs greatly between dunes in consequence. Zones defined on overall floristics are less clearly separated in the Simpson than in the western deserts. A floristically and structurally distinct crest zone is recognizable on all main dunefield sandridges. The only universally applicable zonation is swale, flank, crest. Vegetation patterns are more closely correlated with field soil texture than with topography.     

Changes in aboveground primary production and carbon and nitrogen pools accompanying woody plant encroachment in a temperate savanna

When woody plant abundance increases in grasslands and savannas, a phenomenon widely observed worldwide, there is considerable uncertainty as to whether aboveground net primary productivity (ANPP) and ecosystem carbon (C) and nitrogen (N) pools increase, decrease, or remain the same. We estimated ANPP and C and N pools in aboveground vegetation and surface soils on shallow clay and clay loam soils undergoing encroachment by Prosopis glandulosa in the Southern Great Plains of the United States. Aboveground Prosopis C and N mass increased linearly, and ANPP increased logarithmically, with stand age on clay loam soils; on shallow clays, Prosopis C and N mass and ANPP all increased linearly with stand age. We found no evidence of an asymptote in trajectories of C and N accumulation or ANPP on either soil type even following 68 years of stand development. Production and accumulation rates were lower on shallow clay sites relative to clay loam sites, suggesting strong edaphic control of C and N accumulation associated with woody plant encroachment. Response of herbaceous C mass to Prosopis stand development also differed between soil types. Herbaceous C declined with increasing aboveground Prosopis C on clay loams, but increased with increasing Prosopis C on shallow clays. Total ANPP (Prosopis+herbaceous) of sites with the highest Prosopis basal area were 1.2 × and 4.0 × greater than those with the lowest Prosopis basal area on clay loam and shallow clay soils, respectively. Prosopis ANPP more than offset declines in herbaceous ANPP on clay loams and added to increased herbaceous ANPP on shallow clays. Although aboveground C and N pools increased substantially with Prosopis stand development, we found no corresponding change in surface soil C and N pools (0–10 cm). Overall, our findings indicate that Prosopis stand development significantly increases ecosystem C and N storage/cycling, and the magnitude of these impacts varied with stand age, soil type and functional plant traits     

Prediction of Prosopis species invasion in Kenya using geographical information system techniques

Tree species from Prosopis genus were widely planted for rehabilitation of degraded drylands of Kenya. However, they have invaded riverine ecosystems where they cause negative socio‐economic and ecological impacts. GIS was used to estimate the reverine area threatened by Prosopis invasion in Kenya. Landsat satellite images, field surveys and past studies were also used to assess the resulting potential ecological impacts in the Turkwel ecosystem in Kenya. The study revealed that 3.0 to 27.7 million hectares are threatened by invasion, based on documented riverine forests width of 0.5–3 km. Image analysis showed that 34% of the sites under positive change were invaded, with most invasions occurring in natural forests and abandoned farms. Prosopis had overall occurrence of 39% in all the sampled sites in 2007, in contrast to 0% in 1990 that was reported in an earlier study. In these areas, Acacia tortilis occurrence dropped from 81% in 1990 to 43% in 2007, suggesting that Prosopis could be displacing it. Utilization of Prosopis for fodder, fuel wood and pods for animal feeds is recommended as a management tool to reverse the trend. The methods used in this study are also recommended for invasion prediction and management in other similar ecosystems.     

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.     

Coastal dune vegetation and pollen representation in south Buenos Aires Province, Argentina

Aim To establish the relationship between coastal dune vegetation and its pollen representation as an aid to interpret Holocene vegetation dynamics and environmental changes from pollen assemblages. Location The study area is situated on the temperate Atlantic coast of south Buenos Aires Province, Argentina (c. 39° S and 61°20′ W). Methods The vegetation of the active dune area adjacent to the beach was described on the basis of its floristic composition from 25 plots. Classification of the vegetation into distinct zones was carried out by cluster analysis. Surface samples were collected from each vegetation stand and analysed for their pollen composition. Pollen percentage data were analysed using principal components analysis in order to investigate the degree to which the different vegetation units can be distinguished by their pollen spectra. Pollen–vegetation relationships for selected taxa were explored using simple scatter plots and indices of association, under‐ and over‐representation. Indices of floristic diversity and palynological richness were used to assess the representation of the vegetation in the pollen spectra. Results and conclusions Five vegetation zones are defined on the basis of species composition and their quantitative variation: back shore, mobile dunes, slacks, semi‐fixed and fixed dunes. Pollen assemblages from back shore, mobile dunes and slacks are clearly differentiated from semi‐fixed and fixed dunes. Pollen assemblages differ considerably from the associated vegetation composition. Major discrepancies are caused by large differences in pollen and vegetation proportion of Hyalis argentea and Discaria americana. There is a considerable proportion of non‐local pollen in every spectrum. Pollen representation in the coastal dunes at Monte Hermoso is influenced by differences in pollen production, dispersal and preservation of individual taxa as well as by the spatial distribution of the vegetation, the topography of the dune system and the wind pattern. The pollen–vegetation relationship established in this study has important implication for understanding and interpreting fossil pollen records from coastal dune environments.     

Classification of Prosopis juliflora invasion in the Lake Baringo basin and environmental correlations

The spread of Prosopis juliflora in the Baringo basin, Kenya, has led to severe changes in the ecosystem with negative socio‐economic impacts. The drivers that foster the invasiveness of Prosopis are not fully understood. Thus, a method to quantify the degree of infestation will support the determination of environmental preferences and the risk assessment of future Prosopis invasion. We developed a methodology for characterising and classifying degrees of Prosopis infestation in vegetation stands and propose its application in environmental correlation models. The relative cover was identified as the most suited attribute for assessing and monitoring the invasion of Prosopis. The distance of invaded stands from original plantations and environmental attributes related to water availability (ground water table, rainfall and soil water–holding capacity) have potential to predict potential or future invasion risks.     

Regeneration in fringe mangrove forests damaged by Hurricane Andrew

Mangrove forests along many tropical coastlines are frequently andseverely damaged by hurricanes. The ability of mangrove forests to regeneratefollowing hurricanes has been noted, but changes that occur in vegetationfollowing disturbance by hurricane winds and storm tides have not been studied.We measured changes in plant community structure and environmental variables intwo fringe mangrove forests in south Florida, USA that experienced high windvelocities and storm tides associated with Hurricane Andrew (August1992). Loss of the forest canopy stimulated regeneration via seedlinggrowth and recruitment, as well as resprouting of some trees that survived thehurricane. Initial regeneration differed among species in both forests:Rhizophora mangle L. regenerated primarily via growth ofseedlings present at the time of the hurricane (i.e., release of advancerecruits), but many trees of Avicennia germinans(L.) Stearn and Laguncularia racemosa Gaertn.f.resprouted profusely from dormant epicormic buds. In one forest, which wasformerly dominated by Laguncularia, high densities ofRhizophora seedlings survived the hurricane and grew toform dense stands of saplings and small trees ofRhizophora. In the other forest, there were lowerdensitiesof surviving Rhizophora seedlings (possibly due tohigher storm tide), and extensive bare areas that were colonized byAvicennia, Laguncularia, andherbaceous species. This forest, predominantly Rhizophoraat the time of the hurricane, now contains stands of saplings and small treesofall three species, interspersed with patches dominated by herbaceous plants.These findings indicate that moderately damaged fringe forests may regenerateprimarily via release of Rhizophora advance recruits,leading to single-species stands. In severely damaged forests, seedlingrecruitment may be more important and lead to mixed-species stands.Regeneration of mangrove forests following hurricanes can involve differentpathways produced by complex interactions between resprouting capability,seedling survival, post-hurricane seedling recruitment, and colonizationby herbaceous vegetation. These differences in relative importance ofregeneration pathways, which may result in post-hurricane forestsdifferent from their pre-hurricane structure, suggest that models forregeneration of mangrove forests will be more complex than directregeneration models proposed for other tropical forests whereregeneration after hurricanes is dominated by resprouting.     

Classification and ecology of the mid‐seral Picea mariana forests of British Columbia

Abstract. We sampled vegetation and soils of, and classified mid‐seral, even‐aged, fire‐origin, upland Picea mariana ecosystems in the Boreal White & Black Spruce and Sub‐boreal Spruce zones of British Columbia, Canada. We applied multi‐variate and tabular methods to analyse and synthesize the data from 121 plots according to the methods of biogeoclimatic ecosystem classification. We delineated seven basic vegetation units and described their vegetation and environmental features. However, the delineated units could not be related to neither of the taxonomies proposed for the North American boreal forest communities. Although species‐poor, the under‐storey vegetation in the sampled ecosystems provided for a sufficient floristic differentiation, which matched well the major edaphic differences between the units. The classification of mid‐seral boreal ecosystems may be more useful that based on old‐growth stands that are infrequent or lacking in the landscape due to wildfires.     

Impact of alien trees on mammal distributions along an ephemeral river in the Namib Desert

Ephemeral rivers and the vegetation they support have numerous ecological and economic values to the mammals and people who rely on these systems. Yet, these crucial environments are believed to be threatened by exotic plant invasion. In Africa, invasive trees of the genus Prosopis have detrimental effects on native vegetation, bird and dung beetle communities; however, to date, there is no evidence that Prosopis establishment has affected indigenous wild mammalian distribution and ecology in its introduced range. Using a combination of camera traps and vegetation surveys, we tested the hypothesis that Prosopis invasion has a negative impact on the mammals of the ephemeral Swakop River in Namibia by reducing mammal species richness and species occupancies. Prosopis was found to have no negative impact on species richness; however, evidence for species‐specific responses to Prosopis abundance was found. This is the first study to confirm an impact of Prosopis on sub‐Saharan African mammals, providing a foundation for future research and the development of appropriate management policy.     

Plant response to variations in nitrogen availability in a desert shrubland community

Spatial variations in nitrogen availability were studied in a desert community codominated byLarrea tridentata (DC.) Cov. andProsopis glandulosa Torr. Measurements of natural ¹⁵N values in tissues suggested thatProsopis obtains approximately half of its nitrogen through direct symbiotic fixation. Soils were collected under 1)Prosopis shrubs, 2)Larrea shrubs 2 m fromProsopis (LP), and 3)Larrea 2 m from otherLarrea but> 5 m from the nearestProsopis (LL).Prosopis soils showed significantly higher rates of nitrogen mineralization than LL soils in both A and B horizons. Rates of mineralization in LP soils were significantly higher than rates in LL soils only in the B horizon and were not significantly different from rates inProsopis soils. Leaf nitrogen concentrations were significantly higher in LP shrubs (2.06%) than in LL shrubs (1.78%), although ¹⁵N values did not differ between the two shrub types. Nitrogen concentrations inPerezia nana Gray, a perennial herb, were greater in plants underProsopis shrubs (2.09%) than under LP shrubs (1.93%) or LL shrubs (1.67%). Despite apparent differences in nitrogen availability, biomass ofLarrea and density ofPerezia did not differ significantly among these sites.     

Drought stress influences leaf water content,photosynthesis, and water-use efficiency of <Emphasis Type="Italic">Hibiscus rosa-sinensis</Emphasis> at three potassium concentrations

The influence of drought stress (DS) upon whole-plant water content, water relations, photosynthesis, and water-use efficiency of Hibiscus rosa-sinensis cv. Leprechaun (Hibiscus) plants at three levels of potassium (K) nutritional status were determined after a 21-d gradually imposed DS treatment. Compared to K-deficient plants, adequate K supply improved the leaf water content (LWC) and leaf water relations of Hibiscus by decreasing the , and generally sustained rates of net photosynthesis (P _N) and transpiration (E), and stomatal conductance (g _s), both in DS and non-DS plants. In K-deficient Hibiscus, LWC, turgor potential ( _P), and P _N, E, and g _s as well as instantaneous water-use efficiency, WUE (P _N/E) were consistently lower, compared to K-sufficient plants. Carbon isotope discrimination () was lower (i.e. longterm WUE was greatest) in DS than non-DS plants, but K had no effect on during the 21-d drought treatment period under glasshouse conditions. However, the trend in the value of DS plants suggests that could be a useful index of the response of Hibiscus to DS under glasshouse growing conditions. Thus the incorporation of a properly controlled fertilization regime involving sufficient levels of K can improve the acclimation of P _N to low _leaf, increase P _N/E of Hibiscus, and may have potential benefit for other woody plants species.     

Zonal distribution of coarse woody debris and its contribution to net primary production in a secondary mangrove forest

Coarse woody debris (CWD) plays an important role in long-term carbon storage in forest ecosystems. However, few studies have examined CWD in mangrove forests. A secondary mangrove forest on an estuary of the Trat River showed different structures along vegetation zones ranging from the river’s edge to inland parts of the forest (the Sonneratia–Avicennia, Avicennia, Rhizophora, and Xylocarpus zones, respectively). The mass distribution of CWD stock in downed wood and standing dead trees along these vegetation zones was evaluated. Most of the CWD stock in the Sonneratia–Avicennia and Avicennia zones was found in downed wood, while it mainly accumulated in standing dead trees in the Rhizophora and Xylocarpus zones. The total mass of CWD stock that accumulated in each zone ranged from 1.56–8.39 t ha^?1, depending on the forest structure and inundation regimes. The annual woody debris flux in each zone was calculated by summing the necromass (excluding foliage) of dead trees and coarse litter from 2010 to 2013. The average woody debris flux was 5.4 t ha^?1 year^?1, and its zonal variation principally depended on the necromass production that resulted from forest succession, high tree-density, and lightning. Over all the zones, the above- and below-ground net primary production (ANPP and BNPP, respectively) was estimated at 18.0 and 3.6 t ha^?1 year^?1, respectively. The magnitude of BNPP and its contribution to the NPP was markedly increased when fine root production was taken into consideration. The contribution of the woody debris flux without root necromass to the ANPP ranged from 12 to 28%.     

Floristic composition and diversity of three swamp forests in northwest Guyana

This paper reviews the floristic composition, vegetation structure, and diversity of three types of swamp forest that cover a considerable part of Guyana's North-West District. Trees, shrubs, lianas, herbs, and hemi-epiphytes were inventoried in three hectare plots: one in Mora forest, one in quackal swamp, and one in manicole swamp. The Mora forest, flooded annually by white water, was dominated by relatively few, large individuals of Mora excelsa. The very dense, thin-stemmed quackal forest, almost permanently flooded by black water, was characterized by Tabebuia insignis and Symphonia globulifera and contained few palms. The somewhat less dense manicole swamp, flooded regularly by brackish water, was distinguished by large numbers of Euterpe oleracea. Although the three swamps showed little overlap in floristic composition and densities of dominant species, they represent some of the lowest diversity forest in the Neotropics, with an -diversity of 7.4 for the Mora forest, 8.2 for the quackal forest and 5.7 for the manicole swamp. When compared with similar vegetation types in the Guiana Shield, the swamp forests in this study show some interesting differences in species composition and density. The wetlands of the North-West District form the last stretch of natural coastline in Guyana and play an important role in the protection of riverine ecosystems. Furthermore, there is commercial potential for the extraction of non-timber forest products from these low-diversity forests. Nevertheless, in prolonged dry periods, large tracts of quackal forest are being burnt to give way to almost treeless, flooded savannas. For these reasons, adequate management and conservation strategies must be developed for the area.     

Patterns of vegetation and soil properties in a beaver-created wetland located on the Coastal Plain of Virginia

This study investigated vegetation and soil properties in a beaver-created freshwater wetland located on the Coastal Plain of Virginia near Washington, DC. We focused on the associations among floristic quality, soil physicochemistry, denitrification, and hydrologic conditions of the wetland to understand links between the effects of beaver engineering and ecosystem function. The floristic quality assessment index (FQI) and denitrification are two important indicators often used to examine overall habitat quality and ecosystem functioning of a wetland. Samples were collected from ten plots (10 m × 10 m each) in August 2014. Vegetation attributes included total percent cover, species richness (S), diversity, FQI, and prevalence index (PI). Soil attributes included organic matter (OM), total carbon, total nitrogen, gravimetric moisture (GM), pH, bulk density (D_b), and denitrification potential (DP). FQI was greater in the higher of the two standing water level categories, where D_b was lower, and was negatively associated with D_b but no other soil nutrient properties. DP was positively associated with soil nutrients, OM, and GM, but not with measured vegetation attributes nor standing water levels. We found higher soil GM, lower plant community PI, and lower plot S in this study compared to our previous study, with no changes to other vegetation or soil attributes, indicating enduring beaver activity and a resilient plant community. The outcome of the study includes regression models that best explain the association between structural and functional attributes of the ecosystem, which can be applicable to the study of other beaver-created wetlands. The study also provides partial evidence for the notion that low-lying areas dug out by beaver positively impact the FQI of wetlands.     

The role of alien plants in the natural coastal vegetation in central-northern Spain

Alien plants in coastal habitats and their influence on natural vegetation are studied. After 5 years working on this subject in the Basque Country and surrounding areas, a number of results from the coastal ecosystems are presented. These ecosystems are one of the most threatened and affected by the invasion of alien plants, especially shore dunes, saltmarshes and cliffs. These kinds of habitats, especially the dunes, experience significant pressure from human activities which favours the expansion of some of these species: Arctotheca calendula, Sporobolus indicus and Oenothera spp. The presence and abundance of these invasive plants and others such as Baccharis halimifolia, Cortaderia selloana, Spartina patens and Carpobrotus edulis in the plant communities in an area between the French border and the western part of the region of Cantabria have been studied. The degree of invasion of each plant in each syntaxonomic unit has been analysed.     

Biocontrolled soil nutrient distribution under the influence of an oxalogenic-oxalotrophic ecosystem

Background and aims

Root phenology is important in controlling carbon and nutrient fluxes in terrestrial ecosystems, yet, remains largely unexplored, especially in the Arctic. We compared below- and aboveground phenology and ending of the growing season in two contrasting vegetation types of subarctic tundra: heath and meadow, and their response to experimental warming in autumn.

Methods

Root phenology was measured in-situ with minirhizotrons and compared with aboveground phenology assessed with repeat digital photography.

Results

The end of the growing season, both below- and aboveground, was similar in meadow and heath and the belowground growing season ended later than aboveground in the two vegetation types. Root growth was higher and less equally distributed over time in meadow compared to heath. The warming treatment increased air and soil temperature by 0.5 °C and slightly increased aboveground greenness, but did not affect root growth or prolong the below- and aboveground growing season in either of the vegetation types.

Conclusions

These results imply that vegetation types differ in root dynamics and suggest that other factors than temperature control autumnal root growth in these ecosystems. Further investigations of root phenology will help to identify those drivers, in which including responses of functionally contrasting vegetation types will help to estimate how climate change affects belowground processes and their roles in ecosystem function.

     

Vegetation on avalanche paths in the alps

Vegetation pattern on avalanche paths in the Nordkette Mountains near Innsbruck (Tyrol, Austria) was studied using transect sampling. The plant communities represent a gradient from alpine grassland (Seslerio-Caricetum sempervirentis, via grassland with Trisetum distichophyllum) and nutrient-poor grassland (Carlino-Caricetum sempervirentis) to an avalanche grassland proper. Along this gradient disturbance decreases from higher to lower elevations. The topography of the avalanche path suggests a gradient from the central zone to the edge of the path, although a floristic zonation or grouping of species across the path cannot be detected. Disturbance and local topography are the dominant factors for the vegetation pattern on the avalanche paths investigated.Abbreviations DCA= detrended correspondence analysis     

Vegetation diversity of salt‐rich grasslands in Southeast Europe

Question

How does the plant species composition of Pontic–Pannonian salt‐rich habitats vary on a large geographical scale? Do the floristic differences between Pannonia and the Balkans correspond to the current phytosociological classification?

Location

Pannonia (Hungary, Slovakia, Austria, Czech Republic, Croatia, Serbia, Romania) and the Balkans (Bulgaria, Macedonia, Greece).

Methods

Two thousand four hundred and thirty‐seven relevés from halophytic and sub‐halophytic habitats were classified using a modified TWINSPAN. The crispness of classification was checked. DCA and CCA with climate data as explanatory variables were applied.

Results

The classification was best interpreted at the level of 15 clusters. The vegetation changed along the salinity gradient from sub‐halophytic grasslands (including Trifolion resupinati alliance of the Molinio‐Arrhenatheretalia class and Beckmannion eruciformis and Festucion pseudovinae p. p. alliances of the Festuco‐Puccinellietea class) and reed beds (Bolboschoenion maritimi p. p. alliance; the Phragmito‐Magnocaricetea class), through steppe and wet inland halophytic vegetation (Festucion pseudovinae p. p., Puccinellion limosae, Pucinellion convolutae, Bolboschoenion maritimi p. p. and Juncion gerardii of the Festuco‐Puccinellietea class) towards the extreme halophytic vegetation of the Thero‐Salicornietea, Crypsietea and Juncetea maritimi classes. This gradient was longer in the Balkan region, where it spanned from the sub‐mediterranean salt‐rich grasslands to the extremely halophytic vegetation at the Black Sea coast. The second most important gradient coincided with the water regime. Some vegetation types appeared to be confined to either the Pannonian or the Balkan region (especially within dry sub‐halophytic and steppe halophytic grasslands), while others were distributed across the entire study area. The above‐mentioned pattern did not always correspond with current classification systems.

Conclusions

Variation in salt‐rich vegetation predominantly follows the salinity and water regime gradients. Geographical variation, generally coinciding with climatic and historical effects, is also important, especially in drier salt‐rich habitats. Our large‐scale analysis of the floristic variation of salt‐rich habitats might be useful for the unification of classification systems that differ substantially between the countries involved. In addition, the analysis may be useful for adjustment of a classification system in the poorly explored Balkan region, where particular vegetation types were identified with, or delimited from, Central European vegetation types without detailed comparative analysis until now.