Early succession on lahars spawned by Mount St. Helens

The effects of isolation on primary succession are poorly documented. I monitored vegetation recovery on two Mount St. Helens lahars (mud flows) with different degrees of isolation using contiguous plots. Seventeen years after the eruption, species richness was stable, but cover continued to increase. That isolation affects community structure was confirmed in several ways. The dominance hierarchies of the lahars differed sharply. Detrended correspondence analysis on Lahar I showed a trend related to distance from an adjacent woodland, whereas vegetation on Lahar II was relatively homogeneous. Spectra of growth forms and dispersal types also differed. Lahar I was dominated by species with modest dispersal ability, while Lahar II was dominated by species with better dispersal. Variation between plots should decline through time, a prediction confirmed on Lahar II. Lahar I remained heterogeneous despite having developed significantly higher cover. Here, the increasing distance from the forest has prevented plots from becoming more homogeneous. At this stage of early primary succession, neither lahar is converging towards the species composition of adjacent vegetation. This study shows that isolation and differential dispersal ability combine to determine initial vegetation structure. Stochastic effects resulting from dispersal limitations may resist the more deterministic effects of competition that could lead to floristic convergence.     

Long‐term effects of drainage and initial effects of hydrological restoration on rich fen vegetation

Questions: What vegetational changes does a boreal rich fen (alkaline fen) undergo during a time period of 24 years after drainage? How is plant species richness affected, and what are the changes in composition of ecological groups of species? Is it possible to recover parts of the original flora by rewetting the rich fen? Which are the initial vegetation changes in the flora after rewetting? What are the major challenges for restoration of rich fen flora after rewetting? Location: Eastern central Sweden, southern boreal vegetational zone. Previously rich fen site, drained for forestry purposes during 1978–1979. The site was hydrologically restored (rewetted) in 2002. Method: Annual vegetation survey in permanent plots during a period of 28 years. Results: There were three successional stages in the vegetational changes. In the first stage there was a rapid (< 5 years) loss of rich fen bryophytes. The second step was an increase of sedges and early successional bryophytes, which was followed by an increase of a few emerging dominants, such as Molinia caerulea, Betula pubescens and Sphagnum spp. After rewetting, there are indications of vegetation recovery, albeit at slow rates. Depending on, for instance, initial species composition different routes of vegetation change were observed in the flora after drainage, although after 24 years, species composition became more homogenous and dominated by a few species with high cover. Conclusion: Major changes have occurred after changes in the hydrology (drainage and rewetting) with a severe impact on the biodiversity among vascular plants and bryophytes. Several rich fen bryophytes respond quickly to the changes in water level (in contrast to vascular plants). The recovery after rewetting towards the original rich fen vegetation is slow, as delayed by substrate degradation, dispersal limitation and presence of dominant species.     

Timing of white-tailed deer browsing affects wetland plant communities

White-tailed deer (Odocoileus virginianus Zimm.) have the potential to alter plant community composition and successional trajectory by browsing differentially on forb, graminoid, and woody species. The objective of this study was to determine if seasonal elimination of deer browsing changed wetland plant community composition and structure. We established 66 deer exclosure plots in two wetland vegetation communities in Canaan Valley, West Virginia, USA. Plots were established in April 2005 and monitoring was conducted in June and October, 2005–2007 to obtain data on both early and late species. Composition differed between control and treatment plots in Solidago spp.–Rubus hispidus L. communities in late-protected plots (enclosed July–October) when data were gathered in October. Community composition also varied in early-protected plots (enclosed April–July) when data were gathered in June. Forb cover increased in treatment plots in Solidago spp.–Rubus hispidus communities. Composition differed in Populus tremuloides Michx. communities in late-protected and continuously protected plots. There was no increase in cover by any wetland indicator status categories after 2 years of protection. Timing of browse played an influential role in the effect that white-tailed deer have on wetland plant communities. Our results suggest that reducing browsing pressure seasonally can increase forb species cover.     

Flood disturbance and riparian species diversity on the Colorado River Delta

We investigated the influence of channel migration and expansion on riparian plant species diversity along the lower Colorado River near the United States–Mexico border. Using repeat aerial photography in a GIS we identified and classed areas of low, moderate, and high disturbance frequency caused by channel expansion and migration. Replicate vegetation plots (12m×12m) were sampled in each of the three disturbance classes. One-way ANOVA was used to test for differences in species richness, species diversity (using the Shannon–Weiner Index) and overall percent ground cover of plants between the three disturbance classes. Regardless of disturbance class, plots were dominated by trees or shrubs, especially the non-native Tamarix ramosissima, as well as Pluchea sericea, Baccharis salicifolia and Salix goodingii. Clearly woody species constitute the great bulk of overall species richness, percent ground cover, and species diversity (H) in each disturbance group. No overall statistically significant differences were revealed among the disturbance groups for values of species richness, percent ground cover, or the Shannon–Wiener Index, though paired contrasts of means revealed that total percent ground cover on low disturbance plots was significantly higher than on moderately disturbed plots. Spatial and temporal variability in riparian diversity in the study area appears to hinge on factors other than disturbance frequency such as salt or drought stress. Alternately, our results could be interpreted as suggesting that in the presence of intensive flow regulation, disturbance plays a secondary role to ecological stresses, similar to that demonstrated by others. Intentional flood pulses are advocated as a restorative management strategy for improving plant productivity, management of exotic species (particularly T. ramosissima), and restoration of overall biodiversity.     

Early primary succession on Mount St. Helens,Washington, USA

Abstract. The north slope of Mount St. Helens was sampled with 141 circular 100-m² plots to describe vegetation and environmental patterns 13 yr after the 1980 eruption. At least 114 vascular plant taxa were encountered. We recognized four habitat types: Refugia, Pumice barrens, Pyroclastic surfaces and Drainages. A fifth category, Lupine patches, includes samples on primary surfaces that were rapidly colonized. Refugia provided small enclaves where underground portions of several species survived the eruption. They retained an inconsistent array of forest understory species and contained 86 species (mean = 20.8 per plot). Refugia are dominated by woody species such as Penstemon cardwellii, Rubus spp., Ribes spp. and Alnus sinuata, with herbs such as Agrostis diegoensis, Luzula parviflora and Anaphalis margaritacea. Anaphalis represents a suite of species that invaded Refugia after the eruption. Diversity (N₂ and H′) is significantly greater in Refugia than in any other habitat. No plants survived on primary sites, which remain sparsely vegetated and dominated by readily dispersed taxa. Total richness ranges from 36 species (9.9 per plot) on pyroclastic surfaces, through 42 species (11.2 per plot) in drainages, to 66 (11.7 per plot) on Pumice barrens. H′ and N₂ of the three habitats do not differ significantly. Lupine-dominated vegetation occurs sporadically in Pyroclastic and drainage habitats. Lupine patches are characterized by high Lupinus cover and a suite of invaders. These sites have high cover and 52 species (12.6 per plot). H′ and N₂ scores were significantly lower than any other habitat due to strong lupine dominance. Canonical Correspondence Analysis showed that site history and slope contributed most to species composition. Geographic effects accounted for 10 25 % of the explained species-environment relationship. Forest understory species have migrated only short distances and have made negligible contributions to vegetation development. A few species common in Refugia, including Agrostis diegoensis and Carex mertensii, have invaded barren surfaces, but most have not. Refugia also have been invaded by open site species abundant on the Pumice Plain. The heterogeneity of plots within habitat types and small statistical linkage of vegetation to environmental and spatial factors suggests that stochastic events have played a leading role in early primary succession.     

Vegetation regeneration on blanket mire after mechanized peat-cutting

• 1 Blanket mire in Northern Ireland is an ecologically threatened habitat in which land use for hand peat‐cutting, forestry and agriculture has had a major influence. A recent land use change is the introduction of tractor‐powered peat‐harvesting. In this paper, the effect of machine peat‐cutting on ombrotrophic blanket mire vegetation is assessed from a regional sample of cut and uncut plots.
• 2 Principal components analysis identified water‐table depth and grazing intensity as major factors influencing the species composition of uncut mire. A key variable affecting the composition of machine‐cut mire across the drainage gradient was the number of times cut, with multiple annual cutting causing progressive decreases in acrotelm depth, catotelm bulk density and plant cover. Ericaceous species and Sphagnum spp. were particularly sensitive to cutting, with Eriophorum angustifolium and Campylopus introflexus characteristic of multiple‐cut sites.
• 3 Redundancy analysis, with number of times cut partialled out, showed that recovery time accounted for a significant amount of variance in vegetation composition. Species that significantly increased in abundance with recovery time were Sphagnum spp., Odontoschisma sphagni , Erica tetralix and Drosera rotundifolia.
• 4 Sites cut frequently, or which were grazed, recovered more slowly. Recovery from cutting was partly dependent on the post‐cutting structure of the mire surface and the species that survive cutting. The rate of recovery on sites cut once, then abandoned, is relatively rapid compared with multiple‐cut sites where species colonization is constrained by bare compacted peat.

     

Limits to convergence of vegetation during early primary succession

Questions: Primary succession, measured by changes in species composition, is slow, usually forcing a chronose‐quence approach. A unique data set is used to explore spatial and temporal changes in vegetation structure after a 1980 volcanic eruption. On the basis of data from a transect of 20 permanent plots with an altitudinal range of 250 m sampled through 2005, two questions are asked: Do changes along the transect recapitulate succession? Do plots converge to similar composition over time? Location: A ridge between 1218 and 1468 m on Mount St. Helens, Washington, USA. Methods: Repeat sampling of plots for species cover along a 1‐km transect. Floristic changes were characterized by techniques including DCA, clustering and similarity. Results: Species richness and cover increased with time at rates that decreased with increasing elevation. The establishment of Lupinus lepidus accelerated the rate of succession and may control its trajectory. Diversity (H) at first increased with richness, then declined as dominance hierarchies developed. Primary succession was characterized by overlapping phases of species assembly (richness), vegetation maturation (diversity peaks, cover expands) and inhibition (diversity declines). Each plot passed through several community classes, but by 2005, only four classes persisted. Succession trajectories (measured by DCA) became shorter with elevation. Similarity between groups of plots defined by their classification in 2005 did not increase with time. Similarity within plot groups converged slightly at the lower elevations. Despite similarities between temporal and spatial trends in composition, trajectories of higher plots do not recapitulate those of lower plots, apparently because Lupinus was not an early colonist. Any vegetation convergence has been limited to plots that are in close proximity.     

Bleaching of reef coelenterates in the San Blas Islands,Panama

Starting in June 1983, 25 species of hermatypic corals, gorgonians, hydrocorals, anemones and zoanthids in the San Blas Islands, Panama, began showing signs of a loss of colour leading in some cases to a white bleached appearance. Histologic examination of six coral species indicated that bleaching was associated with drastic reductions in the density of zooxanthellae and with the atrophy and necrosis of the animal tissue. The severity of the bleaching varied among species and many species were unaffected. The species most extensively affected were: Agaricia spp., which became completely bleached and frequently died; Montastraea annularis which bleached and continued to survive; and Millepora spp. which bleached white but quickly regained their colouration. Shallow reefs dominated by Agaricia spp. suffered the most extensive bleaching. At one site, Pico Feo, 99% of the Agaricia (32% of the living cover) was bleached. On fore reers, which were dominated by Agaricia spp. and M. annularis, the proportion of M. annularis bleached ranged from 18 to 100% and that of Agaricia spp. from 30 to 53%. Transects at Sail Rock and House Reef were surveyed in August 1983 and January 1984. At those sites, 53% of the Agaricia cover died between August and January. The remaining living cover of Agaricia and of all other species exhibited normal colouration in January. Salinity and temperature were monitored every second day at 4 m depth between May 10 and August 28, 1983 at one of the localities. Bleaching was first observed within two weeks of a 2 °C rise in temperature which occurred in late May 1983. Temperatures remained at or above 31.5 °C for the following 3 weeks and were at or above 30 °C for an additional 4 weeks. The bleaching of corals in the San Blas was most likely due to those elevanted temperatures.     

Species richness, diversity and biomass production of desert annuals in an ungrazed Rhanterium epapposum community over three growth seasons in Kuwait

Two blocks, each consisting of twelve 0.25 m²permanent plots, were established in a community dominated by desert annuals inan area of Kuwait protected from grazing, and community attributes wereinvestigated over three growth seasons. A linear relationship was found betweenestimated desert annual cover and biomass production. Species frequency wasassessed by the number of 100 cm² subplots occupied byaspecies in a block (block incidence). Over the three seasons,vegetation features varied considerably. The first season (spring 1997) wascharacterised by very sparse vegetation cover, low vegetation block incidence(sum of individual block incidences of each species present in a block) and lowspecies richness. The second season (spring 1998) had high vegetation cover,relatively low vegetation block incidence, but high species richness. In thethird season (spring 2000), vegetation cover was very sparse (as in 1997), butboth blocks had the highest vegetation block incidence of the three years andspecies richness was moderately high, although individual plants were verysmall. The growth period was much shorter in the very productive andspecies-rich 1998 season than in 2000. Fluctuations in biomass and speciesincidence coincided with pronounced variation in key meteorological variables,in particular the onset of the first rains, the amount of rainfall during thegrowing season and its temporal distribution. Species composition, however,appears mainly to be determined by the amount and possibly the timing of thefirst rainfalls of the season to trigger germination. There was little evidenceto suggest that particularly favourable or unfavourable microsites existed inplots for more than one vegetation period, either for individual species or fordiversity in general. Despite substantial between-season fluctuations inincidence, the relative abundances of the more frequent species to each otherremained broadly similar over the three seasons, with Plantagoboissieri being the predominant species and accounting for thelargest proportion of biomass.     

Does understory vegetation reflect the history of fluvial disturbance in a riparian forest?

We have examined the relationship between the history of fluvial disturbance and understory vegetation in a riparian forest. The study site was divided into three sites, by use of aerial photographs and topographical maps, with different histories of fluvial disturbance: (1) Fagus-type on land that has not been flooded for the last 39 years, at least; (2) Populus-type on land that has not been flooded since debris flow occurred 34 years ago; and (3) Salix-type on land that has been flooded periodically from an abandoned channel since debris flow occurred 34 years ago. Species richness in the Salix-type was significantly higher than in the other types. Detrended correspondence analysis revealed obvious floristic differences among the three canopy types. Canonical correspondence analysis showed that herbaceous species were mainly found on lower plots with high moss cover, implying that moss layers may capture seeds transported by the stream. Tall herbs occurred in less shaded plots and on higher plots, suggesting that their rapid growth prevented the occurrence of other species. Fagus-type was dominated by species with ingested fruits which depended on animals for their dispersal. Populus and Salix-types were dominated by species with wind dispersal or no dispersal mechanism, which depended on physical phenomena for dispersal. Attributes of current understory vegetation were connected with historical events, suggesting that riparian vegetation reflects the history of fluvial disturbance.     

Effects of sedimentation on macroalgae: species-specific responses are related to reproductive traits

Although increases in sedimentation have been proposed to interfere with benthic communities in many coastal areas worldwide, few experimental studies have investigated the effect of sedimentation on community composition and assessed species-specific responses. In a field experiment on a rocky shore on the Swedish east coast (northern Baltic Proper) we confirmed the hypotheses that ambient sedimentation influences macroalgal abundance and community composition, and that species-specific responses to sedimentation correlate with reproductive strategies. We followed the establishment and development of macroalgal vegetation on artificial substrates at 8-m and 15-m depth for 4.5 years while manipulating the depositional environment by regularly removing accumulated sediment. Sediment removal significantly favoured macroalgal development and vegetation cover. Responses of macroalgal species to the sediment treatments were clearly species-specific; for example, the ephemeral green algae (Cladophora glomerata and Enteromorpha spp.) were highly tolerant to sedimentation while belt-forming perennial brown algae (Fucus vesiculosus and Sphacelaria arctica) were not. Accordingly, multivariate analyses (redundancy analysis) showed that variance in species abundances were significantly correlated to sediment conditions. The effect of sediment removal was higher at 15-m than at 8-m depth and some species distributions seemed limited in depth by the present sediment load (e.g. F. vesiculosus). Vegetative propagation was common in the study area and many species mainly depended on dispersal by fragmentation. Generally, species with an extended reproductive period, either by long continuous spore release (C. glomerata and Enteromorpha spp.) or vegetative dispersal by fragmentation (e.g. Furcellaria lumbricalis and Polysiphonia fucoides), were most tolerant to sedimentation. This paper demonstrates long-term effects of sediment deposition on the development of a macroalgal community over several growing seasons. The results indicate that variation in sediment loads is an important constraint for species local distributions and abundances, and affects the composition of sublittoral rocky-shore macroalgal communities.     

Changes in forest understory associated with Juniperus encroachment in Oklahoma,USA

Question: Does understory vegetation cover and richness decline along a gradient of increasing Juniperus virginiana midstory canopy cover and is that decline best correlated with litter accumulation? Location: Cross Timbers Forest in Payne County, OK, USA. Methods: We measured vegetation in forest gaps as well as forest areas without J. virginiana, at the inner and outer edge of J. virginiana canopies and near J. virginiana trunks (200 plots) and compared vegetation differences among location to light, litter, soil and microclimate variables. Results: Species richness (11 spp m^?2 to 6 spp m^?2) and summer vegetation cover (53.3% to 12.7%) declined with proximity to trunks. Regression indicated that richness declines (R²=0.08) and cover (R²=0.18) were best correlated with J. virginiana litter accumulation. Partial canonical correspondence analysis (pCCA) revealed two strong canonical axes, one related to litter/light and another to cover of Quercus spp. versus J. virginiana. Tree seedlings and woody vines dominated near J. virginiana. Forbs, graminoids and Quercus spp. seedlings were more common in areas without J. virginiana. Conclusions: Increasing J. virginiana and consequent litter additions alter understory biomass and composition and, through inhibiting Quercus spp. recruitment, may lead to changes in overstory composition. Decreases in herbaceous litter, which historically contributed to fuel accumulation, may have positive feedback effects on midstory encroachment by reducing the potential for prescribed burning.     

Colonisation by native species of abandoned farmland adjacent to a remnant patch of Mediterranean steppe

We studied plant distribution at the margins (0–10 m) of three formerly cultivated plots adjacent to a remnant patch of the only Mediterranean steppe of France: La Crau. We sampled above-ground vegetation, seed bank, seed rain and seed dispersal by ants in order to assess the colonisation of steppe species at margins. Our results showed that (1) present day above-ground vegetation of formerly cultivated plots is influenced more by former agricultural practices (duration of melon cultivation, fertilisation) and time since abandonment than their position in relation to the steppe. (2) An edge effect was identified as the vegetation of the steppe (e.g. Thymus vulgaris, Salvia verbenaca, Linaria arvensis) colonises the formerly cultivated plots (coefficients of similarity between vegetation on margins and steppe vegetation decreased with distance from boundaries (r = -0.65, p < 0.001)). (3) Permanent deep seed bank (10-20 cm) did not contribute to either site or edge effects and was characterised by weed species from previous melon cultivation (e.g. Chenopodium album, Kicksia elatine, Portulaca oleracea, Solanum nigrum). (4) Seed rain density decreased with distance from edges (r = -0.39, p < 0.001) and seemed positively correlated to T. vulgaris cover. (5) The number of seeds in ant-traps seemed correlated to T. vulgaris cover. We concluded that after 19 years of abandonment, only about half of the steppe species have colonised just the few meters of the margins of the formerly cultivated plots and that restoration from seed bank, seed rain or seed dispersal by ants is unlikely. Our results are thus discussed within the context of restoring the steppe plant community on formerly cultivated plots.

     

The role of drought,disturbance, and seed dispersal in dominance shifts in a temperate grassland

Aims

More intense and frequent droughts predicted for the future will heavily affect grasslands worldwide and, along with various other disturbances, possibly trigger major vegetation shifts. Therefore, documenting these changes and understanding the mechanisms behind them is essential. Our study aimed to investigate how dominant species in a semiarid grassland respond to a combination of small-scale experimental disturbances and naturally occurring droughts and uncover the underlying mechanisms.

Location

Central Hungary.

Methods

We conducted a small-scale disturbance experiment in a semiarid temperate grassland and followed recovery for 18 years, including severe drought events. In 1999, we established 16 sites, eight dominated by Festuca vaginata and another eight by Stipa borysthenica, the two dominant species of sand grasslands in the region. At each site, three permanent plots were marked that received either a cutting or digging treatment or remained as controls. We monitored the cover and density changes of Festuca and Stipa annually.

Results

In the early years following the disturbance, Festuca recovered at a similar rate under both disturbance treatments, while Stipa recovered faster in cut than in dug plots. When natural drought events caused major diebacks of both species, Stipa recovered very quickly and regained dominance in initially Stipa-dominated plots, and it also took over in initially Festuca-dominated control and cut plots. However, digging at Festuca-dominated sites delayed drought-induced Stipa colonisation and thus favoured Festuca recovery. We found that the poor performance of Stipa in dug plots was related to sharply reduced seedling establishment, which resulted from the low number of seeds captured by the bare soil surface after digging.

Conclusions

Our results demonstrate that recurring drought events may induce dominance shifts in temperate grasslands, but small-scale disturbances can modulate vegetation responses. Our findings emphasise the importance of post-disturbance regeneration patterns in drought-induced vegetation shifts and show that seed dispersal strategy may have a major effect on vegetation dynamics.     

Size of the local species pool determines invasibility of a C4-dominated grassland

The size of the local species pool (i.e., species surrounding a community capable of dispersal into that community) and other dispersal limitations strongly influence native plant community composition. However, the role that the local species pool plays in determining the invasibility of communities by exotic plants remains to be evaluated. We hypothesized that the richness and abundance of exotic species would be greater in C4‐dominated grassland communities if the local species pool included a larger proportion of exotic species. We also predicted that an increase in the exotic species pool would increase the invasibility of sites thought to be resistant to invasion (annually burned grassland). To test these hypotheses, study plots were established within two long‐term (>20 yr) fire experiments at a tallgrass prairie preserve in NE Kansas (USA). Study plots were surrounded by either a small pool of exotic species (small species pool (SSP) plots; six species) or a larger exotic species pool (large species pool (LSP) plots; 18 species). We found that richness and absolute cover of exotic species was significantly (P<0.001) lower (～70 and 90%, respectively) in annually burned compared to unburned plots, regardless of the size of the exotic species pool. As predicted, exotic species richness was higher (P<0.001) for LSP plots (3.9 per 250 m2) than for SSP plots (0.7 per 250 m2); however, absolute cover was unaffected by the size of the exotic species pool. In the absence of fire, plots with a LSP had four times as many exotic species than SSP plots. An increase in the local exotic species pool also increased the invasibility of annually burned grassland. Indeed, richness of exotic plant species in annually burned LSP plots did not differ from unburned plots with a SSP, indicating that a larger pool of exotic species countered the negative effects of fire. These findings have important implications for predicting how the invasion of plant communities may respond to human‐induced global changes, such as habitat fragmentation. Community characteristics or factors such as frequent fires in grasslands may impart resistance to invasions by exotic species in large, intact ecosystems. However, when a large pool of exotic species is present, frequent fire may not be sufficient to limit the invasions of exotic plants in fragmented landscapes.     

Experimental Restoration of Native Vegetation in Indiana Dunes National Lakeshore

We investigated the effects of prescribed fire, herbicide treatment, and sod removal on the eradication of exotic grasses and the establishment of native plant species in 24 experimental restoration plots in three razed residential sites within the boundary of Indiana Dunes National Lakeshore. During 1992–1995, herbicide treatment and sod removal decreased the combined cover of Poa pratensis (Kentucky blue grass) and Agropyron repens (quackgrass) significantly (from 82% to 13%, and 85% to 8%, respectively), whereas fire did not suppress such exotic lawn grasses. In 1993, several opportunistic species, represented by Cyperus spp. (umbrella sedges), Digitaria sanguinalis (crab grass), and Ambrosia artemisiifolia (common ragweed), filled the gaps left by the removal of lawn grasses. For the same period, Detrended Correspondence Analysis revealed a clear vegetation divergence between the control-fire plots and the herbicide-sod removal plots. While Poa pratensis and Agropyron repens continued to dominate the control and fire plots, the planted native species, represented by Schizachyrium scoparium (little blue-stem), Sorghastrum nutans (Indian grass), Rudbeckia hirta (black-eyed Susan), and Monarda punctata (horsemint), began to dominate in the herbicide and sod removal plots from 1994. In both herbicide and sod removal plots, the ground cover of grasses (68%) was much higher than the forbs (10%). The herbicide plots, where exotic species were removed but nitrogen-rich top soils were not removed, showed a higher diversity of planted native species than the sod removal plots (where both exotic species and top soils were removed) and the control-fire plots (where neither was removed). This finding suggests that an optimum but not excessive concentration of soil nitrogen is needed to support a maximum species diversity in such infertile substrate as sandy soil. In addition, the decrease in potassium in all plots, regardless of treatment, suggests that potassium may become a limiting factor for our restored native vegetation.     

Ungulates increase forest plant species richness to the benefit of non‐forest specialists

Large wild ungulates are a major biotic factor shaping plant communities. They influence species abundance and occurrence directly by herbivory and plant dispersal, or indirectly by modifying plant‐plant interactions and through soil disturbance. In forest ecosystems, researchers’ attention has been mainly focused on deer overabundance. Far less is known about the effects on understory plant dynamics and diversity of wild ungulates where their abundance is maintained at lower levels to mitigate impacts on tree regeneration. We used vegetation data collected over 10 years on 82 pairs of exclosure (excluding ungulates) and control plots located in a nation‐wide forest monitoring network (Renecofor). We report the effects of ungulate exclusion on (i) plant species richness and ecological characteristics, (ii) and cover percentage of herbaceous and shrub layers. We also analyzed the response of these variables along gradients of ungulate abundance, based on hunting statistics, for wild boar (Sus scrofa), red deer (Cervus elaphus) and roe deer (Capreolus capreolus). Outside the exclosures, forest ungulates maintained higher species richness in the herbaceous layer (+15%), while the shrub layer was 17% less rich, and the plant communities became more light‐demanding. Inside the exclosures, shrub cover increased, often to the benefit of bramble (Rubus fruticosus agg.). Ungulates tend to favour ruderal, hemerobic, epizoochorous and non‐forest species. Among plots, the magnitude of vegetation changes was proportional to deer abundance. We conclude that ungulates, through the control of the shrub layer, indirectly increase herbaceous plant species richness by increasing light reaching the ground. However, this increase is detrimental to the peculiarity of forest plant communities and contributes to a landscape‐level biotic homogenization. Even at population density levels considered to be harmless for overall plant species richness, ungulates remain a conservation issue for plant community composition.     

Deer Browsing,Forest Edge Effects,and Vegetation Dynamics Following Bottomland Forest Restoration

Vegetation composition and forest stand development are frequently mediated by browsing herbivores. These relationships have received little attention in a forest restoration context even though White‐tailed deer (Odocoileus virginianus) is likely to influence these agriculture, forest, and restored ecosystem mosaic landscapes. Tree species composition, herbaceous vegetation, and deer browsing patterns were assessed 5 and 7 years following bottomland hardwood forest restoration on a 526‐ha site in the Cache River watershed in southern Illinois, United States. Light‐seeded tree species (Fraxinus pennsylvanica, Acer negundo, Liquidambar styraciflua, and Platanus occidentalis) of volunteer origin dominated the woody vegetation component, with especially high stocking and density near existing forest cover and potential seed sources. At more distant locations, presumably planted Quercus spp. were more likely to dominate and were the only tree species found in 15% of plots in year 7. Quercus stocking increased over the course of the study, constituting 7% of trees during year 7. Deer herbivory was associated with reduced stem height and disproportionately impacted seedlings of Quercus palustris and Celtis spp. Our results suggest that deer browsing influences forest stand composition and density as a function of distance from the nearest forest edge. Herbaceous vegetation had little impact on early stand development. Continued spread of the exotic and invasive Lonicera japonica and potential mortality of F. pennsylvanica due to an anticipated Emerald ash borer (Agrilus planipennis) epidemic, combined with low stand density and delayed canopy closure, may result in persistent overstory gaps and compromise long‐term restoration success.     

Biodiversity impacts of an invasive grass: ant community responses to <Emphasis Type="Italic">Cenchrus ciliaris</Emphasis> in arid Australia

Buffel grass (Cenchrus ciliaris) is a highly invasive species that thrives in semi-arid environments and has the capacity to transform native vegetation outside its native range. However, there is limited information on the effects of buffel grass invasion on native fauna. We used an experimental approach to investigate the impact of buffel grass on the native ant fauna near Alice Springs in semi-arid central Australia. A series of plots where buffel grass was removed and native vegetation had regenerated (B?), paired with adjacent control plots heavily invaded by buffel grass (B+), were used to assess the impact of buffel grass on ant diversity and composition, and on rates of seed dispersal by ants. Differences in ant diversity were also compared between two microhabitat types: bare ground and under cover, to examine the extent to which any impacts were a simple function of change in vegetation cover. Ant abundance and richness were approximately 50 % higher in B? compared with B+ plots, and higher abundance was especially pronounced for the very thermophilic Hot-Climate Specialists. Ant species composition varied significantly between plot types. B? plots supported more species and individuals in both bare and covered microhabitats, which suggests that the differences in ant diversity was not simply through changes in vegetation cover. Rates of seed removal by ants were marginally higher in B? plots. Our findings indicate that buffel grass has a major impact on a dominant faunal group of arid Australia, and possibly reduces the delivery of an important ecosystem service. In addition, our study demonstrates the potential for ecosystem recovery following effective buffel grass management.     

Altitudinal changes in composition and structure of mountain-temperate vegetation: a case study from the Western Carpathians

Changes in composition and structure of plant communities in relation tothe soil and snow cover variation were analyzed along an altitudinal transect(1150–1750 m) from the mountain-temperate forests to a woodyshrub community and alpine meadows on Mt Velký Gápel', Slovakia.The soils below the treeline (1510 m) had a more developedorganic layer above the mineral substratum. Generally, soil depth decreased asthe altitude increased, although the maximum values were recognized at a middlealtitude in a beech stand. Snow was redistributed by westerly winds from theridgeline down to the upper forest margin. Mean snow depth decreased withaltitude up to almost snow-free sites around the summit. In the 48 plots at 16sites we recorded 118 taxa including 6 tree, 7 shrub, 18 grass, 42 herb, 5fern,25 moss and 15 lichen species. The species diversity showed no distinctrelationship to altitude but declined with canopy consolidation. The TWINSPANfloristic classification distinguished five groups of community typescharacterised by different dominants, and a further three clusters of samplesfrom transition zones. Horizontal compositional heterogeneity increased inareaswhere trees were aggregated and tree basal area was smaller. Vegetationcomposition became more patchy at open-canopy Acerpseudoplatanus–Abies alba mixed forest at 1150 m,in Picea abies forest limit 1470 m, andin Pinus mugo krummholz at 1590 m. Speciesturnover of the entire transect was 6.1 half-changes as estimated by DCA.Despite this heterogeneity, none of the 15 elevational bands had significantaggregation of species' limits. Vegetation varied continuously, with individualspecies overlapping in transition zones delimited by dominant taxa. Thecoincident aggregation of up-slope and down-slope boundaries was found at abelt1430–1510 m. This discrete ecotone corresponds to a shiftfrom the closed coniferous forest to P. mugo krummholz.Thesecond inherent up-slope boundary aggregation indicated the P.mugo krummholz – alpine meadow vegetation transition at1700 m. Spatial analysis (K-function) of eight forest plots(0.12 ha each) showed that at lower elevation, adult trees of thebroad-leaf forest were closer to a random arrangement while at higherelevation,trees of evergreen coniferous stands became aggregated toward the forest limitwith the highest intensity from 2 to 4 m. Altitudinal gradient andrelated factors explained 35% of the variance in vegetation data.Canonical correspondence analysis also showed that main vegetation changesabovethe treeline area were associated with the topographic pattern of pine shrubsand snow cover.