Effects of fire on the vegetation of a lowland heathland in North-western Italy

This study focuses on the effect of fire on lowland heathlands at the extreme southern edge of their European distribution (Vauda Nature Reserve, NW Italy). Forty-nine plots (50 m radius) were surveyed between 1999 and 2006. Each year, fire occurrences were recorded and per cent cover of four vegetation types (grassland, heath, low shrubland, and tall shrubland) was estimated in each plot. Vascular plant species richness was also recorded in 255, 1 m² quadrats. After a fire, grassland vegetation expanded, but then declined rapidly as heath and shrubland recovered: 7 years after a fire, tall shrubland encroached on to more than 40% of the plots, and grassland declined from 50% to 20% cover. Between 1999 and 2006, Betula pendula shrubland greatly expanded, while grassland decreased over most of the Reserve, even where fire frequency was high. Tall shrubland had low plant diversity and was dominated by widespread species of lower conservation value. By contrast, early successional vegetation (grassland and low shrubland) had higher richness and more narrowly distributed species, indication that the development of tall shrubland causes significant species loss in the heathland. Italian lowland heathlands are characterized by high rates of shrubland encroachment that threatens both habitat and species diversity. Burning frequencies of once in 3–6 years seem appropriate in this habitat, but burning alone might not suffice without actions to increase herbivore grazing.     

Buried seed populations on the volcano Mt. Usu,northern Japan,ten years after the 1977–78 eruptions

In 1987, a study on buried seed populations was conducted in the crater basin of Mt. Usu, a volcano located in northern Japan, where the vegetation had beeen almost completely destroyed by eruptions in 1977 and 1978. The former vegetation had consisted of grassland and broad-leaved forest. In the areas formerly occupied by this grassland and forest, 2128.0 and 1985.3 seeds per square meter, respectively, were extracted from 12 blocks of the former topsoil using a floattion method. This revealed that many seeds were still viable even after ten years of burial under thick volcanic deposits. The seeds were distributed more in sandy soil than in rocky soil of the former topsoil. Twenty-five species, most of which favored grassland, were detected in both the former grassland and forest. From comparison of α-and β-diversities between the grassland and forest, the structure of the buried seed population was considered likely to have been more diverse in the forest than in the grassland. The determinants of composition of the buried seed populations were discussed with reference to the former vegetation and soil characteristics.     

Absence of snow cover reduces understory plant cover and alters plant community composition in boreal forests

Snow regimes affect biogeochemistry of boreal ecosystems and are altered by climate change. The effects on plant communities, however, are largely unexplored despite their influence on relevant processes. Here, the impact of snow cover on understory community composition and below-ground production in a boreal Picea abies forest was investigated using a long-term (8-year) snow cover manipulation experiment consisting of the treatments: snow removal, increased insulation (styrofoam pellets), and control. The snow removal treatment caused longer (118 vs. 57 days) and deeper soil frost (mean minimum temperature −5.5 vs. −2.2°C) at 10 cm soil depth in comparison to control. Understory species composition was strongly altered by the snow cover manipulations; vegetation cover declined by more than 50% in the snow removal treatment. In particular, the dominant dwarf shrub Vaccinium myrtillus (−82%) and the most abundant mosses Pleurozium schreberi (−74%) and Dicranum scoparium (−60%) declined strongly. The C:N ratio in V. myrtillus leaves and plant available N in the soil indicated no altered nitrogen nutrition. Fine-root biomass in summer, however, was negatively affected by the reduced snow cover (−50%). Observed effects are attributed to direct frost damage of roots and/ or shoots. Besides the obvious relevance of winter processes on plant ecology and distribution, we propose that shifts in the vegetation caused by frost damage may be an important driver of the reported alterations in biogeochemistry in response to altered snow cover. Understory plant performance clearly needs to be considered in the biogeochemistry of boreal systems in the face of climate change.     

A conceptual model of coastal dune ecology synthesizing spatial gradients of vegetation, soil, and geomorphology

Patterns of coastal dune vegetation are closely related with soil conditions controlled by geomorphic forms and processes. This study developed a conceptual model integrating these relationships in a spatially explicit manner. A rectangle of 180 × 280 m containing 126 grids of 20 × 20 m was established in the Sindu coastal dunefield in west Korean Peninsula. Sampling from each grid determined 11 soil properties and identified percent cover of 21 woody and herbaceous plant species. Digital elevation models were generated by topographic survey and used to derive eight topographic parameters. Redundancy analysis and canonical correspondence analysis examined the effect of geomorphic factors on edaphic characteristics and the edaphic influence on spatial distribution of vegetation, respectively. The spatial pattern of soil properties and plant species were inferred from spatial interpolation techniques. In the foredune area, distance from the coastline was a significant indicator of soil nutrients derived from the marine sources by aeolian processes. This favored the dominance by Elymus mollis. Moisture-tolerant species (e.g., Calamagrostis epigeios) had high cover in the acidic soils of dune slacks, which covaried with wetness index, an indirect measure of the depth to the freshwater table. Vegetation–soil interactions (e.g., nitrogen fixation by legumes) were important in secondary dune areas, with topographic effects less significant. Vegetation, soil, and geomorphic factors are closely connected in a causal chain across a whole dune area. Our model thus addresses the importance of integrating foredune, dune slack, and secondary dune into one continuous system.     

Additive Partitioning of Diversity Reveals No Scale-dependent Impacts of Large Ungulates on the Structure of Tundra Plant Communities

Large herbivores can change ecosystem functioning by impacting plant diversity. However, although such impacts are expected to be scale-dependent in ecosystems with wide-roaming ungulates, scaling issues rarely enter empirical assessments. We here test the hypothesis that the impact of increased reindeer abundance on plant diversity in alpine tundra is scale-dependent. Based on potentially high productivity of the focal habitat units and hence the possibility of positive grazer impacts on plant diversity we predicted higher α and β diversity at the habitat scale where reindeer densities are high. We also explored whether there were differences in diversity patterns at larger scales, including the scale of reindeer management districts. We estimated grazing disturbance as high versus low reindeer density in selected districts (a total extent of 7421 km²) of Northern Norway where reindeer-induced vegetation shifts are debated. We focus on dominance patterns because they can quantify the vegetation state and thus performed additive partitioning of Simpson diversity on multiple scales assessing also species’ contributions to diversity. Contrary to our predictions, we found only weak scale-dependent effects of reindeer grazing on plant diversity. Under high reindeer densities there was evidence for a landscape-scale homogenization of the vegetation, but the predicted α and β diversity increases at the habitat scale were not found. Consistently through all scales considered, four shrub species contributed the most to plant diversity. These results contradict the idea that reindeer at high stocking densities induce shifts in plant species dominance in productive habitats. We conclude that context-dependencies such as spatial scales of management units and habitat types need to be explicitly considered in evaluations of the impacts of large ungulates on plant diversity.     

Interrill erosion at disturbed alpine sites: Effects of plant functional diversity and vegetation cover

It has been hypothesized that a diverse vegetation cover with a high number of plant species and plant functional groups may be more effective at governing soil erosion processes than a vegetation cover with few species and fewer different plant functional groups.We investigated the influence of plant cover and diversity on interrill erosion on a disturbed alpine site. Rainfall simulations were conducted on micro-scale plots (25 × 25 cm) with different degrees of vegetation cover and plant functional group diversity. We selected plots with 10%, 30% and 60% of vegetation cover containing different plant functional groups: (i) grasses, (ii) forbs, (iii) cryptogams (moss and/or lichens), and all possible combinations of these three groups. On each plot a rain intensity of 375 ml min^?1 (30 mm) was applied for 5 min. The degree of vegetation cover had the largest effect on interrill erosion. At 60% vegetation cover, the sediment yield was reduced by 83% in comparison to the un-vegetated ground. In the plots with 60% vegetation cover, an increase in functional group diversity decreased the sediment yield significantly. Sediment yield was three times lower in the presence of three plant functional groups than in systems with one plant functional group. Combinations of plant functional groups including grasses reduced the sediment yield more than other combinations.The findings of this study support the view that beside the re-establishment of a closed vegetation cover, a high plant functional diversity can be a relevant factor to further reduce interrill erosion at disturbed sites in alpine ecosystems.     

Cape ground squirrels as ecosystem engineers: modifying habitat for plants,small mammals and beetles in Namib Desert grasslands

Burrowing and foraging of semi‐fossorial rodents can affect species distribution and composition. Ground squirrels dig large burrow systems for refuge from predators and temperature extremes. Burrowing and foraging around burrows by squirrels may affect habitat and resource distributions for other organisms. We examined the impact of Cape ground squirrels (Xerus inauris) on vegetation, small mammals and beetles during winter and summer in grasslands on the edge of the Namib Desert. At each burrow system and paired control site without burrows, we estimated plant cover and height using quadrats (N = 8 paired sites), small mammal abundance and species richness using mark‐recapture techniques (N = 8 paired sites) and beetle abundance and species richness using pitfall traps (N = 6 paired sites, winter only). Squirrel burrowing and foraging activities resulted in lower plant cover and height, higher small mammal abundance and lower beetle abundance and species richness. Squirrels also reduced more plant cover in winter compared to summer, but had no effect on small mammal species richness. Furthermore, plant cover and height were higher in summer, whereas small mammal abundance and species richness were higher in winter. Our results suggest that Cape ground squirrels are important ecosystem engineers that influence plant and animal communities in the Namib Desert grasslands.     

Effects of ants on plant diversity in semi-natural grasslands

Ants (L. niger and L. flavus) build conspicuous mounds that are covered with vegetation. The aim of this study was to investigate whether the vegetation on ant mounds in semi-natural grasslands differed from that around the mounds. Another aim was to investigate whether the changes in the vegetation on ant mounds were influenced by grazing management or by habitat characteristics, semi-dry versus moist. Here, the total number of plant species and total plant cover were lower on ant mounds than in patches off-mound. The plant cover of perennials that form rosettes was twice as high on mounds inhabited by L. niger than on those inhabited by L. flavus. Only a few plant species were restricted to either ant mounds or adjacent field and the effects of ants on the plant diversity in semi-natural grasslands seemed to be low. Grazing management did not affect the differences in the vegetation on ant mounds and in equal-sized patches off-mound, whereas habitat characteristics affected ant-induced changes in vegetation cover of some plant species.     

The antiestrogen ICI 182,780 induces early effects on the adult male mouse reproductive tract and long-term decreased fertility without testicular atrophy

Background  

Estrogen receptors (ER) have important physiological roles in both the female and male reproductive systems. Previous studies using the estrogen receptor-α knockout mouse (αERKO) or antiestrogen treatment in adult rodents have shown that ERα is essential for normal function of the male reproductive tract. In the present study, time-response effects of the antiestrogen ICI 182,780 were determined to better understand ERα function in the adult male.     

Cross-taxon congruence of α and β diversity among five leaf litter arthropod groups in Colombia

In this study α and β diversity patterns of five leaf litter arthropod groups (ants, predatory ants, oribatid mites, spiders and other arachnids) were described and compared in 39 sampling patches of a transformed landscape in southwestern Colombia, that represented five vegetation types: secondary forest, riparian forest, giant bamboo forest, pasture and sugarcane crop. It was also assessed whether some taxa could be used as diversity surrogates. A total of 6,765 individuals grouped in 290 morphospecies were collected. Species richness in all groups was lower in highly transformed vegetation types (pasture, sugarcane crop) than in native ones (forests). In contrast, there were no clear tendencies of β diversity among vegetation types. Considering sampling patches, 0.1–42% of the variation in α diversity of one taxonomic group could be explained from the α diversity of another, and 0.2–33% of the variation of β diversity of a given taxon was explained by that in other groups. Contrary to recent findings, we concluded that patterns of α diversity are more congruent than patterns of β diversity. This fact could be attributed to a sampling effect that promotes congruence in α diversity and to a lack of a clear regional ecological gradient that could promote congruent patterns of β diversity. We did not find evidence for an ideal diversity surrogate although diversity patterns of predatory ants had the greatest congruencies. These results support earlier multi-taxon evaluations in that conservation planning should not be based on only one leaf litter arthropod group.     

Post-fire conifer regeneration hinders digital estimation of understorey plant cover in subalpine forest vegetation

Question: Reliable estimates of understorey (non-tree) plant cover following fire are essential to assess early forest community recovery. Photographic digital image analysis (DIA) is frequently used in seral, single-strata vegetation, given its greater objectivity and repeatability compared to observer visual estimation; however, its efficacy in multi-strata forest vegetation may be compromised, where various visual obstructions (coarse downed wood [CDW], conifer regeneration, and shadows) may conceal plant cover in the digital imagery. We asked whether vegetation complexity influences plant cover estimated by DIA relative to two visual methods: plot-level (20 m²) estimation (PLE) and quadrat-level (1 m²) estimation (QLE)? Location: Greater Yellowstone Ecosystem, USA. Methods: We estimated understorey plant cover in subalpine forest vegetation on permanent plots (n = 141) at two study areas ~30 years after the 1988 Yellowstone fires to: (a) assess differences in visual obstructions between study areas in our digital imagery; (b) compare digital to visual estimates of plant cover; and (c) determine relationships between estimated plant cover and visual obstructions measured in situ. Results: Percent conifer regeneration pixels differed significantly (odds ratio = 8.34) between study areas which represented the greatest difference in visual obstructions. At the study area with lower conifer pixels, DIA estimated 9% (95% confidence interval [CI] = 3%–14%) and 16% (95% CI = 10%–21%) more understorey plant cover than PLE or QLE, respectively, but had comparable variability. At the study area with higher conifer pixels, DIA estimated 28% (95% CI = 24%–32%) and 22% (95% CI = 18%–26%) less understorey plant cover than PLE or QLE, respectively, and had more variability. Furthermore, plot-level subcanopy regeneration (height>137 cm) density was negatively associated with digitally derived plant cover but showed no relationship with visually derived plant cover. Conclusions: Post-fire conifer regeneration hindered the efficacy of DIA in estimating understorey plant cover. Digital estimation is advantageous in single-strata vegetation but should not be used in complex, multi-strata vegetation.     

Habitat diversity enhances ant diversity in a naturally heterogeneous Brazilian landscape

Understanding the factors that drive species richness and composition at multiple scales is of crucial importance for conservation. Here we evaluated how habitat heterogeneity—at the local and landscape scales—affects the diversity of ants in the Brazilian Cerrado. The Cerrado is a biodiversity hotspot that is characterized as a mosaic of habitats, including savannas of variable structure (the dominant vegetation), grasslands, and forests. We sampled ground-dwelling ants in four habitats, representing a gradient of increasing tree cover and decreasing grass cover. Twelve sites, distributed along two degrees of latitude, were sampled. Our sampling revealed a highly diverse and patchily distributed fauna comprising 150 species (from 44 genera), of which nearly 40% were found in only one site. On average, we found fewer species in the least structurally complex habitat. However, there was relatively little variation in species density among the remaining habitats despite strong differences in vegetation structure among them. Ant species composition varied markedly among sites and such differences were related to variations in vegetation structure but not to inter-site distances (latitude). Similar results were obtained when overall ant species richness (γ diversity) was partitioned additively into three components: α₁ (diversity within sampling sites), β₁ (diversity among sites within the same habitat type), and β₂ (diversity among sites from different habitats). The β₂ component contributed much more to γ diversity than did the remaining diversity components, indicating that conservation of the Cerrado ant fauna depends on the maintenance of habitat diversity.     

The effects of reindeer grazing on the composition and species richness of vegetation in forest–tundra ecotone

We conducted an 8-year exclosure experiment (1999–2006) in a forest–tundra ecotonal area in northwestern Finnish Lapland to study the effects of reindeer grazing on vegetation in habitats of variable productivity and microhabitat structure. The experimental sites included tundra heath, frost heath and riparian habitats, and the two latter habitats were characterized by hummock-hollow ground forms. The total cover of vegetation, cover of willow (Salix spp.), dwarf birch (Betula nana), dwarf shrubs, forbs and grasses (Poaceae spp.) increased in exclosures in all habitats. The increase in the total cover of vegetation and in the covers of willow and dwarf birch tended to be greatest in the least productive tundra heath. Opposing to the increase in the dominant vascular plant groups, the cover and species number of bryophytes decreased in exclosures. We conclude that the effects of reindeer grazing on vegetation composition depend on environmental heterogeneity and the responses vary among plant groups. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Canonical correspondence analysis of early volcanic succession on Mt Usu,Japan

Canonical correspondece analysis (CCA) was applied to explore revegetation patterns during early succession on Mt Usu. Vegetation was buried by deposits of ash and pumice from 1 to 3 m in depth from the 1977–78 eruptions. Three habitats were selected: tephra, tephra in gully and original surface. Plant density and plant cover data were analyzed separately. Environmental factors consisted of five quanticative variables (organic matter, elevation, distance from colonizing source, erosion and deposition of volcanic deposits) and three nominal variables (habitat types: tephra, tephra in gully and original surface). Canonical correspondence analysis showed that the original surface played a special role in vegetation development because the old topsoil supplied both nutrients and seed-bank species. The CCA also suggested that the environmental factors that influence plant density and cover differ. Distance from colonizing source affected plant density while erosion affected cover. Using CCA, factors could be distinguished that influenced seedling establishment from vegetation expansion and vegetation recovery dynamics could also be more clearly interpreted.     

The effects of urban or rural landscape context and distance from the edge on native woodland plant communities

The increasing rate of urban sprawl continues to fragment European landscapes threatening the persistence of native woodland plant communities. The dynamics of woodland edges depend on the characteristics of woodland patches and also on landscape context. Our aim was to assess the extent of edge influences on the understorey vegetation of small native woodlands in rural and urban landscapes. The study was carried out in two cities of north-western France. Ten comparable woodlands, each of about 1.5 ha, were surveyed; five were situated adjacent to crops and five adjacent to built-up land. Vascular plant species were recorded in 420 3 × 3 m plots placed at seven different distances from the edge (from 0 to about 45 m from the edge). Soil pH, light levels, level of disturbance and tree and shrub cover were also recorded. Plant species were first classified as non-indigenous or indigenous and then three groups of indigenous species were distinguished according to their affinity for forest habitat (forest specialists, forest generalists and non-forest species). We inferred certain ecological characteristics of understorey vegetation by using Ellenberg values. An inter-class correspondence analysis was carried out to detect patterns of variation in plant community composition. Linear mixed models were used to test the effects of adjacent land use, distance from the edge and their interactions on the species richness of the different groups and on the ecological characteristics of vegetation. Total species richness, richness of forest generalists and of non-forest species decreased from edge to interior in both urban and rural woodlands. The number of non-indigenous species depended mainly on urban–rural landscape context. Urban woodland edges were not as rich in forest specialists as rural edges. More surprisingly, the number of forest specialists was higher in rural edges than in rural interiors. Community composition was mainly affected by urban–rural context and to a lesser degree by the edge effect: the community composition of urban edges resembled that of urban interiors whereas in rural woodlands vegetation near edges (up to 10 m) strongly differed from interiors with a pool of species specific to edges. Urban woodland vegetation was more nitrophilous than rural vegetation in both edges and interiors. A major difference between urban and rural vegetation was the distribution of basiphilous species according to distance from the edge. Generally edge vegetation was more basiphilous than interior vegetation however the presence of basiphilous species fell off quickly with distance from the edge in rural woodlands (in the first 10–15 m) and more slowly (from 25 m onwards) in urban woodlands. This pattern was linked to variation in measured soil pH. As regards the conservation of flora in small native woodlands, it appeared that invasion of exotic and non-forest species was currently limited in both urban and rural landscape contexts but might pose problems in the future, especially in urban woodlands. Forest species were not negatively affected by the edge effect and indeed edges seemed to provide important habitats for this group. Hence conservationists should pay particular attention to the protection of edges in urban woodlands.     

Species and functional responses of ants to inter-row tillage and vegetation in organic Mediterranean vineyards

Ants are arthropods providing crucial ecosystem services such as soil structuring, nutrient cycling, seed dispersal and pest predation. Thus, their abundance and diversity need to be considered in approaches to improve sustainability of land use such as Mediterranean viticulture. In our study, we tested whether (1) inter-row vegetation and the absence of tillage increase the species richness and/or functional diversity of ants in vineyards and (2) ground cover vegetation drives ant species composition. We included 23 Mediterranean organic vineyards in our analyses and distinguished three types of inter-row management: all inter-rows tilled, half of the inter-rows tilled, and all inter-rows are untilled and covered by vegetation. The occurrence of ant species was analysed in six pitfall traps per vineyard. Around each trap, the floristic composition of inter-row vegetation was analysed in 2 × 2 m² plots. We found that inter-row tillage significantly affected ant species richness, being higher in partially than in fully tilled vineyards whereas untilled vineyards were not different from the other tillage types. Grass cover and the perennial/annual rate were positively correlated with ant species richness. Ant functional diversity and the frequency of most predatory ants were not correlated neither with plant functional groups nor with tillage type. In conclusion, ant communities benefit from inter-row vegetation and/or absence of soil disturbance but partial inter-row tillage of vineyards may be tolerated and even benefit several species. In particular, grasses and perennial plant species favour ants in our system and need to be considered in inter-row sowing.     

Type II and VI collagen in nasal and articular cartilage and the effect of IL-1α on the distribution of these collagens

The distribution of type II and VI collagen was immunocytochemically investigated in bovine articular and nasal cartilage. Cartilage explants were used either fresh or cultured for up to 4 weeks with or without interleukin 1α (IL-1α). Sections of the explants were incubated with antibodies for both types of collagen. Microscopic analyses revealed that type II collagen was preferentially localized in the interchondron matrix whereas type VI collagen was primarily found in the direct vicinity of the chondrocytes. Treatment of the sections with hyaluronidase greatly enhanced the signal for both types of collagen. Also in sections of explants cultured with IL-1α a higher level of labeling of the collagens was found. This was apparent without any pre-treatment with hyaluronidase. Under the influence of IL-1α the area positive for type VI collagen that surrounded the chondrocytes broadened. Although the two collagens in both types of cartilage were distributed similarly, a remarkable difference was the higher degree of staining of type VI collagen in articular cartilage. Concomitantly we noted that digestion of this type of cartilage hardly occurred in the presence of IL-1α whereas nasal cartilage was almost completely degraded within 18 days of culture. Since type VI collagen is known to be relatively resistant to proteolysis we speculate that the higher level of type VI collagen in articular cartilage is important in protecting cartilage from digestion.     

Vegetation classification of East China with multi-temporal NOAA-AVHRR data

East China lies in the subtropical monsoon climatic zone and is dominated by subtropical evergreen broad-leaved forests, a unique vegetation type mainly distributed in East Asia with the largest distribution in China. It is important to be able to monitor and estimate forest biomass and production, regional carbon storage, and global climate change impacts on these important vegetation types. In this paper, we used coarse resolution remote sensing data to identify the vegetation types in East China and developed a map of the spatial distribution of vegetation types in this region. Nineteen maximum normalized difference vegetation index (NDVI) composite images (acquisition time span of 7 months from February to August), which were derived from 10 days National Oceanographic and Atmospheric Administration (NOAA) Advanced Very High Resolution Radiometer (AVHRR) channel 1 and channel 2 observations, an unsupervised classification method, and the ISODATA algorithm were employed to identify the vegetation types. To reduce the dimensions of the dataset resulted in a total of 28 spectral clusters of land-cover of which two clusters were urban/bare soil and water, the images were processed using principal component analysis (PCA). The 26 remaining spectral clusters were merged into six vegetation types using the Chinese vegetation taxonomy system: evergreen broad-leaved forest, coniferous forest, bamboo forest, shrub-grass, aquatic vegetation, and agricultural vegetation. The spatial distribution and areal extent for the coniferous forests, shrub-grass, evergreen broad-leaved forests, and agricultural vegetation were calculated and compared with the Vegetation Atlas of China at a 1:1,000,000 scale. The spatial accuracy and the area accuracy for coniferous forests, shrub-grass, evergreen broad-leaved forests, and agricultural vegetation were 79.2%, 91.3%, 68.2% and 95.9% and 92.1%, 95.9%, 63.8% and 90.5%, respectively. The spatial accuracy and area accuracy of the bamboo forest were 28.7% and 96.5%, respectively; the spatial accuracy of aquatic vegetation was 69.6%, but there was a significant difference in its area accuracy because image acquisition did not cover the full year. Our study demonstrated the feasibility of using NOAA-AVHRR to identify the different vegetation types in the subtropical evergreen broad-leaved forest zone in East China. The spatial location of the six identified vegetation types agreed with the actual geographical distribution of the vegetation types in East China. __________ Translated from Acta Phytoecologica Sinica, 2005, 29(3): 436–443 [译自: 植物生态学报, 2005, 29(3): 436–443]     

Non-native competitive perennial grass impedes the spread of an invasive annual grass

Invasive plants are degrading wildlands around the globe by displacing native species, reducing biodiversity, and altering ecological functions. The current approach of applying herbicides to invasive plants in wildlands has not been effective at curtailing their expansion and, in certain circumstances, may do more harm than good. Preventing the spread of invasive species has been identified as an important strategy to protect wildlands. However, few prevention strategies have actually been tested. We hypothesized that establishing competitive vegetation next to infestations would increase the biotic resistance of the plant community to invasion and decrease the invasive species propagule pressure beyond the competitive vegetation. To evaluate this, we established twelve competitive vegetation barriers in front of invasive annual grass, Taeniatherum caput-medusae (L.) Nevski, infestations. The non-native perennial grass Agropyron desertorum (Fisch. ex Link) Schult. was seeded into plant communities adjacent to the infestations to create the competitive vegetation barriers. Soil nutrient concentrations and the spread of T. caput-medusae were compared between where A. desertorum was seeded and not seeded (control treatment) 3 years after treatment. Less T. caput-medusae and lower soil ammonium and potassium concentrations in the competitive vegetation barrier than control treatment (P ≤ 0.01) suggest that establishing competitive vegetation increased the biotic resistance of the plant communities to invasion. Taeniatherum caput-medusae cover and density in the plant communities protected by the competitive vegetation barrier (locales across the barriers from the infestations) were ~42- and 47-fold less, respectively, than unprotected plant communities (P < 0.01). This suggests that invasive plant propagule pressure was decreased in the plant communities protected by competitive vegetation barriers. The establishment of competitive vegetation around infestations may be an effective strategy to prevent or at least reduce the spread of invasive plant species.     

Effect of grazing on vegetation and soil of the heuweltjieveld in the Succulent Karoo,South Africa

We asked how historical and recent grazing intensity affect the patchy landscape of the heuweltjieveld in the semi-arid biodiversity hotspot Succulent Karoo. The study was carried out on a communal farmland 80 km south-west of Springbok, in Namaqualand. Heuweltjies are roughly circular earth mounds that are regularly distributed in this landscape. We sampled plant species and life-form composition, diversity measures, habitat and soil variables in 100 m² plots, placed in three visually distinguishable heuweltjie zones (centre, fringe, and matrix) and distributed across grazing camps with different recent and historic grazing intensities. Differences between heuweltjie zones were assessed with ANOVAs and multiple linear regressions. The effect of past and recent grazing intensity on soil and plant variables was analysed by Generalized Linear Models for each heuweltjie zone separately. The three zones constituted clearly distinguishable units in terms of vegetation and soil characteristics. Soil pH and cover of annual plants increased from matrix to centres, while total vegetation cover, species richness and perennial plant cover decreased in the same direction. Historic (pre-2000) grazing patterns had the strongest effects on fringes, showing the strongest soil and vegetation-related signs of overutilization with increased stocking density. Centres showed signs of overutilization irrespective of the stocking density. The much shorter exposure to recent grazing pattern (post-2000), which was nearly inverse to the historic grazing pattern, showed increase of vegetation cover (centres) and species richness (matrix) with recent grazing intensity. We interpret these effects as still visible responses of the lower grazing intensity in these camps during the historic period. No recovery under recent grazing was observed at any of the zones. We conclude that irrespective of their conducive growing conditions, once transformed to a disturbed state, heuweltjie centres recover slowly, whereas the less impacted soil and vegetation of fringes are more responsive than centres and matrix.