Vegetation Assemblages Research Articles

Breakdown rates, nutrient concentrations, and macroinvertebrate colonization of bluejoint grass litter in headwater streams of the Kenai Peninsula, Alaska

Grass litter can be a dominant detritus type in many streams. However, use of this C source in stream food webs often is viewed as insignificant because of its relatively slow breakdown rates and low nutritional quality. We deployed leaf packs containing senesced bluejoint grass (Calamagrostis canadensis) across a natural nutrient gradient of 6 salmon-rearing headwater streams on the lower Kenai Peninsula, Alaska. We hypothesized that litter-colonizing microbes would use dissolved stream nutrients and enhance breakdown rates, litter nutrient concentrations, and densities of macroinvertebrates across streams. Leaf-pack mass and nutrient concentrations were measured on the material at 0 (predeployment), 2, 4, 6, and 8 wk in all streams. Breakdown rates were calculated from the mass measurements with an exponential decay model. Macroinvertebrate composition and abundance were measured at 8 wk in all streams and every 2 wk in 1 stream. Breakdown rates of bluejoint litter were relatively low (20–30% mass loss over 2 mo), but similar to rates found in previous studies of senesced grass litter. Weighted regressions showed that bluejoint breakdown rates in the 6 streams were significantly (p < 0.05) related to dissolved stream nutrient concentrations (r2 = 0.94 and 0.67 for dissolved inorganic N and PO4-P, respectively), litter nutrient concentration (r2 = 0.72 and 0.96 for leaf % N and % P, respectively), total macroinvertebrates/g (r2 = 0.73), and nonmetric multidimensional scaling-axis-1 scores of macroinvertebrate community structure (r2 = 0.80). Litter nutrients changed after just 2 wk and were increasingly and significantly related to stream nutrient concentrations over time. NMS ordination showed that succession of macroinvertebrates on leaf packs from one stream followed a distinct direction over time, and a large shift in macroinvertebrate community structure occurred between weeks 6 and 8, a result potentially indicating a consumer response to microbial conditioning. The abundance and diversity of macroinvertebrate taxa using bluejoint litter provide evidence that it is an important habitat and energy pathway for consumers in headwater streams of the Kenai Peninsula. In addition, climate change has the potential to change terrestrial vegetation assemblages, which drive differences in stream nutrient concentrations in this region. If N-fixing shrubs become more abundant in the future, litter-decomposition rates will be positively affected by increases in both stream and leaf-litter nutrient concentrations.

Pollen assemblages of cultivated vegetation in central and southern Hebei Province

The study on 82 surface soil pollen samples from different types of cultivated vegetations in central and southern parts of Hebei Province indicates that the pollen assemblages from farmlands in the plain have not only their own plant types, but also the pollen components from the nearby mountains. Arboreal pollen percentages and concentrations (dominated by Pinus) from farmlands in mountain area are higher than those in the plain, and it reduces gradually with the increasing distance away from the mountains. Taking Pinus pollen in Taihang Mountains as an example, its content is 20%–30%, 10%–20%, 20%–30% and below 16% respectively for the samples from the area of 0–50, 50–100, 100–150 and more than 150 km away from the east Taihang Mountains. The increase of Pinus pollen proportion in the central plain is probably related to the fohn effect. The spatial variation of AP from mountains to the plain in Hebei Province may be similar to the forests clearance by human activities in the early historical period. Shrubby pollen proportion is small both in mountains and in the plain, but their major components are different. Elaeagnaceae, Corylus, Ostryopsis and Oleaceae are common in mountain areas, while there are relatively high contents of Rosaceae and Vitaceae in the plain. Herbs content in the plain (about 60%) is 15% higher than that in mountains, among which the Cereals and Cruciferae pollen percentages are 5% and 2% higher respectively. Artemisia pollen percentage in the plain is lower than that in mountains. Since the human activities are weaker in mountains compared with that in the plain, the general trend is that Chenopodiaceae pollen increases from mountains to the plain gradually, reflecting the raising intensity of human activities. The fern spores of Selaginella sinensis in mountains are higher than that in the plain, but it still reaches to about 7% in the plain. The fern spores of Selaginella sinensis are not prone to be spread by wind, indicating that those in the surface soil of the plain may be carried by river water from mountains during the deposition of the plain.

Environmental control and spatial structures in peatland vegetation

Question: What are the relative influences of environment and space in structuring the plant composition in a peatland complex? Location: Lakkasuo, southern boreal zone, Finland. Method: We used principal coordinates of neighbour matrices (PCNM) to model spatial structures in the plant composition of a peatland complex comprising ombrotrophic and minerotrophic, open and forested areas. We used redundancy analyses (RDA) and variation partitioning to assess the relative influences of chemical variables (peat and water characteristics), physical variables (hydrology, soil properties, shade), as well as broad-scale (>350 m) and medium-scale (100–350 m) spatial structures on vegetation assemblages. Results: We identified five different significant spatial patterns circumscribing (1) the minerotrophic–ombrotrophic gradient; (2) dry ombrotrophic and wet minerotrophic areas; (3) open and shaded areas; (4) dry open/shaded and wet patches within the ombrotrophic areas; and (5) dry open patches and dry forested patches. With spatial structures and environmental variables, we were able to model 30% of the variability in plant composition in the peatland complex, 13% of which was attributable to spatial structures alone. Conclusions: We demonstrated that in the peatland complex, the spatial dependence processes were more important at the broadest scale, and found that patterns at a medium scale might reflect finer-scale patterns that were not investigated here. Spatial autocorrelation in vegetation composition in the peatland complex appeared to be driven by Sphagnum species. Our results emphasize that spatial modelling should be routinely implemented in studies looking at species composition, since they significantly increase the explained proportion of variance.

Resource partitioning between sympatric columbian white‐tailed and black‐tailed deer in western Oregon

AbstractWe studied resource partitioning between sympatric populations of Columbian white‐tailed (CWTD; Odocoileus virginianus leucurus) and black‐tailed (BWTD) deer (O. odocoileus hemionus columbianus) in western Oregon to understand potential mechanisms of coexistence. We used horseback transects to describe spatial distributions, population overlap, and habitat use for both species, and we studied diets with microhistological analysis of fecal samples. Distribution patterns indicated that white‐tailed and black‐tailed deer maintained spatial separation during most seasons with spatial overlap ranging from 5%–40% seasonally. Coefficients of species association were negative, suggesting a pattern of mutual avoidance. White‐tailed deer were more concentrated in the southern portions of the study area, which was characterized by lower elevations, more gradual slopes, and close proximity to streams. Black‐tailed deer were more wide ranging and tended to occur in the northern portions of the study area, which had higher elevations and greater topographical variation. Habitat use of different vegetative assemblages was similar between white‐tailed and black‐tailed deer with overlap ranging from 89%–96% seasonally. White‐tailed deer used nearly all habitats available on the study area except those associated with conifers. White‐tailed deer used oak‐hardwood savanna shrub, open grassland, oak‐hardwood savanna, and riparian habitats the most. Black‐tailed deer exhibited high use for open grassland and oak‐hardwood savanna shrub habitats and lower use of all others. The 2 subspecies also exhibited strong seasonal similarities in diets with overlap ranging from 89% to 95%. White‐tailed deer diets were dominated by forbs, shrubs, grasses, and other food sources (e.g., nuts and lichens). Columbian black‐tailed deer diets were dominated mostly by forbs and other food sources. Seasonal diet diversity followed similar patterns for both species with the most diverse diets occurring in fall and the least diverse diets in spring. High overlap in habitat use and diets resulted in high trophic overlap (81–85%) between white‐tailed and black‐tailed deer; however, the low spatial overlap reduced the potential for exploitative competition but may have been indicative of inference competition between the species. Diverse habitat and forage opportunities were available on the study area due to heterogeneous landscape characteristics, which allowed ecological separation between white‐tailed and black‐tailed deer despite similarities in diets and habitat use. We make several recommendations for management of CWTD, a previously threatened species, based on the results of our study. © 2011 The Wildlife Society.

New insights on Late Quaternary Asian palaeomonsoon variability and the timing of the Last Glacial Maximum in southwestern China

A ∼6.35 m core (06SD) was retrieved from Lake Shudu, Yunnan Province, China. The sediments spanning the period ∼22.6–10.5 kcal. yr BP (6.35–1.44 m) were analysed using a combination of variables including pollen, charcoal, particle size, magnetic susceptibility and loss-on-ignition. The resulting palaeorecord provides a high-resolution reconstruction of Late Pleistocene to Early Holocene climatic and environmental changes in southwestern China. Our findings indicate that from c. 22.6 to 17.7 kcal. yr BP, vegetation assemblages were primarily aligned to sparse xerophytic grassland/tundra or cold-tolerant boreal Pinus forest, indicating that climatic conditions in southwestern China were cold and dry. However, from c. 17.7 to 17.4 kcal. yr BP, the Lake Shudu record is punctuated by marked environmental changes. These include the establishment of denser vegetation cover, a marked expansion of boreal Pinus forest and enhanced hydrological activity in the catchment over centennial timescales, perhaps suggesting that stepwise variations in the Asian Monsoon were triggering fundamental environmental changes over sub-millennial timescales. Thereafter, the pollen record captures a period of environmental instability reflected in fluctuations across all of the variables, which persists until c. 17.1 kcal. yr BP. After c. 17.1 kcal. yr BP, the expansion of steppe vegetation cover and cold–cool mixed forest consisting of mesophilous vegetation such as Tsuga and Picea, thermophilous trees including Ulmus and deciduous Quercus inferred from the Lake Shudu pollen record point to the establishment of warmer, wetter and perhaps more seasonal conditions associated with a strengthening Asian Summer Monsoon during the shift from Pleistocene to Holocene climatic conditions.

Palaeoenvironmental changes since Pleistocene–Holocene transition: Pollen analysis from a wetland in southwestern Patagonia (Argentina)

Changes in pollen spectra of a sediment core from a wetland in the southern side of Lake San Martin, which is located at 49° 11′ S; 72° 22′ W (near the eastern limit of the Subantarctic Forest–Patagonian Steppe ecotone) reflect variations in the composition of vegetation since the Pleistocene–Holocene transition. Comparison of fossil to modern pollen assemblages allowed us to interpret these palaeoenvironmental changes in terms of moisture availability. Between 11 300 and 9500 cal yr BP, conditions with low moisture availability from Poaceae– Ephedra–Chenopodiaceae pollen assemblage were inferred. From 9500 to 8000 cal yr BP, the grass steppe dominance was interpreted as an increase in moisture availability. The steppe assemblage was replaced by shrub taxa suggesting drier conditions in the mid-Holocene (8000–3000 cal yr BP). Between 3000 and 100 cal yr BP, wetter conditions were inferred from an increase in herb taxa and a decrease in shrubs, while for the last century a grass steppe with higher amounts of shrubs suggests a decrease in moisture availability. Changes in these vegetation assemblages suggest changes in the precipitation patterns related to the position and strength of the westerlies.

Human hydrographical changes interact with propagule predation behaviour in Sri Lankan mangrove forests

For mangroves with almost no tidal influence and a subsequent mosaic vegetation structure we describe the relation between propagule predators and both vegetation structure and environmental factors on a vegetation assemblage or ‘forest patch’ level. We then report the interaction between natural propagule predation and human influence. In different forest patches dominated by Avicennia officinalis, Excoecaria agallocha, Lumnitzera racemosa, Rhizophora apiculata or R. mucronata or in open or mixed areas identified from aerial photographs, the predation on propagules of A. officinalis, B. gymnorrhiza, R. apiculata and R. mucronata was monitored in a total of 24 experimental plots (3 per forest patch). Relationships to environmental factors (topography, water level, rainfall and season) on the level of predation were investigated. The highest predation intensity by crabs was on A. officinalis propagules, and in E. agallocha forest patches. Predation by crabs, snails, insects and mammals was observed, and the significant differences in predation intensity across species and across forest patches were explained directly by propagule predator identity and abundance, and by the interaction between rainfall, water level and microtopography. We illustrated how hydrography changes alter the behaviour of propagule predators and play a role in the shaping of vegetation structure by reconstructing the lagoon water level of a site over a period of 50 years based on rainfall data. This time frame covered both a condition without and with human impacts, and past and present propagule predation settings were confronted with the simulated hydrology. The importance of spatial and temporal microhabitat variations in opening multiple successional pathways in vegetation dynamics is illustrated, and is highly relevant for ecosystems with unpredictable or short-lived (< 20 years) patchy vegetation structures and microhabitats.

Assessment of the success of headwater restoration through the vegetation diversity analysis of four Oir river's tributaries (Normandy, France)

Safeguarding of riparian ecosystems is a field of major study in the comprehension and the maintenance of the health of rivers. The aim of our study is to analyze vegetation changes after passive restoration on two headwaters. Follow-ups of vegetation were carried out using 36 permanent plots of 15 m2 per brooks during five years. Our results suggest that after restoration, vegetation assemblages are comparable to those present on other headwaters considered in good ecological health. The effectiveness of the passive restoration method employed is discussed in terms of strong potential of resilience for comprehension of ecological functions and in term of sustainability for river managers.

The conservation potential of brook-side key habitats in managed boreal forests

Today, maintaining biodiversity is included in the targets of boreal forest management. A widespread approach in northern Europe is to identify and preserve woodland key habitats within managed forests. Woodland key habitats are expected to be patches that host populations of threatened and declining species, and the preservation of these patches is assumed to enable the persistence of the focal species in the landscape. In Finland, the criteria for selecting woodland key habitats are defined in the Finnish Forest Act, and the selection has been done by forest practitioners. Our objective was to determine whether the surroundings of boreal brooks and rivulets qualified as key habitats are truly different from brook-side habitats not granted the key habitat status, and whether the brook-side habitats of the two types differ from the forest matrix managed for timber production. We found that the two brook-side habitats were in most aspects rather alike but there was a difference in the composition of ground vegetation assemblages. In contrast, the control forests were distinct from the brook-sides in terms of dead wood, species richness and assemblages of polypores, species richness of epiphytic mosses, and the composition of beetle assemblages. We conclude that brook-sides in general provide an important habitat clearly diverging from the surrounding matrix but that the conservation value of the brook-sides granted the key habitat status may not be substantially larger than that of the brook-sides without the status.

CO2 enrichment increases element concentrations in grass mixtures by changing species abundances

Atmospheric carbon dioxide (CO2) enrichment may increase plant growth more than the uptake of chemical elements from soil. Increased CO2 also may alter element levels in biomass from multi-species vegetation by changing plant species abundances. We measured concentrations of ten elements in aboveground tissues of three C4 grasses that had been exposed for 2-3 growing seasons to a continuous gradient in CO2 from 250 to 500 lmol mol -1 . The grasses, Bouteloua curtipendula, Schiz- achyrium scoparium, and Sorghastrum nutans, are competitive dominants in assemblages of tallgrass prairie vegetation growing on each of three soil types along a field CO2 gradient in central Texas, USA. Our objective was to determine whether CO2 influences element concentrations in grass mixtures by changing concentrations in individual species or shifting spe- cies abundances. Increased CO2 had little effect on element concentrations in grasses compared to differences observed among grass species and soils. Increasing CO2 from the pre-Industrial to elevated levels reduced the phosphorus concentration in grasses grown on a clay and sandy loam soil. Concentrations of most other elements did not respond to CO2 treatment. Cover of the mid-grass Bouteloua declined at higher CO2 levels as cover of the taller grass Sorghastrum increased. Concentra- tions of several elements were lower in Bouteloua than Sorghastrum; hence, this exchange of species at higher CO2 increased element concentrations in grass assemblages. Potential consequences include an improvement in the nutritional quality of plants for herbivores. Results highlight the underappreciated impact that CO2 enrichment may have on ecosystem functioning by changing plant composition.

Primary productivity, biogeochemical buffers and factors controlling trophic status and ecosystem processes in Mediterranean coastal lagoons: a synthesis

Coastal lagoons are threatened by natural and anthropogenic factors that have been accelerated in the last decades, with detrimental effects on ecosystem and water quality, especially in sheltered systems. Eutrophication, macroalgal blooms, hypoxia and anoxia are among the main threats, which also impact on human activities, e.g. aquaculture and fishery. Study were performed from late 1980s to date in several Mediterranean lagoons, mainly in the Po river delta, in order to elucidate the main causes of such degenerative processes. Here we review (1) relationships between benthic vegetation and sediment biogeochemistry, with focus on factors determining eutrophication; (2) development of macroalgal blooms, with focus on causes and biogeochemical triggers of bloom onset; (3) perturbation of nitrogen cycling due to changes in benthic vegetation assemblages; (4) relationships between primary producers and benthic fauna, especially farmed species; (5) possible feedback loops among shellfish and primary producers.

Remotely sensed vegetation phenology and productivity along a climatic gradient: on the value of incorporating the dimension of woody plant cover

ABSTRACTAim Woody plants affect vegetation–environment interactions by modifying microclimate, soil moisture dynamics and carbon cycling. In examining broad‐scale patterns in terrestrial vegetation dynamics, explicit consideration of variation in the amount of woody plant cover could provide additional explanatory power that might not be available when only considering landscape‐scale climate patterns or specific vegetation assemblages. Here we evaluate the interactive influence of woody plant cover on remotely sensed vegetation dynamics across a climatic gradient along a sky island.Location The Santa Rita Mountains, Arizona, USA.Methods Using a satellite‐measured normalized difference vegetation index (NDVI) from 2000 to 2008, we conducted time‐series and regression analyses to explain the variation in functional attributes of vegetation (productivity, seasonality and phenology) related to: (1) vegetation community, (2) elevation as a proxy for climate, and (3) woody plant cover, given the effects of the other environmental variables, as an additional ecological dimension that reflects potential vegetation–environment feedbacks at the local scale.Results NDVI metrics were well explained by interactions among elevation, vegetation community and woody plant cover. After accounting for elevation and vegetation community, woody plant cover explained up to 67% of variation in NDVI metrics and, notably, clarified elevation‐ and community‐specific patterns of vegetation dynamics across the gradient.Main conclusions In addition to the environmental factors usually considered – climate, reflecting resources and constraints, and vegetation community, reflecting species composition and relative dominance – woody plant cover, a broad‐scale proxy of many vegetation–environment interactions, represents an ecological dimension that provides additional process‐related understanding of landscape‐scale patterns of vegetation function.

Primary productivity, biogeochemical buffers and factors controlling trophic status and ecosystem processes in Mediterranean coastal lagoons: a synthesis

Coastal lagoons are threatened by natural and anthropogenic factors that have been accelerated in the last decades, with detrimental effects on ecosystem and water quality, especially in sheltered systems. Eutrophication, macroalgal blooms, hypoxia and anoxia are among the main threats, which also impact on human activities, e.g. aquaculture and fishery. Study were performed from late 1980s to date in several Mediterranean lagoons, mainly in the Po river delta, in order to elucidate the main causes of such degenerative processes. Here we review (1) relationships between benthic vegetation and sediment biogeochemistry, with focus on factors determining eutrophication; (2) development of macroalgal blooms, with focus on causes and biogeochemical triggers of bloom onset; (3) perturbation of nitrogen cycling due to changes in benthic vegetation assemblages; (4) relationships between primary producers and benthic fauna, especially farmed species; (5) possible feedback loops among shellfish and primary producers.

The Influence of Time on the Soil Seed Bank and Vegetation across a Landscape‐Scale Wetland Restoration Project

Wicken Fen National Nature Reserve (NNR) in Cambridgeshire, U.K. is a wetland of international importance isolated in a landscape dominated by arable farming. The prospect of species extinctions within the NNR led to the creation of the Wicken Fen Vision, an ambitious project that will eventually expand the reserve boundary by the purchase and restoration of c.50 km2 of arable land. We sampled three fields from each of three distinct age‐categories of restoration land (5, 15, and 60 years post‐arable), and three fields within the adjacent, undrained NNR, to determine (1) differences in seed bank composition across age‐categories, (2) relationships between restoration age, the seed bank and standing vegetation, and (3) changes in species traits across age‐categories. Historic arable management contributed to an apparent “vertical mixing” effect in the seed bank of the youngest two age‐categories, with associated and significant differences in species functional traits across the study area. Almost all plants associated with NNR vegetation were absent from restoration area seed banks and standing vegetation. Seed bank species common to all ages‐categories exhibited a bias toward moderate to high Ellenberg F (moisture) values, persistent seed banks, and lateral vegetative spread. Relatively short (c. 6 years) periods of drainage and plowing impact heavily upon seed bank diversity and soils, resulting in a lack of predrainage vegetation, even after decades of subsequent restoration adjacent to intact, species‐rich habitat. However, the seed banks of highly degraded fields can contribute toward the creation of novel wetland vegetation assemblages over time and under suitable environmental conditions.

From ice age to modern: a record of landscape change in an Andean cloud forest

AbstractAim To investigate the palaeoecological changes associated with the last ice age, subsequent deglaciation and human occupation of the central Andes.Location Lake Pacucha, Peruvian Andes (13°36′26″ S, 73°19′42″ W; 3095 m elevation).Methods Vegetation assemblages were reconstructed for the last 24 cal. kyr bp (thousand calibrated 14C years before present), based on pollen analysis of sediments from Lake Pacucha. An age model was established using 14C accelerator mass spectrometry dates on bulk sediment. Fossil pollen and sedimentological analyses followed standard methodologies.Results Puna brava replaced the Andean forest at the elevation of Lake Pacucha at the Last Glacial Maximum (LGM). Deglaciation proceeded rapidly after 16 cal. kyr bp, and near‐modern vegetation was established by c. 14 cal. kyr bp. The deglacial was marked by the range expansion of forest taxa as grassland taxa receded in importance. The mid‐Holocene was marked by a lowered lake level but relatively unchanged vegetation. Quinoa and maize pollen were found in the latter half of the Holocene.Main conclusions Temperatures were about 7–8 °C colder than present at this site during the LGM. The pattern of vegetation change was suggestive of microrefugial expansion rather than simple upslope migration. The mid‐Holocene droughts were interrupted by rainfall events sufficiently frequent to allow vegetation to survive largely unchanged, despite lowering of the lake level. Human activity at the lake included a 5500‐year history of quinoa cultivation and 3000 years of maize cultivation.

Impact of wildfire on interdune ecology and sediments: An example from the Simpson Desert, Australia

The stability of many sand dunes and their interdunes is dependent on vegetation and surface crust cover. When this cover is removed, the sand can be activated and fine sediments deflated making the dunefields into sources of dust. This paper reports the impact of devegetation by wildfire on an interdune in the Simpson Desert, Australia. The fire occurred in 2001 and six years after the event pronounced differences between a pair of burnt and unburnt sites was clearly discernible. The variables examined included vegetation assemblage, cyanobacteria abundance and sediment aggregation, particle-size distribution and colour; but whether they apply to all such situations is uncertain. Rate of recovery has been slow and the differences are likely to have been sustained by a combination of negative feedback processes and climate.

Effects of Livestock Grazing on Grasshopper Abundance on a Native Rangeland in Montana

Livestock grazing can affect habitat quality for grasshoppers through effects on food and oviposition site availability, microclimate, and other factors. Because of this, some authors have suggested that grazing programs can be used to help manage pest grasshopper populations. In a 6-yr study, we controlled access of cattle to replicated experimental plots on an Agropyron spicatum/Poa sandbergii pasture to create consistent year-to-year differences in postgrazing plant cover, with resultant affects on microclimate. After sampling grasshoppers multiple times after grazing treatments each summer, we found evidence of between-treatment differences in grasshopper abundance for the entire assemblage during 4 of the 6 yr. Some species, including Melanoplus sanguinipes (perhaps the worse rangeland grasshopper pest in the western United States), tended to be more abundant on ungrazed plots, whereas Melanoplus gladstoni often had greater densities on heavily-grazed plots. The effect of grazing on grasshopper densities in this study was lower in magnitude and less consistent among years than in a study we conducted simultaneously at a nearby site where the vegetation was dominated by the exotic species crested wheatgrass (Agropyron cristatum). Our results generally support proposals that grazing could be used to reduce pest grasshopper densities, although the effectiveness of a particular grazing scheme may vary among sites, years, and grasshopper and vegetation assemblages.

Effects of fire on vegetation and small mammal communities in a Mojave Desert Joshua tree woodland

Wildfire size and frequency are increasing in Mojave Desert Joshua tree woodlands principally due to anthropogenic factors. These habitats are generally considered to be fire intolerant and the effects from fire are a major concern for land managers. This study investigated trends of ecosystem response to fire by looking at a chronosequence of historic burns. Plots were chosen at 2, 9, 13, 15 19, and 65 years since burn in which to sample vegetation and rodent communities. Rodent diversity was lower in burned plots and increased over time. The abundance of rodents however, was not significantly different between the burned and unburned plots. Vegetation showed a directional change in species composition with time since fire. However, reestablished vegetation assemblages did not converge to the assumed pre-burn condition. It is probable that this difference relates to the slow rates of establishment of certain vegetation components that make up the pre-burn condition of the plots. There is a concern that invasion by exotic plant species, nitrogen deposition, and global climate change may initiate a fire cycle in this ecosystem that will arrest succession before the Joshua tree woodland is allowed to reestablish.

Surface-active arthropods in organic vineyards, integrated vineyards and natural habitat in the Cape Floristic Region

The Cape Floristic Region (CFR), South Africa, is a biodiversity hotspot challenged by intensive wine production. Innovative approaches are being explored to optimize wine production without compromising biodiversity. As organic farming enhances biodiversity conservation in many other regions, the aim here was to assess the potential of organic vineyard management for conserving CFR soil surface arthropod diversity. Pitfall traps were used to sample arthropods in three study areas, each of which included an organic vineyard, an integrated vineyard and a natural vegetation reference habitat. Overall arthropod morphospecies richness was highest in natural sites, followed by organic vineyards and then integrated vineyards. The same trend was seen for predators, saprophages and phytophages. The ability of organic vineyards to sustain more morphospecies than integrated vineyards were partially due to higher non-crop vegetation complexity and less intense management in the organic vineyards. Arthropod assemblages were similar in organic and integrated vineyards, while both land-uses differed greatly from natural sites. Variation among natural vegetation assemblages in different study areas was also much greater than among assemblages of cultivated sites. Organic vineyard management has the potential to make an important contribution to arthropod conservation in the CFR at the field scale. However, at the landscape scale, natural habitat supports a much wider variety of morphospecies, and the preservation of natural fragments in the vineyard landscape may be the most effective measure to increase biodiversity in the winelands.

Half a century of succession in a temperate oakwood: from species‐rich community to mesic forest

AbstractAim Lowland woodlands in Europe went through dramatic changes in management in the past century. This article investigates the influence of two key factors, abandonment of coppicing and increased pressure of ungulates, in thermophilous oakwoods. We focused on three interconnected topics: (1) Has the assumed successional trend lead to impoverishment of the vegetation assemblages? (2) Has it resulted in vegetation homogenization? (3) Are the thermophilous oakwoods loosing their original character?Location Czech Republic, Central Europe.Methods The vegetation in 46 semi‐permanent plots was recorded three times: firstly, shortly after the abandonment of coppicing (1953) and then, after four to six decades of secondary succession and strong game impact (1992 and 2006). Overall trends and changes in species spectra were analysed.Results There is a marked successional shift towards species‐poorer communities growing in cooler, moister and nutrient‐richer conditions. The change was significantly different in parts affected and unaffected by high numbers of ungulates yet only for herbs, not the woody species. However, observed change in species composition was not accompanied by significant homogenization process that is the general process reported from elsewhere. A sharp decline in plant species typical for thermophilous woodland communities and in endangered species indicates that the original character of the woodland has been gradually lost.Main conclusions Thermophilous oakwoods have been largely replaced by mesic forests. Lowland oakwoods in continental parts of Europe historically depended on active management, which kept the understorey conditions light and warm. Successional processes in the 20th century caused a critical loss of species diversity at various spatial levels. However, artificially high numbers of ungulates, which otherwise have a negative impact, probably held up succession, so that the changes may still be reversible.