Assessment of long-term tallgrass prairie restoration in Manitoba, Canada

Ecological restoration is important in mitigating degradation and habitat loss of tallgrass prairie in North America. In 2002, we assessed the progress of a long-term tallgrass prairie restoration initiated in 1987 in southern Manitoba (Canada). Nine restoration and three reference sites were examined, as was a neighbouring site of future restoration that is now used for agriculture. Vegetation diversity, species composition, and associated soil properties were compared among restoration and reference sites, and changes associated with restoration identified. Restoration had a substantial effect on diversity and species composition, although restoration sites had significantly lower native and higher exotic diversity than reference sites. Overall and native diversity decreased over time, as both exotic and seeded native species were lost from the restoration sites. Particularly vulnerable were native forb species, which represent much of the diversity of prairie habitats. Forb presence was negatively associated with that of warm season native grasses, especially Andropogon gerardii (big bluestem). Similarity of restoration and reference vegetation increased over time, particularly for seeded native graminoids. When species that had been seeded elsewhere and had colonized restorations were examined, similarity between restoration and reference also increased with time, suggesting that older sites may be self-propagating. No significant differences in soil properties variables were observed among restoration sites, indicating that changes in these factors are slow relative to vegetation changes. Although time-since-restoration had a substantial impact on diversity and species composition, this habitat will require ongoing restoration.     

The contribution of roadside grassland restorations to native bee conservation

Marginal habitats such as hedgerows or roadsides become especially important for the conservation of biodiversity in highly modified landscapes. With concerns of a global pollination crisis, there is a need for improving pollinator habitat. Roadsides restored to native prairie vegetation may provide valuable habitat to bees, the most important group of pollinators. Such roadsides support a variety of pollen and nectar sources and unlike agricultural fields, are unplowed, and therefore can provide potential nesting sites for ground-nesting bees. To examine potential effects of roadside restoration, bee communities were sampled via aerial netting and pan trapping along roadside prairie restorations as well as roadsides dominated by non-native plants. Management of roadside vegetation via the planting of native species profoundly affected bee communities. Restored roadsides supported significantly greater bee abundances as well as higher species richness compared to weedy roadsides. Floral species richness, floral abundance, and percentage of bare ground were the factors that led to greater bee abundance and bee species richness along restored roadsides. Traffic and width of roadside did not significantly influence bees, suggesting that even relatively narrow verges near heavy traffic could provide valuable habitat to bees. Restored and weedy roadside bee communities were similar to the prairie remnant, but the prairie remnant was more similar in bee richness and abundance to restored roadsides. Restoring additional roadsides to native vegetation could benefit pollinator conservation efforts by improving habitat on the millions of acres of land devoted to roadsides worldwide, land that is already set aside from further development.     

Habitat associations of the endangered damselfly, Coenagrion mercuriale, in a water meadow ditch system in southern England

The damselfly Coenagrion mercuriale (Charpentier) (Odonata: Coenagrionidae) is threatened throughout Europe. It is listed on the EC Habitats and Species Directive and is the only odonate currently given priority status in the UK Biodiversity Action Plan. Information about the habitat preferences of this species is required to guide conservation and management programmes. We obtained estimates of density of mature adult C. mercuriale during an intensive mark-release-recapture study over 7.65 km of a water meadow ditch network in the Itchen Valley, Hampshire. Detailed habitat information was also collected, including a variety of physical variables, and data about the in-channel and bankside vegetation. C. mercuriale density and movement were analysed in relation to habitat variables and local population size using Generalized Linear Models. Mean adjacent population density was the single most important factor determining density. However the species was also associated with a number of habitat features, the most important of which were: a channel substrate consisting primarily of silt, wide underwater ledges (berms), in-channel emergent dicots, and bankside monocots. The presence of trees was negatively associated with damselfly density. Mean net lifetime movement was greatest from sections with low density, with smaller than average berms, and with deeper water. The causes and consequences of these findings are discussed in relation to the conservation and management of this rare species.     

Voting power and target-based site prioritization

Indices for site prioritization are widely used to address the question: which sites are most important for conservation of biodiversity? We investigate the theoretical underpinnings of target-based prioritization, which measures sites’ contribution to achieving predetermined conservation targets. We show a strong connection between site prioritization and the mathematical theory of voting power. Current site prioritization indices are afflicted by well-known paradoxes of voting power: a site can have zero priority despite having non-zero habitat (the paradox of dummies) and discovery of habitat in a new site can raise the priority of existing sites (the paradox of new members). These paradoxes arise because of the razor’s edge nature of voting, and therefore we seek a new index that is not strictly based on voting. By negating such paradoxes, we develop a set of intuitive axioms that an index should obey. We introduce a simple new index, “fraction-of-spare,” that satisfies all the axioms. For single-species site prioritization, the fraction-of-spare(s) of a site s equals zero if s has no habitat for the species and one if s is essential for meeting the target area for the species. In-between those limits it is linearly interpolated, and equals area(s)/(total area - target). In an evaluation involving multi-year scheduling of site acquisitions for conservation of forest types in New South Wales under specified clearing rates, fraction-of-spare outperforms 58 existing prioritization indices. We also compute the optimal schedule of acquisitions for each of three evaluation measures (under the assumed clearing rates) using integer programming, which indicates that there is still potential for improvement in site prioritization for conservation scheduling.     

Habitat modelling for the conservation of the rare ground beetle species Carabus variolosus (Coleoptera, Carabidae) in the riparian zones of headwaters

Carabus variolosus is a highly endangered insect which is listed in the EC Habitats and Species Directive. Detailed knowledge of the habitat requirements of this semi-aquatic woodland carabid beetle is needed if effective conservation and management strategies are to be developed. Previous habitat models have proved to be a successful analytical and predictive tool for the conservation of species. We conducted an intensive study over a two year period on two extant C. variolosus populations in Westphalia (Germany) using live capture pitfall traps. We analysed the distribution of the beetles over their main activity period in relation to a large number of edaphic and vegetation variables in order to estimate habitat suitability models and describe optimum ranges. C. variolosus is restricted to the fringes of water bodies and to areas of high soil moisture that display patches of bare soil, shows a slight preference for sparse tree vegetation, and avoids acidic soil. Temporal and spatial transferability of the statistically significant habitat models indicates their robustness and validity. Based on the results of our study, we suggest management measures for the conservation of C. variolosus, which promote the rehabilitation of natural flood plains of headwater areas.     

The feasibility of using soil seed bank for natural regeneration of degraded sandy grasslands

Desertification in degraded grasslands is manifested through the development of bare sandy patches, which eventually lead to habitat fragmentation. The ability of these bare sandy patches to regenerate naturally through in-situ soil seed banks is not well understood. To fill this knowledge gap, we randomly selected 24 bare sandy patches with areas ranging from 19 to 898 m² in a desertified grassland of the Horqin sandy land, Northern China to determine whether soil seed bank can be used for natural regeneration of bare sandy patches. Species composition and density of soil seed bank as well as aboveground vegetation composition, abundance and coverage were investigated. We then determined their relationships with in-situ habitat characteristics. Our observations showed that the studied area had low soil seed bank density and species richness, as well as depauperate soil seed bank communities. Consequently, local soil seed bank was not able to provide sufficient seed source for natural regeneration. This was indicated by the relationships between aboveground vegetation, soil seed bank and the in-situ habitat characteristics. For bare patches with an area between 300 m² and 900 m², increase the soil seed bank density and species richness should be the main restoration measures. For bare patches with a small area of less than 50 m², restoration of vegetation density should be the main measure. Our data highlighted that different extents of desertification, indicated by different bare patches, are requiring distinct restoration measures.     

When functional habitat does not match vegetation types: A resource-based approach to map butterfly habitat

The unambiguous recognition of a species’ habitat is a matter of debate. For terrestrial species, habitat is often defined as physical patches of a certain vegetation type in a matrix of non-habitat. Ecological resources that make up the habitat of a species may, however, only cover subsets of vegetation types or can be spatially dispersed in a complex way over different vegetation types. Here we present and test a procedure to recognize and delineate habitat according to a resource-based approach instead of a vegetation-based approach. We used the green hairstreak butterfly (Callophrys rubi) in a heathland landscape as a study case. Our resource-based habitat approach selects those zones that comprise essential resources and conditions within an appropriate spatial window. Variables that were retained in a logistic regression model were used to calculate larval, adult and combined habitat indices in a GIS, taking into account thermal constraints on resource-use, as this is a key habitat aspect for this heliothermous insect. To group different (and sometimes scattered) ecological resources into functional habitat zones, we derived a measure of space-use from mark-release-recapture data. By least-cost modelling this spatial window was adapted to the nature of the vegetation between sets of resources. The habitat zones that were delineated using this approach matched the observed distribution of butterflies significantly better than did a classic approach based on vegetation types with host plants only. Our approach provides concrete output for conservation purposes, like recognizing zones with the highest potential for habitat restoration.     

不同干扰方式对东北山地沼泽土壤肥力的影响

 通过样地法对小浪底水库库区山地生态系统不同群落间的Shannon-Wiener指数(H′)、Simpson指数(D1)、Margalef物种丰富度(D2)、种间相遇概率(P)和Pielou均匀度指数(Jsw)等多样性指数进行研究,利用统计方法分析不同群落的物种多样性指数与其所处环境的关系。结果表明:1)物种多样性指数和丰富度指数与群落类型有密切关系,同一类型的群落中,多样性指数随演替时间表现出复杂的关系;2)土壤含水量对H′、P、Jsw、D1等呈极显著的正相关性,土壤厚度与H′、D1、P呈显著正相关性;多样性指数与坡度无相关性;土壤有机质、速效氮、速效磷等养分指标与多样性指数H′、D1有显著的正相关;3)多样性指数H′与乔木、灌木群落生物量表现为正相关关系,草本群落与D1相关性不显著;4)乔木林群落的恢复时间与Jsw、H′呈正相关关系,其余多样性指数(P、D1、D2)与恢复时间关系不显著(P>0.05);恢复时间每增加10a,群落物种数平均增加约6种;5)物种多样性指数H′与灌木的盖度和高度呈极显著正相关性;有些单优群落随高度增加和盖度提高,多样性指数反而表现出降低;6)草本植物群落的高度和盖度与物种丰富度指数D2与呈显著的负相关关系,与H′相关性不显著。     

浑善达克沙地飞播区植物多样性的变化——以内蒙古正蓝旗为例

[目的]对内蒙古境内浑善达克沙地植被恢复过程中植物群落的物种组成以及多样性的变化规律进行分析,为该地区的植被恢复提供理论依据和科学指导。[方法]采用样带法对植物群落进行调查。[结果](1)沙地植被恢复5年后群落内共有33种植物,分属于10科27属;(2)随着恢复年限的延长,物种丰富度指数、物种多样性指数、物种均匀度指数和群落盖度均逐渐增大,而生态优势度指数则逐渐减小。植物群落物种由6种(未治理)增加到21种(治理5a),物种多样性指数由1.20增加至2.77,物种均匀度指数由0.67升高至0.91,群落盖度从2.06%增加到75.58%,生态优势度指数由0.57减少至0.32。[结论]浑善达克沙地飞播区植被得到明显恢复,沙地恢复到一定阶段后群落趋于稳定,风沙化得到一定程度的遏制。     

Assessing conservation priorities for insects: status of water beetles in southeast Spain

We propose an objective method for assessing the vulnerability of species and for prioritizing species and populations for conservation, especially insects. Species of water beetles from two Spanish provinces of the southeast of the Iberian Peninsula were ranked according to their conservation priority at the local, national and global levels taking into consideration a set of six variables: general distribution, endemicity, rarity, persistence, habitat rarity and habitat loss. Each variable was categorized into four ranks (0-3) of increasing risk for survival. Ochthebius glaber, Ochthebius irenae, Ochthebius montesi, Ochthebius albacetinus and Hydraena mecai were seen to be the most vulnerable, for which reason we propose they should be included in the national red list. Furthermore, O. glaber, O. irenae and O. montesi are proposed for inclusion in the IUCN red list as “Vulnerable”. These species are Iberian endemisms, with geographic ranges restricted to the southeast, and are threatened by habitat loss. Effective protection of these species requires measures directed at the conservation of their habitats. Crucial target habitats for protection in the southeast of the Iberian Peninsula include freshwater streams at medium altitudes, saline streams and endorreic lagoons.     

盐池不同保护及恢复措施对植物多样性的影响

该文以位于我国西北半干旱区的宁夏盐池县为研究对象,研究不同植被保护及恢复措施下植物群落结构及物种多样性。选取4类样地类型:分别为老封育区草地、新封育区草地、退耕地、天然草地。老封育区草地各项植物多样性指数均为4类样地类型中最低,可见,并不是封育年限越长,植被恢复生长效果就越好。退耕地的综合多样性指数及均匀性指数在4类样地类型中均较高,退耕还草是一种非常可取的植被恢复措施。     

Point Source Ammonia Emissions are Having a Detrimental Impact On Prairie Vegetation

Prairie grasslands are very species rich but have declined in their extent considerably due to land-use change and exploitation. Many remaining prairie fragments are situated within an agricultural matrix and can be subjected to high levels of atmospheric ammonia deposition from animal units. Three prairie fragments in Minnesota that were located in close proximity to feedlots were selected, and 500-m transects were studied at an increasing distance from the feedlot. Changes in soil pH, soil nitrate concentration, and soil ammonium concentration with increasing distance from the source were variable between the sites, possibly due to differences in the processing of nitrogen in the soil and the degree of nitrogen limitation. Species richness showed significant negative relationships with ammonia deposition and soil nitrate concentration, whereas aboveground biomass showed a positive relationship with ammonia deposition. Both the richness and biomass of nongraminoid species declined with increasing soil nitrate concentration, whereas graminoid biomass was positively related to ammonia deposition and was negatively associated to richness. Bromus inermis, a non-native perennial grass, was the main species that increased at high deposition. The results of this study have important implications for the conservation and restoration of prairie grasslands.     

Recent declines in northern tall-grass prairies and effects of patch structure on community persistence

Tall-grass prairies are a critically endangered ecosystem in North America. Our objectives were to evaluate potential roles of prairie patch structure (defined in terms of prairie patch area, matrix type, and edge effects) in explaining changes in number, size, and quality of northern tall-grass prairies over time. In 2006, we evaluated changes in remnant tall-grass prairies at the most northern extent of the tall-grass prairie range, by resurveying plant communities in 65 remnant patches in Manitoba, Canada, that were previously surveyed in 1987 or 1988. In 2007 and 2008 we conducted more detailed surveys of vegetation structure and composition at 580, 0.2 × 0.5 m quadrats distributed within 24 remnant patches of northern tall-grass prairie. Our findings suggest remnant northern tall-grass prairies continue to suffer from serious threats: 37% of the patches surveyed in 1987 or 1988 had changed to other habitat types by 2006; patches smaller than 21 ha tended to decrease in size, while larger patches increased in size; and most patches, particularly smaller ones, declined in quality. Both native and alien species responded more strongly to distance to edge than to patch size or matrix type. Edge effects may explain why prairie quality is lower and more likely to decline in smaller remnants. Richness of native plants was negatively correlated with cover and richness of alien species, suggesting that alien species may displace native species. Few existing northern tall-grass prairies are likely to be self-sustaining, and immediate active management is required to prevent further loss of remnant northern tall-grass prairies.     

龙须草复合种植技术对紫色土小生境的影响

紫色土的植被恢复是中国植被恢复难题之一.为了研究龙须草植被改善紫色土生境的效果,将引种龙须草后植物群落物种多样性与土壤环境因子的变化相结合,寻找最适宜紫色土地区生态恢复的龙须草植被恢复模式.设置3种龙须草植被恢复地模式（人工恢复地Ⅰ、Ⅱ和自然恢复地Ⅲ）,于2010年7月中旬在湖南松林村进行野外调查.通过群落分类双向指示种分析和群落排序冗余分析表明：1）土壤全氮量、土壤有机质质量分数、坡位和恢复模式是影响群落多样性的主要环境因子;2）3种植被恢复地模式中,人工恢复地Ⅱ的群落Gleason丰富度指数最大（坡上位2.171,坡下位5.863）,土壤全氮量和土壤有机质质量分数有明显提高.因此,利用龙须草进行植被恢复时应优先选取恢复效果最好的人工恢复地模式Ⅱ.     

Small-scale plant species richness and evenness in semi-natural grasslands respond differently to habitat fragmentation

The study explores whether small-scale species diversity, species evenness and species richness in semi-natural grassland communities are similarly associated with present management regime and/or present and historical landscape context (percentage of different land-cover types in the surroundings). Species diversity, evenness and richness were recorded within 441 50 × 50 cm grassland plots in 4.5 × 4.5 km agricultural landscape on Öland, Sweden. Recent and historical land-cover maps (years 2004, 1959, 1938, 1835, and 1800) were used to characterize the present and past landscape context of the sampled vegetation plots. Partial regression and simultaneous autoregressive models were used to explore the relationships between species diversity measures (Shannon diversity, richness and evenness) and different explanatory variables while accounting for spatial autocorrelation in the data. The results indicated that species richness was relatively sensitive to grassland isolation, while the response of species evenness to isolation was characterized by a degree of inertia. Because the richness and evenness components of species diversity may respond differently to habitat fragmentation, we suggest that monitoring projects and empirical studies that focus on changes in biodiversity in semi-natural grasslands should include the assessment of species evenness - as a complement to the assessment of species richness. In addition, our results indicated that the development and persistence of a species-rich and even grassland vegetation was favoured in areas that have historically (in the 19th century) been surrounded by grasslands. Information on landscape history should, whenever possible, be incorporated into the planning of strategies for grassland conservation.     

Using SPOT images and field sampling to map burn severity and vegetation factors affecting post forest fire erosion risk

Runoff and erosion rates are known to increase substantially after a major forest fire. Erosion control measures therefore need to be put into place quickly after a large fire, and determining where to locate the measures requires accurate mapping of post fire erosion risk. Burn severity can be determined from field observations, but these are costly and time consuming. Satellite imagery is an alternative to quickly map burn severity for erosion mapping purposes. Post fire erosion decreases as forest vegetation recovers and this is related to both pre fire vegetation characteristics and soil properties. The objectives of this study were to test the use of SPOT multispectral images for mapping burn severity, pre fire vegetation density, and longer term (2.5 years) vegetation recovery. Indices tested include the Normalized Burn Ratio (NBR), Normalized Difference Vegetation Index (NDVI), Differenced Normalized Burn Ratio (dNBR), and Differenced Normalized Difference Vegetation Index (dNDVI). Indices were compared to field data gathered immediately after the fire and about 2.5 years later. The multi-temporal indices (dNBR and dNDVI) were more useful for burn severity mapping in the heterogeneous forest–scrubland–vineyard environment where bedrock and vineyard surfaces were confused with burned areas when using single images (NBR and NDVI). All of the post fire indices showed traces of the fire 2.5 years later; this was confirmed using Analysis of Variance where differences in indices were related to original ground cover (pine forest, mixed forest, mostly bedrock and vineyards) and the burn scar. Pre fire vegetation cover was less successfully mapped using the NDVI according to the initial field observations. Similarly, none of the post fire indices were able to distinguish differences in N–S vegetation recovery revealed by field measurements of understory vegetation height and cover; N facing slopes had deeper finer soils and these more favourable conditions led to greater vegetation growth than on S facing slopes and topslope convexities. It is suggested that relationships between topography and soil properties can be useful for mapping both soil erodibility and post fire vegetation recovery.     

黄土丘陵区生态退耕对草本层植物多样性的影响

为研究何种生态退耕对黄土丘陵地区植被恢复较好,以典型黄土丘陵沟壑区大南沟小流域为研究区,采用传统植物群落调查法从退耕方式和退耕年限两个方面探讨生态退耕对草本层植物多样性的影响。结果表明:（1）在生态退耕30 a内,随着退耕年限的增加,草本层植物丰富度指数、两多样性指数（Simpson指数和Shannon-Wiener指数）和均匀度指数都呈现增加的趋势。但前期增加不显著,后期增加显著。（2）不同生态退耕方式对草本层植物多样性的影响差异显著。三种多样性指数均表现为退耕还草 > 退耕还林 > 退耕还灌,且丰富度指数退耕还草（23.875）较退耕还林（14.606）和还灌（14.556）显著增加;Simpson多样性指数和Shannon-Wiener多样性指数退耕还草（0.945,3.048）和退耕还林（0.931,2.992）较还灌（0.912,2.563）显著增加。退耕还草优于退耕还灌和退耕还林,对草本层植物群落多样性影响最小,是最佳生态退耕方式。     

Habitat use and conservation of bumblebees (Bombus spp.) under different grassland management regimes

Declines in the natural populations of several bumblebee species across Britain and Europe are an increasing cause for concern. In this study the habitat use of bumblebees was investigated on Salisbury Plain Training Area, the largest remaining area of unimproved chalk grassland in north-west Europe. Habitat characteristics influencing the overall abundance, species richness and foraging activity of bumblebees included the diversity and abundance of flowering plant species (particularly of favoured forage plants such as Trifolium pratense), vegetation structure and height. It is suggested that different Bombus species respond to these habitat characteristics depending on their specific foraging and nesting requirements, the case of Bombus humilis being especially relevant. The effects of several grassland management practices were considered in terms of their suitability for the conservation of bumblebee habitats. Cattle grazing was shown to be preferable to both sheep grazing and the absence of any management, although the timing and intensity of such grazing was important. Small-scale disturbances caused by vehicle activity were also of value in producing locally abundant forage resources in less intensively managed grasslands.     

How does grazing intensity affect different vegetation types in arid Succulent Karoo, South Africa? Implications for conservation management

The Knersvlakte in the Succulent Karoo Biome (South Africa) is known for its high plant diversity and endemism. In the course of establishing a conservation area there, we assessed baseline data for future management. We investigated the effects of grazing on the vegetation in terms of species diversity and composition as well as reproduction of selected species. Data were sampled on four adjacent farms, which were ungrazed, moderately or intensively grazed by sheep and goats. The data were collected in 27 quartz and 24 non-quartz plots, representing two major habitat types of the region. Within each of the 1000-m² plots, 100 subplots of 400 cm² size were sampled. ANOVAs revealed that species richness and abundance of endemic species on quartz fields decreased with grazing. Abundance of annuals did not increase significantly due to grazing. Fidelity analyses indicated that species composition differed between grazing intensities and that the ungrazed and moderately grazed plots both contained unique locally endemic habitat specialists. Reproduction of two endemic dwarf shrubs Drosanthemumschoenlandianum and Argyrodermafissum (both Aizoaceae) increased under moderate grazing, which in the case of D.schoenlandianum was interpreted as an effect of grazing. We attribute the low number of seedlings and annuals on the moderately grazed farm to lower seasonal rainfall on these plots. From a conservation perspective, no or moderate grazing appear to be necessary to preserve plant diversity and vegetation patterns, and their underlying processes.