Long-term response of spring flora to chronic herbivory and deer exclusion in Great Smoky Mountains National Park, USA

Chronic herbivory by white-tailed deer (Odocoileus virginianus Zimmerman) can have profound impacts on the function and structure of forest ecosystems. We examined the combined influence of intense herbivory associated with a deer population eruption and chronic herbivory by the post eruption population on the spring flora of Cades Cove, Great Smoky Mountains National Park. During the 1970s the deer population reached a peak of 43 deer per km², from which it has slowly declined in recent decades. To examine the influence of intense herbivory, we compared the abundance and flowering rates of early flowering plants in Cades Cove to a nearby reference site with similar bedrock geology, vegetation, and disturbance history but contrasting history of deer abundance. Our results suggest that significant changes (p ? 0.05) in the diversity, evenness, and species richness of the spring flora occurred during the eruptive phase. Trillium spp. and other liliaceous species appeared to be disproportionately impacted. Comparisons between control and exclosure plots established after the deer population eruption indicate that recovery has been largely restricted to species that were able to persist under intense herbivory. These species have increased in number in exclosures, suggesting continued impacts by deer on the plant community outside the exclosures. Little to no recolonization by browse sensitive species was observed. Consequently, to restore the natural diversity of early flowering plants once present in Cades Cove, active restoration may be necessary in addition to maintaining deer densities below current levels.     

Restoring forest herb communities through landscape-level deer herd reductions: Is recovery limited by legacy effects?

White-tailed deer (Odocoileus virginianus) overbrowsing has altered plant species diversity throughout deciduous forest understories in eastern North America. Here we report on a landscape-level (306 km²) project in Pennsylvania, USA that tracked the herbaceous community response to deer herd reductions. From 2001 to 2007, we estimated deer densities, browse impact on woody seedlings, and censused the herbaceous flora in permanent plots throughout the area. We assessed herb layer species richness, abundance, and dominance and measured three known phytoindicators of deer impact: Trillium spp., Maianthemum canadense, and Medeola virginiana. We predicted that browse-sensitive taxa would increase in abundance, size, and flowering as would overall species diversity following deer culls and browse impact that declined by an order of magnitude by 2007. Following intensified deer harvests, we observed a limited recovery of the herbaceous community. Trillium spp. abundance, height, and flowering; M. canadense cover; and M. virginiana height all increased following herd reductions. Similarly, forb and shrub cover increased by 130% and 300%, respectively. Nevertheless, species diversity (i.e., richness and dominance) did not vary. Our work demonstrates that reducing deer densities can provide rapid morphological and population-level benefits to palatable species without a concomitant recovery in diversity. We suggest that decreasing deer populations alone may not promote plant diversity in overbrowsed, depauperate forests without additional restoration strategies to mitigate a browse-legacy layer dominated by browse-resistant species.     

Seeing the forest for the deer: Do reductions in deer-disturbance lead to forest recovery?

High levels of deer browsing can prevent canopy tree regeneration, but little is known about changes to forest size-structure following long-term deer herd reductions. We monitored changes in forest stand structure and composition in southwestern Ontario, Canada, over 28-years using permanent plots. Our study site was the largest remaining tract of Carolinian (deciduous) forest in Canada (11 km²), a habitat type that contains up to a fifth of Canada’s species at risk and is under intense anthropogenic pressures. We recorded declines in all tree size classes between 1981 and 1996, during which densities of white-tailed deer (Odocoileus virginianus) reached a peak of 55 deer km⁻². Despite significant and sustained deer herd reductions between 1996 and 2009, which reduced deer densities to 7 deer km⁻², there was limited recruitment of small trees and declines in basal area of tree species that were sensitive to deer browsing. Our results suggest that recovery from herbivory is a protracted process during which canopy tree regeneration may continue to decline despite a reduction in browsing pressure due to deer culling. Large declines in canopy-tree densities in Carolinian forests may lead to forest size-structures and herbaceous plant communities that resemble rare oak savanna habitat, creating difficult decisions for conservation managers aiming to protect rare and endangered species within native ecosystems. We recommend that managers protect Carolinian forest stands and encourage canopy tree regeneration by increasing seed sources of native trees. While deer control is essential in reducing forest damage, our results highlight the need to explore other forms of active management to expedite otherwise slow increases in tree density.     

Long-term effects of deer browsing and trampling on the vegetation of peatlands

Overabundance of wild ungulates, especially exotic species, is a major threat to several ecosystems worldwide. While the response of forest vegetation to high density of herbivores has been well studied, far less is known about peatland vegetation. In this paper, we assessed the long term impact of white-tailed deer (Odocoileus virginianus) on plant communities of ombrotrophic (bog) and minerotrophic (fen) peatlands in eastern North America. Vegetation of five peatlands that have experienced high deer densities for at least 75 years was compared with that of five peatlands situated at proximity but on deer-free islands. We investigated deer impacts on plant species composition and cover, shrub height and cloudberry (Rubus chamaemorus) fruit/flower production and morphology. In bogs, white-tailed deer had no long-term impact on plant species assemblages, but reduced lichen cover and increased sedges and grasses cover as well as the surface area of bare peat. On the other hand, the floristic composition of fens differed significantly between sites where deer were present or absent. Plant diversity was greater in undisturbed fens than in disturbed fens, especially for shrubs, sedges and liverworts. No detrimental effects of browsing on shrub height were observed. Conversely, deer browsing seemed to have deleterious impacts on cloudberry fruit/flower production as well as on the number of leaves per individual. Overall, our results suggest that white-tailed deer had some important impacts on the vegetation of peatlands that could be harmful for the long-term conservation of peatland plant diversity.     

Dispersal and establishment of floodplain grassland species as limiting factors in restoration

The restoration of grassland and its dependence on the dispersal of characteristic plant species was analysed in the Saale River floodplain near Halle (Germany). Species composition and soil nutrient content were investigated in grassland converted to extensive management in 1989 (“restoration grassland”) and in adjacent grassland that had never been managed intensively (“old grassland”). In two experiments dispersal of Silaum silaus and Serratula tinctoria was studied following introduction of these species into “restoration grassland”. Seedling establishment was recorded and compared with the “old grassland”. Ten years after conversion to extensive management, characteristic floodplain grassland species had only reappeared in locations very close to “old grassland”. There were still differences in soil nutrient content of both grassland sites but a comparison of seedling survival provided evidence that conditions of establishment were similar. However, establishment rates appeared to be low in both grassland types indicating that a large initial input of seeds is required for re-establishment. Seeds of Silaum silaus and Serratula tinctoria were dispersed very short distances. About 75% of the seedlings were found within 1.5 m of parent plants. Management and flooding did not increase dispersal distances. The results strongly suggest that poor dispersal was the main limiting factor in determining the success of restoration. The implications of this result for nature conservation are discussed.     

生态修复措施对干旱半干旱地区生态系统服务影响研究——以河北坝上地区为例

为了揭示生态修复措施对干旱半干旱地区生态系统服务的影响,以对生态可持续发展提供决策参考,基于典型的干旱半干旱地区——河北坝上地区2000年、2018年土地利用数据以及4种与生态修复措施对应的情景,结合InVEST模型分析了生态修复措施对该区3个重要的生态系统服务(水源涵养、生境质量、碳储量)的影响。结果显示:(1) 2000—2018年坝上地区土地利用变化以草地大量缩减以及林地显著扩张为主(>500 km²),期间,水源涵养量下降7.03%,碳储量、生境质量分别增长2.82%,1.29%;(2)相比林地缓冲带、植树造林情景,开垦荒地和综合发展情景对上述3个生态系统服务的提高更为显著;(3)水源涵养、碳储量均与生境质量呈较强协同作用(r>0.42),碳储量与水源涵养呈较弱协同作用(r<0.24)。综上分析,生态修复措施能够提高坝上地区生态系统服务的供给,但以造林为主的生态修复方式在干旱半干旱地区仍需谨慎实施。     

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.     

昆虫野花带在农业景观中的应用

在农业景观中,昆虫野花带是以混播等方式,建植在农田、果园、菜地等农地边缘的条状或片状生态缓冲区。通过配置不同功能植物形成植物群落,为自然天敌及传粉者提供蜜粉源和栖息地,改善农地生境质量;强化害虫天敌支持系统,达到提高授粉率、减少农药使用、改良修复农地土壤、净化水源、抑制杂草等多样的生态系统服务功能。本文回顾了昆虫野花带的应用发展历程,涵盖了中西欧发达国家及美国等地。不同国家昆虫野花带侧重不同,瑞士、比利时等国家作为昆虫野花带的源头,最早将生态保育的思想运用于农业生产,并付诸生态补偿机制的实践;英国昆虫野花带有政策的细化支持,应用方式丰富;美国以本土植物的开发、草原生境的修复及重要传粉者保护为研究与实践的重点。中国的农地周边由于外来物种入侵、人为干预严重等造成了景观异质性低、生境破碎化,亟待引入昆虫野花带的技术手段,进行生境管理与规划。中国的昆虫野花带研究仍处于发展初期,缺少实际应用。未来,中国昆虫野花带的发展,首先要针对现有非作物生境植物群落以及各类昆虫群落展开动态监测与调查,在大尺度上划定生态保护区域,分析现有生境格局,构建生态网络,研究昆虫野花带的规划方案,分清主次和功能需求,并根据节肢动物功能团的时空动态变化,确定最佳群落结构,保持昆虫野花带生境与其他自然与半自然生境的功能连接度,保留多样的景观因素。     

Effects of oak barrens habitat management for Karner blue butterfly (Lycaeides samuelis) on the avian community

The federally endangered Karner blue butterfly (Lycaeides samuelis) is the focal species for a conservation plan designed to create and maintain barrens habitats. We investigated whether habitat management for Karner blue butterflies influences avian community structure at Fort McCoy Military Installation in Wisconsin, USA. From 2007 through 2009 breeding bird point count and habitat characteristic data were collected at 186 sample points in five habitat types including two remnant barrens types, barrens habitat restored from woodland and managed specifically for the Karner blue butterfly, and two woodland habitat types. Although the bird community of managed barrens was not identical to the communities of remnant barrens, the Field Sparrow (Spizella pusilla), a species of conservation concern, and sparse canopy associated bird species, such as the Baltimore Oriole (Icterus galbula) and Eastern Bluebird (Sialia sialis) were predicted to occupy managed barrens and remnant barrens in similar proportions. Adjacent habitat was the most influential factor in determining the community of bird species using the managed barrens. In Wisconsin, and likely throughout the range of the Karner blue butterfly, management for the butterfly creates habitat that attracts a bird community similar to that of remnant barrens, and benefits several avian species of conservation concern. Additionally, the landscape context surrounding the managed habitat influences avian community composition. Managed barrens that are adjacent to remnant barrens, rather than adjacent to woodland habitats, have the highest potential for conserving barrens breeding birds.     

Long-term heathland restoration on former grassland: The results of a 17-year experiment

European lowland heaths have declined by up to 80% due to land use change and lack of management. There has been considerable research into the restoration of this threatened habitat. However, long-term outcomes of restoration are poorly understood, especially in situations where past agricultural land use imposes severe constraints on community re-assembly. In 1989 a large-scale experiment was established to examine the effectiveness of five treatments to restore heathland on formerly productive grassland: (i) natural regeneration; (ii) herbicide application to facilitate regeneration; (iii) cultivation and application of seed-rich heathland vegetation; (iv) soil removal and incorporation of heathland topsoil; and (v) heathland translocation. After 17 years the pH of the unamended agricultural soil remained significantly higher than that of the adjacent heathland. All treatments showed different trajectories of vegetation change in the long-term. Natural colonisation by heathland species was slow due to seed limitation, resulting in formation of an acid grassland community. Heathland community assembly was not facilitated by destruction of the initial grassland with herbicide. Incorporation of topsoil had an intermediate effect on pH reduction. This may explain the subsequent failure of the plant community to assemble in the anticipated proportions, and the dominance of leguminous scrub species (Ulex spp.). Turf translocation was effective in reducing pH to the required range and restoring the heathland community in the long-term. However, this technique should only be considered as a means of ‘rescue’ when habitat destruction is otherwise unavoidable. The only practical and sustainable means of increasing heathland extent on former farmland is the application of seed-bearing vegetation cut as part of routine management. However, this technique needs refining in order to establish the full range of characteristic heathland species.     

Soil microbial community composition as affected by restoration practices in California grassland

Agricultural practices have strong impacts on soil microbes including both the indices related to biomass and activity as well as those related to community composition. In a grassland restoration project in California, where native perennial bunchgrasses were introduced into non-native annual grassland after a period of intensive tillage, weeding, and herbicide use to reduce the annual seed bank, microbial community composition was investigated. Three treatments were compared: annual grassland, bare soil fallow, and restored perennial grassland. Soil profiles down to 80 cm in depth were investigated in four separate layers (0-15, 15-30, 30-60, and 60-80 cm) using both phospholipid ester-linked fatty acid (PLFAs) and ergosterol as biomarkers in addition to microbial biomass C by fumigation extraction. PLFA fingerprinting showed much stronger differences between the tilled bare fallow treatment vs. grasslands, compared to fewer differences between restored perennial grassland and annual grassland. The presence or absence of plants over several years clearly distinguished microbial communities. Microbial communities in lower soil layers were little affected by management practices. Regardless of treatment, soil depth caused a strong gradient of changing habitat conditions, which was reflected in Canonical Correspondence Analysis of PLFAs. Fungal organisms were associated with the presence of plants and/or litter since the total amount and the relative proportion of fungal markers were reduced in the tilled bare fallow and in lower layers of the grassland treatments. Total PLFA and soil microbial biomass were highly correlated, and fungal PLFA biomarkers showed strong correlations to ergosterol content. In conclusion, microbial communities are resilient to the grassland restoration process, but do not reflect the change in plant species composition that occurred after planting native bunchgrasses.     

Multi-species occurrence models to evaluate the effects of conservation and management actions

Conservation and management actions often have direct and indirect effects on a wide range of species. As such, it is important to evaluate the impacts that such actions may have on both target and non-target species within a region. Understanding how species richness and composition differ as a result of management treatments can help determine potential ecological consequences. Yet it is difficult to estimate richness because traditional sampling approaches detect species at variable rates and some species are never observed. We present a framework for assessing management actions on biodiversity using a multi-species hierarchical model that estimates individual species occurrences, while accounting for imperfect detection of species. Our model incorporates species-specific responses to management treatments and local vegetation characteristics and a hierarchical component that links species at a community-level. This allows for comprehensive inferences on the whole community or on assemblages of interest. Compared to traditional species models, occurrence estimates are improved for all species, even for those that are rarely observed, resulting in more precise estimates of species richness (including species that were unobserved during sampling). We demonstrate the utility of this approach for conservation through an analysis comparing bird communities in two geographically similar study areas: one in which white-tailed deer (Odocoileus virginianus) densities have been regulated through hunting and one in which deer densities have gone unregulated. Although our results indicate that species and assemblage richness were similar in the two study areas, point-level richness was significantly influenced by local vegetation characteristics, a result that would have been underestimated had we not accounted for variability in species detection.     

Detection of extinction debt depends on scale and specialisation

Many plants can persist in landscapes for a long time after focal habitats have disappeared or become fragmented, which might contribute to an extinction debt. Delayed responses of plant occurrence have recently received great attention, particularly in conservation, although evidence for extinction debts is incongruent. Here we asked if we could detect an extinction debt for plant species after 100 years of fragmentation, depending on regional or local (gamma or alpha respectively) diversity measure used, and if all plant species or only habitat specialists were investigated. Historical and contemporary grassland patterns were analysed in 33 rural landscapes (each 1 km² in diameter) in south-eastern Sweden. Results show that managed semi-natural grassland had declined from 39% to 3% in 100 years. Diversity measured at regional scale was best explained by grassland extent 100 years ago, for both all species and grassland specialists. Present-day management, but neither present nor past grassland extent, was important for grassland specialists’ occurrence at the local scale, although present-day grassland proportion had a positive influence on species richness at the local scale. We found evidence of an extinction debt at both local and regional scale when all species were included in the analysis, but not for grassland specialist species at the local scale. However, the extinction debt is still to be settled for grassland specialists at the regional scale, and therefore the estimation of extinction debts in fragmented habitats presents one of the greatest challenges for conservation today and in the future.     

The distribution of disturbance-dependent rare plants in a coastal Massachusetts sandplain: Implications for conservation and management

Rare plants in coastal New England sandplains are often restricted to anthropogenically disturbed sites including plowed and mowed firelanes at the Manuel F. Correllus State Forest on Martha’s Vineyard. Little is known about pre-colonial rare plant habitat or how modern management impacts these species. To understand the factors influencing rare plant distribution, we examined the influence of vegetation structure, species composition, environmental characteristics and disturbance history on rare plant populations and potential natural habitat in the 2100-ha Forest. We sampled >100, 100 m² plots - in firelanes and forested/shrubland areas - and conducted extensive searches for rare plants.Linum intercursum and Scleria pauciflora var. caroliniana were frequent in firelanes including in recently plowed areas, whereas Nabalus serpentarius, Sisyrinchium fuscatum, and Aristida purpurascens generally occurred in isolated, locally-abundant patches in firelanes not plowed for many decades. The former group may be characterized by an ability to rapidly establish following disturbances while the latter may take longer to establish and develop large populations. In some respects, rare plants were associated with environmental conditions reflecting the disturbance histories of sites they occupied (e.g., L. intercursum with lower duff depth and N. serpentarius with greater litter cover/depth).In forests and shrublands undisturbed for decades, rare plants only occurred on well-worn paths. Although scrub oak stands supported conditions more similar to those found in firelanes than other native vegetation types, disturbances - far more severe than those in forests/shrublands of the past century - are probably required to create suitable rare plant habitat in sandplain forests and shrublands.     

Fifty years of change in northern upland forest understories: Identity and traits of “winner” and “loser” plant species

Resurveys of plant communities provide valuable information on changes in species composition over time and clues about how species respond to environmental change. We report results from resurveys of 62 upland forest stands in northern Wisconsin and the western Upper Peninsula of Michigan first surveyed around 1950. We identify plant species that have significantly increased or decreased in frequency in 1 m² quadrats (‘winners’ and ‘losers’) and evaluate the traits that distinguish these groups. Twenty-one winner species increased across sites (by 25-400%), while 21 loser species decreased (by 21-95%). Winners include both common, native species and five invading exotics. Many are grasses or sedges and most are abiotically pollinated or dispersed (e.g., Carex, which increased 286%). Losers are mostly rarer native forbs that rely on animals for pollination and/or dispersal. Losers appear sensitive to desiccation, anthropogenic disturbance, and/or herbivory by white-tailed deer (e.g., Streptopus roseus, which decreased 73%). Declines in loser species are heterogeneous and stochastic across sites whereas increases in winners are more uniform and deterministic. Increases in common widespread native species account for most of the community change we observe across sites. The fact that winners resist or tolerate deer herbivory while many losers are sensitive to deer suggests that deer may be a key driver of the shifts we observe in these forests.     

Effects of grassland abandonment, restoration and management on butterflies and vascular plants

When semi-natural pastures are abandoned, specialized grassland species are lost as a consequence of succession. As a counter-measure, previously abandoned grasslands may be restored by clearing shrubs and trees and re-introducing grazing livestock. In order to examine the effects of this type of habitat restoration, we compared species richness of plants and of specialized plants thought to be dependent on continuous management and species richness and abundance of butterflies and red-listed butterflies in 12 sets of matched continuously managed, abandoned and restored grassland in southern Sweden. We found no differences in species richness or abundance between the three grassland types. There were, however, some negative effects of abandonment. The number of management-dependent plants decreased with increasing cover of trees and shrubs, and in restored sites species richness of all groups decreased with increasing cover of trees and shrubs before restoration. Also the present management significantly affected both butterflies and plants. Species richness of both groups increased with increasing vegetation height and differed between sites depending on the species of grazers, with negative effects of sheep compared to cattle or horses. Our study indicates that for grassland management to be efficient, the restoration actions should mainly be directed towards sites where the post-abandonment succession has not proceeded too far.     

荒漠草原不同植被恢复模式的水土保持生态效益

[目的]以内蒙古四子王旗境内退化荒漠草原为研究区域,研究不同植被恢复模式对植物群落组成、土壤含水量、土壤侵蚀的影响,为退化草原水土流失治理和草原生态建设提供理论依据。[方法]针对退化草原特点、水土流失特征,分析不同植被恢复模式下植物群落特征、土壤水分、地表径流和侵蚀量的变化,运用主成分分析对不同植被恢复模式的水土保持生态效益进行评价。[结果]退化荒漠草原的3种植被恢复模式试验样地的植物种类组成、群落总盖度、地上生物量均高于放牧天然草地,"围栏封育+灌木条带+施肥复壮"、"围栏封育+松土补播+草种包衣"2种植被恢复模式的地上生物量与放牧天然草地之间变化差异达到显著水平(p0.05);3种植被恢复模式的实施有效控制了土壤侵蚀,径流量和土壤侵蚀量均低于天然草地。[结论]"围栏封育+松土补播+草种包衣"植被恢复模式在保持水土资源,增加群落稳定性等方面的生态效益最好。