舟山本岛岩质边坡植被恢复植物多样性及群落演替

通过植被演替的时空互代,在舟山本岛选取具有代表性的不同恢复时期的矿山边坡作为研究样地,考察样地内植物物种构成特征,并根据样地内植物群落特征及不同恢复年限将其划分为4个不同的植物群落(草丛、草灌丛、灌丛、乔灌丛)演替阶段,对比分析不同演替阶段的植物多样性变化及植物群落的演替规律。结果表明:随着恢复年限的增加,多样性指数呈上升趋势,但均匀度指数则略呈下降趋势,植物群落演替总体呈良性发展趋势。岩质边坡植被恢复的研究为舟山地区或其它海岛生境条件下的岩质边坡植被重建过程中的植物配置及养护管理提供理论指导。     

Spatial variations of plant species diversity in urban soil seed banks in Beijing,China: Implications for plant regeneration and succession

The near-to-nature urban forestry concept and practices are widely recognized for urban greening, urban ecosystem restoration, urban greenspace management for biodiversity conservation and ecosystem services provision. However, the regeneration and succession of urban vegetation are rarely studied due to the complex settings of the urban environment. To this end, we conducted a large-scale field investigation in the metropolitan area of Beijing, China to explore the spatial variations in plant species composition and diversity in soil seed banks, and their similarity to the aboveground vegetation to assess the potential of urban plant regeneration. Overall, 657 vegetation and soil sampling plots from 219 grids, measuring 2 km × 2 km each, were investigated within two perpendicular 10 km wide transects running across the urban center in north-south and east-west directions within the 6th Ring Road of the city. We recorded a total of 102 plant species in soil seed banks, including 13 tree species, 10 shrub species, and 79 herb species. We found that the soil seed bank species diversity and its similarity to that of the aboveground vegetation communities decreased significantly with the urbanization intensity. Higher urbanization intensity is typically associated with increased human management and a reduction in Greenspace Area (GSA). Soil seed bank species richness increased significantly when GSA exceeded 45 % and the similarity of species composition and diversity between soil seed banks and aboveground vegetation communities was the highest in forest parks. This suggests that habitats under forest park management are more conducive to plant regeneration. Soil seed bank species diversity first increased and then decreased significantly with increased distance to the city center, whereas the species similarity between the soil seed banks and the aboveground vegetation communities showed little change with the ring roads going out. The results of this study have important implications for further understanding the potential for urban vegetation regeneration and sustainability, which have significant implications for urban biodiversity conservation and restoration.     

In the bleak mid-winter: The value of brownfield sites for birds during the winter

Brownfield sites (e.g., wastelands, disused industrial grounds and power stations) are valuable refuges for urban birds during the breeding season. This owes to the presence of vegetation in different stages of succession, which provide a high diversity of food and breeding resources. However, insufficient research has explored their winter value, when temperatures are lower and food is scarcer. Accordingly, 342 bird and habitat surveys were conducted in brownfield sites, and other land-uses, across Greater Manchester. Bird density estimates were then calculated using Distance software and bird-habitat associations were analysed using Canonical Correspondence Analysis (CCA). Moreover, the impact of brownfield site development on winter bird density from 2000 to 2009 in Greater Manchester was explored using the bird density estimates, and historical image function in Google Earth. In brownfield sites, Pica pica had the highest density estimate (142 per km²), although four species had estimated densities > 100 per km² (Turdus merula; Cyanistes caeruleus; Passer domesticus; Aegithalos caudatus). The CCA indicated that Aegithalos caudatus, Cyanistes caeruleus, Parus major, Prunella modularis were associated with Fagus sylvatica, Betula pendula, and Buddleja davidii on brownfield sites, which during the winter 1) produce seeds 2) support overwintering insects, providing a valuable food source. Nevertheless, across land-uses, most species favoured green space and pre-2000 housing. Brownfield sites were most replaced between 2000 and 2009, with 17.8 km², 14.9 km², and 12 km² replaced by commercial, industrial, and post-2000 housing respectively. This is likely to have had a negative impact on the winter density of most bird species, owing to 1) the removal of brownfield site vegetation 2) increases in impervious land cover. Future declines in winter bird abundance could be mitigated by retaining brownfield site vegetation and setting aside brownfield sites in close proximity to green space and pre-2000 housing.     

京津冀地区矿山排渣场植被演替规律

植被自然恢复演替过程对矿山废弃地人工辅助植被恢复设计与实施效果评价均具有重要的借鉴价值。为了探索京津冀地区矿山排渣场植被演替规律，以京津冀地区典型矿山为例，运用典型样地和样方法，在详细调查获取数据的基础上，分析矿山排渣场自然恢复50年内的植物多样性变化特征。结果表明：当年内植物多样性指数变化呈波浪状，先增加后减少，然后再增加；先锋植物为一年生草本植物，植物种群从藜→蒿草；植物种群变化可划分为6个阶段：一年生草本阶段→多年生草本阶段→灌草阶段→灌木阶段→灌木与林木混合阶段→林木阶段。可见，矿山排渣场植被自然恢复具有较强的规律性，基于植物自然演替规律，首年内宜种植一年生草本类植物，有利于促进矿山废弃地植被恢复进程。     

An integrated approach for measuring urban forest restoration success

Rapid urban growth has increased the importance of restoring degraded vegetation patches within these areas. In this study, we reforested a site that was previously dominated by exotic grasses within an urban area. The goal of this study was to evaluate restoration success in a reforested site using four variables of vegetation structure, five groups of organisms, and eight variables of ecosystem processes, and compare these values with a pre-reforested site and a forested reference site using the Subjective Bray Curtis Ordination. The change in vegetation structure provided arboreal habitats that increased species diversity and ecosystem processes in the reforested site. Specifically, the development of a vertical vegetation structure was associated with: (1) a decrease in herbaceous cover, which allowed the colonization of woody seedlings; (2) a change in microclimatic conditions, which enhanced the colonization of ants and amphibians; (3) colonization of arboreal reptiles and birds; and (4) an increase in litter production, which enhanced nutrient inputs. Moreover, the Subjective Bray Curtis Ordination demonstrated an overall recovery of approximately 70%. Planting woody species was sufficient to stimulate rapid recovery of many ecosystem attributes. Future restoration projects should include multiple variables that reflect important ecosystem attributes to determine the success of a project and to direct future management efforts.     

Spatial patterns of Mediterranean land abandonment and related land cover transitions

In Mediterranean France, land abandonment is a widespread change. To understand and predict the land abandonment process and its consequences, land cover change models are used. An essential step in the development of a land cover change model is the identification and quantification of the factors controlling land cover change. In this paper we present a change detection study using aerial photographs in combination with an extensive dataset of field data and geographical data, to identify and quantify these factors for a study area in Mediterranean France, 60 km west of the city of Montpellier. We distinguished 11 land cover change classes and 7 associated “time since abandonment” classes at a detailed scale. Several environmental and non-environmental factors were found to be important variables for the land abandonment process. Differences in soil class explain a large part of the land abandonment pattern and the associated transition paths and transition rates. Most abandoned lands are located on regosols and lithosols, which are marginal soils with respect to water holding capacity. Within soil classes, we could recognise different transition paths and transition rates. However, within the 55 years covered by this dataset detailed transitions from pioneer vegetation to vegetation higher in the succession, as described by other authors, were only found for a limited number of vegetation/soil combinations. We relate these slow transitions for some areas to ongoing grazing and for some other areas to irreversible degradation.     

Influence of forest management alternatives and land type on susceptibility to fire in northern Wisconsin,USA

We used the LANDIS disturbance and succession model to study the effects of six alternative vegetation management scenarios on forest succession and the subsequent risk of canopy fire on a 2791 km² landscape in northern Wisconsin, USA. The study area is a mix of fire-prone and fire-resistant land types. The alternatives vary the spatial distribution of vegetation management activities to meet objectives primarily related to forest composition and recreation. The model simulates the spatial dynamics of differential reproduction, dispersal, and succession patterns using the vital attributes of species as they are influenced by the abiotic environment and disturbance. We simulated 50 replicates of each management alternative and recorded the presence of species age cohorts capable of sustaining canopy fire and the occurrence of fire over 250 years. We combined these maps of fuel and fire to map the probability of canopy fires across replicates for each alternative. Canopy fire probability varied considerably by land type. There was also a subtle, but significant effect of management alternative, and there was a significant interaction between land type and management alternative. The species associated with high-risk fuels (conifers) tend to be favored by management alternatives with more disturbances, whereas low disturbance levels favor low-risk northern hardwood systems dominated by sugar maple. The effect of management alternative on fire risk to individual human communities was not consistent across the landscape. Our results highlight the value of the LANDIS model for identifying specific locations where interacting factors of land type and management strategy increase fire risk.This revised version was published online in May 2005 with corrections to the Cover Date.     

Comparison of establishment methods for extensive green roofs in southern Sweden

The most common technique for establishment of thin extensive green roofs in Sweden has been using prefabricated vegetation mats. Our study investigated (1) how the establishment of green roofs in Sweden was influenced by the establishment method (prefabricated vegetation mat, plug-plant, shoot), substrate composition and species mixture, and (2) whether on-site construction was a possible alternative. The establishment of the vegetation, which in all cases consisted of succulent species, was recorded using the quadrate point intercept method in fixed plots and the success measured as frequency cover.Prefabricated vegetation mats had higher succulent plant cover than on-site constructed roofs. There was no difference in succulent plant cover between plots established using plug-plants compared to shoots. Shoot-established plots had more moss than the other establishment methods. The commercial substrate ‘Roof soil’ had significantly higher succulent plant cover than the other substrates, which might be related to a higher nutrient content. The organic content of the non-commercial substrates was rapidly decomposed. The standard species mixture produced a higher cover than both the mix developed for northern conditions and the mix with an increased proportion of big leaved species. The total cover of the plots was mainly dependent on the cover of two species: Sedum album (L.) and Sedum acre (L.). Few species managed to establish spontaneously but the establishment of woody species highlighted the need for proper maintenance.     

The re-emergence of indigenous forest in an urban environment, Christchurch, New Zealand

Christchurch, the second largest city in New Zealand is a planned city on a coastal plain on the east coast of the South Island. The birth of the city and the subsequent century of development was characterised by colonial values and tree and garden planting with familiar European species along with those from Australia, North America, and eventually all other continents. The image of an “English garden city” with classical parks of oaks and willow-lined rivers became the accepted norm and the way in which the city has been promoted to potential tourists. Gardening is one of the top two recreational activities and exotic species greatly outnumber native species in the flora and in gardens. This has had serious consequences for the highly fragmented and degraded indigenous vegetation and its co-adapted wildlife. A few hardy indigenous species continued to regenerate through this period, but since the 1970s, there has been a progressive change of attitude and interest in reclaiming the natural heritage of the city, manifest in widespread private and public planting of indigenous species and active habitat restoration. In this article we examine the indigenous and exotic shrub and tree components of the Christchurch flora as planted street trees, in domestic gardens, and in parks. We also present data on shrub and tree regeneration in parks and domestic gardens in the city. Indications are that the more sensitive, less intrusive management of urban environments, combined with the greater density of indigenous seed sources, has allowed regeneration of a wide range of indigenous species across a broad spectrum of habitats – from neglected gardens to pavement cracks to exotic plantations. This is despite the competition from the prodigious seed banks and density of exotic trees, shrubs, and ground covers and albeit minimal impacts of introduced browsing and seed eating mammals. If the present trends continue through appropriate management and facilitation, these tentative signs of native forest regeneration should eventually proliferate into a sustainable mixed origin urban forest that resurrects and preserves the natural character of the region.     

Multi-scale factors and long-term responses of Chihuahuan Desert grasses to drought

Factors with variation at broad (e.g., climate) and fine scales (e.g., soil texture) that influence local processes at the plant scale (e.g., competition) have often been used to infer controls on spatial patterns and temporal trends in vegetation. However, these factors can be insufficient to explain spatial and temporal variation in grass cover for arid and semiarid grasslands during an extreme drought that promotes woody plant encroachment. Transport of materials among patches may also be important to this variation. We used long-term cover data (1915–2001) combined with recently collected field data and spatial databases from a site in the northern Chihuahuan Desert to assess temporal trends in cover and the relative importance of factors at three scales (plant, patch, landscape unit) in explaining spatial variation in grass cover. We examined cover of five important grass species from two topographic positions before, during, and after the extreme drought of the 1950s. Our results show that dynamics before, during, and after the drought varied by species rather than by topographic position. Different factors were related to cover of each species in each time period. Factors at the landscape unit scale (rainfall, stocking rate) were related to grass cover in the pre- and post-drought periods whereas only the plant-scale factor of soil texture was significantly related to cover of two upland species during the drought. Patch-scale factors associated with the redistribution of water (microtopography) were important for different species in the pre- and post-drought period. Another patch-scale factor, distance from historic shrub populations, was important to the persistence of the dominant grass in uplands (Bouteloua eriopoda) through time. Our results suggest the importance of local processes during the drought, and transport processes before and after the drought with different relationships for different species. Disentangling the relative importance of factors at different spatial scales to spatial patterns and long-term trends in grass cover can provide new insights into the key processes driving these historic patterns, and can be used to improve forecasts of vegetation change in arid and semiarid areas.     

Linking wind erosion to ecosystem services in drylands: a landscape ecological approach

Context

Wind erosion is a widespread environmental problem in the world’s arid landscapes, which threatens the sustainability of ecosystem services in these regions.

Objectives

We investigated how wind erosion and key ecosystem services changed concurrently and what major biophysical and socioeconomic factors were responsible for these changes in a dryland area of China.

Methods

Based on remote sensing data, field measurements, and modeling, we quantified the spatiotemporal patterns of both wind erosion and four key ecosystem services (soil conservation, crop production, meat production, and carbon storage) in the Mu Us Sandy Land in northern China during 2000–2013. Linear regression was used to explore possible relationships between wind erosion and ecosystem services.

Results

From 2000 to 2013, wind erosion decreased by as much as 60% and the four ecosystem services all increased substantially. These trends were attributable to vegetation recovery due mainly to government-aided ecological restoration projects and, to a lesser degree, slightly increasing precipitation and decreasing wind speed during the second half of the study period. The maximum soil loss dropped an order of magnitude when vegetation cover increased from 10% to 30%, halved again when vegetation increased from 30 to 40%, and showed little change when vegetation increased beyond 60%.

Conclusions

Our study indicates that vegetation cover has nonlinear and threshold effects on wind erosion through constraining the maximum soil loss, which further affects dryland ecosystem services. These findings have important implications for ecological restoration and ecosystem management in dryland landscapes in China and beyond.

     

Context-dependent vegetation dynamics in an African savanna

Understanding the spatio-temporal dynamics of ecological systems is fundamental to their successful management and conservation. Much research and debate has focused on identifying underlying drivers of vegetation change in savannas, yet few have considered the influence of spatial context and heterogeneity. Our goal was to develop deeper understanding of woody vegetation spatio-temporal dynamics through spatially explicit utilization of historical aerial photography and airborne LiDAR (light detection and ranging). We first assessed temporal change in woody vegetation cover through object-based image analysis of an aerial photography record that spanned 59 years from 1942 to 2001. Secondly, we tested the spatial relationships between environmental variables and patterns of woody structure and dynamics at broad (100 ha), medium (10 ha) and fine-scales (1 ha) through canonical correspondence analysis (CCA). Finally, we used LiDAR derived vegetation heights to explore current woody vegetation structure in the context of historical patterns of change. Total percentage woody cover was stable over time, but woody dynamics were highly variable at smaller scales and displayed distinct spatial trends across the landscape. Losses of woody cover on the diverse alluvial substrates were countered by increases of cover on the hillslopes. Analysis of current woody structure in the context of historical change revealed that the increases took place in the form of shrub encroachment and not the replacement of tall trees. We infer that mammalian herbivory contributed substantially to the losses on lowland alluvial soils, whilst shrub encroachment on the upland hillslopes likely stemmed from changes in fire regime and climate. Deeper reflection on spatial variability is needed in the debate around drivers of change in savanna systems, as spatial patterns of change revealed that different drivers underlie vegetation dynamics in different landscape contexts. Spatial heterogeneity needs explicit consideration in the exploration of pattern–process relationships in ecological systems.     

Carbon storage in a peri-urban neotropical forest: Assessing its potential and patterns of change over half a century

Forest ecosystems are associated with environmental regulation services, such as carbon storage, which is an outstanding service. Carbon fluxes in cities are difficult to estimate due to the scale at which they are addressed, particularly at the local level. In this work, we were interested in determining the carbon stored in the aboveground biomass of the tropical montane cloud forest tree species located on the western periphery of the city of Xalapa, Veracruz, Mexico. With these data, we interpolated the storage and sequestration over five decades through image satellites and aerial photography of this unique forest. Additionally, to assess this potential as a basis for a biodiversity contribution to city resilience, we conducted phytosociological sampling. Native species such as Quercus xalapensis, Liquidambar styraciflua var. mexicana and Q. lancifolia showed the most significant values of 72.92, 58.79, and 49.14 Mg ha⁻¹, respectively, of carbon. We used phytosociological sampling to better understand structural and functional features of urban forest biodiversity that can contribute to management practices for adaptation to climate change. In addition, the native species currently studied offer an opportunity for the city to implement better-targeted reforestation and ecological restoration programs for integrated landscaping in urban planning. Our results suggest that between 1966 and 2022, there was a forest recovery of 52.4 ha and an increase in urban areas of 63.4 ha, which is equivalent to an increase from 7,700.86 Mg ha⁻¹ in 1966 to 12,620.00 Mg ha⁻¹ in 2022. In this context, it is possible to both recover the vegetation cover and expand the city, thus avoiding part of the loss of ecosystem services that urbanization usually implies. This should be promoted among decision-makers and citizens in urban planning. Recovery processes can take place successfully in some cases even as urban areas expand. This possibility is relevant due to the many contributions that vegetation provides to citizens, including carbon storage. The opportunity to study five decades allows us to know the history, monitor the processes and make a projection to conserve the vegetation and improve management.     

Successful creation of species-rich grassland on road verges depend on various methods for seed transfer

This study focused on a suite of vascular plant species (six herbs and two grasses) common to traditionally managed, species-rich grasslands in Western Norway. We assessed the suitability of two species transfer methods (seed sowing and soil seed bank) for restoration of species-rich grassland on a newly established road verge. We compared the species' frequencies one and three years after they were sown on a naked, newly created road verge with their frequencies in aboveground vegetation and soil seed banks of comparable, local grasslands. Species frequencies in the aboveground vegetation differed significantly from those in the seed banks. Moreover, the frequencies in the seed banks differed from those recorded one year after sowing, and the frequencies in the aboveground vegetation differed from those recorded three years after sowing. Avenula pubescens and Knautia arvensis, found in more than 25% of the aboveground grassland plots, did not germinate from any of the seed bank samples. Festuca rubra, Galium verum, Pimpinella saxifraga and Silene vulgaris were more frequent in the aboveground plots than in the seed bank samples. Pimpinella saxifraga, Galium verum and Lychnis viscaria emerged quite well both from sown seeds and from the seed bank. Avenula pubescens was frequent in the aboveground vegetation, but did not germinate from sown seeds. Six species established well from seeds, and most increased in frequency in the sown plots from the first to the third year. No species was found in the sown plots only, but three years after sowing, three species were more frequent in the sown plots than in the aboveground vegetation of donor grassland plots. Our fine-scale, point-to-point study demonstrates that different restoration methods produce widely differing species composition even when the donor material is identical. We propose that different substrates and a combination of establishment methods (sowing and hay transfer) are needed as supplements to seed banks to re-establish species-rich grassland.     

Ecosystem-scale spatial heterogeneity of stable isotopes of soil nitrogen in African savannas

Soil ¹⁵N is a natural tracer of nitrogen (N) cycling. Its spatial distribution is a good indicator of processes that are critical to N cycling and of their controlling factors integrated both in time and space. The spatial distribution of soil δ¹⁵N and its underlying drivers at sub-kilometer scales are rarely investigated. This study utilizes two sites (dry vs. wet) from a megatransect in southern Africa encompassing locations with similar soil substrate but different rainfall and vegetation, to explore the effects of soil moisture and vegetation distribution on ecosystem-scale patterns of soil δ¹⁵N. A 300-m long transect was set up at each site and surface soil samples were randomly collected for analyses of δ¹⁵N, %N and nitrate content. At each soil sampling location the presence of grasses, woody plants, Acacia species (potential N fixer) as well as soil moisture levels were recorded. A spatial pattern of soil δ¹⁵N existed at the dry site, but not at the wet site. Woody cover distribution determined the soil δ¹⁵N spatial pattern at ecosystem-scale; however, the two Acacia species did not contribute to the spatial pattern of soil δ¹⁵N. Grass cover was negatively correlated with soil δ¹⁵N at both sites owing to the lower foliar δ¹⁵N values of grasses. Soil moisture did not play a role in the spatial pattern of soil δ¹⁵N at either site. These results suggest that vegetation distribution, directly, and water availability, indirectly, affect the spatial patterns of soil δ¹⁵N through their effects on woody plant and grass distributions.     

Non-linear effects of landscape properties on mistletoe parasitism in fragmented agricultural landscapes

Ecological processes such as plant–animal interactions have a critical role in shaping the structure and function of ecosystems, but little is known of how such processes are modified by changes in landscape structure. We investigated the effect of landscape change on mistletoe parasitism in fragmented agricultural environments by surveying mistletoes on eucalypt host trees in 24 landscapes, each 100 km² in size, in south-eastern Australia. Landscapes were selected to represent a gradient in extent (from 60% to 2% cover) and spatial pattern of remnant wooded vegetation. Mistletoes were surveyed at 15 sites in each landscape, stratified to sample five types of wooded elements in proportion to their relative cover. The incidence per landscape of box mistletoe (Amyema miquelii), the most common species, was best explained by the extent of wooded cover (non-linear relationship) and mean annual rainfall. Higher incidence occurred in landscapes with intermediate levels of cover (15–30%) and higher rainfall (>500 mm). Importantly, a marked non-linear decline in the incidence of A. miquelii in low-cover landscapes implies a disproportionate loss of this species in remaining wooded vegetation, greater than that attributable to decreasing forest cover. The most likely mechanism is the effect of landscape change on the mistletoebird (Dicaeum hirundinaceum), the primary seed-dispersal vector for A. miquelii. Our results are consistent with observations that habitat fragmentation initially enhances mistletoe occurrence in agricultural environments; but in this region, when wooded vegetation fell below a threshold of ~15% landscape cover, the incidence of A. miquelii declined precipitously. Conservation management will benefit from greater understanding of the components of landscape structure that most influence ecological processes, such as mistletoe parasitism and other plant–animal mutualisms, and the critical stages in such relationships. This will facilitate action before critical thresholds are crossed and cascading effects extend to other aspects of ecosystem function.     

Patterns in bat functional guilds across multiple urban centres in south-eastern Australia

Understanding the impacts of landscape change on species behaviour is a major challenge in landscape ecology. A focus on the functional traits of species may improve this understanding if species with similar traits (functional guilds) are impacted by landscape change in similar ways, but this idea has not been widely tested on bat communities in urban landscapes. We examined changes in bat species richness and the activity level of species in different functional guilds within 72 residential neighbourhoods across 18 towns and cities spanning over 250,000 square km in south-eastern Australia. Species richness increased close to native vegetation, declined with increasing urbanization, and had a hump-shaped relationship with neighbourhood vegetation cover. Also, the activity level of all bat species combined peaked at mid-range values of neighbourhood vegetation cover. The activity of species in the open-adapted guild was not strongly related to any urban characteristic, but our results concur with previous findings that the activity of most open-adapted species does not appear to be negatively impacted by urbanization. Conversely, clutter-adapted species appear more sensitive to urbanization and their activity level was negatively related to urban intensity and increased closer to native vegetation, consistent with previous studies. The functional-trait approach may improve the capacity to make generalisations across different landscape contexts for clutter-adapted and open-adapted guilds, but is currently hampered for other bat species owing to variation in the behaviour of different species assigned to the same functional guild, and a lack of ecological knowledge regarding the impacts of different types of landscape change on particular species.     

Increased home size and hardscape decreases urban forest cover in Los Angeles County’s single-family residential neighborhoods

Single-family residential neighborhoods make up large areas within cities and are undergoing change as residences are renovated and redeveloped. We investigated the effects of such residential redevelopment on land cover (trees/shrubs, grass, building, and hardscape) in the 20 largest cities in the Los Angeles Basin from 2000 to 2009. We identified spatially stratified samples of single-family home lots for which additional square footage was recorded and for which additional construction was not recorded by the tax assessor. We then digitized land cover on high-resolution color imagery for two points in time to measure land cover change. Redevelopment of single-family homes in Los Angeles County resulted in a significant decrease in tree/shrub and grass cover and a significant increase in building and hardscape area. Over 10 years, urban green cover (trees/shrubs and grass) declined 14–55% of green cover in 2000 on lots with additional recorded development and 2–22% of green cover in 2000 for single-family lots for which new permits were not recorded. Extrapolating the results to all single-family home lots in these cities indicate a 1.2 percentage point annual decrease in tree/shrub cover (5.6% of existing tree/shrub cover) and a 0.1 percentage point annual decrease in grass cover (2.3% of existing grass cover). The results suggest that protection of existing green cover in neighborhoods is necessary to meet urban forest goals, a factor that is overlooked in existing programs that focus solely on tree planting. Also, changing social views on the preferred size of single-family homes is driving loss of tree cover and increasing impervious surfaces, with potentially significant ramifications for the functioning of urban ecosystems.     

Reconstructing the collapse of wetland networks in the Swiss lowlands 1850–2000

In Central Europe vast wetland areas have been converted into agricultural land over the past few centuries. Long-term spatially explicit reconstructions of wetland cover changes at regional scale are rare but such information is vital for setting appropriate wetland conservation and restoration goals. In this study wetland cover change over the past 150 years was analyzed for the Canton Zurich (Switzerland) using information from historical and current topographical maps. Mapping instructions changed significantly over time, i.e., wetlands were mapped more conservatively on older maps. Therefore a technique was developed to account for changes in mapping instructions and to reconstruct a series of comparable maps spanning 1850–2000. Wetland cover dramatically decreased from 13,759 ha in 1850 (more than 8% of the total study area) to 1,233 ha in 2000 (less than 1%). Largest loss is observed for the first half of the twentieth century when more than 50% of the total wetland loss occurred. In 1850, almost all wetland patches were connected in two large networks defined by a 500 m buffer around all wetland patches to account for typical dispersal distances of wetland animals. Despite extensive wetland loss, this networks remained largely intact until 1950, but then collapsed into many medium and small networks consisting of only few wetland patches. In addition to the direct loss of wetland habitats increased habitat fragmentation is limiting metapopulation dynamics and hindering genetic exchange between populations. Amphibians and other wetland animals are particularly prone to habitat fragmentation because of their limited migration abilities. This may lead to time-delayed extinction in the future because current species occurrence might rather reflect historical than current wetland cover and habitat configuration. Future restoration efforts should focus on reestablishing connectivity between remaining smaller wetland networks.