A multi-region assessment of tropical forest biodiversity in a human-modified world

The fate of much of the world’s terrestrial biodiversity is linked to the management of human-modified forest landscapes in the humid tropics. This Special Issue presents the first pan-tropical synthesis of research on the prospects for biodiversity in such systems, with eight individual regional summaries covering Mesoamerica, Amazonia, Atlantic forest of South America, West Africa, Madagascar, Western Ghats, Southeast Asia and Oceania. Two additional papers compare the state of conservation science in tropical forests with both temperate forests and savannah systems. This overview paper provides a comparative analysis of the threats and opportunities facing tropical forest biodiversity, thereby helping to identify the most pressing areas of future research and region-specific factors that contribute towards the effectiveness of individual conservation initiatives. While many of the threats facing tropical forest biodiversity are commonplace they vary markedly in their relative importance across different regions. There is a critical lack of comparable data to understand scale dependent processes, or the relative importance of varying geographic and historical contexts in determining present-day patterns. Conservation science has a key role to play in safeguarding the future of tropical forest biodiversity, but needs to become more effectively embedded in the context of real-world conservation challenges and opportunities. Significant progress can be achieved by improving the cost-effectiveness of research as well as the exchange of ideas and data amongst scientists working in different, often isolated parts of the world. We hope this special issue goes some way top achieving this exchange of knowledge.     

Old cultural traditions, in addition to land use and topography, are shaping plant diversity of grasslands in the Alps

Socio-economically motivated land use changes are a major threat for species diversity of grasslands throughout the world. Here, we comprehensively explore how plant species diversity of grasslands in the species-rich cultural landscape of the Swiss Alps depends on recent land use changes, and, neglected in previous studies, on old cultural traditions. We studied diversity in 216 grassland parcels at three altitudinal levels in 12 villages of three cultural traditions (Romanic, Germanic, and Walser). In valleys of Romanic villages more different parcel types tended to occur than in those of Germanic and Walser villages, suggesting that socio-economic differences among cultural traditions still play a role in shaping landscape diversity. Moreover, at the village level, higher man-made landscape diversity was associated with higher plant species richness. All observed changes in land use reduced the farmers’ workload. Plant species richness was lower in fertilized than in unfertilized parcels and in abandoned compared with used parcels. Grazing slightly reduced species richness compared with mowing among unfertilized parcels, while in fertilized parcels it had a positive influence. The highest species diversity was found in mown unfertilized subalpine grasslands. Nevertheless, moderate grazing of former meadows can be a valuable alternative to abandonment. We conclude that the ongoing changes in land use reduce plant species richness within parcels and at the landscape level. To preserve plant species diversity at the landscape level a high diversity of land use types has to be maintained.     

Habitat management and patterns of predation of Northern Lapwings on wet grasslands: The influence of linear habitat structures at different spatial scales

In managed landscapes, habitat structure is frequently manipulated through the creation of features such as tracks, hedges, and waterways. If predator and prey activity are concentrated around these features, levels of predation may be elevated in these landscapes. This issue is of particular importance when habitat structures are used to attract species of conservation concern. For example, the installation of linear waterways in wet grasslands is a common form of habitat management to benefit breeding waders and wader nests and foraging chicks tend to be aggregated around wet features. If predator activity is also focused around these features, and if their linearity increases the probability of prey being located, then the conservation benefits of this management technique may be eliminated. We explore predator movement in relation to the structure and complexity of linear wet features within a lowland wet grassland landscape. We examine patterns of nest and chick predation in lapwing (Vanellus vanellus) at the whole-site, between-field and within-field scales. Mammalian predators were responsible for the majority of nest predation. However, we found no evidence that mammalian predators used linear wet features disproportionately within the landscape, or that wet feature distribution influenced the probability of nest or chick predation. At the whole-site scale, nest predation rates were significantly higher in areas with greater predator presence and lowest where the number of breeding neighbours was high. Thus, predation levels were influenced by large-scale patterns of predator presence and lapwing density but not by the use of linear wet features as a habitat management tool. Managing predator impacts is therefore likely to require empirical assessments of local predator distribution and abundance in order to target measures effectively.     

The cost of postponing biodiversity conservation in Mexico

Though Neotropical countries are the most species rich in the world, their biodiversity is threatened by the loss of native vegetation. Land conversion in Mexico during the last 30 years has been extensive and is representative of that of other developing countries. However, the effects of land use change on the required size and configuration of an adequate biological conservation area network are largely unknown. It is shown here that endemic mammals in Mexico could have been protected considerably more economically if a conservation plan had been implemented in 1970 than is possible today due to extensive conversion of primary habitats. Analysis of the distributions of 86 endemic mammal species in 1970, 1976, 1993, and 2000 indicates that the distributions of 90% of the species shrank during this 30-year period. At each time step, optimal conservation area networks were selected to represent all species. 90% more land must be protected after 2000 to protect adequate mammal habitat than would have been required in 1970. In addition, under a realistic conservation budget, 79% fewer species can be represented adequately in a conservation area network after 2000 compared to 1970. This provides an incentive for rapid conservation action in Mexico and other biodiversity hotspots with comparable deforestation rates, including Burma, Ecuador, Indonesia, the Philippines, and Sri Lanka. Due to ongoing habitat degradation, the efficiency of a conservation plan decreases with delays in its implementation.     

Plant species richness and composition in managed grasslands: The relative importance of field management and environmental factors

Decline of grassland diversity throughout Europe within the last decades is threatening biological diversity and is a major conservation problem. There is an urgent need to determine the underlying factors that control vascular plant species richness and composition in managed grasslands. In this study, 117 grasslands were sampled using standardised methods. Explanatory variables were recorded for each grassland site, reflecting the local field management, site-specific environmental conditions and large-scale spatial trends. Using variation partitioning methods, we determined the pure and shared effects of these three sets of explanatory variables on the plant species richness and composition in grasslands. Most of the explained variation in plant species richness was related to the joint effect of local field management and environmental variables. However, the applied variation partitioning approach revealed that the pure effect of spatial variables contributed relatively little to explaining variation in both the plant species richness and species composition. The largest fractions of explained variation in plant species composition were accounted for by the pure effects of environmental and local field management variables. Moreover, the results revealed that the main mechanisms by which these sets of explanatory variables affect plant species vary according to the type of management regime under study. From our findings we could conclude that particularly a reduction of nitrogen fertilisation on meadows and grazing at a low stocking rate on pastures can help to conserve biodiversity.     

Regional climate change adaptation strategies for biodiversity conservation in a midcontinental region of North America

Scenario planning should be an effective tool for developing responses to climate change but will depend on ecological assessments of broad enough scope to support decision-making. Using climate projections from an ensemble of 16 models, we conducted an assessment of a midcontinental area of North America (Minnesota) based on a resistance, resilience, and facilitation framework. We assessed likely impacts and proposed options for eight landscape regions within the planning area. Climate change projections suggest that by 2069, average annual temperatures will increase 3 °C with a slight increase in precipitation (6%). Analogous climate locales currently prevail 400–500 km SSW. Although the effects of climate change may be resisted through intensive management of invasive species, herbivores, and disturbance regimes, conservation practices need to shift to facilitation and resilience. Key resilience actions include providing buffers for small reserves, expanding reserves that lack adequate environmental heterogeneity, prioritizing protection of likely climate refuges, and managing forests for multi-species and multi-aged stands. Modifying restoration practices to rely on seeding (not plants), enlarge seed zones, and include common species from nearby southerly or drier locales is a logical low-risk facilitation strategy. Monitoring “trailing edge” populations of rare species should be a high conservation priority to support decision-making related to assisted colonization. Ecological assessments that consider resistance, resilience, and facilitation actions during scenario planning is a productive first step towards effective climate change planning for biodiversity with broad applicability to many regions of the world.     

Effect of different sampling schemes on the spatial placement of conservation reserves in Utah, USA

We evaluated the effect of three different sampling schemes used to organize spatially explicit biological information had on the spatial placement of conservation reserves in Utah, USA. The three sampling schemes consisted of a hexagon representation developed by the EPA/EMAP program (statistical basis), watershed boundaries (ecological), and the current county boundaries of Utah (socio-political). Four decision criteria were used to estimate effects, including amount of area, length of edge, lowest number of contiguous reserves, and greatest number of terrestrial vertebrate species covered. A fifth evaluation criterion was the effect each sampling scheme had on the ability of the modeled conservation reserves to cover the six major ecoregions found in Utah. Of the three sampling schemes, county boundaries covered the greatest number of species, but also created the longest length of edge and greatest number of reserves. Watersheds maximized species coverage using the least amount of area. Hexagons and watersheds provide the least amount of edge and fewest number of reserves. Although there were differences in area, edge and number of reserves among the sampling schemes, all three schemes covered all the major ecoregions in Utah and their inclusive biodiversity.     

Spatial patterns of grasses influence soil macrofauna biodiversity in Amazonian pastures

Grasslands are often characterized by small-scale spatial heterogeneity due to the juxtaposition of grass tufts and bare ground. Although the mechanisms generating plant spatial patterns have been widely studied, few studies concentrated on the consequences of these patterns on belowground macrofauna. Our objective was to analyze the impact of grass tuft (Brachiaria bryzantha cv. marandu) spatial distribution on soil macrofauna diversity in Amazonian pastures, at a small scale (less than 9 m²). Soil macrofauna was sampled among B. bryzantha tufts, which showed a variable spatial distribution ranging from dense to loose vegetation cover. The vegetation configuration explained 69% of the variation in total soil macrofauna density and 68% of the variation in total species richness. Soil macrofauna was mainly found in the upper 10 cm of soil and biodiversity decreased with increasing distances to the nearest grass tuft and increased with increasing vegetation cover. The size of the largest grass tuft and the micro-landscape connectivity also had a significant effect on biodiversity. The density and species richness of the three principal soil ecological engineers (earthworms, ants and termites) showed the best correlations with vegetation configuration. In addition, soil temperature significantly decreased near the plants, while soil water content was not influenced by the grass tufts. We conclude that soil macrofauna diversity is low in pastures except close to the grass tufts, which can thus be considered as biodiversity hotspots. The spatial arrangement of B. bryzantha tussocks influences soil macrofauna biodiversity by modifying soil properties in their vicinity. The possible mechanisms by which these plants could affect soil macrofauna are discussed.     

Indicator species and the problem of spatial inconsistency in nestedness patterns

The potential as indicators of species richness were investigated for 178 species belonging to six ecologically defined species groups (epiphytic bryophytes on nutrient-rich bark, epiphytic macrolichens on nutrient rich bark, pendant lichens on conifer trees, bryophytes on siliceous rocks, bryophytes on dead conifer wood, and polypore fungi on dead conifer wood), using species data from 0.25 ha plots from three different coniferous forest areas (ca. 200 ha each). A species was defined as a potential indicator species for a species group within a study area if its distribution was statistically significantly nested within the species-plot matrix ranked according to species richness, and if the plot frequency of the species was less than 25%.Only two species were identified as potential indicators within all three areas and on average ≈80% of the potential indicator species were lost from one area to another. The results indicate that inconsistency between areas in the species’ frequency distributions and their position in nested hierarchies may strongly reduce the general predictive power of indicator species of species richness, even if significantly nested patterns are found at the community level. We suggest that indicators related to amount and quality of habitats may be an alternative to lists of indicator species of species richness.     

Amphibian distribution in a traditionally managed rural landscape of Eastern Europe: Probing the effect of landscape composition

A massive decline of biodiversity is caused by land-use changes. Efforts must therefore be made to better understand the factors that govern organismal distribution, especially for countries where traditional management is about to be intensified such as in Romania. We here document the spatial distribution of amphibians from a Romanian rural landscape where land-use is still largely traditional. We related the occurrence of nine amphibian species and species richness to measures of composition and configuration of the landscape surrounding 54 ponds at three spatial scales: circular areas of 400, 600 and 800 m radii. Busy roads most severely impacted single species and amphibian richness whereas landscape composition measures, such as cover of urban areas, agricultural areas, pastures, forests and wetlands were of little importance. We suggest that the relative unimportance of landscape compositional measures on amphibians is a consequence of the traditional management of these landscapes that keep the environmental conditions favorable for most species.     

Nested spatial biodiversity patterns of nematode genera in a New Zealand forest and pasture soil

Biodiversity has a spatial dimension, which we estimated by examining generic turnover (beta diversity) of nematodes in adjacent forest and pasture sites. Dissimilarity was estimated in small and intermediate scale transects, the distribution of sampling points being determined by spatial simulated annealing. On an average, the forest yielded fewer nematodes per 24 mm dia 0-10 cm deep core than did pasture (435 vs 2818) but more genera (23.7 vs 19.1). Dissimilarity analysis suggests generic turnover is higher in forest than pasture, at both scales. At the small scale both communities have comparable dissimilarities up to 0.6 m, but only in forest does increasing distance increase dissimilarity. At the intermediate scale no spatial structure was apparent in the pasture nematode community, but in forest dissimilarity increased with distance, with no plateau. Quantifying the difference in spatial patterns between ecosystems illustrates the utility of geostatistical methods for addressing soil biodiversity.     

Factors contributing to temporal stability in spatial patterns of water content in the tillage zone

The rates of many biological processes vary across an agricultural landscape in response to the spatial patterns of water content in the tillage zone. Although, water content varies temporally through the growing season, the combined effects of soil properties, landscape attributes, tillage or position relative to the crop row on the temporal variation in the spatial pattern in soil water content are not well understood. We measured the soil water content (0–0.20 m) regularly through three growing seasons at 32 positions along each of two transects in a side-by-side comparison of corn under conventional tillage (plowing and secondary tillage) and no till in order to identify factors with the strongest influence on the spatial patterns in water content. The tillage comparison traversed a landscape in which the clay content (cl) varied from 5.8 to 37.4% and the organic carbon content (OC) varied from 0.9 to 3.9%. The spatial pattern in water contents during wetting and drying events were temporally stable, as reflected in R²>0.7 of correlation analysis of water contents on successive measurement dates. Multiple regression analyses indicated that the water contents, averaged over all measurement dates, were positively correlated with cl and ln(OC) and were smaller in the row than the inter-row position. The reduction in water content due to conventional tillage was diminished with increasing OC. However, application of multiple regression analyses to each set of water contents measured on a given day for each year indicated that the impact of soil properties, tillage and position relative to the row varied within and among seasons.     

Stand-scale spatial patterns of soil microbial biomass in natural cold-temperate beech forests along an elevation gradient

This study focuses on spatial heterogeneity in the soil microbial biomass (SMB) of typical climax beech (Fagus crenata) at the stand scale in forest ecosystems of the cold-temperate mountain zones of Japan. Three beech-dominated sites were selected along an altitudinal gradient and grid sampling was used to collect soil samples at each site. The highest average SMB density was observed at the site 1500 m a.s.l. (44.9 gC m⁻²), the lowest was recorded at the site 700 m a.s.l. (18.9 gC m⁻²); the average SMB density at the 550 m site (36.5 gC m⁻²) was close to the overall median of all three sites. Geostatistics, which is specifically designed to take spatial autocorrelation into account, was then used to analyze the data collected. All sites generally exhibited stand-scale spatial autocorrelation at a lag distance of 10-18 m in addition to the small-scale spatial dependence noted at <3.5 m at the 550 m site. Correlation analysis with an emphasis on spatial dependency showed SMB to be significantly correlated with bulk density at the 550 and 1500 m sites, dissolved organic carbon (DOC) at the 700 and 1500 m sites, and nitrogen (N) at the 550 and 700 m sites. However, no soil parameter showed a significant correlation with SMB at every site, and some variables were also differently correlated (negative or positive) with SMB at different sites. This suggests that the factors controlling the spatial distribution of SMB are very complex and responsive to local in situ conditions. SMB regression models were generated from both the ordinary least-squares (OLS) and generalized least-squares (GLS) models. GLS performance was only superior to OLS when cross-variograms were accurately fitted. Geostatistics is preferable, however, since these techniques take the spatial non-stationarity of samples into account. In addition, the sampling numbers for given minimum detectable differences (MDD_s) are provided for each site for future SMB monitoring.     

Influence of single trees on spatial and temporal patterns of belowground properties in native pine forest

Linkages between forest dynamics and ecosystem processes are poorly understood and this limits our ability to adequately estimate future changes in forest ecosystems due to human-induced global change. In particular at the single tree level, our understanding of temporal and spatial changes of belowground properties during forest succession is limited. Thus, our aim was to test whether we find a spatial and temporal gradient in nutrient availability and an associated shift in microbial community structure with increasing distance and age of single trees. We found that inorganic nitrogen was less available below the crown of single trees, while soluble organic carbon (DOC) was much more abundant, in particular in the inner zone of influence, i.e. close to the stem. The fungal:bacterial PLFA ratio was greater while microbial biomass carbon (MicC) was lower below the tree crown, indicating a strong influence of trees on spatial patterns of microbial biomass and community structure. Moreover, the positive correlation between MicC and total extractable N, and the negative correlation between fungal:bacterial biomass and δ¹⁵N, suggested that the microbial biomass was N limited below the tree crown and as a consequence nutrient cycling was presumably decelerated compared to open conditions. We also found a temporal pattern of increasing surface soil C and N content with increasing tree age (up to 250 years), underlining the significant role of single trees in creating spatial and temporal heterogeneity in forests.     

Evaluation of the spatial pattern of surface soil water content of a karst hillslope in Southwest China using a state-space approach

This study aims to evaluate the effects of soil physicochemical properties and environmental factors on the spatial patterns of surface soil water content (SWC) based on the state-space approach and linear regression analysis. For this purpose, based on a grid sampling scheme (10 m × 10 m) applied to a 90 m × 120 m plot located on a karst hillslope of Southwest China, the SWC at 0–16 cm depth was measured 3 times across 130 sampling points, and soil texture, bulk density (BD), saturated hydraulic conductivity (K_s), organic carbon (SOC), and rock fragment content as well as site elevation (SE) were also measured at these locations. Results showed that the distribution pattern of SWC could be more successfully predicted by the first-order state-space models (R² = 67.5–99.9% and RMSE = 0.01–0.14) than the classic linear regression models (R² = 10.8–79.3% and RMSE = 0.11–0.24). The input combination containing silt content (Silt), K_s, and SOC produced the best state-space model, explaining 99.9% of the variation in SWC. And Silt was identified as the first-order controlling factor that explained 98.7% of the variation. In contrast, the best linear regression model using all of the variables only explained 79.3% of variation.     

基于地形因子和随机森林的丘陵区农田土壤有效铁空间分布预测

为了掌握丘陵地区农田土壤有效铁含量及其空间分布,本文以重庆市江津区永兴镇内同源成土母质的典型丘陵(2 km2)为研究区,采集309个土壤样点,利用普通克里格(Ordinary Kriging,OK)、多元线性回归(Multiple Linear Regression,MLR)、随机森林(Random Forest,RF)模型,结合高程、坡度、坡向、谷深、平面曲率、剖面曲率、汇聚指数、相对坡位指数、地形湿度指数等地形因子对土壤有效铁进行空间分布预测,并通过85个验证点评价、筛选预测模型。结果表明:1)土壤有效铁与谷深、地形湿度指数存在极显著水平正相关关系,与坡度、平面曲率、剖面曲率、汇聚指数、相对坡位指数存在极显著水平负相关关系。2)随机森林模型的预测精度明显高于多元线性回归和普通克里格插值,其平均绝对误差为22.33 mg·kg-1、均方根误差为27.98 mg·kg-1、决定系数为0.76,是研究区土壤有效铁含量空间分布的最适预测模型。3)地形湿度指数和坡度是影响该区域土壤有效铁含量空间分布的主要地形因子。土壤有效铁与坡度、谷深、平面曲率、剖面曲率、汇聚指数、相对坡位指数、地形湿度指数均达到极显著水平相关关系。4)研究区土壤有效铁含量范围为3.00~276.97 mg?kg-1,水田有效铁含量大于旱地;土壤有效铁具有较强的空间相关性,土壤有效铁含量空间变异主要受到结构性因素的影响。可见,基于地形因子的随机森林预测模型可以较好地解释丘陵区农田土壤有效铁含量的空间变异,研究结果为丘陵区土壤中、微量元素含量及空间分布预测提供方法借鉴和理论依据。     

Partitioning of molecular variation at local spatial scales in the vulnerable neotropical freshwater turtle, Hydromedusa maximiliani (Testudines, Chelidae): implications for the conservation of aquatic organisms in natural hierarchical systems

Hydromedusa maximiliani is a vulnerable freshwater turtle endemic to mountainous regions of the Atlantic rainforest in southeastern Brazil. Random amplified polymorphic DNA (RAPD) were surveyed with the purpose of assessing the genetic structure and determining the partitioning of molecular variation in H. maximiliani across the natural spatial hierarchical scale of its habitat. The goal of the study was to integrate ecological data with estimates of molecular genetics diversity to develop strategies for the conservation of this freshwater turtle. Specimens were sampled from rivers and streams across three drainages. Nine of the 80 primers used generated 27 scoreable bands of which 10 (37%) were polymorphic and produced 16 RAPD phenotypes. Significant heterogeneity was found in the distribution of RAPD molecular phenotypes across the three drainages. Analysis of molecular variance for molecular phenotypes showed that the heterogeneity had a spatial structure since a significant amount (22%) of the total variance was attributable to variation among rivers and streams. Since the genetic variation of this turtle seems to be structured according to the natural hierarchical system of rivers and streams within drainages, it is suggested that local populations should be considered as separate management units.     

基于地统计学和GIS的化学农药胁迫下桃树桃蚜与草间钻头蛛种群空间格局

化学农药过量施用不仅杀死了害虫和自然天敌,也影响天敌与害虫之间的空间关系。桃园生态系统中草间钻头蛛(Hylyphantes graminicola)是桃蚜(Myzus persicae)的重要捕食性天敌,本文系统调查了化学农药长期胁迫下不同时期(4月中旬至9月上旬)桃树桃蚜和草间钻头蛛种群数量,并运用地统计学方法和地理信息系统(GIS)分析了桃树桃蚜和草间钻头蛛种群的空间结构,并采用基于高斯模型、指数模型、球型模型和圆型模型的普通克立格插值法模拟了其种群空间分布格局。结果表明,桃蚜和草间钻头蛛种群在10次调查期间均呈随机分布格局;桃蚜和草间钻头蛛空间分布距离相关性较弱,其变动范围均为6.863 0~43.174 1 m;桃蚜和草间钻头蛛的空间结构比例分别为0.788 8~0.983 9和0.811 6~0.980 6,块金值分别为0.254 2~4.896 3和0.218 4~0.749 9,偏基台值分别为0.010 5~0.250 0和0.004 8~0.075 7。本研究结果显示,长期使用化学农药致使桃树桃蚜和草间钻头蛛种群的空间结构比例值均大于0.7500,这表明化学农药胁迫下桃蚜和草间钻头蛛种群之间的跟随效应不明显,草间钻头蛛对桃蚜的捕食作用不强。     

Investigating the spatial distribution of soil erosion and deposition in a small catchment on the Loess Plateau of China, using Cs

An understanding of the spatial distribution of soil erosion and deposition in a catchment is important for designing soil and water conservation measures. Traditional monitoring techniques provide limited information on the spatial patterns of erosion and deposition. The fallout radionuclide ¹³⁷Cs was used to document rates and patterns of soil redistribution within a small (0.17 km²) gully catchment located near An'sai in Shaanxi Province, representative of the Loess Plateau of China. The local reference inventory was estimated to be 2266 Bq m⁻² and the ¹³⁷Cs inventories of 198 soil cores collected from the catchment, ranged from 0 to 3849 Bq m⁻². The coefficient of variation of the inventories of the individual cores was 0.85, reflecting the complex pattern of ¹³⁷Cs redistribution by soil erosion and deposition. Estimates of erosion rates derived from ¹³⁷Cs measurement ranged from less than 25 to 150 Mg ha⁻¹ year⁻¹, with about 70% of the net soil loss from the catchment coming from the gully area. The ¹³⁷Cs technique was shown to provide an effective means of documenting the spatial distribution of soil erosion and deposition within the small catchment.