Keep wetlands wet: the myth of sustainable development of tropical peatlands – implications for policies and management

Pristine tropical peat swamp forests (PSFs) represent a unique wetland ecosystem of distinctive hydrology which support unique biodiversity and globally significant stores of soil carbon. Yet in Indonesia and Malaysia, home to 56% of the world's tropical peatland, they are subject to considerable developmental pressures, including widespread drainage to support agricultural needs. In this article, we review the ecology behind the functioning and ecosystem services provided by PSFs, with a particular focus on hydrological processes as well as the role of the forest itself in maintaining those services. Drawing on this, we review the suitability of current policy frameworks and consider the efficacy of their implementation. We suggest that policies in Malaysia and Indonesia are often based around the narrative of oil palm and other major monocrops as drivers of prosperity and development. However, we also argue that this narrative is also being supported by a priori claims concerning the possibility of sustainability of peat swamp exploitation via drainage‐based agriculture through the adherence to best management practices. We discuss how this limits their efficacy, uptake and the political will towards enforcement. Further, we consider how both narratives (prosperity and sustainability) clearly exclude important considerations concerning the ecosystem value of tropical PSFs which are dependent on their unimpacted hydrology. Current research clearly shows that the actual debate should be focused not on how to develop drainage‐based plantations sustainably, but on whether the sustainable conversion to drainage‐based systems is possible at all.     

A pantropical analysis of the impacts of forest degradation and conversion on local temperature

Temperature is a core component of a species' fundamental niche. At the fine scale over which most organisms experience climate (mm to ha), temperature depends upon the amount of radiation reaching the Earth's surface, which is principally governed by vegetation. Tropical regions have undergone widespread and extreme changes to vegetation, particularly through the degradation and conversion of rainforests. As most terrestrial biodiversity is in the tropics, and many of these species possess narrow thermal limits, it is important to identify local thermal impacts of rainforest degradation and conversion. We collected pantropical, site‐level (<1 ha) temperature data from the literature to quantify impacts of land‐use change on local temperatures, and to examine whether this relationship differed aboveground relative to belowground and between wet and dry seasons. We found that local temperature in our sample sites was higher than primary forest in all human‐impacted land‐use types (N = 113,894 daytime temperature measurements from 25 studies). Warming was pronounced following conversion of forest to agricultural land (minimum +1.6°C, maximum +13.6°C), but minimal and nonsignificant when compared to forest degradation (e.g., by selective logging; minimum +1°C, maximum +1.1°C). The effect was buffered belowground (minimum buffering 0°C, maximum buffering 11.4°C), whereas seasonality had minimal impact (maximum buffering 1.9°C). We conclude that forest‐dependent species that persist following conversion of rainforest have experienced substantial local warming. Deforestation pushes these species closer to their thermal limits, making it more likely that compounding effects of future perturbations, such as severe droughts and global warming, will exceed species' tolerances. By contrast, degraded forests and belowground habitats may provide important refugia for thermally restricted species in landscapes dominated by agricultural land.     

Long-term monitoring and the conservation of tropical wetlands: high ideals and harsh realities

Long-term monitoring of wetlands is an essential element of management for wise use. Indeed, the Ramsar Convention requires regular monitoring in order to detect changes in ecological character at listed sites. However, there are few examples of successful long-term monitoring in tropical wetlands. Monitoring schemes run into three kinds of difficulties: conceptual, logistical and political. To be effective, monitoring schemes must be carefully planned and designed. In practice, the questions to be addressed are rarely made explicit. Strictly defined, monitoring should assess deviations from a pre-set level so that appropriate corrective action can be taken. This assumes that good baseline information exists, and that we have sufficient knowledge of the system to set sensible signal levels. Neither is usually the case in tropical wetlands. This means that carefully focused surveillance (a time-series of systematic observations) is an essential first step. Providing resources and co-ordination for surveillance or monitoring is challenging over the long term, especially if the variables being measured require expensive analyses and highly trained staff. I suggest that surveillance or monitoring programmes should focus on likely threats, and ecological or economic concerns, should be as simple, robust and inexpensive as possible, should be sustained and consistent, and should involve local people and volunteers. If it is to be effective, monitoring must have a clear linkage to wetland management. Ideally, it should form part of each country's wetland policy. I suggest some variables that could be incorporated in sustainable long-term monitoring programmes. Two examples of successful surveillance work at Kenyan wetlands illustrate that the challenges involved in long-term programmes can, at least in part, be overcome.     

Conversion of coastal wetlands,riparian wetlands,and peatlands increases greenhouse gas emissions: A global meta‐analysis

Land‐use/land‐cover change (LULCC) often results in degradation of natural wetlands and affects the dynamics of greenhouse gases (GHGs). However, the magnitude of changes in GHG emissions from wetlands undergoing various LULCC types remains unclear. We conducted a global meta‐analysis with a database of 209 sites to examine the effects of LULCC types of constructed wetlands (CWs), croplands (CLs), aquaculture ponds (APs), drained wetlands (DWs), and pastures (PASs) on the variability in CO₂, CH₄, and N₂O emissions from the natural coastal wetlands, riparian wetlands, and peatlands. Our results showed that the natural wetlands were net sinks of atmospheric CO₂ and net sources of CH₄ and N₂O, exhibiting the capacity to mitigate greenhouse effects due to negative comprehensive global warming potentials (GWPs; ?0.9 to ?8.7 t CO₂‐eq ha^?1 year^?1). Relative to the natural wetlands, all LULCC types (except CWs from coastal wetlands) decreased the net CO₂ uptake by 69.7%?456.6%, due to a higher increase in ecosystem respiration relative to slight changes in gross primary production. The CWs and APs significantly increased the CH₄ emissions compared to those of the coastal wetlands. All LULCC types associated with the riparian wetlands significantly decreased the CH₄ emissions. When the peatlands were converted to the PASs, the CH₄ emissions significantly increased. The CLs, as well as DWs from peatlands, significantly increased the N₂O emissions in the natural wetlands. As a result, all LULCC types (except PASs from riparian wetlands) led to remarkably higher GWPs by 65.4%?2,948.8%, compared to those of the natural wetlands. The variability in GHG fluxes with LULCC was mainly sensitive to changes in soil water content, water table, salinity, soil nitrogen content, soil pH, and bulk density. This study highlights the significant role of LULCC in increasing comprehensive GHG emissions from global natural wetlands, and our results are useful for improving future models and manipulative experiments.     

Global change and the distributional dynamics of migratory bird populations wintering in Central America

Understanding the susceptibility of highly mobile taxa such as migratory birds to global change requires information on geographic patterns of occurrence across the annual cycle. Neotropical migrants that breed in North America and winter in Central America occur in high concentrations on their non‐breeding grounds where they spend the majority of the year and where habitat loss has been associated with population declines. Here, we use eBird data to model weekly patterns of abundance and occurrence for 21 forest passerine species that winter in Central America. We estimate species’ distributional dynamics across the annual cycle, which we use to determine how species are currently associated with public protected areas and projected changes in climate and land‐use. The effects of global change on the non‐breeding grounds is characterized by decreasing precipitation, especially during the summer, and the conversion of forest to cropland, grassland, or peri‐urban. The effects of global change on the breeding grounds are characterized by increasing winter precipitation, higher temperatures, and the conversion of forest to peri‐urban. During spring and autumn migration, species are projected to encounter higher temperatures, forests that have been converted to peri‐urban, and increased precipitation during spring migration. Based on current distributional dynamics, susceptibility to global change is characterized by the loss of forested habitats on the non‐breeding grounds, warming temperatures during migration and on the breeding grounds, and declining summer rainfall on the non‐breeding grounds. Public protected areas with low and medium protection status are more prevalent on the non‐breeding grounds, suggesting that management opportunities currently exist to mitigate near‐term non‐breeding habitat losses. These efforts would affect more individuals of more species during a longer period of the annual cycle, which may create additional opportunities for species to respond to changes in habitat or phenology that are likely to develop under climate change.     

Biodiversity loss under existing land use and climate change: an illustration using northern South America

Aim Species richness depends on climate and land use. Maintaining locations with favourable climate and land‐use patterns is critical for protecting biodiversity because the loss of either can reduce the species richness that an area supports. Currently, the Guiana Shield (GS) receives abundant precipitation and has relatively light land use. For species richness this constitutes a good–good combination of climate and land use, respectively. In contrast, much of eastern Brazil receives low levels of precipitation and has heavy land use, which is a bad–bad combination for species richness. Thus, the current distribution of precipitation and land use in northern South America is relatively favourable for biodiversity. Palaeoclimate and model studies suggest, however, that the precipitation patterns for the two regions have switched before and could switch in response to greenhouse gas emissions. This paper examines the potential consequences of reconfiguring climate with respect to existing land‐use patterns using South America as an example. Location South America north of 20° S and east of the Andes. Methods Ecosystem structure and function are modelled under (1) historical climate and (2) altered precipitation following a shift in the location of the Inter‐Tropical Convergence Zone (ITCZ). The distribution of precipitation, biomes, net primary productivity (NPP) and land use are then used to predict levels of species richness under the two climate scenarios. Results Climate changes could shift the distribution of vegetation and NPP such that conditions favourable for species richness in the GS region disappear. If land‐use patterns were not prohibitive in eastern Brazil, the improved climate conditions there could compensate for the GS loss (assuming migratory barriers are overcome). Instead, existing land‐use patterns cause the combined species richness projected for the two regions to plummet. Main conclusions Human activities will alter current configurations of land use and climate throughout the world. For species richness, new configurations are likely to include both positive and negative combinations of climate and land use. However, the irreversibility of past extinctions due to land‐use patterns loads the dice against species richness.     

Climate implications of biomass burning since the 19th century in eastern North America

Recent predictions that tropospheric aerosols have counterbalanced greenhouse warming assume aerosol emissions were low before ad 1850 and then increased dramatically with industrialization of the Northern Hemisphere and biomass burning in the Tropics. We assembled the lake sediment record of emissions across northeastern North America, where temperatures are predicted to have been substantially affected by industrial aerosols. Sediment evidence suggests a systematic shift in source and an overall decline in emissions since the 19th century. The geographical shift results from high presettlement emissions from wildfires in the Midwest that collapsed with tillage and fire suppression. Meanwhile, emissions were increasing in the North-east with European settlement. These regional changes produced a shift from the continental interior to the North-east. An overall decline results because decreases in the Midwest more than compensate for increases in the North-east. Results suggest the Central Plains as an important source of emissions in the recent past, consistent with pioneer accounts of dense smoke clouds emanating from prairie in the 19th century. Contrary to recent models that suggest increased 20th century combustion emissions could have offset warming effects of rising greenhouse gases, our data suggest that aerosols could have actually decreased over this interval. Although we cannot directly quantify aerosols from our methods, the emissions of large particles suggest assumptions of 20th century aerosol declines should be reconsidered.     

量化气候和土地利用变化对生态资产变化的相对贡献——以房山区为例

生态资产与人类福祉密切相关,开展生态资产评估并定量区分气候和人类活动对生态资产变化的相对贡献,对于评估区域生态文明建设成效、生态补偿、干部离任的自然资产审计等均具有重要意义。在单位面积价值当量因子方法的基础上,重新定义了标准生态服务价值当量因子,并构建了一个能够定量区分气候变化和土地利用变化对生态资产变化相对贡献的方法,以北京市房山区为例,分析了2000年至2019年房山区生态资产的变化,以及气候变化和土地利用变化对生态资产变化的相对贡献,结果表明:(1)房山区2019年生态资产总价值177.14亿元。森林、草地、农田和湿地的生态资产分别占生态资产总价值的82.33%、11.76%、5.25%和0.095%。(2)房山在2000-2019年期间,生态资产总价值增加了2.275亿元,气候变化使得房山区的生态资产总价值增加了2.689亿元,而土地利用变化使得生态资产总价值减少了0.414亿元。(3)房山区生态资产西高东低,其中霞云岭乡生态资产总价值最高;琉璃河镇的生态资产增加最多,而拱辰街道下降最显著。过去20年是房山区社会经济快速发展的时期,由于气候变化和生态保护与修复使得生态资产增加,抵消了由于建设用地扩张所带来的生态资产损失。     

Environmental controls on the distribution and diversity of lentic Chironomidae (Insecta: Diptera) across an altitudinal gradient in tropical South America

To predict the response of aquatic ecosystems to future global climate change, data on the ecology and distribution of keystone groups in freshwater ecosystems are needed. In contrast to mid‐ and high‐latitude zones, such data are scarce across tropical South America (Neotropics). We present the distribution and diversity of chironomid species using surface sediments of 59 lakes from the Andes to the Amazon (0.1–17°S and 64–78°W) within the Neotropics. We assess the spatial variation in community assemblages and identify the key variables influencing the distributional patterns. The relationships between environmental variables (pH, conductivity, depth, and sediment organic content), climatic data, and chironomid assemblages were assessed using multivariate statistics (detrended correspondence analysis and canonical correspondence analysis). Climatic parameters (temperature and precipitation) were most significant in describing the variance in chironomid assemblages. Temperature and precipitation are both predicted to change under future climate change scenarios in the tropical Andes. Our findings suggest taxa of Orthocladiinae, which show a preference to cold high‐elevation oligotrophic lakes, will likely see range contraction under future anthropogenic‐induced climate change. Taxa abundant in areas of high precipitation, such as Micropsectra and Phaenopsectra, will likely become restricted to the inner tropical Andes, as the outer tropical Andes become drier. The sensitivity of chironomids to climate parameters makes them important bio‐indicators of regional climate change in the Neotropics. Furthermore, the distribution of chironomid taxa presented here is a vital first step toward providing urgently needed autecological data for interpreting fossil chironomid records of past ecological and climate change from the tropical Andes.     

Interrogating recent range changes in South African birds: confounding signals from land use and climate change present a challenge for attribution

Aim Apparent anthropogenic warming has been underway in South Africa for several decades, a period over which significant range shifts have been observed in some indigenous bird species. We asked whether these range shifts by birds are clearly consistent with either climate change or land use change being the primary driver. Location South Africa. Methods We categorized recent range changes among 408 South African terrestrial bird species and, using generalized linear mixed models, analysed ecological attributes of those species that have and have not changed their ranges. Results Fifty‐six of the 408 taxa studied have undergone significant range shifts. Most extended their ranges towards the south (towards cooler latitudes, consistent with climate‐change drivers) or west (towards drier and warmer habitats, inconsistent with climate drivers but consistent with land use drivers); very few moved east or north. Both southward and westward movers were habitat generalists. Furthermore, southward movers were mobile taxa (migrants and nomads), whereas westward movers were associated with human‐modified elements in the landscape, such as croplands, plantations or buildings. Main conclusions The results suggest that both land use changes and climate change may simultaneously be influencing dynamic range shifts by South African birds, but separating the relative strengths of these two drivers is challenging, not least because both are operating concurrently and may influence some species simultaneously. Those species that respond to land use change by contracting their ranges are likely to be among the species that will be most impacted by climate change if land use practices with negative impacts are occurring in areas anticipated to become climatic refugia for these species. This highlights a pressing need to develop dynamic models of species’ potential range shifts and changing abundances that incorporate population and dispersal processes, as well as ecological processes that influence habitat suitability.     

Terrestrial models and global change: challenges for the future

A wide variety of models have illustrated the potential importance of terrestrial biological feedbacks on climate and climate change; yet our ability to make precise predictions is severely limited, due to a high degree of uncertainty. In this paper, after briefly reviewing current models, we present challenges for new terrestrial models and introduce a simple mechanistic approach that may complement existing approaches.     

辽河三角洲湿地以丹顶鹤生境保护为核心的退耕预案研究

在遥感 (RS)和地理信息系统 (GIS)的支持下 ,结合野外实地调查 ,运用预案研究方法和景观生态决策与评价支持系统(L EDESS)的决策与规划评价思想 ,针对辽河三角洲大洼小三角洲部分的过度农业开发对野生动物生境的严重影响后果 ,对本区土地利用规划进行了以丹顶鹤生境保护为核心的退耕预案设计 ,并对其生态后果进行了空间模拟和评价。根据不同的经济和生态发展要求设计了 4个预案 ,分别为 1988年原状 (预案 1)、1998年原状 (预案 2 )、苇带设计 (预案 3)和生境恢复 (预案 4 ) ,通过对各预案进行生境适宜性、生态承载力及经济效益评价 ,可以得到以下结论 :预案 1尽管生态效益很高 ,但经济效益很低 ,在区域发展需求下由现状年恢复到预案 1具有不现实性 ;而预案 2为强烈经济需求下的典型发展模式 ,生态效益偏低 ,与经济效益的比例失调 ;预案 3和预案 4为生态与经济的协调发展模式及丹顶鹤生境恢复提供了有效参考 ,可将其视为近期和远期规划目标分步实施。这说明合理的土地开发利用方式和生境恢复措施不仅可以获得经济的高效发展 ,而且还可为稳定的生态环境提供有力保障 ,从而为区域经济与环境的协调发展提供参考性依据 ,具有一定的典型性     

Disentangling direct and indirect effects of water table drawdown on above‐ and belowground plant litter decomposition: consequences for accumulation of organic matter in boreal peatlands

Pristine peatlands are carbon (C)‐accumulating wetland ecosystems sustained by a high water table (WT) and consequent anoxia that slows down decomposition. Persistent WT drawdown as a response to climate and/or land‐use change affects decomposition either directly through environmental factors such as increased oxygenation, or indirectly through changes in plant community composition. This study attempts to disentangle the direct and indirect effects of WT drawdown by measuring the relative importance of environmental parameters (WT depth, temperature, soil chemistry) and litter type and/or litter chemical quality on the 2‐year decomposition rates of above‐ and belowground litter (altogether 39 litter types). Consequences for organic matter accumulation were estimated based on the annual litter production. The study sites were chosen to form a three‐stage chronosequence from pristine (undrained) to short‐term (years) and long‐term (decades) WT drawdown conditions at three nutrient regimes. The direct effects of WT drawdown were overruled by the indirect effects through changes in litter type composition and production. Short‐term responses to WT drawdown were small. In long‐term, dramatically increased litter inputs resulted in large accumulation of organic matter in spite of increased decomposition rates. Furthermore, the quality of the accumulated matter greatly changed from that accumulated in pristine conditions. Our results show that the shift in vegetation composition as a response to climate and/or land‐use change is the main factor affecting peatland ecosystem C cycle, and thus dynamic vegetation is a necessity in any model applied for estimating responses of C fluxes to changing environment. We provide possible grouping of litter types into plant functional types that the models could utilize. Furthermore, our results clearly show a drop in soil summer temperature as a response to WT drawdown when an initially open peatland converts into a forest ecosystem, which has not yet been considered in the existing models.     

Introduction to the Special Section on Alternative Futures for Great Basin Ecosystems

Natural and anthropogenic processes are causing extensive and rapid ecological, social, and economic changes in arid and semiarid ecosystems worldwide. Nowhere are these changes more evident than in the Great Basin of the western United States, a region of 400,000 km² that largely is managed by federal agencies. Major drivers of ecosystems and human demographics of the Great Basin include human population growth, grazing by domestic livestock, extraction of minerals, development and production of energy, changes in fire and other disturbance regimes, and invasion of non-native annual plants. Exploration of alternative futures may increase the ability of management and policy to maximize the system's resistance and resilience to changes in climate, disturbance regimes, and anthropogenic perturbations. This special section examines the issues facing the Great Basin and then provides examples of approaches to predicting changes in land cover and avifaunal distributions under different management scenarios. Future sustainability of the Great Basin's natural and human systems requires strong, collaborative partnerships among research and management organizations that are capable of obtaining public support and financial resources and developing effective policies and institutional mechanisms.     

Natural and man-induced changes in a tidal channel mangrove system under tropical semiarid climate at the entrance of the Maracaibo lake (Western Venezuela)

Caño Paijana is a tidal channel that connected, until recently, theUruba bay at the mouth of the Limón river, to the Gulf of Venezuelanorth of Maracaibo, Venezuela. It separated the Island of San Carlos fromthe mainland. In the last 50 years the channel has been drying out rapidly,to the extent that presently there is no water flow into or from the seathrough its mouth opening on the Gulf of Venezuela. This mouth wascovered by healthy mangroves (mainly Avicennia germinans) until atleast 1952. The two extremes of the Paijana water channel differ radicallytoday. At Uruba bay end the channel is fringed by dense mangrovevegetation dominated by Rhizophora mangle, while at the Gulf ofVenezuela mouth the vegetation cover is mostly constituted by scrubby,scattered trees of Avicennia germinans, xerophytic shrubs acting asdune fixers, and halophytic strand vegetation. The process is the result ofcomplex interaction between: a) high frequency of low-rainfall years; b)high dune activity during dry years c) dam construction on tributaries ofthe Limón river that reduced discharge of fresh water into Uruba bay.     

Successional and seasonal variations in soil and litter microbial community structure and function during tropical postagricultural forest regeneration: a multiyear study

Soil microorganisms regulate fundamental biochemical processes in plant litter decomposition and soil organic matter (SOM) transformations. Understanding how microbial communities respond to changes in vegetation is critical for improving predictions of how land‐cover change affects belowground carbon storage and nutrient availability. We measured intra‐ and interannual variability in soil and forest litter microbial community composition and activity via phospholipid fatty acid analysis (PLFA) and extracellular enzyme activity across a well‐replicated, long‐term chronosequence of secondary forests growing on abandoned pastures in the wet subtropical forest life zone of Puerto Rico. Microbial community PLFA structure differed between young secondary forests and older secondary and primary forests, following successional shifts in tree species composition. These successional patterns held across seasons, but the microbial groups driving these patterns differed over time. Microbial community composition from the forest litter differed greatly from those in the soil, but did not show the same successional trends. Extracellular enzyme activity did not differ with forest succession, but varied by season with greater rates of potential activity in the dry seasons. We found few robust significant relationships among microbial community parameters and soil pH, moisture, carbon, and nitrogen concentrations. Observed inter‐ and intrannual variability in microbial community structure and activity reveal the importance of a multiple, temporal sampling strategy when investigating microbial community dynamics with land‐use change. Successional control over microbial composition with forest recovery suggests strong links between above and belowground communities.     

Using an artificial neural network to characterize the relative suitability of environments for forest types in a complex tropical vegetation mosaic

A predictive understanding of the environmental controls on forest distributions is essential for the conservation of biodiversity and management of landscapes in the tropics. This is particularly true now because of potentially rapid climate change. The floristic complexity of tropical forests and the lack or absence of data severely limits the applicability of modelling methods based on the ecology or distribution of individual species. Here we present an artificial neural network (ANN) model using the information available in the humid tropics of North Queensland: a structural classification of forest types, maps of the forest mosaic, and estimates of spatial environmental variables. The ANN model characterizes the relative suitabilities of environments for 15 forest classes defined by their physiognomy and canopy structure. Inputs include seven climate variables, nine soil parent-material classes, and seven terrain variables. The data used to train the model consisted of a stratified random sample of 75000 points. Output of the model is used to measure the dissimilarity between the environment at each location and the environment that would be most suitable for the forest type that is mapped there. The model is highly successful at distinguishing the relative suitability of environments for the forest classes with 75% of the region's forest mosaic accurately predicted by the model at a one hectare resolution. In contrast, a comparable maximum likelihood classification has an accuracy of only 38%. In the remaining 25% of the region the environments are quite dissimilar to what would be expected for the forest types present there. This is especially the case at boundaries between forest classes and for a transitional forest class. Areas mapped as this disturbed, transitional class are generally classified by the model as having environments suitable to the forest type they are most likely to become. The approach has high potential for the analysis of climate change impacts as well as inferring vegetation patterns in the past and should be applicable wherever vegetation maps and spatial estimates of climate variables are available.