A review of influences of land use and land cover change on ecosystems

随着人口的增长和人类社会的发展, 土地利用与土地覆盖变化已经是不可避免。土地利用与土地覆盖变化不仅对生态系统的要素、结构和功能产生深远的影响, 也会对全球变化产生反馈作用。针对土地利用与土地覆盖变化的过程、驱动机制以及在各个方面可能产生的生态环境效应的科学研究已经全面开展。该文综述了土地利用与土地覆盖变化对气候、土壤、生物地球化学循环、生物多样性以及区域生态环境等影响方面的研究进展, 并提出了相关研究的前沿方向展望。随着新技术的不断发展, 学者们将更多地侧重预测未来全球变化背景下的土地利用与土地覆盖变化趋势、合理性以及适应性, 为可持续发展提供基础资料和理论依据。     

土地利用与土地覆盖变化对生态系统的影响

随着人口的增长和人类社会的发展, 土地利用与土地覆盖变化已经是不可避免。土地利用与土地覆盖变化不仅对生态系统的要素、结构和功能产生深远的影响, 也会对全球变化产生反馈作用。针对土地利用与土地覆盖变化的过程、驱动机制以及在各个方面可能产生的生态环境效应的科学研究已经全面开展。该文综述了土地利用与土地覆盖变化对气候、土壤、生物地球化学循环、生物多样性以及区域生态环境等影响方面的研究进展, 并提出了相关研究的前沿方向展望。随着新技术的不断发展, 学者们将更多地侧重预测未来全球变化背景下的土地利用与土地覆盖变化趋势、合理性以及适应性, 为可持续发展提供基础资料和理论依据。     

Critical land change information enhances the understanding of carbon balance in the United States

Large‐scale terrestrial carbon (C) estimating studies using methods such as atmospheric inversion, biogeochemical modeling, and field inventories have produced different results. The goal of this study was to integrate fine‐scale processes including land use and land cover change into a large‐scale ecosystem framework. We analyzed the terrestrial C budget of the conterminous United States from 1971 to 2015 at 1‐km resolution using an enhanced dynamic global vegetation model and comprehensive land cover change data. Effects of atmospheric CO₂ fertilization, nitrogen deposition, climate, wildland fire, harvest, and land use/land cover change (LUCC) were considered. We estimate annual C losses from cropland harvest, forest clearcut and thinning, fire, and LUCC were 436.8, 117.9, 10.5, and 10.4 TgC/year, respectively. C stored in ecosystems increased from 119,494 to 127,157 TgC between 1971 and 2015, indicating a mean annual net C sink of 170.3 TgC/year. Although ecosystem net primary production increased by approximately 12.3 TgC/year, most of it was offset by increased C loss from harvest and natural disturbance and increased ecosystem respiration related to forest aging. As a result, the strength of the overall ecosystem C sink did not increase over time. Our modeled results indicate the conterminous US C sink was about 30% smaller than previous modeling studies, but converged more closely with inventory data.     

Rapid warming is associated with population decline among terrestrial birds and mammals globally

Animal populations have undergone substantial declines in recent decades. These declines have occurred alongside rapid, human‐driven environmental change, including climate warming. An association between population declines and environmental change is well established, yet there has been relatively little analysis of the importance of the rates of climate warming and its interaction with conversion to anthropogenic land use in causing population declines. Here we present a global assessment of the impact of rapid climate warming and anthropogenic land use conversion on 987 populations of 481 species of terrestrial birds and mammals since 1950. We collated spatially referenced population trends of at least 5 years’ duration from the Living Planet database and used mixed effects models to assess the association of these trends with observed rates of climate warming, rates of conversion to anthropogenic land use, body mass, and protected area coverage. We found that declines in population abundance for both birds and mammals are greater in areas where mean temperature has increased more rapidly, and that this effect is more pronounced for birds. However, we do not find a strong effect of conversion to anthropogenic land use, body mass, or protected area coverage. Our results identify a link between rapid warming and population declines, thus supporting the notion that rapid climate warming is a global threat to biodiversity.     

Land Transitions in the Tropics: Going Beyond the Case Studies

Estimates of the percent of Earth's land surface that has either been transformed or degraded by human activity range between 39 and 50 percent, with agriculture accounting for the vast majority of these changes. Although much of the focus of research on land use and cover change in the tropics has been on deforestation, ongoing socioeconomic changes both locally and globally have made land transitions in the tropics extremely fluid. In addition, feedbacks between land cover change and human behavior constrain the extent and trajectories of land transitions. The sustainability of land use systems in the tropics depends on an understanding of coupled human–natural systems that can lead to general frameworks for management and prediction. The unprecedented availability of land use/cover data together with ecological data collected at large spatial scales offer exciting opportunities for advancing our understanding of socioecological systems. We rely on six studies of land transitions in the tropics to illustrate some promising approaches and pose critical questions to guide this body of research.     

Reforestation and surface cooling in temperate zones: Mechanisms and implications

Land‐use/cover change (LUCC) is an important driver of environmental change, occurring at the same time as, and often interacting with, global climate change. Reforestation and deforestation have been critical aspects of LUCC over the past two centuries and are widely studied for their potential to perturb the global carbon cycle. More recently, there has been keen interest in understanding the extent to which reforestation affects terrestrial energy cycling and thus surface temperature directly by altering surface physical properties (e.g., albedo and emissivity) and land–atmosphere energy exchange. The impacts of reforestation on land surface temperature and their mechanisms are relatively well understood in tropical and boreal climates, but the effects of reforestation on warming and/or cooling in temperate zones are less certain. This study is designed to elucidate the biophysical mechanisms that link land cover and surface temperature in temperate ecosystems. To achieve this goal, we used data from six paired eddy‐covariance towers over co‐located forests and grasslands in the temperate eastern United States, where radiation components, latent and sensible heat fluxes, and meteorological conditions were measured. The results show that, at the annual time scale, the surface of the forests is 1–2°C cooler than grasslands, indicating a substantial cooling effect of reforestation. The enhanced latent and sensible heat fluxes of forests have an average cooling effect of ?2.5°C, which offsets the net warming effect (+1.5°C) of albedo warming (+2.3°C) and emissivity cooling effect (?0.8°C) associated with surface properties. Additional daytime cooling over forests is driven by local feedbacks to incoming radiation. We further show that the forest cooling effect is most pronounced when land surface temperature is higher, often exceeding ?5°C. Our results contribute important observational evidence that reforestation in the temperate zone offers opportunities for local climate mitigation and adaptation.     

Defining the importance of including transient ecosystem responses to simulate C‐cycle dynamics in a global change model

The ability of plant species to migrate is one of the critical issues in assessing accurately the future response of the terrestrial biosphere to climate change. This ability is confined by both natural and human‐induced changes in land cover. In this paper we present land‐cover and Carbon (C) cycle models designed to simulate the biospheric consequences of different types of land‐cover changes. These models, imbedded in the larger integrated assessment model IMAGE 2, were used to demonstrate the importance of considering spatial aspects for global C‐cycle modelling. A gradual‐migration, an unlimited‐migration and a no‐migration case were compared to show the range of possible consequences. Major differences between these cases were simulated for land‐cover patterns and the carbon budget. A large geographical variation in the biospheric response was also simulated. The strongest response was simulated in high‐latitude regions, especially for the migration cases in which land‐cover changes were permitted. In low‐latitudes regions the differences between the migration cases were smaller, mainly due to the effects of land‐use changes. The geographical variation among, and the different responses, the migration cases clearly demonstrate how essential it is to assess biospheric responses to climate change and land use simultaneously. Moreover, it also shows the urgent need for enhanced understanding of spatial and temporal dynamics of the biospheric responses.     

Climate warming feedback from mountain birch forest expansion: reduced albedo dominates carbon uptake

Expanding high‐elevation and high‐latitude forest has contrasting climate feedbacks through carbon sequestration (cooling) and reduced surface reflectance (warming), which are yet poorly quantified. Here, we present an empirically based projection of mountain birch forest expansion in south‐central Norway under climate change and absence of land use. Climate effects of carbon sequestration and albedo change are compared using four emission metrics. Forest expansion was modeled for a projected 2.6 °C increase in summer temperature in 2100, with associated reduced snow cover. We find that the current (year 2000) forest line of the region is circa 100 m lower than its climatic potential due to land‐use history. In the future scenarios, forest cover increased from 12% to 27% between 2000 and 2100, resulting in a 59% increase in biomass carbon storage and an albedo change from 0.46 to 0.30. Forest expansion in 2100 was behind its climatic potential, forest migration rates being the primary limiting factor. In 2100, the warming caused by lower albedo from expanding forest was 10 to 17 times stronger than the cooling effect from carbon sequestration for all emission metrics considered. Reduced snow cover further exacerbated the net warming feedback. The warming effect is considerably stronger than previously reported for boreal forest cover, because of the typically low biomass density in mountain forests and the large changes in albedo of snow‐covered tundra areas. The positive climate feedback of high‐latitude and high‐elevation expanding forests with seasonal snow cover exceeds those of afforestation at lower elevation, and calls for further attention of both modelers and empiricists. The inclusion and upscaling of these climate feedbacks from mountain forests into global models is warranted to assess the potential global impacts.     

A Land System representation for global assessments and land‐use modeling

Current global scale land‐change models used for integrated assessments and climate modeling are based on classifications of land cover. However, land‐use management intensity and livestock keeping are also important aspects of land use, and are an integrated part of land systems. This article aims to classify, map, and to characterize Land Systems (LS) at a global scale and analyze the spatial determinants of these systems. Besides proposing such a classification, the article tests if global assessments can be based on globally uniform allocation rules. Land cover, livestock, and agricultural intensity data are used to map LS using a hierarchical classification method. Logistic regressions are used to analyze variation in spatial determinants of LS. The analysis of the spatial determinants of LS indicates strong associations between LS and a range of socioeconomic and biophysical indicators of human‐environment interactions. The set of identified spatial determinants of a LS differs among regions and scales, especially for (mosaic) cropland systems, grassland systems with livestock, and settlements. (Semi‐)Natural LS have more similar spatial determinants across regions and scales. Using LS in global models is expected to result in a more accurate representation of land use capturing important aspects of land systems and land architecture: the variation in land cover and the link between land‐use intensity and landscape composition. Because the set of most important spatial determinants of LS varies among regions and scales, land‐change models that include the human drivers of land change are best parameterized at sub‐global level, where similar biophysical, socioeconomic and cultural conditions prevail in the specific regions.     

Tropical understory herbaceous community responds more strongly to hurricane disturbance than to experimental warming

The effects of climate change on tropical forests may have global consequences due to the forests’ high biodiversity and major role in the global carbon cycle. In this study, we document the effects of experimental warming on the abundance and composition of a tropical forest floor herbaceous plant community in the Luquillo Experimental Forest, Puerto Rico. This study was conducted within Tropical Responses to Altered Climate Experiment (TRACE) plots, which use infrared heaters under free‐air, open‐field conditions, to warm understory vegetation and soils + 4°C above nearby control plots. Hurricanes Irma and María damaged the heating infrastructure in the second year of warming, therefore, the study included one pretreatment year, one year of warming, and one year of hurricane response with no warming. We measured percent leaf cover of individual herbaceous species, fern population dynamics, and species richness and diversity within three warmed and three control plots. Results showed that one year of experimental warming did not significantly affect the cover of individual herbaceous species, fern population dynamics, species richness, or species diversity. In contrast, herbaceous cover increased from 20% to 70%, bare ground decreased from 70% to 6%, and species composition shifted pre to posthurricane. The negligible effects of warming may have been due to the short duration of the warming treatment or an understory that is somewhat resistant to higher temperatures. Our results suggest that climate extremes that are predicted to increase with climate change, such as hurricanes and droughts, may cause more abrupt changes in tropical forest understories than longer‐term sustained warming.     

新疆焉耆盆地人类活动与气候变化的效应机制

通过对新疆焉耆盆地及其周边近40a(1973—2014)的气候变化趋势检测、LUCC和生物量估算,探讨气候变化和人类活动的生态效应机制,研究区域陆地生态系统演变及其归因。分析结果表明:(1)焉耆盆地山区和平原区降水变化都有明显的突变点,并呈现增加趋势,蒸发量在山区减少,在平原区波动性减少趋势;(2)LUCC分析表明,山区裸地面积减少5.40%,冰川面积减少3.36%,高地植被面积增加8.76%;同时平原区天然绿洲面积增加1.96%,沙漠面积减少1.62%,水域面积减少1.30%,人工绿洲面积增加15.41%,湿地面积增加1.27%;(3)山区陆地生态系统对区域气候变化非常敏感,其中降水变化是决定山区地表植被生存状态和分布的重要因素;(4)人类活动的推动作用和有益气候变化的支撑是绿洲平原区生态系统好转的原因,其中人口急剧增加和社会经济快速发展,导致绿洲平原区生态系统结构及其时空分布的主要因素。焉耆盆地及其周围区域陆地生态系统的演变对气候变化和人类活动有明显的时空尺度效应,其反应程度各不相同。     

Large‐scale degradation of Amazonian freshwater ecosystems

Hydrological connectivity regulates the structure and function of Amazonian freshwater ecosystems and the provisioning of services that sustain local populations. This connectivity is increasingly being disrupted by the construction of dams, mining, land‐cover changes, and global climate change. This review analyzes these drivers of degradation, evaluates their impacts on hydrological connectivity, and identifies policy deficiencies that hinder freshwater ecosystem protection. There are 154 large hydroelectric dams in operation today, and 21 dams under construction. The current trajectory of dam construction will leave only three free‐flowing tributaries in the next few decades if all 277 planned dams are completed. Land‐cover changes driven by mining, dam and road construction, agriculture and cattle ranching have already affected ~20% of the Basin and up to ~50% of riparian forests in some regions. Global climate change will likely exacerbate these impacts by creating warmer and dryer conditions, with less predictable rainfall and more extreme events (e.g., droughts and floods). The resulting hydrological alterations are rapidly degrading freshwater ecosystems, both independently and via complex feedbacks and synergistic interactions. The ecosystem impacts include biodiversity loss, warmer stream temperatures, stronger and more frequent floodplain fires, and changes to biogeochemical cycles, transport of organic and inorganic materials, and freshwater community structure and function. The impacts also include reductions in water quality, fish yields, and availability of water for navigation, power generation, and human use. This degradation of Amazonian freshwater ecosystems cannot be curbed presently because existing policies are inconsistent across the Basin, ignore cumulative effects, and overlook the hydrological connectivity of freshwater ecosystems. Maintaining the integrity of these freshwater ecosystems requires a basinwide research and policy framework to understand and manage hydrological connectivity across multiple spatial scales and jurisdictional boundaries.     

土地利用/覆盖变化对陆地生态系统碳循环的影响

土地利用/覆盖变化是学术界最为关注的环境变化问题之一,它能够影响陆地生态系统的生物多样性、水、碳和养分循环、能量平衡,引起温室气体释放增加等其它环境问题。不同类型的土地利用/覆盖变化对生态系统碳循环的作用不同,由高生物量的森林转化为低生物量的草地、农田或城市后,大量的CO₂将释放到大气中。全球土地利用/覆盖变化具有很强的空间变异性,对生态系统碳循环的影响同样具有明显的空间差异:热带地区的土地利用/覆盖变化造成大量的碳释放,而中高纬度地区土地利用/覆盖变化则表现为碳汇。目前,土地利用/覆盖变化引起的生态系统碳循环变化主要是通过模型模拟来估算的。尽管土地利用/覆盖变化及其相关过程与生态系统碳循环的关系已经比较清楚,但是,由于土地利用/覆盖变化过程复杂且影响广泛,对于如何量化两者之间的关系还存在很多不确定性。目前的量化过程主要是利用经验数据来实现的,机理性不强,使得对土地利用/覆盖变化造成的陆地生态系统CO₂释放量的估测差异很大。除了进一步加强长期定位研究以获得土地利用/覆盖变化与生态系统碳循环过程的定量关系外,土地利用/覆盖变化模型与植被动态模型、生态系统过程模型的耦合也是今后模型发展的主要方向之一。采用合理的管理措施能够大量增加土地利用/覆盖变化过程中的碳储存量,降低碳释放量,因此在模型中耦合管理措施来研究土地利用/覆盖变化过程对生态系统碳循环的影响是未来几年的工作重点。     

南疆生态脆弱区土地利用变化及其生态影响评价--以新疆阿克苏市为例

在城市化速度加快的背景下,研究LUCC对生态脆弱区的生态环境影响过程,对了解区域生态环境变化具有重要意义。利用南疆生态脆弱区———阿克苏市1995、2000和2003年的TM遥感影像,采用景观生态学的空间格局指数对城乡土地利用动态变化特征进行了研究,参照Costanza等对全球不同生态系统类型服务功能价值测算结果的比例关系,分析了阿克苏市城乡土地利用类型的生态价值,定量综合评价了阿克苏市城乡区域LUCC的生态影响。结果表明,阿克苏市域景观总体构成表现为景观破碎度较高,斑块数目较多;农业用地中有近半数不稳定,水土条件差致使农用地和未利用地相互转换。研究时段内市域土地利用变化带来了较好的生态影响,土地利用生态效益持续提高,并表现出了较大空间差异。     

An empirical test of the relative and combined effects of land‐cover and climate change on local colonization and extinction

Land‐cover and climate change are two main drivers of changes in species ranges. Yet, the majority of studies investigating the impacts of global change on biodiversity focus on one global change driver and usually use simulations to project biodiversity responses to future conditions. We conduct an empirical test of the relative and combined effects of land‐cover and climate change on species occurrence changes. Specifically, we examine whether observed local colonization and extinctions of North American birds between 1981–1985 and 2001–2005 are correlated with land‐cover and climate change and whether bird life history and ecological traits explain interspecific variation in observed occurrence changes. We fit logistic regression models to test the impact of physical land‐cover change, changes in net primary productivity, winter precipitation, mean summer temperature, and mean winter temperature on the probability of Ontario breeding bird local colonization and extinction. Models with climate change, land‐cover change, and the combination of these two drivers were the top ranked models of local colonization for 30%, 27%, and 29% of species, respectively. Conversely, models with climate change, land‐cover change, and the combination of these two drivers were the top ranked models of local extinction for 61%, 7%, and 9% of species, respectively. The quantitative impacts of land‐cover and climate change variables also vary among bird species. We then fit linear regression models to test whether the variation in regional colonization and extinction rate could be explained by mean body mass, migratory strategy, and habitat preference of birds. Overall, species traits were weakly correlated with heterogeneity in species occurrence changes. We provide empirical evidence showing that land‐cover change, climate change, and the combination of multiple global change drivers can differentially explain observed species local colonization and extinction.     

黄河三角洲自然保护区1992～2010年土地覆被变化分析

基于黄河三角洲自然保护区1992年、2000年和2010年三期遥感图像,分析近20年黄河三角洲自然保护区土地利用/覆被变化(LUCC)情况。结果表明,在1992～2010年间,黄河三角洲自然保护区内同种土地覆被类型的空间分布较一致,均以海域、滩涂和旱地为主,但同种土地覆盖类型的比重均发生不同程度的变化。总体上,旱地、河渠、水库、居民地和其他用地类型的变化程度不明显,但年际间有波动变化;草地面积虽持续减少,但总体变化不明显;灌木面积总体变化也不明显,但年际间波动较大;芦苇面积呈减少趋势,尤其是1992～2000年间,大量芦苇覆被地转化为旱地类型;养殖塘面积增加明显,近20年间增加约6.24×103 hm2,主要由滩涂、柽柳、碱蓬等开发形成;海域面积变化剧烈,海域转化为滩涂是造成海域面积减少的主要原因。黄河三角洲自然保护区LUCC改变了自然保护区的生态系统结构,降低了自然保护区的生态服务功能。造成黄河三角洲LUCC的原因既有自然因素,也有人为因素,但在该区LUCC的驱动力主要为人类活动。     

我国三北地区植被变化的动因分析

地表植被变化是气候变化、人类活动等多种因素共同作的结果。然而,以往的研究要么集中在与气候变化有关的气象因素,要么集中在与人类活动有关的人为因素,鲜有基于长期数据监测下对自然与社会因素之间相互作用的定量评估。因此,气候变化和人为因素对地表植被变化的相互作用并不明确,各个因素对植被变化影响的量化贡献仍然不确定。为了评价生态修复项目对荒漠化防治的效果、以及在土地荒漠化防治中自然与社会因素对我国植被变化的影响、及其复杂的相互作用机理,该研究应用卫星遥感影像资料,通过面板数据混合回归模型大数据分析方法,计算了1983年至2012年气候变化和人类活动对我国北方地区植被变化的贡献率。结果表明,气候变化和人类活动对NDVI变化均有重要作用,其中人类活动对植被覆盖度变化的影响占58.2%—90.4%、气候变化占9.6%—41.8%;不同地区表现出不同的地理分异特征,并存在时滞效应。由此可见,荒漠化防治必须充分考虑不同因素的综合作用和地域特征,才能取得事半功倍的效果。研究结果较好地体现了卫星遥感影像资料在大尺度(省域尺度)下与社会经济统计指标的融合,为进一步中尺度(县域尺度)研究提供了方法借鉴。     

Land‐use change affects water recycling in Brazil's last agricultural frontier

Historically, conservation‐oriented research and policy in Brazil have focused on Amazon deforestation, but a majority of Brazil's deforestation and agricultural expansion has occurred in the neighboring Cerrado biome, a biodiversity hotspot comprised of dry forests, woodland savannas, and grasslands. Resilience of rainfed agriculture in both biomes likely depends on water recycling in undisturbed Cerrado vegetation; yet little is known about how changes in land‐use and land‐cover affect regional climate feedbacks in the Cerrado. We used remote sensing techniques to map land‐use change across the Cerrado from 2003 to 2013. During this period, cropland agriculture more than doubled in area from 1.2 to 2.5 million ha, with 74% of new croplands sourced from previously intact Cerrado vegetation. We find that these changes have decreased the amount of water recycled to the atmosphere via evapotranspiration (ET) each year. In 2013 alone, cropland areas recycled 14 km³ less (?3%) water than if the land cover had been native Cerrado vegetation. ET from single‐cropping systems (e.g., soybeans) is less than from natural vegetation in all years, except in the months of January and February, the height of the growing season. In double‐cropping systems (e.g., soybeans followed by corn), ET is similar to or greater than natural vegetation throughout a majority of the wet season (December–May). As intensification and extensification of agricultural production continue in the region, the impacts on the water cycle and opportunities for mitigation warrant consideration. For example, if an environmental goal is to minimize impacts on the water cycle, double cropping (intensification) might be emphasized over extensification to maintain a landscape that behaves more akin to the natural system.     

3S技术在绿洲土地覆盖变化研究中的应用研究--以新疆于田绿洲为例

土地利用／覆盖变化（LUCC）是全球变化研究的重要核心问题之一,基于区域和地方尺度的绿洲土地覆盖变化信息的定量提取在干旱区生态环境演变研究中具有重要的价值,也是对全球变化研究的重要补充。选择干旱区典型绿洲新疆于田地区为研究靶区,利用2期不同时相的TM卫星影像,结合多年实地调查所获得的大量数据,根据当地实际情况,选择适宜的分类指标体系,利用遥感、全球定位系统以及地理信息系统技术（3S技术）对图像进行了综合技术处理,获得了较高精度的该区域绿洲LUCC不同类型分类精度统计以及土地利用／覆盖转换矩阵。在此基础上,对跨度近10年的于田绿洲LUCC时空变化格局进行了分析,提出了相应的生态环境改良措施,其方法和结论对塔里木盆地南缘绿洲地区生态环境改良及其可持续发展研究具有一定参考价值。