基于无人机影像的草方格生态恢复区植被空间格局演化研究

理解植物群落组成结构的演化对于阐明荒漠化的过程与驱动机制、制定有效的干旱区生态系统恢复措施具有重要价值。研究干旱区植物群落的空间格局的演化过程有助于深入理解荒漠化和生态恢复的过程与机理。目前大量研究关注于植被退化过程中的群落组成结构变化,而对于生态恢复过程中的植物群落空间格局演化的研究尚不多见。干旱区生态系统中植物通常较为稀疏且个体较小,准确提取植物的分布往往需要分辨率极高的遥感数据。近年来,低空无人机遥感技术的快速发展为精细尺度上植被空间格局的研究提供重要技术支持。利用2 cm空间分辨率的低空无人机遥感数据结合地面群落调查,在精细尺度上研究了宁夏沙坡头草方格生态恢复区内植物群落的空间格局变化。研究结果表明,沙坡头地区草方格生态恢复工程实验区域,相对于未实施生态恢复工程的裸露沙丘区域,植物物种多样性和植被盖度显著提高。恢复工程实施4年后,平均植被盖度增加3倍,物种丰富度增加1倍。在植被恢复过程中,随着植被盖度的增加,植被斑块表现出规模上升、破碎化程度下降、形状复杂化、空间自相关减弱等格局特征变化。这些空间格局特征的变化表明大型植被斑块趋于恢复,整体微环境的改善有利于单独生长的植物个体存活,整体上生态系统退化为裸地的风险降低。利用低空无人机遥感手段,对草方格生态恢复工程的植被恢复过程进行了详细、高分辨率的空间格局调查及分析,结合地面群落调查,从多个方面证明了草方格生态恢复措施的有效性。基于无人机的系统格局连续长期监测有助于深入理解干旱区生态恢复机理,对于科学开展荒漠化生态恢复措施也具有重要价值。     

生态系统的多稳态与突变

许多生态系统可能在短时间内发生难以预料的状态突变, 其中一些生态系统突变的机理可以用多稳态理论进行解释。近年来生态系统的多稳态和突变现象及其机理吸引了研究者和管理者的广泛关注。本文重点对生态系统多稳态的理论基础、识别方法及稳态转换发生的早期预警信号进行综述, 并基于典型生态系统过程对现实世界中可能观测到的稳态转换进行实例分析, 最后对多稳态概念框架和理论应用中的潜在争议进行讨论, 以期为非线性生态系统动态的理论研究、管理实践和生物多样性保护等提供参考。     

Rising variance: a leading indicator of ecological transition

Regime shifts are substantial, long-lasting reorganizations of complex systems, such as ecosystems. Large ecosystem changes such as eutrophication, shifts among vegetation types, degradation of coral reefs and regional climate change often come as surprises because we lack leading indicators for regime shifts. Increases in variability of ecosystems have been suggested to foreshadow ecological regime shifts. However, it may be difficult to discern variability due to impending regime shift from that of exogenous drivers that affect the ecosystem. We addressed this problem using a model of lake eutrophication. Lakes are subject to fluctuations in recycling associated with regime shifts, as well as fluctuating nutrient inputs. Despite the complications of noisy inputs, increasing variability of lake-water phosphorus was discernible prior to the shift to eutrophic conditions. Simulations show that rising standard deviation (SD) could signal impending shifts about a decade in advance. The rising SD was detected by studying variability around predictions of a simple time-series model, and did not depend on detailed knowledge of the actual ecosystem dynamics.     

A spatially explicit method for evaluating accuracy of species distribution models

Aim Models predicting the spatial distribution of animals are increasingly used in wildlife management and conservation planning. There is growing recognition that common methods of evaluating species distribution model (SDM) accuracy, as a global overall value of predictive ability, could be enhanced by spatially evaluating the model thereby identifying local areas of relative predictive strength and weakness. Current methods of spatial SDM model assessment focus on applying local measures of spatial autocorrelation to SDM residuals, which require quantitative model outputs. However, SDM outputs are often probabilistic (relative probability of species occurrence) or categorical (species present or absent). The goal of this paper was to develop a new method, using a conditional randomization technique, which can be applied to directly spatially evaluate probabilistic and categorical SDMs. Location Eastern slopes, Rocky Mountains, Alberta, Canada. Methods We used predictions from seasonal grizzly bear (Ursus arctos) resource selection functions (RSF) models to demonstrate our spatial evaluation technique. Local test statistics computed from bear telemetry locations were used to identify areas where bears were located more frequently than predicted. We evaluated the spatial pattern of model inaccuracies using a measure of spatial autocorrelation, local Moran’s I. Results We found the model to have non‐stationary patterns in accuracy, with clusters of inaccuracies located in central habitat areas. Model inaccuracies varied seasonally, with the summer model performing the best and the least error in areas with high RSF values. The landscape characteristics associated with model inaccuracies were examined, and possible factors contributing to RSF error were identified. Main conclusions The presented method complements existing spatial approaches to model error assessment as it can be used with probabilistic and categorical model output, which is typical for SDMs. We recommend that SDM accuracy assessments be done spatially and resulting accuracy maps included in model metadata.     

A test of critical thresholds and their indicators in a desertification‐prone ecosystem: more resilience than we thought

Theoretical models predict that drylands can cross critical thresholds, but experimental manipulations to evaluate them are non‐existent. We used a long‐term (13‐year) pulse‐perturbation experiment featuring heavy grazing and shrub removal to determine if critical thresholds and their determinants can be demonstrated in Chihuahuan Desert grasslands. We asked if cover values or patch‐size metrics could predict vegetation recovery, supporting their use as early‐warning indicators. We found that season of grazing, but not the presence of competing shrubs, mediated the severity of grazing impacts on dominant grasses. Recovery occurred at the same rate irrespective of grazing history, suggesting that critical thresholds were not crossed, even at low cover levels. Grass cover, but not patch size metrics, predicted variation in recovery rates. Some transition‐prone ecosystems are surprisingly resilient; management of grazing impacts and simple cover measurements can be used to avert undesired transitions and initiate restoration.     

Plant species as indicators of the extent of desertification in four sandy rangelands

We examined the distribution of plants in sandy rangelands with different degrees of desertification in (i) Horqin and Mu Us sandy lands in north China, (ii) Darfur district in north‐west Sudan and (iii) southern Tunisia. The severity of desertification in these areas was classified as light, moderate, severe or extreme. The following vegetation changes were observed with increasing severity of desertification: a decrease in the number of plant species, an increase in drought‐tolerant plants, a decrease in the proportion of palatable grasses and the occurrence of some species in only one category of desertification, whereas other species occurred in several categories. Plant species with unique niche requirements were identified and recommended as indicators of the degree of desertification for particular areas. We discuss the characteristics of species in areas with severe desertification and the method of using plant species as indicators of the extent of desertification.     

干旱区生态系统稳态转换及其预警信号——基于景观格局特征的识别方法

在日益加剧的气候变化和土地开垦、放牧等人类活动干扰下,具有多稳态特征的干旱区生态系统可能会经历从相对健康状态到退化状态的稳态转换,导致生态系统的功能下降。早期预警信号的识别是生态系统稳态转换研究的热点,也是管理实践中防止生态系统退化的关键环节。以往预警信号研究聚焦于通用信号如自相关性、方差等统计学指标,然而这些指标对于具有特定机制的干旱区生态系统可能并不适用。基于干旱区景观格局特征所发展起来的空间指标为生态系统稳态转换提供了独特的空间视角,对于理解干旱区生态系统退化过程和机理具有科学意义和实践价值。介绍了干旱区生态系统稳态转换现象及其转换机制;聚焦景观生态学的指标和方法,从空间视角总结基于干旱区景观格局特征的关键预警指标(植被覆盖度、植被斑块形态、植被斑块大小频率分布和水文连通性等),重点剖析这些关键指标的概念、量化方法、识别特征及其实践应用;最后针对指标的优势和局限性对未来的研究方向进行展望,包括发掘潜在景观指标,加强干旱区生态系统变化的多种驱动要素的相互作用机制研究,开展多时空尺度的实证研究,构建生态系统稳态转换预警信号的整体分析框架,以及加强指标阈值的量化研究等方面。     

Indicators of transitions in biological systems

In the face of global biodiversity declines, predicting the fate of biological systems is a key goal in ecology. One popular approach is the search for early warning signals (EWSs) based on alternative stable states theory. In this review, we cover the theory behind nonlinearity in dynamic systems and techniques to detect the loss of resilience that can indicate state transitions. We describe the research done on generic abundance‐based signals of instability that are derived from the phenomenon of critical slowing down, which represent the genesis of EWSs research. We highlight some of the issues facing the detection of such signals in biological systems – which are inherently complex and show low signal‐to‐noise ratios. We then document research on alternative signals of instability, including measuring shifts in spatial autocorrelation and trait dynamics, and discuss potential future directions for EWSs research based on detailed demographic and phenotypic data. We set EWSs research in the greater field of predictive ecology and weigh up the costs and benefits of simplicity vs. complexity in predictive models, and how the available data should steer the development of future methods. Finally, we identify some key unanswered questions that, if solved, could improve the applicability of these methods.     

生态系统多稳态研究进展

在多稳态的生态系统中,外力可能导致生态系统状态突然之间发生不可逆转的转变,从而达到一个新的平衡状态。但目前对多稳态理论的系统研究很少,如何使用预警信号来预测生态系统的状态转变依旧是个难题。通过多稳态理论的梳理提出了一个更加综合的多稳态定义,并以放牧模型为例,系统总结了多稳态理论的相关概念,将多稳态理论应用在生态系统演替和扰沌理论的解释中;通过对生态系统稳态转换预警信号的原理、优缺点和应用条件的分析,对不同尺度下多稳态的研究方法进行了归纳;最后提出了目前多稳态领域的研究问题和未来的研究重点。结果表明:(1)将时间和空间预警信号结合在一起,并量化正确预警信号的概率,对错误预警信号的比例进行加权,可能会提供更准确的稳态转换的预报。(2)定量观测试验适用于小尺度的研究,而较大尺度的研究则采用简化的模型来模拟研究,选择正确的尺度极有可能改变预警信号的可靠性。(3)结合多稳态理论研究生态系统临界转换和反馈控制机制,并将基于性状的特征指标和进化动力学纳入其中,是生态系统修复实践的重要研究方向。(4)将多稳态相关理论和生态保护管理政策的实践相结合,是多稳态理论未来应用的前景。本研究为多稳态理论和实践的...     

Directional climate change and potential reversal of desertification in arid and semiarid ecosystems

Our objective was to determine if long‐term increases in precipitation can maintain grasslands susceptible to desertification, and initiate a reversal of historic regime shifts on desertified shrublands. Perennial grass production and species richness in a multi‐year wet period were hypothesized to be greater than expected based on precipitation in a sequence of dry years. These responses were expected to differ for grasslands and shrublands with different dominant species and topo‐edaphic properties. Long‐term trends in desertification were documented using vegetation maps beginning in 1858, 1915, 1928, and 1998). These trends were compared with herbaceous and woody species responses to a sequence of dry (1994–2003) and wet years (2004–2008) for two grassland (uplands, playas) and three desertified shrubland types (honey mesquite, creosotebush, tarbush) in the Chihuahuan Desert. Analyses showed that both types of grasslands decreased in spatial extent since 1858 whereas areas dominated by mesquite or creosotebush increased. Production of upland grasslands in the wet period was greater than expected based on responses during the dry period whereas the relationships between species richness and precipitation was the same for both periods. Precipitation was not important to responses in playa grasslands in either period. For all ecosystem types, the production response in wet years primarily was an increase in herbaceous plants, and the most pronounced responses occurred on sandy sites (upland grasslands, mesquite shrubland). Results suggest that multiple wet years are needed to initiate a sequence of grass establishment and survival processes that can maintain upland grasslands without management inputs and lead to a state change reversal in desertified shrublands. Restoration strategies need to take advantage of opportunities provided by future climates while recognizing the importance of ecosystem type.     

A spatially explicit analysis of seedling recruitment in the terrestrial orchid Orchis purpurea

Seed dispersal and the subsequent recruitment of new individuals into a population are important processes affecting the population dynamics, genetic diversity and spatial genetic structure of plant populations. Spatial patterns of seedling recruitment were investigated in two populations of the terrestrial orchid Orchis purpurea using both univariate and bivariate point pattern analysis, parentage analysis and seed germination experiments. Both adults and recruits showed a clustered spatial distribution with cluster radii of c. 4-5 m. The parentage analysis resulted in offspring-dispersal distances that were slightly larger than distances obtained from the point pattern analyses. The suitability of microsites for germination differed among sites, with strong constraints in one site and almost no constraints in the other. These results provide a clear and coherent picture of recruitment patterns in a tuberous, perennial orchid. Seed dispersal is limited to a few metres from the mother plant, whereas the availability of suitable germination conditions may vary strongly from one site to the next. Because of a time lag of 3-4 yr between seed dispersal and actual recruitment, and irregular flowering and fruiting patterns of adult plants, interpretation of recruitment patterns using point patterns analyses ideally should take into account the demographic properties of orchid populations.     

短期极端干旱事件干扰后退化沙质草地群落恢复力稳定性的测度与比较

利用对不同沙漠化程度的6个沙质草地群落样地的调查资料,并通过构建恢复力指数,尝试性地对沙漠化过程草地群落在经历约为0.5个生长季的短时间尺度极端干旱事件干扰后、在当年后0.5个生长季表现出的恢复力稳定性进行了定量测定与比较。结果表明:6个不同退化程度沙质草地群落在降水条件恢复后具有反应快速和补偿生长的能力,从而表现出良好的恢复力,即使最严重沙漠化程度的群落也恢复到甚至超过了其在干旱前的状况。各群落恢复力综合指数在2.21-1.16之间,分别以多度、高度、盖度和生物量指标计算的恢复力分指数在4.69-1.23,1.21-0.98,1.59-1.15和1.28-1.00之间,基本呈随沙漠化程度提高而减小的趋势。恢复力指数的计算结果表明,在经历短时间尺度干旱事件干扰后,所研究的退化沙质草地群落具有以较强的恢复力维持植被稳定的倾向和能力。群落之间的比较显示,恢复力随沙漠化程度的发展而降低。对群落恢复力来源与构成进行的分析表明,以多度指标计算的恢复力分指数最大,显示各群落都有充足的种源条件和土壤种子库为群落恢复力提供基本保障条件;群落恢复力不仅来源于1年生植物,也来源于多年生植物;一些群落的优势物种在恢复过程中发生了快速转换。通过综合分析本研究以群落内部生态过程为基础对群落恢复力进行的数量测定结果以及对该群落在同一干旱事件干扰下的抵抗力进行的已有研究结果,认为退化沙质草地群落较低的抵抗力和较高的恢复力都说明了植被稳定性对降水条件的依赖不可替代和无法超越。因而,群落在短时间尺度上具有随降水波动的必然性和不稳定性,而在较长时间尺度上又具有主要由群落恢复力所维持的稳定性;恢复过程中发生的群落优势物种快速转换现象是生物多样性的表现形式之一,进一步证明生物多样性对维持生态系统功能和促进植被稳定性具有重要作用,是植被生态系统的一个基本特征。     

河西走廊天然固沙植被区地表甲虫多样性及其对沙漠化的指示作用

干旱、半干旱区沙漠化强烈影响动植物分布及多样性,地表甲虫是荒漠中主要的动物类群,它们对沙漠化引起的植被和土壤环境变化响应十分敏感。鉴于此,以河西走廊中部张掖绿洲外围的天然固沙植被区作为研究区,依据沙漠化发育程度选择流动沙丘（ASD）、丘间低地（IL）、半固定（SFSD）和固定沙丘（FSD）4种生境,调查了地表甲虫群落组成及影响甲虫分布的植被和土壤环境。研究发现,4种生境地表甲虫群落组成明显不同并存在季节变异,5月ASD与IL、SFSD和FSD生境地表甲虫群落的相异性大于8月。5月和8月SFSD生境地表甲虫活动密度均显著高于其他生境,8月FSD生境地表甲虫多样性指数显著高于其他生境。不同大小甲虫对沙漠化的响应模式不同,大中型甲虫对沙漠化的响应较小型甲虫敏感,这在5月表现尤为明显。地表甲虫与环境因子的RDA分析结果表明,12个植被和土壤环境因子解释了49.8%的地表甲虫群落变异,其中植被环境解释了甲虫群落变异的16.3%,土壤环境解释了甲虫群落变异的4.2%,植被和土壤环境相互作用解释了甲虫群落变异的29.3%。pRDA分析结果表明,草本物种丰富度、灌木盖度、土壤有机碳含量和粗砂含量是影响地表甲虫分布的主要环境因子,它们解释了43.7%的地表甲虫群落变异。Pearson相关分析表明,草本物种丰富度与地表甲虫活动密度呈显著正相关,而与地表甲虫均匀度呈显著负相关;灌木盖度与地表甲虫多样性呈显著正相关;地表甲虫物种丰富度与灌木盖度和草本物种丰富度均呈显著正相关。此外,研究还发现戈壁琵甲、克氏扁漠甲、中华砚甲和甘肃齿足象可以用于指示FSD生境,东鳖甲属昆虫可以用于指数SFSD生境,谢氏宽漠王可以用于指示IL及ASD生境。     

典型喀斯特地区石漠化景观格局对土地利用变化的响应

土地利用是人类活动最基本的表现形式,探讨石漠化与土地利用变化之间的响应关系,对于石漠化治理和区域的可持续发展是非常重要的。基于贵州道真县2005年、2015年LANDSAT和石漠化数据,再利用ENVI 5.3进行监督分类,将道真县土地利用分为8种类型。通过景观格局空间分析技术和3S技术,对道真县土地利用时空演变和石漠化景观格局进行综合分析,结果表明:(1) 2005—2015年间,道真县建设用地和灌木林地面积增加,大部分灌木林地由水田和旱地转化而来,其面积增加了7.51%,建设用地增加了1.30%。(2)近10年间,研究区石漠化等级间的转移表现为轻、中、重度转化为潜在石漠化,其斑块转移面积分别为11.26、38.79、2.71 km2,表明研究区石漠化景观得到了恢复,低等级石漠化斑块面积增加,降低了原有高等级石漠化斑块的优势度。(3) 2005—2015年间道真县土地利用和石漠化景观格局,多样性指数分别下降了0.6434和2.4309,均匀度指数各减少了0.0552和0.5436,分维度指数各提高了0.0061和0.0801,蔓延度指数各增加0.1751、25.5396和聚合度指数分别增加1.8688和2.9112,景观形状指数分别减少0.9812和4.536,石漠化景观格局的变化对应土地利用景观格局指数的变化,随着人们土地利用方式的改变,石漠化也发生相应的改变。通过该研究的进行,有助于提高人们对石漠化和土地利用景观格局的认识,基于景观生态学背景对石漠化治理成效进行评估,为之后的石漠化治理工作的进行及研究提供了参考。     

How noise and coupling influence leading indicators of population extinction in a spatially extended ecological system

Anticipating critical transitions in spatially extended systems is a key topic of interest to ecologists. Gradually declining metapopulations are an important example of a spatially extended biological system that may exhibit a critical transition. Theory for spatially extended systems approaching extinction that accounts for environmental stochasticity and coupling is currently lacking. Here, we develop spatially implicit two-patch models with additive and multiplicative forms of environmental stochasticity that are slowly forced through population collapse, through changing environmental conditions. We derive patch-specific expressions for candidate indicators of extinction and test their performance via a simulation study. Coupling and spatial heterogeneities decrease the magnitude of the proposed indicators in coupled populations relative to isolated populations, and the noise regime and the degree of coupling together determine trends in summary statistics. This theory may be readily applied to other spatially extended ecological systems, such as coupled infectious disease systems on the verge of elimination.     

Reorganization of a large marine ecosystem due to atmospheric and anthropogenic pressure: a discontinuous regime shift in the Central Baltic Sea

Marine ecosystems such as the Baltic Sea are currently under strong atmospheric and anthropogenic pressure. Besides natural and human-induced changes in climate, major anthropogenic drivers such as overfishing and anthropogenic eutrophication are significantly affecting ecosystem structure and function. Recently, studies demonstrated the existence of alternative stable states in various terrestrial and aquatic ecosystems. These so-called ecosystem regime shifts have been explained mainly as a result of multiple causes, e.g. climatic regime shifts, overexploitation or a combination of both. The occurrence of ecosystem regime shifts has important management implications, as they can cause significant losses of ecological and economic resources. Because of hysteresis in ecosystem responses, restoring regimes considered as favourable may require drastic and expensive management actions. Also the Baltic Sea, the largest brackish water body in the world ocean, and its ecosystems are strongly affected by atmospheric and anthropogenic drivers. Here, we present results of an analysis of the state and development of the Central Baltic Sea ecosystem integrating hydroclimatic, nutrient, phyto- and zooplankton as well as fisheries data. Our analyses of 52 biotic and abiotic variables using multivariate statistics demonstrated a major reorganization of the ecosystem and identified two stable states between 1974 and 2005, separated by a transition period in 1988–1993. We show the change in Baltic ecosystem structure to have the characteristics of a discontinuous regime shift, initiated by climate-induced changes in the abiotic environment and stabilized by fisheries-induced feedback loops in the food web. Our results indicate the importance of maintaining the resilience of an ecosystem to atmospherically induced environmental change by reducing the anthropogenic impact.     

浅水湖泊稳态转换预警识别方法局限与展望

浅水湖泊水体底泥交换强烈,极易受人类活动干扰,超过一定阈值即可能发生灾难性的稳态转换,对其有效识别有助于湖泊富营养化的及时防控与修复。浅水湖泊稳态转换可通过系统关键变量(叶绿素、溶解氧、浮游动物、鱼类等)的时间序列(判别不同稳态)、预警信号及阈值等进行识别,其中预警识别可为湖泊生态系统稳态转换提供预判信息,有利于早预警早行动。目前,浅水湖泊稳态转换预警识别因子(方差及自相关性等)主要用于"临界慢化"现象,但在强大外力作用、强烈随机扰动及极端事件下,这些"临界慢化"因子则可能出现误用或错用。基于浅水湖泊基本特征,针对稳态转换的不同驱动机制,探讨"临界慢化"因子的适用性与局限性,并展望其未来发展方向,旨在为湖泊生态系统稳态转换预警识别提供科学参考。     

韧性：三角洲地区规划转型的新理念

三角洲地区经过近几十年的快速发展,在城市建设方面取得举世瞩目的成就,然而长期积累的生态问题也更加突出,暴露出的空间脆弱性问题日益显著。面对自然基底脆弱、自然灾害扰动趋势增强等因素在时空上的高度叠合,迫切需要提升三角洲地区应对未来不确定性扰动的能力。首先从景观角度分析三角洲地区自然环境的特殊性,提出韧性规划是对现有三角洲地区规划转型的论点,认为鲁棒性、适应性、学习—转化能力是三角洲地区韧性规划的核心能力,系统性、协同性、底线性、预判性是三角洲地区韧性规划的主要思维特征。其次,进一步从优化整体格局、构建流动性载体、加强对韧性技术策略的研究和应用、重视跨尺度协作与管理等方面提出了构建“格局—连通—关键点”的韧性规划框架。最后,阐述韧性规划作为三角洲地区规划转型的新理念,应用于具体案例的空间布局时须以人为本,依托自然环境,以自然流动性为规划导向;须基于预判式过程,充分构想能够应对不同情景的预案;须整合生态智慧与现代技术,明晰兼顾鲁棒性与适应性的功能分区管治体系。     

Influences of 20th‐century warming at the upper tree line contingent on local‐scale interactions: evidence from a latitudinal gradient in the Rocky Mountains,USA

Aims Twentieth‐century climate, the spatial pattern of tree establishment and positive feedback influence upper tree line ecotones. Here, I investigate how these factors interact to gain a more holistic understanding of how broad‐scale abiotic and local‐scale site conditions regulate tree establishment within upper tree line ecotones. Location A latitudinal gradient (c. 35–45° N) in the US Rocky Mountains. Study sites (n= 22) were located in the Bighorn (BH), Medicine Bow (MB), Front Range (FR) and Sangre de Cristo (SDC) mountain ranges. Methods Dendroecological techniques were used to reconstruct tree establishment dates that were compared with 20th‐century climate data using correlation and regime shift analyses. Spatial patterns of tree establishment were analysed by Ripley's K and used to determine local‐scale interactions capable of ameliorating broad‐scale climate inputs through positive feedback. Results Significant correlations (P < 0.01) between tree establishment and climate were confined to the FR, where a positive correlation was found with summer (June–August) and cool season (November–April) temperature range (T_max?T_min). These trees were almost exclusively situated in a random spatial pattern. Similar patterns exist in the BH, yet their establishment was contingent on the availability of local shelter in the lee of boulders. Trees in the MB and SDC were primarily clustered in space and had no significant correlations with climate. Considerable lag times exist between regime shift changes in climate towards more favourable growing conditions and corresponding shifts in tree establishment in all mountain ranges except the FR, where synchronous shifts occurred in the early 1950s. Main conclusions These results suggest that the influence of broad‐scale climate on upper tree line dynamics is contingent on the local‐scale spatial patterns of tree establishment and related influences of positive feedback. This research has important implications for understanding how vegetation communities will respond to global climate change.     

The effect of aquatic and terrestrial habitat characteristics on occurrence and breeding probability in a montane amphibian: insights from a spatially explicit multistate occupancy model

Understanding species distribution and predicting range shifts are major goals of ecology and biogeography. Obtaining reliable predictions of how species distribution might change in response to habitat change requires knowledge of habitat availability, occupancy, use for breeding, and spatial autocorrelation in these parameters. Amphibians in alpine areas provide an excellent model system for disentangling habitat drivers of occupancy from that of breeding while explicitly accounting for spatial autocorrelation. We focused on the widespread common frog (Rana temporaria) inhabiting alpine lakes in the Southern Carpathians, Romania. We used single season multistate occupancy models developed to account for imperfect detection and spatial autocorrelation to estimate the occupancy and breeding probabilities and to evaluate their response to habitat characteristics. We found that frogs do not occur in all water bodies [occupancy probability: 0.697; 95% credible interval (0.614, 0.729)] and do not breed in a substantial proportion of water bodies where they occur [breeding probability conditional on occupancy: 0.707; 95% credible interval (0.670, 0.729)]. Habitat characteristics explain water body occupancy but not breeding probability; and altitude, water body surface area, water body sinuosity and permanency, presence of invertebrates, and grazing along the banks all had positive effects on occupancy. We also detected strong spatial autocorrelation in occupancy and breeding probabilities. Thus, our results indicate that habitat choice by montane amphibians is influenced by both spatial autocorrelation and habitat characteristics. Because spatial autocorrelations matter and because the presence of adults is not the same as the presence of a reproducing population, it will be difficult to predict the effects of habitat change on high altitude amphibian populations.