黄土高原森林植被对流域径流的调节作用

对黄土高原腹地子午岭典型森林流域与非森林流域年径流变化的对比分析结果表明,森林流域径流年内分配比非森林流域相对均匀,汛期（6～9月）总径流量减少了8.9mm（葫芦河比蒲河）和7.1mm（合水川比东川）,枯季径流与汛期降水及枯水季节降水的回归分析可见,森林植被能将雨季蓄积的部分降水转化为地下径流,增大枯水季节的径流量,但由于黄土区土层深度,植被蒸腾耗水强烈,森林植被对枯水期河川径流的调节作用十分有限,森林植被对10～12月径流总的补枯效应仅为1.69mm（葫芦河比蒲河）和0.5mm（合水川比东川）,对1～4月径流无调节作用,说明森林植被拦蓄的大部分降雨被植物吸收利用,消耗于蒸腾,从而揭示了森林植被对河川径流的削洪补枯效应及其机理。     

基于氢氧同位素示踪的黄土区不同植被类型小流域降雨-径流分割

流域径流过程及其组分来源识别是水资源合理利用的前提。为明确植被类型对流域径流组分的影响与定量贡献,本研究以山西吉县蔡家川主沟流域及5个不同植被类型小流域为研究对象,监测2场典型降雨产流过程及其氢氧同位素时空变化特征,探讨小流域径流过程差异及其组分来源。结果表明：在中雨条件下,事件水对各个流域河道流量的贡献率为封禁森林(94.3%)>蔡家川主沟(83.1%)>农牧复合(64.3%)>人工-次生林(52.4%)>农地(0.3%)>次生林(0.0%);而在小雨条件下,人工-次生林(52.4%)>封禁森林(58.5%)>农地(40.6%)>次生林(15.8%)>农牧复合(12.5%)>蔡家川主沟(9.3%),次生林、封禁森林小流域事件水对径流贡献率大于人工林,次生林具有更强的径流调蓄能力。封禁森林、农牧复合流域在中雨强度条件下事件水的贡献率大于小雨强度条件,而农地、人工-次生林、次生林流域则相反。事件水对林地小流域径流贡献率大于农地小流域,可能与农地小流域沟口建有淤地坝有关。本研究结果可为晋西黄土区水源涵养和径流变化归因分析提供科学依...     

长江上游森林影响流域水文过程模拟分析

用森林流域水文模型(FCHM)模拟分析长江上游森林植被变化下的平通河流域和刘家河流域森林水文过程。可知随着两个流域森林覆盖率(FR)的提高,林冠截留量的增加和土壤入渗能力的改善,使得径流成分比例也随之发生变化,地表径流Rf逐渐减少,快速流转换为慢速流,因此延迟了流域降水汇流时间,洪峰流量得以削减。以平通河为例,当该流域全部被森林覆盖以后,则流域百年一遇的设计洪水标准可由非森林地时的4520m3/s降到3380m3/s,因此森林的存在可大大提高流域的防洪能力;而两个流域又由于区域结构等条件的不同,使得流域径流成分所占比例不同。其中平通河流域径流成分主要以浅层径流Rs和深层径流Rp为主,而刘家河流域径流成分主要以壤中流Ri为主,且都随森林覆盖的增加而有所增加。不同的径流成分为流域蒸散发带来了不同的水分条件,因此流域蒸散发量随着森林覆盖率的增加各有不同的变化趋势。其中平通河流域随着森林覆盖率的增加,流域蒸散发总量将由非森林地时候的373.3mm减少至289.3mm,根据水量平衡原理,该流域径流总量则会增加,呈流域径流正效应(23.7%);而后者流域则相反,随着森林覆盖率的增加,流域蒸散发总量反而会逐步增加,则流域径流总量会随之减少,呈流域径流负效应(-8.6%)。     

中国森林生态系统地表径流调节特征

径流调节是森林生态系统重要生态服务功能之一,包含着大气、水分、植被和土壤等生物物理过程,其变化将直接影响区域气候水文、植被和土壤等状况,是区域生态系统状况的重要指示器。在区域尺度上评估森林生态系统地表径流特征,对于科学认识和合理保护森林生态系统水源涵养功能具有重要意义。以森林生态系统定位监测数据为基础,探讨地表径流与降水,径流系数与植被的关系,建立径流系数与植被的回归方程,分析全国森林生态系统地表径流调节特征。结果表明:(1)各森林类型地表径流与降水相关性显著,其对地表径流的影响为37%—76%。此外,径流系数与植被也显著相关,其对径流系数的解释能力为27%—47%。(2)基于植被覆盖数据,通过植被与径流系数回归方程估算全国森林生态系统的地表径流调节特征。全国各森林生态系统径流调节能力存在差异,强弱顺序为:落叶针叶林落叶阔叶林针阔混交林常绿针叶林常绿阔叶林。     

漓江上游典型森林植被对降水径流的调节作用

利用野外同步长期定位观测林外降雨、地表径流和河川径流的方法,对漓江上游典型森林植被的生态水文过程进行观测研究。结果表明:1)流域降水年内分配极不均匀,50a年降雨量总体变化趋势不明显。林冠截留受林外降雨特征的影响,也与植被类型密切相关。2)地表径流平均滞后时间为70 min。在连续降雨的情况下,降雨滞后效应不再明显,甚至出现地表径流与降雨同步的现象,小降雨可能产生大的地表径流,从而加大流域在雨季发生洪灾的风险。3)湿季径流系数略大于旱季,干季降水量减少,且森林植被消耗大量水分,减少了枯水期径流的产生,增大发生旱灾的风险。森林植被延长河川径流持续时间,使一次持续18 d的降水过程形成的径流,在降水停止后能延续24 d。降雨后退水持续时间与前期降水及后期降水叠加有关。目的为揭示漓江上游森林植被对降水径流的调节作用,客观评估漓江上游水资源潜力、加强流域水资源管理和森林经营提供科学依据。     

小兴安岭森林采伐对河川径流的影响

采用大流域径流测定与小流域对比实验相结合的方法,利用35年的径流和森林资源变化资料,对小兴安岭林区森林采伐后河川径流发生的一系列变化进行了全面系统的研究.结果表明,森林采伐后营造落叶松人工林,造林初期10年内,河川径流量表现为增加趋势;随着落叶松人工林的不断生长和郁闭成林,采伐流域的径流量逐渐减少,并趋于采伐前水平或低于采伐前水平（与对照流域相比）.河川年径流量与年降水量、森林采伐面积及更新造林面积密切相关.森林采伐面积与年径流量呈正相关,森林采伐能增加河川年径流量;更新造林面积与年径流量呈负相关,更新造林能减少年径流量.而森林采伐对洪峰流量和融雪径流量均有显著增加作用.     

泾河流域上游土石山区和黄土区森林覆盖率变化的水文影响模拟

泾河流域上游是黄土高原的重要水源地和退耕还林工程区,在较大空间尺度上定量评价区内森林覆盖增加的水文影响对科学指导林业生态环境建设、保障区域水安全和可持续发展均有重要意义。为了在尽量排除地形、土壤、气候等作用的基础上定量评价森林的影响,将泾河上游划分为土石山区和黄土区,分别制定了多种森林恢复情景,利用分布式流域生态水文模型(SWIM)模拟评价了森林覆盖率及其空间分布变化对流域年蒸散量、年产流量、年地下水补给量、年土壤深层渗漏量及日径流洪峰的影响。土石山区模拟结果表明,增加森林覆盖将增加流域蒸散和减少流域产流,如现有森林覆盖(占全流域面积比例为13.8%)情景与现有森林变为草地(占全流域面积比例为0)情景相比时,流域年蒸散量从445.4 mm变为427.7 mm(减少了17.4 mm和4%);年产流量从42.4 mm变为53.5 mm(增加了11.1 mm和26.3%),年地下水补给量从61.6 mm变为76.9 mm(增加了15.3 mm和24.8%),年深层渗漏量从72.9 mm变为88.3 mm(增加了17.7 mm和24.3%);平均森林覆盖率每增加10%,导致流域年蒸散量增加12.8 mm,年产流量减少8.0 mm,年地下水补给量减少11.1 mm。在比较干旱和土层深厚的黄土区,增加森林覆盖将同样增大流域蒸散和减少流域产流,但变化幅度明显小于降水相对丰富和土层浅薄的土石山区,平均森林面积增加10%导致流域年蒸散量增加9.0 mm,年产流量减少4.5 mm,年地下水补给量减少8.8 mm;此外,在较缓坡面造林的水文影响大于较陡坡面造林。从森林水文影响的年内变化来看时,森林覆盖率升高的水文影响在土石山区和黄土区也有差别,如土石山区5—7月份的蒸散显著增加,5—10月份的深层渗漏均有减少;而黄土区是蒸散量在5—10月均有增加,深层渗漏在7—10月份显著减少。另外,土石山区森林覆盖率增加对日径流峰值的影响不显著,而黄土区则能明显削弱,这可能主要是因土石山区的高石砾含量土壤的渗透性能明显高于黄土区的黄土,而黄土区的森林能够明显改善土壤入渗性能和减少地面径流形成。     

基于扩展的Budyko模型定量评估平江流域森林恢复和气候变异对季节性径流的影响

流域季节性径流变化反映了年内水资源的动态特征。在以森林为主的流域中,森林变化和气候变异被普遍认为是影响流域水文过程的两大驱动因素。因此在全球气候变化背景下,研究流域森林恢复和气候变异对流域季节性径流的影响,可为协调区域碳-水关系和制订可持续的森林经营管理策略提供参考。选择鄱阳湖流域上游的平江流域为研究对象,根据流域历史森林覆盖率变化情况,将研究期划分为参考期（1961-1985）和森林恢复期（1986-2006）,采用Mann-Kendall趋势分析研究流域长时期水文气象数据是否存在显著变化趋势。同时引入月干旱指数（潜在蒸散发和有效降雨的比率）,将一年定义为能量限制季（1-6月）和水分限制季（7-12月）,结合扩展的Budyko模型定量分析平江流域森林恢复和气候变异对季节性径流的相对贡献。在本研究流域整个研究期内（1961-2006）,通过Mann-Kendall趋势分析发现,研究流域水分限制季径流呈现显著增加趋势,而能量限制季水文和气候变量变化趋势均不显著。其次,相较于参考期,流域森林恢复使能量限制季径流降低了11.71 mm/a （24.40%）,使水分限制季径流增加了12.27 mm/a （17.23%）。同时,气候变异导致能量限制季径流减少了36.28 mm/a （75.60%）,而使水分限制季径流增加了58.94 mm/a （82.77%）。上述研究结果表明,森林恢复对径流影响具有累积效应。森林恢复对季节性径流具有积极的调节作用,同时季节性径流对森林恢复的响应存在时间差,而且森林恢复对径流的影响在能量限制季和水分限制季具有相互抵消的作用,气候变异与森林恢复的影响效应类似。此外,本研究也证实,平江流域季节性径流变化主要是受气候变化主导,但森林恢复对季节性径流的贡献也不容忽视。     

黄土地区森林植被水土保持作用研究

 选取黄土地区不同森林植被1)类型的两组4个试验流域为研究对象,通过6年(1988～1993)近70场暴雨洪水的实地观测,对次暴雨(是指一场降雨从开始到终止这一时段)产沙量同森林植被的关系进行了定量分析,提出了含森林覆被率的5因子次暴雨产沙模型,进而对森林植被的水土保持效益进行了分析。木家岭小流域和庙沟小流域相比,无林流域的产沙量比森林流域高33.4倍,森林的拦沙效益达到96.80％;木家岭流域和庙沟流域相比,少林流域比多林流域产沙量高4.3倍,森林的相对拦沙效益可达75.53％。同时通过黄土地区森林植被减沙作用的分析,提出了森林植被的拦沙量计算公式,据此可以求得不同降雨条件下,对比流域森林植被的拦沙量。     

濂水流域降雨变化和景观格局演变的径流效应

降雨和景观格局是影响流域径流过程的两大主要因素,开展二者的径流效应研究对流域水资源管理、生态建设等具有重要意义。本研究以赣南红壤丘陵区的濂水流域为对象,基于1958—2020年的降雨、径流和土地利用数据,分析降雨、景观格局和径流的变化特征,以及降雨、景观格局与年径流、洪枯径流的关系。结果表明: 研究期间,流域年降雨量、年径流量、年最大1 d径流量均呈非显著下降趋势,年最小1 d径流量呈非显著上升趋势且年际变化幅度最大;有林地为流域内占比最高的景观类型,其他林地的变化最剧烈;景观水平上,流域的Shannon多样性指数、Shannon均匀度指数、斑块密度、景观形状指数分别由1980年的1.125、0.541、0.667、16.925上升至2020年的1.348、0.614、0.731、18.172,景观蔓延度指数由1980年的68.237下降至2020年的64.293,流域整体景观多样性、破碎化程度、形状复杂程度提高,空间分布趋于均匀,连通性降低。降雨量与年径流、洪水径流、枯水径流的相关系数分别为0.907、0.594、0.558;类型水平上,耕地减少对年径流、洪枯径流的影响均较大,而景观水平上的整体变化促进了年径流和洪水径流减少、枯水径流增加。降雨变化和景观格局演变对年径流、洪水径流和枯水径流变化的贡献率分别为17.8%、82.2%,1.5%、98.5%和-8.8%、108.8%。研究成果可为流域景观格局配置、水土流失综合治理等提供理论参考。     

Evidence for a Regime Shift in Nitrogen Export from a Forested Watershed

In this study, we document a functional regime shift in stream inorganic nitrogen (N) processing indicated by a major change in N export from a forested watershed. Evidence from 36 years of data following experimental clearcut logging at Coweeta Hydrologic Laboratory, NC, suggests that forest disturbance in this area can cause elevation of dissolved inorganic N (DIN) loss lasting decades or perhaps longer. This elevation of N export was apparently caused by an initial pulse of organic matter input, reduced vegetation uptake, increased mineralization of soil organic N, and N fixation by black locust-associated bacteria following clearcut logging. In forested reference watersheds at Coweeta, maximum DIN concentration occurs in summer when base flow is low, but the clearcut watershed shifted to a pattern of maximum winter DIN concentration. The seasonal pattern of DIN concentration and export from reference watersheds can be explained by terrestrial and in-stream processes, but following clearcutting, elevated DIN availability saturated both terrestrial and in-stream uptake, and the N export regime became dominated by hydrologic transport. We suggest that the long-term elevation of stream DIN concentration and export along with the changes in seasonality of DIN export and the relationship between concentration and discharge represent a functional regime shift initiated by forest disturbance.     

Control of Nitrogen Loss from Forested Watersheds by Soil Carbon:Nitrogen Ratio andTree Species Composition

Leaching losses of nitrate from forests can have potentially serious consequences for soils and receiving waters. In this study, based on extensive sampling of forested watersheds in the Catskill Mountains of New York State, we examine the relationships among stream chemistry, the properties of the forest floor, and the tree species composition of watersheds. We report the first evidence from North America that nitrate export from forested watersheds is strongly influenced by the carbon:nitrogen (C:N) ratio of the watershed soils. We also show that variation in soil C:N ratio is associated with variation in tree species composition. This implies that N retention and release in forested watersheds is regulated at least in part by tree species composition and that changes in species composition caused by introduced pests, climate change, or forest management could affect the capacity of a forest ecosystem to retain atmospherically deposited N. Received 4 March 2002; Accepted 4 June 2002.     

黄土高原不同植被覆盖对流域水文的影响

以山西省吉县蔡家川流域为对象,研究了植被覆盖类型对流域水文的影响.结果表明:不同植被覆盖的流域年径流系数分别为:林地流域1.6%～2.3%,以农、牧为主的流域3.1%～3.9%;各流域基流系数差异显著,人工林流域为零,次生林为主的流域1.0%～1.5%,以农、牧为主的流域2.5%～2.8%;在雨季人工林流域的径流总量是次生林流域的3.37倍、农地流域的1.9倍,而农地流域的基流量是次生林流域的2.2倍;短历时高强度降雨条件下,人工林流域、次生林流域地表径流量分别是农地流域的10.8倍和2.2倍;在历时较长的暴雨条件下,人工林流域单位面积上的洪峰流量是农地流域的3.4倍,次生林流域的6.9倍;在长历时、大雨量条件下,农地流域的径流量是次生林流域的1.8倍.水平梯田的水源涵养功能与次生林植被相当,次生林植被的水源涵养功能远好于人工植被,在水资源短缺的黄土高原应提倡植被的自然恢复.     

Interactive influences of ozone and climate on streamflow of forested watersheds

The capacity of forests to mitigate global climate change can be negatively influenced by tropospheric ozone that impairs both photosynthesis and stomatal control of plant transpiration, thus affecting ecosystem productivity and watershed hydrology. We have evaluated individual and interactive effects of ozone and climate on late season streamflow for six forested watersheds (38–970 000 ha) located in the Southeastern United States. Models were based on 18–26 year data records for each watershed and involved multivariate analysis of interannual variability of late season streamflow in response to physical and chemical climate during the growing season. In all cases, some combination of ozone variables significantly improved model performance over climate‐only models. Effects of ozone and ozone × climate interactions were also consistently negative and were proportional to variations in actual ozone exposures, both spatially across the region and over time. Conservative estimates of the influence of ozone on the variability (R²) of observed flow ranged from 7% in the area of lowest ozone exposure in West Virginia to 23% in the areas of highest exposure in Tennessee. Our results are supported by a controlled field study using free‐air concentration enrichment methodology which indicated progressive ozone‐induced loss of stomatal control over tree transpiration during the summer in mixed aspen‐birch stands. Despite the frequent assumption that ozone reduces tree water loss, our findings support increasing evidence that ozone at near ambient concentrations can reduce stomatal control of leaf transpiration, and increase water use. Increases in evapotranspiration and associated streamflow reductions in response to ambient ozone exposures are expected to episodically increase the frequency and severity of drought and affect flow‐dependent aquatic biota in forested watersheds. Regional and global models of hydrologic cycles and related ecosystem functions should consider potential interactions of ozone with climate under both current and future warmer and ozone‐enriched climatic conditions.     

Climate variability masks the impacts of land use change on nutrient export in a suburbanizing watershed

Suburbanization negatively impacts aquatic systems by altering hydrology and nutrient loading. These changes interact with climate and aquatic ecosystem processes to alter nutrient flux dynamics. We used a long term data set (1993–2009) to investigate the influence of suburbanization, climate, and in-stream processes on nitrogen and phosphorus export in rivers draining the Ipswich and Parker River watersheds in northeastern MA, USA. During this timeframe population density increased in these watersheds by 14 % while precipitation varied by 46 %. We compared nutrient export patterns from the two larger watersheds with those from two nested headwater catchments collected over a nine year period (2001–2009). The headwater catchments were of contrasting, but stable, land uses that dominate the larger watersheds (suburban and forested). Despite ongoing land use change and an increase in population density in the mainstem watersheds, we did not detect an increase in dissolved inorganic nitrogen (DIN) or PO₄ concentration or export over the 16-year time period. Inter-annual climate and associated runoff variability was the major control. Annual DIN and PO₄ export increased with greater annual precipitation in the Ipswich and the Parker River watersheds, as well as the forested headwater catchment. In contrast, annual DIN export fluxes from the suburban headwater catchment were less affected by precipitation variability, with inter-annual export fluxes negatively correlated with mean annual temperature. The larger watershed exports diverged from headwater exports, particularly during summer, low-flow periods, suggesting retention of DIN and PO₄. Our study shows suburban headwater exports respond to inter-annual variation in runoff and climate differently than forested headwater exports, but the impacts from headwater streams could be buffered by the river network. The net effect is that inter-annual variation and network buffering can mitigate higher nutrient exports from larger suburbanizing watersheds over decadal time periods.     

河流流量对流域下垫面特性的响应

以美国切斯比克湾地区为例,对该区域150个小流域的下垫面特性(包括土地利用类型、地面不透水系数和土壤物理属性)进行了提取,根据1984—2004年间逐日流量观测数据计算出了33个水文指标,运用逐步回归方法在不同地理区分析了9种下垫面特性对其中17个重要水文指标的影响。结果表明:随着草地和林地比例的增加,流量趋于减小、流量变化趋于稳定,随着建设用地和不透水层的增加,流量增加、流量变化剧烈,随着土壤水文组等级的升高,流量减少;在整个切斯比克湾流域,对流域下垫面特性响应最为显著的水文指标是高脉冲个数及历时,在阿巴拉契亚高地地区响应最为显著的水文指标是年极值流量、高脉冲个数及历时,在皮德蒙特山地响应最为显著的水文指标是高脉冲个数及历时,在沿海平原地区响应最为显著的水文指标是高脉冲个数及历时、流量变化的速率与频率。     

Deforestation of watersheds of Panama: nutrient retention and export to streams

A series of eight watersheds on the Pacific coast of Panama where conversion of mature lowland wet forest to pastures by artisanal burning provided watershed-scale experimental units with a wide range of forest cover (23, 29, 47, 56, 66, 73, 73, 91, and 92 %). We used these watersheds as a landscape-scale experiment to assess effects of degree of deforestation on within-watershed retention and hydrological export of atmospheric inputs of nutrients. Retention was estimated by comparing rainfall nutrient concentrations (volume-weighted to allow for evapotranspiration) to concentrations in freshwater reaches of receiving streams. Retention of rain-derived nutrients in these Panama watersheds averaged 77, 85, 80, and 62 % for nitrate, ammonium, dissolved organic N, and phosphate, respectively. Retention of rain-derived inorganic nitrogen, however, depended on watershed cover: retention of nitrate and ammonium in pasture-dominated watersheds was 95 and 98 %, while fully forested watersheds retained 65 and 80 % of atmospheric nitrate and ammonium inputs. Watershed forest cover did not affect retention of dissolved organic nitrogen and phosphate. Exports from more forested watersheds yielded DIN/P near 16, while pasture-dominated watersheds exported N/P near 2. The differences in magnitude of exports and ratios suggest that deforestation in these Panamanian forests results in exports that affect growth of plants and algae in the receiving stream and estuarine ecosystems. Watershed retention of dissolved inorganic nitrogen calculated from wet plus dry atmospheric deposition varied from 90 % in pasture- to 65 % in forest-dominated watersheds, respectively. Discharges of DIN to receiving waters from the watersheds therefore rose from 10 % of atmospheric inputs for pasture-dominated watersheds, to about 35 % of atmospheric inputs for fully forested watersheds. These results from watersheds with no agriculture or urbanization, but different conversion of forest to pasture by burning, show significant, deforestation-dependent retention within tropical watersheds, but also ecologically significant, and deforestation-dependent, exports that are biologically significant because of the paucity of nutrients in receiving tropical stream and coastal waters.     

大兴安岭5种典型林型森林生物碳储量

森林生态系统是陆地生态系统的重要碳库,森林生态系统的生物碳储量作为森林生态系统碳库的重要组成部分,对全球碳循环与碳平衡产生重要作用。以大兴安岭5种典型林型为研究对象,结合森林资源清查资料,采用地理信息技术(GIS),将5种林型分龄组分别对乔木层、林下的灌木层、草本层和凋落物层各组分的单位面积生物量、含碳率和生物碳储量进行测定和计量估算,并从林分水平上,采用分龄组的方法,计量估算了生物碳储量。结果表明:大兴安岭5种典型林型不同龄组的生物碳储量分别为:兴安落叶松幼龄林、中龄林、近熟林和成熟林的生物碳储量分别为15.20、50.96、95.80t/hm2和109.33t/hm2;白桦幼龄林、中龄林、近熟林和成熟林的生物碳储量分别为15.36、30.67、41.62t/hm2和64.35t/hm2;樟子松幼龄林、中龄林、近熟林和成熟林的生物碳储量分别为29.89、59.92、90.01t/hm2和117.08t/hm2;蒙古栎幼龄林、中龄林、近熟林和成熟林的生物碳储量分别为11.17、11.90、34.94t/hm2和59.49t/hm2;山杨幼龄林、中龄林、近熟林和成熟林的生物碳储量分别为21.81、28.58、42.84t/hm2和64.39t/hm2。研究发现:5种典型林型不同龄组的森林生物碳储量均随着林龄(幼龄林、中龄林、近熟林和成熟林)的增长而增加,但不同林型的碳汇功能存在差异,同一种林型在不同林龄的生物碳储量增幅差异亦较大。尤其是大兴安岭目前林分质量比较差,幼龄林和中龄林所占的比重较大,若能对现有林分加以更好地抚育和管理,该区森林植被仍具有较大的碳汇潜力,碳汇功能将进一步增强,大兴安岭在国家的生态功能区建设中将发挥更重要的碳汇功能,对此提出了森林生态系统碳增汇管理策略与管理路径。研究结果为正确认识森林生物碳储量对区域碳平衡及生态环境的影响具有重要意义,以及在未来营林、造林活动中充分发挥人工林碳汇效应提供参考依据。     

Unraveling the drivers of intensifying forest disturbance regimes in Europe

Natural disturbances like wildfire, windthrow and insect outbreaks are critical drivers of composition, structure and functioning of forest ecosystems. They are strongly climate‐sensitive, and are thus likely to be distinctly affected by climatic changes. Observations across Europe show that in recent decades, forest disturbance regimes have intensified markedly, resulting in a strong increase in damage from wind, bark beetles and wildfires. Climate change is frequently hypothesized as the main driving force behind this intensification, but changes in forest structure and composition associated with management activities such as promoting conifers and increasing standing timber volume (i.e. ‘forest change’) also strongly influence susceptibility to disturbances. Here, we show that from 1958 to 2001, forest change contributed in the same order of magnitude as climate change to the increase in disturbance damage in Europe's forests. Climate change was the main driver of the increase in area burnt, while changes in forest extent, structure and composition particularly affected the variation in wind and bark beetle damage. For all three disturbance agents, damage was most severe when conducive weather conditions and increased forest susceptibility coincided. We conclude that a continuing trend towards more disturbance‐prone conditions is likely for large parts of Europe's forests, and can have strong detrimental effects on forest carbon storage and other ecosystem services. Understanding the interacting drivers of natural disturbance regimes is thus a prerequisite for climate change mitigation and adaptation in forest ecosystem management.     

Climate Change Sensitivity Index for Pacific Salmon Habitat in Southeast Alaska

Global climate change may become one of the most pressing challenges to Pacific Salmon conservation and management for southeast Alaska in the 21^st Century. Predicted hydrologic change associated with climate change will likely challenge the ability of specific stocks to adapt to new flow regimes and resulting shifts in spawning and rearing habitats. Current research suggests egg-to-fry survival may be one of the most important freshwater limiting factors in Pacific Salmon''s northern range due to more frequent flooding events predicted to scour eggs from mobile spawning substrates. A watershed-scale hydroclimatic sensitivity index was developed to map this hypothesis with an historical stream gauge station dataset and monthly multiple regression-based discharge models. The relative change from present to future watershed conditions predicted for the spawning and incubation period (September to March) was quantified using an ensemble global climate model average (ECHAM5, HadCM3, and CGCM3.1) and three global greenhouse gas emission scenarios (B1, A1B, and A2) projected to the year 2080. The models showed the region''s diverse physiography and climatology resulted in a relatively predictable pattern of change: northern mainland and steeper, snow-fed mountainous watersheds exhibited the greatest increases in discharge, an earlier spring melt, and a transition into rain-fed hydrologic patterns. Predicted streamflow increases for all watersheds ranged from approximately 1-fold to 3-fold for the spawning and incubation period, with increased peak flows in the spring and fall. The hydroclimatic sensitivity index was then combined with an index of currently mapped salmon habitat and species diversity to develop a research and conservation priority matrix, highlighting potentially vulnerable to resilient high-value watersheds. The resulting matrix and observed trends are put forth as a framework to prioritize long-term monitoring plans, mitigation experiments, and finer-scale climate impact and adaptation studies.