全球变暖背景下高山林线交错带的动态综述（英文）

高山林线交错带是亚高山森林与苔原之间、亚高山森林与无树草原之间的过渡带状区域,是生物多样性热点区域,具有营养物质输入源和低海拔生态系统的碳固存等不可替代的生态功能,提供着各种生态系统服务。与高山林线交错带相关的三种树线是树种线、林线和木材线。由于高山林线交错带占据了树种耐受温度极限的极端区域,对气候变化非常敏感,经常被用作植被对全球变暖响应的指标。随着全球气候变暖的加剧和不同气候区海拔梯度的变化,高山林线交错带中的树高和生物量也会发生显著变化。同时分布在全球不同气候带上的林线变化也表现出不同的规律,其中的原因包括温度升高程度的不一致、优势种和植物群落的不同、人为干扰程度的不同等。另外,关于林线推进的驱动因素也无一致的研究结果,不同气候区之间的研究结果可能会相互矛盾。然而,目前在气候变化下的高山林线发展领域,缺乏全面的综述。因此,本文从以下四个方面对此前的研究进行了总结,并探讨了高山林线动态变化的理论基础和挑战：（1）高山林线动态变化的生态功能和生态问题;（2）监测高山林线动态变化的研究方法;（3）全球不同气候区的林线迁移;（4）林线向上迁移的驱动因素。     

Geomorphic Controls of Spatial Pattern and Process at Alpine Treeline*

This study examines the role of surface geomorphic features in tree establishment at the alpine treeline in Glacier National Park, Montana, through the presentation of a multiscale, conceptual model of biogeomorphic relationships at alpine treeline. Empirical observations gathered through a multiscale field methodology over three summers serve as a base for the model. The model highlights the importance of surface geomorphic features, specifically boulders and terrace risers, in creating favorable local site conditions, largely by protecting seedlings from wind. The sheltering effect of surface features enables initial seedling establishment, and in some cases survival, above current treeline locations, thereby initiating a positive feedback effect that encourages subsequent tree establishment. Geomorphic features are therefore important in linking scales of pattern and process at the alpine treeline ecotone.     

CHANGES IN THE FOREST-ALPINE TUNDRA ECOTONE: COLORADO FRONT RANGE

On Niwot Ridge, alpine climatic factors dominate today within the upper part of the forest-alpine tundra ecotone on the east slope of the Colorado Front Range. This study provides evidence that the climatic conditions controlling the distribution of the upper limit of tree species and growth forms within the ecotone have changed through time. It appears that much of the present forest-alpine tundra ecotone is a relict of past warm climate episodes. There is much evidence that, in the past, tree forms were more symmetrical and less deformed, tree trunks with larger diameters existed, and the trees were more extensive in areal coverage. However, no evidence exists to show that the upper limit of tree species growth was more than marginally higher in the past than today. The treeline appears to be stable to historical and Holocene climatic fluctuations, but the altitudinal limits of seedling establishment and survival are not stable. The liming of climatic changes in the Front Range and their possible influence on the distribution of the trees within the ecotone are reviewed. Because of its extreme easterly location, slight but significant climatic variations may be observed within the forest-alpine tundra ecotone of Niwot Ridge, but are not observed elsewhere.     

新疆策勒沙漠-绿洲过渡带不同下垫面地表蚀积变化特征

沙漠-绿洲过渡带天然植被具有良好的防风阻沙效益,对绿洲内部农田起到重要生态保护作用。在新疆策勒沙漠-绿洲过渡带流沙地、半固定沙地、绿洲边缘固定沙地6个不同植被覆盖度样地风蚀、风积变化观测基础上,结合地表风速数据,探讨流沙地、半固定沙地、固定沙地不同植被覆盖度和地形下地表风蚀风积变化特征及其影响因素。结果表明：流沙地表现出较强烈的地表风蚀;半固定沙地整体表现出强烈的地表风积;固定沙地上植被覆盖度越高、植株越高和排列方式越均匀、整体地势越低,单位面积风积量也就越大、风蚀量越小,风蚀主要发生在灌丛沙堆的上风向、侧翼、背风风向的裸低凹沙地表面,较高沙堆侧翼的地表风蚀量最大。植被覆盖度与单位面积风蚀量呈多项式或指数函数关系递减,植被覆盖度与单位面积风积量不呈函数分布,说明除了植被覆盖度外,植株类型、高度、排列方式、地形等都会对地表风积量产生一定影响。     

‘WHY FAMILIES MOVE’: A RE-EXAMINATION

Abstract

This study examines the role of surface geomorphic features in tree establishment at the alpine treeline in Glacier National Park, Montana, through the presentation of a multiscale, conceptual model of biogeomorphic relationships at alpine treeline. Empirical observations gathered through a multiscale field methodology over three summers serve as a base for the model. The model highlights the importance of surface geomorphic features, specifically boulders and terrace risers, in creating favorable local site conditions, largely by protecting seedlings from wind. The sheltering effect of surface features enables initial seedling establishment, and in some cases survival, above current treeline locations, thereby initiating a positive feedback effect that encourages subsequent tree establishment. Geomorphic features are therefore important in linking scales of pattern and process at the alpine treeline ecotone.     

中国北方农牧交错带土壤风蚀时空分布

土壤风蚀是干旱、半干旱地区土壤退化的主要过程,定量评价土壤风蚀是分析土壤退化的重要手段。中国北方农牧交错带是土壤风蚀的典型治理区。采用张春来风蚀预报经验模型,以半月为步长,计算中国北方农牧交错带2000-2012年的土壤风蚀模数。结果表明：中国北方农牧交错带的土壤风蚀状况整体有好转;沙地的土壤风蚀最严重,农田次之,草地的土壤风蚀最低;土地利用方式、风速和植被盖度均对土壤风蚀有一定的影响。     

Landform Influences on Treeline Patchiness and Dynamics in a Changing Climate

Local landforms and microtopography control site conditions, spatial patterns, and dynamics in treeline landscapes. Several topography-related treeline types are presented and their responses to a warming climate discussed. On rugged mountain terrain, pronounced changes in vertical range and variety of treeline landscapes will not take place as long as debris slides and avalanches occur regularly. On intensively eroded steep terrain, trees will mainly colonize convexities. On trough shoulders and similar gentle topography with irregular mosaics of convex and concave landforms, tree establishment is most likely to take place on convex topography. On gentle slopes and rolling uplands, where the proportion of wind-swept terrain is comparatively large, microsite facilitation appears to be a precondition for tree establishment. At higher elevations, the relative importance of shelter-providing landforms will increase due to windier conditions. At the beginning of treeline rise, seedling establishment, growth, and survival are closely related to local landforms and microtopography and their effects on site conditions. Later, the feedback from trees on their environment may overrule the effects of landforms.     

基于RWEQ和WEPS模型的中国北方农牧交错带潜在风蚀模拟

中国北方农牧交错带是一个典型的受气候和人类活动共同影响的敏感区域,存在严重的土壤风蚀和土地退化问题.风蚀模型是目前获得区域风蚀模数的最有效方法之一.利用修正风蚀方程(RWEQ模型)和风蚀预报系统(WEPS模型)对北方农牧交错带2000-2012年潜在风蚀进行评估.结果表明:两个模型模拟得到的多年平均潜在风蚀量不同,但空...     

柴达木盆地东北部哈勒腾河流域风况特征及其对风沙地貌发育的影响

风况是影响风沙地貌发育的重要因子,在一定程度上决定了沙丘类型.为探究区域风沙地貌发育与风况之间的关系,对哈勒腾河流域不同区域一个完整年度的风况进行分析.结果表明:流域年平均风速为2.78 m·s-1,起沙风集中在春夏季,平均风速为7.78 m· s-1,起沙风事件平均持续时间为4.1 h;流域输沙势122-254 VU...     

长白山北坡林线长白落叶松与岳桦对环境适应的对比分析

以长白山北坡林线长白落叶松（Larix olgensis）和岳桦（Betula ermanii）为研究对象,通过野外样方调查、树轮技术分析,采用趋势线模型拟和、单因素方差等统计方法从各种参数分析长白落叶松和岳桦径向树高生长的对比关系并揭示2个种群动态对环境适应性的对比差异。结果显示：垫状生长形的长白落叶松海拔最高（均值：2 017 m）,其次为旗形树（2 005 m）,正常形态的海拔最低（1 992 m）,所在生境差异显著（p < 0.05）。正常形态的长白落叶松生长速度大于岳桦（树高方程斜率：长白落叶松0.750 9>岳桦0.253 6）,随着旗形树的出现,速度相似（斜率：长白落叶松0.375 4>岳桦0.253 6）,变成垫状后,岳桦占优。长白落叶松受到压制种群扩张速度不如岳桦,长白山林线上侵表现为以岳桦种群为主力,长白落叶松仍是岳桦主要的伴生树种。     

Low recruitment above treeline indicates treeline stability under changing climate in Dhorpatan Hunting Reserve,Western Nepal

A treeline can respond to climate change by shifting position, infilling, increasing recruitment, and increasing radial growth. More studies from understudied areas and their associated species are needed to understand treeline structure and dynamics. We established two transects of 20 m width and 120 m length (100 m above and 20 m below the forestline) in the Betula utilis subalpine forest of the Dhorpatan Hunting Reserve in Western Nepal. All individuals of B. utilis within the transects were classified into three height classes – trees (>2 m), saplings (0.5–2 m), and seedlings (<0.5 m) – and measured for morphometric features. Tree-ring cores were collected for age structure analysis. B. utilis forms an abrupt treeline in the region, and the mean forestline and treeline elevations were 3893 and 3898 m, respectively. The average age (57 yr) of trees at the treeline ecotone suggests a young stand. Poor regeneration was observed above the forestline in both transects when compared to below the forestline. Low regeneration at the treeline ecotone suggests site-specific biotic and abiotic controlling factors. Seedling and sapling establishment above the forestline is limited by a lack of moisture, absence of suitable microsites, and presence of herbivores.     

黑河流域中游沙漠风能环境与风沙地貌

在黑河流域中游,沙漠分布在绿洲附近或绿洲之间。近年来,由于气候变化和人类活动的影响,该地区的生态与环境恶化。目前,虽然对该地区的生态与环境等问题进行了大量的研究,但关于绿洲及沙漠风能环境的研究较少。本文利用自动气象站的风资料、环境减灾卫星影像（HJ-1A/B）和Google Earth高清影像,对黑河流域中游沙漠的风能环境与风沙地貌进行探讨。结果表明：黑河流域中游沙漠的北部为高风能环境（>400）,中部为中风能环境（200～400）,南部为低风能环境（<200）;合成输沙势方向总体为东南方向,但在不同区域有所差异;方向变率在北部和中部属于中等变率,南部属于低变率。内陆河流域下游的冲积-洪积物是该地区沙漠形成的物质基础。风能环境与风况对风沙地貌沙丘的形成起着重要作用,但沙源供应对沙丘形态特征的作用不可忽略,在相同的风况下,新月形沙丘（链）、格状沙丘和金字塔沙丘可能共同存在,造成这种格局的主要原因在于沙源的供应程度,按新月形沙丘（链）—格状沙丘—金字塔沙丘顺序,沙源供应逐渐增加。研究区的沙丘类型包括新月形沙丘链、格状沙丘、灌丛沙丘、沙垄、金字塔沙丘、线形沙丘等。     

小网窄带防护林叠加防风效果风洞实验

小网窄带防护林在干旱区防护林构建中发挥着重要作用,研究小网窄带防护林叠加防风效果对指导防风固沙林空间配置与结构优化具有重要意义。选取两种典型小网窄带防护林网,对连续6个林网叠加的防护林开展基于流场分析防风效果的风洞模拟试验。结果表明:小网窄带防护林叠加后随着林网数量的增加各林网内的风速逐渐减小且在中间林网位置趋于稳定,乔木纯林林网在第3林网基本达到稳定,乔灌混交林网在第2林网达到稳定;两种防护林各林网内风速均符合正态分布特征,风速稳定后多为右偏态高狭峰;16 m·s^-1风速下,乔木纯林网叠加(0~252 cm)的防风效能分布范围为16%~74%,整体在60%防风效能下发挥着良好防风效果,乔灌混交林林网叠加的防风效能分布范围为15%~89%,整体在70%防风效能下发挥着良好防风效果;16 m·s^-1风速下,乔木纯林林网叠加(0~42H,H=6 cm)的风速加速率为0.25~0.94,乔灌混交林林网叠加的风速加速率为0.1~0.94;根据风速加速率的分布特征划分出4个不同的风速分布区,分析还发现灌木对林带枝下高范围的近地层气流影响显著,对削弱近地层风速起到了重要作用。     

RWEQ模型在河北坝上地区的适用性

土壤风蚀是中国北方干旱半干旱地区重要的生态环境问题。坝上地区位于中国北方农牧交错带核心地段,是典型风蚀治理区。本研究实测了2015年（翻耕地）和2016年（莜麦留茬地）13个单次风暴风蚀和8个时段风蚀距离上风向（不可蚀边界）50 m 和100 m输沙通量,并根据RWEQ模型预测出距离上风向50 m 和100 m处的输沙通量。通过对比预测和实测输沙通量对RWEQ模型进行验证。结果表明：对于单次风暴风蚀事件,RWEQ模型对莜麦留茬地的预测效果要好于翻耕地,距离上风向100 m处的输沙通量好于50 m处;对于时段风蚀事件,对翻耕地的预测效果要好于莜麦留茬地,距离上风向100 m处的输沙通量好于50 m处;虽然两种时间尺度对于小风蚀事件的预测效果较差,但是预测和实测风蚀通量总体相关性较好。RWEQ模型的预测结果具有参考性,对河北坝上地区的风蚀具有一定的预测能力,但是需要经过进一步的参数修订才能取得更精确的风蚀预报结果。     

Sigmoid wave transitions at alpine treeline

Ecotones that are controlled by a single environmental gradient or a set of correlated environmental factors are hypothesized to show a sigmoid wave form in percentage cover as the ecotone is crossed. This study investigates the sigmoid wave hypothesis at the alpine treeline in Glacier National Park, Montana, USA. We find that approximately half of the sampled locations exhibit a sigmoid wave form in percentage cover across the ecotone. These results indicate that in some cases treeline is controlled by a single environmental gradient or a set of correlated environmental factors. However, in other cases, additional factors that are not correlated with the primary controlling gradient act to change the form of the transition. We investigated surficial geology as a possible controlling factor that would not be correlated with the primary climatic gradients found along transects across the alpine treeline. In at least some of the cases, surficial geology type was shown to be significantly associated with differences between sigmoidal and non‐sigmoidal transitions. These results support previous evidence for sigmoid wave transitions at the boreal forest—tundra ecotone, but also show that the alpine treeline case is more complex. We argue that in cases where ecotones are used as sites for monitoring the effects of climate change on vegetation, care should be taken to utilize only sites that exhibit a sigmoidal transition so as to minimize the effects of non‐climate‐related controlling factors on the interpretations.     

晴天和沙尘天气下沙漠绿洲过渡带近地表风速脉动特征

以敦煌黑山嘴沙漠绿洲过渡带为例,利用可移动梯度风测量系统,获取晴天和沙尘暴天气过程中沙漠绿洲过渡带近地表风速脉动特征,研究沙尘天气对近地表风速脉动影响。结果表明：无论晴天或沙尘暴,相同测点各高度层脉动风速具有很好的相关性,相邻高度脉动风速的相关性更加显著,脉动风速的波动范围与高度和风速呈正比。沿沙漠至绿洲方向,晴天环境下脉动强度先增大后减小,沙尘暴环境下脉动强度逐渐减小。沙尘暴和晴天环境下脉动风速的变化规律相近,但沙尘暴环境下风向相关性更加显著,风速脉动强度更大。风速与脉动强度呈正相关,沙尘对脉动强度产生一定抑制作用。     

Directional Characteristics of Potentially Damaging Wind Gusts in the Southeast United States

Annual estimated storm damage in the United States is seven billion dollars. Much of that damage is caused by tree blowover that is induced by high wind gusts. The prevailing directions of these wind gusts dictate the zones around structures in which trees may potentially fall and cause damage. To gain a better understanding of hazardous wind gusts, this research examines the directional component of wind gusts in the Southeast United States. Regional patterns of wind gusts are identified and tied to atmospheric and terrestrial patterns. Results indicate the following: (1) gusts along the northeast coast of the study area are bidirectional, being from the northeast and southwest; (2) the southeast coast has a predominantly westerly component to the gusts with little impact from the east; (3) the Piedmont is strongly influenced by westerly gusts, but an easterly component increases gradually to the northeast; and (4) high gusts in the mountains demonstrate a strong relationship with the regional and local topographic characteristics.     

高山树线交错带的景观格局与生态过程

由于对气候变化的敏感性, 近年来高山树线交错带成为全球变化研究中的热点问题。高 山树线交错带所指示的是一个复杂生态系统的特征, 反映出了由低处植被向高山植被的转化, 其 景观格局是综合了种子定居, 树木生长以及树木繁殖等多个树木生态过程和特定高山环境下的 地理特征格局的适应结果。一方面, 树木通过自身生理生态学上的调整对高山极端环境进行适 应。一方面, 高山特定地理环境特征对树线的景观格局进行影响, 因而高山树线交错带成为研究 景观格局- 生态过程相互关系的一个重要载体。通过运用3S 技术, 可以将高山树线交错带研究中 的树线景观结构和生理生态过程结合在一起, 并验证在其景观格局形成过程中地理特征和人为 因子的相对重要性。     

Patterns of Winter Desiccation in Krummholz Forms of Abies Lasiocarpa at Treeline Sites in Glacier National Park, Montana, USA

Winter desiccation-induced foliage loss at high-elevation locations is an important determinant of positive carbon balance for trees and thus influences the location of the alpine treeline ecotone. In this study, data are presented that describe the amount of winter desiccation incurred by krummholz growth forms of subalpine fir ( Abies lasiocarpa (Hook) Nutt.) at treeline locations in Glacier National Park, Montana, USA, for the winter of 1998/1999. An average 8.68% of the krummholz canopy was lost due to desiccation.
Winter desiccation is not predictable based on any single environmental variable. When outliers are removed, winter desiccation shows a strong correlation with elevation ( r = 0.97). Patch level winter desiccation amounts are, however, highly predictable from elevation, slope, aspect and topographic context when considered together. In general, injury increases with elevation and on more southwesterly facing hillslopes. High slopes and sheltered locations decrease winter desiccation.
Within patches, most winter desiccation is located at the windward edge of the patch. This trend may be modified by the presence of leaders above the mean canopy surface of the krummholz patch, or by local microtopographic features such as dead branches or the proximity of large rocks.
The winter of 1998/1999 was a high winter desiccation year compared to the two previous winters. The winter of 1998/1999 had high snowfall, and meltout did not occur until later than the previous two winters. The extended period of snow cover is hypothesized to be one of the causes of the increased winter desiccation for the 1998/1999 winter.     

The Role of Thresholds and Fine-Scale Processes in Driving Upper Treeline Dynamics in the Bighorn Mountains,Wyoming

This research investigates whether abrupt changes indicative of a threshold response occurred in the spatial and temporal patterns of tree establishment within upper treeline ecotones in the Bighorn Mountains of north-central Wyoming, with a particular focus on assessing whether treeline advance occurred. Dendroecological techniques were used to reconstruct the spatiotemporal patterns of tree establishment at multiple spatial scales (local and landscape). Increases in the elevational extent of treeline and tree density above timberline were reconstructed for each decade of the 20^th century. Regime-shift analysis was used to detect threshold changes in tree establishment. Marked increases in tree establishment and density occurred at local and landscape scales during the 20th century, particularly during the post-1970 period and in areas above timberline. Varying degrees of treeline advance occurred during this time, yet establishment upslope from timberline was often contingent on the availability of sheltered microsites in the lee of boulders. This highlights the importance of both broad-scale climate inputs and fine-scale site conditions in governing the rate and pattern of tree establishment in high-elevation treeline environments. Overall, the abrupt changes in tree establishment over time and space since 1970 suggest that bioclimatic thresholds can strongly influence ecotonal dynamics at upper treeline.