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1.
《The Professional geographer》2013,65(2):124-129
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. 相似文献
2.
The alpine treeline ecotone is defined as a forest-grassland or forest-tundra transition boundary either between subalpine forest and treeless grassland, or between subalpine forest and treeless tundra. The alpine treeline ecotone serves irreplaceable ecological functions and provides various ecosystem services. There are three lines associated with the alpine treeline ecotone, the tree species line (i.e., the highest elevational limit of individual tree establishment and growth), the treeline (i.e., the transition line between tree islands and isolated individual trees) and the timber line (i.e., the upper boundary of the closed subalpine forest). The alpine treeline ecotone is the belt region between the tree species line and the timber line of the closed forest. The treeline is very sensitive to climate change and is often used as an indicator for the response of vegetation to global warming. However, there is currently no comprehensive review in the field of alpine treeline advance under global warming. Therefore, this review summarizes the literature and discusses the theoretical bases and challenges in the study of alpine treeline dynamics from the following four aspects: (1) Ecological functions and issues of treeline dynamics; (2) Methodology for monitoring treeline dynamics; (3) Treeline shifts in different climate zones; (4) Driving factors for treeline upward shifting. 相似文献
3.
The Role of Thresholds and Fine-Scale Processes in Driving Upper Treeline Dynamics in the Bighorn Mountains,Wyoming 总被引：1，自引：1，他引：0
《自然地理学》2013,34(2):129-145
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 20th 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. 相似文献
4.
高山树线交错带的景观格局与生态过程 总被引：1，自引：1，他引：1
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。 相似文献
5.
An overview of scale, pattern, process relationships in geomorphology: a remote sensing and GIS perspective 总被引：6，自引：0，他引：6
Satellite remote sensing and geographic information systems are emerging technologies in geomorphology. They offer the opportunity to gain fresh insights into biophysical systems through the spatial, temporal, spectral, and radiometric resolutions of remote sensing systems and through the analytical and data integration capability of GIS. The two technologies can be linked together into a synergistic system that is particularly well suited to the examination of landscape conditions through the interrelationships of scale, pattern, and process, a paradigm that has gained prominence in the fields of biogeography and landscape ecology. In this study, we apply optical and microwave remote sensing systems and GIS methodologies to case studies framed within the fluvial and alpine environments. We use the scale, pattern, and process paradigm to explore landscape relationships in those environments. Satellite image processing, change-detection analyses, digital elevation models, GIS-derived geomorphic indices and variables, composition and pattern metrics of landscape organization, and scale-dependent analyses are described and related to the study of river channel abandonment and the alpine treeline ecotone. We describe appropriate remote sensing and GIS techniques for geomorphic research, and demonstrate the use of such techniques in the application of the scale, pattern, and processes perspective in geomorphic studies. 相似文献
6.
Himalayan region represents the highest and most diverse treeline over the world. As one of the most conspicuous boundaries between montane forests and alpine vegetation, the alpine timberline attracted the interest of researchers for many decades. However, timberline in the Himalayas is understudied compared with European counterparts due to remoteness. Here we review the distribution pattern of timberline and its climatic condition, the carbon and nutrient supply mechanism for treeline formation, and treeline shift and treeline tree recruitment under climate change scenarios. Growth limitation, rather than carbon source limitation is the physiological cause of timberline under the low temperature condition. Nutrient limitation and water stress are not the direct cause of timberline formation. However, more clear local limitation factors are need to integrate in order to enable us to predict the potential impacts and changes caused by human activity and related global change in this sensitive region. 相似文献
7.
Wind as an Ecological Agent at Treelines in North America,the Alps,and the European Subarctic 总被引：2，自引：1，他引：1
《自然地理学》2013,34(3):203-233
The altitudinal treeline ecotone is a windy environment where wind velocities and directions are controlled by local mountain topography and also by the distribution pattern and structures of tree stands. Wind may override the role of heat deficiency in determining treeline position, spatial pattern, ecological conditions, and tree growth. Regular strong permanent winds restrict tree height and usually cause asymmetric and suppressed growth forms that are common in the treeline ecotone. Apart from direct physiological and mechanical effects on trees and ground vegetation, wind also disperses seeds, relocates snow, and locally erodes soils in the treeline ecotone. Wind effects must be considered an important factor that may delay or even preclude establishment of seedling trees on wind-swept terrain. Discussions of a potential climatically driven upward shift of the treeline at the landscape and smaller scales should give greater attention to the varying wind effects because warming cannot compensate for these other factors. The relative importance of microsite facilitation providing shelter from the wind will increase in parallel with the upslope migration of the tree limit into a much windier environment. 相似文献
8.
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. 相似文献
9.
Feedback in the establishment of vegetation has been shown to produce spatial patterns that differ from the geomorphological basis for resources. The dynamics of these spatial patterns have been characterized as self-organization because local processes produce them at landscape scales. Geomorphic patterns could, however, enhance or disrupt the processes that lead to patterns and the interpretation of self-organization. A simulation model that showed such indication of self-organization at alpine forest-tundra ecotones is modified to incorporate a geomorphic feature commonly seen in this environment – solifluction steps – as an exogenous condition in the model. Analyses linking spatial patterns and rates of advance of vegetation indicate that such geomorphic patterns do not alter the dynamics of vegetation until the size of the patterns is about double that of the dimension within which endogenous dynamics operate. The sizes of some geomorphic patterns incorporated in the model are probably larger than any realistic solifluction feature at such ecotones in western North America. 相似文献
10.
《自然地理学》2013,34(5):403-437
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. 相似文献
11.
Topographic Shelter and Conifer Establishment and Mortality in an Alpine Environment,Glacier National Park,Montana 总被引：4，自引：2，他引：2
《自然地理学》2013,34(2):112-125
We examined the importance of periglacial shelter in the spatial distribution of conifers at and above alpine treeline. Using a detailed field-based method, we sampled a total of 211 conifer patches at three study locations in Glacier National Park (GNP), Montana. Conifers were found to be nonrandom spatial associates of three periglacial shelter types: boulders, terrace risers, and combination shelters. Our results indicate that conifer establishment and survival in this extreme mountain environment is connected to shelter availability and shelter type. 相似文献
12.
13.
Precipitation and Temperature Estimation Error at Alpine Treeline Ecotones Using the Mountain Climate Simulator Model (MT-CLIM) 总被引：1，自引：1，他引：0
《自然地理学》2013,34(4):285-307
In order to improve modeling of alpine treeline responses to climate change, estimations of snowfall at treeline sites are needed. The MT-CLIM climate model was evaluated for this purpose by extrapolating precipitation and temperature from standard weather stations at lower elevations to 30 alpine SNOTEL study sites across the western United States. Quantification of the topography between the base stations and the SNOTEL sites was used in inverse distance weighting and compared to straight-line weighting. The predicted temperature and precipitation under different weighting methods were compared to observed data over three months during the winter of 2006-2007. The errors were mapped and their spatial pattern analyzed. Error patterns indicate strong gradients, particularly in the Pacific Northwest, that are suggestive of areas where additional characteristics of atmosphere-land interactions and boundary layer climatology need to be considered in modeling applications. 相似文献
14.
Sigmoid wave transitions at alpine treeline 总被引：3，自引：0，他引：3
David M. Cairns John D. Waldron 《Geografiska Annaler: Series A, Physical Geography》2003,85(1):115-126
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. 相似文献
15.
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。 相似文献
16.
Dasvinder Kambo 《自然地理学》2018,39(5):471-486
Fine-scale disturbance can increase seed access to suitable substrates, facilitating germinant emergence and survival, which are necessary elements for treeline advance. We conducted an experiment to test this hypothesis in a white spruce (Picea glauca) treeline ecotone in southwest Yukon, Canada. Sixty seed germination quadrats were established at two elevations (treeline and alpine tundra) and subjected to three levels of simulated disturbance. We sowed 125 seeds in half of the quadrats (30) and measured their emergence and survival over 3 years. Soil temperature, moisture, and organic depth were recorded in all treatments. Treeline quadrats had significantly greater seedling emergence and survival than alpine tundra quadrats. Mean soil temperature, moisture, and organic layer depth were all greater in treeline quadrats. Partially scarified quadrats had the highest germinant emergence compared to unscarified and completely scarified quadrats. Completely scarified quadrats had the highest temperature range and the lowest soil moisture. The results indicate that moderate levels of disturbance can positively influence seedling emergence, while more severe disturbance can lead to high temperature ranges and moisture loss that negate the benefits of lower interspecific competition. Collectively, our findings suggest that fine-scale disturbance can play a significant role in influencing seedling presence in treeline ecotones. 相似文献
17.
Treelines are widely studied worldwide in relation to climate changes because they are hypothesized to be sensitive climate proxies. However, forest treeline expansion toward higher altitudes may be influenced both by a warming climate and by other factors, such as surface morphology and, in the European Alps, the decline in alpine farming. Our results from five valleys in the inner and peripheral regions of the Alps show that present-day treeline altitudes mostly depend on anthropogenic and orographicgeomorphologic factors. Climatic treelines are limited to steep and inaccessible slopes, and occur at higher altitudes and farther from mountain peaks in the inner regions than in the peripheral regions of the mountain range. Looking for sites in which to study treeline responses to climate change, we recommend investigating the inner regions of the Alps where treelines are farther from human disturbances and from geomorphologic constraints, potentially resulting in freer upward shifts under warmer temperature conditions. We also found that, in the valleys selected, human disturbance is mainly concentrated about 165 m below non-climatic treelines, suggesting a homogeneous influence on treelines, regardless of geographic position. 相似文献
18.
Advancing ecotones, such as treelines and frontiers of human settlement, may share some characteristic dynamics because both include feedbacks between spatial pattern and process. Both might be examined as complex, self‐organizing systems in terms of complexity theory and thus be usefully compared. A cellular automaton of advancing alpine treeline in Montana shows attractors in power‐law frequency distributions of spatial and temporal pattern. Frontiers of study areas in the Amazonian region of Ecuador, analyzed using change detection of Landsat Thematic Mapper imagery, have power‐law distributions of advancing deforestation. Alternative approaches in self‐organized complexity, including self‐organized percolation, and the inverse cascade model, and an approach to complexity involving optimization, highly optimized tolerance, are considered. Some combination of these, based on their common ancestry in percolation theory (with its ties to geocomputation), might provide insights into population‐environment interactions at settlement frontiers and ecotones together, given comparisons drawn between the spatial feedbacks at alpine treeline and in Ecuador. GIScience and landscape ecology can develop synergies by building on this area of geocomputation and complexity theory, as in analysis of attractors in state spaces of spatial metrics from spatially explicit simulations and representing their uncertainty. 相似文献
19.
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. 相似文献
20.
太白山高山林线植被的数量分析 总被引：8，自引：2，他引：6
通过对太白山南坡高山林线（ａｌｐｉｎｅｔｉｍｂｅｒｌｉｎｅ）及其附近的草本植物群落的聚类,排序,物种多样性以及生态种组等研究分析表明：１．太白山高山植物群落的物种多样性随着海拔高度的升高而增加;２群落交错带（ｅｃｏｔｏｎｅ）的物种多样性要比相邻群落内部高;３．在太白山高山带,随着海拔升高,种一面积相关值呈波动增加,但在群落交错带比相邻群落的内部小。 相似文献