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Ecotone meaning5/5/2023 ![]() We postulate here that spatial patterns of treeline ecotones may also be predictable globally, even if requiring more predictors than potential treeline elevation does. The global pattern in potential treeline elevation is therefore well explained by latitude and regional thermal modifiers such as mountain mass, continentality and cloudiness (Paulsen and Körner 2014, Karger et al. This transition zone (also referred to here as ‘treeline' for simplicity) is the focus of this paper.Īt the global scale, the predictability of treeline elevation has long been recognized (von Humboldt and Bonpland 1807, Brockmann-Jerosch 1919, Hermes 1955) and can be captured well by the mean growing-season temperature and a minimum growing-season length (Körner and Paulsen 2004). The realized treeline, a line connecting the uppermost trees of a certain size (sizes reviewed in Holtmeier 2009), is located somewhere within the transition zone between forest and low-stature alpine vegetation, i.e. Due to different combinations of stochastic, ecological and climatic processes, the space downslope of the potential treeline is rarely filled completely with trees. the highest elevation at which tree growth is possible in a region before thermal conditions become unsuitable. In this context, it is important to distinguish the treeline ecotone from the potential treeline, i.e. However, some broad treeline ecotone patterns are repeated globally. The spatial patterns of treeline ecotones vary greatly and, to some extent, every treeline ecotone is unique, reflecting ecological processes produced by particular combinations of climatic conditions, the topographic template, species composition and disturbance history (Brockmann-Jerosch 1919, Holtmeier 2009). At vegetation boundaries, such as alpine treeline ecotones, spatial patterns may be a key to understanding the dynamic processes that determine the current and future distribution of species and ecosystems (Harsch and Bader 2011). Recognizing recurrent patterns in vegetation transitions or ecotones should provide similar advantages (Brown et al. It has enabled the formulation of globally-applicable hypotheses about the factors and processes determining vegetation cover and has facilitated meaningful extrapolations of research finding across continents. Recognizing globally recurrent vegetation physiognomies has organized our perception of the natural world and has facilitated communication among ecologists and biogeographers at least since the times of Alexander von Humboldt (von Humboldt and Bonpland 1807). Introduction Why is a globally consistent description of treelines useful and needed? The improved recognition of treeline patterns should allow more effective comparative research and monitoring and advance our understanding of treeline-forming processes and vegetation dynamics in response to climate warming. ![]() ![]() To quantify the dimensions and facilitate comparative research, we advocate a joint effort in gathering and analysing spatial patterns from treelines globally. Our graphical representation of this framework can be used to place any treeline pattern in the proposed multi-dimensional space to guide hypotheses on underlying processes and associated dynamics. These patterns mainly indicate growth and dieback processes.Īdditionally, tree population structure can help distinguish alternative hypotheses about pattern formation, while analysing the functional composition of the ecotonal vegetation is essential to understand community-level processes, controlled by species-specific demographic processes. Variation along these dimensions results in more or less ‘abrupt' or ‘gradual' treelines with or without the formation of environmental krummholz. 2) Changes in tree stature: a) decline in tree height, and b) change in tree shape. These patterns mainly indicate demographic processes: establishment and mortality. Variation along these dimensions results in more or less ‘discrete' or ‘diffuse' treelines with or without islands. ![]() To help better understand treeline-forming processes, we present a new framework for describing alpine treeline ecotones, focusing on hillside-scale patterns, using pattern dimensions with distinct indicative values: 1) the spatial pattern in the x-y plane: a) decline in tree cover, and b) change in the level of clustering. However, existing spatial categorizations of treelines are very loosely defined, leading to ambiguities in their use and interpretation. Describing these patterns consistently along ecologically meaningful dimensions is needed for generalizing hypotheses and knowledge about controlling processes and expected treeline shifts globally. These spatial patterns contain information about the processes that control treeline dynamics. Globally, treeline ecotones vary from abrupt lines to extended zones of increasingly small, stunted and/or dispersed trees. ![]()
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