Treeline Research—From the Roots of the Past to Present Time. A Review

Abstract

Elevational and polar treelines have been studied for more than two centuries. The aim of the present article is to highlight in retrospect the scope of treeline research, scientific approaches and hypotheses on treeline causation, its spatial structures and temporal change. Systematic treeline research dates back to the end of the 19th century. The abundance of global, regional, and local studies has provided a complex picture of the great variety and heterogeneity of both altitudinal and polar treelines. Modern treeline research started in the 1930s, with experimental field and laboratory studies on the trees’ physiological response to the treeline environment. During the following decades, researchers’ interest increasingly focused on the altitudinal and polar treeline dynamics to climate warming since the Little Ice Age. Since the 1970s interest in treeline dynamics again increased and has considerably intensified from the 1990s to today. At the same time, remote sensing techniques and GIS application have essentially supported previous analyses of treeline spatial patterns and temporal variation. Simultaneously, the modelling of treeline has been rapidly increasing, often related to the current treeline shift and and its implications for biodiversity, and the ecosystem function and services of high-elevation forests. It appears, that many seemingly ‘new ideas’ already originated many decades ago and just confirm what has been known for a long time. Suggestions for further research are outlined.

Alpine and Polar Treelines in a Changing Environment

“…Their results suggest that due to climate change, seedling regeneration will mainly benefit in cold and wet locations. The review of Holtmeier and Broll [25] provides a literature overview of treeline research from its onset to the present. They detected a reiterative pattern: a moderate number of ideas that, at present, are considered novel, that originated several decades ago, and tend to confirm prior knowledge.…”

Warming enhanced the climate temporal effects on vegetation across Siberia

“…In contrast, the increasing summer precipitation across most of the arctic region and substantial permafrost thawing would reduce the water deficit that affects vegetation (Douglas, Turetsky & Koven 2020). The land cover changes in the treeline ecotone in the arctic and subarctic, such as shrub tundra succession and the northward shift of boreal forests, have attracted the attention of several studies (Devi et al 2008;Holtmeier & Broll 2019;Walther et al 2019).…”

The importance of dispersal and species establishment in vegetation dynamics and resilience

“…Treelines are, in some ways, the canaries of climate change; their shifting upwards illustrates how rapidly communities might track climate change (Smith et al, 2009). But, even here, environmental tolerances (to bioclimatic conditions) have predominated in assessing treeline dynamics (Holtmeier and Broll, 2020). Anadon‐Rosell et al (2020, this issue) study a treeline‐forming species in the Pyrenees and show the importance of seed production and seed dispersal in limiting the advance of the treeline.…”