Abisko Scientific Research Station in northern Swedish Lapland has acted as a logistic centre for high-quality subalpine/subarctic geoecological research for nearly a century. Most of the research attention in recent years has been on complexities of the treeline ecotone, motivated by the possibility of alleged man-made global warming. Field observations, analyses, and interpretations resulting from research conducted in the Abisko area are discussed in light of recent observations and analyses in this context. The treeline rise of local mountain birch (Betula pubescens ssp. czerepanovii) by up to 230 metres over the last 100 years is quantitatively consistent with data obtained further south in the Scandes. This widespread inter-regional coincidence suggests that a single operative agent is to blame. Secular temperature warming of 2.5°C is the most likely candidate. This argument is backed up by age structure analysis in the birch treeline advance region, which shows that vegetative initiation of new trees peaked during the warm 1930s, when reindeer numbers were high, and peaked again during the cold 1960s and 1970s, when reindeer herds were smaller. These findings indicate that, in comparison to climate change, reindeer browsing strength has had a slight impact on birch treeline dynamics, contrary to previous hypotheses. Over the mainly warm past 100 years, the upper limit of closed mountain birch and pine stands has changed relatively insignificantly in elevation. Over the same time period or longer, low-growing krummholz (stunted growth forms) of common aspen (Populus tremula) have appeared frequently in the mountain birch area. Rapid height increment began in the warm 1930s, and has continued to this day, just as it did with birch. As a result, many people have grown to be the size of trees in recent decades. As a result, aspen (Populus tremula) has become a more prominent feature in the mountain birch forest, probably as a result of climate change. Prior arguments that aspen regeneration is achieved by seed regeneration rather than phenotypic modification of old-growth creeping individuals are refuted by the current research. In the Abisko field, new species such as Picea abies and Larix sp. have been discovered. Megafossil data indicate that Scots pine treelines are similar to those found in other parts of the Scandes (Pinus sylvestris), Summer temperatures may have surpassed those of the last few decades by around 3.0°C, based on the elevational disparity between early Holocene and present treeline positions (adjusted for 100 m land uplift). Recent reports that aspen is spreading upslope and westward in the birch forest belt through seed establishment of new individuals are questioned by this report. As a result of recent warming, they have grown to the size of trees and have become a more noticeable feature of the landscape.
Author (s) Details
Department of Ecology and Environmental Science, Umeå University, SE 901 87 Umeå, Sweden.
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