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Northern Treelines as Indicators of Climate and Land Use Changes - A Literature Review

Oddvar Skre

The alpine and arctic treelines are results of long-term processes involving adaptation to a cold climate with environmental stress, and with low soil temperatures and nutrient uptake rates. Global warming and changed land use as a result of changes in global economy and agricultural policy may interfere with the treeline changes. The global warming is expected to enhance tree growth and seed reproduction, thereby increasing treeline altitudes and latitudes. Expansion of the forested area as a result of reduced logging and grazing would also reduce the albedo and enhance global warming in treeline areas. Feedback effects caused by increased soil temperatures and related output of greenhouse gases is expected to further increase global warming and treeline advance. On the other hand, local disturbance factors like increased risks of insect outbreaks, windthrow, grazing, anthropogenic disturbance and paludification would reduce or interfere with these changes, or even lead to a retreat of treelines. These limitations have to be taken into account when evaluating treelines as climatic indicators.