Structural change in a subalpine birch woodland in North Sweden during the past century

摘要: An isolated subalpine woodland with predominant mountain birch (Betula pubescens Ehrh. subsp. tortuosa (Ledeb.) Nyman) was studied respect to structural change during the past century. Present-day age and size data of tree populations field-layer flora were analysed against perspective an early twentieth century account forest structure flora. Air temperature recordings some periods 1980s provided information on local thermal characteristics in relation physiological tolerances species. Extensive invasion spruce (Picea abies (L.) Karst.), a lesser extent pine (Pinus sylvestris L.), peaked 1930s, coinciding general summer warming (about 1?C) first half The changed mainly by increased height proliferation basal shoots. spacing individuals, however, largely unaffected climatic change. Presumably, vegetative growth related breakage main stems from rime ice, snow wind combination (loss apical dominance), nutrient mineralization. Conceivably, mechanical impact has selected for predominance restricted abundance coniferous Tree into open occurred despite vigour pre-existing dominant, although it possibly preceded facilitated disturbance form transient defoliation insect attack (Epirrita autumnata Bkh.) or other agent.