Recently Enhanced Pine (Pinus sylvestris L.) Regeneration and Extensive Penetration towards the Head of the Handölan Valley: Reversal of a Long-Term Retrogressional Trend – Contrasting Responses to Climate Change of Tree- and Forest Line

With an emphasis on climate change, this study examines the latest history and output of widely spaced pine (Pinus sylvestris L.) tree- and forest lines in a mountain valley in the southern Swedish Scandes. Over the last two decades, the treeline ecotone’s geriatric structure and physiognomy have been significantly rejuvenated. By the early twentieth century and the mid-1970s, historical documents had clearly defined these “lines.” Following that, their diverse performances have been studied up to the present day. Both lines are currently found within the subalpine mountain birch forest belt (Betula pubescens ssp. czerepanovii). As a result, the evolution of the birch forest matrix has an effect on their history, current, and future changes. Between the early twentieth century and the mid-1970s, the pine forest and treeline locations remained relatively stable. In response to 20th century climate warming, forest line populations increased in number and density, but their positions remained unchanged. By the mid-1970s, the treeline, which consists of dispersed solitary, fast-growing, and vigorous trees, had moved 135 metres up-valley through the birch forest belt to a site about 12 kilometres south of the spot. The existence of the subalpine birch forest belt is thought to be responsible for the vast separation of forest and tree line. This claim is backed by the outlier old-established pine trees’ robust growth and proliferous reproduction, resulting in a radical generation change in the treeline ecotone. This process is most visible in birch forest gaps. As a result, under current climatic conditions, the future pine forest line is thought to be much farther south (and higher) than it is now within the competing birch forest belt. This forest range is likely to be realised in the case of future climate change, given the subalpine birch forest’s demise due to drought. This would be a return to the early and middle Holocene, when pine dominated the upper tree line ecotone and the birch belt was underdeveloped.

Author (s) Details

Leif Kullman
Department of Ecology and Environmental Science, Umeå University, ZSE 901 87 Umeå, Sweden.

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