Limited prospects for future alpine treeline advance in the Canadian Rocky Mountains. (1st July 2018)

• Record Type: Journal Article
• Authors: Davis, Emma L.; Gedalof, Ze'ev
• Is Part Of: Global change biology. Volume 24:Number 10(2018)
• Page Start: 4489
• Page End: 4504
• Publication Date: 2018-07-01
• Subjects: alpine treeline -- engelmann spruce -- herbivory -- microclimate -- microsite limitation -- seed addition -- species distributions -- subalpine fir; Climatic changes -- Environmental aspects -- Periodicals; Troposphere -- Environmental aspects -- Periodicals; Biodiversity conservation -- Periodicals; Eutrophication -- Periodicals; 551.5
• DOI: 10.1111/gcb.14338
• Languages: English
• ISSNs: 1354-1013

Abstract

Abstract: Treeline advance has occurred throughout the twentieth century in mountainous regions around the world; however, local variation and temporal lags in responses to climate warming indicate that the upper limits of some treelines are not necessarily in climatic equilibrium. These observations suggest that factors other than climate are constraining tree establishment beyond existing treelines. Using a seed addition experiment, we tested the effects of seed availability, predation and microsite limitation on the establishment of two subalpine tree species ( Picea engelmannii and Abies lasiocarpa ) across four treelines in the Canadian Rocky Mountains. The effect of vegetation removal on seedling growth was also determined, and microclimate conditions were monitored. Establishment limitations observed in the field were placed in context with the effects of soil properties observed in a parallel experiment. The seed addition experiment revealed reduced establishment with increasing elevation, suggesting that although establishment within the treeline ecotone is at least partially seed limited, other constraints are more important beyond the current treeline. The effects of herbivory and microsite availability significantly reduced seedling establishment but were less influential beyond the treeline. Microclimate monitoring revealed that establishment was negatively related to growing season temperatures and positively related to the duration of winter snow cover, counter to the conventional expectation that establishment is limited by low temperatures. Overall, it appears that seedling establishment beyond treeline is predominantly constrained by a combination of high soil surface temperatures during the growing season, reduced winter snowpack and unfavourable soil properties. Our study supports the assertion that seedling establishment in alpine treeline ecotones is simultaneously limited by various climatic and nonclimatic drivers. Together, these factors may limit future treeline advance in the Canadian Rocky Mountains and should be considered when assessing the potential for treeline advance in alpine systems elsewhere Abstract : Average proportional effect size of biotic and abiotic controls on tree seedling establishment, averaged across four study sites in the Canadian Rocky Mountains. Together, predation, microsite availability, and soil properties reduce the establishment potential of tree seedlings within and beyond the treeline.