A century of high elevation ecosystem change in the Canadian Rocky Mountains

Andrew Trant,Eric Higgs,Brian M Starzomski

doi:10.1038/s41598-020-66277-2

Andrew Trant, Eric Higgs + Show 1 more

Open Access

https://doi.org/10.1038/s41598-020-66277-2

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Journal: Scientific Reports	Publication Date: Jun 16, 2020
Citations: 21	License type: open-access

Affiliation: University of Victoria, University of Waterloo

Abstract

Mountain ecosystems serve as sentinels of change, and those in the Canadian Rocky Mountains have undergone a pronounced shift over the past century. We present quantitative analyses of 81 high-resolution image pairs of systematic historic surveys and repeat photographs of Canadian Rocky Mountain habitats, measuring treeline advance, changes in tree density, and shifts in growth form from krummholz to trees. With a time-lapse of 68 to 125 years (mean 93.5 years) between image pairs, these photographs contain novel information about long-term ecological change across broad spatial scales. In the 197 linear km of mountain habitat over 5 degrees of latitude examined, we found evidence of treeline advance at 90/104 sites, increases in tree density at 93/104 sites, and many sites (79/95) showing detectable changes in the growth form of trees from krummholz to erect tree form. Using generalized linear mixed models, we found that treeline at higher altitudes and further north had a greater probability of advancing while regional climate factors in our model did not significantly explain our results. Historic references, such as those documented here, are invaluable for providing conservation targets and for contextualizing disturbance and broad scale ecosystem change.

Highlights

Mountain ecosystems serve as sentinels of change
We present quantitative analyses of 81 high-resolution image pairs of 104 treeline ecotones spanning approximately 100 years and 197 linear km to address the following research questions: 1) How much treeline advance, tree density change, and shifts from krummholz to tree growth forms has occurred in these mountain ecosystems over the last century?; and 2) To what extent can observed changes be explained by regional climate change, disturbance, and site factors? We will explore the value of
Over a mean time period of 93.52 ± 1.20 years, we examined a combined total of 197 km of treeline ecotones across 5 degrees of latitude in the Canadian Rocky Mountains

Summary

Introduction

Mountain ecosystems serve as sentinels of change. Understanding these changes is important for water and food security, forestry, biodiversity, and many forms of tourism and recreation[1,2]. Remotely-sensed products can be used to examine treeline change at large spatial scales, far exceeding 1 km[2], but lack species-specific information and with the wide-spread availability of satellite imagery only beginning in the early 1980s, these methods lack the temporal depth of other approaches[15,16]. We present quantitative analyses of 81 high-resolution image pairs of 104 treeline ecotones spanning approximately 100 years and 197 linear km to address the following research questions: 1) How much treeline advance, tree density change, and shifts from krummholz to tree growth forms has occurred in these mountain ecosystems over the last century?; and 2) To what extent can observed changes be explained by regional climate change, disturbance, and site factors (e.g. slope and altitude)?

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