Influences of fine-scale disturbance on germinant success in a treeline ecotone

ABSTRACT

Fine-scale disturbance can increase seed access to suitable substrates, facilitating germinant emergence and survival, which are necessary elements for treeline advance. We conducted an experiment to test this hypothesis in a white spruce (Picea glauca) treeline ecotone in southwest Yukon, Canada. Sixty seed germination quadrats were established at two elevations (treeline and alpine tundra) and subjected to three levels of simulated disturbance. We sowed 125 seeds in half of the quadrats (30) and measured their emergence and survival over 3 years. Soil temperature, moisture, and organic depth were recorded in all treatments. Treeline quadrats had significantly greater seedling emergence and survival than alpine tundra quadrats. Mean soil temperature, moisture, and organic layer depth were all greater in treeline quadrats. Partially scarified quadrats had the highest germinant emergence compared to unscarified and completely scarified quadrats. Completely scarified quadrats had the highest temperature range and the lowest soil moisture. The results indicate that moderate levels of disturbance can positively influence seedling emergence, while more severe disturbance can lead to high temperature ranges and moisture loss that negate the benefits of lower interspecific competition. Collectively, our findings suggest that fine-scale disturbance can play a significant role in influencing seedling presence in treeline ecotones.

KEYWORDS:

• Bioturbation
• treeline
• zoogeomorphology
• seedlings
• G-TREE

Acknowledgements

We thank the Kluane First Nation and Lù′àn Män Ku Dän (Kluane Lake People) for giving us permission to work on their land. We also thank the Arctic Institute of North America’s Kluane Lake Research Station and its managers Sian Williams and Lance Goodwin for logistical support. Thanks to the National Tree Seed Centre and its Manager, Dale Simpson, for providing the seeds. Comments provided by Charles Lafon and two anonymous reviewers helped improve the manuscript and we thank these individuals for their time and effort.