Mycorrhizal networks and distance from mature trees alter patterns of competition and facilitation in dry Douglas-fir forests |
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Authors: | François P Teste Suzanne W Simard |
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Institution: | (1) Department of Forest Sciences, University of British Columbia, Vancouver, BC, V6T 1Z4, Canada |
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Abstract: | The distribution of dry Douglas-fir forests in western North America is expected to shift northward with climate change and
disappear from the grassland interface in the southern interior of British Columbia. This shift may be accentuated by clearcutting,
a common harvesting practice that aims to reduce the competitive effects of residual mature trees on new regeneration, but
in so doing, ignores their facilitative effects. In this study, we investigated the net effects of competition from and facilitation
by mature trees retained on harvested sites on seedling establishment in the dry interface Douglas-fir forests. We demonstrate
that access to a mycorrhizal network (MN) and proximity to trees have important influences on seedling performance. On six
sites, we established trenched plots around 24 mature Pseudotsuga menziesii var. glauca (Douglas-fir) trees, then planted Douglas-fir seedlings into four mesh treatments that served to restrict MN access (i.e.,
planted into mesh bags with 0.5-, 35-, or 250-μm pores, or without mesh) or into impermeable bags (grown in isolation) at
four distances (0.5, 1.0, 2.5, or 5.0 m). Seedling survival tended to be greater and water stress lower where seedlings had
full access to the MN. Seedling height, shoot biomass, needle biomass, and nutrient uptake peaked at 2.5–5.0 m from mature
trees. Seedlings 0.5 m from mature trees had lower CO2 assimilation rates and wood δ13C compared to seedlings 5.0 m away. Competition for soil resources was highest near mature trees but facilitation was relatively
greater at further distances, resulting in a zone of net benefit for seedlings. These results show that intraspecific tree-seedling
interactions are both competitive and facilitative in dry Douglas-fir forests, and that they are spatially dependent. After
disturbance, maintaining residual mature trees may be important for their beneficial regeneration zones.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. |
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Keywords: | Tree-seedling interactions Competition Facilitation Mycorrhizal network Pseudotsuga menziesii var glauca |
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