Old‐growth forest structure in a low‐productivity hypermaritime rainforest in coastal British Columbia, Canada

Kira M Hoffman,Ian J W Giesbrecht,Brian M Starzomski,Andrew J Trant,Ken P Lertzman

doi:10.1002/ecs2.3513

Kira M Hoffman, Ian J W Giesbrecht + Show 3 more

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https://doi.org/10.1002/ecs2.3513

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Abstract

AbstractDendrochronological analyses were conducted across a gradient of productivity and soil drainage quality characterizing four vegetation types in a low‐productivity hypermaritime (perhumid) temperate rainforest on the Central Coast of British Columbia, Canada. We examined the structure, composition, and stand dynamics of trees growing in 400 m2 plots located in blanket bog, bog woodland, bog forest, and zonal forest vegetation types. We sampled over 2500 trees and 1500 seedlings and saplings and our dendrochronological reconstruction of six tree species revealed establishment ages extending to 660 A.D. (1350 yr). All forest plots contained numerous old trees (>250 yr) and the zonal forest and bog forest vegetation types contained significantly taller trees and also had the greatest amount of suppressed, shade‐tolerant tree species. The bog woodland vegetation type contained more seedlings and saplings than the other three vegetation types combined. The bog forest vegetation type had the highest density of dead standing trees (~530 per hectare). Blanket bogs contained an open structure with very few old trees (>250 yr). Significant differences in the ages of trees existed between forested vegetation types and the more open blanket bog vegetation type. Several trees exceeded 1000 yr in age and were situated in lower‐productivity bog forest and bog woodland sites. We found no evidence of widespread tree cohort establishment, indicating that small‐scale disturbances such as individual tree mortality and gap‐forming dynamics are likely the most frequent disturbance in the study area.

Highlights

Natural and anthropogenic disturbances occur across temporal and spatial scales and play an important role in forest ecosystem dynamics (Pickett and White 1985, Turner 1989, White et al 2018)
All vegetation types contained multi-aged stands and old trees (>250 yr), but the average number of old trees was higher in the zonal forest, bog forest, and bog woodland vegetation types when compared to the blanket bog vegetation type (Fig 4)
Dendrochronological reconstructions of tree ages confirm that trees (>7.5 cm dbh) have persisted at densities of approximately 80 trees per hectare in the zonal forest vegetation type, 85 trees per hectare in the bog forest type, 95 trees per hectare in the bog woodland vegetation type, and 15 trees per hectare in the blanket bog vegetation type for at least 200 yr (Figs. 3, 5)

Summary

Introduction

Natural and anthropogenic disturbances occur across temporal and spatial scales and play an important role in forest ecosystem dynamics (Pickett and White 1985, Turner 1989, White et al 2018). In the coastal temperate rainforest (CTR) of North America are generally dominated by small-scale, multicohort disturbances such as standing tree mortalities or single-tree fall (Spies and Franklin 1988, Lertzman 1992, Lertzman et al 1996, Banner et al 2005, Daniels and Gray 2006). Gap-forming disturbances as a result of tree mortality (standing dead or fallen trees) affect large portions of old-growth temperate rainforests annually, and millennia of these small-scale disturbances coupled with conifer adaptations to withstand disease and fungal pathogens have promoted old growth, multi-age forests across the northern CTR (Swanson and Franklin 1992, Lertzman et al 1996, MacKinnon 2003, Daniels and Gray 2006, DellaSala et al 2011, White et al 2018).

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