OVERSTORY STRUCTURE DRIVES FINE-SCALE COUPLING OF UNDERSTORY LIGHT AND VEGETATION IN TWO TEMPERATE RAINFOREST FLOODPLAINS

Riparian ecosystems – particularly floodplains – of temperate rainforest regions are productive, diverse, functionally important and socially valued, yet we lack key information about their structure and function to guide conservation and management. In two one-hectare floodplain sites in coastal British Columbia, we mapped tree locations, classified gap processes, and described understory vegetation and light transmission on a systematic grid. We used hemispheric photography and spatial interpolation to map understory light and we examined how environmental heterogeneity affects understory vegetation. Understory light levels are high (overall median 18% full sun) but vary appreciably over short distances (0.5% to 19% full sun over 14 m). Understory composition varies in relation to light transmission, indicating that overstory structure drives fine-scale spatial structure in the understory plant community. Overstory trees appear to create “shade refuges” from competition with dominant shrubs. Shrub cover increases with light and may also play a role in maintaining persistent canopy openings by slowing conifer recruitment. Despite substantial differences in age and development history, each stand exhibits fine-scale spatial coupling of understory light and vegetation. Management practices encouraging structural complexity may accelerate development of similar processes and patterns to restore floodplain function in high-density second growth stands.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author