Evaluation of relationships between understory light and aspen basal area in the British Columbia central interior

Abstract

Data from twenty, 9–40-year-old, aspen ( Populus tremuloides Michx.) stands in four biogeoclimatic zones of northeastern and central British Columbia (BC) were analyzed to determine whether relationships between under- and within-canopy light availability (measured using the LiCor LAI-2000) and aspen abundance were similar between ecosystems. A logarithmic model provided the best-fit for these data, explaining 51–81% or 51–82% of the variation in light availability when aspen basal area (BA a) or aspen relative density (RD a), respectively, was the independent variable. Relationships between understory light and BA a or RD a differed significantly ( p < 0.001) between biogeoclimatic zones, indicating that zone-specific models are appropriate. The BWBS and SBS zones were similar, but differed from the drier IDF and SBPS zones, which also differed from each other. These results indicate that differences in relationships between resource capture and plant dimensions may be one reason for differences in competitive influences of aspen in different areas. Basal area and relative density of aspen were also found to be higher in moister zones than in drier zones, and also contribute to differences in the competitive effects of aspen. Vertical light gradients were also measured to a height of 8 m within aspen canopies. Light availability increased rapidly with relative height in the canopy, especially where transmittance to the understory was low. As with understory light, relationships differed significantly ( p < 0.001) between biogeoclimatic zones.