Characterization of leaf area index and understory vegetation development following pre-commercial thinning in boreal mixedwood forests

I examined the effect of pre-commercial thinning (PCT) on overstory leaf area (LAI) and understory vegetation in young boreal mixedwood stands ten years post-thinning. Results indicated that reducing aspen density to <1500 trees/ha (7m2/ha) reduced overstory LAI and increased white spruce root collar diameter. Three methods for measuring LAI were compared. The direct method for measuring LAI using litter traps, was considered the reference, but provided the most variable estimates. Both hemispherical photography and LAI-2000 measurements underestimated LAI, likely due to the non-random distribution of leaves. The understory plant community responded to thinning with an increase in cover and a shift in abundance towards shade intolerant species. Understory species richness was not affected by thinning and introduced species abundance did not increase in response to thinning. Small shifts in understory cover and dominance observed are consistent with the fact that most understory boreal species are adapted to disturbance.