Measuring forest canopy cover is critical for forest ecology research. Several different canopy cover measurement methods are available, but the decision of which method to utilize is often based on availability or ease of use, as opposed to objective comparison. To investigate which method provided the most useful data, we planted and monitored tree seedlings in plots with and without canopy disturbance (32 total) in central Virginia. In spring 2018, over a thousand seedlings of flowering dogwood (Cornus florida), sweetgum (Liquidambar styraciflua), tupelo (Nyssa sylvatica), red maple (Acer rubrum), and black cherry (Prunus serotina) were planted. Canopy cover directly over each “seedling station” (15 per plot) was recorded in July via: a) a traditional spherical densiometer and b) a CI-110 Plant Canopy Imager (CID Bio-Science). Seedling height and leaf number were recorded in both June and August. Seedling growth was then analyzed, separately for each species and response variable (height and leaf number), as a function of the two different canopy cover estimates, to determine which measurement method was the best predictor of growth.
Results/Conclusions
Overall, the two canopy estimation methods yielded similar results. However, growth was better predicted by the traditional spherical densiometer than the modern canopy imager system; in all cases, either predictive ability (r2) was slightly higher for the densiometer or neither method proved predictive (p > 0.05 for both). Height growth of dogwood, tupelo, and sweetgum were negatively related to canopy cover (both methods), while height growth of red maple and cherry were unrelated to canopy cover (both methods). The largest discrepancy between canopy estimation methods was for dogwood (densiometer r2 = 0.14; canopy imager r2 = 0.10; both methods p-val < 0.0001). Leaf growth of tupelo was negatively affected by canopy cover, with nearly identical results for both methods. For dogwood and sweetgum, leaf growth was significantly negatively related to canopy cover only when canopy cover was estimated with a spherical densiometer (although r2 values were very low, never exceeding 0.05). Matching the other response variable, leaf growth of red maple and cherry were unrelated to canopy cover (both methods). Our findings demonstrate that these two methods are largely interchangeable, but also suggest that – surprisingly – the old-fashioned method may be superior, at least for the purposes of predicting seedling growth.