© 2002 Heron Publishing—Victoria, Canada
The influence of the forest canopy on nutrient cycling
Cindy E. Prescott (1)
1. Department of Forest Sciences, University of British Columbia, 2424 Main Mall, Vancouver, B.C. V6T 1Z4, Canada (cpres@interchange.ubc.ca) / Received January 16, 2002; accepted June 26, 2002; published online October 1, 2002
Summary
Rates of key soil processes involved in recycling of nutrients in forests are governed by temperature and moisture conditions
and by the chemical and physical nature of the litter. The forest canopy influences all of these factors and thus has a large
influence on nutrient cycling. The increased availability of nutrients in soil in clearcuts illustrates how the canopy retains
nutrients (especially N) on site, both by storing nutrients in foliage and through the steady input of available C in litter.
The idea that faster decomposition is responsible for the flush of nitrate in clearcuts has not been supported by experimental
evidence. Soil N availability increases in canopy gaps as small as 0.1 ha, so natural disturbances or partial harvesting practices
that increase the complexity of the canopy by creating gaps will similarly increase the spatial variability in soil N cycling
and availability within the forest.
Canopy characteristics affect the amount and composition of leaf litter produced, which largely determines the amount of nutrients
to be recycled and the resulting nutrient availability. Although effects of tree species on soil nutrient availability were
thought to be brought about largely through differences in the decomposition rate of their foliar litter, recent studies indicate
that the effect of tree species can be better predicted from the mass and nutrient content of litter produced, hence total
nutrient return, than from litter decay rate. The greater canopy complexity in mixed species forests creates similar heterogeneity
in nutritional characteristics of the forest floor.
Site differences in slope position, parent material and soil texture lead to variation in species composition and productivity
of forests, and thus in the nature and amount of litter produced. Through this positive feedback, the canopy accentuates inherent
differences in site fertility.
Keywords:
canopy gaps, clearcut, decomposition, litterfall, nitrification, nitrogen mineralization, site fertility, species influences,
species mixtures.
