Effects of red alder and paper birch competition on juvenile growth of three conifer species in southwestern British Columbia
Cortini, F. and P. G. Comeau . 2008. Forest Ecology and Management 256: 1795-1803
Abstract
We examined the effects of competition from red alder (Alnus rubra Bong.) and paper birch (Betula
papyrifera Marsh.) on the growth of western redcedar (Thuja plicata Donn), western hemlock (Tsuga
heterophylla Sarg.), and Douglas-fir (Pseudotsuga menziesii Franco) at a site near Maple Ridge, British
Columbia, Canada. At this site, the three coniferous species and two broadleaf species had been planted in
1999 as part of a long-term experiment examining effects of broadleaf density on conifer growth. Red
alder and paper birch were planted alone and as a 50:50 mixture at four densities (0, 277, 556, and
1150 stems ha-1). Red alder density was positively correlated with total available nitrogen in soil measured using ionexchange
membranes whereas density of paper birch was not. For Douglas-fir only, foliarN concentration
was positively related to red alder density. Relationships between stem volume increment and
competition indices varied between the three conifer species: (1) For Douglas-fir the highest correlations
were obtained using a distance-independent competition index based on broadleaf crown surface area
and diffuse transmittance (DIFN) measured using LAI-2000 plant canopy analyzers had the lowest R2 of
the competition measures tested; (2) for western redcedar the highest correlations were with DIFN and
the second best competition measures were distance-dependent indices; (3) for western hemlock
broadleaf competition did not have significant effects on growth. Height of each species at the time of
measurement and crown surface area appear to be more important than shade tolerance in affecting
conifer growth. At this site, significant reductions in stem volume (30%) of Douglas-fir and western
redcedar occurred when red alder density exceeded 500 stems ha-1 while paper birch was not
detrimental to western redcedar growth until densities exceeded 1000 stems ha-1 and birch density did
not significantly affect Douglas-fir. The influence of red alder on soil N and foliar N of Douglas-fir may be
leading to a weaker relationship between growth and DIFN for Douglas-fir compared to that for western
redcedar.
Key Words
Interspecific plant competition, Nutrients availability, Nitrogen, Tree growth, Light transmittance, Competition index, Red alder, Paper birch, Douglas-fir, Western redcedar, Western hemlock
