An Unexpected Change in Spatial Pattern Across 10 Years in an Aspen-White Pine Forest

The change in spatial pattern due to mortality over a period of 10 years was examined in a c. 60-year-old second-growth aspen-white-pine forest in northern Michigan, USA. It is predicted that unitary plants undergoing competitive thinning will shift toward a more regular distribution of stems. Such a pattern has been reported for temperate jack pine (Pinus banksiana) and four tropical tree species, but was not seen in our population of canopy aspen. The distribution of aspen living in 1989 tended toward greater clumping than that expected from random mortality of aspen living in 1979. It is suggested that this contrast to theoretical predictions was due to the clonal nature of aspen. White pine invading under aspen was clumped at all scales, both in 1979 and 1989, and its distribution showed significant repulsion from aspen at scales of 11 m and 14 m in 1989. This suggests that the net effect of the initially dominant aspen on invading white pine was one of inhibition of establishment, and that the spatial location and therefore the abundance of white pine was constrained by the locations of aspen ramets.