Legacy of forest composition and changes over the long-term on tree radial growth

Abstract

The forests of North America have undergone important changes since European settlement, particularly in terms of stand composition and associated changes in soil properties. While soil nutrients availability is known to influence forest productivity, the causes and consequences of its variation through time remain poorly understood. This study investigates the effects of long-term changes in forest composition and soil properties on the radial growth of sugar maple (Acer saccharum Marsh.) and balsam fir (Abies balsamea (L.) Mill.), two important species of northeastern North America’s forests. Using data from 130 plots measured in 1930 and in 2012–2014 and a mixed-effects modelling approach, we studied the links between radial growth, soil nutrients availability, current stand composition, and shifts in vegetation. The radial growth of balsam fir was found to vary with soil available nitrogen and present-day relative basal area of yellow birch in the stand, while that of sugar maple was found to be invariant to soil characteristics, but proportional to present-day spruce (Picea spp.) relative basal area. However, no direct effects of vegetation change on radial growth were detected. Our results suggest that prior stand composition had no influence on radial growth of both studied species, yet vegetation change could indirectly influence balsam fir growth through an improvement of litter quality with an increase in the abundance of yellow birch (Betula alleghaniensis Britton). Moreover, despite clear differences between the studied species, we conclude that maintaining a certain proportion of compositional diversity may enhance radial growth of both balsam fir and sugar maple.