Modeling climatic effects on stand Height/Site index of plantation-grown jack pine and black spruce trees

Abstract

Stand height/site index equations that incorporate climate variables were developed for plantation-grown jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] B.S.P.). Study data came from stem analysis of three dominant or codominant trees sampled from 73 plots for jack pine and 75 plots for black spruce within even-aged monospecific plantations located on 50 sites (25 sites per species) in the Canadian boreal forest region of Northern Ontario. A nonlinear mixed-effects approach was applied to fit the stand height equations. The climate variables that were significant in explaining the variation in heights of dominant and codominant trees were growing season mean temperature and growing season total precipitation. Including climate variables significantly improved the fit statistics of the stand height model for both species. For each species, stand heights were predicted for a randomly selected location for the growth period of 2011 to 2040 under A2 and B2 climate change scenarios. At th end of the growth period, projected heights were reduced by 8 and 2% for jack pine and 28 and 16% for black spruce under A2 and B2 climate change scenarios, respectively, compared with heights projected under a current climate scenario. The site index of a stand can be estimated using the stand height model by calculating height at a given base (index) age. In the absence of climate data, the model fitted to only the height-age pair data can be used as a stand height/site index equation.