Soil-site relations for trembling aspen (Populus tremuloides Michx.) in Northwestern Ontario / by Yanjun Li

Soil-site relations for trembling aspen in Northwestern Ontario were
\nstudied using 98 site plots representing a wide range of glacial
\nlandforms, soil conditions, and site quality. Site index was related to
\nfeatures of soil and topography using multivariate statistical analyses
\nincluding principal component analysis, multiple regression analysis and
\ncluster analysis. Site index ( SI = height of dominant and codominant
\ntrembling aspen trees at 50 years breast-height age) was used as the
\ndependent variable; 45 soil and topographic values were used as
\nindependent variables. Principal component analysis combined with
\ncorrelation coefficients was used to select 10 variables from 22
\nvariables that were closely associated with site index; these 10 variables
\nare not closely correlated with each other. Preliminary regressions
\nindicated that the soil-site relationships were much better expressed
\nwhen plots were stratified into three landform types as opposed to a
\nsingle regression combining all plots.
\nFinal regression equations were computed describing soil-site
\nrelationships on soils developed from glaciofluvial, morainal, and
\nlacustrinal landforms. The final regression equation for the glaciofluvial
\nsoils included depth to root restricting layer and drainage class as site index
\npredictor variables. The final regression equation for the morainal
\nsoils included silt plus clay content of the A horizon, coarse fragment
\ncontent of the C horizon, and depth to root restricting layer. The final
\nregression equation for the lacustrine soils included the clay content of
\nthe C horizon, and depth to mottles.
\nThe 98 plots were clustered into six groups representing different soil
\nconditions. The FEC soils S3, S4, S5 were the best sites; the SS8, SS7, S7,
\nS8, SS5, SS4 were the worst sites for aspen. However, cluster results
\nwere not significant due to a wide range of site indices within each of the
\nsix defined groups. Large standard deviations and standard errors of the
\nmean exist in most groups. Thus the use of these groups is not
\nrecommended for estimating aspen site index.

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