Site quality evaluation of jack pine in Northern Ontario using site-index curves

Abstract

Jack pine stem analysis data from 383 fully stocked, mature, undisturbed plots were collected from studies located in four Ontario Ministry of Natural Resources regions (Northeast, Northern, North Central, Northwestern) and four broad landforms (lacustrine, glaciofluvial, morainal, shallow depth to bedrock). Comparisons of height-growth patterns in the regions and in the landforms were made using covariate analysis for nonlinear equations. Several different height-growth models and site-index prediction models were fitted to stem analysis data from 323 plots; the remaining 60 plots were used as verification plots. Results show that height growth was best described by a model developed by Ek (1971) and later modified by Newnham (1988). The 95% prediction interval for differences (observed - predicted) were within +/- 1.39 m and -i-/- 1.59 m for the computation and verification data sets respectively. A linear model developed by Monserud predicted site index better than an exponential or difference equation. But site-index predictions made indirectly from Newnham's height dependent model were as accurate as using the linear Monserud model. Early growth before 20 years breast-height X age (BHA) was highly variable and resulted in poor prediction of site index at 50 years. Site index prediction intervals for data older than 20 years BHA were within +/- 1.69 m. Jack pine height-growth patterns were similar among regions, but some significant differences were found among landforms. Jack pine growing on good sites on all landforms had similar height-growth patterns. But significant differences in height-growth patterns were found on poor quality sites; the upper asymptote flattens more sharply on shallow soils when compared to glaciofluvial soils. Height-growth patterns were similar to patterns found for other studies in North Central Region (Lenthall 1986, Carmean and Lenthall 1989, Goelz and Burk 1992). Results show that the anamorphic curves developed by Plonski (1974) slowed more rapidly after index age as site quality decreased. Jack pine height-growth patterns in Ontario are similar to published curves from other areas in Canada with the exception of more rapid early growth on poor quality sites and a flatter upper asymptote on good sites.