Comparison of growth intercept and site index models of black spruce plantations and natural stands in Northern Ontario

Abstract

Black spruce (Picea mariana Mill. B.S.P.) is one of the most important tree species in Canada, both ecologically and commercially. The forest industry has steadily increased efforts to artificially regenerate areas that have been harvested resulting in expanding areas of black spruce plantations. The increase in amount o f area and the number of trees that are planted requires accurate tools for height and yield estimation in these stands to ensure sustainable forest management and a dependable future wood supply. Currently these tools are unavailable resulting in underestimated site productivity in black spruce plantations by a site index and growth and yield model that was derived from natural stands. In this study, 62 sites were sampled across northern Ontario ranging from Kirkland Lake in the east to Kenora in the west. Within each plot 3 undamaged dominant or co-dominant trees with no indication o f suppression were felled for stem analysis. These sites were planted, contained a minimum black spruce composition of 70%, and were at least 40 years old. Within each plot a soil sample was collected from the C horizon and relationships between soil characteristics and site quality were examined. Accurate and precise growth intercept and site index models were developed from the stem analysis data collected from black spruce plantations. These models were compared to models for natural stands using Carmean’s (2006) data. Comparison of site index curves between planted and natural stands showed a significant difference. Planted stands displayed increased height growth patterns, especially in early breast height ages, as well as enhanced total height prediction accuracy when compared to natural stands. These height growth increases may be directly related to silvicultural activities that occur on productive upland sites. Soil characteristics from the C horizon were related to site productivity in black spruce plantations. Soil pH in calcium chloride, elevation, sand, and silt content were shown to be significant factors. Factor analysis concluded that many soil characteristics, such as soil pH in calcium chloride, soil pH in water, Ca, Mg, Na and clay content attributed for similar variances to site quality in terms of site index. Due to its shallow rooting nature, and previous studies that have shown black spruce to have a maximum attainable height of 20 to 21 m before becoming susceptible to windthrow, a rotation age of 60 years on productive upland sites is recommended. In a 300 year scenario, productive upland black spruce sites harvested at a 60 year rotation produced 223 % more merchantable volume than natural stands. If these stands are not harvested until 80 years, stands could incur volume losses of at least 30 % due to windthrow and tomentosus root rot.