Experimental determination of soil characteristics optimal for the growth of ten hardwoods planted on abandoned farmland

Abstract

The growth and survival of ten hardwood tree species, planted in abandoned fields in southern Québec, over a range of soil and geological conditions, were analyzed in order to identify optimal site conditions for species growth. From a total of 23 experimental blocks, in which a total of 5750 seedlings was planted, we described six different soil types based on a cluster analysis of 12 soil variables. Factorial analysis linked species growth, in height and diameter, to gradients of soil nutrient richness and soil moisture. A statistical indicator of the degree of specificity of species toward soil variables was obtained by Kaiser's measure of sampling adequacy (Kaiser, 1970. Little jiffy, mark IV. Educational and Psychological Measurement 34, 111–117). After four growing seasons, heights of red ash, red oak and bur oak are markedly different among soil types. Best red ash growth occurred on the most nutrient-rich and humid soils, as opposed to red oak whose best growth occurred at the nutrient-poor and dry endpoints of the edaphic gradients. Bur oak differs from red oak in having good growth over a wide range of soil moisture conditions. Sugar maple growth was best on well drained and relatively nutrient-rich soils, but had high within-site variability. Yellow birch, with a low overall survival, attained its best growth in the most nutrient-poor, as well as above-average soil moisture conditions. The optimal edaphic conditions are weakly defined in the case of bitternut hickory and black walnut, the largest size of which was attained in below-average and in better-than-average soil nutrient conditions respectively. Silver maple performed equally well on the majority of soil types, but achieved exceptional growth on the wettest soil type. White ash and butternut growth also suggest a wide ecological amplitude, the first having good growth and the second having slow growth on all soil types. A synthesis of the experimental results is presented as a decisional chart for silviculturalists. Soil texture, moisture and pH are ordered according to their potential for the optimal growth of species. Identified geological, geomorphologic and pedological site constraints on species growth must be considered in the species selection process, especially for species which attain their best growth in narrower segments of the edaphic gradients.