Chemical composition of stemflow from some eastern Canadian tree species

Stemflow samples from three hardwood and six softwood species were collected during May through October and concentrated by the freeze-concentration method and then freeze-dried. Liquid samples were used for pH determinations and the freeze-dried materials were analyzed for carbohydrates; carbon, hydrogen, nitrogen, and oxygen of the organic fraction; and calcium, magnesium, sodium, potassium, and iron of the inorganic constituents.In comparison with hardwoods, the stemflow from softwoods was more acidic and contained larger concentrations of total solids (organic + inorganic constituents).Except for nitrogen, which was present in larger proportions in hardwood than in softwood stemflow, there was no distinct difference in the composition of other constituents of the organic fraction. Concentrations of cations in the stemflow from the majority of the species decreased in the order of potassium, calcium, sodium, and magnesium. Only potassium and carbohydrates were returned to the soil in kilogram quantities per hectare whereas the other nutrients were returned in amounts less than 1 kg/ha. </jats:p

NUTRIENT CYCLING AND AVAILABILITY IN FOREST SOILS

Nutrient availability in different forest soils must be known before increased wood production can be sustained either by adding supplemental nutrients or by judicious silvicultural operations to optimize the linkage between the variable nutrient requirements of forest crops. This is complicated by the variable availability of nutrients on forest sites during crop development. Forest crops unlike agricultural crops have long rotation periods which make it difficult to apply agricultural methods of estimating potentially available nutrients directly to forest soils. Presented in this review are (i) various approaches used in forestry to estimate the nutrient supplying potential of different sites, (ii) factors affecting nutrient availability, and (iii) evidence to suggest that nutrient cycling processes in forest ecosystems are important factors affecting tree growth. It is suggested that data from chemical analyses of soil samples collected at specific times and sites should be used with caution for both practical decision making and simulation modelling purposes. Key words: Nitrogen, phosphorus, litterfall, throughfall, stemflow, mineralization </jats:p