Nitrogen Fixation: A Biotechnological Opportunity for Canadian Forestry

Intensive harvesting and forest management systems will increase nitrogen and organic matter losses from forest soils, and there will be a need to manage the soils using both fertilizers and nitrogen-fixing techniques to maintain site productivity. Legumes and non-legumes with nitrogen-fixing symbioses can fix up to 300 kg ha−1 year−1 of nitrogen and provide soil organic matter, but poor soils will need fertilization to maintain the nitrogen-fixing process. There are many species and cultural techniques the forester can use, including green manuring and mixed stands, but carefully designed field trials are needed to solve cultural problems. In addition, there are many opportunities for genetic selection of both the trees and shrubs and the bacteria (actinomycetes) involved. Before the systems can be used effectively the operational foresters will need to be better informed about the soil biota and the interaction with site and vegetation. The development of nitrogen-fixing systems offers a biotechnological opportunity for Canadian foresters to increase tree yield while maintaining site productivity. </jats:p

EFFECT OF FOREST HARVEST ON DECOMPOSITION AND COLONIZATION OF MAPLE LEAF LITTER BY SOIL MICROARTHROPODS

The effect of whole-tree and conventional forest harvest on sugar maple leaf litter decomposition and the colonization of litter bags by soil microarthropods was investigated in a mixed conifer/hardwood forest on the Canadian Shield for 2 yr, beginning 17 mo after forest harvesting. Decomposition of leaves in litter bags was significantly greater (P &lt; 0.05) on harvested plots than on the uncut plot (U), and was greater on the whole-tree harvest plot (W) than on the conventionally harvested plot (C). The increase in nitrogen (N) concentration of the litter over the 2-yr study was greater (P &lt; 0.05) on the C than on the other plots and was in the order C &gt; W &gt; U. Colonization of leaf litter by soil microarthropods was greater (P &lt; 0.05) on the U than on harvested plots, and was greater (P &lt; 0.05) on the C than on the W plot. Thus, soil microarthropods did not appear to be responsible for the faster decomposition on harvested plots compared to the uncut plot, nor were differences in soil temperatures or moisture content among plots responsible for the faster rates of decay. More rapid decay on harvested plots suggests that harvesting increased the availability of nutrients contained in the forest floor. This may result in a loss of both nutrients and long-term productivity, especially with whole-tree harvesting, unless mechanisms are in place to conserve nutrients. Key words: Decomposition, soil microarthropods, whole-tree harvest, soil nitrogen, nutrient cycling, mineralization </jats:p