Root Decomposition and Nutrient Flux Following Whole-Tree Harvest of Northern Hardwood Forest

Abstract

Abstract Decomposition of roots of four dominant species (Acer saccharum, Betula alleghaniensis, Fagus grandifolia, Picea rubens) in a northern hardwood ecosystem was measured following whole-tree harvest of watershed 5 at Hubbard Brook Experimental Forest, New Hampshire. To quantify the importance of element release from tree root systems after forest harvest, measurements of macronutrient (N, K, P, Ca, Mg) release from roots of seven diameter (mm) classes (< 0.6, 0.6-1.0, 1.0-2.5, 2.5-5.0, 5-10, 10-20, 20-100) were combined with information on root system nutrient content. Decay of fine roots (all species) was initially rapid but declined abruptly after the first summer. Ash-free weight loss from small woody roots decreased with increasing root diameter and was much slower than decay rates for corresponding aboveground tissues (twigs and branches). Weight loss rates among species generally were not significantly different; however, large woody roots (10-100 mm diameter) of sugar maple decayed much more rapidly than the other species. Rapid release of K and Mg was observed for all roots. Initially high rates of N and P release were observed for fine roots, whereas these nutrients were effectively retained in decaying woody roots. Retention of Ca was observed for all roots, and significant accumulation of Ca was observed in the larger size classes of woody roots. Particularly for N and K, release from decaying roots was an important nutrient flux pathway supplying stream outflow and vegetation regrowth in the first two years following forest harvest. For Sci. 34(3):744-768.