COARSE WOODY DEBRIS AS A FUNCTION OF AGE, STAND STRUCTURE, AND DISTURBANCE IN BOREAL NEWFOUNDLAND

We examined the structural attributes of coarse woody debris (CWD) in balsam fir and mixed balsam fir-black spruce forests in western and ce ntral Newfoundland. The purpose of the study was to document CWD abund ance and structure within various stages of stand development, and to generate simple models to predict CWD availability as habitat for fore st wildlife. Our objectives were threefold: (1) determine the temporal patterns of CWD following clear-cut disturbance, and compare these se cond-growth stands to old sites (>80 yr) of natural origin; (2) relate the temporal patterns of CWD to stand development; and (3) demonstrat e how factors such as site conditions and disturbance may influence th ese temporal patterns. Our chronosequence included 19 second-growth st ands with a mean tree age ranging from 33 to 80 yr, and 7 old-growth s tands ranging from 87 to 110 yr. The Volume of coarse woody debris (CW D), here defined as downed wood, was relatively low to intermediate ea rly in the chronosequence (e.g., 32.3 m(3)/ha in a 36-yr-old stand), l owest in a 58-yr-old stand (15.2 m(3)/ha), and highest in an 80-yr-old stand (78.1 m(3)/ha). Results indicated that CWD volume followed the general ''U-shaped'' temporal trend observed in other forest systems. The presence of CWD early in the sequence was strongly influenced by r esidual hardwoods (i.e., birch) left by the original logging operation , The highest observed volume of CWD corresponded with stand senescenc e and appeared to be maintained within old-growth stands. Snag (standi ng dead wood) density was low within the youngest stands (<200 snags/h a), and peaked within mature second growth, Defoliation disturbance in creased both the volume and the structural diversity of CWD within sil viculturally mature second-growth stands. Results from our study indic ate that CWD in stands >50-60 yr of age is not residual but generated primarily from:regenerating tree structure, Factors affecting the rate of stem growth, e.g,, site quality and initial stocking levels, shoul d influence the accumulation and overall abundance of CWD within later stages of forest development. We therefore applied yield-density rela tionships as a method of examining stand-level dynamics of CWD.