THE RELATIONSHIP BETWEEN FINE-ROOT DEMOGRAPHY AND THE SOIL ENVIRONMENT IN NORTHERN HARDWOOD FORESTS

We used minirhizotrons to measure growing-season fine root dynamics at 0-30 and 50-100 cm depths in two northern hardwoods forests. Concomit ant measurements of several soil and site environmental variables were also made. We then used regression models to quantify the relationshi ps between these environmental variables and fine root demography. Gen erally, environmental factors had a moderate effect on broad, inherent phenological patterns of root activity and abundance. For example, bo th shallow fine root length density and potential evapotranspiration r eached their maximum in mid-summer, but the relationship between the t wo was not strong at either site (R(2)=0.12). Deep root length density was not significantly related to any measured environmental factor. P eriods of high water demand during which soil moisture was also abunda nt (i, e., late spring and early summer) were related to increased sha llow root production. Root length mortality was low at these times, bu t the correlation with soil moisture was statistically significant onl y in the shallow depth increment. Quantifying the relative importance of the environment on root growth in large field studies like ours is complicated by a number of factors. These include the difficulty of in tensive sampling, interactive effects of environmental factors, and th e uncertainty of encountering environmental conditions sufficiently se vere to elicit a measurable root response during the study period.