You are here:
ROOT GROWTH AND TURNOVER IN DIFFERENT AGED PONDEROSA PINE STANDS IN OREGON, USA
Citation:
ANDERSEN, C. P., D. L. PHILLIPS, P. T. RYGIEWICZ, AND M. J. STORM. ROOT GROWTH AND TURNOVER IN DIFFERENT AGED PONDEROSA PINE STANDS IN OREGON, USA. Presented at Forests Under Anthropogenic Pressure: Effects of Air Pollution, Climate Change, and Urban Development, Riverside, CA, September 10 - 15, 2006.
Description:
The impacts of pollution and climate change on soil carbon dynamics are poorly understood, in part due to a lack of information regarding root production and turnover in natural ecosystems. In order to examine how root dynamics change with stand age in ponderosa pine forests (Pinus ponderosa Laws.), we installed more than 80 root minirhizotron tubes at two sites, one with 18 yr old (young trees) and one with 60 (intermediate-age trees) and > 250 yr old trees (old trees). The goal was to determine if root distribution, production and turnover varied with tree age. The sites examined are part of the Ameriflux network of sites.
Estimates of standing crop over the 4 year study were greatest around young trees and least around intermediate-aged trees. Root production was highly synchronized in all age-classes, showing a single peak in late May-early June each year. There was no indication of a late season peak in root production in ponderosa pine, refuting an apparent misconception that conifers exhibit a flush of root growth in the fall. Rates of root turnover did show summer and fall peaks in two of the four years (late June-July and again in October). Root production and turnover were proportional to standing root crop (biomass), suggesting that allocation to new root growth was proportional to root density regardless of tree age. During the last 3 yrs the average turnover index (proportion of standing crop turned over each year) was 0.83, 0.87 and 0.62 in young, intermediate and old trees, respectively, resulting in increased standing crop over the study in all age classes. It appears that young ponderosa pine stands have greater rates of root production than older stands, but also lose more each year through root turnover. The results indicate that soil carbon accumulates faster in young than old ponderosa pine stands.