| Disturbance and stand age have strong but poorly understood effects on the structure and function of boreal forests, forests that play a central role in regional and global climate and carbon cycles. The primary goal of this dissertation was to examine the effects of disturbance and stand age on the carbon dynamics of a black spruce (Picea mariana (Mill.) BSP) chronosequence in northern Manitoba, Canada. The objectives were to: (i) quantify and examine the effects of stand age on select structural and biophysical parameters (allometric relationships, leaf area, conifer needle geometry, woody debris); (ii) measure biomass net primary production across the chronosequence and calculate net ecosystem production; and (iii) quantify the contribution of root respiration to soil surface carbon dioxide (CO 2) flux. I addressed these objectives using field measurements, laboratory experiments, and computer modeling during the period 1999--2003.; Leaf area index (LAI), allometric relationships for biomass and sapwood area, and the cross-sectional geometry of conifer needles changed dramatically across the chronosequence. Understory LAI was an important contributor to total LAI in all but the oldest stands. Rarely measured as a source of CO 2 flux, woody debris on the forest floor emitted up to 50% as much CO 2 as did the soil. Net primary production ranged from 72 to 521 g C m-2 yr-1 and peaked in the young chronosequence stands; its sources depended significantly on soil drainage and stand age. The root contribution to soil surface CO2 flux was insignificant four years after wildfire but increased rapidly to ∼50%, before declining in the oldest chronosequence stands; it also varied seasonally, peaking concurrently with soil temperatures. Total annual CO2 flux showed promise as a useful proxy for heterotrophic soil respiration, particularly on a regional to global scale. |
