Forest harvesting and succession have a major impact on the dynamics of carbon
exchange between forests and the atmosphere. This thesis examines the differences
in stand-level fluxes of carbon dioxide (C02) and the biophysical factors, which affect
respiration and photosynthesis in three different coastal Douglas-fir stands at different
stages of development after harvesting. The eddy covariance technique was used to
measure stand-level CO2 fluxes in Douglas-fir stands established in 2000, 1988, and
1948 on the east coast of Vancouver Island, British Columbia. A portable soil chamber
system was used to measure CO2 efflux from the soil in each stand. One year of
measurements (2002) was used to contrast net ecosystem production (NEP) between
the three stands, while three consecutive years (September 2000 to September 2003)
were used to examine interannual variability in NEP in the recently clearcut-harvested
stand.
Total annual NEP, ecosystem respiration (Re) and gross ecosystem production
(GEP) increased with increasing stand age. In 2002, the 3-year-old stand was a large
carbon (C) source (NEP = -610 g C m~2 y_ 1), the 14-year-old stand was a small C
source (NEP = -130 g C m - 2 y_ 1), and the 53-year-old stand was a moderate C sink
(NEP = 250 g C m~2 y- 1). Seasonal variations in both soil and ecosystem respiration
were related to soil temperature, while within- and between-stand variability in soil
respiration was related to the concentration of soil nitrogen. Differences in annual Re
in these forests were better related to productivity than to soil temperature. Seasonal
variations in NEP differed between stands and were related to differences in stand
structural characteristics such as canopy roughness, leaf area, biomass, species composition
and phenology. The effect of advection on NEP estimates was greatest in
the 53-year-old stand and was also related to these structural characteristics as well
as site characteristics. In the first three years after harvesting, leaf area increased
with the growth of Douglas-fir seedlings, and pioneer and understory species in the
youngest stand. Changes in the relationships between respiration and soil temperature
and between GEP and radiation were linked to leaf area index. Results from
this study emphasize the importance of stand structure and succession as well as site
characteristics and weather variability on C exchange processes. / Land and Food Systems, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/15825 |
| Date | 05 1900 |
| Creators | Humphreys, Elyn R. |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Format | 10143540 bytes, application/pdf |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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