See our poster on above ground carbon results from the 2009’s ESA meetings.


In order to determine patterns in carbon (C) storage and flux rates in a
Pacific Northwest second-growth forest, we assess variability in tree
above-ground net primary productivity (ANPP- litterfall=ANPPtree), net
soil CO2 efflux (NCER) and understory community in relation to
diversity of multiple coniferous, deciduous, and a nitrogen (N) fixing
tree species (Alnus rubra). Four major findings arose from our study:
1) We find a positive linear relationship between ANPPtree and tree
species richness, where overstory richness explained 35% of ANPPtree
(r2=0.35, P=0.005; Figure 2); 2) There was no significant difference in
mean ANPPtree among stands dominated by multiple evergreen,
deciduous, and an N-fixing tree species (P=0.18). Generally, trends
suggested decreases in ANPPtree with biomass stand dominance for 4
of the 5 most abundant tree species (Figure 3). Presence of the soil
modifying A. rubra had no significant effect on ANPPtree, NCER, or
above-ground C stocks (P>0.05; Figure 4); 3) We find a positive
relationship between average growing-season NCER (April-October)
and ANPPtree (r2=0.75, P<0.05). Additionally, stands with higher
overstory richness typically had higher NCER (r2=0.71, P=0.0015;
Figure 5). Other indices of diversity were also predictive of NCER,
where more diverse stands typically had higher NCER (Figure 5). 4)
Variation in overstory stand dominance was not only mildly predictive
of understory plant community composition (r2=0.1073, P<0.001)
(Figure 6). Understory plant diversity was unrelated to ANPPtree,
above-ground C stocks, and NCER using species richness (P>0.05),
Shannon’s (P>0.05) or Simpson’s (P>0.05) diversity measures. These
data highlight variability in second-growth forests that may have strong
implications for net ecosystem productivity (NEP). We estimate
ANPPtree at 7.75 Mg C ha-1 yr-1. This and other plot level
measurements imply NEP between ~ 5 and 2 Mg C ha-1 yr-1 at our
lowland second growth forest site.

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