Abstract:
Gaps in the forest canopy allow more light to reach the understory. Since
light in the understory is heterogeneous, understanding the physiological
processes in gaps and non-gaps will improve estimates of carbon balance. This
research outlines an approach for defining carbon balance for Salal (Gaultheria
shallon Pursh.), a dominant understory shrub in Pacific Northwest old growth
forests, growing in gaps and non-gaps.
The carbon balance of salal foliage was estimated using a three-step
approach. Ambient photosynthesis of salal was surveyed in gaps and non-gaps
using a LiCor Photosynthetic Gas Exchange System. The LAI and percent cover
of salal in gaps and non-gaps was measured using a species/area curve and the
line intercept method. Finally, leaf-based measurements were scaled to
determine stand-level carbon use of salal in and out of gaps.
I hypothesized that photosynthetic capacity and respiration value
differences between gap and non-gap salal foliage could be accounted for by
water potential and nitrogen content measurements. To further characterize
salal in gaps and non-gaps in the understory, sun/shade leaf characteristics such
as leaf mass to leaf area ratios, light curves and A/C; curves were compared.
Scaling from individual plant based estimates to stand-level estimates
show the importance of gaps in the understory carbon balance. While salal
covers the forest floor equally, the multileveled leaf-canopy of salal in gaps and
the higher photosynthetic capacity of salal foliage in gaps contribute to the larger
carbon balance role that salal foliage in gaps has when compared to salal foliage
in non-gaps.
