- Respiratory rates were measured, in situ, for the litter, the
soil, and the litter-soil subsystems of a Pseudotsuga menziesii forest
as a function of type of understory vegetation. The major objectives
were to demonstrate the utility of the litter layer as a distinct subsystem
of this forest ecosystem, to demonstrate the existence of
respiratory patterns in the litter subsystem related to type of understory
vegetation, to determine if moisture and/or temperature were
important factors in creating these patterns, and to generate an estimate
of annual rate of respiration of the litter subsystem of a
Pseudotsuga menziesii forest.
Six understory types (Holodiscus discolor, Acer circinatum,
Gaultheria shallon, Tsuga heterophylla, Castanopsis chrysophylla, and
Polystichum munitum) were sampled. All differences in annual respiratory
rates for all subsystems were significant at F₀[subscript .]₀₅, however the
range of differences between types in the respiratory rates of the litter
subsystems, normalized to a per gram of litter basis, were higher by
an average factor of six and exhibited a hierarchy of magnitudes different
from those of the unnormalized litter, the soil, or the litter-soil
subsystems. The litter subsystem was found to be a useful and meaningful
division of the forest ecosystem.
Due to suspected methodology related errors associated with
lateral movements of carbon dioxide into the sample areas from without,
the soil and the litter-soil measurements were probably in error,
possibly quite large. Error in absolute rate of respiration for the
litter subsystem is also suspected but probably to a smaller degree
and not affecting the hierarchy related to type.
The litter subsystems for two of the types were found to have
moisture contents different by a relatively large percentage from that
of the litter subsystems of the other types. It appeared, however,
that moisture difference was not the major cause of the hierarchy by
type of respiratory rates of the litter subsystem.. Temperature was
not a significant factor in the observed hierarchy. The annual respiration
yields based on the litter subsystem, as a probable result of the
specific methodology used, appeared to yield more reasonable estimates
for rates of decomposition of organic matter in a forest floor
than do previously published studies based on the litter-soil subsystem.
It appears that Pseudotsuga menziesii forests compared to other temperate
coniferous forests have a rapid turnover rate for organic matter
entering the litter subsystem.