TITLE:
Anthropogenic Edges and Effective Preserve Size in the Coast Redwood (Sequoia sempervirens (D.Don) Endl.) Forest
AUTHORS:
Will Russell, Nanako Oba, Swapna Deshpande
KEYWORDS:
Edge, Core Area, Exurban, Coast Redwood
JOURNAL NAME:
Open Journal of Forestry,
Vol.12 No.4,
October
19,
2022
ABSTRACT: Ecological
edges created through human activities influence both biotic and abiotic
factors within forest communities. The extent of this influence within a
preserve is informed by the arrangement, location, and abruptness of edges, as well as the nature of
the disturbances that created them. The purpose of this study was to evaluate
the impacts of anthropogenic edges on soil and vegetation in the Sequoia sempervirens (D.Don) Endl.
(coast redwood) forest, and to compare two methods for estimating the effective
size of forest preserves. We used a combination of field data and remote image
analysis collected in six forest preserves in the Santa Cruz Mountains of
California. Analysis of field data collected on randomly distributed transects
indicated an average depth of influence of 200 meters based on correlations
between abiotic and biotic metrics and distance from the forest edge. Abiotic
factors including soil temperature and compaction were negatively correlated to
distance from the edge in the direction of the forest interior, while soil pH, moisture,
and duff depth exhibited positive relationships. Positive correlations were
also found for biotic variables including tree canopy cover, the dominance of
coast redwood and Notholithocarpus densiflorus (Hook. and Arn.) Manos,
C.H. Cannon, and S. Oh (tanoak), total understory plant cover, and the cover of
coast redwood forest associated plant species. In contrast, the cover and
richness of non-native species were highest for samples closest to the edge. To assess the effective size of
preserves, high resolution digital areal images were accessed on an ArcGIS
platform. Analysis indicated variation in abruptness between types of edges,
with the greatest abruptness found on edges associated with urban development
and roads and the lowest abruptness associated with agricultural, grazing, and
commercial timber uses. Little variation was exhibited in sinuosity between
land use types or in the relative influence of edges for exurban versus urban
parks. The cumulative result of edges in the parks studied, based on the depth
of influence assessed from field analysis, was a substantial reduction in the
operative size of the preserves. Comparison of two methods of estimating this
influence indicated a mean affected area of >26% using the “perimeter”
method and >64% of the preserved area affected when using an “aggregated” method. These results suggest
that including internal anthropogenic edges created by roads,
developments, and management activities in estimates of effective preserve size
is more accurate and significantly reduces the estimated size of the core area. With an
increasing level of active management occurring within coast redwood preserves,
it is important to consider the cumulative impact of internal anthropogenic
edges and the subsequent potential decline in the effective size of preserves.