National Forest management in the Pacific Northwest is shifting
from a focus on commodity production to ecosystem management, in which
the health of the entire forest ecosystem is considered, rather than that
of a few key species. Ecosystem management includes retention of some
live trees following timber harvest (green-tree retention) to preserve
biodiversity, imitating the natural fire regime of large, but patchy
fires that leave many live trees. How ecosystem management will affect
growth and species composition of future forests is an important
question. This study takes a retrospective approach to this question by
using past disturbance as an analogue to green-tree retention following
timber harvest. Using USDA Forest Service timber inventory plot data
from the Cascade Mountains of Oregon and SW Washington, 132 unmanaged
stands were identified with a tree cohort of 70-110 years old
(regeneration) or a tree cohort of 70-110 years old with an overstory of
large trees 200+ years old (remnants). All stands were in the Tsuga
heterophylla (Raf.) Sarg. zone (Franklin and Dyrness 1973). Single-aged
stands represented clearcuts, while two-aged stands served as analogues
to stands harvested with green-tree retention. Regeneration basal
area/hectare (ba/ha) declined when remnant-tree densities exceeded about
15 remnant trees/ha (R��=0.51) in a relationship roughly described by a
sigmoidal curve. Conceptually removing remnant-tree space occupancy
effects decreased remnant-tree density's value as a predictor of
regeneration ba/ha by about 50% at management-level remnant densities
(���45 remnant trees/ha). Thus, it appears that remnant "effects" were a
result of both remnant-tree space occupancy and remnant resource use.
Douglas-fir ba/ha in the regeneration also declined when remnant-tree
densities exceeded about 15 remnant trees/ha (R��=0.60). Western hemlock
ba/ha in the regeneration increased slightly with increasing remnant-tree
densities (R��=0.19). Western redcedar ba/ha in the regeneration was
apparently not related to remnant-tree density (R��=0.02). The degree of
aggregation in remnant trees did not appear to affect regeneration ba/ha,
but few stands contained the isolated clumps of remnant trees likely
under a management scenario. Neither measured site characteristics nor
regeneration density was related to regeneration ba/ha across species.
Remnant-tree density was apparently unrelated to tree-species diversity
in the regeneration. Total-stand ba/ha remained relatively constant
across remnant densities. / Graduation date: 1994
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/35877 |
| Date | 18 November 1993 |
| Creators | Rose, Coulter R. |
| Contributors | Muir, Patricia S. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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