Historical structure and composition of ponderosa pine and mixed-conifer forests in south-central Oregon

•Reference conditions based upon a timber inventory conducted from 1914 to 1922.•Large ponderosa pine dominated basal area on pine and mixed-conifer sites.•Forests were predominantly low density at less than a third of current density.•Fire regime influenced structure and composition more than site...

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Published in:	Forest ecology and management Vol. 304; pp. 492 - 504
Main Authors:	Hagmann, R. Keala, Franklin, Jerry F., Johnson, K. Norman
Format:	Journal Article
Language:	English
Published:	Kidlington Elsevier B.V 15.09.2013 Elsevier
Subjects:	Animal and plant ecology Animal, plant and microbial ecology Biological and medical sciences coniferous forests conifers Dry forest restoration dry forests Forest management. Stand types and stand dynamics. Silvicultural treatments. Tending of stands. Natural regeneration Forestry Fundamental and applied biological sciences. Psychology habitats Historical range of variation history inventories landscapes Mixed conifer national forests Oregon Pinus ponderosa Ponderosa pine Reference conditions stand basal area stand density Stand types and stand dynamics. Silvicultural treatments. Tending of stands. Natural regeneration surveys Synecology Terrestrial ecosystems trees USDA Forest Service wildfires Oregon United States North America America Dry forest restoration Mixed conifer Ponderosa pine Historical range of variation Reference conditions Forest stand Forest ecology Variations Temperate zone Case history Geographical division Pinus ponderosa Softwood forest tree Gymnospermae Forestry Coniferales Spermatophyta Ecological recovery Structure Mixed forest stand Coniferous forest
ISSN:	0378-1127, 1872-7042
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Summary:	•Reference conditions based upon a timber inventory conducted from 1914 to 1922.•Large ponderosa pine dominated basal area on pine and mixed-conifer sites.•Forests were predominantly low density at less than a third of current density.•Fire regime influenced structure and composition more than site productivity. We summarized structure and composition of dry forests from a 90-year-old timber inventory collected by the Bureau of Indian Affairs on the former Klamath Indian Reservation (now part of the Fremont-Winema National Forest). This analysis includes data from 424,626 conifers ⩾15cmdbh on 3068 transects covering 6646ha. The data represent a 10–20% sample of 38,651ha of forest growing on sites that are classified as ponderosa pine (Pinus ponderosa) and mixed-conifer habitat types distributed within the 117,672 ha of the study area. Large, drought- and fire-tolerant ponderosa pine dominated these forests. Large tree (>53cmdbh) basal area (13±7m2/ha) contributed 83±16% of total basal area; 81±20% of the large-tree basal area was ponderosa pine. Composition and structure of forests on mixed-conifer sites were very similar to those on ponderosa pine sites. Variability in composition and structure was recorded on all habitat types and was highest on moist mixed-conifer sites. Stand densities (trees per hectare, tph) have more than tripled over the past 90years from 68±28tph to a current density of 234±122tph recorded in Current Vegetation Survey data collected by the United States Forest Service. Mean basal area, however, increased by less than 20%. Basal area of large trees (>53cmdbh) has declined by >50%, and the abundance of large trees as a proportion of the total number of trees per hectare has decreased by more than a factor of five. This landscape-level record of historical forest conditions allows inferences about structure and composition across tens of thousands of hectares. A historical landscape emerges which supports current working hypotheses that frequent, low- to moderate-severity wildfires maintained a predominantly low-density forest dominated by large, fire- and drought-tolerant ponderosa pines across a significant moisture and productivity gradient from the driest ponderosa pine to the mixed-conifer habitat types.
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ISSN:	0378-1127 1872-7042
DOI:	10.1016/j.foreco.2013.04.005