Historical structure and composition of ponderosa pine and mixed-conifer forests in south-central Oregon
详细信息 查看全文
- 作者：R. Keala Hagmann ; Jerry F. Franklin ; K. Norman Johnson
- 关键词：Mixed conifer ; Ponderosa pine ; Reference conditions ; Historical range of variation ; Dry forest restoration
- 刊名：Forest Ecology and Management
- 出版年：2013
- 出版时间：15 September, 2013
- 年：2013
- 卷：304
- 期：Complete
- 页码：492-504
- 全文大小：1542 K
文摘
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 ?15 cm dbh on 3068 transects covering 6646 ha. The data represent a 10-20 % sample of 38,651 ha 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 (>53 cm dbh) basal area (13 ¡À 7 m2/ha) contributed 83 ¡À 16 % of total basal area; 81 ¡À 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 90 years from 68 ¡À 28 tph to a current density of 234 ¡À 122 tph 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 (>53 cm dbh) 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.