Great Basin Naturalist


An isolated stand of ponderosa pine (Pinus ponderosa) is surviving on an extremely harsh site in southeastern Oregon. Seed production is low because of insects, primarily pine coneworm (Dioryctria auranticella), feeding in developing cones. Seedling establishment is infrequent and difficult because of drought and coarse, rocky soils. A rock-mulch soil surface probably reduces interspecific competition. Because stand size is small (< 2 ha, 57 individuals in 1977) and genetic variability is therefore limited, individual differences in diameter growth are probably due to microsite differences. Mycorrhizae, which could aid tree survival, were absent from a small sample of surface roots. Although the stand was enlarging in 1977, the site is sufficiently severe that local extinction is a possibility.