Fig. 3. Distribution of forest types, maximum tree ages, and stand basal areas in the Apiladda and Laizigou watersheds. (A) A rough approximation of the distribution of forest cover in the Apiladda and Laizigou watersheds, extrapolated from point data for 83 points collected during GPS surveys conducted along well-used forest and meadow trails. Shaded areas indicate variation in dominant and sub-dominant canopy species throughout the watershed: PIYU = Yunnan pine (Pinus yunnanensis); PIAR = Chinese white pine (Pinus armandii); ALFE = Alnus ferdinani-obergii; mixed as sub-dominant = PIYU, alder, or oak; mixed as dominant = PIAR, alder, oak, or rhododendron. Forest cover transitions from dry, open-canopy stands of stunted Yunnan pine to wet, closed-canopy, mixed conifer and hardwood forests with increased distance from villages and with increasing elevation and latitude in the watershed. Patterns in species distribution, tree age, and stand basal area agree with local accounts of periodic intensive harvests, as well as studies of grazing and chronic, low-intensity biomass removal; however, geophysical influences on forest cover have not been quantitatively isolated from anthropogenic influences. (B) The ages of the largest trees (PIYU or PIAR) sampled at the points indicated using an increment corer at breast height. (C) Basal area of trees, recorded in 2002 using tree counts and size measurements in 400-m² plots, and in 2008 using a keyhole prism. The circle size indicates relative basal area as a percentage of the largest recorded; specific basal areas are shown in tree area per ground area (m²/ha). Maximum tree age (B) and basal area (C) increase with elevation and distance from population centers.

Fig. 3