Decadal-scale dynamics at the Gus Pearson Natural Areas: evidence for inverse (a)symmetric competition?

Abstract

The Gus Pearson Natural Area is one of the longest maintained individual-based forest-monitoring sites in the world. It is an 800 × 400 m plot established in 1908 within pristine ponderosa pine (Pinusponderosa Dougl. ex Laws, van scopulorum) forest near Flagstaff, Arizona. I quantified decadal-scale growth trends of individual trees and of the entire stand from timber inventories repeated at 10-year intervals between 1920 and 1990. A mixed linear model for longitudinal data was used to test significance of temporal trends. Stand density increased throughout the 20th century because of successful regeneration pulses, active fire control, and no tree cutting. Aboveground growth rates of the stand as a whole did not change significantly from 1920 to 1990, but individual growth rates declined. Mixed linear model results indicated that decadal basal area increment of large pines declined more than that of small pines. In 1920–1930 large pines were growing faster than small pines, but by 1980–1990 large pines were growing slower than small pines. Since the number of small pines multiplied and the number of large pines changed slightly, I inferred that competition for resources was more detrimental for large pines than for small pines.