Separating the effects of environmental, spatial and disturbance factors on forest community structure in the Russian Far East

We used partial canonical correspondence analysis to decipher the relationships among abiotic environmental variables, disturbance history and spatial gradients and the composition of the forest communities in the Sikhote-alin Mountains in the Russian Far East. Through a series of partial canonical ordinations, we decomposed the variance in the forest tree community that is explainable by these three sets of factors into its seven discrete components of partial effects and interactions. We determined that the forests of the Sikhote-alin Range are structured primarily by the interaction of three things: elevation, physiographical position and disturbance history. Over the past 100 years, the disturbance regime in the study area has changed dramatically, with vast increases in the frequency of catastrophic wildfires. The effects these changes in disturbance regime have had are seen at different strengths across the altitudinal gradient. At lower elevations, the change in disturbance regime occurred very early on, and the community is now in a fire-maintained condition that is dominated by Quercus mongolica. Mature Pinus koraiensis, which formerly was co-dominant, has been nearly eliminated from the lowland forest. The increase in fire disturbance has moved in a wave across the study area and now is impacting upper-elevation primary forest as well. In the near-future, it is likely that P. koraiensis forest remnants at middle elevations will be drastically reduced and that large proportions of the upper-elevation Picea and Abies primary forest will be converted to Betula, Larix and Populus tremula. (C) 2002 Elsevier Science B.V. All rights reserved.