PARENT SESSION
Oral Session # 79: Forest Ecology V: Structure; Dispersal; Competition.
Presiding: J Schnurr
Thursday, August 7. 1:30 PM to 5:00 PM, SITCC Meeting Room 104.
Tree competition: Species and soil fertility in mixed stands of Eucalyptus saligna and Facaltaria mollucana.
Bird, Suzanne 1, Binkley, Dan1, Senock, Randy2, 1 Colorado State University, Fort Collins, CO2 University of Hawaii at Hilo, Hilo, HI
ABSTRACT- The growth of forests has been examined at the scales of hectares and landscapes for more than a century, but quantitative information is sparse on the growth interactions of trees sharing a neighborhood (at a scale of 10 to 100 m2). An understanding of the immediate competitive neighborhood of trees (the number, size, distance, and identity of neighbors), and how these vary with soil fertility, may lead to better predictions of stand-level growth and structural characteristics. An individual tree, neighborhood analysis was used to asses the relative importance of inter- and intra-specific competition and facilitation for tree growth along a fertility gradient. We conducted our research in a 20-year replacement series of Eucalyptus saligna and nitrogen-fixing Facaltaria mollucana in Hawaii. Eucalyptus and Facaltaria showed a synergistic growth response in mixtures. Increasing mortality and size differentiation in recent years suggests that competition has intensified between neighboring individuals. We used diameter measurements from Age 18 and 20 years to calculate annual above-ground net biomass increment for individual trees, and mapped all stems. Mortality in the 2 year period studied was highest in Facaltaria , regardless of the species mix, while Eucalyptus have their greatest mortality in pure stands. The growth of both Eucalyptus and Facaltaria declined with increasing biomass of neighborhood trees within a 2 meter radius. Neighborhood biomass explained more of the variation in growth than the number of neighbors, and the impact of neighbor biomass on Eucalyptus growth was smaller when the neighbors were Facaltaria . The nutrient status of the soil varied by a factor of more than 2 among plots, and had a significant effect on these competitive interactions.
Key words: plantations, growth, competition, fertility