Speakers: Dr Ann Russell and Dr Jim Raich, Iowa State University
Where: UNEP-WCMC 219 Huntingdon Road, Cambridge CB3 0DL
When: Monday, Nov 9, 13h00 – 14h00
Abstract
In one of the earliest replicated experimental sites for investigating growth of native tropical trees in Central America, we examined traits of tree species in relation to their effects on forest C balances, mechanisms of influence, and consequences for C sequestration. The mono-dominant stands, established in abandoned pasture in 1988 at La Selva Biological Station, Costa Rica, contained five species in a complete randomized block design.
Native species were: Hieronyma alchorneoides; Pentaclethra macroloba; Virola koschnyi; and Vochysia guatemalensis. The exotic species was Pinus patula. In all species, LAI, biomass and SOC content were roughly equivalent to that of the mature forest by 16 years. The lack of differences among species in some attributes suggested strong abiotic control in this environment, where conditions are very favorable for growth.
These attributes included aboveground net primary productivity (ANPP), averaging 11.7 Mg C ha-1 yr-1 across species, and soil organic C (0-100 cm, 167 Mg C/ha). Other traits differed significantly however, indicating some degree of biological control. In Vochysia plots, both aboveground biomass of 99 Mg C/ha, and belowground biomass of 20 Mg C/ha were 1.8 times that of Virola (P = 0.02 and 0.03 respectively). Differences among species in overstory biomass were not compensated by understory vegetation. Belowground NPP of 4.6 Mg C ha-1 yr-1 in Hieronyma was 2.4 times that of Pinus (P < 0.01). Partitioning of NPP to belowground components in Hieronyma was more than double that of Pinus (P = 0.03). Carbon sequestration, highest in Vochysia (7.4 Mg C ha-1 yr-1, P = 0.02), averaged 5.2 Mg C ha-1 yr-1, close to the annual per capita fossil-fuel use in the U. S. of 5.3 Mg C. Our results indicated that differences in species effects on forest C balances were related primarily to differences in growth rates, partitioning of C among biomass components, tissue turnover rates, and tissue chemistry.
Inclusion of those biological attributes may be critical for robust modeling of C-cycling across the moist tropical forest biome.