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STAND DYNAMICS, NITROGEN ACCUMULATION, AND SYMBIOTIC NITROGEN FIXATION IN REGENERATING STANDS OF ACACIA KOA
Author(s) -
Pearson Holly L.,
Vitousek Peter M.
Publication year - 2001
Publication title -
ecological applications
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.864
H-Index - 213
eISSN - 1939-5582
pISSN - 1051-0761
DOI - 10.1890/1051-0761(2001)011[1381:sdnaas]2.0.co;2
Subject(s) - biology , diameter at breast height , nitrogen fixation , acacia , biomass (ecology) , basal area , litter , stand development , agronomy , thinning , botany , ecology , genetics , bacteria
Recently, abandonment of montane cattle pastures in Hawaii has stimulated interest in forest restoration both for expansion of habitat for native species and for plantation forestry. Acacia koa is one of the most common forest trees in Hawaii, the most abundant native legume, and the most economically valuable native tree; it could be important to restoration efforts in many areas. Using an age sequence of even‐aged, 6‐ to 20‐yr‐old stands of A. koa, we evaluated stand characteristics, N accumulation, and rates of N fixation. Average diameter at breast height (dbh) and height increased linearly during the first 20 yr of tree growth, while stem density, dbh increment, and leaf area index declined. An experimental thinning in the 9‐yr‐old stand more than doubled dbh increment, suggesting that high tree densities could constrain tree growth. In contrast, N fertilization did not affect dbh increment. Nodule biomass was more than an order of magnitude less in the 20‐yr‐old stand than in the 6‐yr‐old stand, which corresponded to a similar decline in estimated input of N via fixation. Neither thinning nor N fertilization affected nodule biomass, but measurements of foliar and root phosphorus (P) suggest that a decline in P availability over time may have contributed to the decline in N fixation. In these stands, large amounts of decomposing litter remaining from stand establishment may have provided much of the N that accumulated in koa biomass. In more degraded sites, N fixation by A. koa may play a relatively more important role in restoration and in soil and ecosystem development.