Impacts of Falcataria moluccana Invasion on Decomposition in Hawaiian Lowland Wet Forests: The Importance of Stand-level Controls |
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Authors: | R Flint Hughes Amanda Uowolo |
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Institution: | (1) Institute of Pacific Islands Forestry, USDA Forest Service, P.O. Box 4370, Hilo, Hawaii 96720, USA |
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Abstract: | Invasive species have the capacity to substantially alter soil processes, including rates of litter decomposition. Currently,
the few remaining native-dominated lowland wet forests in Hawai’i are being invaded by Falcataria moluccana, a large, fast-growing, N2-fixing tree. In this study, we sought to determine the extent to which Falcataria invasion alters decomposition in these lowland wet forests, and whether changes resulted from differences in litter substrate
type, lava flow age and type, forest stand type and associated soil biota, or some combination of these factors. We measured
decomposition rates and nitrogen (N) and phosphorus (P) dynamics of Metrosideros
polymorpha and Falcataria leaf litter in native-dominated and Falcataria-invaded stands on 48- and 300-year-old a’a lava flows and a 213-year-old pāhoehoe flow in the Puna district of eastern Hawai’i.
Despite significant differences in the initial quality of Metrosideros and Falcataria litter, in nearly all cases mass remaining of the two litter types did not differ within a given forest stand, whether native-dominated
or invaded. Instead, stand type accounted for large differences in the decomposition of both litter types, and litter decomposed
two to 10 times faster in Falcataria-invaded stands than it did in their native-dominated counterparts on each lava flow. Dynamics of N (that is, immobilization
or release) during decomposition were affected by stand, litter, and lava flow type; P dynamics were affected by stand and
flow type, but not litter type. Although not definitive proof of causality, the decay rates of both species were positively
correlated to previously measured inputs of N mass and P mass via litterfall as well as availability of soil N and P, characteristics
that all increased substantially with Falcataria invasion. Given the degree of change to a host of ecosystem processes, including decomposition, after invasion by Falcataria, these transformed forest ecosystems may best be viewed as fundamentally new and different, in both structure and function,
from the native ecosystems they have replaced. |
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Keywords: | Metrosideros polymorpha nitrogen phosphorus albizia primary succession mass loss invasive species ecosystem processes nutrient availability lava flows |
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