Pacific Southwest Research Station
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Research Topics: Biological Control
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No stranger to Hawaii, biological control complements other techniques and offers a safe and effective means for managing invasive species.
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- Zimmerman, Naupaka; Hughes, R. Flint; Cordell, Susan; Hart, Patrick; Chang, Heather Kalei; Perez, David; Like, Ryan Kaipoalohaakala; Ostertag, Rebecca. 2008. Patterns of primary succession of native and introduced plants in lowland wet forests in Eastern Hawaii. Biotropica 40(3): 277-284.
 Abstract
The majority of Hawaii's lowland wet forests no longer exist, with many of the last remaining patches found on the eastern, windward sides of the largest islands. To better understand successional patterns and invasion in these native systems, we quantified basal area (BA) and densities of woody species and understory cover at nine sites in the Puna district on the Island of Hawaii, representing age gradients of native stand development on both 'a' ā and pāhoehoe lava flows. On both flow types, BA of native species increased (from 5 to 50 m2/ha) and stem densities decreased (from 3700 to 2600 stems/ha) with increasing stand/flow age. Both native and introduced species compositions diverged between substrate types on older flows. We found that lowland wet native forests remain at least partially intact in several locations, but their functional and compositional integrity is increasingly compromised by invasion of nonnative species, such as Psidium cattleianum and Melastoma candidum, which become more common at sites greater than 300-yr old. This time period may represent a threshold, after which abiotic environmental conditions no longer constrain recruitment of introduced species. On older flows, nonnative stem densities swamped those of native species by an order of magnitude, with nonnative stems (height > 1.3 m) achieving densities as high as 18,000 stems/ha. In addition, all stands lacked recruitment of native woody species in the understory, suggesting that without management, the native componentsof these forests may soon no longer be self-sustaining.
- Asner, Gregory P.; Hughes, R. Flint ; Varga, Timothy A.; Knapp, David E.; Kennedy-Bowdoin, Ty. 2008. Environmental and biotic controls over aboveground biomass throughout a tropical rain forest. Ecosystems DOI: 10.1007/s10021-008-9221-5. Abstract
The environmental and biotic factors affecting spatial variation in canopy three-dimensional (3-D) structure and aboveground tree biomass (AGB) are poorly understood in tropical rain forests. We combined field measurements and airborne light detection and ranging (lidar) to quantify 3-D structure and AGB across a 5,016 ha rain forest reserve on the northeastern flank of Mauna Kea volcano, Hawaii Island. We compared AGB among native stands dominated by Metrosideros polymorpha found along a 600-1800 m elevation/climate gradient, and on three substrate-age classes of 5, 20, and 65 kyr. We also analyzed how alien tree invasion, canopy species dominance and topographic relief influence AGB levels. Canopy vertical profiles derived from lidar measurements were strong predictors (r2 = 0.78) of AGB across sites and species. Mean AGB ranged from 48 to 363 Mg ha-1 in native forest stands. Increasing elevation corresponded to a 53-84% decrease in AGB levels, depending upon substrate age. Holding climate constant, changes in substrate age from 5 to 65 kyr corresponded to a 23-53% decline in biomass. Invasion by Psidium cattleianum and Ficus rubiginosa trees resulted in a 19-38% decrease in AGB, with these carbon losses mediated by substrate age. In contrast, the spread of former plantation tree species Fraxinus uhdei corresponded to a 7- to 10-fold increase in biomass. The effects of topographic relief at both local and regional scales were evident in the AGB maps, with poorly drained terrain harboring 76% lower biomass than forests on welldrained relief. Our results quantify the absolute and relative importance of environmental factors controlling spatial variation in tree biomass across a rain forest landscape, and highlight the rapid changes in carbon storage incurred following biological invasion.
- Asner, Gregory P.; Hughes, R. Flint; Vitousek, Peter M.; Knapp, David E.; Kennedy-Bowdoin, Ty; Boardman, Joseph; Martin, Roberta E.; Eastwood, Michael; Green, Robert O. 2008. Invasive plants transform the three-dimensional structure of rain forests. Proc. Natl. Acad. Sci. USA. 105(11):4519-4523. Abstract
Biological invasions contribute to global environmental change, but the dynamics and consequences of most invasions are difficult to assess at regional scales. We deployed an airborne remote sensing system that mapped the location and impacts of five highly invasive plant species across 221,875 ha of Hawaiian ecosystems, identifying four distinct ways that these species transform the three-dimensional (3D) structure of native rain forests. In lowland to montane forests, three invasive tree species replace native midcanopy and understory plants, whereas one understory invader excludes native species at the ground level. A fifth invasive nitrogen-fixing tree, in combination with a midcanopy alien tree, replaces native plants at all canopy levels in lowland forests. We conclude that this diverse array of alien plant species, each representing a different growth form or functional type, is changing the fundamental 3D structure of native Hawaiian rain forests. Our work also demonstrates how an airborne mapping strategy can identify and track the spread of certain invasive plant species, determine ecological consequences of their proliferation, and provide detailed geographic information to conservation and management efforts.
- Kling, Jim; Featured: Denslow, Julie; Johnson, Tracy; Cordell, Susan 2008. Repelling invaders: Hawaiian foresters use ecology to counter invasive species. Science Perspective PSW-SP-010. Albany, CA: U.S. Department of Agriculture, Forest Service, Pacific Southwest Research Station. 6 p. Introduction
The Hawaiian Islands are one of the United States' most treasured natural resources. Their natural beauty attracts legions of visitors every year, and they represent a unique set of ecosystems. Despite their limited geographic size, Hawai`i hosts a remarkable range of habitats. On some islands, dry tropical forest, wet rain forest, and alpine ecosystems are found within 20 miles of each other. The Hawaiian Islands are the most geographically isolated archipelago on Earth. Of the thousands of species native to the islands, 90 percent are found nowhere else. These native treasures are threatened by a host of invaders.
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