Ecosystem Fluxes in Native and Non-native Hawaiian Forests
Background
In Hawai'i, invasive species are the greatest threat to healthy and functioning native ecosystems, and climate change is expected to further constrain these ecosystems. More information is needed to understand how different species and ecosystems will respond to projected changes in temperature and rainfall. We seek to identify the sensitivity of two ecosystems; a native Hawaiian forest and a nearby forest invaded by strawberry guava, to changes in climate, and project how carbon and water cycling of these ecosystems will change in a changing climate. Working in collaboration with local resource managers, results will provide critical information for devising appropriate land-management strategies.
Observations
We are currently conducting comprehensive measurements in the field for all components of water flux into, out of, and within the vegetative layer at two forest sites on Hawai‘i Island. The two field sites are located in native forest and a forest invaded by an alien tree species, both within the cloud zone. These sites are equipped with the full array of instruments, including eddy covariance sensors, to monitor fluxes of water and carbon between the atmosphere and the surface.
The red arrows show where the guava invasion at the invaded site has reached the canopy.
Research Sites
Non-native Forest Site
The photo at left shows the installation of the Ola‘a flux tower in Hawai‘i Volcanoes National Park in June 2005. This former native cloud forest is being invaded by strawberry guava (Psidium cattleianum), the most extensive invasive tree species in Hawai‘i. Remnant ‘ōhi‘a (M. polymorpha) remain, and the native tree fern, hapu‘u (Cibotium spp.) is abundant. Measurements at this site began in February 2006.
Native Forest Site
The photo at left shows the Nahuku flux tower, an intact native cloud forest site located in Hawai‘i Volcanoes National Park. The dominant canopy tree species at this site is ‘ōhi‘a (Metrosideros polymorpha). A secondary mid-level canopy is formed by the Hawaiian tree fern, hapu‘u (Cibotium spp.). Measurements at this site began in February 2005. A paper was led by Tom Giambelluca was pubished on evapotranspiration at this site (Giambelluca et al. 2009).
Canopy Water Balance Study
In addition to the eddy covariance flux instrumentation, these sites were previously also instrumented with automated throughfall and stemflow gauges to measure the partitioning of rainfall and cloud water interception in canopies. This work was published in a paper led by Mami Takahashi (Takahashi et al., 2011).
Funding
This work is currently supported by funding from the Department of Interior Pacific Islands Climate Science Center and the USGS Pacific Islands Ecosystem Research Center. Previously, work at these sites was supported by the National Science Foundation under Grant No. EAR-0309731, the endowment of the Carnegie Institution, and by the USGS Biological Resources Discipline Global Change Research Program.
Publications
Giambelluca, T.W., Martin, R.E., Asner, G.P., Huang, M., Mudd, R.G., Nullet, M.A., DeLay, J.K, and Foote, D. 2009. Evapotranspiration and energy balance of native wet montane cloud forest in Hawai‘i. Agricultural and Forest Meteorology. 149: 230-243, doi: 10.1016/j.agrformet.2008.08.004.
Takahashi, M., Giambelluca, T.W., Mudd, R.G., DeLay, J.K., Nullet, M.A., and Asner, G.P. 2011. Rainfall partitioning and cloud water interception in native forest and invaded forest in Hawai‘i Volcanoes National Park. Hydrological Processes. 25: 448-464, doi: 10.1002/hyp.7797.
Projects on Oʻahu: Mākaha Valley and Koʻolau Canopy Interception Projects
These initiatives are being supported by the Honolulu Board of Water Supply to understand how vegetation changes through invasion and restoration will affect groundwater recharge.