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Background
The Little HaleNet climate array, installed in 2005 on windward Haleakalā, Maui, adds a spatial dimension to the windward HaleNet transect. Little HaleNet consists of 12 stations and expands westward across slope, near the elevation of the mean Trade Wind Inversion (TWI). Little HaleNet measures rainfall, air temperature, relative humidity, soil moisture, and photosynthetically active radiation.
Little HaleNet (red stars in figure at right) is tightly integrated with a network of 136 permanent vegetation plots (black dots) and is strategically located around the cloud forest’s upper limit – an area expected to be sensitive to climate change. With HaleNet (white stars) and Little HaleNet combined, climate station density is 3.5 stations km-2, greatly improving uncertainty in climate measurements in a highly dynamic location.
Little HaleNet helps to fill an important gap in Hawai‘i's climate station coverage. The image below shows Little HaleNet stations plotted on the Rainfall Atlas Uncertainty map along with other rain gauges on East Maui. The coverage from Little HaleNet provides invaluable information in this ecologically important data-sparse region.
List of the Little HaleNet stations with coordinates and elevations. Note how the elevations bracket the mean TWI level (2200 m).
We use HaleNet and Little HaleNet to generate high-resolution (5 m) gridded climate surfaces with ordinary kriging. We can then extract values for each microclimate variable from the gridded surfaces at each of the 136 vegetation plots. This dataset allows us to analyze vegetation-climate relationships.
Little HaleNet recorded microclimate during the 2009-2010 strong El Niño and has allowed us to build species distribution models that incorporate data during extreme drought events. Through this work, we have shown that El Niño-driven droughts are strongly associated with vegetation structure and composition, including the upper elevational limit of cloud forest. In the graphs below, white dots represent subalpine shrubland sites, and black dots represent cloud forest sites.
Publications using Little HaleNet:
Gotsch S., Crausbay S., Weintraub A., Giambelluca T., Longman R., Asbjornsen H., Hotchkiss S., and Dawson T. 2014. Water relations and microclimate around the upper limit of cloud forest in Maui, Hawai‘i. Tree Physiology 34:766-777
Crausbay S., Frazier A., Giambelluca T., Longman R., and Hotchkiss S. 2014. Moisture status during a strong El Niño explains a tropical montane cloud forest’s upper limit. Oecologia 175:273-284
Crausbay S. and Hotchkiss S. 2010. Strong relationships between vegetation and two perpendicular climate gradients high on a tropical mountain in Hawai‘i. Journal of Biogeography 37:1160-1174
Funding for Little HaleNet:
USGS Biological Resources Discipline Global Change Research Program
National Science Foundation Dissertation Improvement Grant (award number DEB-0808466)
The Pacific Islands Climate Change Cooperative (PICCC; award number 12170-B-G100)
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