Webinar: Measurement of ENSO-related climate variables and ecosystem responses in Hawaiʻi
Wednesday, December 6th at 12:00 pm HST [3 pm PDT/6 pm EDT/11 pm UTC/Dec 7th, 8 am ChST]
The forest line in Hawaiʻi is an important ecological boundary, marking the upper limit of forest bird habitat. Around the world, particularly in temperate regions, the upper limits of forests are generally controlled by temperature, but in tropical and subtropical regions, paleo-ecological evidence suggests that the forest line environment is sensitive to changes in moisture caused by climate variations, particularly during extreme, short-duration, drought-inducing climate events (e.g., El Niño events). Future climate change in Hawai’i is anticipated to cause shifts in moisture at the forest line, making it important to improve the understanding of forest line ecosystem responses to moisture stress, in order to provide the best information to managers of the area.
Supporting the assertion that tropical forest lines are not simply controlled by average climate is the pattern of the forest line elevation across windward Haleakalā, Maui. In our study area, the forest line is highest (2200 m) at the wetter, eastern-most end (NE Rift), with annual rainfall averages ~6900 mm at the forest line. Five kilometers further west (Pu‘u Alaea), the forest line is 200 m lower and annual rainfall measures ~5600 mm. We used sapflow stations set to bracket the forest line across the windward slope, along with other eco-physiological measurements, to collect ecosystem data to compare with microclimate information already accumulated by a network of stations (HaleNet) that span the forest line in other locations across Haleakalā. This study provides crucial data, measured for the first time, on how ecophysiological characteristics of Metrosideros polymorpha (ʻōhiʻa lehua trees) vary in response to climate variability and how the response differs along the cross-slope gradient.