Modeling bark beetle outbreak and fire interactions in western U.S. forests and the invasion potential of an invasive Puerto Rican frog in Hawaii using remote sensing data.

摘要

I used Moderate-Resolution Imaging Spectroradiometer (MODIS) imagery to answer two ecological questions. In the first project, I investigated the interactions between bark beetle-caused tree mortality and fire occurrence in western U.S. forests. I used remotely sensed fire data detected by MODIS satellite and bark beetle-caused tree mortality data. I tested the hypothesis that there is an increased probability of fire incidence in bark beetle-damaged forests compared to healthy forests using conditional probability modeling across the national forests of the western U.S. regardless of forest type. My results did not show a consistent pattern (increase or decrease of conditional probability of fire occurrence, DeltaCP) across all lag time periods considered. However, when DeltaCP is averaged across the 5-year study period (2001-2005) fire probability increased at 2-year (16%) and 3-year (9%) lags with 0, 1, 4, and 5-year lags showing no positive effect of bark beetle activity on fire probability. Further, when I analyzed fire-bark beetle-caused tree mortality separately for persistent fires (fires that lasted for at least two 8-day composite periods per season) and transient fires (fires that lasted for only one 8-day composite period per season), the DeltaCP increased in all lag periods except the 5-year lag for persistent fires. In the second stage of this project, I used a non-parametric modeling approach to test how important bark beetle-caused tree mortality is in influencing fire occurrence relative to other climate and topography-derived variables in spruce-fir, Douglas-fir, lodgepole, and ponderosa pine forests. My results showed that climate and topography-derived predictors were consistently selected as important predictors of fire occurrence while bark beetle-caused tree mortality showing the least importance. In the second project, I predicted the invasive potential of a Puerto Rican frog species in Hawaii using the following MODIS products: land surface temperature; normalized difference vegetation index and enhanced vegetation index; and leaf area index/fraction of photosynthetically active radiation absorbed by plant canopies. My predicted maps showed that the invasive frog species in Hawaii is likely to expand its current habitat. My results also showed that MODIS-derived biophysical variables are able to characterize the suitable habitats of the invasive frog species.