Improved fuel moisture prediction in non-native tropical Megathyrsus maximus grasslands using Moderate-Resolution Imaging Spectroradiometer (MODIS)-derived vegetation indices

Abstract

The synergistic impacts of non-native grass invasion and frequent human-derived wildfires threaten endangered species, native ecosystems and developed land throughout the tropics. Fire behaviour models assist in fire prevention and management, but current models do not accurately predict fire in tropical ecosystems. Specifically, current models poorly predict fuel moisture, a key driver of fire behaviour. To address this limitation, we developed empirical models to predict fuel moisture in non-native tropical grasslands dominated by Megathyrsus maximus in Hawaii from Terra Moderate-Resolution Imaging Spectroradiometer (MODIS)-based vegetation indices. Best-performing MODIS-based predictive models for live fuel moisture included the two-band Enhanced Vegetation Index (EVI2) and Normalized Difference Vegetation Index (NDVI). Live fuel moisture models had modest (R2=0.46) predictive relationships, and outperformed the commonly used National Fire Danger Rating System (R2=0.37) and the Keetch–Byram Drought Index (R2=0.06). Dead fuel moisture was also best predicted by a model including EVI2 and NDVI, but predictive capacity was low (R2=0.19). Site-specific models improved model fit for live fuel moisture (R2=0.61), but limited extrapolation. Better predictions of fuel moisture will improve fire management in tropical ecosystems dominated by this widespread and problematic non-native grass.

Soil moisture as an indicator of growing-season herbaceous fuel moisture and curing rate in grasslands

“…The fuel moisture of the mixed live and dead herbaceous fuels (MFM) observed here is comparable with typical grassland LFM values in the literature. For example, LFM in guinea grassdominated sites in Hawaii, USA, ranged from 50 to 300% (Ellsworth et al 2017), which is comparable with the range of MFM in our study (20-200%). Similarly, fuel moisture of mixed live and dead herbaceous materials from grassland in Spain ranged from 10 to 250% (Chuvieco et al 2004), in Germany, it ranged from 20 to 300% (Wittich 2011), and in California, USA, from 6 to 304% (Livingston and Varner 2016).…”

“…Perhaps most importantly, why is it necessary to separately represent live and dead fuel moisture in grassland fuelbeds given the fact that DFM is typically ,30% and exhibits trivial variation relative to that of the total fuelbed ( Fig. 3 and Kidnie et al 2015;Ellsworth et al 2017)? Experiments in Australian grasslands have shown that LFM was not significantly related to the damping of the rate of fire advance in grasslands (Pearson correlation .…”

Boots on the Ground and Eyes in the Sky: A Perspective on Estimating Fire Danger from Soil Moisture Content

“…In this study, it was found that microwave root zone soil moisture was better at capturing the variability of LFMC than near-surface soil moisture. The MODIS-derived Enhanced Vegetation Index (EVI2) and NDVI estimated live fuel moisture content in non-native tropical grasslands in Hawaii with R 2 = 0.46, which was better than the National Fire Danger Rating System (R 2 = 0.37) and KBDI (R 2 = 0.06) [62].…”