Abstract

AbstractExotic grasses capable of increasing frequency and intensity of anthropogenic fire have invaded subtropical and tropical dry forests worldwide. Since many dry forest trees are susceptible to fire, this can result in decline of native species and loss of forest cover. While the contribution of exotic grasses to altered fire regimes has been well documented, the role of native grasses in contributing to fuel loads in dry forest has received little attention. We assessed differences in fuel conditions among native and exotic grasses within a subtropical dry forest preserve in Puerto Rico. We quantified fine fuel loads, fuel continuity, and seasonal changes in percent dead grass among the following grass patch types: (1) native grass with no known history of recent fire, (2) exotic grass that had burned once (single burn), and (3) exotic grass that burns frequently. Sampling was conducted during one wet season (August to October 2008) and again in the following dry season (February to March 2009). Overall, fine fuel loading was highest in native grass, but this was due to woody fuels rather than grass fuels. Percent of dead grass fuels increased with the transition from wet to dry season, and this increase was more pronounced for exotic grasses. Fuel continuity was highest in frequently burned exotic grass. Differences in grass phenology and fuel continuity may contribute to differences in fire frequency among native and exotic grass patches. Fuel management focused on prescribed fire should be used in conjunction with restoration of tree canopy to reduce fuels and limit development of a grass-fire cycle.

Highlights

  • Invasive non-native plant species have been linked to altered fire regimes in ecosystems worldwide (Brooks et al 2004)

  • Linear contrasts indicated that the overall difference between native grass and exotic grass pooled was significant (P = 0.044), but the difference between frequently burned and single burn exotic grass was not (P = 0.185)

  • Differences in fuel biomass among grass patch types related to differences in the amount of small dead wood (1 hr TL fuels) and live shrubs, rather than differences in grass fuels

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Summary

Introduction

Invasive non-native plant species have been linked to altered fire regimes in ecosystems worldwide (Brooks et al 2004). By affecting fuel loads and structure, invasive grasses can alter the frequency, timing, intensity, and spatial extent of fires. This can result in altered fire effects that can change ecosystem structure and function. Invasive exotic grasses, through their effects on fire, represent a threat to tropical dry conservation and management.

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