Non-native invasive plants in tropical dry forests: a global review of presence, impacts, and management

Tropical dry forests (TDF) are among the most-threatened terrestrial ecosystems, experiencing ongoing conversion to agricultural fields, pasture, and human settlements. Human disturbances are often precursors to invasion of ecosystems by non-native species, but research on invasion patterns in tropical ecosystems is sparse, and there is no comprehensive synthesis of invasive species in TDF. We conducted a review of published scientific literature to catalog and synthesize information about invasion by non-native plants in TDF ecosystems across the globe, drawing out patterns in the invasion of these ecosystems. We found that 130 invasive plant species were documented as present in TDF, but only 25 of these species were mentioned in three or more articles. Almost all 25 of these more-studied invasive species-mostly pasture grasses, woody legumes, and climbers-have been intentionally cultivated for agricultural or ornamental purposes. Many of these plants are native to open-canopy savanna or forest edge habitats and benefit from human-altered disturbance regimes (burning, grazing, and fuelwood and timber harvesting) of TDF fragments within agricultural landscapes. Field studies show that management approaches incorporating invasive removal, native plantings, and reduction in agricultural disturbance (e.g. ungulate fencing and fire control) simultaneously are often the most successful at reducing invasive plant cover. However, management studies in TDF have focused on a limited number of invasive species, and most were conducted in India and Hawaii. Global differences in TDF soils, natural fire regimes, and historic and current land use by humans influence modern biogeographic patterns of invasion and the feasibility of restoration options.