Investigating post-fire survivorship and methods for increasing native grass coverage in a dry tropical forest ecosystem

Background/Question/Methods

Healthy ecosystems and well-managed agricultural lands within tropical dry zones have the potential to support a range of goods and services including wildlife habitat, nutrient cycling, and non-timber forest products. However, 97% of these forests are at risk from multiple threats in particular invasion from exotic grasses which can increase the risk of damaging human caused fires and limit restoration on degraded sites. Part of the issue has been the use of exotic grass species to help mitigate against erosion within cultivated or roadside areas. The native grass Uniola virgata may be an alternative method for erosion control in dry tropical areas. However, whether this species can successfully persist in a system with introduced fire disturbance remains uncertain. Furthermore, more information is required to determine under what conditions U.virgata can be successfully propagated for use in future application in soil erosion mitigation and native forest regeneration.  We assessed survivorship of U.virgata up to three years post-fire by measuring ground coverage and native tree density. To determine ways for successful propagation we harvested seeds and stolons from native stands of U.virgata and compared germination/survival rates across different treatments including soaking of seeds as well as and litter and hormone addition. 

Results/Conclusions

U.virgata appears capable of significant short-term recovery post-fire. U.virgata coverage had recovered approximately 25% and 37% of mature forest values after one and three years respectively. Furthermore, where U.virgata recovery was highest, the percentage of native woody plant regeneration was also highest. This appears to indicate this native grass positively facilitates in native tree species regeneration. Overall, the success rate of U.virgata germination and survival under greenhouse conditions were low. Of 875 total seeds and stolons planted, 316 (36%) successfully germinated and remained alive seven months post-planting. Moreover, survival of stolons was higher than germination and survival of seeds. The addition of leaf litter without the use of growth hormones appears to have the greatest impact on stolon survival amongst treatments (42% survival). By contrast, none of the stolons planted with growth hormones but without leaf litter survived beyond six weeks. Variation in the time seeds were soaked in water prior to planting had little impact on germination success with neither 12hour or 24hour treatments exceeding 20% germination success. In all, this native grass appears to show some resilience to fire however, successfully increasing the presence of U.virgata in local ecosystems through greenhouse propagation remains a challenge.