Variation in plant water use and water use efficiency of planted monocultures and mixtures: Toward proper species selection for reforestation efforts in the seasonally dry tropics

Monday, 6 June 2016
Katherine Sinacore1,2, Heidi Asbjornsen2 and Jefferson S Hall3, (1)Smithsonian Tropical Research Institute, Applied Ecology Lab, Panama, Panama, (2)University of New Hampshire Main Campus, Durham, NH, United States, (3)Smithsonian Tropical Research Institute, Balboa, Panama
Abstract:
Background/Question/Methods

SMART REFORESTATION™ is the process by which land is managed to maximize the flow of different goods and services for the benefit of multiple stakeholders in response to global change. This includes selecting tree species for reforestation that enhance forest-related ecosystem services, while reducing negative impacts of unsustainable land use. In the seasonally dry tropics of the Panama Canal Watershed (PCW), a critical factor to consider in tree species selection is the quantity and efficiency by which trees regulate water and carbon. A better understanding of tree interactions related to water-carbon cycling and trade-offs will enable better decision-making in reforestation and restoration within the PCW, where water can be limiting during the dry season and abundant during the wet season, and where forest productivity contributes to local livelihoods and climate change mitigation. My work addresses two central questions 1) how do different species mixtures and monocultures vary in water and carbon use efficiency, and 2) how do mechanisms of species interaction (complementarity, facilitation, competition) explain ecosystem level responses? I use a combination of water use and productivity measurements in mixed and monoculture plantings, focusing on two key reforestation species, Terminalia amazonia and Dalbergia retusa.

Results/Conclusions

Plant water use efficiency (transpiration divided by productivity) varied significantly by species and whether the tree was planted in mixtures or monocultures. Terminalia amazonia was significantly more water-use efficient in mixtures than monocultures (p = 0.03), potentially from enhanced nitrogen availability due to nitrogen fixation by D. retusa. In contract, D. retusa was significantly less water-use efficient in mixtures than monocultures (p = 0.005). These data provide important insights regarding species-specific ecophysiological strategies that will affect appropriate selection of species for reforestation efforts.

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