Drought Differentially Affects Growth, Transpiration, and Water Use Efficiency of Mixed and Monospecific Planted Forests

19 páginas.-- 7 figuras.-- 2 Tablas.--61 referencias.-- The following are available online at http://www.mdpi.com/1999-4907/10/2/153/s1Drought conditions may have differential impacts on growth, transpiration, and water use efficiency (WUE) in mixed species and monospecific planted forests. Understanding the resistance (i.e., the capacity to maintain processes unchanged) of different tree species to drought, and how resistance is affected by complementary interactions within species mixtures, is particularly important in the seasonally dry tropics where projected increases in the frequency and severity of drought threaten tree planting efforts and water resources. Complementary interactions between species may lead to more resistant stands if complementarity leads to greater buffering capacity during drought. We examined growth, transpiration, and WUE of mixtures and monocultures of Terminalia amazonia (J.F. Gmel.) Exell and Dalbergia retusa Hemsl. before and during a prolonged drought using intensive measurements of tree sap flow and growth. Tree sapwood area growth was highest for T. amazonia in mixtures during normal (6.78 ± 4.08 mm 2 yr -1 ) and drought (7.12 ± 4.85 mm 2 yr -1 ) conditions compared to the other treatments. However, stand sapwood area growth was greatest for T. amazonia monocultures, followed by mixtures, and finally, D. retusa monocultures. There was a significant decrease in stand transpiration during drought for both mixtures and T. amazonia monocultures, while Dalbergia retusa monocultures were most water use efficient at both the tree and stand level. Treatments showed different levels of resistance to drought, with D. retusa monocultures being the most resistant, with non-significant changes of growth and transpiration before and during drought. Combining species with complementary traits and avoiding combinations where one species dominates the other, may maximize complementary interactions and reduce competitive interactions, leading to greater resistance to drought conditionsThis work is a contribution of the Agua Salud Project and the Smart Reforestation® program of the Smithsonian Tropical Research Institute (STRI). Agua Salud is part of ForestGEO and is a collaboration with the Panama Canal Authority (ACP), the Ministry of the Environment (MiAmbiente) of Panama, and other partners. The plantation is also part of the TreeDIVNet network. Plantation establishment was supported by the HSBC Climate Partnership and management is supported by the ACP. Funding for this work came from Stanley Motta, the Silicon Valley Foundation, the Hoch Family, the University of New Hampshire, the SmithsonIan Institution’s Competitive Grants for Science, the Smithsonian Institution’s Grand Challenge to BiodiversiTREE, the Heising-Simons Foundation, and the National Science Foundation grant (NSF grant EAR-1360391).Peer reviewe