title: Threshold Responses to Soil Moisture Deficit by Trees and Soil in Tropical Rain Forests: Insights from Field Experiments.
abstract: Many tropical rain forest regions are at risk of increased future drought. The net effects of drought on forest ecosystem functioning will be substantial if important ecological thresholds are passed. However, understanding and predicting these effects is challenging using observational studies alone. Field-based rainfall exclusion (canopy throughfall exclusion; TFE) experiments can offer mechanistic insight into the response to extended or severe drought and can be used to help improve model-based simulations, which are currently inadequate. Only eight TFE experiments have been reported for tropical rain forests. We examine them, synthesizing key results and focusing on two processes that have shown threshold behavior in response to drought: (1) tree mortality and (2) the efflux of carbon dioxdie from soil, soil respiration. We show that: (a) where tested using large-scale field experiments, tropical rain forest tree mortality is resistant to long-term soil moisture deficit up to a threshold of 50% of the water that is extractable by vegetation from the soil, but high mortality occurs beyond this value, with evidence from one site of increased autotrophic respiration, and (b) soil respiration reaches its peak value in response to soil moisture at significantly higher soil moisture content for clay-rich soils than for clay-poor soils. This first synthesis of tropical TFE experiments offers the hypothesis that low soil moisture-related thresholds for key stress responses in soil and vegetation may prove to be widely applicable across tropical rain forests despite the diversity of these forests.
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: Patrick
authors.initials: P
authors.lastname: Meir
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: Tana E
authors.initials: TE
authors.lastname: Wood
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: David R
authors.initials: DR
authors.lastname: Galbraith
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: Paulo M
authors.initials: PM
authors.lastname: Brando
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: Antonio C L
authors.initials: AC
authors.lastname: Da Costa
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: Lucy
authors.initials: L
authors.lastname: Rowland
authors.affiliation: Patrick Meir is affiliated with the Research School of Biology at Australian National University, in Canberra, and with the School of Geosciences at the University of Edinburgh, in the United Kingdom. Tana E. Wood is affiliated with the US Department of Agriculture Forest Service's International Institute of Tropical Forestry, in Rio Piedras, Puerto Rico, and with the Fundación Puertorriqueña de Conservación, in San Juan, Puerto Rico. David R. Galbraith is affiliated with the School of Geography at the University of Leeds, in the United Kingdom. Paulo M. Brando is with the Instituto Pesquisa Ambiental Amazonia, in Belém, Brazil. Antonio C. L. da Costa is affiliated with the Universidade Federal de Para, in Belém, Brazil. Lucy Rowland is with the Research School of Biology at Australian National University, in Canberra. Leandro V. Ferreira is affiliated with the Museu Paraense Emílio Goeldi, in Belém, Brazil.
authors.forename: Leandro V
authors.initials: LV
authors.lastname: Ferreira
keywords: drought; physiology; soil respiration; tree mortality; tropical rain forest