National Science Foundation’s Pan-American Advanced Studies Institute (PASI)
Interdisciplinary Studies on Global Climate Change, and the Ecology and Management of Tropical Montane Ecosystems
Cordillera Central, Dominican Republic March 6th-March 14th, 2010
What is a PASI?
The Pan American Advanced Studies Institute (PASI) program was developed jointly by the U.S. National Science Foundation and Department of Energy with the aim of disseminating advanced scientific knowledge and stimulating cooperation and collaboration between scientists who work in the Americas. To this end, PASI\’s solicit participants from the countries of North and South America, and scientists of other nationalities who work in the Americas. A PASI is intended to be a jumping-off point for future projects and collaborations.
Introduction and PASI Rationale
The tropical montane forests of Latin America constitute a rich ecological laboratory for studying the effects of climate change on natural ecosystems. Simultaneously, climate change presents an enormous challenge to scientists and managers throughout the Americas. By bringing together an interdisciplinary group of ecologists, botanists, hydrologists, climatologists, ecosystem scientists, physiologists, and protected area managers in a remote but science-friendly location, we hope to stimulate innovative thinking and novel approaches for studying and managing climate change impacts in Latin America\’s montane ecosystems.
Neotropical Montane Ecosystems: a macrocosm of global climate change
Tropical montane ecosystems (TMEs) throughout Latin America hold some of the highest levels of biodiversity in the world and are one of the largest remaining areas of hotspots of biodiversity in the tropics (Myers et al. 2000). Yet their future is in jeopardy as climate change and human encroachment threaten their ecological integrity, and integrated, cross-cutting studies of current and future climate change on tropical montane ecosystems are limited. Over 15 years ago, the FAO (1993) reported that tropical mountain forests were disappearing at a rate of >1% per year, faster than any other biome in the world. Furthermore, conversion of forest to mixed-use landscapes has direct feedbacks on meso-climatic drivers of TMEs (e.g. Lawton et al. 2001). As direct and indirect human pressure on the integrity of tropical montane ecosystems continues to increase, the urgency of efforts to characterize, understand and protect these ecosystems grows apace.
Tropical montane ecosystems will be especially prone to climate change impacts, given the critical role climate plays in their biological and functional organization. Early classifications of tropical montane forests maintained that distinctive elevational thresholds in climate result in floristically distinct zones with discrete boundaries (Richards 1952, Holdridge 1967). Tropical mountains have a largely aseasonal temperature regime, which results in discrete thermal zones with little temperature overlap, and temperature discontinuities along the elevational gradient (Janzen 1967). Many tropical montane mesoclimates are further stratified by a synoptic subsidence inversion – the trade-wind inversion (TWI). The TWI traps moist air and clouds on windward slopes below a roughly constant elevation (Riehl 1979, Schubert et al. 1995), above which pronounced decreases in humidity and precipitation can occur over short distances. Low temperatures and frosts are also important influences on vegetation patterns on tropical mountains, where they limit the elevational maxima of most tropical cloud-forest tree species, in effect creating a high-elevation ‗tropical–temperate\’ boundary (Ohsawa 1995, Ashton 2003). Tropical montane regions are being targeted for protection by conservation groups for both their remarkable biodiversity and their presumed role in providing refugia to species during climate change. Ironically, TMEs are also anticipated to be highly sensitive to climate change given the dominant role climate plays in these ecosystems.
The importance of climate in TMEs suggests that rising global temperatures will have profound effects, particularly on frost and cloud formation patterns. The projected rise in tropical temperatures under a doubling of CO2 concentrations is expected to raise the temperature optima of TMF species by several hundred meters (Foster 2001). Likewise, a number of climate change models project a reduction in the cloudiness which envelopes tropical cloud forests (Foster 2001). Deforestation in areas below cloud forests can also significantly shift the elevation of cloud formation upwards on mountain slopes (Lawton et al. 2001). Forecasts for the TWI are less clear. The ‗lifting cloud-base\’ hypothesis predicts that the elevation of the TWI will rise (Hamilton et al. 1995), while other climate-change models project a high-elevation drought on tropical mountains due to reduced cloud formation and a lower elevation of the TWI (Foster 2001, Loope and Giambelluca 1998). However altered, fire regimes will be strongly influenced by any disruption of the average elevation and magnitude of the TWI. The intensification of fire regimes in response to human activity and climate change is already been documented in Southern Mexico (Román-Cuesta et al. 2003, Asbjornsen et al. 2005). Models also forecast a general increase in wildfires in tropical forests as dry-season length, droughts, El Niño and lightning frequency are all predicted to increase (Goldammer and Price 1998). An increase in hurricane severity (Foster 2001) may alter future disturbance regimes in the subtropics, increasing canopy turnover from wind damage.
Fig. 1. Map of the Cordillera Central, Dominican Republic, including the Madre de las Aguas Conservation Area and two large, largely pristine national parks
Madre de las Aguas Conservation Area (MACA), Cordillera Central, Dominican Republic
Research in Madre de las Aguas Conservation Area (MACA) and other reserves throughout the Neotropics have been instrumental to our understanding of these complex patterns. The MACA of the Dominican Republic (Fig. 1) consists of five separate protected areas covering over 323,760 ha of the Central Cordillera. MACA is regarded among the highest priority reserve areas nationally and regionally because of its crucial value in biodiversity protection and hydrologic benefit (Dinerstein 1995). MACA spans elevations from 700 to over 3000 m, including the highest point in the Caribbean, Pico Duarte (3087 m). The geology of these mountains is complex, dominated by Cretaceous volcanic, metamorphic and plutonic rocks which contrasts with the rest of the island where Tertiary and Quaternary rocks are dominant at the surface (Lewis 1980). Many interesting ecological patterns relevant to climate change research have been documented in this area. For example, our research in the Dominican Republic shows that vegetation response to elevation—and associated change in temperature and moisture—is not continuous (Sherman et al. 2005, Martin et al. 2007); hence, an assumption that species-rich communities will migrate upslope in response to climate change may be unwarranted. Vegetation below the ecotone is a complex and diverse mix of broadleaf species dominated by tree ferns (Cyathea spp.) and a dozen cloud forest trees. At higher elevations (above 2300 m) and on all leeward slopes, a monospecific pine forest covers the landscape.
MACA is well situated for our PASI. A system of trails allows access into the core areas of MACA. Ecological features include a network of permanent plots, some of which are paired along the ecotone (Fig. 2). There are also extant gradients in landuse, including recovering secondary forests (Martin et al. 2004), mapped areas of known fire including recent landscape-scale fires in 2005 (Martin & Fahey 2006, Sherman et al. 2008) and hurricane disturbance (Sherman et al. 2005, Martin et al. 2007).
Fig. 2. Core sampling areas and climate stations in Bermudez and Ramirez parks, Cordillera Central, D.R. “Extensive plots” are permanent 0.1 ha vegetation plots.
Asbjornsen, H., C. Gallardo-Hernández, N. Velázquez-Rosas, R. García-Soriano. 2005. Deep ground fires cause massive above- and below-ground biomass losses in tropical montane cloud forests in Oaxaca, Mexico. Journal of Tropical Ecology 21(4): 427-434.
Ashton, P.S. 2003. Floristic zonation of tree communities on wet tropical mountains revisited. Perspectives in Plant Ecology, Evolution and Systematics 6: 87-104.
Dinerstein, E. 1995. A conservation assessment of the terrestrial ecoregions of Latin America and the Caribbean. The World Bank, Washington, DC.
Foster, P. 2001. The potential negative impacts of global climate change on tropical montane cloud forests. Earth-Science Reviews 55: 73–106.
Goldammer, J.G. and Price, C. 1998. Potential impacts of climate change on fire regimes in the tropics based on MAGICC and a GISS GCM-derived lightning model. Climatic Change 39: 273–296.
Hamilton, L.S., Juvik, J.O. and Scatena, F.N. 1995. Tropical montane cloud forests, proceedings of an international symposium, San Juan, Puerto Rico. Ecological Studies no. 110, Springer- Verlag, New York. 407 pp.
Holdridge, L.R. 1967. Life zone ecology. Tropical Science Center, San Jose, Costa Rica.
Janzen, D.H. 1967. Why mountain passes are higher in the tropics. American Naturalist 101: 233−249.
Lawton, R.O., U.S. Nair, R.A. Pielke Sr., and R.M. Welch. 2001. Climatic impact of tropical lowland deforestation on nearby montane cloud forests. Science 294: 584–587.
Lewis, J.F. 1980. Cenozoic tectonic evolution and sedimentation in Hispaniola. Trans. 9th Carrib. Geol. Conf., Santo Domingo 1:65-73.
Loope, L. L. and Giambelluca, T. W. 1998. Vulnerability of island tropical montane cloud forests to climate change, with special reference to East Maui, Hawaii. Climate Change 39:503–517.
Martin, P.H. and T.J. Fahey. 2006. Fires above the clouds: fire history along environmental gradients in the subtropical pine forests of the Cordillera Central, Dominican Republic. Journal of Tropical Ecology 22: 1–14.
Martin, P.H., R.E. Sherman, and T.J. Fahey. 2004. Forty years of tropical forest recovery from agriculture: structure and floristics of secondary and old growth riparian forests in the Dominican Republic. Biotropica 36: 297–317.
Martin, P.H., R.E. Sherman, and T.J. Fahey. 2007. Tropical montane forest ecotones: climate gradients, natural disturbance, and vegetation zonation in the Cordillera Central, Dominican Republic. Journal of Biogeography 34: 1792–1806.
Myers, N., Mittermeier, R.A., Mittermeier, C.G., Gustavo A. B. da Fonseca, G.A.B and J. Kent. 2000. Biodiversity hotspots for conservation priorities. Nature 403: 853–858
Ohsawa, M. 1995. The montane cloud forest and its gradational changes in Southeast Asia. Tropical montane cloud forests (ed. by L. S. Hamilton, J. O. Juvik, and F. N. Scatena), pp. 254-265. Ecological Studies, Vol. 110. Springer-Verlag, New York, NY, USA.
Richards, P.W. 1952. The tropical rain forest. Cambridge University Press, London, UK.
Riehl, H. 1979. Climate and weather in the tropics. Academic Press, New York, NY, USA.
Román-Cuesta, R.M., Gracia, M., and J. Retana. 2003. Environmental and human factors influencing fire trends in Enso and non-Enso years in tropical Mexico. Ecological Applications 13: 1177–1192.
Schubert, W. H., Ciesielski, P. E., Lu, C. & Johnson, R. H. 1995. Dynamical adjustment of the trade wind inversion layer. American Meteorological Society 52: 2941−2952.
Sherman, R.E., P.H. Martin, and T.J. Fahey. 2005. Vegetation-environment relationships in forest ecosystems of the Cordillera Central, Dominican Republic. Journal of the Torrey Botanical Society 132: 293–310.
Sherman, R.E., P.H. Martin, T.J. Fahey, and S.D. DeGloria. 2008. Fire and vegetation dynamics in high-elevation neotropical montane forests of the Dominican Republic. Ambio 37: 535–541.