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Clouds persistently engulf many tropical mountains at elevations cool enough for clouds to form, creating isolated areas with frequent fog and mist. Under these isolated conditions, thousands of unique species have evolved in what are known as tropical montane cloud forests (TMCF) and páramo. Páramo comprises a set of alpine ecosystems that occur above TMCF from about 11° N to 9° S along the Americas continental divide. TMCF occur on all continents and island chains with tropical climates and mountains and are increasingly threatened by climate and land-use change. Climate change could impact a primary feature distinguishing these ecosystems, cloud immersion. But where and in what direction cloud immersion of TMCF and páramo will change with climate are fundamental unknowns. Prior studies at a few TMCF sites suggest that cloud immersion will increase in some places while declining in others. Other unknowns include the extent of deforestation in protected and unprotected cloud forest climatic zones, and deforestation extent compared with projected climate change. Here we use a new empirical approach combining relative humidity, frost, and novel application of maximum watershed elevation to project change in TMCF and páramo for Representative greenhouse gas emissions Concentration Pathways (RCPs) 4.5 and 8.5. Results suggest that in <25–45 yr, 70–86% of páramo will dry or be subject to tree invasion, and cloud immersion declines will shrink or dry 57–80% of Neotropical TMCF, including 100% of TMCF across Mexico, Central America, the Caribbean, much of Northern South America, and parts of Southeast Brazil. These estimates rise to 86% of Neotropical TMCF and 98% of páramo in <45–65 yr if greenhouse gas emissions continue rising throughout the 21st century. We also find that TMCF zones are largely forested, but some of the most deforested areas will undergo the least climate change. We project that cloud immersion will increase for only about 1% of all TMCF and in only a few places. Declines in cloud immersion dominate TMCF change across the Neotropics. [ABSTRACT FROM AUTHOR]

Four generalizations are made. 1/ Despite the varying interpretations made by the respective authors, previous studies indicate that urban growth in Latin America is caused by both rural-urban migration and a positive rate of urban natural increase. Thus to ascribe Latin American urban growth to a single prime causal factor is a misleading oversimplification. 2/ Net in-migration apparently plays a larger role in determining the rate of growth of large metropolitan centers than is the case with smaller urban areas. 3/ A significant portion of urban growth in a given intercensal period may be attributed to the growth of localities previously too small to be classified as "urban". 4/ Urban natural increase is the weighted sum of the natural increase of in-migrants (after their arrival) and urban natives. Improper recognition of this last point may lead to an overstatement of the relative importance of urban natural increase as a component of urban growth. [ABSTRACT FROM AUTHOR]