Forest Cover–rainfall Relationships in a Biodiversity Hotspot: The Atlantic Forest of Brazil

Abstract

It is now generally accepted that the relationship between vegetation and climate is dynamic: vegetation is influenced by climate, but feedbacks between terrestrial ecosystems and the atmosphere mean that vegetation also affects climate. From this it follows that land‐use changes may have climatic consequences. Specifically, it is widely believed that forest clearance may inhibit rainfall. Although models often support this view, this is not universally the case, and empirical evidence is scarce. We have compiled a database of forest cover and precipitation for the state of São Paulo, which lies within the diverse and highly endangered Atlantic forest region of Brazil. We do not find a strong relationship between forest cover and total rainfall, which appears to be influenced primarily by factors such as distance to the coast; but significant positive relationships between tree cover and the number of rain days consistently emerge. The degree of forest fragmentation seems to influence this relationship, with patchier forests associated with fewer rain days; and tree cover also predicts interannual variability in rainfall. The directionality of these relationships is inferred by considering only sites which are known to have been forested in the recent past. Given that across São Paulo state there is no overall trend for a reduction in rainfall over the study period (1962–1992), it would appear that important local‐scale processes may be hidden by regional trends. We discuss these results with reference to conservation strategies in fragmented landscapes. For instance, the spatial scale over which tree cover–precipitation relationships occur appears to be somewhat larger than that over which studies of tropical forest fragmentation typically operate, but similar to the area of habitat deemed necessary to maintain viable populations of several Atlantic forest species.

Trends in Agriculturally-Relevant Rainfall Characteristics for Small-scale Agriculture in Northern Ghana

“…The role of vegetation cover as a factor of rainfall causation and the effects of anthropogenic activities like deforestation in modifying rainfall has been investigated and reported (Pielke, 2007;Webb, 2005;Meher-Homji, 1991). Deforestation affects rainfall through changing rates of physical evaporation, transpiration, surface albedo, and aerodynamic roughness (Pielke, 2001;Ray et al, 2006;Pielke et al, 2007).…”

Intercepción de lluvia por matorral inerme espinoso en Atotonilco el Grande, Hidalgo

“…Aun cuando la intercepción de la lluvia no es el principal factor contabilizado en las estimaciones hidrológicas (Webb et al, 2005), sí constituye una de las formas que permiten identificar como las modificaciones en la cobertura arbórea afectan el balance hidrológico de un área arbolada (Dunne y Leopold, 1978;Burgos y Maass, 1999).…”

“…Aún cuando los bosques no tienen influencia preponderante en la precipitación (Webb et al, 2005), su participación no se puede considerar como insignificante, en particular cuando se contabiliza la cantidad y la distribución de la lluvia que llega al piso forestal; ésta es una de las razones principales por la que diversos estudios de ecología forestal, se hayan enfocado en la generación de relaciones entre la composición y variabilidad espacial de la estructura de los bosques con la intercepción de la lluvia (Nadkarni y Sumera, 2004). En el proceso de intercepción, la vegetación forestal participa en la distribución espacial de la lluvia que golpea a dicha vegetación en distintos estratos y que llega al piso forestal presentando patrones de temporalidad (Loescher et al, 2002;Cameron, 2007), constituye un proceso de gran complejidad, debida a los elementos estructurales del bosque y a su interacción con el ambiente (Sinoquet y Le Roux, 2000).…”

“…Although the interception of rain is not the main factor in hydrological estimates recorded (Webb et al, 2005), it is one of the ways that allows to identify how the modifications in tree cover affect the water balance of a wooded area (Dunne and Leopold, 1978;Burgos and Maass, 1999).…”

“…Even when forests have no major influence on precipitation (Webb et al, 2005), their participation can´t be considered as insignificant, particularly when counts the amount and distribution of rainfall reaching the forest floor; this is one of the main reasons why diverse studies on forest ecology, have focused in generating relationships between the composition and spatial variability of forest structure with the interception of rain (Nadkarni and Sumera, 2004). In the process of interception, forest vegetation is involved in the spatial distribution of the rain that hits such vegetation in different layers and reaching the forest floor presenting temporal variability (Loescher et al, 2002, Cameron, 2007, is a complex process, due to the structural elements of the forest and its interaction with the environment (Sinoquet and Le Roux, 2000).…”