Ecosystem vulnerability is related to the degree of expancion of anthropic activities, also known as the pressure index.
In many countries, areas with tropical dry forest ecosystems present special conditions of anthropic development, such as the price of the land, intensive livestock development, and a broad range of social and economic groups, in addition to those related to the geographical location of these forest. Many of this ecosystems are located in rural-urban transitions areas, which are where the greatest development occurs in most countries(Crump, 2003); Colombia is not the exception. Compared with other areas, these transitions zones undergo a faster rate of development with dramatic ecological and socioeconomic impacts (Wilcove et al., 1998; Huston, 2006), mainly in terms of loss and fragmentation of habitats (Theobald et al., 1997; Falcucci el al., 2007), loss of ecosystem services (Daily 1997; Pejchar et al., 2006; Lamb el at., 2005), and introduction of exotic species (Conway and Lathrop, 2005).
These are highly complex systems in which socioeconomic, biophysical, and cultural subsystems are tightly interwoven. Therefore the negative impact that subsystems have on ecosystem and ecosystem services cannot be attributed to one single subsystem. Causes and effects do not respond to simple and atheoretical models. Without clear and solid causal models that explain the different relationships from the ecosystem perspective and incorporate control variables, it is difficult to establish possible strategies to reduce negative impacts, propose solutions, and then implement these solutions in complex systems scenarios using an ecosystem approach. Even in those cases where a causal relationship can be taken for granted, analyses may be weak and statistical test limited (Barrett et al,. 2006).
It is in these subsystems that the fragments of dry forest of the department of Risaralda, COlombia, are imbedded, in the limits of the Cauca river valley and, as all other dry forests of this type worldwide, is severely threatened. Although it is quite probably that the area under dry forest in the country is underestimated given the difference in scales used by different organizations, according to the Nature Conservancy (TNC) there are four areas in Colombia where the ecosystems exist: the Magdalena river valley, the Cauca river valley, the Patía river valley, and Sinú river valley (Walschburger and León, 2009). The dry forest of Risaralda are located in a landscape of approximately 24,000 ha, of which forest fragments account for 8% of total coverage.