Assesing Riparian Structure and Composition in Quebrada Chiclana, Puerto Rico, a Restored Tropical Creek
Manrique Hernández, Harold
MetadataShow full item record
The global human population is increasing and this growth will be reflected mainly in urban areas across the World. Populations living in urban areas are projected to increase from 3.6 billion in 2011 to 6.3 billion in 2050 (UN Population Division, 2011). Land-use policies are changing in order to meet the needs of this sprawling population leading to drastic landscape alterations and ecosystem disruptions. The needs to respond to the demands of this growing population have led to an increase in urban expansion, one of the major forces driving land cover change (Wu et al. 2006). As an example, changes to a more impermeable and less forested environment resulted in the loss of ecologically valuable natural habitats (Paul and Meyer, 2001). Around 45% of rivers in the United States are classified as endangered or impaired (U.S. EPA, 2000). The humid tropics are not an exception. Islands, like Puerto Rico, have been experiencing significant land-use changes (Ramos, 2001). After the 1950’s, Puerto Rico experienced an increased demand for urban structures. This has caused an increase in the construction of residential and commercial projects, some with poor infrastructure planning damaging natural ecosystems (Pares-Ramos et al. 2008). Changes in land-use and in the natural hydrologic regime of rivers have altered ecosystem services and natural processes leading to an abrupt loss of ecological integrity in river ecosystems. Changes and loss of riparian and aquatic habitats for numerous species are an inevitable effect of these activities. The presence of stable human structures near rivers could lead to permanent loss of aquatic habitat and serves as a barrier for different species (Pedroli et al. 2002). The effect on species is easily reflected on changes in community structure and composition. Natural processes and biological cycles are also disrupted by human activities such as agriculture, deforestation, and impermeabilization, among others. The chain effect of these activities will affect nearby habitats (e.g. valleys, downstream reaches) due to the continuous and dynamic nature of rivers. This is explained by the River Continuum Concept (Vannote et al. 1980) which describes the river as an ecosystem with physical variables that changes on a continuous gradient from the headwaters to the mouth. The concept describes headwaters metabolism as one dominated by respiration. This is due to low aquatic photosynthesis because of high allochthonous inputs of organic matter from the surrounding vegetation. Unimpacted headwaters are usually surrounded by a landscape dominated by forest due to their remoteness and steep slopes. This vegetation, known as riparian vegetation, plays an important role in maintaining the ecological integrity of the system. The area that constitutes the riparian vegetation is known as the riparian zone. Naiman et al. (2005) defines it as a transitional semi terrestrial zone regularly influenced by fresh water, usually extending from the edges of water bodies to the edges of the upland communities. It functions as a filter and regulates the flux of biotic and abiotic elements that move across the riverine landscape (Naiman, et al. 2005). Enhanced species diversity, biological productivity, home of diverse habitats, and flood and erosion control, are other services characteristic of the zone (Naiman, et al. 2005). The riparian zone is also considered a buffer that could mitigate the effects of non-point source pollution, therefore, preventing poor water quality conditions (Anbumozhi, 2005). The disconnection of the components of the natural riverine landscape is an important threat to the integrity of insular environments such as Puerto Rico (Lagabrielle et al. 2011). Islands across the World are experiencing high rates of land cover change, some due to the lack of proper management strategies (Cook et al. 2006). Over time, humans have developed different strategies to approach a successful management practice considering the current condition of the ecosystem of interest. For example, for a natural or semi-natural river system, preservation or conservation strategies can be considered (Boon, 1992). However, when the riverine integrity is affected, the river’s natural processes and species communities are degraded to critical levels, and the ecosystem integrity cannot be maintained on its own. Under these circumstances, mitigation becomes the option and restoration becomes a priority (Boon, 1992). In Puerto Rico, numerous restoration activities have been conducted targeting environments such as marshes, lagoons, sand dunes, rivers, coral reefs, forest, among others ecosystems. However, with an alarming 40% tendency of urban sprawling across the Island (Martinuzzi et al. 2007), these environments are still vulnerable to the effects of human activities. This research evaluated the outcome of a reforestation project developed in a headwater tropical creek impacted by a residential development. Particularly, we focused on the dynamics of forest succession along the restored riparian zone. The following chapter will focus on the core research aspect of this research: an assessment of riparian vegetation structure in a restored tropical creek. Later, Chapter 3 will summarize my thoughts on the social community elements that promoted the restoration and the recovery process of Quebrada Chiclana.