Mangrove colonization in unutilized fishponds in Brgy. Sabang, Sibunag, Guimaras

Mangrove forests in the Philippines have declined since the 1920’s mainly due to human activities such as cutting of trees for wood and conversion to brackish-water ponds. However, productivity of brackish-water ponds diminishes over time and as a consequence are usually left idle, which has given mangroves an opportunity to recolonize these areas. This study aims to determine the rate of mangrove colonization in unutilized fishponds in Sibunag, Guimaras based on the changes in mangrove areal cover over several years, and to compare the community structure of fishponds and adjacent natural mangrove forest. The changes in mangrove areal cover were determined using Google Earth satellite images and used as proxy for mangrove colonization. Field surveys were also conducted to determine community structure. From a mangrove areal cover of 0 - 800m 2 (0-4%) in nine fishponds in 2006, it increased to 360m 2 - 16,750m 2 (28-73%) in 2011 and 520m 2 - 20,870m 2 (40-93%) in 2012.  The average colonization rate of 1,660m 2 y -1 in the fishponds is 50% higher than the adjacent natural mangroves. The higher colonization rate in the fishponds may be due to its protected location, providing a suitable environment for faster mangrove colonization. However, there were only three mangrove species in the fishpond while there were eight in the natural forest. Although tree density is higher in the fishpond, the average tree height and basal area were lower compared to the natural forest. These results show that the natural mangrove stands are more mature than those in the fishpond which concurs with anecdotal accounts that report the non-operation of the fishpond for 12 years and that the natural forest has been standing for more than 50 years. In fishponds, mangroves were able to naturally colonize 40-93% of the area in just under 12 years.