BRANTA — Florencia A. Trama
Active management and restoration of the Palo Verde wetland: vegetation cover changes and waterbird responses
Institution: ICOMVIS, Universidad Nacional, Costa Rica
Supervisors: M Colton
Details: MSc 2005 (Completed)
Address: Ducks Unlimited, Inc., One Waterfowl Way, Memphis, TN. 38120, USA (Nov 2005) Email
Subject Keywords: Palo Verde Wetland, land cover changes, waterbirds' responses
Species Keywords: Waterbirds
Abstract
Restoration activities in about 200 ha were started in July 2002 to reduce cattail, a dominant vegetation cover since 1985, at Palo Verde marsh, Costa Rica. As a component of the biological monitoring carried out to assess restoration success, vegetation cover changes and aquatic bird responses were evaluated from July 2002 to April 2004. Interviews and informal conversations with key actors were conducted to assess traditional management of the Palo Verde wetland . Restoration activities were following during this study, focusing on Fangueo but also grazing, fires, tree cutting and hydrologic restoration activities carried out by several actors. Three adjacent treatments were delimited (each area about 80 ha): plot 1987 and 2002 with active management (Fangueo) and a control plot with passive management (without Fangueo). Vegetation cover changes in each plot were assessed for 3 dates: November 1998 (before the OTS-MINAE restoration project started), December 2002 and March 2003 (During restoration activities) using a geographic information system.
At the same time, counts of aquatic birds were conducted every 15-20 days from two high vantage points close to the marsh. Species richness and abundance of individuals were registered; also, behavior and use of vegetation by each individual species or group was observed. Cattail cover decreased from 35% and 62% to 9% and 7% in the plots under Fangueo activities (1987 and 2002 respectively), while in control plot the percentage was always higher than 60 %. Open shallow water areas, managed cattail, floating vegetation, emergent vegetation and exposed land increased in1987 and 2002 plots and remained at low frequency in the control plot. A maximum of 62 aquatic bird species, 70 % of the total aquatic bird species for this wetland, were registered in 32 samplings. Species richness, abundance of individuals and species diversity were higher at the 1987 and 2002 plots that in the control plot. Also, these variables were higher in the dry season compared to the wet season. Shallow water, floating vegetation and exposed land were preferred and cattail, Palo Verde trees and emergent vegetation were avoided by aquatic birds in all plots. However, some species used cattail and Palo Verde trees as breeding and resting sites. Twelve species were observed nesting at the marsh, 30% in cattail and 30 % in Palo Verde trees. A negative relation between aquatic birds and the average depth was observed. Management activities reduced cattail, but improved habitat for aquatic birds. However, cattails and Palo Verde trees have been used for some resident birds as resting and roosting sites and these are an integral part of the wetland ecosystem. In this way, it is necessary to continue with restoration and maintaining activities to improve habitat for birds, controlling cattails and Palo Verde trees, but leaving some patches of these. Habitat heterogeneity is necessary to provide optimal conditions to all birds that use this wetland.