Event ecology in the Philippines: Explaining mangrove tree cutting and planting and their environmental effects.

摘要

Event ecology was employed as a research method to explain mangrove tree cutting and planting in Bais Bay and Banacon Island, Philippines, and evaluate their ecological effects on forest composition, structure and regeneration.;Mangroves have been cut to make space for fish ponds and residential settlement and for fuel and construction wood. Empirical measures confirm historically high rates of cutting, although these have declined recently in response to the cancellation of commercial firewood concessions and enforcement of cutting restrictions by government officials and private mangrove claimants. Data show considerable size and species selectivity in wood harvesting for construction, but not for fuel.;Mangrove planting emerged and spread on both Banacon and in Bais in as part a response to wood scarcities created by the imposition of commercial firewood concessions over natural forests. People have planted to ensure a ready supply of construction posts for fish traps, to protect their homes and fish ponds from wave and wind damage, to establish tenure claims over intertidal lands, and to appease officials who have promoted planting. Almost all people plant only R. mucronata in Bais and R. stylosa on Banacon because these are highly valued for construction wood and are especially easy to plant.;Planters varied in terms of their knowledge and experience with planting and this was found in cases to influence their planting success. Little active knowledge-sharing occurs among planters; most learn by imitating their neighbors or parents. Learning by direct experience is important for many, but opportunities are limited by the lack of suitable and available planting sites. Attempts to plant mangroves in Bais Bay often failed because environmental events, especially shell infestations and wave damage, destroyed planted seedlings.;Cutting was found to be the major cause of mangrove tree mortality and has dramatically changed forest structure. Yet, cutting is not substantially changing forest composition in the sites studied because most of the common species regenerate well by stump regeneration into gaps caused by cutting.;Compared to natural forests, mangrove plantations are characterized by high densities of small stems, more numerous but smaller canopy gaps, and fewer species. Some of these characteristics change with plantation age, but species composition does not. There was almost no post-planting recruitment of other, non-planted mangrove species into plantations up to 50 and 60 years of age, suggesting strong recruitment limitation.;In conclusion, human influences on mangrove forests in both Bais Bay and on Banacon Island are pervasive and often severe. Event ecology offers important advantages for studying both the nature of human actions and the influences these actions have on mangrove forests.