Ecological perspective on bioinvasion of the Makiling forest [Philippines] by alien plant taxa-policy implications

Bioinvasion is a recent issue that heralds the threat that alien organisms intentionally or unwittingly introduced by man may sow chaos against the integrity of natural ecosystems worldwide. The present paper focuses on invasive alien tree species in Mt. Makiling after 100 years of intentional introduction of alien trees for education, research and extension purposes. The results of a twelve year period of research on plant bioinvasion in Mt. Makiling conducted by the author together with his advisees and supervised UP Rural High School students are compiled, tabulated and supported by photographs and figures to present the paper's thesis 'plant bioinvasion in Mt. Makiling is real and therefore should alarm authorities to take action'. Big Leaf Mahogany Swietenia macrophylla, Palosanto Triplaris cumingiana and Paper Mulberry Broussonetea papyrifera are the alien trees that were mainly studied although other species are in passing also included and documented. A thesis discovered Big Leaf Mahogany wildlings are fairly dispersed under the canopy of a forest stand dominated by native trees. Another had the same conclusion using different sampling techniques. One student working with trees found that the degree Big Leaf Mahogany contaminates a given stand can be graphically presented through ordination analysis. Through correlation analysis another worked on the undergrowth to prove that an increase in Big Leaf Mahogany cover elicit corresponding decline in undergrowth diversity. Two students did their respective theses to explain this negative relationship. One proved Mahogany leaf extract inhibits the growth of Narra Pterocarpus indicus seedlings, while the other proved that litter-mat covered soil under deciduous mahogany plantations are unhealthy substrate for seed germination. Later, high school students showed that mahogany does not spread out into well-lighted open and thicket vegetations but instead favor shaded forested stands. The light-demanding Paper Mulberry dominates in open, thickets and forest edges through prolific seeds that is bird-dispersed asid from ability to produce stolons/or underground lateral branches that sprout new individual trees. Paper mulberry, is excluded in well-shaded forest stands. Interestingly, a belt-transect one kilometer long showed an almost pure mahogany stand at the first 500 metes and the next 500 meters are a mixture of alien trees. The one-kilometer strip was 69% alien against only 31% native trees. Two students found out that Big Leaf Mahogany can penetrate lowland dipterocarp forest at the rate of about 200 meters in a time span of 70 years. The pattern of spread of Big Leaf Mahogany and Palosanto is a function of the timing of fruiting that coincides well with the blowing of the northeast trade monsoon wind (Amihan), hence the strong recruitment toward the southwest direction even if the terrain is uphill. Recommendation for neutralizing both fast and gradual spreading invasive tree species in Mt. Makiling are presented. It includes purging bioinvasives in places where they should be off-limits while in places they are allowed, like in botanic gardens, street containment is imperative. Policy recommendations for both national and international relevance are also presented especially on addressing the conduct of transboundary traffic of tree species and criteria on entry and non-entry protocols. A major overhaul of the forestry sector is anticipated to appropriately address and proactively respond to the issues and concerns brought about by bioinvasion of forest ecosystems. Overhaul comes with rethinking and retooling the sector. This may require a re-examination of contentious paradigms of traditional forestry that are by their nature among the causes of plant bioinvasion in forests. There is therefore the need to create an enabling environment that calls for the revision of forestry curricula in state colleges and universities offering B.S. Forestry, a corresponding change in line agency policy dealing with introduction and planting of alien tree species and the major amendment of forestry laws to relax the prohibition of cutting of trees if it is done in the act of preventing or checking bioinvasion of Nature Forest Parks and other protected areas.