Spatiotemporal Risk of Species Colonization of Palo Santo <i>(Triplaris cumingiana</i> Fisch, &amp; C.A.Mey) in the Quezon Protected Landscape, Philippines

Abstract Invasive Alien Plant Species threaten the sustainability of remaining forest ecosystems including those in Protected Areas. Unfortunately, there are only a few investigations on their colonization and dispersal over time, particularly most protected areas in the Philippines. This study aimed to assess the spatial extent of areas at risk of species colonization and dispersal of T. cumingiana that was introduced in the Quezon Protected Landscape over 40 years. A tree inventory following a combined belt transect and purposive sampling was made to determine occurrences of their natural regenerations. The spatial extent and areas at risk of species colonization were determined by modeling its species distribution using species occurrence and 9 environmental predictor variables via Random Forest Classification in a Geographic Information System. The species occurrences of T. cumingiana at different growth stages were used to project areas at risk to species colonization at different time slices. Results revealed a total of 996 individuals composed of 547 seedlings , 375 saplings , 54 poles , and 20 standard trees. Projections showed an increase in spatial extent and areas at risk to species colonization from 12.54 ha (1.29 %) in the 2000s to 39.28 ha (4.05 %) by the 2020s, with distance to seed sources and topography-related features, specifically slope , aspect , and elevation, among the most important variables determining its occurrence. These results indicated slow colonization of T. cumingiana in QPL which can provide foundations for understanding biology and impacts of this invasive species, as well as identifying its optimal management and control strategies for sustaining the ecology of the landscape.