Diversity of trees and structure of forest habitat types in Mt. Tago Range, Mindanao, Philippines

Abstract

Mt. Tago Range in Bukidnon has been subjected to deforestation and forest fragmentation due to logging ca. 35–40 years ago or as direct result of land conversion for agriculture, human settlements and wildlife product harvesting. It is currently not a protected area. This study aimed to provide data on the tree species diversity, structure, composition, conservation status and threats of the forest habitats in the site. Tree survey in the range was conducted in 2018–2019 using thirty-nine 20 x 20 m sampling plots and six one-kilometer transect lines. A total of 1,032 tree individuals from 54 families, 85 genera and 121 species were documented. The site is composed of four tropical forest habitat types namely: lower montane rainforest, upper montane rainforest, mossy-pygmy and forest over ultramafic rocks. These forest habitats also differed in species composition, elevation, substrate, dominance and structure in terms of height and diameter at breast height. The highest diversity index was observed in the mid-elevation and decreasing toward the peak. The diversity pattern herein is attributed to elevation, forest degradation due to anthropogenic activities and nature of habitat. The most abundant families were the Myrtaceae (23%), Podocarpaceae (12.8%) and Fagaceae (12.6%). At the family level the most dominant taxa included the Moraceae (8.7%), Rubiaceae (6.5%) and Myrtaceae (5.8%). Highest importance value index (IVI) in all forest types fell within the range of IVI’s for tropical forests. Assessment of conservation and ecological status revealed that 11 species (8%) are threatened, 28 (22%) Least Concern (LC) and 16 (12%) are Philippine endemics. Threats to tree diversity in Mt. Tago Range included land conversion for agriculture and settlement, illegal logging and lack of legislative protection. The implementation of conservation strategies by stakeholders is recommended to protect the tree species communities and population across the forest habitat types in the site. KEYWORDS: biodiversity, flora, Shannon-Weiner Index, Importance Value Index, non-Protected Area