Relationship Between Tree Vegetation Dominance and Understory Plant Community Structure in Alas Pinggan, Prigen, Pasuruan Hubungan Dominansi Vegetasi Pohon terhadap Struktur Komunitas Tumbuhan Bawah di Alas Pinggan, Prigen, Pasuruan

Abstract

Tree vegetation dominance is a key ecological factor that shapes the microenvironmental conditions of the forest floor and is associated with the structure and composition of understory plant communities. This study aimed to analyze the relationship between tree vegetation dominance and understory plant community structure in Alas Pinggan, Prigen Sub-district, Pasuruan Regency, East Java, Indonesia. The research was conducted on 27 April 2026 using a quadrat plot method across 11 observation plots. Tree vegetation was sampled in 20×20 m plots, while understory plants were recorded in nested 2×2 m subplots. Quantitative parameters calculated included the Importance Value Index (IVI) for tree species, and the Shannon-Wiener diversity index (H’), Simpson dominance index (C), and Pielou evenness index (E) for understory communities. Results revealed 14 tree species comprising 89 individuals, with Pinus merkusii as the dominant species (IVI = 128.41%) and Swietenia mahagoni as the subdominant (IVI = 75.13%). Tree dominance varied among plots, with Pinus merkusii dominating six plots and Swietenia mahagoni dominating four plots. Understory community structure exhibited H’ values ranging from 2.09 to 3.01 (moderate to high diversity), C values from 0.06 to 0.17 (low dominance), and E values from 0.76 to 0.92 (high evenness). Plots dominated by Pinus merkusii consistently displayed higher understory diversity than those dominated by Swietenia mahagoni, likely attributable to differences in canopy architecture and light penetration to the forest floor. These findings indicate that the identity of the dominant tree species is associated with the heterogeneity of understory plant communities in Alas Pinggan, suggesting a meaningful ecological linkage between overstory dominance and understory community structure.