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Dryad

The structural and functional impacts of invasive Psidium cattleianum in forests on the Island of Hawaiʻi

Seely, Tara1; Fortini, Lucas Berio2; Liang, Yuton3; Battles, John1

Research facility: Pacific Island Ecosystems Research Center
Published Dec 18, 2025 on Dryad. https://doi.org/10.5061/dryad.80gb5mm1g

Data files

Dec 18, 2025 version files 1.30 GB

Click names to download individual files

Abstract

During the past century, the proliferation of invasive species has contributed to the loss of biodiversity and ecosystem degradation. In forests, invasive tree species can alter ecosystem function, but the underlying mechanisms of these changes are not fully understood. We use the ongoing invasion of P. cattleianum on the Island of Hawaiʻi to test the hypotheses that invasive structural changes drive changes to forest evapotranspiration (ET). The aim of our study is first to quantify the structural changes to native ʻōhiʻa -dominated forest impacted by a gradient of P. cattleianum invasion. Our results suggest that invasive P. cattleianum causes significant changes to the vegetation density and structure of native forest on the Island of Hawai’i, including increased vegetation area index (VAI), decreased mean leaf height, and decreased structural heterogeneity. Second, we strove to understand the functional implications of structural changes through a biophysical modeling simulation, testing the sensitivity of ET to canopy structure under contrasting scenarios. Modeling the functional impact of structural change, we found that plots with P. cattleianum invasion importance value (IVinv) above 0.35 have a higher likelihood to increase ET compared to plots with P. cattleianum invasion less than 0.35 IVinv. Modeled increases in ET due to invasion ranged from 19% and 123% relative to native transects. The large variation in ET increases is caused by structural variation because the modeling scenarios did not include potential species differences in leaf physiology. Diagnostic scenario modeling shows the effect size of increased leaf area on modelled ET is constrained by the structural arrangement, i.e., vertical distribution, of the increased vegetation. Thus, an invasion structure that increases vegetation density in taller, more sunlit forest strata will lead to a greater increase in ET compared to an invasion structure that increases vegetation density in the shaded forest understory. Overall, we conclude that the vertical distribution of vegetation is an important factor shaping the impact of invasive P. cattleianum on the forest water balance.

This dryad repository contains: 

  • Point clouds of forest structure derived from terrestrial LiDAR for each sample site (.las files).
  • The vegetation area index (VAI) for each 1 m3 voxel corresponding to each point cloud dataset (.csv files).