# Plant Litter Trait Variation Between Native and Invasive Species Across Steep Climate Gradients in the Hawaiian Islands

## TL;DR

The study compares plant litter traits between native and invasive species in Hawaii, finding that climate has a bigger impact on litter quality than whether a plant is native or invasive.

## Contribution

This study reveals that climate gradients strongly influence plant litter traits, challenging the assumption that invasive species consistently produce higher-quality litter.

## Key findings

- Invasive species do not consistently produce higher-quality litter than native species in Hawaii.
- Climate gradients have a stronger influence on litter traits than species origin.
- Intraspecific variation in litter traits is greater than interspecific variation.

## Abstract

Oceanic islands have high biodiversity, which is severely threatened by invasive species. Functional traits serve as a framework to investigate invasive‐native dynamics, but most studies investigating native‐invasive plant functional trait differences on islands focus on live foliage traits, while litter traits remain understudied. It is hypothesized that invasive species produce higher quality litter (e.g., high nutrient content, low tannins and leaf mass per area) than native species, and furthermore, that this high‐quality litter decomposes more rapidly, in turn providing a positive feedback that facilitates their expansion. To investigate native vs. invasive plant litter quality in a highly endemic island flora, we conducted a systematic review to synthesize litter trait data from Hawaiʻi. To account for the extensive heterogeneity that occurs across the Hawaiian Islands, litter trait variability was synthesized with respect to elevation and climate gradients. Litter quality varies extensively across the Hawaiian Islands in native and invasive species. Although invasive plants have higher quality litter than native species overall, species origin accounts for relatively little trait variance, and native and invasive species overlap considerably in litter multivariate trait space. Moreover, intraspecific variation exceeds interspecific variation, highlighting the important role of environmental heterogeneity for widespread species. Climate influences native and invasive litter quality in distinct ways, leading to a reversal in strategy across climate gradients. When controlling for the full direct effects of climate, native and invasive plant litter traits are not significantly different. Climate heterogeneity, more than plant species origin, plays a key role in shaping plant litter trait variation and resource‐use strategies at the landscape or archipelago scale. Litter quality could be more commonly sampled as part of the functional syndrome of plants and for a better understanding of how traits differ between native and invasive plants.

Plant litter quality (nutrient content and toughness) varies extensively within native and invasive Hawaiian plants, with strong links to climate. Minimal differentiation between native and invasive species indicates weak support for the prediction that invasives have higher quality litter associated with fast decomposition and resource use strategies.