Interaction of seed dispersal and environmental filtering affects woody encroachment patterns in coastal grassland

Natasha N Woods,Donald R Young,Laura J Moore,Evan B Goldstein,Benjamin L Dows,Julie C Zinnert

doi:10.1002/ecs2.2818

Abstract

AbstractEncroachment of woody plants into grasslands has occurred worldwide and includes coastal ecosystems. This conversion process is mediated by seed dispersal patterns, environmental filtering, and biotic interactions. As spatiotemporally heterogeneous, harsh environments, barrier islands present a unique set of challenges for dispersal and establishment. Environmental conditions act as filters on dispersed seeds, thereby influencing encroachment and distribution patterns. Seldom have patterns of propagule dispersal been considered in the context of woody encroachment. We quantified dispersal and post‐dispersal processes of an encroaching woody population of Morella cerifera relative to directional rate of encroachment and observed distribution patterns on an Atlantic coastal barrier island with strong environmental filtering. We analyzed historic foredune elevation as a proxy for reduced interior environmental stress. The dispersal kernel was leptokurtic, a common characteristic of expanding populations, but rate of encroachment has slowed since 2005. Expansion pattern was related to foredune elevation, which limits encroachment below a threshold elevation. This difference between dispersal kernel behavior and encroachment rate is due to limited availability of suitable habitat for Morella and temporal variability in chlorides during the time of germination. Our results demonstrate that processes mediating seeds and seedling success must be accounted for to better understand establishment patterns of encroaching woody plants.

Highlights

Woody encroachment into grassland communities has occurred on nearly every continent throughout the Americas, Australia, and Africa, within the past 150 yr (Hagenah et al 2009, Brantley and Young 2010, D’Odorico et al 2012, Anadon et al 2014)
Study site and system Among systems that have experienced woody encroachment are the barrier islands of the Virginia Coast Reserve (VCR), a Long Term Ecological Research site owned by The Nature Conservancy (Hayden et al 1991) and left in a natural state
Our results highlight the interaction between seed dispersal and environmental filtering post-dispersal processes that determine encroachment rates and influence the resulting establishment patterns that emerge (D’Odorico et al 2012)

Summary

Introduction

Woody encroachment into grassland communities has occurred on nearly every continent throughout the Americas, Australia, and Africa, within the past 150 yr (Hagenah et al 2009, Brantley and Young 2010, D’Odorico et al 2012, Anadon et al 2014). For woody species growth are reduced, which vary by ecosystem (D’Odorico et al 2012, Archer et al 2017). Seldom has propagule dispersal been considered when investigating woody encroachment. Propagule expansion can occur independently or in combination with other drivers resulting in a change of species distribution across a landscape (McConkey et al 2012). We examined seed dispersal of an encroaching woody species into a coastal environment where it is unclear if woody species encroachment is facilitated by seed dispersal and if environmental heterogeneity limits establishment

Objectives

Methods

Results

Discussion

Conclusion