Investigating Banksia Coastal Woodland Decline Using Multi-Temporal Remote Sensing and Field-Based Monitoring Techniques

Rose-Anne Bell,J. Nikolaus Callow

doi:10.3390/rs12040669

Rose-Anne Bell, J. Nikolaus Callow

Open Access

https://doi.org/10.3390/rs12040669

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Journal: Remote sensing	Publication Date: Feb 18, 2020
Citations: 5	License type: CC BY 4.0

Affiliation: University of Western Australia

Abstract

Coastal woodlands, notable for their floristic diversity and ecosystem service values, are increasingly under threat from a range of interacting biotic and abiotic stressors. Monitoring these complex ecosystems has traditionally been confined to field-scale vegetation surveys; however, remote sensing applications are increasingly becoming more viable. This study reports on the application of field-based monitoring and remote sensing/(Geographic Information System) GIS to interrogate trends in Banksia coastal woodland decline (Kings Park, Perth and Western Australia) and documents the patterns, and potential drivers, of tree mortality over the period 2012–2016. Application of geographic object-based image analysis (GEOBIA) at a park scale was of limited benefit within the closed-canopy ecosystem, with manual digitisation methods feasible only at the smaller transect scale. Analysis of field-based identification of tree mortality, crown-specific spectral characteristics and park-scale change detection imagery identified climate-driven stressors as the likely primary driver of tree mortality in the woodland, with vegetation decline exacerbated by secondary factors, including water stress and low system resilience occasioned by the inability to access the water table and competition between tree species. The results from this paper provide a platform to inform monitoring efforts using airborne remote sensing within coastal woodlands.

Highlights

The geographical and ecological position that coastal woodlands occupy means these ecosystems are under threat from a changing climate [1,2] and an expanding coastal-focused urban population [3,4]
Tree keystone species mapped in the high and low elevation sites included A. fraseriana, B. menziesii, B. attenuata, C. calophylla and E. marginata, mapped by training from expert ecologist, with a total of 332 and 271 trees mapped within the two sites, respectively
In both sites, change in canopy survival between the 2013–14 and 2015–16 datasets was significant for most species, with a positive change for A. fraseriana and overall negative change for Banksia species (Table 7)

Summary

Introduction

The geographical and ecological position that coastal woodlands occupy means these ecosystems are under threat from a changing climate [1,2] and an expanding coastal-focused urban population [3,4]. Tree mortality is defined as a reduction in overall plant health over a period of time, which, in the most extreme case, can include tree death [10,11]. This can include decline in overall ecosystem structure and function [12,13], changes in relative competitive capability of specific species relative to one another or the loss of less resilient species, resulting in a transition of the system floristics [7,14,15,16]. The ability to monitor time-space patterns of tree health is an important component in determining potential drivers of tree mortality and informing management of coastal woodlands [4,17,18]

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