Remote sensing of seasonal changes and disturbances in mangrove forest: a case study from South Florida

Michael Ross,Bina Thapa,Daniel Gann,Keqi Zhang

doi:10.1002/ecs2.1366

Abstract

AbstractKnowledge of the spatial and temporal changes caused by episodic disturbances and seasonal variability is essential for understanding the dynamics of mangrove forests at the landscape scale, and for building a baseline that allows detection of the effects of future environmental change. In combination with LiDAR data, we calculated four vegetation indices from 150 Landsat TM images from 1985 to 2011 in order to detect seasonal changes and distinguish them from disturbances due to hurricanes and chilling events in a mangrove‐dominated coastal landscape. We found that normalized difference moisture index (NDMI) performed best in identifying both seasonal and event‐driven episodic changes. Mangrove responses to chilling and hurricane events exhibited distinct spatial patterns. Severe damage from intense chilling events was concentrated in the interior dwarf and transition mangrove forests with tree heights less than 4 m, while severe damage from intense hurricanes was limited to the mangrove forest near the coast, where tree heights were more than 4 m. It took 4–7 months for damage from intense chilling events and hurricanes to reach their full extent, and took 2–6 yr for the mangrove forest to recover from these disturbances. There was no significant trend in the vegetation changes represented by NDMI over the 27‐yr period, but seasonal signals from both dwarf and fringe mangrove forests were discernible. Only severe damage from hurricanes and intense chilling events could be detected in Landsat images, while damage from weak chilling events could not be separated from the background seasonal change.

Highlights

Mangroves are one of the most productive forest ecosystems but are ideal for monitoring biological response to global climate change (Saintilan et al 2014, Spalding et al 2014)
In addition to these gradual changes, mangroves have been altered by episodic disturbances from hurricanes, freezes, or lightning strikes (Lugo and Patterson- Zucca 1977, Smith et al 1994, Sherman et al 2001, Stevens et al 2006, Zhang 2008, Cavanaugh et al 2014, Thapa 2014) that are more evident at the landscape scale, though they may contribute to or interact with global change factors that influence broader distributional trends
As normalized difference vegetation index (NDVI), soil adjusted vegetation index (SAVI), enhanced vegetation index (EVI), and normalized difference moisture index (NDMI) used different combination of spectral bands, it was expected that one index would perform better than the others in detecting mangrove changes

Summary

Introduction

Mangroves are one of the most productive forest ecosystems but are ideal for monitoring biological response to global climate change (Saintilan et al 2014, Spalding et al 2014). Mangroves have been experiencing significant changes worldwide due to sea level rise, escalation in atmospheric CO2 concentration, global surface temperature increase, and human development of coastal areas. In addition to these gradual changes, mangroves have been altered by episodic disturbances from hurricanes, freezes, or lightning strikes (Lugo and Patterson- Zucca 1977, Smith et al 1994, Sherman et al 2001, Stevens et al 2006, Zhang 2008, Cavanaugh et al 2014, Thapa 2014) that are more evident at the landscape scale, though they may contribute to or interact with global change factors that influence broader distributional trends. It is important to document both episodic and gradual changes experienced by mangrove forests in order to understand coastal forest dynamics at the landscape level

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Conclusion