Mangrove Phenology and Water Influences Measured with Digital Repeat Photography

Abstract

The intertidal habitat of mangroves is very complex due to the dynamic roles of land and sea drivers. Knowledge of mangrove phenology can help in understanding mangrove growth cycles and their responses to climate and environmental changes. Studies of phenology based on digital repeat photography, or phenocams, have been successful in many terrestrial forests and other ecosystems, however few phenocam studies in mangrove forests showing the influence and interactions of water color and tidal water levels have been performed in sub-tropical and equatorial environments. In this study, we investigated the diurnal and seasonal patterns of an equatorial mangrove forest area at an Andaman Sea site in Phuket province, Southern Thailand, using two phenocams placed at different elevations and with different view orientations, which continuously monitored vegetation and water dynamics from July 2015 to August 2016. The aims of this study were to investigate fine-resolution, in situ mangrove forest phenology and assess the influence and interactions of water color and tidal water levels on the mangrove–water canopy signal. Diurnal and seasonal patterns of red, green, and blue chromatic coordinate (RCC, GCC, and BCC) indices were analyzed over various mangrove forest and water regions of interest (ROI). GCC signals from the water background were found to positively track diurnal water levels, while RCC signals were negatively related with tidal water levels, hence lower water levels yielded higher RCC values, reflecting brownish water colors and increased soil and mud exposure. At seasonal scales, the GCC profiles of the mangrove forest peaked in the dry season and were negatively related with the water level, however the inclusion of the water background signal dampened this relationship. We also detected a strong lunar tidal water periodicity in seasonal GCC values that was not only present in the water background, but was also detected in the mangrove–water canopy and mangrove forest phenology profiles. This suggests significant interactions between mangrove forests and their water backgrounds (color and depth), which may need to be accounted for in upscaling and coupling with satellite-based mangrove monitoring.

Higher dung seedling density increases livestock dung greenhouse gas emissions in an alpine meadow

“…We took photographs of each dung pot and marked the position of the seedlings in the picture (i.e. Digital Repeat Photography; Songsom et al, 2021; Figure S2). When the seedlings were identifiable, the number of individual species (i.e.…”

“…We took photographs of each dung pot and marked the position of the seedlings in the picture (i.e. Digital Repeat Photography; Songsom et al, 2021;Figure S2).…”

Monitoring nature's calendar from space: Emerging topics in land surface phenology and associated opportunities for science applications

“…However, RGB digital number values are generally not directly used to conduct phenological analysis due to both external and internal factors—scene illumination affected by clouds, aerosols, solar azimuth, and so on, and control of exposure and color balance adjustment—could bring uncontrollability in image processing (Sonnentag et al, 2012 ). To better track phenology variability, the respective chromatic coordinates of RGB DN values (RCC, GCC, and BCC) are widely used in phenology studies (Brown et al, 2016 ; Klosterman et al, 2014 ; Liu, Fu, et al, 2016 ; Migliavacca et al, 2011 ; Moon et al, 2022 ; O'Connell & Alber, 2016 ; Songsom et al, 2021 ). Other color indices have since been construed by the nonlinear transformation of RGB DN values, including the VARI (Visible Atmospherically Resistant Index) (Sakamoto et al, 2012 ), grR (green‐red ratio) (Sonnentag et al, 2011 ), as well as the excess green (ExG) (Woebbecke et al, 1995 ).…”

Impacts of environmental pollution on mangrove phenology: Combining remotely sensed data and generalized additive models

“…Mangrove vegetation phenology studies have adopted a wide range of methods in recent decades, from field observations of phenology events such as flowering and fruiting (de Lima Nadia et al, 2012) to digital repeat photography or phenocams (Songsom et al, 2021). Satellite-based vegetation phenology has also emerged as a tool to address larger geographical scales.…”