Examining the Influence of Seasonality, Condition, and Species Composition on Mangrove Leaf Pigment Contents and Laboratory Based Spectroscopy Data

Francisco Flores-De-Santiago,Jinfei Wang,Chunhua Zhang,Francisco Flores-Verdugo,Fernando González-Farías,John Kovacs

doi:10.3390/rs8030226

Abstract

The purpose of this investigation was to determine the seasonal relationships (dry vs. rainy) between reflectance (400–1000 nm) and leaf pigment contents (chlorophyll-a (chl-a), chlorophyll-b (chl-b), total carotenoids (tcar), chlorophyll a/b ratio) in three mangrove species (Avicennia germinans (A. germinans), Laguncularia racemosa (L. racemosa), and Rhizophora mangle (R. mangle)) according to their condition (stressed vs. healthy). Based on a sample of 360 leaves taken from a semi-arid forest of the Mexican Pacific, it was determined that during the dry season, the stressed A. germinans and R. mangle show the highest maximum correlations at the green (550 nm) and red-edge (710 nm) wavelengths (r = 0.8 and 0.9, respectively) for both chl-a and chl-b and that much lower values (r = 0.7 and 0.8, respectively) were recorded during the rainy season. Moreover, it was found that the tcar correlation pattern across the electromagnetic spectrum was quite different from that of the chl-a, the chl-b, and chl a/b ratio but that their maximum correlations were also located at the same two wavelength ranges for both seasons. The stressed L. racemosa was the only sample to exhibit minimal correlation with chl-a and chl-b for either season. In addition, the healthy A. germinans and R. mangle depicted similar patterns of chl-a and chl-b, but the tcar varied depending on the species. The healthy L. racemosa recorded higher correlations with chl-b and tcar at the green and red-edge wavelengths during the dry season, and higher correlation with chl-a during the rainy season. Finally, the vegetation index Red Edge Inflection Point Index (REIP) was found to be the optimal index for chl-a estimation for both stressed and healthy classes. For chl-b, both the REIP and the Vogelmann Red Edge Index (Vog1) index were found to be best at prediction. Based on the results of this investigation, it is suggested that caution be taken as mangrove leaf pigment contents from spectroscopy data have been shown to be sensitive to seasonality, species, and condition. The authors suggest potential reasons for the observed variability in the reflectance and pigment contents relationships.

Highlights

Mangroves are salt tolerant trees distributed along intertidal coasts of tropical and subtropical regions [1,2]
When comparing the two conditions it is apparent that the spectral curves for the mangroves showsunder muchstress higher in the between green tothe red portions of the electromagnetic spectrum
Mangrove forests are one of the most important coastal ecosystems within tropical and subtropical regions, and yet, these forested wetlands are under a constant degradation due to many anthropogenic perturbations

Summary

Introduction

Mangroves are salt tolerant trees distributed along intertidal coasts of tropical and subtropical regions [1,2]. Mangrove forests are extremely important contributors to global organic carbon dynamics [4,5,6], to primary productivity [7,8], for nutrient recycling [5,9], and can help to mitigate climate change impacts [10]. Despite their ecological relevance, mangrove forests are under considerable degradation due to anthropogenic perturbations including aquaculture expansion [11,12]. Many techniques, including remote sensing, have been investigated in order to properly classify and monitor these forested wetlands (e.g., [14,15,16,17,18])

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