Diversity, stand structure, biomass and carbon storage potential of natural

Introduction

Mangrove forests are coastal wetland ecosystems considered one of Earth's most highly productive ecosystems, contributing various functions and services to surrounding coastal areas (Van Oudenhoven et al., 2015). It provides many useful human products, such as charcoal, medicines, and building materials (Barbier et al., 2011). Moreover, mangroves aid in regulating floods, erosion, and saltwater intrusion (Camacho et al., 2020) and as a buffer for coastal communities against storms and typhoons (Polidoro et al., 2010). Aside from that, this habitat also provides food and livelihood for coastal residents (Gevaña et al., 2018). Furthermore, mangroves play an important role in the health of coastal ecosystems. Their intricate root network stabilizes sediments and enhances water clarity, providing a perfect home for many marine organisms (Arceo-Carranza et al., 2021). 

Recently, blue carbon ecosystems like mangroves have received international attention as a valuable tool for mitigating the impacts of climate change. This coastal ecosystem is rich in biodiversity and one of the world's most significant carbon sinks, trapping and storing a remarkable amount of carbon within its dense root systems and forest soils (Alongi, 2014; Howard et al., 2014). Since the carbon trapped in the soil is difficult to decompose, this allows the stored carbon to stay in the soil for a long time, further emphasizing its vital importance in moderating the global climate (Castillo and Breva, 2012). Mangroves can hold up to 1023 t C ha-1 and five times more organic carbon than rainforests (Donato et al., 2011; Kaufman et al., 2018). Previous studies have emphasized that the bulk of this carbon is stored belowground, particularly in soil and roots (Donato et al., 2011).

Despite their importance, mangrove forests face numerous threats and challenges. Anthropogenic activities such as urbanization (Marchio et al., 2016), aquaculture (Primavera, 2006; Garcia et al., 2014), and overexploitation (McLeod and Sam, 2006) have led to the widespread degradation of mangrove habitats. Climate change also poses a significant risk to mangroves with rising sea levels and increased frequency and intensity of storms (Gilman et al., 2008; Abino et al., 2014a). Globally, it is estimated that mangrove forests lost at a rate of 2.74% in 1996- 2007 and 1.58% in 2007-2016 (Hagger et al., 2022). Brander et al. (2012) forecast a decline from 6,042 to 2,082 ha for the mangrove forests in Southeast Asia between 2000 to 2050. According to Gevaña et al. (2018), the country's mangrove forest cover is estimated at 356,000 ha with a decadal deforestation rate of 0.5%. The main drivers of this huge loss are various anthropogenic activities, including deforestation, land conversion for agriculture, aquaculture, and coastal development (Primavera et al., 2004; Garcia et al., 2014). 

The western part of Samar has a relatively long coastline, extending over 300 km (Abino et al., 2014a). Its mangrove forests constitute 7% of the total mangrove area of the country (FMB, 2011). As one of the provinces in the Philippines with the most extensive remaining mangroves, its biomass carbon sequestration and storage potential is also expected to be huge. However, there is limited information on Samar's natural and planted mangrove stands' composition, structure, and carbon storage potential. Hence, this study provides information on the diversity, structural complexity, and carbon storage potential of mangroves in the province. The objectives of the present study were to (i) identify mangrove species composition and diversity, (ii) determine the mangrove community structure, and (iii) evaluate the biomass and carbon stock concentration. The data collected from this study provides more comprehensive information for properly implementing mangrove conservation programs and developing local-specific climate change mitigation strategies.