The its inhabitants, as well as providing new livelihoods

The Fisheries Code defines mangroves as a community of
intertidal plants including all species of trees shrubs, vines and herbs found
on coasts swamps or on border of swamps. Mangroves are among the most important
components of the coastal ecosystems. They are essential for the following
reasons: they serve as habitats for species of marine fauna and flora,
especially breeding and nesting grounds for fish, along with food and
livelihoods for local communities; they can provide protection from the impacts
of climate change, including sea-level rises and coastal erosion caused by
storm surges and extreme weather events; they are also good source of important
commodities such as food, fuel, timber, medicine and building materials; they serve
as shelter belt for they can cushion the impact of strong winds and provide
protection against soil erosion with its extensive air root system; has the
capacity to stabilize shorelines and protect inshore fish habitats from
sediment pollution; and they can transport accumulated nutrients to adjacent
areas and serve as natural nurseries or breeding places for a large number of
fishes, crabs, sea creatures and other commercially important species. Because
of their importance, several community based mangrove restoration projects have
been implemented in the Philippines aimed at protecting and rehabilitating this
significant ecosystem. Sound mangrove management can provide adaptation
strategies such as increasing resilience of the coastal line and its
inhabitants, as well as providing new livelihoods options to the local
communities (Bambalan, 2013).Mangrove
forests are the dominant coastal ecosystem in tropical and subtropical regions.
They form an important link between aquatic and terrestrial ecosystems.
Although mangroves grow in difficult environments regularly inundated by
saltwater, their primary productivity of 2.5 g carbon m?2 day?1 makes them the
most productive aquatic ecosystem (Fatoyinbo, Simard, Washington-Allen, and
Shugart, 2008). Mangroves also provide vital role in the seagrass and coral
reef production and continuity in the coastal ecosystem. According to DENR
(2017), there are 70 existing species of mangroves all over the world. From
this figure, 46 species are found in the Philippines. Mangrove forest is a part
of the marine coastal ecosystem that provides productive natural resources.  Existence of mangrove forest provides
ecological benefits including the prevention of erosion, and as a place of life
of millions species of mangrove ecosystems. The presence of mangrove forests in
ASEAN countries provides benefits to the surrounding communities, such as
protection against tsunami waves or strong winds coming from the sea, economic
benefits such as fruit and other parts of mangrove trees, as well as supporting
the production levels of fish and a good habitat for a variety of typical flora
and fauna in this area. ( Kusano and Santoso, 2013). Kusano and Santoso further stated that the mangrove area in
many places have not been managed optimally these days. In urban areas,
mangroves are often used for housing after conversion through reclamation,
while in rural areas the mangrove areas are often used for fishing businesses
which sometimes tend to violate the rules of conservation or protection.  Spatial Distribution of
Mangrove Forest  In the
study conducted by Long and Giri (2011), they stressed that in the Philippines,
current, accurate, and reliable information on
the areal extent and spatial distribution of mangrove forests is limited.
Previous estimates of mangrove extent do not illustrate the spatial
distribution for the entire country. They used publicly available Landsat data
acquired primarily from the Global Land Survey to map the total extent and
spatial distribution. What they did was ISODATA clustering, an unsupervised
classification technique which was applied to 61 Landsat images. Statistical
analysis indicates the total area of mangrove forest cover was approximately
256,185 hectares circa 2000 with overall classification accuracy of 96.6% and a
kappa coefficient of 0.926. These results differ substantially from most recent
estimates of mangrove area in the Philippines. They further concluded that the
results of their study may assist the decision making processes for
rehabilitation and conservation efforts that are currently needed to protect
and restore the Philippines’ degraded mangrove forests.Spatial
mapping of the vertical structure of mangroves at the landscape scale is needed.
One of the reasons for this lack of information is that mangrove forests are
particularly difficult to survey due to the high density of trees and roots,
and the extent of tidal channels that permanently or tidally flooded the land
surface. (Simard, Zhang, Rivera-Monroy, Ross, Ruiz, Castañeda-Moya, Twilley,
and Rodriguez, 2006)  Landsat ETM+ and SRTM
DEM Data  The Shuttle Radar Topography Mission (SRTM) elevation data
is available with high spatial resolution (30 m) throughout the U.S. These data
can be used to determine the significance of mangrove forest as carbon sinks by
relating tree height to available ground estimates of mangrove forest biomass
at local scales, particularly since mangrove tree height is a good indicator of
forest must be calibrated. Recent emerging airborne light detection and ranging
(lidar) technology provides an ideal tool to calibrate radar data since the
tree height data can be derived directly from lidar measurements. It was proven
that airborne lidar systems are capable of measuring objects on the earth
surface with a horizontal resolution of several meters and centimeter vertical
accuracy (Hyppa et al.,).In their study, Castañeda-Moya, (2006) were able to
show that SRTM elevation can be used to estimate mangrove mean tree height and
biomass accurately and could potentially be used to map mangrove forests around
the world. Optical Remote Sensing techniques have proven a reliable tool for the
estimation of mangrove forest area, productivity and species distribution Aschbacher
et al., 1995; Smith et
1998; Dahdouh-Guebas
et al., 2000; Kovacs et
2001; Satyanarayana
et al., 2001; Dahdouh-Guebas
et al., 2002; Sulong et
al., 2002; Cohen and
2003; Dahdouh-Guebas
et al., 2004; Gesche et
al., 2004; Wang et
2004. The combination of
optical and radar remote sensing is a technique that can provide greater
insight into mangrove structure estimations Rasolofoharinoro
et al., 1998; Pasqualini
et al., 1999; Held et
2003; Simard et
2006. Data from the Shuttle
Radar Topography Mission (SRTM) has proven particularly well suited, due to its
accuracy and worldwide coverage Simard et
2006; Rodriguez
et al.,
2006.  Biomass and Carbon
Stocks of Mangrove Forest  Mangrove forest can play an important role in
GHGs reduction because it can serves as carbon sinks (Pillodar, Mero,
Mostrales, Astillero & Ignacio, 2017; Fatoyinbo & Simard, 2017;
Camacho, L.D., Gevaña, Carandang, Camacho, S.C., Combalicer, Rebuquio, &
Yon, 2011; Jones, Ratsimba, Ravaoarinorotsihoarana, Cripps & Bey, 2014). As
manifested also in the discussion of mangroves on global climate change
particularly on Reduced Emission from Forest Degradation and Deforestation Plus
(REDD+) (Pillodar et al., 2017). Several studies on biomass and carbon stocks estimation of
mangrove forest were undertaken at different parts of the world (Camacho, L.D.
et al. 2011; Fatoyinbo and Simard, 2017; Jones, et al. 2014; Komiyama,
Poungparn and Kato, 2005; Komiyama, Ong, and Poungparn, 2008; Pillodar, et al.
2017). All of their works pointed out to the works of Kauffman and Donato
(2012) in terms of allometric equations for calculating biomass of mangroves. This standardized the measurement on biomass and carbon stocks
among mangrove forests.Carbon
pools of mangrove forests are among the highest of tropical forest types
(Bouillon et al., 2008). Of great interest is the mangroves’ potential value in
carbon mitigation programs such as REDD+ and other financial incentives for its
conservation of standing forests (Kauffman and Donato, 2012). Mangroves are
currently being advanced as an essential
component of climate change strategies such as REDD+ and blue carbon (Alongi,
2012). However, distribution of mangrove trees has decreased to the half in the
last five decades due to land conversion for urbanization, agriculture, and
aquaculture, especially shrimp farms. They are planted to recover its
distribution and rehabilitate the coastal
ecosystems. To account for mangrove biomass, only ten allometric methods are
approved by UNFCCC (United Nations Framework Convention on Climate Change) so
far (Putz and Chan 1986, Day et al.1987, Clough and Scott 1989, Chavez et al.
2005, Smith and Whelan 2006). The allometric method relies on some empirical
relationships between growth factors such as diameter at breast height (1.3 m
from the ground), tree height and tree biomass. Although these factors are
periodically measured in the field, it requires laborious and time-consuming
work to correlate the growth relationships. The constant tidal out welling of mangrove litter provides
large amounts of carbon (C) to coastal and offshore marine ecosystems and
contributes over 10% of the dissolved organic Carbon (DOC) to ocean sediments
worldwide (Cintrón and Shaeffer-Novelli, 1984; Dittmar et al.,
2006). Feng, (2015) indicated that mangrove forests are
highly productive and have large carbon sinks while also providing numerous
goods and ecosystem services. However, effective management and conservation of
the mangrove forests are often dependent on spatially explicit assessments of
the resource. Given the remote and highly dispersed nature of mangroves,
estimation of biomass and carbon in mangroves through routine field-based
inventories represents a challenging task which is impractical for large-scale
planning and assessment. Alternative approaches based on geospatial
technologies are needed to support this estimation in large areas.From
the study of Gevaña, Pulhin and Pampolina, (2008), it was stressed that in the
context of climate change and global warming, carbon sequestration receives a
considerable attention now. In the latest assessment report of the
Intergovernmental Panel on Climate Change (IPCC), global mean temperature has
dramatically increased over the past decades. There is also mounting evidence
that this increase will remain as problems on land use change and industrial
emissions continue to worsen. Among the GHGs, CO2 is the most abundant. Forest
ecosystems such as mangroves play a significant role in the climate change
problem because they serve as sinks of atmospheric. Great attention is focused
on tropical forests to offset carbon emissions.