On the hidden half: testing precision o f techniques used in
estimating below groun d biomass in mangrove forests
Ndegwa Gladys' 2, James Kairo2and Nico Koedam'
' Plant Biology and Nature Management, Faculty o f Sciences and Bio-engineering Sciences, Vrije
Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels, Belgium
E-mail: qndeqwa@ vub.ac.be
2 Kenya Marine and Fisheries Research Institute, PO Box 81651, 8 01 00-Mombasa, Kenya
Tropical deforestation has been associated w ith the net em ission o f 20% o f carbon dio xide to the
atm osphere (IPCC 2007). Reducing Emissions fro m D eforestation and fo re st degradation com m only
called REDD+, is a potential m arket based approach in fo re stry th a t can be considered in m itig atin g
clim ate change th ro ug h carbon capture and storage (Donato et al., 2011). For REDD to work,
accurate m on itoring o f C pools and em issions is required thus the im portance o f robust C storage
estim ates fo r various forested ecosystems. Overlooked in clim ate change m itig a tio n strategies are
mangroves, which are hig hly e fficie n t carbon sinks fo r atm ospheric C 0 2 along trop ical coastlines
(Donato et al., 2011). C ritical uncertainties remain, however, before s u ffic ie n tly accurate and precise
estim ates o f m angrove C storage and land use em issions can be given. Field studies o f m angrove
biomass and p ro d u ctivity are d iffic u lt due to the soil co nd itio ns and the site and species-specific
dependencies render universal conclusions unreliable (Komiyam a e t al., 2000). In mangrove
forestry, m ost biomass studies have tended to concentrate on aboveground com ponents and there
is no standardized m ethodology to estim ate below ground biomass, which was estim ated to
co ntribu te about half o f the vegetative carbon sequestered by these forests. Three com m on
m ethods are used in mangrove biomass estim ation: com plete excavation (Ong e t al., 2004), coring
m ethod (Saintilan, 1997) and the trench m ethod (Komiyama et al., 2000) . Several biomass studies
have been carried o ut at Gazi Bay in Kenya on m angrove biomass in both replanted and natural
stands. Following these studies there has been a great desire to im prove on the m ethodology o f
d eterm ining below ground root biomass in mangroves. To test the accuracy and precision o f the
three m ethods used in mangrove forestry, sam pling was done at Gazi Bay, Kenya from A ugust 2008
to December 2009 using Ceriops ta g a l (Perr.) C.B. Robinson. The objective is to use root biomass as
a pro xy to estim ating below ground carbon storage. Prelim inary results indicate roo t biomass
reduction w ith increasing distance from the tree base and increasing depth fo r both the coring and
trench m ethods. We found root biomass consisted o f 58%±9.7 o f to ta l plant biomass co nfirm in g the
bottom -heavy structure o f mangroves. Parallel to th is we intend to fu rth e r apply a llo m e tric scaling
techniques in estim ating tree w eight from measureable tree dim ensions based on e xisting models.
R eferen ces
Donato D.C., J.B. Kauffman, D. M urdiyarso, S. Kurnianto, M. Stidham and M. Kanninen. 2011.
Mangroves among the m ost carbon-rich forests in the tropics. Nature Geoscience 4:293-297.
IPCC. 2007. Climate change 2007: Synthesis Report. C on trib u tion o f W orking Groups I, II and III to
the Fourth Assessm ent Report o f the Intergovernm ental Panel on Climate Change. Pachauri R.K.
and A. Reisinger (Eds). Geneva, Switzerland.
Komiyama A., S. Flavanond, W. Srisawatt, Y. Mochida, K. Fujim oto, T. Ohnishi, S. Ishihara. and
T. Miyagi. 2000. T o p /ro o t biomass ratio o f a secondary m angrove (Ceriops tagal (Perr.) C.B.
Rob.) forest. Forest Ecology and M anagem ent 139:127-134.
Ong J.E., W.K. Gong and C.FI. Wong. 2004. A llo m e try and p a rtitio n in g o f mangrove, Rhizophora
apiculata. Forest Ecology and Management 188:395-408.
Saintilan N. 1 997. Above- and below -ground biomasses o f tw o species o f m angrove on the
Flawkesbury River estuary, New South Wales. Marine Freshwater Research 48:147-152.
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