Soil respiration studies in two sites of different post-logging ages in a moist-semi deciduous forest in Ghana
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Date
NOVEMBER, 2015
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Abstract
A large proportion of carbon is stored up in forest soils. Nevertheless, carbon is also released into
the atmosphere via soil respiration, a process which determines ecosystem function and a great
contributor in the global carbon cycle. This study investigated soil respiration in the Bobiri
Forest Reserve, a moist- semi deciduous forest in Ghana. The aim was to investigate the
seasonality, magnitude and abiotic controls on total soil respiration and its component
contributions from root-and-rhizosphere, mycorrhizae, surface litter and soil organic matter in a
12- and 55-year-old post-logged site over a full seasonal cycle. Soil respiration was measured at
monthly intervals from May 2013 to April 2014, by means of a dynamic closed chamber method.
Total soil respiration had a strong seasonal influence whereby average fluxes were higher during
the wet season and lower during the dry season. Estimated total soil respiration was 18.03 and
17.83 Mg C ha
-1
year
-1
at the 12- and 55-year-old sites respectively. In addition, estimated
component contributions at the 12- and 55-year-old post-logged sites were 24.02 and 34.58 % for
root-and-rhizosphere, 16.97 and 14.26 % for mycorrhizae, 27.42 and 25.17 % for litter and 31.59
and 25.99 % for soil organic matter, respectively. This depicted a higher autotrophic percentage
at 55-year-old post-logged site (48.84 %) in comparison to 12-year-old post-logged site (40.99
%) and conversely, a higher heterotrophic percentage at 12-year-old post-logged site (59.01 %)
in comparison to 55-year-old post-logged site (51.16 %). Relationship between soil respiration
and soil moisture was quadratic, however observed variation was only explained at 12-year-old
post-logged site (R
2
= 0.75; p < 0.01). A quadratic—quadratic regression of soil respiration and
both soil temperature and soil moisture accounted for 83 % of observed variation in soil
respiration at 12-year-old post-logged site (p < 0.01) but still did not improve variation at the 55-year-old post-logged site (p = 0.84). The study shows the influence of forest age on soil
respiration and confirms the importance of separating total soil respiration into source
components. Thus, the information should serve as a baseline for respiration studies in Ghana as
iv
well as assist in the understanding of forests and their influence on carbon cycling and global
warming
Description
A thesis submitted in partial fulfillment of the requirements for the degree of Master of Philosophy in Silviculture and Forest Management.