The influence of post-harvest treatments on the coppice response of two woody savanna species
Date
2017
Authors
Rankin, Christopher James
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Abstract
Fuelwood is still heavily relied upon by rural communities as a source of energy. The current
levels of wood harvesting have been deemed unsustainable, with models predicting the
local exhaustion of wood resources in most cases. However, wood depletion has generally
not happened to the level of severity predicted by the models. This may partially due to
under-accounting for coppice regeneration. Many savanna species that are harvested for
fuelwood demonstrate strong coppicing ability, which allows for regrowth after a
disturbance. This ability to regrow or coppice is a key functional trait which allows species
to persist and survive in frequently disturbed environments. There is surprisingly limited
knowledge about coppice dynamics in savanna trees and how managerial actions might
influence the coppice response and production of savanna species. To address this
problem, this study investigated the influence of four post-harvest treatments on various
aspects of the coppice response of Terminalia sericea and Dichrostachys cinerea – two
important savanna fuelwood species – in a field experiment. A total of 108 felled trees per
species were exposed to one of four treatments, which were applied monthly for 12
months. The treatments were (1) Control – no coppice shoots were removed for 12
months, (2) Harvest – all coppice shots were removed monthly, (3) Single prune – the
coppice shoot with the widest diameter was left on the stump, and (4) Usable – coppice
shoots that reached a diameter of 2 cm were removed. The effect that these treatments
had on the average diameter, length and cumulative number of coppice shoots produced
per stump was compared. The measurements of diameter and length were used in
developing allometric equations for the prediction of coppice shoot biomass. The predicted
biomass produced through the study was compared across treatments to gain an
understanding of how productivity could be influenced by management of coppice shoots.
The mean shoot diameter, length, as well as cumulative number of coppice shoots produced
per stump was higher in the single prune treatment for both species while the harvest
treatment resulted in high numbers of coppice shoots but with low average diameter and
length. Applying the growth rates of coppice shoots found in this study it can be assumed
that unmanaged coppice shoots will take approximately 5.5 years to reach a preferred
harvestable diameter of 4 cm, while single prune coppice shoots would take 3.3 years to
reach the preferred harvestable diameter. Diameter had more of an influence on the
predicted coppice biomass production of T. sericea while D. cinerea biomass prediction was
more influenced by shoot length. However, only diameter was used to compare the
prediction of coppice biomass with previously developed equations as these equations did
not consider length for predicting biomass of different components of trees. From the
derived models, the calculated biomass at the end of the study period as well as the
calculated biomass produced through the year was greatest for the control treatment. The
predicted dry shoot stem biomass at the harvestable diameter of 4 cm was 114.60 g for T.
sericea and 95.88 g for D. cinerea. From the findings of this study it is clear that post-harvest
management can be utilised to manipulate coppice response and biomass production.
Keywords: Fuelwood; Coppice shoot; Post-harvest treatment; Diameter; Length; Biomass
Description
A dissertation submitted to the Faculty of Science,
University of the Witwatersrand,
in partial fulfilment of the requirements
for the degree of Master of Science,
Johannesburg, South Africa
2017.
Keywords
Citation
Rankin, Christopher James (2017) The influence of post-harvest treatments on the coppice response of two woody savanna species, University of the Witwatersrand, Johannesburg, <http://hdl.handle.net/10539/25000>