The effects of neighbor, distance, and organic fertilizer on the establishment and early performance of three woody species in a restoration trial in the Kunene region, Namibia
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Date
2025
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University of Namibia
Abstract
Land degradation poses a significant challenge in arid ecosystems across Africa,
adversely affecting the livelihoods of many who depend on the environment. It has
become an urgent priority to restore these ecosystems. While various restoration
approaches have been studied globally, few have explicitly considered how
neighboring plant species and plant spacing as well as organic fertilizer influence
restoration outcomes. This study evaluated the effects of neighbor identity, planting
distance, and organic fertilizer on the growth, survival, and leaf traits of three woody
species – Vachellia erioloba, Colophospermum mopane, and Combretum imberbe.
Experiments were conducted in outdoor and indoor environments using a "two-factor
(2x9) complete randomized factorial design" with nine neighbor combinations and two
levels of distance/fertilizer. Results from field experiments showed that neighbor
effects varied by species. C. imberbe experienced improved stem length and biomass
when paired with V. erioloba, while C. mopane had reduced survival when grown with
V. erioloba at close spacing. Leaf nitrogen and surface area were generally lower when
species were paired with heterospecific neighbors, with V. erioloba exerting the
strongest influence. Wider spacing (1 m) enhanced growth and leaf traits for most
species, although the impact on survival and nutrient uptake varied depending on
species. In the greenhouse, manure produced mixed results, enhancing leaf traits for
C. imberbe and V. erioloba when grown alone or with conspecifics, but reducing
growth and survival in the presence of heterospecific neighbors. Recruitment of native
species was positively associated with C. mopane and C. imberbe, especially under 1
m spacing, while V. erioloba showed a negative association. These findings could
inform future revegetation initiatives and help design planting strategies that enhance
target species performance in restoration
Description
A thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science in Environmental Science
Keywords
Land degradation, Ecological restoration, Plant interactions, Neighbors, Distance, Fertilizer, Woody species, Namibia, University of Namibia