Thesis (MScFor) (Forest and Wood Science)--University of Stellenbosch, 2003. / Planting of upperstorey trees along boundaries has been introduced in KabaleUganda
with good reception from local farmers. Trees have been planted along
agricultural fields, but both Alnus acuminata and Grew/lea robusta out-compete food
crops. Managing competition between trees and crops for water, light, and
nutrients to the benefit of farmers is a determinant of successful agroforestry.
The scarcity and fragmentation of farmland coupled with the hilly nature of
Kabale, highlights the need to address the question of tree-crop competition for
resources if the technology of on-farm tree planting is to be widely disseminated
and adopted in its different guises.
Five-year old trees of A acuminata and G. robusta were subjected to
treatments of pollarding, or a combination of pollarding and one side root
pruning and compared with unpruned controls. The objectives were to assess
their potential in reducing competition with food crops and providing firewood to
farmers as well as their effects on tree growth. Pollarding has many benefits to
farmers because it provides firewood and stakes for climbing beans, it reduces
competition for resources between trees and crops and enables continued tree
planting on-farm. Continued on-farm tree planting alleviates problems associated
with limited land and contributes to environmental resilience. To ensure this,
effect of pollarding and root pruning of upperstorey boundary trees of A
acuminata and G. robusta was tested on 12 farmers' fields in Kabale.
Food crops (beans and maize) grown in the sequence beans-maize-beans,
grew very well at less than 50 em from trees that had been pollarded and root
pruned one side. In general, pooled data from 12 sites over 5 m away from trees
indicated that a combination of pollarding and root pruning increased bean yield
by 240% and maize by 154%, while pollarding alone increased bean yield by 181%
and maize yield was increased by 123% in comparison to non-pruned trees.
However, pollarding and root pruning treatments reduced tree growth rates.Notable was more competition with crops by A. acuminata than by G.
robusta. This was attributed to differences in root architecture, diameter at breast
height (dbh) sizes, crown spread and crown density between the two species.
Five-year-old A. acuminata had bigger dbh (12.40 cm), wider crown spread (6 m)
and a dense crown, while G. robusta had dbh 10.82 em, 3 m crown spread and a
light crown. A. acuminata also had more branches per tree (34) compared to G.
robusta with only 25. These factors influence water uptake, light penetration
through the canopy and transpiration rates, and thus affect tree-food crop
competition.
It is concluded that pollarding and root pruning have a great potential to
reduce tree-crop competition, thereby paving the way for continued on-farm tree
planting. The effect of pollarding on timber quality, moisture seepage into timber
through the cut surface, if any, and the extent of its damage are areas for further
research. The rate of root recovery is also to be followed closely to determine an
appropriate frequency for cutting back of roots to recommend to farmers how
often they need to prune their trees. It is also suggested that a thorough study be
conducted on the amount of water uptake from the soil by each of the species
Alnus acuminata and Grevillea robusta. This will help further explain the differences
in competition between the two species.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/2355 |
| Date | 12 1900 |
| Creators | Sande, Bueno Dickens |
| Contributors | Theron, J. M., Van Wyk, G., University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science. |
| Publisher | Stellenbosch : University of Stellenbosch |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 4099634 bytes, application/pdf |
| Rights | University of Stellenbosch |
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