Rodent damage control in commercial forestry in the Natal Midlands, South Africa.
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Date
1996
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Abstract
Rodents cause damage in commercial forests by gnawing at the bark of the trees. It is currently
estimated that rodent damage in commercial forestry costs the industry R50 million per annum.
The species of rodents which cause the damage are not known, neither is the reason behind this
behaviour. Through stomach analysis it has been established that 3 species are involved Otomys
irroratus, Rhabdomys pumilio and Mastomys natalensis, however this behaviour is confined to the
winter. Chemical analysis of the bark reveals that the percentage concentration of nitrogen varies
seasonally. The period of high concentration correlates with periods when the natural food of the
rodents is restricted and when bark gnawing is most prevalent. In the past the industry's response
to the damage has been to treat the areas with rodenticides. Using standard CMR methods, the two
commercially-licensed rodenticides and raptor perches were tested to examine their efficacy as
rodent control strategies. It was found that at a lower application of I block of rodenticide every
third tree there is little difference in the effectiveness of the rodenticide brands and there is also
little reduction in the abundance of the rodents. At a higher application rate of I block per tree, the
abundance of rodents is reduced but termination of the treatment results in the rodent numbers
quickly recovering, indeed they surpassed their original population numbers within 4 months.
Apart from the environmental dangers of applying such concentrations of poison, this is clearly an
uneconomic solution. My results indicate that at first planting, the sites should be provisioned with
raptor perches at a density of 16 ha⁻².
Contrary to accepted policy the perches do not require cross
pieces, which add to the expense and offer no advantage in raptor residency time. In areas of very
high rodent abundance the provisioning of tree collars provide physical protection to the trees. An
additional benefit of the collars is that the collars cause a beneficial microclimate around the tree
which enhances its growth rate. When the tree is around 2 years old it should be pruned to a height of I ffi, the slash being left in the inter-row. Results show that trees treated in such a way
experience no further attack and the rodents browse on the prunings. As the cost of the perches is
reduced and the cost of pruning is non-recurring the recommendations provide an economical and
environmentally sympathetic alternative to rodenticide application.
Description
Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 1996.
Keywords
Rodents--Control., Trees--Diseases and pests., Forest protection., Rodenticides., Forest management., Agricultural pests., Theses--Zoology.