Impacts of livestock on rehabilitating post-mining Dune forest in Zululand

Abstract

Richard's Bay Minerals (RBM) disturbs the natural vegetation by mining heavy minerals (zircon, rutile and ilmenite) along the northern coast of KwaZulu-Natal province of South Africa. The disturbed area has to be rehabilitated in order to be reused by the future generation. RBM initiated a rehabilitation program in 1978 where the mining commenced, and that has resulted in stands of different ages, however, little is known about the impact of cattle from neighbours grazing in this rehabilitating forest. The study of the impact of cattle grazing on the oldest stand which has been under ecological rehabilitation for 28 years (during the time of the study) was conducted in order to assess the effect of cattle grazing. The following questions were addressed. • What is the impact of cattle on the structure and functioning of rehabilitating forests on the coastal sand dunes? • What impact do grazing cattle have on the micro-environment of the rehabilitating forest? • Do communal cattle disperse some exotic tree species from the community to the rehabilitating forest?

The study comprised of two components which are field and laboratory experiments. Field experiment was conducted on the 28 years old rehabilitating stand (see figure 2.2 in chapter two) and lab experiment was conducted at the University of Zululand in KwaZulu-Natal Province of South Africa. Field experiment addressed the impact of livestock grazing in the rehabilitation. Therefore a one-hectare plot was demarcated and divided into two halves. One half was fenced (exclosure) to prevent cattle grazing and the other half was unfenced (control) to allow cattle grazing. Eight transect belts of 80 m2 each were marked per subplot and three markers were pinned (one on each end of the transect belt and one in the middle) per transect belt. Transect belts were 5 m apart. A total of sixteen 0.25 m2 quadrats were clipped between the markers per subplot (exclosure and control). Clipped biomass was oven dried and weighed and further analysed for NDF and CP. Seed germination surveys was also conducted per subplots around each marker in a complete randomised design with four replicate.

Laboratory experiment was conducted at the University of Zululand as a multi-factorial experiment which evaluated the external (possible damaging) factor(s) on Acacia karroo and the experiment was arranged in complete a randomised design with four replicate. A total of 972 Acacia karroo seeds were sown in 324 pots which were filled with sandy soil and each pot was planted with three seedlings. Seedlings were subjected to the following treatment: damage, water, fertilizer and shade each having three levels. At the termination of the experiment seedling height was measured and seedlings were oven dried at 60°C for 48 hours, after which shoot and root dry mass were recorded separately.

Another experiment was proposed based on findings that guava was a dispersed tree species in the rehabilitating forest. Therefore a pot experiment was conducted in order to check the effects of grass, damage and water in guava establishment in the rehabilitating forest. The Psidium guajava experiment differed from the Acacia karroo experiment because shade was standardised (all pots were shaded by 80% shade cloth) and fertiliser was replaced by grass competition, making three factors. Another difference was that treatments were replicated eight times with one pot per treatment. Guava seeds were sown in 216 pots and seeds were not counted, but before guava was sown LM grass was sown in two thirds of the pots and it was given two months for establishment prior guava seeds being sown. One month after germination, seedling height was measured and three of eight replicates per factor was terminated prior to infliction of damage treatment. The remaining seedling height was measured weekly until the experiment was terminated month later. Seedlings were oven dried at 60°C for 48 hours, and thereafter root and shoot was weighed separately and in three out of five remaining replicates seedling leaf was weighed separately.

Statistical significance was considered at the 5% level (P < 0.05). Cattle grazing in the rehabilitating forest was found to reduce seedling establishment significantly (P = 0.041) by 49.8%. Communal cattle which grazed in the rehabilitating forest reduced herbaceous biomass by 51.8% (P < 0.001). There was no significant difference in NDF and CP between the subplots (P = 0.165 and P = 0.453 respectively). Cattle consumed guava seeds and they dispersed them in rehabilitating forest which was the most preferred for gazing. Germination tests done on guava seeds that had passed through livestock alimentary canals as compared with fresh seeds (from tree), showed that the passage of guava seed in the digestive track did not trigger germination. Livestock play a major role in the livelihood of Kwa-Mbonambi communal farmers, however livestock mortality and shortage of grazing land were their major constraints in livestock operation. Communal farmers in Kwa-Mbonambi keep livestock for cultural activities and to support their families since they are unemployed. Their cattle invade the rehabilitating forest where they disturb the rehabilitation programme. Therefore cattle grazing in the rehabilitating forest hinders seedling establishment and herbaceous cover and that disturbed the micro-environmental condition of the forest. Damage in the form of clipping significantly reduced height of Acacia karroo seedlings (P < 0.001), by 75.9%. There was no significant effect on seedling height due to factor interactions (P = 0.338). Shades decreased shoot mass of seedlings by 19.9% (P < 0.001). Moreover there was a significant effect of interaction of three factors namely fertiliser, water and damage (P = 0.020). Daily watering reduced shoot mass in the absence of fertiliser. Shade reduced root mass significantly (P < 0.001) by 33.1%. Clipping also reduced root mass significantly (P < 0.001), however watering daily increased root mass of clipped seedlings in the absence of fertiliser.

Grass had a significant effect on guava seedling establishment (P < 0.001). Irrigation also had a significant effect on growth of guava seedlings (P < 0.001). Grass reduced the growth rate of guava seedlings. Clipping reduced root mass significantly (P < 0.001). The highest interaction had a significant (P.< 0.028) effect on root mass, where as in seedling height and shoot mass the highest interaction of three factors had no significant effect (P = 599 and P = 0.186).

Damage in the form of clipping significantly reduced seedling height, in other words it hinders growth rate and the establishment of tree species. Acacia karroo is known to allocate more nutrients in root growth, however clipping reduced root growth in order to compensate shoot regrowth after clipping. Though guava is dispersed by communal livestock grazing in the rehabilitating forest their establishment is hindered by grass.

In conclusion Acacia karroo was found to be suitable for the rehabilitating programme with low supervision. Acacia karroo is regarded as an invasive tree species, and since it is a legume it has nitrogen fixing bacteria in roots hence it enriches soil with nitrogen and it has a competitive ability in nitrogen poor soil. Though guava found to be dispersed by cattle in the forest, its establishment was found to be hindered by grass, therefore it is very rare for guava to invade the forest. The follows recommendations are proposed for the smooth operation of rehabilitation. There is a need for research on the long-term impacts of livestock. The two communities of Kwa-Mbonambi and RBM need to reach a point where they agree on the importance of rehabilitation.