WILDLIFE MANAGEMENT- REPLANTING DEGRADED WATERCOURSES
Indigenous afforestation of degraded watercourses
J Wyatt
Water catchments can be used as the basic unit of environmental care, and riverine vegetation is essential for catchment stabilization, which in turn leads to a healthy coastline and marine zone.  
 
Riverine vegetation plays a major role in the regulation of water flow, the maintenance of water quality and the reduction in intensity of floods and the frequency of droughts. It also helps prevent soil erosion by protecting steep banks and the immediate slopes from direct heavy rain and rain damage, and root weirs maintain the streambed. Furthermore, afforested strips supply wildlife with suitable habitats and form corridors for animal proliferation and movement.

The planting of suitable tree species in denuded watercourses as a means of stabilizing the streambanks should thus be seen as a fundamental long-term strategy for sound catchment management. Such re-afforestation not only enhances ecological stability but also creates recreational and educational opportunities. Commercial prospects should not be overlooked. Some indigenous timbers have a high market value, and other forest products, notably bark, are widely sought after for traditional medicines. Riverine forest restoration will therefore alleviate what is now a serious threat to the few remaining indigenous forests.

Afforestation site selection and scope of plantings
Any perennial or seasonal watercourse, which is subject to site erosion, should be considered for afforestation. However, man-made waterways are often best stabilized by structural means and the planting of creeping grasses. Likewise, naturally grassed or fire-maintained waterways are best left as is, while marshes or very wet waterways are best vegetated with reeds and sedges.

Cropland areas (sugarcane, maize, vegetables, etc) should, according to current legislation, maintain a minimum crop exclusion zone of 10m beyond the flood area of a stream. It is this strip plus the flood area, which is often best, converted to forest. (Referred to in this article as the riparian zone). However, one can initiate an afforestation program within a 5m strip.

Timber plantations should maintain an exclusion zone of approximately 30m on either side of a watercourse. This will vary from 60m in the lower reaches of a catchment where the stream gradient is low and the soil moisture is high, to 15m where the slope is steep and rapidly drained; resulting in a narrower moisture saturated zone.

Forests, wetlands and vleis in the exclusion zone should not be disturbed, drained or damaged, and the felling of trees and dumping of plantation and crop debris into riparian zones should be avoided at all costs.

Tree planting in riparian zones should not be formal or in straight line, but at random, with approximately 3m between trees. This seems close, but the aim is to try and establish a closed canopy and extensive root system cover quickly and furthermore, not all the trees survive. The first trees should be planted as close to the stream as possible; but not on steep banks. Where bank "slumps" have occurred, reshaping of the banks or the building of protective works should be first considered.

It is useful to draw up a priority list of the catchments and streams on, and influencing your land, then in conjunction with your neighbors, attempt a common project. It is often preferable to start a project upstream and to work downstream over the years.

Site preparation and maintenance
In many cases vigorous alien weeds have invaded denuded watercourses. The first step in site preparation is to remove and then to control the alien invader weeds with periodic follow-up operations.

Where crops such as sugarcane, are presently growing up to the edge of the bank, conservation tillage can be employed to eradicate the crop. The indigenous trees can then be planted amongst the crop residue.

The holes for planting the seedlings should be cubes with sides between 400mm and 700mm, depending on the soil type. Stony or low fertility soils require fairly large holes with pre-mixes added to them in order to give the seedlings a good start. A suitable mix would be equal amounts of good topsoil, coarse sand for drainage and compost.

It is preferable to plant out seedlings once the wet season has started, as this will eliminate the need for frequent watering. Place a painted stake about 1m high alongside each seedling for the first couple of years. This identifies the areas that require slashing and helps monitor the progress of young plants. Exclude domestic stock from plantings. Hot fires can be avoided by clearing moribund or rank grass from around the young trees during weeding operations. The weeding or clearing of grass should be done by slashing around planted trees. Do not hoe as the young trees have roots near the surface that could easily be damaged. Do not use mowers or slash all grass, as the cover provided is important in reducing water run-off and shielding seedlings. If the area is protected by a firebreak such as a road, the watering and weeding or slashing can be minimized by placing mulch around the young trees.

Choice of tree species
Whilst there may be several aims in afforestating riparian lands the priority should be the stabilization of watercourse banks.

Rapidly growing trees with vigorous rooting characteristics are essential. The ideal is to use local species native to river banks, interspersed with forest precursor species that are fast growing, can tolerate full sun when young and will create partial shade for other seedlings and tees to follow. Precursors fruit at an early stage and attract fruit eating birds, which will introduce seeds of other local tree species. Trees of commercial or ornamental value may be added to areas away from bank edges.

Availability and propagation of plants
Although some of the suitable plants are available from commercial nurseries, few are readily available in large numbers. It is best to contact your local KwaZulu-Natal Nature Conservation Service District Conservation officer for this information.

Propagating and growing your own plants is easiest, cheapest, most rewarding and ecologically correct. In addition, you will benefit from having created a propagation area that could be a commercial asset. There is a growing demand for indigenous plants. The seed material should be fresh and of local origin. Resist using plants from far afield, as they may not be best suited to local climatic or soil condition.

For best germination remove the flesh from those seeds which are embedded in soft fruits and plant them as soon as possible into a seedbed to a depth corresponding to the seeds’ diameter. Seeds can be planted close together (20mm and 30mm apart) in rows of 100mm apart. Finely milled well-decomposed pine bark or a mixture of coarse sand and peat or compost with a depth of approximately 100mm makes a good germinating medium.

It is advisable to line the bottom of the seedbeds with old plastic fertilizer bags or any other plastic material (punctured for drainage) so as to prevent the seedlings’ roots from growing too deep. If seed is to be stored for a short period it is best stored in a paper bag in a refrigerator (not a deep freeze unit).

The seedlings may be transplanted into 5-litre plastic soil bags when they are between 40mm to 100mm high. The potting mixture is made up of equal parts of topsoil, compost and river sand. To every three wheelbarrow loads, mix in 0,5kg 2:3:2 granular fertilizer, and 0,5kg single super phosphate fertilizer, with 1kg of dolomitic lime.

For smaller projects where only a few thousand trees are required it is not necessary to build any nursery structure as long as both the seedbeds and the pots have partial shade under large trees. Most of the seedlings should be moved to less shady conditions when they are approximately 200mm high, then into about 80% sun for the hardening off process prior to planting out. At this stage, the plants will be about 700mm high.

Large-scale propagation requires a simple pole and wire structure constructed with 60% shade cover made from shade cloth, reeds, bamboo or woodslats.

An alternative to seed collection is to uproot small seedlings between 40mm and 100mm high from an area of mature forest undergrowth where there are many. Remember that small seedlings are likely to transplant more successfully than will large ones. These should be potted until they are large enough to plant out.Evaluate the progress of your project by taking photographs once a year from a marked point.

KEY POINTS
Riverine vegetation is essential for catchment stabilization.
It regulates waterflow and quality, prevents soil erosion, and acts as an ecological corridor.Plant only local species adapted to riverside conditions.
Seed and seedlings collected locally are the best source of materials.