2.2 Agriculture, forrestry and alien plants  (Page 2/3)

Unfortunately, forests everywhere are under increasing pressure from pollution and acid rain (although there are some doubts in this regard), unsustainable logging, the gathering of fuel-wood, bark stripping for traditional medicine, and clearing for agriculture and urbanisation.

In South Africa, indigenous evergreen forest is the smallest and most widely dispersed of the country’s seven major biomes, and covers just 0,25 per cent of the land surface. With the arrival of the European settlers in the 17 ^th century, these forests were heavily exploited, with many areas being completely destroyed or reduced to scrub. The remaining state-owned indigenous forests, particularly those in the southern Cape, are now carefully managed for sustainable yields of timber like yellowwood, stinkwood and ferns, although there is major concern in several areas about alien plant invaders and the encroachment of exotic species. Other indigenous forests in private hands are mostly not adequately protected and are rapidly diminishing.

As a result, ecosystems have been degraded, biodiversity reduced, soil eroded and valuable water resources wasted.

South Africa is an important exporter of especially pine, wattle and blue gum timber.

To investigate ways to reduce the exhaustion of timber as a resource

[lo 3.3]

1. Suggest an alternative substance from which each of the following products could be manufactured:

• Bottle corks (tree bark)
• Rayon material
• Wooden planks for the manufacturing of furniture
• Sawdust
• Paper
• Sleepers (rails)
• Wooden boxes (fruit)
• Pencils

2. Which functions performed by trees (forests) as a life-sustaining system cannot be replaced by anything else? (See par. 1)

Activity 3:

To indicate the most important forestry areas on a map

[lo 1.1]

• Draw an outline map of the RSA.Consult an atlas and fill in the most important forestry areas on the map..

A lien plant species

South Africa’s natural environment has already been invaded by more than 100 species of alien fauna and flora. It has caused widespread ecological damage and incurred losses to the value of several millions of rands in respect of lost agricultural potential and other land uses. Moreover, the extermination of alien species is a costly and time-consuming process.

The alien plants that have spread fastest over the past decades, eating into hundreds of thousands of hectares, include hakea , Australian Acacia , the Mauritius-thorn, paraffin-bush, lantana, water-lily, nasella tussock, various types of pine, and the jointed cactus.

Alien fish species such as trout and bagger have already eliminated the indigenous fish of various river systems, while extinct bird species such as the European starling and Indian myna birds have become a nuisance in urban and possibly rural

areas. Their exact numbers, however, are not known. Alien rats and mice are problem animals in human settlements, while the Argentine ant is a threat to South Africa’s fynbos as it eliminates the seed-dispersing indigenous ant.

South Africa’s most precious water resources are also badly affected by alien plants. River-bank habitats are particularly vulnerable to invasion and many of the upper and middle river courses have almost been completely overgrown with dense patches of silver and black wattle trees ( Acacia species).