Natural forests ate constantly disturbed by man. In the Sinharaja the two main forms of interference have been shifting cultivation and mechanized logging.

                           Regeneration studies carried out in modified areas at Sinharaja such as those recuperating from selective mechanized logging and shifting cultivation have helped to identify those pioneer species which colonise disturbed sites (Table 7). These are usually fast growing, short-lived species that are  able to establish themselves and grow under unfavourable conditions of high light intensity, low humidity and poor soil conditions. There are other species which have pioneer qualities but are not truly pioneers. These either follow in the wake of pioneers or respond to slight disturbance. 

                            Although mechanized logging drastically altered the structure of the forest, the altered structure of the forest, the forest shows considerable recovery after 10 years of rest. Nevertheless, long term changes in species composition seem inevitable with light-loving plants such as Shores trapezifolia dominating the new growth. The under-storey species appear to be the group most adversely affected  by logging as they are only adapted to living under specialized ecological conditions created by the presence of an undisturbed canopy. Judging by the present recovery, it is clear that logging based on a polycyclic system of 20 years which was planned for the Sinharaja world no doubt have been highly unsuitable, particularly as mechanized logging methods were to be used.

 

	Macaranga peltata (Kenda)
	Shorea trapezifolia (Thiniya)
	Artocarpus nobilis (Wal del)

                           The Broad leaved Honduran Mahogany (Swietenia macrohylly) has been planted along abandoned skid trails within the forest as an enrichment species during the logging period. Its growth has been phenomenal and it now comprises 75% of all individuals of 10 centimeters in girth or more along the skid trails. This has caused some anxiety among scientists that it may displace the nature species of the forest particularly since it is a prolific seed producer, and several attempts have been made to eradicate these trees. Fortunately, however instances of weed trees invading natural forest are unknown.

                            The abandoned shifting cultivation areas in Sinharaja, appear to recover very slowly. Studies of a site abandoned around 25 to 30 years ago reveal that despite a plentiful source of seed from the surrounding natural forests, the site was still dominated by pioneer species. Species which re-established through seed such as Shorea have had very little chance of success, while those that are able to regenerate as coppice-shoots such as Anisophyllea cinnamomoides have had grater success.