Subsistence harvesting of pole-size understorey species from Ongoye Forest Reserve, South Africa: Species preference, harvest intensity, and social correlates

We investigate the effect of subsistence harvesting on the ecological status of the pole-size tree component of the understorey at the Ongoye Forest Reserve (OFR; 2611 ha), KwaZulu-Natal province, South Africa. Using generalised linear modelling (GLM) we examine the ecological and social correlates of species preference and harvest intensity. Data were collected from 22 strip transects (5 m × 300 m; 0.15 ha). Only 11.6% of the available pole-size trees (2 cm < DBH < 15 cm) were harvested, mostly for building materials. No instance of canopy tree logging was recorded. Sixty-eight species were identified; however, only seven species (82% of harvested stems) were preferred: Englerophytum natalense (33%), Garcinia gerrardii (19%), Drypetes gerrardii (9%), Tabernaemontana ventricosa (9%), Rinorea angustifolia (4%), Oxyanthus speciosus (4%), and Chrysophyllum viridifolium (4%). Size-class distributions for these seven species were inverse J-shaped, typical of fine-grained species that regenerate over small spatial scales, suggesting that current harvesting intensities may be sustainable. Pole-size stem density was significantly similar among residual stands in harvested areas (2014 ± 31 stems ha−1) suggestive of a stem-density harvest threshold below which further effort was unprofitable. The number of harvested stems increased with increasing stem availability across species and stem size-classes. Small size-classes (2-5 cm DBH) were harvested most intensely, followed by the intermediate (5-10 cm) and the large (10-15 cm) size-classes, for all species except C. viridifolium. For the latter, the harvesting intensity was greatest for the 10-15 cm size-class. Lastly, harvest intensity was greatest in those areas closest to households near the reserve boundary but was not affected by household density. Although subsistence harvesting at the OFR appears to be sustainable at current levels, we note that similar harvest intensities of pole-sized stems in studies from smaller forests (<60 ha) led to local extinction of tree species. In addition, because the dominant understorey species at OFR are almost exclusively harvested, the mid- to long-term effects of this harvesting preference on forest dynamics must be assessed to develop sound ecological forest management policies.