Background: Urban forests are under increased pressure from invasion by exotic (alien) species. The vegetation present in the matrix of urban sites is a rich source of alien invasive propagules, which increases the risk of alien invasion in forests within an urban space, leading to a decline in indigenous species. Therefore, determining the distribution patterns of native and exotic species as influenced by environmental factors can assist in quantifying the impact of exotic species at broad scales based on responses on a finer scale. Quantifying the effects of multiple environmental factors on the distribution patterns of both indigenous and alien species in the ecosystem may help in prescribing suitable management efforts. Methods: Fifteen forest patches were sampled in the eThekwini (Durban) Municipality and data collected from 74 100-m 2 plots with different degrees of invasion. Indigenous and alien species of trees, shrubs and climbers occurring in ten and more plots were considered for analysis and the CANOCO 5.1 package was used to run various constrained ordination analyses. Variation partitioning analysis was used to assess the impact of environmental variables at different spatial scales, namely the plot and patch scales. Results: Canopy gaps are the major controlling factor for invasive alien plants (IAPs) occurrence at fine scale. At patch level, residential and industry areas outside the boundaries (buffer area) of forest patches have a high influence on the distribution of IAPs. Communities dominated by the invasive Chromolaena odorata (L.) R.M. King are most common on the lowland coastal forests while communities dominated by either Litsea glutinosa (Lour.) C.B.Rob. or Cardiospermum grandiflorum Sw. can prevail in both lowland coastal and scarp forests. Conclusions: Canopy gaps in lowland forests can facilitate the transition of native forests to novel communities containing a variety of alien plant species. Communities of shrub, climber and tree IAPs occur in lowland coastal forests while climber and tree IAPs dominate the high-elevation scarp forests. The resilience shown by some native species to the tree, shrub and climber IAPs by remaining when IAPs establish makes these species very suitable for restoration projects. Forest patches surrounded by a high incidence of residential and industrial areas in the buffer matrix are likely to have a high diversity of IAPs. Larger patch size and high connectivity to nearby native forests are key in reducing invasion by IAPs.

Background: Concern is growing about the future of forestry productivity due to intensive nutrient removal, as a result of different harvesting operations. This study aimed to determine the effects on forest productivity when using different slash-retention scenarios with the recommended amounts of mineral fertiliser in Usutu forest. Usutu is a plantation forest that grows mostly softwood where the predominant species is Pinus patula Schiede ex Schltdl. & Cham.Methods: The first trial series (F) comprised of one trial located in each of five forest blocks. It was established in 1971 and compared the effects of various site preparation scenarios (slash removal, slash retention and cultivation) on the early growth of Pinus patula for adjacent first (F1R) and second rotation (F2R) sites (i.e. grassveld and clearfelled first-rotation sites). The second (S) trial series was re-established in April 1991 on exactly the same position as the first trial series, and involved second (S2R) and third rotation (S3R) sites. Three main treatments, standard pitting through harvest residue (control); manual pitting after removal of harvest residue and forest floor (cleared); and manual pitting and broadcast application of dolomitic lime (2 t ha