Interference of Choricarpia leptopetala by Lantana camara with nutrient enrichment in mesic forests on the central coast of NSW

Suppression of Choricarpia lepropetala (F. Muell.) Domin., an early native coloniser of mesic forests, by Lantana camara L. was evaluated using field-based variable density and substitution experiments. Sites were located in disturbed areas within wet sclerophyll forest and warm temperate rainforest near Lake Macquarie on the Central Coast of NSW. In the variable density experiment, C. leptopetala growth was significantly suppressed by 36.4% from 3.3 to 2.1 g plant(-1) in the presence of equal proportions of L. camara at a total density of 20 seedlings m(-2) only when nutrients (60 g m(-2) of a slow release NPKS fertiliser) were added to the soil surface. Lantana camara growth significantly increased by 14.6% from 4.1. to 4.7 g plant(-1) when nutrients were added. At a density of 40 seedlings m-2, growth of C. leptopetata was suppressed by 37.5% from 3.2 to 2.0 g plant(-1) in the zero nutrient treatment with equal proportions of L. camara, and was further suppressed by 40.0% from 2.0 to 1.2 g plant(-1) with the addition of nutrients. Lantana camara growth significantly increased by 43.7% from 2.3 to 3.3 g plant(-1) when nutrients were added. Pure stands of C. leptopetala did not respond significantly to nutrient addition at either density. In the substitution experiment (with a constant density of 20 seedlings m-2), C. leptopetala growth was significantly suppressed by 44.1% from 3.4 to 1.9 g plant(-1) when L. camara reached 75% of stand composition in the zero nutrient treatment and by 43.2% from 3.7 to 2.1 g plant(-1) when it reached 50% of stand composition in the nutrient addition treatment. The results link interference and suppression of native colonisers by exotic invaders with demonstrated increases in resource availability following ecosystem disturbance. Lantana camara is able to take better advantage of increased resource availability than C. lepropetala, thereby accumulating more biomass and suppressing the growth of C. leptopetala. Suppression of C. leptopetala also increased when the density of L. camara was increased. Consequently, the negative effect of the invading species on the indigenous species is both nutrient-addition and density dependent, Models describing interference in ecosystem recovery following disturbance need to include interference processes associated with weed invasion that disadvantage indigenous species.