Community Matrix Model Predictions of Future Forest Composition at Russell State Forest

The data of Lloyd (1971) on the 'chosen tree' and 'chosen seedlings' in 5607 4 x 4 m plots in Russell forest are analysed using a simple transition matrix model. The most realistic analysis predicts little change in relative species composition, other than a slight increase in the softwoods. The virtue of the approach lies more in the questions it raises than in the predictions obtained. Before such models can be applied satisfactorily in New Zealand basic data on seedling survival, tree growth rates and average life spans are required for most indigenous species.

Site conditions affect seedling distribution below and outside the crown of kauri trees (Agathis australis)

It has been suggested that plants can change soil characteristics via their litter to favour their own species. The New Zealand kauri tree (Agathis australis) presents an interesting case for studying such a positive feedback between plant and soil because it has a huge impact upon the soil. We hypothesised that, under mature kauri trees, compared with sites outside the projection of the crown, seedlings of angiosperm trees are relatively rare, while kauri seedlings are relatively common, due to the poor soil conditions and the higher light intensity.

Kauri trees (Agathis australis) affect nutrient, water and light availability for their seedlings

Plants can change the soil that they grow on, for example by producing litter. If litter characteristics are such that their effect on the soil increases a plant's fitness, a positive feedback can develop between the plant and the soil. Several studies indicate that New Zealand kauri trees (Agathis australis) lower the availability of nutrients in the soil beneath their crown. Low nutrient availability would be positive for the survival of kauri seedlings as they are known to use nutrients more efficiently than angiosperm species.