Topic 4.1: Maintenance of Forest Ecosystem Productivity

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Topic Introduction

A basic principle of forest management is to maintain or increase in the productivity of the forest ecosystem. This refers to all products of the forest, including both timber and non-timber forest products. Early forestry, as we saw in Module I, tended to focus on the production of timber, with ‘scientific forestry’ focusing on establishing and maintaining the yield of timber (known as sustained yield). This remains a focus of many forest operations, particularly plantations, but is becoming less important in the management of natural forests, where other values, such as the maintenance of biodiversity may be more important. Forest managers need to understand some of the basic principles surrounding ecosystem productivity, so that they can focus interventions at those points most likely to create a desirable effect.

There are a number of instances where forest productivity has not been maintained during forestry operations. Many harvesting operations have concentrated on the best trees in a forest, in a process now known as “high grading”. This is believed to have damaged the productivity of many forests due to the loss of some of the best genetic stock, although the actual evidence that this process is important in the long-term is limited. More often, declines in productivity have been associated with plantation species. In these cases, there has been poor species to site matching, or the available nutrients in the soils have been very limited and easily exhausted. For example, some Chinese fir (Cunninghamia lanceolata) plantations in China appear to have been established on very poor soils, and are showing signs of nutrient deficiency. Nutritional problems are particularly apparent on peat soils, as the nutrients in these are entirely derived from the atmosphere.

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