Silviculture research - Future challenges

These include:

  • Changing requirements
  • Defining programmes in terms of stand dynamics
  • Links with Ecological Site Classification (ESC)
  • Integrating knowledge and computer models
  • Adaptive management approach
  • Field validation and access to long-term experiments.

Changing requirements

The shift towards forestry for multi-purpose objectives has appreciably widened the focus of silvicultural research (e.g. not only Sitka spruce but also native woodlands). Accommodating these demands at a time of declining resources requires a focused and an integrative approach to the research programmes.

The recent years has seen a major increase in the computing power and techniques available to forest managers and scientists. For example:

  • Geographical Information Systems (GIS) for displaying spatial information about forests
  • Computers for monitoring harvesting outputs
  • Remote sensing methods for assessment of canopy structure.

There is increasing awareness of the potential of computer based decision support systems (DSS) for providing guidance and appraisal techniques for managers which can be linked with existing methods such as financial appraisal packages, production forecasts, or yield tables. Developing these DSS will require a structured approach to formulating existing knowledge, which take both stand dynamics and site factors into account. The emphasis must be on integrating existing knowledge first to identify gaps that will be resolved by further field investigations.

Defining programmes in terms of stand dynamics

A conceptual model of stand dynamics formulated in NW America has considerable potential as a guide to silvicultural research. The Oliver-Larson model (named after its two authors) distinguishes four stages of even-aged stand development:

  • Stand initiation (or formation) - the establishment phase up to canopy closure
  • Stem exclusion - from thicket to sawlog dimensions when the canopy is unbroken and no regeneration occurs
  • Understorey reinitiation - the canopy starts to open up and regeneration occurs
  • Old growth - a 'steady-state' phase where there is a mosaic of old trees dying and regeneration developing.

The process of moving from an early to a later stage is 'succession'. The return to an earlier stage as consequence of wind damage or harvesting is 'disturbance'. For much of the last 50 years silvicultural research, particularly in northern Britain, has focused upon the first stage (stand initiation) with a lesser emphasis upon stem exclusion.

However, changes in policy are altering the emphasis given to the various stages. For example, interest in alternative silvicultural systems involves study of successional processes in the understorey reinitiation stage while maintenance of native woodlands involves consideration of the 'old growth' stage to promote habitats of high conservation value (e.g. the occurrence of lichens in western oakwoods).

Since the processes being studied take place over a longer time scale than that of the stand initiation phase, mathematical modelling and simulation will become increasingly important tools in the development of hypotheses for validation in field studies. The Oliver-Larson model also provides an underpinning theme for our research. To a greater or lesser degree, many of the silviculture research programmes involve stand manipulation techniques that are used to control successional and/or disturbance processes to achieve a desired output.

Links with Ecological Site Classification (ESC)

A prerequisite for successful development of silvicultural techniques for sustainable forest management is a site based approach to silvicultural problems.

The development of ESC by Forest Research woodland ecology scientists represents an important advance in forestry site classification in Britain.

It is planned that much of our existing silvicultural knowledge should be explicitly linked to ESC to provide managers with site-based silvicultural prescriptions. This will require linkage with the ESC Decision Support System. Our initial aim is to test the approach using existing recommendations for fertiliser inputs to conifer stands in the establishment phase and to extend it to the wider establishment field and to aspects of predicting stand stability. If successful, we think that these links could be expanded to provide site-yield predictions.

Integrating knowledge and computer models

It follows from the above that the major challenge for each programme over the next few years is to develop a body of knowledge which provides general predictive understanding of the main silvicultural problems confronting our customers and practical solutions to them.

As a further stage, this understanding should be formulated in prototype models that present knowledge in a predictive form that ultimately can be used by managers. These models need not be created de novo, but may often be adaptations of those created in other countries.

The most advanced is the ForestGALES model which is now in its third commercial release, whilst others at an earlier stage include:

  • EMIS model for advising on establishment practice
  • TIMBER quality model examining the interaction between silviculture and spruce wood properties.

Achieving this task will not be trivial since it will require access to additional computing/modelling skills and may identify appreciable gaps in our knowledge. An example of the latter has been the need for additional tree pulling in the initial development of ForestGALES and the current tests of the assumptions of this model in irregular stands.

Adaptive management approach

Traditional replicated forest experiments normally occupy a scale of 0.5 to 5.0 hectares. However, current silvicultural questions are often focused at a compartment, catchment or even a landscape scale. This requires an approach that links intensive study and operational trials so that both managers and researchers participate in the design of the work and so gain from shared experience.

This type of approach is particularly useful when developing novel methods of stand management e.g. in the evaluation of alternative systems to clearfelling in production forests.

Field validation and access to long-term experiments

The preceding paragraphs emphasise the need for a research programme that gives priority to developing computer-based silvicultural tools to provide advice to managers and identify gaps in knowledge. However, it is critical that the predictions of any models are carefully validated against experimental and other data collected from field trials. It will be important for the research programmes to continue to have access to field sites and to be laying down new trials designed to test predictions.

For this reason, we continue to control a network of long-term forest experiments located in all major forest regions of Great Britain. The routine management of these experiments is delegated to staff of the appropriate field station of within Forest Research Technical Services Unit.

The oldest experiment which we manage dates from 1922 and amongst the classic trials for which we are responsible are the famous species mixtures at Gisburn Forest, monitoring plots in the native Scots pinewoods of the Blackwood of Rannoch and underplanting trials in Thetford forest.

We encourage use of these experiments by outside bodies such as universities and are always interested in shared research programmes at these sites. Please contact us if you would like to explore such possibilities further.