Managing stands using continuous cover forestry

Crown thinning in Douglas fir Sitka spruce in transformation Regeneration of SP using the seed tree method at Sandringham

Summary

This project aims to improve understanding of the effects of stand manipulation on factors that influence the successful transformation of stands from an even-aged structure to continuous cover.

Background

Manipulation of the stand, through the use of thinning regimes, is one of the main tools available to managers when transforming stands to continuous cover silviculture. Traditional thinning regimes are primarily designed to maintain cumulative volume production and prepare the stand for clearfelling. However, when carrying out continuous cover forestry it is important that management is adaptive. This means basing silvicultural interventions on stand level information, monitoring what happens and learning from the results. It is a simple two-stage process:

  1. Collecting useful stand level data
  2. Using that information to specify silvicultural interventions .

Regeneration

Objective information is produced on species composition, size, distribution and browsing damage on regeneration. This is useful because many forest managers:

Over-estimate the amount of regeneration in a stand

Under-estimate the level of browsing (often this will be one of the main reasons why there is little, or no, regeneration)

Give emphasis to seedling regeneration, especially where there is a lot of it, rather than saplings that are much more likely to become part of the new stand

Only focus on the preferred target species to regenerate instead of considering the wider species mix that will develop

Have no way of assessing the distribution of regeneration (this can have important implications for thinning CCF stands). Some users linked their stand level data to a Graphical Information System (GIS) by using a handheld Global Positioning System (GPS). This has enabled them to examine the data spatially; an example is shown on the right.

Stand structure

Objective information is presented on species composition, basal area and diameter distribution of stands. This can be useful for two main reasons:

The structure of a stand is critically important when deciding how to thin it.

The software allows the forest manager to test if the diameter distribution is ‘symmetric’ (similar to a normal distribution) or ‘skewed’ as shown in the example on the right. As can be seen, a skewed distribution would have a large number of small trees, a moderate number of medium trees and a low number of large trees, and is similar to the ‘reverse-j distribution’ much discussed as an option for managing continuous cover forests. If the stand has a symmetric diameter distribution this must be taken into account when thinning the stand, especially if the aim is to develop a structure with three or more canopy strata.

It enables forest mangers to be objective about their approach to CCF management and record the results of their interventions.

At present we have some information concerning the correct range of basal areas to use when transforming stands (see Forestry Commission Information Note 40) but have little understanding of how this will vary with site and during different stages of transformation. It is imperative that we develop this experience and share it.

Contacts

Gary Kerr

Resources and guidance

Further guidance and tools and software for managing stands using continuous cover can be found on our resources page