ZONING AND SITE CLASSIFICATION FOR THE EVEN-AGED TEAK PLANTATIONS

Abstract

The relatively high accuracy possible with growth and yield models for uniform standsresults partly from the precision with which it is possible to classify site. The height of auniform stand, at a given age is a good indicator of the productivity of that type of forest onthat particular site. Hence the construction of height/age curves corresponding to differentsite classes is the first step in growth and yield modeling. However the mean height of astand is usually sensitive not only to age and site, but also to stand density. Site for a standis area specific, where the site of a particular stand cannot be improved significantly bybetter management. Therefore, dominant height which is almost entirely insensitive tostand density, could be used as a good indicator for site classification. Dominant heightcan be defined in various ways, but the definition with the widest used is that the dominantheight of a stand is the mean height of the 100 thickest stems per hectare.

In this study, when dominant height/age scatter graphs were constructed separately foreach district, it was clearly observed that these diagrams were similar in some districts andwere significantly different compared for others. The districts and were similar site trendcurves were combined together to give one teak zone where, within one zone, the variationin dominant height growth is very similar in all districts falling under that zone. Usingthis zonal categorization, it was easy to separate the growth variations among the teakgrowing areas in Sri Lanka. This zonal effect may possibly be due to genetic variation, butthis cannot be analysed because the genetic information is not available.

Three zones have been identified for teak growing areas in the country. This was doneusing 'mean dominant height - age graphs, and constructing maximum, minimum andmedium trend curves for each district. These curves and scatter graphs were comparedwith each other and grouped into selected sets using graphical methods. Different zoneswere identified using this method.

Once the zonal categorization had been done, each zone was considered separately for itssite classification. This was done using the mean dominant height-age-site indexrelationships, which are basic to uniform forest growth predictions. The relationships areusually referred to simply as the site index curves for a species in a given environment.

For each zone the site index curves have been constructed using 20 years as the index age.The Schumacher equation was used in fitting a model for the medium trend curve. For siteindex curves both common slope and common intercept methods were used