Growth Studies in Plantations of European Larch (Larix decidua Mill.) and Japanese Larch (Larix kaempferi (Lamb.) Carr.) in Western Norway. 2. Forecasting growth and Yield by Various Site-indices and Thinnings

1993

23 Lit. Ang.

Unselbständiges Werk

2693

200037981

The models are based on stand data from up to 50 year of field studies in European and Japanese larch in Western Norway. The intention of this study is to develop growth models and present yield tables for the species from that part of the country. Age at breast height, site-index and the number of trees per hectare at start of simulation are used as model inputs. Other variables are found as functions of these variables or are calculated from them. In addition, a thinning regime must be specified. In the simulations, a continuous and moderate self-thinning is assumed. Active thinnings are few (1-3) but quite strong. Active thinning starts when the S% falls under a given value and stops at a given upper S%. These values should be chosen according to the production goals. The input material does not cover very dense or unthinned stands. Most plots in the input material are treated with frequent and weak thinnings. In the yield table examples (Table 1) the number of thinnings vary with the spacing at the start of each simulation. When the initial density is set to 2600-3000 trees per hectare, two thinnings usually occur. After the first active thinning 1100-1200 trees per hectare are left and after the second active thinning 10-15 years later 300- 600 are left. With an initial number of trees per hectare of 1300-1500, only one active thinning occurs. After the thinning 300-600 trees are left per hectare. The agreement between model predictions and the measured plot data is shown for total volume production, height and diameter in Figs. 7 and 8, and in Table 2. Results from tests against independent data are shown in Figs. 9 and 10, and in Table 3. Both verification and tests indicates that the two larch models are able to describe stand development well. As expected, in the models larch showed more rapid growth in young stands than other coniferous trees at the same site-index (Fig. 6), but the gtowth decreased with age (particularly in European larch). There were no data available to compare growth patterns and productivity at a given location. Generally, the mean annual volume increment culminates after about 60-90 years (T1,3) for both larch species.