Metla Project 3370
Modelling of regeneration result and early development in forest stands
Keywords: early development, forest regeneration, growth modelling, management of sapling stand
Research project group: Distinct projects - Forest-based enterprise and business activities
Objectives The prediction of regeneration and ingrowth using tree-level models has been found to be problematic in stand simulators, e.g. in the MELA system. Also, the effects of silvicultural treatments should be incorporated in predicting regeneration result and early development in forest stands. Data for modelling regeneration success have been collected in the project 3256 'Methods for monitoring forest regeneration results'.
The aims of the project are 1) to predict the forest regeneration result in 3 - 5 -year-old sapling stands, and 2) to predict the early development of sapling stands up to the height of 5 - 8 m using stand-level models.
Empirical models constructed will be included in decision support tools (MELA and MOTTI) in order to study the effects of regeneration and treatment of young stands on the profitability of forest management.
Results 1) A model was constructed to predict the regeneration establishment on 3-yr-old Norway spruce plantations in southern Finland using regeneration survey data. Regeneration establishment was described by seven response variable: the number of planted spruces, natural Scots pines, natural spruces, natural seed-origin birches and other broadleaves (i.e. sprout-origin birches and other broadleaves than birch), as well as height of crop-tree spruce and dominant height of broadleaves. Due to the multivariate (several responses for each plot) and multilevel (plot, stand, municipality, forest centre) structure, regeneration establishment was modelled by fitting a multivariate multilevel model with explanatory variables such as temperature sum, site fertility, soil quality and site preparation method.
In the model, the numbers of tree seedlings were modelled using over-dispersed Poisson distributed equations, and the tree heights were modelled using normally distributed linear equations. The estimated fixed and random parameters of the equations were logical and there was no serious bias in predicting the regeneration establishment in the independent data set. The modelling approach can be used to predict the regeneration establishment stochastically by taking into account the large unexplained variation in regeneration models. Preliminary models for other tree species and regeneration methods have also been constructed.
2) Stand-level growth models were prepared for young even-aged Scots pine stands in Finland using the repeatedly measured sample plots. The study material covered all appropriate site types for Scots pine and all wood production area in Finland. Non-linear mixed-effect models were prepared for the survival and dominant height and diameter of crop-tree pines. Models for stand basal area and volume, as well as the difference between the dominant and mean stand variables (height and diameter) were prepared using linear mixed-effect modelling.
The estimated models could be connected to a stand simulator where they would facilitate, together with size distribution models, predictions of juvenile stand growth until the dominant height is 10–15 m or the stand age is 30–40 years depending on the site fertility. The stand variables modelled in this study can be used to predict the height and diameter distributions.
The Finnish Forest Research Institute,
PL 68, FI-80101 JOENSUU, FINLAND
Phone: +358 29 532 3106
Heinonen, Jaakko, JO (2005-06), Leskinen, Pekka, JO (2004)
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