Browsing by Subject "thinning quality assessment"

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  • Käld, Tobias (Helsingfors universitet, 2013)
    In Finland thinning quality is assessed on a yearly basis by the Finnish Forest Centre. During recent years the results of these assessments have been a source of concern within the coastal region of operation. Metsäliitto, being one of the largest forest operators within the coastal region and Finland as a whole, is concerned by the high residual stand damage found. Metsäliitto perform follow-ups on the feedback received from the Finnish Forest Centre but also performs thinning quality assessments off their own. The thinning quality method used by the Finnish Forest Centre is time consuming and therefore poorly suitable for use by wood procurement companies. This led to the development of an alternative method by Metsäteho Oy. Metsäliitto was represented in the work group that developed this new method but has chosen to develop a method of its own. The purpose of this master thesis is to clarify whether the results from Metsäliittos thinning quality assessment method correlate in a sufficient manner with those of the method developed by the Forestry Development Centre TAPIO. Furthermore the thesis study how the results of two alternative methods correlate. Focus is placed on residual stand damage but also the possibility of a potential connection between TAPIOs placement of sample plots and residual stand damage results is studied. As Metsäliittos method includes a complete inventory of soil compaction it is studied how TAPIOs and Metsätehos results hold up against those of Metsäliittos method. A study of the correlation between results for forwarder track distance between Metsäliittos and Metsätehos methods is also conducted. The sites of this study were chosen based on the Finnish Forest Centres random sampling for thinning quality assessments performed during 2010 and 2011. From those thinning quality assessments the ones performed in the Swedish speaking parts of Ostrobotnia where thinning actions had been performed by Metsäliittos contractors were sieved and chosen to form the sample of this study. The fieldwork of this study was performed in July 2011. Thinning quality assessments according to Metsäliittos and Metsätehos models were performed on all sites. The results of the thinning quality assessments performed according to TAPIOs method were acquired from the Finnish Forest Centre. This study being a method comparison study where the true values of the objects are not known, methods of analysis based on hypothesis testing was not used. In order to create an overview of the trends in results for the different methods, as well as their correlation to each other, Bland&Altman diagrams were created (Altman & Bland 1983 and Bland & Altman 1999). The main results of this study show that Metsäliittos and TAPIOs results for residual stand damage do not differ in a statistically significant way. Metsäliittos and Metsätehos results on the other hand are not to be compared. Metsätehos and TAPIOs results are not either to be compared which has been stated by Poikela (2003b). TAPIOs and Metsätehos methods estimate the proportion of soil compaction in a sufficient manner compared to Metsäliittos method. Furthermore it was concluded that results for forwarder track distance correlate well between Metsäliittos and Metsätehos methods. Any connection between TAPIOs sample plot placement and results for residual stand damage could not be detected. The conclusions of this study are that Metsäliittos and TAPIOs results for residual stand damage, with reservation for the small sample size of this study, are comparable. Metsäliittos and Metsätehos results are not compatible from which we conclude that Metsäliittos method is not replaceable with the one developed by Metsäteho. Nor shall Metsätehos method be used as a complement to Metsäliittos as one will then acquire two incompatible data sets. Both Metsätehos and TAPIOs results for soil compaction are compatible with those of Metsäliittos method. This could be utilized in order to improve the time effectiveness of Metsäliittos method. For further method improvement Metsäliitto could adopt Metsätehos method for determination of forwarder track distance. As results from Metsäliittos and TAPIOs thinning quality assessments can be compared without a loss of reliability, Metsäliitto could compile the results from their own assessments and TAPIOs assessments in order to get a more statistically representative picture of the quality of their thinnings. This would result in even better future possibilities of monitoring and evaluating how well the company’s goals are met.