Assessment of the Density of Wood with Stem Decay of Norway Spruce Trees Using Drill Resistance
Radu Vlad, Miglena Zhiyanski, Lucian Dincă, Cristian Gheorghe Sidor, Cristinel Constandache, Gheorghe Pei, Alexandra Ispravnić, Tatiana Blaga
ABSTRACT
In European forests, Norway spruce ( Picea abies L.) trees commonly suffer damage caused by decay, which is one of the most important defects in timber assortments. To evaluate the mass of wood with stem decay, it is necessary to quantify its density. Drill resistance measurements are introduced as an approach to estimate the density of wood with stem decay. Norway spruce trees from a northern part of the Romanian Eastern Carpathians site were used as a test system to compare the new method with conventional predictors of gravimetric wood density. The model, which comprises only drill resistance as a predictor, explained half of the variation in wood with stem decay density ( 
= 0.550) and was significantly better than models with one or two considered predictors. The research revealed that the relationship between drill resistance and gravimetric wood density is sensitive to the decay features. Therefore, the best model combines drill resistance and decay proportion from horizontal trunk area ( = 0.618). Precise prediction of the standing trees mechanical properties has many benefits for wood producers or processors. It underlies decisions concerning the forest management (by trees selection), planning and placement of wood harvesting depending on trees (forest) quality. Simulation and forecasting models in conjunction with other models (e.g. assessing the probable volume of the wood with stem decay and the windfalls volume) should be of great significance for scientific and industrial analyses.
Key words: Norway spruce, wood with stem decay, timber quality, linear model
Topic: BIOLOGY