Browsing by Subject "stand structure"

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  • Kellomäki, Seppo; Hänninen, Heikki; Kolström, Taneli; Kotisaari, Ahti; Pukkala, Timo (Suomen metsätieteellinen seura, 1987)
  • Sarkkola, Sakari; Alenius, Virpi; Hökkä, Hannu; Laiho, Raija; Päivänen, Juhani; Penttilä, Timo (NRC Canada, 2003)
    Size-structural dynamics of naturally established Norway spruce (Picea abies (L.) Karst.) stands growing on peatlands drained for forestry were investigated. The study was based on modelling of diameter at breast height (DBH) distributions of repeatedly measured stands in southern Finland. The Weibull function was used to parameterize the DBH distributions and mixed linear models were constructed to characterize the impacts of different ecological factors on stand dynamics. Initially, the positive skewness of the DBH distributions increased after drainage as a result of increases in stem numbers and a reduction in mean diameters. Simultaneously, the size inequality among trees increased. These changes were due to regeneration and (or) ingrowth and indicated only little competition from the larger trees. Subsequently, the DBH distributions changed from positively skewed to normal and finally to negatively skewed resulting from tree growth and a reduction in the number of small DBH trees. This indicated increased asymmetric intertree competition. Size inequality did not change during this later stage in stand development, suggesting a concurrent component of symmetric competition. Thinnings had little impact on DBH distribution trends. The observed stand dynamics allow the allocation of growth resources to the desired crop component by appropriate silvicultural treatments.
  • Danquah, Jones Abrefa; Appiah, Mark; Ari, Pappinen (2011)
  • Kojola, Soili; Penttilä, Timo; Laiho, Raija (2004)
    Drained peatlands in northern Europe comprise more than 10 million ha of forestland and thus constitute a considerable production potential in forestry. Much of this area consists of stands dominated by Scots pine and close to maturity regarding commercial thinning. The trees within these stands typically vary in terms of age, size, and growth rate. The impacts of silvicultural cuttings on these uneven-structured stands are inadequately known. We simulated the impacts of a control regime with no thinnings, and three different thinning regimes, involving different thinning intensities, on the development of fifteen pine-dominated stands in Finland. The simulations started from the first thinnings and were continued until regeneration maturity. The predicted total yields ranged from 244 to 595 m3ha-1, depending on site and thinning regime. The highest total yields were observed for the control regime in which 18-38% of the yield was, however, predicted to self-thin by the end of the simulation. Thus, the differences in the yields of merchantable wood were fairly small among the compared regimes. However, the regimes involving thinnings generally needed less time than the control regime to reach regeneration maturity. The mean annual increment of total stem volume was at its highest in the control regime. The highest mean annual increment of merchantable wood was obtained in the regime involving two moderate thinnings, but excluding the most low-productive sites where thinnings did not increase the yield of merchantable wood.
  • Lindberg, Henrik; Aakala, Tuomas; Vanha-Majamaa, Ilkka (2021)
    Forest fire risk in Finland is estimated with the Finnish Forest Fire Index (FFI), which predicts the fuel moisture content (FMC) of the forest floor. We studied the FMC variation of four typical ground vegetation fuels, Pleurozium schreberi, Hylocomium splendens, Dicranum spp., and Cladonia spp., and raw humus in mature and recently clear-cut stands. Of these, six were sub-xeric Pinus sylvestris stands, and six mesic Picea abies stands. We analysed the ability of the FFI to predict FMC and compared it with the widely applied Canadian Fire Weather Index (FWI). We found that in addition to stand characteristics, ground layer FMC was highly dependent on the species so that Dicranum was the moistest, and Cladonia the driest. In the humus layer, the differences among species were small. Overall, the FWI was a slightly better predictor of FMC than the FFI. While the FFI generally predicted ground layer FMC well, the shape of the relationship varied among the four species. The use of auxiliary variables thus has potential in improving predictions of ignitions and forest fire risk. Knowledge of FMC variation could also benefit planning and timing of prescribed burns.