Prawdopodobieństwo wystąpienia szkód w odnowieniach podokapowych wskutek pozyskiwania drewna oraz model ich szacowania
Authors:   University of Agriculture in Krakow, Stańczykiewicz Arkadiusz 
Published: November 2021

An analysis of the existing literature on the issue of damage to regeneration caused by timber harvesting, revealed that a great majority of results reported in those publications was obtained through laborious and time-consuming field research conducted in two stages. Field research methods for gathering data, employed by various authors, differed in terms of the manner of establishing trial plots, the accuracy of counting and evaluating the number of saplings growing on the investigated sites, classification systems used for distinguishing particular groups of regeneration based on quantitative (diameter at breast height, tree height) and qualitative features (biosocial position within the certain layer and the entire stand), classification systems used for identifying types of damage caused by cutting and felling, as well as transporting operations, and finally the duration of observation intervals and time spent on gathering data on the response of damaged saplings from both, the individual and collective perspectives. Obviously, the most reliable manner of gathering such data would be to count all damaged elements of the environment being a subject of interest of particular investigators at the certain point of time. However, due to time and work consumption of this approach, which is besides very costly, any research should be designed in such a manner as to reduce the above-mentioned factors. This paper aimed to (1) analyse the probability of occurrence of damage to regeneration depending on the form of timber assortments dragged from the felling site to the skidding routes, and timber harvesting technology employed in logging works, and (2) identify a method ensuring that gathered data is sufficient for performing reliable evaluation of share of damage to regeneration at acceptable accuracy level, without necessity to establish trial plots before commencing harvesting works. The scope of these studies enclosed a comparison between two motor-manual methods of timber harvesting in thinned stands, with dragging of timber in the first stage of skidding from the stand to landings. According to one of these methods, a classical one, operations of felling and delimbing of trees were carried out by sawmen at the felling site. Timber obtained using different methods was skidded by carters and horses, and operators of a light-duty cable winch, driven by the chainsaw’s engine, as well as operators of cable winches combined with farm tractors. In the latter, alternative method, sawmen performed only cutting and felling of trees. Delimbing and cross-cutting of trunks, dragged from the felling sites, was carried out by operators of processors combined with farm tractors, worked on skidding routes. The research was conducted in the years 2002–2010 in stands within the age classes II–IV mostly, located in the territories of Regional Directorates of State Forests in Krakow and Katowice, and in the Forest Experimental Unit in Krynica-Zdrój. In the course of a preliminary stage of investigations 102 trial plots were established in stands within early and late tinning treatments. As a result of the field research carried out in two stages, more than 3.25 thsd. circular sites were established and marked, on the surface of which over 25 thsd. saplings constituting the regeneration layer were inventoried. Based on the results of investigations and analyses it was revealed that regardless of the category of thinning treatment, the highest probability of occurrence of destroying P(ZN) to regeneration (0.24–0.44) should be expected when the first stage of timber skidding is performed using cable winches. Slightly lower values of probability (0.17–0.33) should be expected in stands where timber is skidded by horses, while in respect to processor-based skidding technology the probability of destroying occurrence oscillates between 0.12 and 0.27, depending on the particular layer of regeneration. P(ZN) values, very close to those of skidding technology engaging processors, were recorded for skidding performed using the light-duty cable winch driven by the chainsaw’s engine (0.16–0.27). The highest probability of damage P(USZK) to regeneration (0.16–0.31) can be expected when processors are used in the first stage of timber skidding. Slightly lower values of probability (0.14–0.23) were obtained when skidding was performed with the use of cable winches, whereas engaging horses for hauling of trunks results in probability of damage occnrrence oscillating between 0.05–0.20, depending on the particular layer of regeneration. With regard to the probability of occurrence of both, destroying and damage P(ZNUSZK) to regeneration (0.33–0.54), the highest values can be expected when cable winches are engaged in the first stage of skidding. Little lower (0.30–0.43) was the probability of their occurrence if processor-based technology of skidding was employed, while in respect to horse skidding these values oscillated between 0.27–0.41, depending on the layer of regeneration. The lowest values of probability of occurrence of damage P(USZK), and destroying and damage treated collectively P(ZNUSZK), within all layers of regeneration, were recorded in stands where thinning treatments were performed using the light-duty cable winch driven by the chainsaw’s engine. The models evaluated and respective equations, developed based on those models, for evaluating the number of destroyed saplings ZNha (tab. 40, 42, 44, 46, 48) could be used for determining the share of damage expressed as a percentage, upon conducting only one field research at the investigated felling sites, once the timber harvesting and skidding would have been completed. As revealed by the results of analyses, evaluation of statistically significant regression models was possible for all layers of regeneration (tab. 39, 41, 43, 45, 47). Nevertheless, the smallest part of these models that could be considered positively verified, were those for the natural young regeneration, although almost a half of them revealed to be significant. Within the medium-sized regeneration over three-fourths of all models could be considered positively verified, four of which explained more than 50% of variability. Within the high-sized regeneration almost two-thirds of evaluated regression models were statistically significant, five of which were verified positively, moreover, one of them explained more than 50% of variability. The most promising results were those obtained for the advance growth. Nearly 90% of the evaluated models revealed to be statistically significant, ten of which could be considered positively verified. Furthermore, four statistically significant models explained over 50% of general variability. With regard to the entire regeneration more than 80% of evaluated models were statistically significant. However, due to insignificant coefficients of regression, eight of them could be considered positively verified. At this point it should be stressed that in respect to logging technology employing the light-duty cable winch FKS it was impossible to evaluate statistically significant models of regression. Whereas, in the case of processor-based logging technology, firstly regarding the advance growth, and then the entire regeneration, all of the evaluated statistically significant models could be considered positively verified, in terms of both, all of the stands, and particular categories of thinning treatments individually. This latter case also revealed the highest degree of matching of evaluated models (R2 popr 0.73–0.76 for advance growth and 0.78–0.94 for the entire regeneration). A significant impact of the kind of form of hauled timber on the probability of damage occurrence P(USZK), mainly in early thinning treatments, could have been reflected in the results obtained for all stands (early and late thinning treated collectively). Moreover, due to an insignificant impact of the form of hauled timber and logging technology employed, on the probability of occurrence of damage in late thinned stands, and a significant impact of the above-mentioned variables on early thinned stands, it should be assumed that for performing an evaluation of destroying and damage caused by timber harvesting the both thinning treatment categories should be analysed separately. Furthermore, when evaluating the probability of occurrence of destroying and damage caused by timber harvesting, the layers of natural young regeneration and advance growth should be analysed separately. As proved by the results presented in this paper, varying values of probability computed for each of the layers of regeneration seem to indicate that when investigating damage to regeneration caused by timber harvesting, it would be reasonable and recommended to perform a separate analysis of damage to the highest saplings as well, namely individuals with diameter at breast height close to 7 cm. In respect to studies on damage to regeneration caused by logging technologies mentioned above, the evaluation of number of destroyed saplings within the advance growth can be carried out using the proportions of damaged and undamaged saplings per 1 ha of the stand. The numbers evaluated in this manner can be used to calculate the damage share expressed in relative values (percentage of damaged saplings compared with the entire number of saplings before commencing the logging works). However, one should keep in mind that this is true only if the field research have been carried out based on the methodology described in this paper.