The work studied the effects of site conditions on the amount of deadwood (DW) in managed forests in south−western Poland. Measurements included standing dead trees, snags with a diameter at breast height of at least 7 cm, and lying deadwood (logs, branches, uprooted trees, etc.) with a diameter at the thicker end of at least 10 cm. The study excluded snags and deadwood pieces with a diameter of less than 7 cm as well as stumps. Site conditions are presented according to the Polish site classification system taking into account both site fertility and water abundance. With respect of the fertility gradient, sites are classified as dystrophic, oligotrophic, mesotrophic, and eutrophic. In terms of water abundance, there are two types of sites: mesic (low or very low contribution of groundwater, rainwater, and floodwater, with an approximate springtime water table depth of more than 1.8 m) and moist (moderate or considerable contribution of groundwater, rainwater, and floodwater, with an approximate springtime water table depth of 0.5−1.8 m). We analyzed data from 2522 sampling plots with area ranging from 50 to 500 m² and depending on forest stand age. The plots were established in forest stands older than 21 years old. The predominant tree species in the study area were Pinus sylvestris, Quercus robur, Quercus petraea, Betula pendula, Fagus sylvatica, Alnus glutinosa, Fraxinus excelsior and Picea abies. In a separate analysis of data from 233 sampling plots, we studied the relationship between DW volume and the site index evaluated using a five−level classification (level I denotes sites with the highest productive capacity). Forest stands aged >80 years with the dominance of Pinus sylvestris were studied. The study showed a significant influence of site conditions on the DW volume in managed forests. Forest stands exhibiting better site conditions not only provided more timber, but also contributed with a greater amount of deadwood to the ecosystem. Forest stands with a site index of I contained as much as 4.9 m³ of DW/ha, while stands with a site index of III only 2.4 m³ of DW/ha. In terms of the 8 studied site types, it was also found that the average volume of DW increased with site fertility. The lowest volume of DW occurred on very nutrient−poor and mesic sites (0.6 m³/ha). In contrast, nutrient−rich and moist sites contained 15 times as much DW (9.5 m³/ha). Of paramount importance was water abundance. The volume of DW on moist sites was on average by 2.2−4.5 m³/ha higher than on mesicsites with the same fertility.
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