Influence of environmental factors on the distribution pattern of centipedes (Chilopoda) and other soil arthropods in temperate deciduous forests

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The distribution pattern of centipedes (Chilopoda) and other soil arthropods in temperate
deciduous forests was investigated in four complementary studies that covered a wide range of environmental parameters, including soil chemical properties and microclimatic
parameters. The results of this study culminate in a multitude of implications for forest
management which would help avoid an impoverishment of the soil fauna and a reduced
productivity of forests. In two field studies, the distribution pattern of centipedes (Chilopoda) in primeval forests of Slovakia (Investigation I) and in managed forests of western Germany (Investigation II) was studied. The four primeval forests are located in two different mountain ranges (Kremnické vrchy and Pol’ana Mountains) and are exposed either on southern or northern slopes. The twelve managed forests are located in three different mountain ranges (Eifel, Bergisches Land, Westerwald) on either southern slopes, plateaus or northern slopes. In these sixteen forests, the influence of coarse woody debris (CWD) on centipede distribution was studied by distinguishing sampling sites on the forest floor close to CWD (c-CWD) and distant from CWD (d-CWD). In the four primeval forests (Investigation I), a total of 2,706 individuals from 20 species of centipedes were collected. Average species richness and number of individuals per forest ranged from 8 to 12 species/m² and from 244 to 486 individuals/m². The oak forests on southfacing slopes harboured several species which did not occur in the more northern exposed firbeech forests. The number of species as well as individuals, however, varied more within than between individual forests. Increase of species richness and density was mainly caused by the presence of CWD and was more pronounced on the southern slopes characterized by high temperatures and low precipitation than on the northern slopes characterized by low temperatures and high precipitation. However, CWD did not always increase species diversity in primeval forests. In the twelve managed forests (Investigation II), a total number of 2,876 individuals belonging to 22 species of centipedes were collected. The average species richness and number of individuals per forest ranged from 6 to 13 species/m² and from 40 to 237 individuals/m². The forests on northern slopes and plateaus harboured several species which did not occur on southern slopes. Species richness as well as density, however, varied more within than between individual forests. In total, more species and individuals were collected in c-CWD sites than in d-CWD sites. The positive effect of CWD was observed in all aspects of slope. The diversity according to rarefaction analysis corresponded to the results obtained for density and species richness and was higher at sites c-CWD. The effect of soil chemistry on centipedes and other soil organisms was studied in deciduous forests of western Germany (Investigation III). Kiln areas offer the opportunity to investigate small-scale effects of soil chemistry. The investigation was performed in three forests (Kermeter, Arzbach, Loope). The Ah-horizon in kiln areas (kilns) was generally characterized by higher levels of basic cations, nitrogen, carbon and higher (Ca+Mg+K)/Al molar ratios than soil samples taken distant from kilns (>10 m from kiln edge; control sites). Additionally, most soil parameters were affected by forest, as the highest contents were found in Kermeter and lowest in Loope. Microbial activity was higher at kilns than at control sites, but microbial biomass was not affected. Forest had a strong effect on microbial activity and biomass. In contrast to soil chemical parameters and microbial parameters, soil fauna was mostly unaffected by charcoal accumulation at kilns. However, arthropods with a calcareous exoskeleton (Isopoda and Diplopoda) showed higher abundances at kilns than at control sites
in two of the three forests. A significant influence of forest on the distribution pattern of Oribatei, Collembola, Chilopoda, Isopoda, Diplopoda and Coleoptera larvae was found. The macrofauna showed highest densities in Arzbach and lowest densities in Loope, whereas mesofauna showed highest densities in Loope and lowest densities in Arzbach. For microbial parameters, the highest correlations were found for the (Ca+Mg+K)/Al molar ratio. Arthropods with a calcareous exoskeleton demonstrated the highest correlations within the soil fauna, as they were positively correlated to pH-value and (Ca+Mg+K)/Al molar ratio. In a field experiment (Investigation IV), the litter mass of the forest floor was manipulated to determine the effects of microclimate on the abundance of macroarthropods. Litter accumulation treatments were performed distant from (litter) and close to (litter+logs) fallen logs. The investigation was performed in two forests (Arzbach, Elbert) of the Westerwald (Germany). In the litter layer, increased mean temperatures during the cold season and decreased mean temperatures during the warm season were found when compared to macroclimatic data. Minimum and maximum temperatures were buffered in litter accumulation treatments. The mean moisture content of litter was higher in litter accumulation treatments. Litter accumulation also significantly increased the abundances of Araneida, Pseudoscorpionida, Diplopoda, Lithobiomorpha, Geophilomorpha, Isopoda and Coleoptera and the species richness of centipedes in litter treatments. The abundances of Geophilomorpha, Isopoda and Coleoptera showed a further increase in +litterlog treatments. A stepwise linear regression revealed strong correlations between microclimate and litterdwelling
macroarthropods. At least in one season, Isopoda and adult Coleoptera preferred
sites in which the daily temperature range was low. The abundance of Lithobiomorpha and Diplopoda was correlated to the moisture content of leaf litter. Although fallen logs did not directly influence the abundance of most litter-dwellingarthropods, they had an indirect effect by causing an increase of litter mass and, hence, by improving the microclimatic environment of the forest floor.