Oribatid fauna (Acari, Oribatida) in fallen spruce trees in the Babia Góra National Park

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1 ORIBATID FAUNA IN FALLEN TREES 243 BIOLOGICAL LETT. 2006, 43(2): Available online at Oribatid fauna (Acari, Oribatida) in fallen spruce trees in the Babia Góra National Park PIOTR SKUBA A and MAGDALENA SOKO OWSKA University of Silesia, Department of Ecology, Katowice, Bankowa 9, Poland; pskubala@us.edu.pl (Received on 19 December 2005; Accepted on 20 November 2006) Abstract: The purpose of this study was to contribute to our understanding of inhabitation of fallen spruce trees by oribatid mites. The research was carried out in the spruce forest in the Babia Góra National Park (Western Carpathians). Five samples of decaying wood were taken from each of 5 downed spruce logs. Fifteen soil samples were additionally collected around logs in the forest. Overall, specimens of Oribatida belonging to 95 species were collected in the 40 samples. Decaying wood of Norway spruce was colonized by numerous oribatid mites. The abundance and species richness of oribatids in lying logs tended to increase with log age; peak values occurred in the decay class IV log. With regard to oribatid fauna, decaying wood appeared not to be impoverished in comparison with forest litter and soil. Thirtytwo species, e.g. Anachipteria deficiens, Caleremaeus monilipes, Lauroppia maritima and Melanozetes meridianus, seemed to be obligate members of the intra-log community. Only 9 species of the oribatid inhabitants of lying logs can feed upon decaying wood particles. Key words: decaying wood, logs, oribatid mites, succession, forest INTRODUCTION It is striking to observe that our accumulation of data on the life associated with dead wood is far slower than is our cutting of old-growth trees and removal of coarse woody debris (CWD) from forests. Still relatively little is known about the fauna inhabiting CWD in forests (SEASTEDT et al. 1989). Attention was paid to saproxylic insects (i.e. species depending on dead wood, e.g. Coleoptera, Diptera) during the last decade. This group of animals appears to be seriously threatened as a result of sylvicultural practices. Mites were usually omitted from studies on decaying wood. FAGER (1968), SEASTEDT et al. (1989), JOHNSTON & CROSSLEY (1993), PAVIOUR- SMITH & ELBOURN (1993) and TRAVÉ (2003) made the only detailed studies on Acari associated with dead wood. This is surprising, given the number of studies of forest floor mites, as their authors unfortunately investigated mainly litter and soil. CWD in forests constitutes a set of microsites that offer food and shelter for communities of soil mites. The successional stages of wood decomposition provide a large number

2 244 Piotr Skuba³a and Magdalena Soko³owska of microhabitats, in which saprophagous, microphagous, mycophagous, xylophagous species and predators can be abundant. The main group of microarthropods in the forest floors of temperate regions are oribatid mites (WALTER & PROCTOR 1999). They are generally considered as a fungivore-detritivore group. Their occurrence and role in various kinds of dead wood in forest is virtually unrecognized. In this study we offer a preliminary interpretation of the importance of fallen logs (the main kind of CWD) for the oribatid fauna. We addressed the following hypotheses: 1. Population densities of oribatids increase with log age (i.e. with time after felling). 2. Forest litter and soil are richer in oribatids than decaying wood is. 3. No oribatid species are obligate members of the intra-log community. 4. Species that feed directly on wood are the most numerous representatives of oribatids in decaying logs. MATERIAL AND METHODS The research was conducted in the spruce forest Plagiothecio-Piceetum tatricum typicum in the Babia Góra National Park (Western Carpathians), which is one of UNESCO MAB Biosphere Reserves. The study area lies in the upper montane belt at the altitude of 1180 m (49 40 N, E). The stand is dominated by the Norway spruce Picea abies (L.) Karst. We selected 5 downed spruce logs of similar size (length ~12 m, diameter ~50 cm), representing all the decay classes [I V] on PYLE & BROWN s (1998) scale. From each log, 5 samples of decaying wood (18 g of dry matter each) were taken. Fifteen soil samples were additionally collected around logs in the forest [S]. In order to reduce variability due to differences between localities, all samples were taken from a small area (50 m 50 m) in November Overall, specimens of Oribatida were collected in 40 samples, and 55% of the animals originated from decaying wood. Mites were extracted from the samples using a modified Tullgren extractor, the procedure lasting 6 days. Differences in the abundance of microarthropods between logs in different decay classes and in soil were tested by 1-way analysis of variance (ANOVA). MVSP 3.1 was used to perform correspondence analysis. We excluded from the analysis the species represented by fewer than 5 individuals. The numbers of individuals were log(x+1) transformed. RESULTS The total abundance of oribatid mites (adult as well as juvenile stages) generally increased with log age (i.e. with time after felling). However, the one-way ANOVA did not reveal any significant differences in oribatid abundance among the logs. Peak values (3698 ind./100 g of dry matter, DM) occurred in the decay class IV log. The abundance of oribatids in the decay class V log was less high (2103 ind./100 g DM). The number of oribatids in the youngest log was still high (745 oribatid speciemens/100 g DM). Population abundance of oribatids from lying logs was compared with similar estimates obtained from the top 7.5 cm of litter and soil

3 ORIBATID FAUNA IN FALLEN TREES 245 Fig. 1. A plot of the first 2 axes of correspondence analysis (CA) of sampling sites and species in decaying logs, litter and soil Codes of the species: Ad Anachipteria deficiens; As Atropacarus (A.) striculus; Cm Caleremaeus monilipes; Cl Carabodes labyrinthicus; Ct Carabodes tenuis; Cb Chamobates borealis; Fs Fuscozetes setosus; Lm Lauroppia maritima; Lh Liochthonius hystricinus; Mm Melanozetes meridianus; On Oppiella nova; Pa Phthiracarus anonymus; Qq Quadroppia quadricarinata; Sv Suctobelbella vera; Tv Tectocepheus velatus of adjacent forest floor. These results indicate that decaying wood is not a poor substrate for oribatid mites. The average abundance of oribatids in nearby litter and soil (2695 ind./100 g DM) was lower than the number of oribatids in the log of decay class IV and only slightly higher than in other decaying logs, but the differences were only significant with regard to adults (F 5,24 =2.90, P<0.05). A general trend towards increased numbers of species from decay class I (25 species) to decay classes IV and V (52 species) was evident. In general, 80 oribatid species were recorded in decaying wood of downed logs, whereas the number of species found in litter and soil was lower (63 species). Ordination by Correspondence Analysis (CA) was used to assess community similarities and relations between species and communities in logs and litter and soil. The scores for the first 2 axes are shown in Fig. 1. Symbols of dominant species are shown on the diagram. Eigenvalues of axes 1 and 2 were (significant) and 0.118, respectively. Over 68% of the variance was explained by those axes. Overall, axis 1 appears to reflect a gradient from young (right) to older logs (left). The species and sites are grouped into 4 clusters. Cluster A contains species most abundant in the decay class I and II logs. Anachipteria deficiens Grandjean, 1932 and Caleremaeus monilipes (Michael, 1882) (the most abundant species in these logs) occurred only in decaying wood. A. deficiens is a species of Palaearctic distribution (SCHATZ 1983), recorded for the first time in Poland. C. monilipes is regarded as an arboricolous

4 246 Piotr Skuba³a and Magdalena Soko³owska forest species (SCHATZ 1983), previously recorded only in 2 regions in Poland (OLSZANOWSKI et al. 1996). With regard to trophic preferences, the species is regarded as a macrophytophage, i.e. is able to ingest dead or decaying tissues of higher plants, including leaves and wood (SCHATZ 1983). Cluster B is composed of species that occurred abundantly only in the logs of medium age (e.g. Lauroppia maritima (Willmann, 1929), Melanozetes meridianus Sellnick, 1928, Carabodes labyrinthicus (Michael, 1879), C. tenuis Forsslund, 1953, Liochthonius hystricinus (Forsslund, 1942)). The first 2 species occurred exclusively in decaying logs, whereas the others also in litter and soil but were infrequent there. Of these species only C. labyrinthicus is known as a macrophytophage associated with forest. Also other authors reported that it is abundant in CWD (FAGER 1968, PAVIOUR-SMITH & ELBOURN 1993). M. meridianus and L. maritima have rarely been recorded in Poland so far (OLSZANOWSKI et al. 1996). Species associated with older logs (IV and V) were ordinated along the negative part of axis 1 (cluster C). Quadroppia quadricarinata (Michael, 1885) (over 12% of the total number in log V) are known as eurytopic species of broad geographic distribution (SCHATZ 1983, OLSZANOWSKI et al. 1996). Several species, e.g. Phthiracarus anonymus Grandjean, 1933, Atropacarus (A.) striculus (C. L. Koch, 1836), Tectocepheus velatus (Michael, 1880), Chamobates borealis (Trägårdh, 1902), and Fuscozetes setosus (C. L. Koch, 1841), were crowded around the intersection point of the 2 axes (cluster D). The species show no preference for any site. In this group, 2 species (P. anonymus and A. striculus) are known as important in the physical breakdown of wood invaded by fungi (SEASTEDT et al. 1989). They were also present in decaying logs but were less frequent there than in wood. There was no species characteristic for litter and soil (Fig. 1). Seventeen species occurred exclusively in these habitats but they were found occasionally. The only dominant species in litter and soil, significantly less abundant in logs, was Oppiella nova (Oudemans, 1902). DISCUSSION Oribatids are among the most characteristic elements of soil fauna. Possibly they play an important role in biotopes related to the ground, e.g. in decomposing wood. The food base for most oribatid mites consists of fungal hyphae (abundant in decaying wood), although some species appear to use leaf litter or woody materials directly. It is worth mentioning that the calcium-rich bark of decaying wood may be especially important for oribatids, which use calcium oxalate or calcium carbonate as cuticular hardening agents (NORTON & BEHAN-PELLETIER 1991) Our hypothesis 1 was partly confirmed. It was both surprising and interesting to find so many individuals and species of oribatids in dead wood. The mean abundance of oribatids in lying logs tended to increase with log age. It might be concluded that dead wood becomes a more rewarding food resource in the course of decomposition. Also species richness increased with the progress of decomposition of a log, indicating that resource heterogeneity increased with log age. However, the abundance and number of species in the decay class V log were lower than in class IV log. Such a trend could be expected, because the remaining material at older logs will become more and more homogenous again.

5 ORIBATID FAUNA IN FALLEN TREES 247 A general trend of increasing abundance with decaying wood age was previously observed for Diptera (HÖVEMEYER & SCHAUERMANN 2003), Coleoptera (IRM- LER et al. 1996) and some other groups of invertebrates (ABBOTT & CROSSLEY 1982, BRACCIA & BATZER 2001). MASER & TRAPPE (1984) stressed that the mite fauna began to flourish as a fallen tree approached class IV. On the other hand, SEASTEDT et al. (1989) found peak values of microarthropods in decay class II logs, but the values were not statistically different from those for older decay classes. Hypothesis 2 was also partly confirmed. Decaying wood of the class IV log appeared to be richer in oribatids than surrounding litter and soil. Furthermore, the total number of mite species in lying logs (80 species) was higher than in the surface soil layer (0 7.5 cm in depth). Our results are to some extent surprising, taking into account other authors. They usually described the mite fauna in wood as impoverished in comparison with that found in forest litter and soil. SEASTEDT et al. (1989) recorded 2 10-fold lower densities of microarthropods in decaying wood than in equivalent amounts of litter and soil. Similarly, the number of species was 2-fold lower in CWD than in litter. They recorded only 22 oribatid species inside decaying wood. Likewise, FAGER (1968) found 26 species of oribatids in decaying logs. However, JOHNSTON & CROSSLEY (1993) recorded 60 species in CWD, PAVIOUR-SMITH & ELBOURN (1993) found 44 species in aerial dead wood on deciduous trees, and TRAVÉ (2003) noted 68 species in decomposing wood. Nevertheless, mite species diversity in wood was lower than in litter (JOHSTON & CROSSLEY 1993). This aspect needs further studies. Hypothesis 3 was rejected. In the 5 decaying logs, 80 oribatid species were recorded, of which 32 were found exclusively in dead wood. Some of the dominant species, e.g. Anachipteria deficiens, Caleremaeus monilipes, Lauroppia maritima and Melanozetes meridianus appeared to be obligate members of the intra-log community. JOHSTON & CROSSLEY (1993) stressed that the major role of large branches and fallen logs in forest floor habitats appeared to be that of a refuge for mite species normally occurring in litter or soil. However, they also found some species that use exclusively CWD, e.g. Atropacarus sp. Ocellatus omnatocepheus, Scheloribates pallidus. SEASTEDT et al. (1989) recorded members of the Oppiidae and Suctobelbidae as the most numerous in decaying wood and they were also the most abundant species found in litter and wood. Nearly all oribatid species obtained from dead wood were also present in litter. Only Microtritia sp., Gehypochthonius sp. and Epilohmannia sp. appeared to be restricted to decaying wood (SEASTEDT et al. 1989). In our studies the dominant species found in wood were not generally the same species that dominate the fauna of litter and soil. Hypothesis 4 was also rejected. The number of species that possibly can feed upon decaying wood particles (9 species) was small. Among 15 dominants in decaying logs, only Caleremaeus monilipes, Carabodes labyrinthicus, Phthiracarus anonymus and Atropacarus striculus are regarded as wood-feeding mites (LUXTON 1972, KRANTZ 1978, SCHATZ 1983). Similarly, JOHSTON & CROSSLEY (1993) noted few wood feeders, e.g. Atropacarus sp., Carabodes sp., among dominants in woody debris. This phenomenon was also observed by SEASTEDT et al. (1989). They found that wood-feeding microarthropods constitute a small proportion of the fauna found in decaying boles. Those authors concluded that oribatids were actually feeding on the microflora contained on the wood instead of the wood.

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