Diversity and Succession of Vascular Plants, Bryophytes and Lichens on Decaying Logs of Beech (Fagus Sylvatica) in Two Forest Reserves (Flanders, Belgium)
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Biology Department Research Group Terrestrial ecology _____________________________________________________________________________________ DIVERSITY AND SUCCESSION OF VASCULAR PLANTS, BRYOPHYTES AND LICHENS ON DECAYING LOGS OF BEECH (FAGUS SYLVATICA) IN TWO FOREST RESERVES (FLANDERS, BELGIUM) Siska Van Parys Studentnumber: 01304847 Supervisor: Prof. Dr. Maurice Hoffmann Scientific tutors: Dr. Ir. Luc De Keersmaeker Wouter Van Landuyt Master’s dissertation submitted to obtain the degree of Master of Science in Biology Academic year: 2017 - 2018 © Faculty of Sciences – research group Terrestrial Ecology All rights reserved. This thesis contains confidential information and confidential research results that are property to the UGent. The contents of this master thesis may under no circumstances be made public, nor complete or partial, without the explicit and preceding permission of the UGent representative, i.e. the supervisor. The thesis may under no circumstances be copied or duplicated in any form, unless permission granted in written form. Any violation of the confidential nature of this thesis may impose irreparable damage to the UGent. In case of a dispute that may arise within the context of this declaration, the Judicial Court of Gent only is competent to be notified. SUMMARY Two strict forest reserves (Wijnendalebos and Joseph Zwaenepoel) that are unmanaged for more than two decades offer an increasing amount of large deadwood in various stages of decay. The decaying wood serves as a long-term supply of nutrients and functions as a water-storing element, and can be colonized by specialized biodiversity. This research aims to study diversity and succession of bryophytes, vascular plants and lichens on decomposing large logs of beech (Fagus sylvatica). Species of the three groups were inventoried in 2016 (bryophytes and lichens) and 2017 (vascular plants). 197 logs were surveyed in total: 131 in Joseph Zwaenepoel and 66 in Wijnendalebos. On each log the abundance of bryophytes, lichens and vascular plants was assessed using a simplified Braun-Blanquet scale. Also, the surface area of the logs, decay stage, light availability and wood chemistry were determined. Rarefaction/extrapolation curves, non-parametric estimators for incidence and sample coverage indices were performed to assess species richness and Shannon and Simpson diversity in the two forest reserves. Generalized linear models were used to determine the factors influencing species richness. Canonical correlation analysis (CCA) was used to determine the factors influencing species composition. Rarity of the species was evaluated, using the KFK-scale (a rarity scale for Dutch flora). The relationship of the Mean KFK values of the species present on a log with its species richness was investigated using Spearman’s correlations, a nonparametric statistic that measures the strength of a monotonic relationship between paired data. Ellenberg indicator values of nitrogen, moisture and light availability were compared with measured values. The relationship between the measured values and the mean Ellenberg indicator values of the species present on a log was assessed through Pearson’s correlations. For one of the sites, an identical inventory was already performed in 2001. A selection of these logs was resampled in 2016 (for bryophytes) and 2017 (for vascular plants). The species colonization capacities and the change in diversity are evaluated on this subset of logs. Both the species richness and diversity were found to be higher on logs in Joseph Zwaenepoel compared to Wijnendalebos. Even though both reserves have been unmanaged for the same amount of time, the Sonian forest is older in terms of forest continuity, resulting in a higher abundance of well-decayed logs of large diameter. Large logs provide a broader variety of microhabitats, and can therefore support more species. Since the amount of large, well-decaying deadwood in Joseph Zwaenepoel is only expected to increase, the species richness is also expected to increase in the future, especially in the parts that recently became unmanaged. Besides forest continuity, also the greater size of Joseph Zwaenepoel and of the surrounding forest can be of importance to explain the difference in species richness and diversity between the two reserves, since many bryophytes are characterized as dispersal limited at local scales and dispersal limitation has been proven to be an important structuring factor in temperate‐forest herb communities. The total species richness of the sum of all studied plant groups of a log increased with mean decay stage and phosphor content, and decreased with increasing mean canopy cover and potassium content. This is in line with many previous studies, emphasizing the role of nutrient and light availability and decay stage. Decay stage came out as one of the most important variables determining species richness. Species richness of bryophytes and vascular plants increases until it reached its peak at decay stage 4 (on a scale of 5) in both forest reserves. In intermediate stages of decay, species associated with all stages of decay overlap and therefore the overall number is relatively high. There was a significant interaction between forest reserve and outer surface area: the species richness of a log increased faster with outer surface area in Wijnendalebos than in Joseph Zwaenepoel. Large logs provide a broader variety of microhabitats, and can therefore support more species. Species richness and diversity were not significantly different in the two periods. However, logs with decay stage 4 (on a scale of 5) had a significantly higher richness and diversity in 2016/17 than logs with the same decay stage in 2001. This could be explained by the fact that the reserve has since been through more than 15 more years of unmanaged development, resulting in an increase in big old tree logs that are well decaying. Tree logs that went through an extensive change in decay from 2001 to 2016/17, generally also experienced a relatively big increase 2 in species richness. Change in decay appears to be highest for logs with an early decay stage in 2001 and lowest for logs with a late decay stage. The mean KFK value of a log, which is lower when less common species are present, was on average lower in Joseph Zwaenepoel than in Wijnendalebos, indicating a higher abundance and/or number of relatively rare species. This could be explained by the longer forest continuity and higher habitat diversity in Joseph Zwaenepoel. Relatively rare bryophyte species generally appear on more species rich logs, in other words, rare bryophyte species are nested. No nestedness of rare species could be detected for vascular plants and lichens. For vascular plant species, this this can be explained the fact that none of the species that were found is a specific epiphyte of (decaying) wood. The lichen species found were for the majority species that were already present on the living tree, found on logs in the earliest stage of decay. They are not necessarily adapted to growing on deadwood, in contrast to many bryophyte species that are specifically epiphytes of decaying wood. Species composition of bryophyte species was affected by the standard deviation of mean canopy cover (a proxy for the variation in light regimes on a log), phosphor content, mean decay stage and forest reserve. However, only a small part of the total variability in the data was explained, so we do not have conclusive results regarding bryophyte species composition. Bryophytes and lichens show a relatively high species richness in the first decay stage. This could be explained by the fact that fresh, poorly decayed deadwood shares a considerable proportion of epiphyte species with living trees. Especially for lichens, competition with the more productive vascular plants and bryophytes is less strong in early decay stages than on soft wood. Decay stage did not come forward as a determinant of vascular plant species composition. Altering light and nutrient availability seem to be more important. We found a moderate correlation between the measured values of nitrogen of a tree log with the average Ellenberg’s indicator values for the plants found on it, in both forest reserves. Ellenberg’s indicator values for nitrogen thus seem to be relatively reliable for tree logs in the two forest reserves. However, for moisture and light availability (as the inverse of mean canopy cover), no correlation was found. Ellenberg’s indicator values are derived from field experience of plant ecologists rather than field measurements, which is rather subjective, and they could be influenced by multiple ecological factors acting together. Also, these values have been developed for central Europe, so their application in other areas often asks for calibration of the values according to regional deviations. 3 SAMENVATTING In twee bosreservaten in België (Wijnendalebos en Joseph Zwaenepoel) zijn na meer dan twee decennia zonder beheer meer en meer grote dode beuken aanwezig in verschillende stadia van verval. Het verterend hout fungeert als een langetermijnaanvoer van voedingsstoffen en als wateropslagplaats, en wordt gekoloniseerd door gespecialiseerde biodiversiteit. Dit onderzoek bestudeert diversiteit en successie van bryophyten, vaatplanten en korstmossen op liggend dood hout van beuk (Fagus sylvatica). Soorten van de drie groepen werden geïnventariseerd in 2016 (bryophyten en korstmossen) en 2017 (vaatplanten). In totaal werden 197 logs bekeken: 131 in Joseph Zwaenepoel