Epiphytic lichen diversity in old-growth and managed Picea abies stands in Alpine spruce forests

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Abstract

In the last decades, a large body of literature has grown to evaluate the impact of forest management on epiphytic lichens in boreal coniferous forests. However, information is still lacking on coniferous forests of the Alps. This study compares lichen diversity between spruce forest stands of four successional stages: (1) young, (2) intermediate, (3) mature forests managed for timber production with a rotation cycle of 120–180 years, and (4) old-growth protected forests. The emphasis was placed on the occurrence of nationally rare and calicioid species (lichens and fungi traditionally referred to as Caliciales, known to be indicative of forest age and continuity). For each forest successional stage, four plots were selected. In each plot, 7 spruce individuals were surveyed for epiphytic lichens according to a standardised sampling method. Species richness increased from young to mature stands, while no difference was detected between mature and old-growth stands. This pattern was also confirmed for rare and calicioid species which are, however, more frequent in old-growth stands. Differences in species composition were also found between the different forest successional stages. Mature and old-growth plots slightly overlap, indicating that to some extent comparable lichen assemblages could be found in these stands. A nested pattern of species assemblages was found, old-growth stands hosting most of the species which were also found in stands belonging to the previous forest successional stages. Our results support the hypothesis that the management regime applied to spruce forests of the Italian Alps renders mature stands managed for timber production somewhat similar to old-growth stands as lichen habitat. However, we found a higher complexity in old-growth forests, and many species of conservation concern clearly preferred old-growth stands. In this perspective, a further prolongation of the normal cycle it is likely to be a most favourable conservation-oriented management to be recommended at least within protected areas and Natura 2000 sites, where conservation purposes should receive a high priority.

Introduction

In the last decades, a large body of literature has grown to evaluate the impact of forest management on epiphytic lichens in order to provide guidelines for lichen conservation in boreal coniferous forests (e.g. Dettki and Esseen, 1998, Dettki and Esseen, 2003, Esseen et al., 1996, Gustafsson et al., 2004, Kuusinen and Siitonen, 1998, Johansson, 2008, Lommi et al., 2009, Perhans et al., 2007, Pykälä, 2003). However, information is still lacking on coniferous forests of the Alps (but see e.g. Nascimbene et al., 2009) and management guidelines for sustainable forestry developed in boreal regions may not necessarily be applicable in mountain regions of South Europe.

Boreal spruce forests are mainly logged by clearcutting over large areas with relatively short rotation cycles (e.g. Dettki and Esseen, 2003). For instance Penttilä et al. (2004) reported that in southern Finland the regeneration cutting age of spruce-dominated forests is 90–100 years and forests older than 120 years have traditionally been considered as overmature from the forestry point of view. Analogously, Gustafsson et al. (2004) reported that in Sweden productive forests (mainly coniferous forests) are managed with a rotation cycle of 60–120 years. Due to economic goals, rotation cycles tend to become progressively shorter (e.g. Bauhus et al., 2009, Linder and Östlund, 1998).

Spruce forests are also one of the most widespread and economically relevant formations in the Italian Alps (Pignatti, 1998). Management is less intensive than in the boreal zone, being mainly based on progressive thinning of even-aged trees (shelterwood system) and clear-cut over relatively small areas (<1 ha), rotation cycles being longer (120–180 years) than in boreal forests. Despite the fact that management practices of Alpine forests should include biodiversity conservation, their ability to sustain rich epiphytic lichen communities and to preserve habitats for sensitive and rare species has never been thoroughly evaluated.

Epiphytic lichen communities are influenced by several factors whose importance depends on the scale of the analysis, from the tree-level (e.g. Fritz et al., 2008, Fritz and Heilmann-Clausen, 2010, Johansson et al., 2007, Lie et al., 2009, Nascimbene et al., 2008, Nascimbene et al., 2009, Ranius et al., 2008) to the biogeographical scale (e.g. Bolliger et al., 2007, Ellis et al., 2007, Jovan and Mc Cune, 2004, Martínez et al., 2006). Forest management mainly acts at the stand level, where stand-age is known to be a key factor influencing epiphytic lichen communities. Several studies, mainly conducted in boreal coniferous forests, showed that forest age and species diversity are positively related, and that community composition varies with increasing forest age (e.g. Dettki and Esseen, 1998, Hilmo et al., 2009, Hyvärinen et al., 1992, Moning and Müller, 2009, Peterson and Mc Cune, 2001, Rogers and Ryel, 2008). In this framework, research has also focused on the comparison between forests managed for timber production and forests managed for old-growth, showing that old-growth forests play a key role for the conservation of rare (e.g. Pykälä, 2003) and calicioid species (Tibell, 1992, Selva, 2002). Nevertheless, a balance should be found between conservation and productivity, estimating to what extent the oldest age classes in forests managed for timber production could compensate for the scarcity of forests managed for old-growth conditions. In boreal areas, longer rotation cycles (>120–150 years) have been suggested to improve the effectiveness of lichen conservation by enhancing the presence of lichen species associated with old-growth in stands managed for timber (e.g. Dettki and Esseen, 1998, Dettki and Esseen, 2003, Kuusinen and Siitonen, 1998, Johansson, 2008, Peterson and Mc Cune, 2001).

This study compares lichen diversity between stands of different age managed for timber production, and old-growth forests managed for nature protection, with emphasis on the occurrence of nationally rare and calicioid species. The main aims are: (1) to compare species richness between young (40–70 years), intermediate (80–120 years), mature (>120 years old) stands managed for timber production and old-growth protected stands (>200 years); and (2) to explore species composition patterns in the four forest successional stages, testing also for community nestedness. The study was planned to answer the conservation questions of which successional stages need to be conserved as important habitats for specialized lichen species and whether mature stands for timber production could be considered as good surrogates of old-growth-forests managed for nature protection.

Section snippets

Study area

The study was carried out in the Paneveggio spruce forest (Paneveggio-Pale di San Martino Natural Park, Trentino-Alto Adige, N-Italy; 46°18′N, 11°45′E) which extends over 3000 ha. Altitude ranges from 1500 to 1900 m, average annual temperature is 2.4 °C, annual rainfall is 1200–1300 mm year−1. The bedrock is porphyry and the soils are rankers and podsols.

This forest is one of the larger spruce forests of the Italian Alps (Pignatti, 1998) and has a long history of forestry. Exploitation of the

Species richness

Sixty-four lichens and two non-lichenised fungi (Chaenothecopsis pusilla and Microcalicium disseminatum) were found (Appendix A). The overall number of species increased from young to old-growth stands (18, 31, 45, and 56). Old-growth and mature stands pooled together hosted 95% of the total flora. Nineteen percent of the species occurred in all forest successional stages, the most abundant being Hypogymnia physodes, Ochrolechia microstictoides, Parmelia saxatilis, P. sulcata, and Platismatia

Discussion

Species richness increased from younger to older stands, but mature stands managed for timber production and old-growth stands host a comparably richer lichen biota, even if a higher complexity was found in old growth stands. A similar pattern was also found by Kuusinen and Siitonen (1998) in their evaluation of epiphytic lichen communities in old-growth and managed spruce forests of Southern Finland, while in boreal Sweden Gustafsson et al. (2004) demonstrated that also old mature (≥110 years)

Management implications

Our results support the hypothesis that the management regime applied to spruce forests of the Italian Alps renders mature stands managed for timber production somewhat similar to old-growth stands as lichen habitat. However, we found a higher complexity in old-growth forests, and many species of conservation concern preferred old-growth stands. Some differences could be less pronounced for timber managed stands which are felled at the maximum of the rotation cycle. In this perspective, a

Acknowledgements

The work was funded and supported by the Parco Naturale Paneveggio-Pale di San Martino (Trento). We are also grateful to the Agenzia Provinciale delle Foreste Demaniali for providing information on forest management and for logistic support during the field work. Andrea Laschi (Firenze) and Marilena Dalle Vedove (Feltre) are thanked for their contribution during the field work.

The Editor, Péter Ódor, and two anonymous referees are thanked for providing stimulating improvements to the manuscript.

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