**Vitality and Growth of the Threatened Lichen** *Lobaria pulmonaria* **(L.) Ho**ff**m. in Response to Logging and Implications for Its Conservation in Mediterranean Oak Forests**

**Elisabetta Bianchi 1, Renato Benesperi <sup>2</sup> , Giorgio Brunialti <sup>3</sup> , Luca Di Nuzzo <sup>2</sup> , Zuzana Faˇckovcová <sup>4</sup> , Luisa Frati <sup>3</sup> , Paolo Giordani <sup>5</sup> , Juri Nascimbene 6, Sonia Ravera 7, Chiara Vallese <sup>6</sup> and Luca Paoli 8,\***


Received: 7 August 2020; Accepted: 11 September 2020; Published: 16 September 2020

**Abstract:** Forest logging can be detrimental for non-vascular epiphytes, determining the loss of key components for ecosystem functioning. Legal logging in a Mediterranean mixed oak forest (Tuscany, Central Italy) in 2016 heavily impacted sensitive non-vascular epiphytes, including a large population of the threatened forest lichen *Lobaria pulmonaria* (L.) Hoffm. This event offered the background for this experiment, where the potential effects of logging in oak forests are simulated by means of *L. pulmonaria* micro-transplants (thallus fragments <1 cm). Our working hypothesis is that forest logging could negatively influence the growth of the thalli exposed in logged stands compared to those exposed in unlogged stands. One hundred meristematic lobes and 100 non-meristematic fragments are exposed for one year on 20 Turkey oak trees (*Quercus cerris*), half in a logged and half in an unlogged stand. Chlorophyll (Chl) *a* fluorescence emission and total chlorophyll content are used as a proxy for the overall vitality of the transplants, while their growth is considered an indicator of long-term effects. Generally, vitality and growth of the transplants in the logged stand are lower than in the unlogged stand. Both vitality and growth vary between the meristematic and non-meristematic fragments, the former performing much better. Hence, irrespective of forest management, meristematic fragments show higher growth rates (0.16–0.18 cm2 year<sup>−</sup>1) than non-meristematic ones (0.02–0.06 cm2 year<sup>−</sup>1). Considering that a conservation-oriented management for this species should be tailored at the habitat-level and, especially, at the tree-level, our results suggest that for appropriate conservation strategies, it is necessary to consider the life cycle of the lichen, since the probability of survival of the species may vary, with meristematic fragments having more chance to survive after logging.

**Keywords:** biodiversity conservation; chlorophyll fluorescence; epiphytic macrolichens; forest management; growth rates; indicator species

#### **1. Introduction**

Biodiversity is increasingly threatened by several anthropogenic factors [1–5]. Among them, five main pressures have been recently pinpointed [6], including the overexploitation of species; the introduction of invasive alien species; pollution from industrial, mining and agricultural activities; changes in land use; climate change. Due to these pressures, some models predict that up to 50% of the species are expected to become extinct in the next 50 years [7–9]. Pollution, land use (including forest management) and climate change cause habitat loss and fragmentation, changes in species range, population size and abundance, vitality and reproductive capacity [10–12]. Epiphytes may be particularly at risk due to their dependence on trees for their entire life cycle [13]. Specifically, growing on other plants they depend on their host for physical support and on tree host-specific throughfall chemistry to satisfy their nutrient requirements [14,15]. Non-vascular epiphytes fulfill various ecological functions in forests. They contribute to water and nutrient cycling by intercepting and retaining nutrients from atmospheric humidity, with some also adding nitrogen by nitrogen fixation [16–18]. Moreover, they provide resources and microhabitats for bark-dwelling invertebrates, birds, and mammals [19,20].

Intensive logging and forest fragmentation can be particularly detrimental for epiphytic lichens, causing a break in the availability of their primary habitat [21,22], especially for species with low dispersal capacity (e.g., [23]). The foliose lichen *Lobaria pulmonaria* (L.) Hoffm. is considered an "umbrella" species requiring spatial and temporal continuity of the forest habitat to maintain viable populations [24–27]. It is a tripartite species in which the fungus is associated with both a green alga (phycobiont) and a nitrogen-fixing cyanobacterium (cyanobiont). It is often accompanied by other rare or endangered lichens [28–31] and sensitive to abrupt changes in light conditions (especially in the dry state [32]), such as those occurring after forest logging. Its vulnerability to logging may be exacerbated in dry environments, such as in the Mediterranean region, where oak-dominated forests represent its main habitat (e.g., [33]). Actually, the results of a recent work carried out in Italy suggest that oak (*Quercus* sp.pl.)-dominated forests provide more suitable habitat conditions for *L. pulmonaria* than montane mixed forests, with chestnut forests in an intermediate position [34]. Regarding Mediterranean Italy, the climatic niche of *L. pulmonaria* widely overlaps (>70%) with that of oak dominated forests [35], therefore the conservation of forest habitats with suitable ecological conditions (e.g., [36]) is important.

Due to its heterothallic nature, self-incompatibility, poor dispersal capacity, long generation cycles (up to 25 years) and susceptibility to environmental parameters (such as air pollution) [37–39], this sensitive species is decreasing across Europe [40]. Considering all the above reasons, it is deemed (and often used as) a model species to assess the response of epiphytic lichens to multiple environmental factors [41]. Current forest management practices can hardly sustain future viable populations of this species [42,43]. Additionally, air pollution still may limit recolonization of potentially suitable forest habitats [44]. However, despite being declining and threatened in Southern Europe [43,45–47], the species is not often recognized in conservation policies in Mediterranean regions [48].

This research began in 2016 with a legal logging in a Mediterranean mixed oak forest in Tuscany, Central Italy, that heavily impacted a large population of *L. pulmonaria*. It was estimated that 40% of *L. pulmonaria* biomass (8.5–12.3 kg ha<sup>−</sup>1) was lost (in the mostly colonized area, up to 1.8 kg 100 m−2), including large and fertile thalli [48]. More than one year later, the analysis of chlorophyll *a* fluorescence emission revealed a significant reduction of the vitality of the thalli left on retained-isolated trees [49]. Here, the potential effects of logging on *L. pulmonaria* in this oak forest have been simulated by means of micro-transplants (thallus fragments <1 cm). Our working hypothesis is that forest logging could negatively influence the growth of the thalli exposed in logged stands compared to those exposed in unlogged stands, with potential consequences for the conservation of the species. Since the viability of *L. pulmonaria* populations in relation to forest management often depends on the regenerative capacity of the thalli, we focus our attention on the behavior of thalli (fragments) with meristematic (young) and non-meristematic (adult) properties. Hence, healthy young and adult fragments of *L. pulmonaria* are

transplanted for one year to a logged and an adjacent unlogged mixed oak stand, two and half years after the conclusion of logging. Afterwards, ecophysiological responses (vitality and growth) of the species are recorded. To optimize survival and growth, the response to logging is tested under the most suitable conditions for lichen growth (north side of the trunk, breast height) [34,50]. The following questions were addressed: (i) does forest management influence the growth capacity of the model species in logged and unlogged stands? (ii) do vitality and growth vary between meristematic and non-meristematic thalli?
