Contrasting functional traits maintain lichen epiphyte diversity in response to climate and autogenic succession

Abstract

Aim Lichen epiphytes are important for biodiversity conservation and are also widely applied as environmental indicators. However, biogeographical and ecological knowledge underpinning lichen epiphyte conservation, and the use of lichens as indicators, is based primarily on a limited range of ‘macrolichen’ species. Wider trends in epiphyte biodiversity remain largely unexplored. This paper examines the community structure of lichen epiphytes on aspen (Populus tremula L.) in Scotland, including species across all functional groups and comprising, therefore, taxonomically difficult ‘microlichens’. Location Northern Britain (Scotland). Methods Epiphytes were sampled from 12 sites throughout Scotland and examined at two scales: between and within aspen stands. Species were classified into contrasting functional groups and ordination by detrended correspondence analysis was used to summarize community structure. Results Within aspen stands (between trees) epiphyte communities showed successional patterns related to tree age. These successional patterns changed predictably for stands aligned along a climatic gradient (between stands). Main conclusions A dual climatic–successional trend in epiphyte community structure is presented. Large‐scale trends in epiphyte diversity are explained as the local response of species with contrasting functional traits to climate and autogenic succession. Turnover of functional groups between stands is positively related to β‐diversity, and ecological limits to the frequency of contrasting functional groups are presented. Accordingly, the study and application of lichen species with similar functional traits may inadequately represent patterns of biodiversity. This prompts criticism of the currently accepted conservation strategy, i.e. (1) an emphasis in the conservation literature on ‘macrolichen’ species with similar ecologies and (2) the application of lichen indices over climatically variable geographical areas.

Evaluating macrolichens and environmental variables as predictors of the diversity of epiphytic microlichens

“…A typical habitat dominated by various ombrophobous and aerohygrophilous microlichens consists of dry bark of forest trees in old growth stands (Barkman 1958;Holien 1998). Ellis & Coppins (2006) showed that effects of F. 5.…”

“…For example, size and age of trees may have different effects on richness or frequency of macro-and microlichens (Ihlen et al 2001;Ellis & Coppins 2006). In general, succession of epiphytic lichen communites starts with crustose lichens, followed by foliose lichens and, eventually, fruticose lichens (Ochsner 1927;Barkman 1958;Ellis & Coppins 2006). At least in one of the two best models the number of trees with DBH>36 cm had a negative effect on microlichen richness, which can be seen as a confirmation of the general successional trend.…”

“…While many macrolichens are rather easy to sample and identify, microlichens generally require much more effort for species identification by specialized taxonomists (Dietrich & Scheidegger 1996;Ellis & Coppins 2006). Furthermore, in many regions and habitats, microlichens are considerably richer in species than macrolichens (Dietrich & Scheidegger 1997;Bergamini et al 2005;Ellis & Coppins 2006).…”

“…Hyvärinen et al 1992;Uliczka & Angelstam 1999), other abiotic variables such as altitude (Dietrich & Scheidegger 1997;Gustafsson et al 2004), and climatic variables (e.g. Werth et al 2005;Ellis & Coppins 2006). Forest-stand, phorophyte-related, and other abiotic variables (referred to here as 'field variables') are often readily available as they are assessed in forest inventories in many countries (e.g.…”

Lichen community change in response to succession in aspen forests of the southern Rocky Mountains

“…In short, epiphytic macrolichens were systematically examined on a 0.378 ha plot for up to 2 h. We did not sample microlichens (crustose forms) as they are not easily distinguished for purposes of a national monitoring system (McCune, 2000;Will-Wolf, 2002) and they appear to comprise a minor component of the local epiphytic flora; in contrast to the greater diversity of crustose species found at some riparian sites (Carmer, 1975) or in moister environments on European aspen (Lipnicki, 1998;Ellis and Coppins, 2006). Only species occurring on woody substrates at least 0.5 m above the forest floor were sampled.…”