Outline
- Abstract
- Keywords
- 1. Introduction
- 2. Methods
- 3. Results
- 4. Discussion
- Acknowledgements
- References
رئوس مطالب
- چکیده
- کلید واژه ها
- 1. مقدمه
- 2. روش ها
- 3. نتایج
- 4. بحث
- 4.1. خلاصه
Abstract
For lichen epiphytes the loss of trees from a site represents a complete break in the availability of their primary habitat. Epiphytic species are therefore expected to provide powerful indicators for the ecological continuity of woodlands. Suites of lichen indicators have been developed in a semi-quantitative way, and represent working hypotheses which are cautiously interpreted against site-specific conditions by expert field biologists. Here, we test the utility of lichen indicators in a more generic fashion, by attempting to falsify the null hypothesis that the occurrence of lichen indicators is unrelated to variation in woodland continuity. We compared the association of recommended lichen indicators with woodlands in different continuity classes, after adjusting for sampling bias. We demonstrated differences in accuracy for contrasting sub-groups of indicators related to their biogeography; a sub-group of ‘western’ indicators tended to be more strongly associated with long-continuity woodland compared to an ‘eastern’ indicator sub-group. Our results underpin the need for further research into the fundamental biology which explains the value of indicators, before these tools can be applied generally and independently of expert-led opinion in a site-specific context.
Keywords: Ancient woodland - Bioindicator - Ecological continuity - Epiphyte - LichensConclusions
Records for the five common and widely distributed lichen species demonstrated a bias in sampling effort away from younger secondary regenerated woodlands, towards ancient and longestablished woodland sites. Approximately, 93%, 91% and 94% of species occurrences were restricted to Class 1 (ancient) and Class 2 (long-established) woodlands within the WSIEC, EUOCIEC, and ESIEC regions, respectively. There were only two records of an indicator species from AWI Class 1b woodlands (both for Hypotrachyna laevigata), and this continuity class was dropped from further analysis. Correcting for sampling bias (see Methods), there were mixed results in the statistical association of lichen indicators of ecological continuity with Class 1a (ancient, semi-natural) woodlands (Table 1). For the WSIEC sub-group, c. 80% of tested species (8/10) showed a significant association with Class 1a woodland stands. This value decreased to c. 33% of tested species (3/9) for the EUOCIEC sub-group, with Usnea filipendula significantly associated with Class 2b sites (long-established plantations). Likewise for the ESIEC sub-group, only c. 14% (2/14) of species were associated with Class 1a woodland sites, with Parmeliella triptophylla significantly associated with Class 2a sites (long-established seminatural woodlands). In a majority of cases for indicators sampled from the EUOCIEC and ESIEC sub-groups, the observed records from sites that had evidence for a break in the continuity of tree cover (AWI Class 3) was consistent with the expected number of records when corrected for sampling effort. Furthermore, there was no discernible pattern in the distribution of ecological traits for species showing a significant association with the AWI classes (Table 1), with representation across all growth forms (fruticose, foliose, squamulose and crustose), including lichens with green-algal and cyanobacterial photobionts, and with different reproductive strategies comprising sexual spore-dispersal and asexual species dispersed via larger diaspores (isidia and soredia).
Considering lichen records within AWI Class 1 and Class 2 sites as a single grouping, the association test remained significant at P < 0.05 (1 df) for only two species: Leptogium burgessii (v2 = 5.1) and Pyrenula occidentalis (v2 = 5.82), both within the WSIEC subgroup.