Terricolous lichens as indicators of nitrogen deposition: evidence from national records

Large areas of Great Britain currently receive nitrogen (N) deposition at rates which exceed the thresholds above which there is risk of damage to sensitive components of the ecosystem (critical loads for nutrient nitrogen and critical levels for ammonia), and are predicted to continue to do so. Excess N can damage semi-natural ecosystems. Lichens are potentially sensitive to air quality because they directly utilise nutrients deposited from the atmosphere thus may be good indicators of air quality. We used data from the British Lichen Society (BLS) database, which records the presence of all lichen taxa growing in Britain at 10 km resolution. The probability of presence of a taxa at a given level of N deposition was analysed together with driver data for climate, change in sulphur deposition, land-use and N deposition using generalised additive models (GAMs). Many taxa showed negative responses to N deposition with reductions in the probability of presence as N deposition increased. In all of the habitats, there were a mix of terricolous taxa which showed negative or no significant relationship with N deposition. Most of the taxa with negative relationships with N deposition started to decline in prevalence at the lowest levels of deposition found in this study. Levels of deposition over which a negative response apparently occurs are lower than those at which critical loads have been set for some habitats. These findings suggest that some terricolous lichen taxa are sensitive to atmospheric N deposition and even low levels of nitrogen deposition could be damaging terricolous lichen communities making then potentially good indicators of N deposition

Parasitic plants indirectly regulate below-ground properties in grassland ecosystems

Parasitic plants are one of the most ubiquitous groups of generalist parasites in both natural and managed ecosystems, with over 3,000 known species worldwide1, 2, 3. Although much is known about how parasitic plants influence host peformance1, 2, 3, 4, their role as drivers of community- and ecosystem-level properties remains largely unexplored5. Parasitic plants have the potential to influence directly the productivity and structure of plant communities because they cause harm to particular host plants, indirectly increasing the competitive status of non-host species6, 7, 8, 9, 10. Such parasite-driven above-ground effects might also have important indirect consequences through altering the quantity and quality of resources that enter soil, thereby affecting the activity of decomposer organisms3, 11, 12, 13. Here we show in model grassland communities that the parasitic plant Rhinanthus minor, which occurs widely throughout Europe and North America14, has strong direct effects on above-ground community properties, increasing plant diversity and reducing productivity. We also show that these direct effects of R. minor on the plant community have marked indirect effects on below-ground properties, ultimately increasing rates of nitrogen cycling. Our study provides evidence that parasitic plants act as a major driver of both above-ground and below-ground properties of grassland ecosystems

Air pollution and its effects on lichens, bryophytes, and lichen-feeding Lepidoptera: review and evidence from biological records

Changing air quality has been one of the most important drivers of change for bryophytes and lichens in Britain and Ireland over the 20th Century, with acidic pollutants such as sulphur dioxide having large effects on the ranges and abundances of many species. At the same time, expert amateur and professional naturalists have put enormous efforts into recording the distributions of species within these groups. These efforts have provided much evidence for declines and recoveries within the bryophytes and lichens, with species distribution data being linked to airborne pollutants in many different ways. We provide a broad overview of some of the changes that have occurred in affected species, using biological records collected by national recording schemes to illustrate the various effects of air pollution; we also review the direct and indirect impacts of air pollutants on these groups. Environmental change affecting one group of species is also likely to cascade to other groups where trophic or other relationships exist between them. Using data from the volunteer-based National Moth Recording Scheme, we provide the first evidence for an indirect association between reductions in air pollution and increases in lichenivorous moths