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Himalayan forests are biodiverse and support the cultural and economic livelihoods of their human communities. They are bounded to the south by the Indo-Gangetic Plain, which has among the highest concentrations of atmospheric ammonia globally. This source of excess nitrogen pushes northwards into the Himalaya, generating concern that Himalayan forests will be impacted. To estimate the extent to which atmospheric nitrogen is impacting Himalayan forests we focussed on lichen epiphytes, which are a well-established bioindicator for atmospheric nitrogen pollution. First, we reviewed published literature describing nitrogen thresholds (critical levels and loads) at which lichen epiphytes are affected, identifying a mean and confidence intervals based on previous research conducted across a diverse set of biogeographic and ecological settings. Second, we used estimates from previously published atmospheric chemistry models (EMEP-WRF and UKCA-CLASSIC) projected to the Himalaya with contrasting spatial resolution and timescales to characterise model variability. Comparing the lichen epiphyte critical levels and loads with the atmospheric chemistry model projections, we created preliminary estimates of the extent to which Himalayan forests are impacted by excess nitrogen; this equated to c. 80–85% and c. 95–98% with respect to ammonia and total nitrogen deposition, respectively. Recognising that lichens are one of the most sensitive bioindicators for atmospheric nitrogen pollution, our new synthesis of previous studies on this topic generated concern that most Himalayan forests are at risk from excess nitrogen. This is a desk-based study that now requires verification through biological surveillance, for which we provide key recommendations.

Executive summary • This report presents the work carried out during the 2nd year of the project (June 2009-June 2010). We report on the current status of the project, present provisional analysed data (using currently available data) and outline the work plan for July 2010 - May 2011. • Twenty-eight out of the original planned 29 regional sites have been fully surveyed. The one remaining site (Halladale) has been excluded due to ongoing access permission difficulties. • All outstanding identifications (lichens and bryophytes) will be completed by end of June 2010. • Bark and branch pH’s will be completed by end of June 2010. • As only 19 of the 28 regional sites had current NH3 monitoring, 9 additional sites were set up in August 2009 at sites without current NH3 monitoring. These additional sites will be monitored until August 2010 and are operated by local conservation and regulatory agency staff. • Using combined tree species (Quercus and Betula) data, lichen species richness was found to be greater for branches compared to trunks. • Eighty-six microlichen, 67 macrolichen and 11 bryophytes and liverworts species have been identified from the 21 regional sites examined to date. • Bryophyte species richness (1-2 species) was significantly lower than that found for epiphytic lichens on both trunks and branches. • There were significant differences (p<0.001) in species richness for both micro and macrolichens between the trunks and branches. The combined mean species richness for trunks was 17 compared to 27 for branches. • For both Betula and Quercus, at least 5 trunks and 5 branches are required to be assessed at a site to give an accurate estimate of total species richness. • Greater species richness was found in the 6-10 and 11+ age classes compared to the 1-5 age class. • Mean species richness for Betula was found to be slightly greater for microlichens compared to macrolichens, whereas in Quercus the opposite was found. • There were strong logarithmic relation

Udgivelsesdato: March 2009, Two surveys of the lichen and bryophyte flora growing on oak twigs from a Welsh and a Danish locality were compared with additional data on bark pH and % nitrogen in thalli of Hypogymnia physodes. Despite differences in climate and lichen flora, both sites showed a shift in the lichen communities from nitrogen sensitive (nitrophobe) to nitrogen tolerant (nitrophile) species, which was correlated with both increasing bark pH and an increase in total nitrogen in thalli of H. physodes. The floristic survey from Wales was a repetition of a study eight years earlier (Wolseley & Pryor 1999) now showing a loss of nitrophobes in all sites and the appearance of nitrophiles in pasture sites in 2003. This study demonstrates that lichens on twigs can be used as an early warning system to detect a response to changes in land management and nitrogen deposition.