Anthropogenic impactsClimate change: 1961-2004 Temperature Average 1°C rise since 1961 Precipitation 60% increase in winter rainfall Snowfall 30% reduction in days with snow cover
Alpine vegetation is exposed to multiple drivers of change… How has biodiversity responded over the last 40 years?
Birse and Robertson Survey 700+ plots recorded 1960-1980 205 plots resurveyed 2004-6 Range of typical alpine communities Recorded species composition & sward structure
Overall change: plot scale Mean species richness Plot-level diversity increased from 16 to 19 (Shannon) has declined 25 2.0 *** *** Mean Shannon Index HMean species richness 20 1.5 15 1.0 10 0.5 5 0 0.0 old new Old New
Overall change: landscape scale New sill is significantly lower (P<0.001) Spatial turnover of composition reduced – more homogeneous Old data New data
Habitat specific changes Richness change differs between 4 Mean change in species richness higher plants and Highers Bryos bryophytes 3 Higher plants increase most in 2 snowbed and springs, no change 1 in fell field 0 Bryophytes increase most in fell field, he ath eath eath l field wbed rings land land land s h na ium rium h l Fe Sno Sp rass ras grass decline in tall Juncus llu in Ca acc comi t G sG s du cu V a un Nar grassland R J
Species trendsWinners: Losers: Middle altitude, widespread High altitude, northern species species
How do observed changes compare with experimental studies?
Driver responses – Higher plants Survey finding: increased 40 35 Mean shoot extension (mm) Calluna cover 30 Experimental response: 25 20 Positive response to 0 kg N 10 kg N both N addition and 15 20 kg N 50 kg N warming 10 1998 2000 2002 2004 2006 2008 2010 Increased shoot Year growth 45 OTCs installed -OTC Increased flowering 40 +OTC Mean shoot extension (mm) 35 No change in species 30 composition (after 10 25 20 years) 15 10 1998 2000 2002 2004 2006 2008 2010 Year
Driver responses - lichens Survey finding: decreased lichen cover 10 Experimental response: 8 Lichen species richness rapid decline in cover and 6 richness with N addition 4 Sensitive to low loads & 2 concentrations 0 0 kg 10 kg 20 kg 50 kg Lichen abundance also N addition (kg N ha-1 y-1) related to sward height – indirect effect of climate and/or grazing
Conclusions UK alpine habitats are changing Species of sub-alpine habitats are expanding while alpine specialists decline Nature of change is habitat specific Experimental studies show that multiple drivers can contribute to observed changes Future studies: avoid considering single drivers in isolation
Acknowledgements Scottish Government & DEFRA for fundingJulia Fisher, Dave Riach and Heather Armitage for help with field work Thank YOU for listening