A statistical approach to decompose ecological variation

As indicators of pollutant deposition, epiphytic algae on Norway spruce needles and lichens on Scots pine trunks were monitored at 15 sites over Sweden for 4 and 12 years, respectively. Pollutant deposition was measured simultaneously. The algae and lichens were strongly correlated to three groups of environmental factors namely geographical position, climate and pollutant deposition. Use of partial Redundancy Analysis (RDA) showed that the major part, 67%, of the total explained variation of algae was the joint effect of the three environmental factor groups. Climatic factors alone and the joint effects of S and N deposition and climate make up 13% and 12%, respectively. Pure geography and deposition accounted for less than 5% each. Also with lichens the main variation, 41%, was due to the joint effect of the three groups whereas 27% was due to pure geography and 14% to pure climate. Deposition alone and the joint effect of deposition and climate made up 5% and less. It suggests that the algae were mainly influenced by climate and deposition, and the lichens by climate and geographic position.