Aptroot, A., van Herk, C. M. & Sparrius, L. B. 2017. Twenty-two years of monitoring the lichen flora of megalithic monuments in the Netherlands. – Herzogia 30: 483–495.
Over the past 22 years, the lichen flora of 54megalithic monuments in The Netherlands has been monitored. In 2010, they harboured 133 lichen species. In 1988, 1993, 2000, 2005 and 2010, the lichen flora of all granite monuments were re-examined. Between 1988 and 2010 the number of lichen species per monument increased, especially those that grow normally as epiphytes and nitrophytes or have a southern distribution. Typical species of acidic rock decreased, together with other acidophytic epiphytes, lignicolous and terricolous species. The main driver for the observed changes is the increase in tree cover above and around the monuments. Changes in epiphytic lichen composition largely reflect changes in acid deposition, eutrophication and climate.