Lichen herbaria may offer unique opportunities to assess changes in lichen biodiversity over time. Here we present the results of a case study on changes in the lichen flora of Guadeloupe since the 1960s based on the massive and largely unexamined lichen collections of father Casimir Le Gallo (1906–1976) held in the Cryptogamic Herbarium (PC) of the National History Museum of Paris. Le Gallo made hundreds of foliicolous lichen collections in Guadeloupe during 1955–1968 with remarkably precise information, including aerial photographs of collecting localities. In each locality he collected up to 20-100 leaves from about 12 different tree species. Sixty years after Le Gallo, the diversity of foliicolous lichens in low altitude areas of Guadeloupe has been re-evaluated. Le Gallo's lichen samples have been identified and selected collecting localities were revisited and inventoried (for the same tree species). These included swamp forests and seasonally dry tropical forest remnants, all below 50 m of altitude. We found stability of foliicolous lichen community composition during sixty years in some forest fragments and a complete turn-over in others. The results revealed unexpectedly high lichen diversity at these low elevations. The herbarium data and recent collections yielded 103 foliicolous lichen species including 31 new to Guadeloupe and possibly 6 new to science. To the best of our knowledge, this is the first study to examine temporal changes in the composition of foliicolous lichen communities in the tropics. Funding: This study was financed by DGD REVE - Museum National d’Histoire Naturelle (MNHN - France) as part of ATM.
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