The Role Of Ground Type, Moisture And Temperature On The Vertical Growth Of Lichens: A Test Of Hypotheses With Paramo Lichens

There is little reliable information about determinants of vertical growth in terricolous lichens, traditionally divided into short "crustose", intermediate "foliose" and tall "fruticose" growth forms, a practice that artificially hides a growth continuum. Substrate, temperature and especially water are thought to affect, but such factors are hard to measure, because, for example, the water actually available to lichens does not match rainfall patterns or even over ground levels. To reliably assess the effect of those factors, I recorded the temperature, moisture and substrate in and under individual lichen colonies in 415 fixed PVC frame quadrats (Cerro de la Muerte, Costa Rica, 9°33'N; 83°45'W), on April, August, October and December of 2015. The measurements are more reliable because they were taken inside the colonies themselves (rather than on the general environment), because they covered hundreds of cases during a year, and because they are from the relatively simple paramo habitat, where animals or vegetation have less impact on lichens than in lower ecosystems. The hypotheses were that lichens would grow taller on softer, warmer and moister ground, on the moister Caribbean versant and on the moister part of the year. Results matched the hypotheses, with one exception: lichens on soft ground were not taller than those on rock. Caribbean colonies were, on the average, 7 cm taller than those on the drier Pacific versant. Foliose, fruticose and crustose lichens were equally frequent as dominant in the quadrats. Crustose species, together with their bacterial and microinvertebrate communities, with suffer the most with global warming.