Abstract booklet - gtö – Society for Tropical Ecology

60 PARALLEL SESSION | H IV | RAIN FOREST STRUCTURE & DYNAMICSPARALLEL SESSION | H IV | RAIN FOREST STRUCTURE & DYNAMICS 61THE ROLE OF FOG IN THE SPATIAL DISTRIBUTION OF A NEW TROPI-CAL LOWLAND FOREST TYPELONG TERM DYNAMICS OF AN EPIPHYTE COMMUNITY IN A LOW-LAND RAINFOREST IN PANAMAAndre Obregon 1 , Christine Gehrig-Downie 2 , S. Robbert Gradstein 3 , JörgBendix 1Glenda Mendieta-Leiva1, G. Wagner 1 , K & G. Zotz 11 University of Oldenburg, Department of Functional Ecology, Oldenburg, DE, glen-1 University of Marburg, Marburg, DE, obregon@staff.uni-marburg.de, 2 University ofGöttingen, Göttingen, DE, 3 Muséum National d’Histoire Naturelle, Paris, FRdamendieta@gmail.comTUESDAY 11:45 Hall H IVFog occurrence is extensively studied in the outer Tropics and in tropical montanecloud forests, but investigations of the spatio-temporal distribution of fogin tropical lowland forests are virtually lacking. We studied the meteorologicalprocesses leading to fog formation in central French Guiana by installing a climatestation directly above the forest canopy (45 m above ground). Horizontalvisibility (and thus fog occurrence) was observed by using a visibility sensor.Our studies provide detailed evidence of frequent occurrence of radiation fogin lowland valleys. Comparable high fog frequencies are only reported from tropicalmontane cloud forests. The main trigger of fog development in the lowlandforest seemed to be precipitation, leading to higher soil moisture, greaterevapotranspiration and, thus, higher water content of air.The frequent occurrence of fog in the valleys correlated with significantly higherepiphyte diversities in valley forests as compared to hill forests, and supportedthe occurrence of the hitherto undescribed, epiphyte-rich “tropical lowlandcloud forest” (LCF) in the valleys. The higher epiphyte diversity in LCF coincidedwith significantly higher relative air humidity than in hill forest. The ecologicalbenefits of fog for the epiphytes in LCF are surplus of moisture and delayedonset of the stress period, particularly in the dry season.The spatial extent of fog, and hence the propable distribution of LCF, was analyzedby means of night-time AVHRR and MODIS satellite data using an algorithmrelying on brightness temperature differences between the long-wave and mediuminfrared bands. The output of the fog detection scheme was validatedagainst horizontal visibility data from the ground station. The results indicatea widespread distribution of night and morning fog in river valleys throughoutFrench Guiana. It must be assumed that fog is not an azonal phenomenon butcould be widely distributed throughout the lowland tropics, with significantconsequences for vegetation.Epiphyte community dynamics differs greatly from that of trees, but is associatedand influenced in turn by the growth and mortality of the latter. The natureof this interaction changes with scale from individual tree, to the local populationof a tree species to all trees in a local patch of forest. Here, we followthe structure and dynamics of all epiphytes on all trees of a particular host treespecies, the palm Socratea exorrhiza, in ca. 1 ha of lowland rainforest in Panamaover a period of 10 years.The first census in 1999 yielded 99 palm trees, of which 59% held epiphytes.This percentage increased to 74% in 2010, although the total number of palmsdecreased to 89 trees. Both the number of epiphyte species and individuals increasedwith time; from 59 to 64 and 756 to 1839, respectively. These numbersconceal considerable fluctuation: on average, only about 50% of the speciespresent in one census were also found during the subsequent census. Such variationcould be linked to the changes in relative abundance, while rare specieswere comparably the same and occurred with a similarly low frequency in time;some of the most abundant species gradually switched their abundance rank.Overall diversity was maintained, with a rather high rate of replacement, especiallyof fast growing species; whereas overall abundance increased by morethan twofold. In conclusion, whilst there is variation in the relative abundanceof individuals and diversity in time, the structure of the entirely epiphyte communityremains rather stable. A future expansion of the study, through inclusionof different host treespecies, will enable the possibilityof further analysis ata larger spatial scale.TUESDAY 12:00 Hall H IVgtöSociety for Tropical Ecology | Gesellschaft für Tropenökologie e.V. Status and future of tropical biodiversity | Frankfurt, 21 - 24 February 2011gtö