Epiphyte diversity and microclimate of the tropical lowland cloud forest in French Guiana
by Christine Gehrig-Downie née Gehrig
Date of Examination:2013-05-30
Date of issue:2013-11-06
Advisor:Prof. Dr. Robbert Gradstein
Referee:Prof. Dr. Robbert Gradstein
Referee:Prof. Dr. Michael Kessler
Referee:Prof. Dr. Erwin Bergmeier
Referee:Prof. Dr. Hermann Behling
Referee:Prof. Dr. Holger Kreft
Persistent Address:
http://dx.doi.org/10.53846/goediss-4101
Files in this item
Name:GehrigDownie_DissertationXX.pdf
Size:1.86Mb
Format:PDF
The following license files are associated with this item:
Abstract
English
Lowland cloud forests are well known from temperate regions, e.g. the coasts of California and northern Chile (Bruijnzeel 2001), but in the Tropics have remained uninvestigated. We tested the hypothesis that tropical lowland cloud forest (LCF) and lowland rain forest (LRF) exist as distinct forest types with a higher abundance of epiphytes in LCF and differing in epiphyte species composition and microclimate. Furthermore, these forest types seem to occur in close proximity to one another, with LCF in valleys and LRF on adjacent slopes. To validate this hypothesis, we compared epiphyte diversity and abundance at two localities in Central French Guiana (Saül, Nouragues Nature Reserve). Using the single rope technique (ter Steege & Cornelissen 1988), we climbed 48 canopy trees from putative LCF and LRF during a 6 month field trip to French Guiana. On each of the 48 target trees, we removed epiphytes growing in 24 sample plots of 600 cm². The plots were positioned at each cardinal direction in six height zones (Johansson 1974, Cornelissen & ter Steege 1989): trunk base, lower trunk, upper trunk, lower canopy, middle canopy, and outer canopy. Biomass of epiphytic angiosperms, pteridophytes, lichens and bryophytes was determined and three groups of epiphytic plants identified at species level: macrolichens, filmy ferns and liverworts. Trees were classified as belonging either to LCF or LRF based on geography and validated by microclimate measurements. Species were identified using appropriate methods for the different taxa, and overall forest species composition evaluated for each forest type and statistically compared. In total we found 39 (morpho-) species of macrolichens, 9 species of Hymenophyllaceae, and 129 liverwort species. LCF contained a significantly higher mean species number per tree for both liverworts (LCF: 33.6; LRF: 25.0) and Hymenophyllaceae (LCF: 2.4; LRF: 0.3) than LRF. Moreover, 8 species of Hymenophyllaceae and 21 of liverworts were statistically determined as indicator species for LCF. These indicators of LCF included shade epiphytes and generalists that also occur in montane forests. As LCF is more humid than LRF, the differences in liverwort and filmy fern diversity can be attributed to the greater atmospheric water content. Although the number of macrolichen species per tree was similar in both forest types, lichens with cyanobacterial photobionts (cyanolichens) were 2.5 times more common in LCF. Cyanolichens are known to prefer humid habitats and this study showed that they are good indicators for LCF. The observed differences in species diversity of liverworts, filmy ferns and cyanolichens support the hypothesis that LCF and LRF contain distinguishable epiphytic biodiversity, a finding which is further supported by the measurement of higher overall epiphyte biomass in LCF and more tree surface area covered by epiphytes (70 % in LCF, 15 % in LRF). Species composition differed greatly in all height zones for all studied groups of epiphytes. Hygrophilous taxa (shade epiphytes) were more common in LCF, while LRF harbored more xeric taxa (outer canopy specialists). Moreover, comparison of the vertical distribution of epiphyte species in LRF and LCF showed an upward shift of certain species of lichens, bryophytes and ferns inhabiting lower strata in LRF towards higher strata in LCF. It had been previously observed that morning fog was present in LCF of Saül (Montfoort & Ek 1990). Fog can lead to higher humidity by providing a surplus of liquid water. To investigate whether there was an increased incidence of fog in LCF over LRF, we measured air humidity, calculated vapor pressure deficit, and frequency and duration of fog. LCF plots were more humid than LRF plots during both wet and dry season. LCF experienced higher overall mean air humidity, while high humidity events occurred both more frequently and longer than in LRF. The overall higher humidity is caused by fog formation in LCF at night; at early morning the moist air lifts into the canopy and acts as a radiation shield. Vapor pressure deficit in LCF was calculated to be lower than in LRF, especially in the early morning and significantly longer in duration. The prolonged availability of high air humidity in LCF and the additional input of liquid water through fog enhance epiphyte growth and influence species composition and diversity in LCF by shortening the desiccation period and lengthening the period of photosynthetic activity of the plants.
Keywords: epiphytes; Hymenophyllaceae; filmy ferns; macrolichens; liverworts; microclimate; tropical lowland cloud forest; tropical lowland rain forest; biomass; fog; diversity; French Guiana
