Browsing by Subject "TROPICAL RAIN-FOREST"

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  • Stam, Åsa; He, Xiaolan; Kaasalainen, Ulla; Toivonen, Mikko Evert; Enroth, Johannes; Räsänen, Matti; Rikkinen, Jouko (2020)
    The dispersal ecology of tropical non-vascular epiphytes has rarely been experimentally investigated. We studied epiphyte colonisation on 1 × 1 m polyethene nets placed for four years at seven sites at different elevations in montane forests in the Taita Hills, Kenya. During the first year the nets were also used to measure fog deposition. We predicted that differences in growth conditions would affect colonisation and subsequent growth of non-vascular epiphytes and result in clear differences in epiphyte cover and biomass, and community composition among sites. After four years the nets were taken down for determination of epiphyte cover and biomass. The diversity of established liverworts and macrolichens was also examined. Many liverwort and macrolichen species established diverse communities on the nets placed in the moist upper-montane zone. This was in contrast with the situation in the drier lower-montane zone where only green algae and crustose lichens were able to colonise most nets. Light intensity was an important determinant of epiphyte community composition, with liverworts dominating on nets under closed forest canopies and lichens dominating at more open sites. Atmospheric moisture was also important, with lichens benefiting from abundant fog deposition at open and windy sites. The dry weight of epiphytes (per unit area) on lichen-dominated nets was greater than on liverwort-dominated nets, while the highest cover was generally observed on liverwort-dominated nets. Our results demonstrate that polyethylene nets can be effectively used to study colonisation of non-vascular epiphytes as well as the abiotic and biotic factors controlling epiphyte colonisation and community composition in tropical forests. The liverworts Acanthocoleus chrysophyllus and Diplasiolejeunea kraussiana were new additions to the Kenyan bryophyte flora.
  • Hellen, Heidi; Praplan, Arnaud P.; Tykkä, Toni; Ylivinkka, Ilona; Vakkari, Ville; Bäck, Jaana; Petäjä, Tuukka; Kulmala, Markku; Hakola, Hannele (2018)
    The concentrations of terpenoids (isoprene; monoterpenes, MTs; and sesquiterpenes, SQTs) and oxygenated volatile organic compounds (OVOCs; i.e. aldehydes, alcohols, acetates and volatile organic acids, VOAs) were investigated during 2 years at a boreal forest site in Hyytiala, Finland, using in situ gas chromatograph mass spectrometers (GC-MSs). Seasonal and diurnal variations of terpenoid and OVOC concentrations as well as their relationship with meteorological factors were studied. Of the VOCs examined, C-2-C-7 unbranched VOAs showed the highest concentrations, mainly due to their low reactivity. Of the terpenoids, MTs showed the highest concentrations at the site, but seven different highly reactive SQTs were also detected. The monthly and daily mean concentrations of most terpenoids, aldehydes and VOAs were highly dependent on the temperature. The highest exponential correlation with temperature was found for a SQT (beta-caryophyllene) in summer. The diurnal variations in the concentrations could be explained by sources, sinks and vertical mixing. The diurnal variations in MT concentrations were strongly affected by vertical mixing. Based on the temperature correlations and mixing layer height (MLH), simple proxies were developed for estimating the MT and SQT concentrations. To estimate the importance of different compound groups and compounds in local atmospheric chemistry, reactivity with main oxidants (hydroxyl radical, OH; nitrate radical, NO3; and ozone, O-3) and production rates of oxidation products (OxPRs) were calculated. The MTs dominated OH and NO3 radical chemistry, but the SQTs greatly impacted O-3 chemistry, even though the concentrations of SQT were 30 times lower than the MT concentrations. SQTs were also the most important for the production of oxidation products. Since the SQTs show high secondary organic aerosol (SOA) yields, the results clearly indicate the importance of SQTs for local SOA production.
  • Durand, Maxime; Matule, Baiba; Burgess, Alexandra J.; Robson, T. Matthew (2021)
    Light in canopies is highly dynamic since the strength and composition of incoming radiation is determined by the wind and the Sun's trajectory and by canopy structure. For this highly dynamic environment, we mathematically defined sunflecks as periods of high irradiance relative to the background light environment. They can account for a large proportion of the light available for photosynthesis. Based on high-frequency irradiance measurements with a CCD array spectroradiometer, we investigated how the frequency of measurement affects what we define as sunflecks. Do different plant canopies produce sunflecks with different properties? How does the spectral composition and strength of irradiance in the shade vary during a sunfleck? Our results suggest that high-frequency measurements improved our description of light fluctuations and led to the detection of shorter, more frequent and intense sunflecks. We found that shorter wind-induced sunflecks contribute most of the irradiance attributable to sunflecks, contrary to previous reports from both forests and crops. Large variations in sunfleck properties related to canopy depth and species, including distinct spectral composition under shade and sunflecks, suggest that mapping canopy structural traits may help us model photosynthesis dynamically.