Browsing by Subject "LIMITS"

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    Quantification of Peat Thickness and Stored Carbon at the Landscape Scale in Tropical Peatlands: A Comparison of Airborne Geophysics and an Empirical Topographic Method
    (Journal of Geophysical Research: Earth Surface, 2019-12-01) Silvestri, S; Knight, R; Viezzoli, A; Richardson, CJ; Anshari, GZ; Dewar, N; Flanagan, N; Comas, X
    ©2019. The Authors. Peatlands play a key role in the global carbon cycle, sequestering and releasing large amounts of carbon. Despite their importance, a reliable method for the quantification of peatland thickness and volume is still missing, particularly for peat deposits located in the tropics given their limited accessibility, and for scales of measurement representative of peatland environments (i.e., of hundreds of km2). This limitation also prevents the accurate quantification of the stored carbon as well as future greenhouse gas emissions due to ongoing peat degradation. Here we present the results obtained using the airborne electromagnetic (AEM) method, a geophysical surveying tool, for peat thickness detection at the landscape scale. Based on a large amount of data collected on an Indonesian peatland, our results show that the AEM method provides a reliable and accurate 3-D model of peatlands, allowing the quantification of their volume and carbon storage. A comparison with the often used empirical topographic approach, which is based on an assumed correlation between peat thickness and surface topography, revealed larger errors across the landscape associated with the empirical approach than the AEM method when predicting the peat thickness. As a result, the AEM method provides higher estimates (22%) of organic carbon pools than the empirical method. We show how in our case study the empirical method tends to underestimate the peat thickness due to its inability to accurately detect the large variability in the elevation of the peat/mineral substrate interface, which is better quantified by the AEM method.
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    rbcL phylogeny of the fern genus Trichomanes (Hymenophyllaceae), with special reference to Neotropical taxa
    (International Journal of Plant Sciences, 2003-01-01) Dubuisson, JY; Hennequin, S; Douzery, EJP; Cranfill, RB; Smith, AR; Pryer, KM
    In order to estimate evolutionary relationships within the filmy fern genus Trichomanes (Hymenophyllaceae), we performed a phylogenetic analysis using rbcL nucleotide data from 46 species of Trichomanes belonging to all four of C. V. Morton's subgenera: Achomanes, Didymoglossum, Pachychaetum, and Trichomanes. Outgroups included four species of Hymenophyllum in three different subgenera, plus the monotypic genus Cardiomanes, from New Zealand. We find high resolution and robust support at most nodes, regardless of the phylogenetic optimization criterion used (maximum parsimony or maximum likelihood). Two species belonging to Morton's Asiatic sections Callistopteris and Cephalomanes are in unresolved basal positions within Trichomanes s.l., suggesting that rbcL data alone are inadequate for estimating the earliest cladogenetic events. Out of the four Morton trichomanoid subgenera, only subg. Didymoglossum appears monophyletic. Other noteworthy results include the following: (1) lianescent sect. Lacostea is more closely related to sect. Davalliopsis (traditionally placed in subg. Pachychaetum) than to other members of subg. Achomanes; (2) sections Davalliopsis and Lacostea, together with species of the morphologically different subg. Achomanes, make up a strongly supported Neotropical clade; (3) all hemiepiphytes (but not true lianas) and strictly epiphytic or epipetric species (Morton's subgenera Trichomanes and Didymoglossum) group together in an ecologically definable clade that also includes the terrestrial sect. Nesopteris; and (4) sect. Lacosteopsis (sensu Morton) is polyphyletic and comprises two distantly related clades: large hemiepiphytic climbers and small strictly epiphytic/epipetric taxa. Each of these associations is somewhat unexpected but is supported by cytological, geographical, and/or ecological evidence. We conclude that many morphological characters traditionally used for delimiting groups within Trichomanes are, in part, plesiomorphic or homoplastic. Additionally, we discuss probable multiple origins of Neotropical Trichomanes.