Robert A. Gastaldo

Department of Geology

Auburn University, AL 36849-5305

Although recent empirical studies have demonstrated that a variable proportion of leaves from canopy and subcanopy taxa are incorporated into forest-floor litters, a cautionary note has been sounded concerning the fidelity of such autochthonous/parautochthonous assemblages. This assertion was developed from a data set collected in a north-temperate forest where sequential leaf litters were collected from the forest floor during the autumnal and winter months. At the time of each collection, all leaves were removed from the study site, leaving a barren forest floor upon which newly dehisced leaves were allowed to collect over the following ten-days. Each leaf collection was assessed individually and all collections were combined to evaluate differences in "short-term" and "long-term" assemblages. "Short-term" assemblages were considered to vary temporally in relative taxonomic abundance, and it was concluded that such assemblages found in the fossil record should be treated as suspect requiring caution when using these in any analysis.

Does any natural system follow this paradigm? For a natural system to parallel this interpretation, not only would accumulation would have to be synchronous but the half-life of discarded leaves would have to be very short (on the order of days) in order to "sweep clean" the forest floor. Decomposition is influenced by a number of factors including macroclimate, microclimate, soil bacteria, soil nutrients, substrate piece size and leaf quality. Decomposition rate standardization is based around the calculation of the decay constant (k), expressed as the amount of decay/year. An evaluation of published leaf-litter half lives from arctic to tropical climates indicates wide variability: k=0.18-0.09 in subalpine, montane and high-latitude forests (144-322 weeks); k=2.46-0.3 in temperate forests (11-90 weeks); k=7.5-0.5 in tropical forests (4-60 weeks). Faster decay rate s have not been reported. Hence, the proposal that "short-term" assemblages should be treated with caution is an artifact of interpretation because no natural forest system presently, and presumably in the past, experiences complete loss of accumulated leaf litters within two-week periods. All such assemblages are time-averaged, providing a reliable data set from which paleoclimate analyzes can be made.

Citation: Geological Society of America, Abstracts with Program V. 29(6):A420.

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