A TEMPERATE FOREST'S REFLECTION IN LEAF LITTER: IMPLICATIONS FOR INTERPRETING PALEOECOLOGY FROM FOSSIL LEAF ASSEMBLAGES

A pressing issue in paleoecology is the question of how accurately fossil assemblages reflect the living community from which they are produced. In this study we examined leaf litter in a temperate deciduous forest in Pennsylvania to assess its fidelity in representing the woody vegetation that produces it. The life cycle of a deciduous leaf includes its growth and use on a tree, its abscission, and its decomposition on the forest floor. Taphonomic biases may accumulate through these stages and can alter how well the leaf litter reflects the living forest ecosystem.

We made collections over two consecutive years from a 9 m² plot within the same mature tree stand near Belfast, PA (MAT = ~11 C , MAP = ~150 cm). In 2008-09, collections were made bi-weekly throughout the fall and winter and in 2009-10 a solitary collection was made after complete leaf fall. These two collection methods allowed us to investigate differences between two sampling protocols; (1) leaves collected soon after abscission and (2) litter that had time for degradation in early humus forming processes. Overall results for both collection protocols indicate that, at year’s end, leaf abundance in the litter is less strongly correlated with stem number than it is with wooded area (stem number * x-sectional area at BH); a factor that should be considered when interpreting fossil leaf assemblages. We also note that published leaf decay constants (k) of 0.3 to 2.5 for temperate forests suggest that litter half-lives could alter the relative taxon composition in the litter over the abscission season. Also, because leaf release for different species peaked differentially throughout the abscission period, the potential fossil record of a floodplain forest may vary depending on the timing of a sedimentation event that includes the litter already accumulated that year on the forest floor. As expected, insect damage, detritivore activity, and necrolysis/decomposition on leaves was greater for the end-of-the-year collection than for biweekly assemblages collected throughout the fall. This pattern varied by taxon however, as most species exhibited about twice the total damage if let sit on the forest floor as compared to frequent collection, while others, such as Acer rubrum, showed just as much overall damage upon initial fall as they did after extended time in the litter.