Autochthonous leaf assemblages as records of deciduous forest communities: an actualistic study



How well do autochthonous leaf assemblages reflect live plant communities? How do leaf assemblages accumulating over different time scales compare in paleoecologic information content? Forest-floor leaf assemblages accumulating over ten-day intervals (referred to here as short-term assemblages) and over a five-month season of leaf abscission (referred to here as a long-term assemblage) were compared with the surrounding community in a modern temperate deciduous forest in northern Ohio. Leaf number in the long-term leaf assemblage is strongly correlated with the abundance of taxa (stem number) around the accumulation site and weakly correlated with both average taxon size (stem circumference) and average taxon distance from the accumulation site. Of the variance in leaf number, 45% is explained solely by stem number and 67% by stem number and average distance together. Average size explains an insignificant amount of the variance in leaf number. Like the long-term assemblage, leaf number in the short-term leaf assemblages is usually strongly correlated with stem number and usually weakly correlated with average taxon size and average taxon distance. However, these patterns are not consistent, and the correlations are highly variable. Similarly, there is high variability in the degree to which stem number, average taxon size and average taxon distance account for variance in leaf number. Short-term leaf assemblages are characterized by great fluctuations in taxonomic relative abundance, caused by seasonal variation in the timing and rate of leaf abscission among taxa. While autochthonous leaf assemblages accumulating over several months can reflect the surrounding community with fair accuracy, leaf assemblages accumulating over shorter time spans are inconsistent records of the surrounding community. The depositional circumstances producing short-term assemblages (i.e. event burial) may result in well-preserved specimens, but community data from such assemblages should be treated with caution and, if possible, compared with data from contemporaneous long-term assemblages.Paleobotany, taphonomy, actualism, paleocommunity reconstruction, time-averaging.

Keith H. Meldahl, Damon Scott and Karen Carney, Department of Geology, Oberlin College, Oberlin, Ohio, 44074, USA; 6th June, 1994; revised 8th February, 1995.