TAPHONOMIC STUDY OF TROPICAL FOREST LEAF LITTER FROM QUEENSLAND, AUSTRALIA AND IMPLICATIONS FOR THE INTERPRETATION OF FOSSIL LEAF LITTER

To better understand the taphonomic biases inherent in leaf litter, a two-year study of modern leaf litter was conducted along Noah Creek, in the Cape York Peninsula rainforest in Queensland, Australia (16.15°S, 145.45°E). A total of 20,417 specimens were evaluated, representing 354 identified species. Three methods were used to collect the leaf litter: 11 autochthonous samples were collected by placing a 1m2 frame on the ground and gathering all the leaves that were at least 1/3 complete that lay on the forest floor within the frame; 4 autochthonous samples were collected by elevating ¼ m2 leaf traps 1 m above the forest floor and gathering the contents for 12 consecutive months; and 17 allochthonous samples were collected by “grabbing” leaves from the bottom of creeks, rivers and a pond. Each leaf was identified and the margin type and leaf area were recorded, enabling calculation of diversity, mean annual temperature (MAT), and mean annual precipitation (MAP). The allochthonous samples were more diverse than the autochthonous samples with rarefied richness (at 300 specimens) ranging from 44-60 in the stream versus 6-24 on the forest floor and 19-25 in the aerial litter traps. The most diverse sample was located at the mouth of the river.

In addition, the trees > 5 cm dbh (diameter at breast height) were mapped and identified in a 0.5 hectare forest plot, and the basal area and tree height were documented. Fifteen of the 33 litter samples were located within this forest plot. A total of 526 trees were mapped representing 87 species and 36 families. A comparison of the number of leaves collected from the aerial litter traps (3,179 / m2 over 12 months) versus the number of leaves in the forest floor samples (average of 600 / m2) indicates that on average, the leaf litter in this rainforest biodegrades within 2-3 months. The spatial heterogeneity patterns, MAT and MAP estimates, and species lists from the autochthonous and allochthonous samples within the mapped forest were compared to document how the amount of transportation biased the interpretations of source forest composition and climate. Finally, the results of this study were applied to several Colorado fossil rainforest localities which were reinterpreted based on their relative location in the landscape and their inferred depositional environments.