Higher taxa as paleoecological and paleoclimatic indicators: A search for the modern analog of the Florissant fossil flora

We used higher taxonomic composition of 241 modern forest plots from across the New World to identify the closest modern analog of the Florissant fossil flora and to infer late Eocene paleotemperature for Florissant. Nonmetric multidimensional scaling (NMS) based on both genus and family presence-absence placed Florissant in a no-analog taxonomic space surrounded by North American warm temperate broad-leaved forests, Mexican humid pine-oak forests, and subtropical moist forests from Florida, Mexico, and Argentina. The site most similar to Florissant, as indicated by the mean of Euclidean distances in genus and family NMS space, was a subtropical moist forest in southern Florida, followed by the humid pine-oak forests of central and northeastern Mexico, and the broad-leaved deciduous forests of eastern North America. Weighted-averaging partial least-squares regression (WAPLS) based on genus composition predicted a mean annual temperature (MAT) for Florissant of 14.7 ± 2.2 °C. WAPLS based on family composition predicted a MAT of 15.6 ± 2.5 °C. Our estimates fall between the relatively cool temperatures predicted by leaf physiognomy and the higher temperatures predicted by the nearest living relative method. Although this study demonstrates the feasibility of using higher taxa for paleoclimate reconstruction and analog analysis, its methods are subject to many of the same biases and assumptions as other biological proxy techniques. Furthermore, interpreta-tion of differences between results obtained using different taxonomic levels remains unclear. Some of these limitations may be resolved by employing methods based on phylogenies rather than taxonomic ranks.