Predicting Pleistocene climate from vegetation in North America

Abstract

Abstract. Climates at the Last Glacial Maximum have been inferred from fossil pollen assemblages, but these inferred climates are colder for eastern North America than those produced by climate simulations. It has been suggested that low CO 2 levels could account for this discrepancy. In this study biogeographic evidence is used to test the CO 2 effect model. The recolonization of glaciated zones in eastern North America following the last ice age produced distinct biogeographic patterns. It has been assumed that a wide zone south of the ice was tundra or boreal parkland (Boreal-Parkland Zone or BPZ), which would have been recolonized from southern refugia as the ice melted, but the patterns in this zone differ from those in the glaciated zone, which creates a major biogeographic anomaly. In the glacial zone, there are few endemics but in the BPZ there are many across multiple taxa. In the glacial zone, there are the expected gradients of genetic diversity with distance from the ice-free zone, but no evidence of this is found in the BPZ. Many races and related species exist in the BPZ which would have merged or hybridized if confined to the same refugia. Evidence for distinct southern refugia for most temperate species is lacking. Extinctions of temperate flora were rare. The interpretation of spruce as a boreal climate indicator may be mistaken over much of the region if the spruce was actually an extinct temperate species. All of these anomalies call into question the concept that climates in the zone south of the ice were extremely cold or that temperate species had to migrate far to the south. An alternate hypothesis is that low CO 2 levels gave an advantage to pine and spruce, which are the dominant trees in the BPZ, and to herbaceous species over trees, which also fits the observed pattern. Thus climate reconstruction from pollen data is probably biased and needs to incorporate CO 2 effects. Most temperate species could have survived across their current ranges at lower abundance by retreating to moist microsites. These would be microrefugia not easily detected by pollen records, especially if most species became rare. These results mean that climate reconstructions based on terrestrial plant indicators will not be valid for periods with markedly different CO 2 levels.

Ecological Drivers of Species Distributions and Niche Overlap for Three Subterranean Termite Species in the Southern Appalachian Mountains, USA

“…Our analyses predicted extensive co-occurrence of all three Reticulitermes species in the mid-latitudes of the southern Appalachians (Figure 2; Figures S4 and S5). Based on paleoclimatic [59], biogeographic [60] and comparative phylogeographic [61] data, the southern Appalachians remained free from Pleistocene ice sheets and served as a major refuge for many species during glacial periods, consequently maintaining higher levels of biodiversity. Indeed, the present-day complexity of this mid-latitude region harbors many different niches, which could facilitate long-term coexistence of closely related species.…”

A multi‐proxy palaeoecological and palaeoclimatic record within full glacial lacustrine deposits, western Tennessee, USA

“…11). One potential complication is that reduced atmospheric CO 2 concentrations during the LGM may have favoured spruce and other conifers over deciduous genera, thus creating a slight northern bias in modern analogues (Jackson et al, 2000;Loehle, 2007). Additionally, some of the Picea spp.…”

Conservation genetics of Magnolia acuminata, an endangered species in Canada: Can genetic diversity be maintained in fragmented, peripheral populations?

“…The Great Lakes region of North America is home to many of these peripheral or disjunct populations, which colonized the region following the retreat of the last glacial maximum (Hewitt 2004;Ehlers and Gibbard 2008). Prior to this colonization, the Southern Appalachians provided potential glacial refugia for numerous species that now inhabit the Great Lakes region, although the numbers and locations of refugia, the recolonization routes, and hence the dispersal of genetic diversity into this region, are generally not well known (Austin et al 2002;Waldron 1993;Flannery 2003;Church et al 2003;Hewitt 2004;Loehle 2007). Genetic diversity of peripheral plant populations around the Great Lakes has been assessed in a small number of species, and in some cases was found to be low relative to core populations (Hamilton and Eckert 2007;Row et al 2011;Paul et al 2013), although this is not inevitable (Freeland et al 2010).…”