Inferences about winter temperatures and summer rains from the late Quaternary record of C₄ perennial grasses and C₃ desert shrubs in the northern Chihuahuan Desert

Abstract

Late Quaternary histories of two North American desert biomes-C 4 grasslands and C 3 shrublands-are poorly known despite their sensitivity and potential value in reconstructing summer rains and winter temperatures. Plant macrofossil assemblages from packrat midden series in the northern Chihuahuan Desert show that C 4 grasses and annuals typical of desert grassland persisted near their present northern limits throughout the last glacialinterglacial cycle. By contrast, key C 3 desert shrubs appeared somewhat abruptly after 5000 cal yr B.P. Bioclimatic envelopes for select C 4 and C 3 species are mapped to interpret the glacialinterglacial persistence of desert grassland and the mid-to-late Holocene expansion of desert shrublands. The envelopes suggest relatively warm Pleistocene temperatures with moist summers allowed for persistence of C 4 grasses, whereas winters were probably too cold (or too wet) for C 3 desert shrubs. Contrary to climate model results, core processes associated with the

Isotopic paleoecology of Clovis mammoths from Arizona

“…Clovis mammoths had consistent seasonal dietary patterns over a period of some years: Peak C 4 grass consumption occurred during summer, and fewer C 4 grasses were consumed during winter. This study provides direct evidence for the presence of C 4 grasslands that "greened up" during summer, as proposed by Holmgren et al (13). We suggest that mammoths in the SPV sought the greenest portions of the landscape, as do modern elephants (47).…”

“…Clovis Mammoth Behavior and Extinction. During the Clovis period, evidence for C 4 grasses in the SPV riparian corridor is lacking, but C 4 grasses probably grew on the bajada and nearby hillsides (9,12,13,17). We propose that Clovis mammoths sought new C 4 plant growth farther from the river during the summer rainy season and remained closer to the river, foraging on mixed C 3 -C 4 plants, during the winter.…”

“…Large pluvial lakes were surrounded by hillsides covered with pinyon-juniper woodlands and rich understories of C 3 shrubs, C 4 annuals, and C 4 grasses (11,12); springs and shallow ponds were supported by a high water table (10); and a C 4 grassland stretched from southern Arizona to central Texas (12)(13)(14)(15)(16)(17). A warm and arid period began around 13,000 14 C yBP (15,000 cal BP), culminating in a severe drought that coincided with mammoth extinction and Clovis occupation of the SPV (10,900 14 C yBP or 12,800 cal BP) (18).…”

“…Since the last glacial-interglacial transition, precipitation in the region has occurred primarily in winter and summer (13,20). However, little else is known about seasonality in the Late Pleistocene SPV or how it affected mammoth ecology.…”

Ecology and the ratchet of events: Climate variability, niche dimensions, and species distributions

“…However, in many regions this transition was probably accompanied by an increase in length of the growing season (Fig. 2), fostering northward expansion of phenologically sensitive species during a period of cooling summers (49). Growing-degree days or other heat sums might also have decreased, depending on the extent of midsummer daytime temperature decrease.…”