Artículo de publicación ISIThe significance and cause of the decline in biomass burning across the Americas after ad 1500 is a topic of considerable debate. We synthesized charcoal records (a proxy for biomass burning) from the Americas and from the remainder of the globe over the past 2000 years, and compared these with paleoclimatic records and population reconstructions. A distinct post-ad 1500 decrease in biomass burning is evident, not only in the Americas, but also globally, and both are similar in duration and timing to ‘Little Ice Age’ climate change. There is temporal and spatial variability in the expression of the biomass-burning decline across the Americas but, at a regional–continental scale, ‘Little Ice Age’ climate change was likely more important than indigenous population collapse in driving this decline

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[1] Humified soil organic matter storage in boreal forests is large, and its responses to warming over relatively long timescales is critical for predicting soil feedbacks to climate change. To derive information relevant across decades to centuries from manipulative short-term experiments, we conducted incubations of soils from two forested sites along the Newfoundland-Labrador Boreal Ecosystem Latitude Transect in eastern Canada and assessed linkages between incubation data and these sites' profile characteristics. The sites differ in mean annual temperature by 3.4C, but vegetation and soil types are similar. Organic soils (Oe + Oa) were incubated for 120 days at 15 C and 20 C, with and without a replaced Oi subhorizon possessing a distinct d 13 C signature. Laboratory warming induced significantly greater mineralization and leaching of humified SOM relative to replaced Oi, congruent with greater warming-induced increases in phenol oxidase activity relative to enzymes associated with labile C acquisition (percent increases of 101% versus 50%, respectively). These data suggest that warming can influence microbial communities and their enzymatic dynamics such that relative losses of humified SOM are disproportionately enhanced. This is consistent with stable isotopic, C:N, and radiocarbon profile differences between the two sites, which suggest a greater degree of microbial processing and greater relative losses of older SOC over the preceding decades at the warmer site, given our knowledge of organic inputs in these soils. This study is a first step toward linking the divergent timescales represented by soil profiles and laboratory manipulations, an important goal for biogeochemists assessing climate change impacts on SOM dynamics.Citation: Li, J., S. Ziegler, C. S. Lane, and S. A. Billings (2012), Warming-enhanced preferential microbial mineralization of humified boreal forest soil organic matter: Interpretation of soil profiles along a climate transect using laboratory incubations,

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