LAUSR

In PNAS, Nanavati et al. (1) study the available highresolution pollen and microcharcoal columns for the last 1,000 y along a latitudinal transect in Patagonia. The result is a serious effort to understand the degree of alteration of landscapes by the human use of fire and the introduction of nonnative plants. It is well accepted that Native American land use altered landscapes since before the arrival of Europeans, but this paper adds an articulation with relevant historical and archaeological information. Even when this evidence is not perfect, the presentation of the main cultural processes after European contact is useful, since it is the time when human influences are evident and relatively easier to track. I will concentrate my comment on the historical and archaeological evidence used to discuss some of the patterns, as well as the chronological problems exhibited by archaeological information for the last 500 y. It must be noted that, while the earliest human presence in South Patagonia altered the distribution of tool stones and affected the fauna, it produced no evident impact on the plants. Ephemeral occupations, followed by abandonment and reoccupation thousands of years later, inform about nomadic peoples with large annual ranges. The use of fire certainly was within their toolkits, as demonstrated by hearths found at most early sites, but their low-intensity occupations failed to produce detectable impact on the environment. Nanavati et al. (1) show that the human imprint on the landscapes is not always evident, and—more important—is not exclusively dependent on population size. What population increase does is to augment the number of localities where pertinent information can be searched. In that sense, more interesting than the wider range of taxa exploited by foragers during the Late Holocene is the wider range of habitats that they occupied. This is true even though retreat from the high elevations was recorded near El Sosneado during the Late Holocene and there was a sharp demographic decrease that started during the 18th century CE—particularly in North Patagonia—as a result of the European contact. The point is that human dispersal and the existence of webs of contact through which foragers were connected along different habitats, ranging from the oceanic coasts to the Andean high mountains, are probably the main cause of the swift dispersal of nonnative plants, and this is a result that does not require full settlement, but simply circulation of people.