Knowledge of the direct role humans have had in changing the landscape requires the perspective of historical and archaeological sources, as well as climatic and ecologic processes, when interpreting paleoecological records. People directly impact land at the local scale and land use decisions are strongly influenced by local sociopolitical priorities that change through time. A complete picture of the potential drivers of past environmental change must include a detailed and integrated analysis of evolving sociopolitical priorities, climatic change and ecological processes. However, there are surprisingly few localities that possess high-quality historical, archeological and high-resolution paleoecologic datasets. We present a high resolution 2700-year pollen record from central Italy and interpret it in relation to archival documents and archaeological data to reconstruct the relationship between changing sociopolitical conditions, and their effect on the landscape. We found that: (1) abrupt environmental change was more closely linked to sociopolitical and demographic transformation than climate change; (2) landscape changes reflected the new sociopolitical priorities and persisted until the sociopolitical conditions shifted; (3) reorganization of new plant communities was very rapid, on the order of decades not centuries; and (4) legacies of forest management adopted by earlier societies continue to influence ecosystem services today.

The influence of Native American land-use practices on vegetation composition and structure has long been a subject of significant debate. This is particularly true in portions of the western United States where tribal hunter-gatherers did not use agriculture to meet subsistence and other cultural needs. Climate has been viewed as the dominant determinant of vegetation structure and composition change over time, but ethnographic and anthropological evidence suggests that Native American land-use practices (particularly through the use of fire) had significant landscape effects on vegetation. However, it is difficult to distinguish climatically driven vegetation change from human-caused vegetation change using traditional paleoecological methods. To address this problem, we use a multidisciplinary methodology that incorporates paleoecology with local ethnographic and archaeological information at two lake sites in northwestern California. We show that anthropogenic impacts can be distinguished at our Fish Lake site during the cool and wet ‘Little Ice Age’, when we have evidence for open-forest or shade-intolerant vegetation, fostered for subsistence and cultural purposes, rather than the closed-forest or shade-tolerant vegetation expected due to the climatic shift. We also see a strong anthropogenic influence on modern vegetation at both sites following European settlement, decline in tribal use, and subsequent fire exclusion. These results demonstrate that Native American influences on vegetation structure and composition can be distinguished using methods that take into account both physical and cultural aspects of the landscape. They also begin to determine the scale at which western forests were influenced by Native American land-use practices and how modern forests of northwestern California are not solely products of climate alone.

The ability to evaluate accurately the response of the environment to climate change ideally involves long‐term continuous in situ measurements of climate and landscape processes. This is the goal of the Nevada Climate‐Ecohydrology Assessment Network (NevCAN), a novel system of permanent monitoring stations located across elevational and latitudinal gradients within the Great Basin hydrographic region (Figure 1). NevCAN was designed, first, to quantify the daily, seasonal, and interannual variability in climate that occurs from basin valleys to mountain tops of the Great Basin in the arid southwest of the United States; second, to relate the temporal patterns of ecohydrologic response to climate occurring within each of the major ecosystems that compose the Great Basin; and, last, to monitor changes in climate that modulate water availability, sequestration of carbon, and conservation of biological diversity.

Ethnographic accounts document widespread use of low-intensity surface fires by California's Native Americans to manage terrestrial resources, yet the effects of such practices on forest composition and structure remain largely unknown. Although numerous paleoenvironmental studies debate whether proxy interpretations indicate climatic or anthropogenic drivers of landscape change, available data sources (e.g., pollen, charcoal) are generally insufficient to resolve anthropogenic impacts and do not allow for hypothesis testing. We use a modeling approach with LANDIS-II, a spatially explicit forest succession and disturbance model, to test whether the addition of Native American–set surface fires was necessary to approximate vegetation change as reconstructed from fossil pollen. We use an existing 1,600-year pollen and charcoal record from Holey Meadow, Sequoia National Forest, California, as the empirical data set to which we compared modeled results of climatic and anthropogenic fire regimes. We found that the addition of anthropogenic burning best approximated fossil pollen–reconstructed vegetation change, particularly during periods of prolonged cooler, wetter periods coinciding with greater regional Native American activity (1550–1050 and 750–100 cal yr BP). For lightning-caused wildfires to statistically approximate the pollen record required at least twenty times more ignitions and 870 percent more area burned annually during the Little Ice Age (750–100 cal yr BP) than observed during the modern period (AD 1985–2006), a level of natural fire increase we consider highly improbable. These results demonstrate that (1) anthropogenic burning was likely an important cause of pre-Columbian forest structure at the site and (2) dynamic landscape models provide a valuable method for testing hypotheses of paleoenvironmental change.

Climatic variations of the last few millennia can reveal patterns of variability beyond that recorded by the instrumental record. In this study we use pollen and sediments to generate a high resolution 3000 year record of vegetation and climate along the southern California coast. An increase in Pinus and Quercus pollen found in the top 100 years of the record is a result of known planting and fire suppression by the forest service. In the pre-historic record, a period of high Salix percentages and high pollen concentration from 500-250 cal yr BP represents the wettest period of the record and coincides with the Little Ice Age. We also find evidence for 3 warm periods between 1350 and 650 cal yr BP which are identified in the record by the presence of Pediastrum boryanum var. boryanum. The latter two of these periods, dating from 1070-900 and 700–650 cal yr BP correspond to Medieval Climatic Anomaly droughts identified in other records. In addition to these events, we identify a multi-centennial scale drought between 2700 and 2000 cal yr BP in Zaca Lake, corroborating evidence from across the Great Basin and extending the regional spread of this multi-centennial drought to southern California. Corresponding wetter conditions in the northwest indicate that the modern ENSO precipitation dipole also occurred during this persistent drought. Today this dipole is associated with La Niña conditions and we note a coincidence with intriguing evidence for a change in ENSO dynamics from marine records in the tropical Pacific. This dry period is remarkably persistent and has important implications for understanding the possible durations of drought conditions in the past in California.