Bryan G. Valencia

Millennial-Scale Ecological Changes in Tropical South America Since the Last Glacial Maximum

An analysis of rates of ecological change (RoC) from thirteen pollen records from tropical South America is presented here. The analysis aims to identify the periods of fastest change since the last glacial maximum (LGM) and possible driving mechanisms. Despite rapid cooling periods, region-wide profound droughts, fire and human disturbances, RoC analysis showed that the speed of these climate changes never exceed the species response capabilities. Our results legitimize concerns regarding the resilience of species to accommodate future change and emphasize the urgency for integrative environmental measures.

Anthropogenic control of late-Holocene landscapes in the Cuzco region, Peru

The rise of complex Andean cultures is tied to increasingly sophisticated use of natural resources and infrastructural development. Considerable debate surrounds the extent to which these societies were forced to respond to changing climates or whether their modifications to the landscape minimized climate impacts. Here, we present a region-wide perspective of paleoecological changes around Cuzco, Peru using three lake sediment records. We investigate whether vegetation shifts in the three records occurred simultaneously, and explore whether such changes were due to climatic conditions or human activities, or both. A new paleoecological record from Lake Huaypo reveals a transition from Amaranthaceae (i.e. quinoa) cultivars to maize at c. 2800 cal. yr BP. This agricultural change is also documented at two other Andean lakes: Marcacocha (Chepstow-Lusty A (2011) Agro-pastoralism and social change in the Cuzco heartland of Peru: A brief history using environmental proxies. Antiquity 85: 570–582) and Pacucha (Valencia BG, Urrego DH, Silman MR et al. (2010) From ice age to modern: A record of landscape change in an Andean cloud forest. Journal of Biogeography 37: 1637–1647). Wetter climatic conditions are inferred to be a leading cause behind the change from Amaranthaceae to maize cultivation. At 1300 cal. yr BP, a rapid increase in Andean forest pollen types, especially Alnus, is observed at Huaypo, with similar changes occurring at Marcacocha at c. 1000 cal. yr BP and at Pacucha at c. 500 cal. yr BP. Drier paleoclimatic conditions at the time and the importance of Alnus, a species well-known for its ability to grow quickly and its widespread use for fuel and timber, suggest that the expansion was due partly to agroforestry. The Huaypo paleoecological record reveals that the practice of agroforestry first began during the Wari Period, and then continued through the Late Intermediate Period and period of Incan rule.

Automated pollen identification system for forensic geo-historical location applications

The use of pollen grain analysis for forensic geo-historical location has been explored for several decades, yet it is not widely adopted in the United States. We confirmed significant improvement in geographic precision, i.e., from 2.5×107 to 1.2×105 km2, by simultaneously applying flowering plant data from four different taxa at the genus and species levels. Moreover, when we calculated precision using collected pollen data, we found that co-occurring, pairwise genus-level distinctions based on expert-provided indicator taxa resulted in average precision values of 4° and 4.5° in latitude and longitude, respectively - corresponding to roughly 1.8×105 km2. We also applied computer vision techniques to identify morphologically similar pollen grains, which resulted in grain-identification error rates of 2.18% and 6.24% at the genus and species levels, respectively, surpassing previously published records. Collectively, our results demonstrate that algorithmic identification of species-specific pollen morphology, founded on established computer vision techniques, when combined with species-level pollen distribution, has the potential to revolutionize the scope, accuracy, and precision of forensic geographic attribution.

A 2000-year history of disturbance and recovery at a sacred site in Peru’s northeastern cloud forest

The last 2000 years in the tropical Andes was both a time of major pre-Hispanic and Hispanic period cultural developments, and increased climate variability. From c. AD 1000, Andean societies underwent significant transformation and many sites previously integrated under imperial Wari hegemony were abandoned. It has been argued that this sociopolitical reorganization was, in part, a response to the heightened climate variability of the late-Holocene. Here, we present a 2000-year diatom record from the cloud forest setting of Laguna de los Condores, in the Peruvian Andes. Cliff tombs overlooking the lake and a nearby abandoned village form one of the most important archaeological complexes in the Peruvian Chachapoyas region. The presence of diatoms that indicate high productivity (e.g. Planothidium frequentissimum and Amphora pediculus) from as early as 2000 cal. yr BP suggest the lake was impacted by human activity predating the construction of monumental architecture and the regional Chachapoya cultural identity. The diatom fauna is consistent with sediment geochemical evidence that suggests high terrigenous input during the same period that would indicate that the surrounding catchment was disturbed. After c. AD 900 (1050 cal. yr BP), the diatom assemblage becomes dominated by species more indicative of a less productive system, coincident with a declining sedimentation rate, and a decrease in total biogenic silica: conditions that persist to modern times. The transition from a lake with high productivity receiving high erosional input to a less productive more stable system is contemporaneous with an increase in archaeologically documented mortuary and settlement activity. This period of declining terrigenous input is at odds with regional climate, which suggests a wetter than average period. Our data suggest the occupants of Laguna de los Condores changed their land use practices, as the region became wetter, and, in so doing, reduced erosion around the lake.