ECR Feature: William Nanavati on monkey-puzzle trees and global change

William “Buzz” Nanavati is a postdoc at Portland State University. He is a palaeoecologist and biogeographer, interested in how environmental changes through time affect ecosystems. William shares his recent work on previous climates and land-use change on the dynamics of monkey-puzzle forests in Patagonian.

William “Buzz” Nanavati, a monkey-puzzle tree, and a canine companion (Eddy Nanavati).

Personal links. Web page | Twitter

Institute. Global Environmental Change Lab, Department of Geography, Portland State University

Academic life stage. National Science Foundation Postdoctoral Fellow

Research themes. I focus on palaeoecology, biogeography, and the nonlinear, interacting relationships between fire, climate, humans and the environment through time.

Current study system. My current research focuses on the environmental histories of two regions: the forest-steppe ecotone of Patagonia, Argentina and Chile, and forests of the western Cascade Mountain Range in Pacific Northwest of the United States of America. Forest-grassland transitions (or ecotones) in temperate latitudes are regions that are sensitive to natural (i.e., climate-driven) and anthropogenic pressures and are thus valuable for understanding ecosystem dynamics under changing climate and disturbance regimes. In these biomes, forest is typically promoted by high levels of moisture and/or low fire activity, whereas in drier settings, grassland is maintained by seasonal or annual moisture deficits and/or high levels of burning.

Recent paper in JBI. Nanavati, William, Cathy Whitlock, Valeria Outes, and Gustavo Villarosa. “A Holocene history of monkey puzzle tree (pehuén) in northernmost Patagonia.” Journal of Biogeography (2020).

A pollen grain of Araucaria araucana.

Motivation behind this paper. In our recent paper, we try to provide a better understanding how changes in climate and land use have altered monkey-puzzle tree (pehuén; Araucaria araucana) forest ecosystem dynamics through time. We believe that by better understanding such complexities in socioecological history, we can better interpret management goals in the face of future disturbance and climate change. Recognizing the Patagonian forest-steppe ecotone as a mosaic of nearly-pristine and humanized landscapes can provide a pragmatic guide for land management strategies and intensities, where natural processes can be left to play out in nearly-pristine landscapes, while active management of humanized landscapes can either restore ecosystems to nearly-pristine states or preserve cultural landscapes, dependent on the decisions of stakeholders and community members. As land use increases throughout Patagonia and anthropogenic global warming changes climate conditions at an alarming rate, we believe that combined paleoecological-archaeological efforts can help inform projections of future ecosystem dynamics and guide management decisions to protect native ecosystems.

This picture was taken near the Laguna Portezuelo paleoecological site in northwestern Neuquén, Argentina. It features an open monkey-puzzle (pehuénAraucaria araucana) forest at its northeasternmost border with grass (Poaceae) steppe. Antarctic beech (ñireNothofagus antarctica) is in the foreground and the Copahue stratovolcano is in the background.

Key methodologies. Sedimentary pollen and charcoal from Laguna Portezuelo (37.9°S, 71.0°W; 1730 m elevation; 11,100 cal yr BP bottom date) were compared with other paleoecological, independent paleoclimate, and historical records to assess how changes in climate and land use influenced local-to-regional environmental history. An important aspect about this study is its reliance on high-resolution pollen and charcoal counting that facilitates nearly decadal interpretation of change in local vegetation and fire history for the last 1000 years. By focusing our analyses at such a high resolution, it made it much easier for us to compare our results with historical and dendroecological research from the region.  

Major results. Araucaria was present in the central valley of Chile during the last glaciation until rapid postglacial warming and drying limited its distribution in the valley. In the middle and late Holocene, decreased temperatures and greater seasonality and El Niño-Southern Oscillation activity increased precipitation variability allowing Araucaria expansion at its north-eastern limit, near Laguna Portezuelo. Greater abundance of Araucaria and heightened fire activity at Laguna Portezuelo after about 440 years ago coincided with increased Mapuche-Pehuenche American Indian land use, suggesting that Araucaria may have been managed in a human-altered landscape. Our results suggest that past American Indian land use likely altered natural ecosystem dynamics at local-to-landscape spatial scales in northernmost Patagonia. Variations in human land-use intensity and location in the late Holocene likely created a mosaic of landscapes that ranged from the nearly pristine to highly altered prior to European arrival.

Unexpected outcomes. There were two unexpected results that came out of this study: (1) Araucaria migrated into the Laguna Portezuelo watershed relativity recently, with sporadic presence between from 6500 to 440 years ago, when its presence increased coincident with increased fire activity and an influx of Mapuche peoples east of the Andes. We attribute the arrival and expansion of Araucaria in the Laguna Portezuelo watershed to wetter-than-before middle- and late-Holocene conditions and, possibly, American Indian management. (2) Non-native, Eurasian taxa likely arrived in the Laguna Portezuelo watershed prior to Euro-American settlement, this supports the hypothesis that the spread of non-native plants outpaced Euro-American settlement in the Patagonian forest-steppe ecotone.

This photo depicts the dry, shrub-steppe that dominates east of the forest-steppe ecotone in Patagonia, near Tecka, Chubut, Argentina.

Next steps. We intend to compare changes in postglacial vegetative composition and fire activity with simulations of ecosystem dynamics. These comparisons could determine where and when the vegetation and fire history of individual sites does not match simulated climate-fuel-fire relationships. Anomalous events recorded in the paleoecological data could be compared with the archaeological record to determine if land use explains the deviation from the model and if so, to what extent land use altered ecosystem dynamics. Furthermore, following model validation through data-model comparison, we hope to co-develop model simulation scenarios with local land managers and community members to inform land management decisions in Araucaria forest ecosystems.

If you could study any organism on Earth, what would it be? I would probably pick the most confusing one of them all: humans! I am specifically interested in how we interact and coevolve with our environments. Humans had and will continue to have an incredible imprint on the environment. Hopefully by better understanding linkages between climate, humans, vegetation, and fire, we can help inform management and policy decisions that lead to a more sustainable future.

Published by jbiogeography

Contributing to the growth and societal relevance of the discipline of biogeography through dissemination of biogeographical research.

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