2019 saw the release of five papers first-authored by TPRG members, three of them led by Heather and one each by Maca and me. In an ideal world each could be explored in its own dedicated blog post, as with this one on Maca’s paper, but as time is constantly getting away from me I’m afraid these brief summaries will have to do! You can find the full and updated list of TPRG publications here.
In this paper, Heather, Bronwen and Frank compare the sensitivity of pollen and phytoliths to changes in evergreen forest, dry forest and savanna ecosystems in southwestern Amazonia. Using data from ecological plots, they set thresholds for changes in each proxy which differentiate compositional change from ecosystem turnover. While both proxies are equally sensitive to changes in savanna, pollen is more sensitive in evergreen forest and phytoliths in dry forest. Applying these thresholds to fossil pollen records, as the authors do twice here, can help assess the magnitude of past vegetational changes in the region.
In their second paper, Heather, Frank and Bronwen look at what phytoliths in lakes can tell us. Comparing them with pollen records shows (as above) that the two complement each other well, but no work had previously examined how lake phytolith assemblages relate to potential source vegetation. This paper finds that phytoliths in lakes come from more local vegetation than pollen assemblages do (ie they have a smaller catchment area), and that phytolith assemblages are therefore more variable within a given lake. These findings suggest that combining phytolith and pollen studies from the same sedimentary archive could give multi-scale insights into an area’s past vegetation change.
The third in the Heather-Frank-Bronwen triptych, this paper examines 10,000 years of vegetation change from Laguna Mandioré, in the Bolivian Chiquitano dry forest. This study site is near the previously studied Laguna La Gaiba, allowing the spatial scale of changes to be approximated. The multiproxy evidence finds that, during the mid-Holocene dry period, upland savanna expanded downhill at the expense of dry forest, defying its modern edaphic constraints. However, away from the ecotone the dry forest maintained its canopy, albeit with compositional changes towards more drought-tolerant trees – a relevant finding for conservation in the face of 21st-Century climate changes.
With Débora and Alexander from Brazil’s Federal University of Blumenau, Frank, Richard and I looked to predict what impact 21st-Century climate change will have on Brazil’s iconic Araucaria tree. Specifically, we were looking for potential microrefugia – small areas where topographic features might retain suitable conditions amid wider climatic changes. We were also interested in how 20th-Century habitat losses might interact with climate-caused range reductions. We found that the coming decades will loosen Araucaria’s grip on its present strongholds; microrefugia will play an important role in the species’ persistence, but 37% have already lost their natural vegetation and very few are found in protected areas. I wrote a summary of the article for The Conversation, which led to a fair amount of interest in the Brazilian media – you can see some examples here.