January 20, 2023

Research Roundup | Jan. 20

Nebraska Sandhills
Craig Chandler | University Communication and Marketing

Craig Chandler | University Communication and Marketing
A view of the Sandhills near Whitman, Nebraska.

Welcome to the Research Roundup: a collection of highlights from the latest Husker research and creative activity.

Minimally invasive?

Ecologists have historically classified certain regions as too arid to allow encroachment by the eastern redcedar tree, an invasive species that has already overtaken much of the southern Great Plains. One region considered more or less immune to invasion? The relatively dry western portion of the Nebraska Sandhills, which often averages fewer than 20 inches of precipitation per year — generally believed the minimum needed to support the tree’s spread.

As detailed in the Journal of Vegetation Science, Husker researchers Dillon Fogarty, Dirac Twidwell and Craig Allen set out to test that conventional wisdom. Supplemented by satellite imagery, the trio sampled 40 tracts of the Sandhills that received anywhere between 15.7 and 25.8 inches of precipitation, recording the presence and dispersal of eastern redcedar in the process.

Fogarty, Twidwell and Allen found no evidence that the supposed precipitation threshold prevented the establishment of eastern redcedar, as the invasive tree peppered even the most arid of the 40 tracts. Of the roughly 270,000 adult specimens counted by the team, nearly 47,000 were growing on land that received fewer than 20 inches of annual precipitation. Though the actual density of encroachment did vary some with precipitation, the mere presence and proximity of planted, seed-bearing trees accounted for a good deal of that encroachment.

The fact that eastern redcedar can grow and spread in semi-arid grasslands should inform future conservation practices, the researchers said. Planting stands of eastern redcedar as shelterbelts, which do help guard against windstorms and erosion, should be undertaken with care. And even dry tracts should be monitored for potential encroachment, the team said.

Lakeshore drive

Sherilyn Fritz, George Holmes University Professor of Earth and atmospheric sciences, partnered with colleagues from Europe, South America and North America on a recent study published in Proceedings of the National Academy of Sciences. The team’s focus: Lake Titicaca, situated on the border of Bolivia and Peru in the central Andes.

Using measurements of carbon atoms in sediment samples extracted from the lake, Fritz and the team refined estimates of the lake’s depth over the past 4,200 years, a period that also saw the rise and fall of multiple civilizations in its vicinity. Though in decent agreement with prior studies, the team’s estimates suggest that the lake’s level climbed and receded more gradually than once thought — a pattern more consistent with fluctuations seen over the past century.

But when the waters of Lake Titicaca did rise, societal developments arose in turn. The largest recorded rise in water level, around 500 CE, coincided with the emergence of the Tiwanaku civilization, which came to preside over several neighboring peoples by about 600 CE. Titicaca’s advancing shoreline ultimately flooded those adjacent civilizations, sparing only the Tiwanaku capital of Tiahuanaco, which was located farther inland. That flooding likely drove migrations to Tiahuanaco, the researchers said, driving up its population and, ultimately, its sociopolitical power.

If you have a published study that you would like to see featured in Nebraska Today’s Research Roundup, contact Scott Schrage at sschrage2@unl.edu.

Dillon Fogarty
Dirac Twidwell
Craig Allen
Sherilyn Fritz