Costa Rica figures in study to adjust fossil and ecological data

Benjamin Blonder photo
Brad Boyle, the research associate who led the time, is up a
tree in the Río Savegre watershed.

Costa Rica figured in a major scientific advance that is overturning the conception experts have of past climates.

The finding is the degree that leaves shrink when they dry, something no one had documented previously.

A University of Arizona graduate student and a university research lab undertook this first systematic study of how much plant leaves shrink when they dry out, said the Tucson institution. The results are published in the November issue of the American Journal of Botany, a top publication in the botanical sciences, the university said. Also involved in the study were about 40 middle school students.

The doctoral student is Benjamin Blonder.

“Our simple observation that leaves shrink when they dry out has very important consequences for our understanding how ecosystems work,” said Blonder, a student in the university’s department of ecology and evolutionary biology. “Many studies in ecology, especially reconstructions of past climate, depend on knowing how big leaves are. By relying on measurements of dried leaves, a very large number of climate and ecology studies may have obtained biased conclusions.”

When leaves dry out, they shrink about 20 percent on average, the team discovered, said the university. In the most extreme case, the leaves of the mountain meadow-rue (Thalictrum fendleri), an herb from the Rocky Mountains, shriveled down to one-fifth of the original size, it added.

Blonder said in an email that he was part of a study team from the university that made a month-long expedition to forests on the Pacific slope of Costa Rica. A research associate at the university, Brad Boyle, led the team. Brian Enquist, an associate professor and Blonder’s dissertation adviser, also was on the expedition.

“”We made systematic surveys of tree diversity in undisturbed areas near the Río Savegre drainage,” said Blonder. They worked from almost sea level at Parque Nacional Manuel Antonio to treeline at Cerro de la Muerte, he said, adding that the team was interested in how species diversity and function, for example, the shrinkage, changed with climate,

“Our fieldwork involves hiking to remote areas with surveying equipment and plant collecting materials, such as long metal poles for trimming leaves, spikes for tree climbing, plant presses, measuring tapes.”

The Instituto Nacional de Biodiversidad in Heredia supported the work here, he said. Surveys also were done in Hawaii and Colorado.

When scientists reconstruct climate and precipitation in the past to figure out whether an area was subjected to droughts or whether it was wet, they often turn to fossilized leaves, Blonder said. The specific area of a leaf in relation to its mass also is a very useful parameter in predicting how much carbon a plant can capture from the atmosphere, he added, said the university in a summary of the work.

If leaves undergo dramatic changes in size during fossilization, the conclusions are likely to be off, he noted, adding that the same effect would be expected when researchers use dried leaves from museum collections for their calculations.

An unusual aspect of the research is that students in the sixth through eighth grade at a local middle school were involved. Almost half of the participating students completed the necessary prerequisites and assignments to qualify as co-authors on the scientific paper that resulted from the study, said the university.

“At the beginning, we thought there would be a very simple explanation,” Blonder said in a university report. “But it turned out that we ended up with many variables that determine the amount of shrinkage in a leaf of a given species. We used data from hundreds of species, yet there is no simple answer.”

The group did find that the amount of structural investment a plant puts into its leaves is a crucial factor determining how much a leaf will shrink when it dries out, according to the study.
“The more mass and tissue the plant invests into its leaves in terms of components that provide mechanical strength, the less shrinkage will occur,” Blonder was quoted as saying.

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