Migrating trees

Below is the abstract and FIU NEWS article by  about the new article that colleagues and I recently published in the Proceedings of the National Academy of Sciences USA, entitled “Thermophilization of adult and juvenile tree communities in the northern tropical Andes“.

Thermophilization of adult and juvenile tree communities in the northern tropical Andes. by Alvaro Duque, Pablo R. Stevenson, and Kenneth J. Feeley

Abstract. Climate change is expected to cause shifts in the composition of tropical montane forests towards increased relative abundances of species whose ranges were previously centered at lower, hotter elevations. To investigate this process of “thermophilization,” we analyzed patterns of compositional change over the last decade using recensus data from a network of 16 adult and juvenile tree plots in the tropical forests of northern Andes Mountains and adjacent lowlands in northwestern Colombia. Analyses show evidence that tree species composition is strongly linked to temperature and that composition is changing directionally through time, potentially in response to climate change and increasing temperatures. Mean rates of thermophilization [thermal migration rate (TMR), °C⋅y−1] across all censuses were 0.011 °C⋅y−1 (95% confidence interval = 0.002–0.022 °C⋅y−1) for adult trees and 0.027 °C⋅y−1 (95% confidence interval = 0.009–0.050 °C⋅y−1) for juvenile trees. The fact that thermophilization is occurring in both the adult and juvenile trees and at rates consistent with concurrent warming supports the hypothesis that the observed compositional changes are part of a long-term process, such as global warming, and are not a response to any single episodic event. The observed changes in composition were driven primarily by patterns of tree mortality, indicating that the changes in composition are mostly via range retractions, rather than range shifts or expansions. These results all indicate that tropical forests are being strongly affected by climate change and suggest that many species will be at elevated risk for extinction as warming continues.

Migrating Amazonian trees are a cause for concern
by Evelyn Perez

Tropical forests in the Andes Mountains are changing in the face of climate change.

A new study published in PNAS reveals the number of highland tree species is decreasing as a result of lowland tree species moving upslope along South America’s longest mountain chain in response to rising temperatures and changing rainfall patterns. Instead of shifting to different locations, the highland trees are retracting, or dying back. The results suggest tropical tree species in the Andes are at risk of extinction with ongoing warming.

“The effects of climate change are everywhere – you can’t escape it,” said Kenneth J. Feeley, a researcher in FIU’s Department of Biological Sciences and International Center for Tropical Botany (ICTB). “Some people hold the notion that the Amazon is an isolated and pristine ecosystem, immune to disturbances. We need to change our mindset and open our eyes to the fact that even in the middle of the Amazon or the remote Andes Mountains, species are at risk. Tropical forests, and the thousands of rare or endemic species they support, are highly sensitive to changes in climate and that they are perhaps some of the most threatened ecosystems of all. Climate change is pervasive and dangerous.”

Feeley, who has studied the ecology, biogeography and conservation of tropical plant and animal communities for more than 15 years, is the corresponding author on the paper.

Kenneth Feeley measures the diameter of a tree in the lowland Amazonian rainforest [and yes – I do know that the measuring tape is crooked! I was in the process of straightening it when they took the picture].

Very few studies have looked at the effects of climate change on tropical forests. And, of those studies, nearly all have focused exclusively on adult trees, many of which are thought to be centuries old. This study, led by Alvaro Duque of the Universidad Nacional de Colombia (Medellin, Colombia) and 2014 Fulbright Research Fellow at FIU, integrated smaller individuals, including both shrubs and juvenile trees.

The researchers mapped and measured more than 32,000 individual plants representing more than 1,820 species in the northern Andes Mountains and northwestern Colombia. By looking repeatedly at the composition species occurring in a series of 16 forest plots spanning a nearly 3,000-meter elevation gradient, the researchers were able to show highland species are decreasing in abundance through time relative to lowland heat-tolerant species.

The compositional changes, which the authors refer to as thermophilzation, are occurring in both the large and small stems which suggests that the cause is a long-term disruption, such as global warming, rather than any single past climate event.

“This data is invaluable for assessing the consequences of climate change,” said Christopher Baraloto, director of the ICTB. “It is not easy to compile long-term information with precise botanical determinations in remote tropical forests, and we must invest in research projects like this across the tropics so that we can continue to monitor the impacts of climate change.

“We hope to promote exactly this type of research initiative as part of the new International Center for Tropical Botany at FIU.”

This study adds to the growing body of evidence compiled by Feeley and colleagues, showing upward migration of tropical plant species in recent decades in Peru and Costa Rica. With the addition of these new results from Colombia, the scientists now have a more complete understanding of how the highly complex and understudied ecosystems of tropical montane forests are being affected by changes in climate.

This knowledge will be integral in improving predictions of how these forests will fare in the future and for designing effective conservation strategies.

A migrating tree


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