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AAMU Scientists Link Tree Diversity and Forest Productivity

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To mix, or not to mix


Two scientists from Alabama A&M University have published a seminal paper in the prestigious multidisciplinary scientific journal PLOS ONE, a decade-old, peer-reviewed open access publication of the Public Library of Science. The journal covers primary research from any discipline within science and medicine. 


Dr. Santosh Ojha and Dr. Luben Dimov are the first to analyze the relationship between tree diversity and forest productivity for forest ecosystems from the entire eastern half of the United States. Previous studies either used much smaller datasets, or such studies did not control for some critical factors, such as latitude, forest age, or prior disturbance history.




A map with the locations of the almost a thousand plots used in the study by the Alabama A&M University researchers.




The relationship between ecosystem diversity and its productivity has been a topic of interest at least as far back as 1859, when Charles Darwin contemplated in his “On the Origin of Species” that a plot of land growing distantly related grasses would probably be more productive than a plot with a single species of grass. Since then, Darwin’s conjecture has been largely confirmed for grasslands, but much less is known for forests.


Forests are critically important ecosystems, both in terms of their economic, but also ecological importance. Thus, understanding the relationship between diversity and productivity would enable the production of greater amount of timber per unit of land, but also for greater amount of carbon being removed from the atmosphere and sequestered in the wood. Additionally, forests provide critical habitat for many game and non-game wildlife species, pollinators, and myriad of other ecosystem services.


The AAMU researchers used data from almost a thousand plots, with forest age under 30 years, located in the conterminous 31 eastern states, and satisfying strict selection requirements.


Overall, mixed-species forests were as productive as or even somewhat more productive than forests that were composed of only one species. Moreover, greater diversity was particularly important in conditions where soil quality was low and in forests in which tree cover was rather sparse.


As forests generally get more diverse and more productive the further from the poles and closer to the equator, the scientists tested if the relationship between tree diversity and forest productivity changed depending on the latitude. It turned out that in the eastern United States, tree diversity was more important for productivity in the northern forests than in those growing to the south.


 A mixed-species forest in north Alabama. The study examined the productivity of single-species and mixed species forests from the entire eastern half of the United States.  (Photo by L. Dimov)



As a whole, single-species forests did not seem to have a clear productivity advantage over mixed species forests. And, as different tree species provide habitat and forage for a greater variety of organisms that depend on them, it is important to consider the additional benefits of mixed-species forests. A better understanding of this relationship may help scientists and forest landowners execute more successful strategies for forest management and restoration in the future.


The authors acknowledge that their study only examines the relationship between the studied variables, so to confirm that greater diversity causes the frequently observed increase in productivity, long-term manipulative experiments would be necessary.


The study was supported by the National Science Foundation’s Alabama Experimental Program to Stimulate Competitive Research (Alabama EPSCoR) Graduate Research Scholars Program (GRSP); the USDA National Institute of Food and Agriculture, McIntire-Stennis Formula Fund; the National Science Foundation, Center of Research Excellence in Science and Technology (CREST); and by a United States Department of Agriculture, Forest Service Cooperative Agreement.


Link to the article:



Dr. Santosh Ojha, an Alabama A&M University alumnus, is a postdoctoral researcher, and Dr. Luben Dimov is an associate professor in the Forestry, Ecology, and Wildlife Program in the Department of Biological and Environmental Sciences, Alabama A&M University. For correspondence, contact Dr. Luben Dimov at, or, 256-372-4545. 


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