For the study, published this week in the journal Global Change Biology, scientists at the University of Freiburg analyzed data from the longest-running field trial on tree diversity in the tropics.
Previous research efforts have drawn connections between biodiversity and ecological health, but according to the authors of the latest study, the brevity of previous surveys made it difficult to isolate the influence of biodiversity from other factors.
The plots of trees analyzed by Freiburg researchers, the so-called Sardinilla experiment, were planted in Panama in 2001. For nearly two decades, researchers tracked 22 plots planted with one, two, three or five native tree species. Scientists used the size and height of trees in each plot as a proxy for productivity and ecological stability.
The findings showed plots with two and three tree species experienced a 25 to 30 percent boost in productivity compared to monocultures. Plots with five species enjoyed a 50 percent increase in productivity.
During the experiment, scientists were able to record the effects of a severe dry period, triggered by an El Niño climate pattern. Trees in diverse plots were more stable and resilient under drought stress. When it comes to absorbing and sequestering carbon, plots featuring a diversity of trees can offer the same carbon storage as monoculture plots, but in less space.
The authors of the latest study said none of their conclusions would have been realized had they completed their study after only a few years. Early in the experiment, the data suggested plots with two and three species were superior to plots with five species. But the plots with the greatest diversity simply needed more time to mature.
Thus, if only early years of the experiment were analyzed, very different conclusions would be drawn regarding optimal richness levels for the productivity of mixed‐species plantations, that is, few versus many species.
"Differences between species likely required time to develop into complementary interactions," researchers wrote.
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