Monday, January 4, 2016

Trees grow in crowds—we call them forests. Competition between neighboring trees has a big impact on their growth, but researchers have found it challenging to generalize across the huge species diversity found in the estimated 3 trillion trees covering all of Earth’s biomes, with up to 53,000 tree species in the tropical biome alone.

Transition between two different forest communitiesAn international team of researchers published the most extensive study on tree competition to date on December 23, 2015 in the journal Nature. The study revealed that wood density, specific leaf area and maximum height affect competition in predictable ways across all forested biomes worldwide. Further, these traits capture trade-offs between growth in the open versus growth under intense competition.

The study resulted from an international collaboration of nearly 40 plant biologists and brought together national forest inventories and research plot data spanning 3 million trees in over 140,000 plots across the world. University of Maryland Associate Professor of BiologyNathan Swenson co-authored the study and contributed data from his long-term research program studying tree biodiversity in the rainforests of Puerto Rico.

Forests are crucial elements of the Earth system and cover large areas. They host an astonishing diversity of tree species encompassing many forms and strategies. Complex interactions among neighboring species strongly influence the dynamics of forests and their functioning as ecosystems. Ecologists have long sought an approach that might allow competition to be predicted in a general way across the tens of thousands of different tree species worldwide.

Functional traits—wood density, specific leaf area and maximum height—were known to have globally consistent effects on individual plant physiological functions. The new study reinforces that functional traits can provide a foundation for predicting dynamics and interactions between plant species on Earth.

Interestingly and perhaps surprisingly, trait dissimilarity between species did not soften their competitive impact on each other. Rather, traits underpinned trade-offs. For example, species with high wood density grew more slowly in open ground but were more tolerant of competition. In a landscape where disturbances created patches of open ground that then became more crowded over time, both low and high wood densities could coexist despite competition.

The research paper, “Plant functional traits have globally consistent effects on competition,” Georges Kunstler et al., was published on December 23, 2015 in the journal Nature.

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