COS 119-3
Benefits of using tree-mixes rather than monocultures in carbon plantings

Friday, August 9, 2013: 8:20 AM
101J, Minneapolis Convention Center
Kristin B. Hulvey, School of Plant Biology, University of Western Australia, Crawley, Australia
Richard J. Hobbs, School of Biological Sciences, The University of Western Australia, Perth, Australia
Rachel J. Standish, School of Plant Biology, University of Western Australia, Crawley, Australia
David B. Lindenmayer, Australian National University, Canberra, Australia
Lori Lach, School of Plant Biology, University of Western Australia, Crawley, Australia
Michael P. Perring, School of Plant Biology, University of Western Australia, Australia
Background/Question/Methods

Increasingly governments and the private sector are using planted forests to offset carbon emissions.  Few studies, however, examine how tree diversity affects C-sequestration and storage in these plantings.  Here we consider arguments for planting tree species mixes rather than monocultures in C-offset projects.  First, using above-ground biomass as a proxy for C-sequestration/storage, we use meta-analysis to synthesize studies comparing mixtures to monoculture plantings.  We conducted three separate meta-analyses designed to address the following questions:  (1) On average, are tree mixtures more productive than their species grown in monoculture?  (2) Do tree mixtures produce at least as much above-ground biomass as their most productive species grown in monoculture?  (3) Is there evidence that the addition of individual species or key functional groups increase above-ground biomass?  We next examined additional motivations for incorporating tree richness into planted forests including the likely role diversity plays in forming multiple C-pools, its contribution to C-pool stability, and its contribution to additional ecosystem services. 

Results/Conclusions

We found that tree mixtures are more productive than their average monoculture. Most importantly for the design of C-plantings, mixtures also produced equal and sometimes more biomass than their most productive species grown in monoculture. This suggests that diverse C-plantings sequester/store at least as much carbon as monocultures and can potentially outperform monoculture plantings.  We also found that nitrogen-fixing trees increase biomass, and by extension, C-sequestration/storage in plantings.  Our findings highlight the benefit of a two-pronged strategy for designing C-plantings including:  (1) increased tree species richness and (2) the addition of species that contribute to C-sequestration/storage as well as to other target processes and functions.