RESEARCH PAPER Land surface skin temperature captures thermal environments of C 3 and C 4 grasses Christopher J. Still 1,2 *, Stephanie Pau 3,4 and Erika J. Edwards 5 1 Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, USA, 2 Department of Geography, University of California, Santa Barbara, CA 93106, USA, 3 National Center for Ecological Analysis and Synthesis (NCEAS), University of California, Santa Barbara, CA 93106, USA, 4 Department of Geography, Florida State University, Tallahassee, FL 32306, USA, 5 Department of Ecology and Evolutionary Biology, Brown University, Providence, RI 02912, USA ABSTRACT Aim Numerous studies have documented ecological sorting of C3 and C4 grasses along air temperature gradients. However, phylogenetically structured analyses suggest that closely related C3 and C4 grasses (in the same PACMAD clade: Panicoideae, Arundinoideae, Chloridoideae, Micrairoideae, Aristidoideae and Danthonioideae) occur in environments with similar air temperature, challenging our understanding of how the photosynthetic pathway influences grass biogeogra- phy. To better understand thermal differences between C3 and C4 grass lineages, we analysed the surface radiative temperature as an alternative measure that is more closely aligned with plant microclimate. Location Hawaiian Islands, USA. Methods We used the MODIS land surface temperature (LST) product, a satellite-based measurement of radiative temperature. We compared LST with mean annual air temperature (MAT) for locations where C3 and C4 grass species were collected. We also utilized other satellite products, like MODIS tree cover, as a proxy for relative habitat openness where these grasses occur. Results Comparisons of C3 lineages [in BEP (Bambusoideae, Ehrhartoideae and Pooideae) and PACMAD clades] and C4 lineages (PACMAD clade only) illustrate the differing thermal environments for each group. C4 taxa are found in the envi- ronments with the highest MAT, followed by C3 PACMAD species. By contrast, C3 PACMAD species are found in the environments with the coolest LST, and the LST values for C3 BEP species are substantially higher than their MAT values. The difference in LST between C3 and C4 PACMADs is larger than the difference in MAT between these groups. Main conclusions Though LST has been used infrequently in ecology and bio- geography, it is intimately related to water and energy balance and ecosystem structure, and should more accurately capture plant temperatures and micro- climates than MAT. Our results provide support for a pronounced thermal differ- ence in the environments of closely related C3 and C4 grass taxa, and show that C3 PACMADs occur in the coolest and least variable thermal environments, probably due to the greater tree cover of these habitats. Keywords BEP, C3,C4, clade, distribution, land surface temperature, niche, PACMAD, photosynthetic pathway. *Correspondence: Christopher J. Still, Forest Ecosystems and Society, Oregon State University, 321 Richardson Hall, Corvallis, OR 97331, USA. E-mail: chris.still@oregonstate.edu INTRODUCTION AND SCIENTIFIC CONTEXT Grasses are some of the most ecologically successful plants on earth. Grasslands and savannas cover c. 30% of earth’s ice-free surface, and grasses provide much of the food for humanity. The photosynthetic pathway composition (C3/C4 fraction) of grasses is a fundamental physiological and biogeographical distinction in tropical, subtropical and temperate savannas and grasslands. Of the c. 11,000 grass species on earth, some 4500 use the C4 pathway and the remainder are C3 (Kellogg, 2001). Although Global Ecology and Biogeography, (Global Ecol. Biogeogr.) (2013) © 2013 John Wiley & Sons Ltd DOI: 10.1111/geb.12121 http://wileyonlinelibrary.com/journal/geb 1