Overview
I am an ecosystem ecologist with broad interests in other related fields of ecology and Earth System Science. I study the patterns, mechanisms, and consequences of vegetation-environment interactions, especially in the context of novel climate regimes under the on-going global change. Answering this question requires consideration of fine-scale plant ecophysiology (e.g. organism-level regulatory mechanisms), large-scale land surface processes and element cycles (e.g. terrestrial carbon-nutrient-water-energy nexus), and key ecological and evolutionary processes linking these questions across scales (e.g. competition, acclimation, and adaptation). To this end, my research program uses process-based ecosystem models as 'numerical greenhouses' to integrate the ever-increasing heterogenous data sets in ecology (e.g. synthesis in traits, ground census, flux tower, and remote sensing) and to conduct experiments that help to answer the above questions. I have worked extensively in the tropics, including tropical moist forests in Panama and the Amazon, dry forests in Costa Rica and Thailand, and savannas and woodland in more arid tropics. My research also extends to temperate forests with a focus in leaf phenology.
Research Focus
Currently the research of my lab focuses on 1) how plants respond to water stress with likely more frequent extreme droughts under a warmer world; 2) ecophysiological understanding of canopy phenology in both tropical and temperate forests; 3) using novel observation tools such as drones and terrestrial lidar scanners to monitor forests; and 4) the interaction between vegetation dynamics with biogeochemical cycles of key nutrients. In answering these questions, we pay particular attention to the roles of plant functional diversity (How diverse? What are the leading dimensions of diversity? Does it matter at larger spatio-temporal scales?) and environmental heterogeneity (What are the disturbance regimes? How important is micro-topography? How do they interact with vegetation dynamics?).
Publications
Xi Yang, Xiangtao Xu, Atticus Stovall, Min Chen, Jung-Eun Lee. (2021) Recovery: Fast and Slow – vegetation response during the 2012-2016 California Drought. Journal of Geophysical Research-biogeosciences.
F. Meunier, H. Verbeeck, B. Cowdery, S. A. Schnitzer, C. M. Smith-Martin, J. S. Powers, X. Xu, M. Slot, H. P. T. De Deurwaerder, M. Detto, D. Bonal, M. Longo, L. S. Santiago, M. Dietze, Unraveling the relative role of light and water competition between lianas and trees in tropical forests: A vegetation model analysis. J. Ecol. 109, 519–540 (2021).
S. Wu, J. Wang, Z. Yan, G. Song, Y. Chen, Q. Ma, M. Deng, Y. Wu, Y. Zhao, Z. Guo, Z. Yuan, G. Dai, X. Xu, X. Yang, Y. Su, L. Liu, J. Wu, Monitoring tree-crown scale autumn leaf phenology in a temperate forest with an integration of PlanetScope and drone remote sensing observations. ISPRS J. Photogramm. Remote Sens. 171, 36–48 (2021).
X. Xu, A. G. Konings, M. Longo, A. Feldman, L. Xu, S. Saatchi, D. Wu*, J. Wu, P. Moorcroft, Leaf surface water, not plant water stress, drives diurnal variation in tropical forest canopy water content. New Phytol. (2021), doi:10.1111/nph.17254.
X. Xu, A. T. Trugman, Trait-Based Modeling of Terrestrial Ecosystems: Advances and Challenges Under Global Change. Curr. Clim. Chang. Reports, 1–13 (2021).
D. Wu*, S. Piao, D. Zhu, X. Wang, P. Ciais, A. Bastos, X. Xu, W. Xu, Accelerated terrestrial ecosystem carbon turnover and its drivers. Glob. Chang. Biol. 26, 5052–5062 (2020).
M. Detto, X. Xu, Optimal leaf life strategies determine Vc,max dynamic during ontogeny. New Phytol. 228, 361–375 (2020).
J. S. Powers, G. Vargas G., T. J. Brodribb, N. B. Schwartz, D. Pérez-Aviles, C. M. Smith-Martin, J. M. Becknell, F. Aureli, R. Blanco, E. Calderón-Morales, J. C. Calvo-Alvarado, A. J. Calvo-Obando, M. M. Chavarría, D. Carvajal-Vanegas, C. D. Jiménez-Rodríguez, E. Murillo Chacon, C. M. Schaffner, L. K. Werden, X. Xu, D. Medvigy, A catastrophic tropical drought kills hydraulically vulnerable tree species. Glob. Chang. Biol. 26, 3122–3133 (2020).
C. M. Smith-Martin, X. Xu, D. Medvigy, S. A. Schnitzer, J. S. Powers, Allometric scaling laws linking biomass and rooting depth vary across ontogeny and functional groups in tropical dry forest lianas and trees. New Phytol. 226, 714–726 (2020).
J. H. Levy-Varon, S. A. Batterman, D. Medvigy, X. Xu, J. S. Hall, M. van Breugel, L. O. Hedin, Tropical carbon sink accelerated by symbiotic dinitrogen fixation. Nat. Commun. 10, 5637 (2019).
D. Medvigy, G. Wang, Q. Zhu, W. J. Riley, A. M. Trierweiler, B. G. Waring, X. Xu, J. S. Powers, Observed variation in soil properties can drive large variation in modelled forest functioning and composition during tropical forest secondary succession. New Phytol. 223, 1820–1833 (2019).
- Xu, X., Medvigy, D., Trugman, A.T., Guan, K., Good, S.P. & Rodriguez-Iturbe, I. (2018) Tree cover shows strong sensitivity to precipitation variability across the global tropics. Global Ecology and Biogeography, 27, 450–460.
- Wang, X., Wu, J., Chen, M., Xu, X., Wang, Z., Wang, B., Wang, C., Piao, S., Lin, W., Miao, G., Deng, M., Qiao, C., Wang, J., Xu, S. & Liu, L. (2018) Field evidence for the positive effects of aerosols on tree growth. Global Change Biology. (published online)
- Fisher, R.A., Koven, C.D., Anderegg, W.R.L., Christoffersen, B.O., Dietze, M.C., Farrior, C.E., Holm, J.A., Hurtt, G.C., Knox, R.G., Lawrence, P.J., Lichstein, J.W., Longo, M., Matheny, A.M., Medvigy, D., Muller-Landau, H.C., Powell, T.L., Serbin, S.P., Sato, H., Shuman, J.K., Smith, B., Trugman, A.T., Viskari, T., Verbeeck, H., Weng, E., Xu, C., Xu, X., Zhang, T. & Moorcroft, P.R. (2018) Vegetation demographics in Earth System Models: A review of progress and priorities. Global Change Biology, 24, 35–54.
- McDowell, N., Allen, C.D., Anderson-Teixeira, K., Brando, P., Brienen, R., Chambers, J., Christoffersen, B., Davies, S., Doughty, C., Duque, A., Espirito-Santo, F., Fisher, R., Fontes, C.G., Galbraith, D., Goodsman, D., Grossiord, C., Hartmann, H., Holm, J., Johnson, D.J., Kassim, A.R., Keller, M., Koven, C., Kueppers, L., Kumagai, T., Malhi, Y., McMahon, S.M., Mencuccini, M., Meir, P., Moorcroft, P., Muller-Landau, H.C., Phillips, O.L., Powell, T., Sierra, C.A., Sperry, J., Warren, J., Xu, C. & Xu, X. (2018) Drivers and mechanisms of tree mortality in moist tropical forests. New Phytologist, 219, 851–869.
- Xu, X., Medvigy, D., Joseph Wright, S., Kitajima, K., Wu, J., Albert, L.P., Martins, G.A., Saleska, S.R. & Pacala, S.W. (2017) Variations of leaf longevity in tropical moist forests predicted by a trait-driven carbon optimality model. Ecology Letters, 20, 1097–1106.
- Wu, J., Serbin, S.P., Xu, X., Albert, L.P., Chen, M., Meng, R., Saleska, S.R. & Rogers, A. (2017) The phenology of leaf quality and its within-canopy variation is essential for accurate modeling of photosynthesis in tropical evergreen forests. Global Change Biology, 23, 4814–4827.
- Allen, K., Dupuy, J.M., Gei, M.G., Hulshof, C., Medvigy, D., Pizano, C., Salgado-Negret, B., Smith, C.M., Trierweiler, A., Van Bloem, S.J., Waring, B.G., Xu, X. & Powers, J.S. (2017) Will seasonally dry tropical forests be sensitive or resistant to future changes in rainfall regimes? Environmental Research Letters, 12, 023001.
- Xu, X., Medvigy, D., Powers, J.S., Becknell, J.M. & Guan, K. (2016) Diversity in plant hydraulic traits explains seasonal and inter-annual variations of vegetation dynamics in seasonally dry tropical forests. The New phytologist, 212, 80–95.
- Oh, Y., Stackhouse, B., Lau, M.C.Y., Xu, X., Trugman, A.T., Moch, J., Onstott, T.C., Jørgensen, C.J., D’Imperio, L., Elberling, B., Emmerton, C.A., St. Louis, V.L. & Medvigy, D. (2016) A scalable model for methane consumption in arctic mineral soils. Geophysical Research Letters, 43, 5143–5150.
- Trugman, A.T., Fenton, N.J., Bergeron, Y., Xu, X., Welp, L.R. & Medvigy, D. (2016) Climate, soil organic layer, and nitrogen jointly drive forest development after fire in the North American boreal zone. Journal of Advances in Modeling Earth Systems, 8, 1180–1209.
- Xu, X., Medvigy, D. & Rodriguez-Iturbe, I. (2015) Relation between rainfall intensity and savanna tree abundance explained by water use strategies. Proceedings of the National Academy of Sciences, 112, 12992–12996.
- Wang, X., Piao, S., Xu, X., Ciais, P., Macbean, N., Myneni, R.B. & Li, L. (2015) Has the advancing onset of spring vegetation green-up slowed down or changed abruptly over the last three decades? Global Ecology and Biogeography, 24, 621–631.
- Xu, X., Piao, S., Wang, X., Chen, A., Ciais, P. & Myneni, R.B. (2012) Spatio-temporal patterns of the area experiencing negative vegetation growth anomalies in China over the last three decades. Environmental Research Letters, 7, 035701.