Landsat

We developed a series of studies aimed at unraveling how ecosystems respond to changes in the environment. By using time series data from satellite-remote sensing, these studies test hypotheses about biological invasion and changes in vegetation cover across large gradients in latitude and elevation.

Using measurements from the NASA Landsat program, we decomposed spectral reflectance into green vegetation cover within the historical range of mangroves near the northern range limit in Florida, and asked whether there was a change in vegetation cover over a 28-year time series. Our study found that the area of mangrove forests doubled at the northern end of the historic range. This expansion was caused by a threshold response to a decrease in the frequency of extreme cold, an interpretation we confirmed in a follow-up experimental study. Building on these efforts, we showed that realized velocities of vegetation were failing to keep pace with changes in temperature in mountain ranges of western North America. Using a 27-year time series from Landsat for mountain ranges spanning coastal California to interior deserts, and from subarctic Canada to tropical Mexico, we found that increases in vegetation cover were ubiquitous at the highest elevations in these ranges over the last three decades. But in three of five mountain ranges with long-term climate data, vegetation failed to keep pace with changes in temperature, a finding that challenges a cornerstone of conservation planning.

Collaborators:
Dr. Gregory P. Asner (ASU), Dr. Kyle Cavanaugh (UCLA), Dr. Susan Cordell (USDA Forest Service) Dr. Dov Sax (Brown University).

Publications: 

High-velocity upward shifts in vegetation are ubiquitous in mountains of western North America.
Kellner, J. R., Kendrick, J., Sax, D. F. PLoS Climate. 10.1371/journal.pclm.0000071. [ Full Text ]

Integrating physiological threshold experiments with climate modeling to project mangrove species’ range expansion.
Cavanaugh, K. C., Parker, J. D., Cook-Patton, S. C., Feller, I. C., Williams, A. P. and J. R. Kellner. Global Change Biology. 2015. [ Full Text ]

Reply to Giri and Long: Freeze-mediated expansion of mangroves does not depend on whether expansion is emergence or reemergence.
Cavanaugh, K. C., J. R. Kellner, A. J. Forde, D. S. Gruner, J. D. Parker, W. Rodriguez and I. C. Feller. PNAS. 2014. [ Full Text ]

Poleward expansion of mangroves is a threshold response to decreased frequency of extreme cold events.
Cavanaugh, K. C., J. R. Kellner, A. J. Forde, D. S. Gruner, J. D. Parker, W. Rodriguez and I. C. Feller PNAS. 2014. [ Full Text ]

Remote analysis of biological invasion and the impact of enemy release.
Kellner, J. R., G. P. Asner, K. M. Kinney, S. R. Loarie, D. E. Knapp, T. Kennedy-Bowdoin, E. J. Questad, S. Cordell, and J. M. Thaxton Ecological Applications. 2011. [ Full Text ]