Experimental warming and phenology

Phenology is the study of the timing of biological events. The phenology of organisms is a critical component of the functioning of our biosphere. Migratory animals time their movements to secure food resources. Plants time their leaf production to minimize exposure to harsh conditions.

No one would state that the everything in the natural world is perfectly optimized, but changes in climate are likely to alter then phenology of organisms in ways that the consequences are not understood. In response, the scientific community has monitored phenology for a long time--in some places hundreds of years--and conducted experiments to aid in forecasting future responses.

Published recently, Wolkovich et al. led a team that compared observed and experimental consequences of warming for phenology. Their conclusion was that experiments consistently underestimated the phenological consequences of warming.

Two commentaries were published along with the paper. Both sets of authors presented the case in defense of experiments that can be summarized as "nature is complicated".

Neither commentary undercuts the value of the work, but understanding the consequences of different types of warming and why phenology might not respond consistently to experimental warming underpins basic questions we have about the interactions between climate and the biotic world.

Wolkovich, E. M., B. I. Cook, J. M. Allen, T. M. Crimmins, J. L. Betancourt, S. E. Travers, S. Pau, J. Regetz, T. J. Davies, N. J. Kraft, et al. 2012. Warming experiments underpredict plant phenological responses to climate change. Nature 485:494-497.

Grazers in a warmer world

If the world gets warmer, what happens to grazers?

Not an easy question. There are many grassland climate change experiments, but these are of limited utility here. Grazed and ungrazed grasslands are starkly different such that the consequences of warming for ungrazed grasslands are unlikely to apply to grazed grasslands.

If experiments don't help, then we need to look at how grazers respond to short-term variability in climate and compare that with geographic patterns that might represent long-term patterns.

When I've looked at how bison respond to inter-annual variation in climate, hot years don't affect them.

Yet, when we look across temperature gradients, hot places have small bison. Across 22 herds and a quarter million weights of bison, it's clear that herds in hotter places have smaller animals. Sometimes up to 500 lbs lighter.

Why the difference between short- and long-term patterns?

This is where experiments come in handy. When exposed to elevated temperatures short-term, grasslands begin to lose nitrogen. Over the long-term, these losses accumulate which drives down the quality of grass for grazers to eat.

One hot year, no problem. Many hot years and grazers don't grow as big.

The differences among bison are dramatic.

Back of the envelope calculation shows that just a 1°C increase in temperature across the US could cost the cattle industry $1 billion. Considering projections are for multiple degree C increases, those costs would accumulate.

[Regarding details, I'm about to submit this paper. We'll see how it's met.]