Friday, May 25, 2012

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.

Wednesday, May 23, 2012

this spring was warm

Not news to most at this point, but March was warm. At Konza, our first flowering phenologies were running 30 days ahead. Upper Midwest was even more extreme in temperatures.

I'm writing this just to post the maps...

This NASA depiction of land-surface temperature anomalies between March 8 and 15 shows the effects of the Great Warm Wave kicking off across the Great Plains of the United States and central Canada. In some areas, the land surface was more than 18°F (10°C) warmer than average. (Image courtesy NASA Earth Observatory.)

Another map for March:

This is for March 2012, departure from normal (1980-2011).

Friday, May 18, 2012

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.]

Monday, May 14, 2012

How to be laconic

When Philip II of Macedon threatened to invade Sparta, he sent a message "You are advised to submit without further delay, for if I bring my army into your land, I will destroy your farms, slay your people, and raze your city."

Sparta's reply was just one word "If". 

Philip chose not invade Sparta.

Laconia was the region surrounding Sparta, and both names came to symbolize a bareness: laconic and spartan.

There are times in scientific arguments, be it a reviewing a paper, responding to criticism, or summarizing intellectual arguments, where it is critical to be laconic. The Spartans could have responded point-by-point. Instead they chose to reduce the argument to its essence, "If".

In science, long, negative reviews often mask vested interests or laziness of thought. The best antidote is brevity. 

Friday, May 11, 2012

Global Nitrogen Budgets

It's been said that the global nitrogen budget is currently at the stage that the carbon budget was 50 years ago. Some pools and fluxes are well constrained. Others not so well constrained.

As we continue to examine the global carbon and energy budgets, it becomes even more important to make sure the N cycle is nailed down. For example, N2O has the 300x the warming potential of CO2. And N availability is a key for understanding productivity and ecosystem C sequestration. It fuels productivity, can suppress decomposition, and influences water quality.

One of the least constrained parts of the global N budget is the terrestrial biosphere sink--how much N gets stored on land each year.

Schlesinger (2009) puts the biospheric increment of anthopogenically fixed N at 9 Tg N. His estimate is derived from the amount of N being deposited on land (46 Tg/y) * fraction deposited on forests (0.39) * fraction of deposited N stored in forested ecosystems (0.5) = 9 Tg. That's a pretty rough calculation. By his first-cut estimates, about the fate of 50 Tg y-1 is unknown.

Compare that number with a top-down estimate. Le Quéré estimate that the land sink for C averages 2.6 Pg C y-1 (1990-2000) and were as high as 4.7 Pg C y-1 in 2008.

The typical C:N of soil organic matter is 12, but can be as high as 20. If so, 4.7 Pg C would require 390 Tg of N. C:N of 150 (wood) would require 30 Tg N.

So how much N is currently accumulating in ecosystems today? 10 Tg N? 100? 400?

It's an incredibly unconstrained number, but probably one of the most pivotal for understanding how much C ecosystems. How it will become more constrained is not clear at this point. We aren't committed to the types of measurements required to narrow this number.

Until it does, a major part of the Earth's biotic metabolism goes unknown.