Thursday, July 26, 2007

Wolves bring aspen back to Yellowstone

Blogging on Peer-Reviewed Research
Aspen (Populus tremuloides) was a major species in Yellowstone, but over the twentieth century populations declined and there was little regeneration. While elk were initially blamed for this lack of regeneration, changing policies by the Park Service led to a change in this policy:
Until 1968, Park Service officials contended that an unnaturally large elk population, which had built up in Yellowstone during the late 1800s and early 1900s, had severely damaged the park’s northern winter range, including aspen (Populus tremuloides) communities. However, agency biologists now hypothesize that elk and other ungulates in Yellowstone are “naturally regulated,” being resource (food) limited, and that the condition of the ecosystem today is much like it was at park formation (Houston 1982; Despain et al. 1986). Elk influences on Yellowstone’s vegetation are now thought to be “natural” and to represent the “pristine” condition of the park.
According to the Park Service, Yellowstone is not now nor has it ever been
overgrazed, and all previous studies to that effect are wrong (Houston 1982).
[Kay, Charles E. 2001. Long-Term Aspen Exclosures in the Yellowstone Ecosystem. USDA Forest Service Proceedings RMRS-P-18.]

This conclusion was challenged by available evidence. For example, Kay showed the change in herbivore exclosures between 1946, 1963 and 1987 (images from Kay, 2001). The aspen clone is bisected by the exclosure's fence. While the two portions of the clone seem fairly similar in 1963, by 1987 the portion of the clone that was protected from herbivores has spread considerably.

William Ripple
and Eric Larsen found* that the aspens had stopped regenerating in 1920, about the same time that wolves were eliminated from Yellowstone. However, there were questions on the role that wolves might play in regulating the elk population.

To this end, Ripple and Robert Beschta** looked at the level of browsing and the height of aspen saplings in areas with and without logs (which can provide cover for wolves). In both upland and riparian sites, aspen saplings were taller when downed logs were present.

The reintroduction of wolves has allowed allowed aspen to return to riparian areas (although not, so far, in upland areas). Willows and cottonwoods also returned - more quickly than the aspen, which are a preferred browse for elk. While populations reductions have played a role, so has the 'ecology of fear'.

*Ripple,W.J., Larsen, E.J., 2000. Historic aspen recruitment, elk, and wolves in northern Yellowstone National Park, USA. Biological Conservation 95, 361–370.
**Ripple, W.J., Beschta, R.L., Restoring Yellowstone’s aspen with wolves, Biological Conservation (2007), doi:10.1016/j.biocon.2007.05.006

Story at Science Daily.

Thursday, July 19, 2007

Can organic agriculture sustain current levels of food production?

A recent report by Ivette Perfecto, Catherine Badgley and others at the University of Michigan suggests the organic agriculture is capable of sustaining or increasing current levels of food production globally.
Organic farming can yield up to three times as much food as conventional farming on the same amount of land—according to new findings which refute the long-standing assumption that organic farming methods cannot produce enough food to feed the global population.
According to the press release, the authors found that organic agriculture, which they define as "practices referred to as sustainable or ecological; that utilize non-synthetic nutrient cycling processes; that exclude or rarely use synthetic pesticides; and sustain or regenerate the soil quality", can maintain current levels of production in developed countries, and as much as triple production in developing countries.

The original article was published in Renewable Agriculture and Food Systems. There's a more detailed review at New Scientist and a two-part story(part 1, part 2) at

H/T Meteor Blades at dKos.