The great oracular head speaks words of wisdom

[altivo]

No, I'm not making this up... er, well, maybe I am. But it's fun. Read it and see.

New installment here

Cumulative word cound: 19930

Went to the Audubon meeting to hear a conservation district guy talk about restoration, which was actually interesting mostly because he admitted that no one really knows what they are doing.

It got even more interesting when we got to the Q&A period and someone asked him about oak savannas, which is one of his specialties. I actually understood what he was saying and the theories he advanced. In short, bur oak savannas are not expanding or reproducing here at all. It turns out that the reason is white footed mice, who eat all the acorns. No, not squirrels, but mice. He has all the evidence. Yet the oak, the squirrel, the mouse have all co-existed for millennia. One natural predator of mice that was widespread here a century ago is missing today: the gray wolf! Another even bigger mouse-eater is even less likely to be successfully reintroduced: the Massassauga rattlesnake. All very interesting.

And it snowed more today. None of it lasted though.

Comments

[hrrunka]

Yeah, it's fascinating (and, sometimes, deeply worrying) how just a small change in nature's balance can tip things one way or the other, and how hard it can be to learn the whole story.

[altivo]

Indeed. He mentioned one example of the Bobolink, a native grassland bird that seems to be in decline. They tried to duplicate what they thought should be the correct mix of native grasses and the birds left the area immediately.

[frith]

Top-down population control for mice? By rattlesnakes and dogs? And foxes, shrews and feral cats figure how in this equation? I'm not buying this at all. It reeks of the gardening, "balance of nature" model of population dynamics. While he was at it, did he go on to say that white footed mice were eating all the mast and eliminating all trees with large seeds, such as maples, pines and beech? What of all the other species of small rodents like voles and jumping mice? Why aren't we over-run with mice like in Australia where at some point they were as thick as cockroaches in a slum?

[altivo]

I think you're overextending the study and its implications. His examination applies to the specific preserve in which he is working, only a couple hundred acres or so. Oaks are the primary trees there. He examines large sample areas for acorns fall and spring. When he put down 5/8 inch hardware cloth over an area with a known number of acorns at squirrel level (about 1/2 inch down) all the acorns survived. A control area without the hardware cloth lost every single acorn. Squirrels dig the acorns up, leaving little holes and a spoil of earth. The mice eat the acorn in situ by making a tiny shaft just wide enough for their head and muzzle. He has infrared photos and video of the mice doing this. So far no evidence of voles or any other "acorn predator" being involved. Further examination finds that areas of very short or no grass coverage do allow acorns to survive and sprout, apparently because the mice don't like to forage in the open where they are exposed to owls, foxes, and similar predators still present in the area.

He still doesn't claim to know everything that's going on, or exactly why the mice are now the top acorn consumers in the area. However, additional observations seem to support the idea. The white oaks in the area are all aged between about 140 and 110 years. These are primarily bur oak, the dominant white oak species in the area. They are also oaks with "sweet" acorns. There are no oaks in the intermediate ages that would indicate oak reproduction after about 1900. Oaks prior to 1870 or so were all removed for lumber and as land was cleared for farming.

A new growth surge of oak occurs after the 1920s to about 1940 or so, but those are red oaks and Hill's oaks, species with bitter acorns that the mice do not eat as readily (though squirrels and jays do consume them.) The second growth of white oaks seems to stop right about the time that wolves were eliminated from the area, which may of course be coincidental but it's interesting. Red oak growth seems to match up with the Depression, when much farmland here was allowed to languish unworked, giving the seedlings a chance to sprout and establish themselves.

Of course there must be many other factors, but I think he has pretty good evidence that in the current ecological structure of the area, white footed mice are largely responsible for inhibiting the expansion of the white oak. The existing trees are nearing the end of their lifespans, which may mean that we are about to see major loss of this native species unless they are deliberately protected and nurtured.

On my own land we find that the acorns do sprout, but only in areas that were mowed the previous autumn. He also suggested that late summer/dry spell fires may have been an important factor in oak reproduction. The mature trees resist them, and the burn off leaves gaps where the seedlings can survive and sprout the next season while mice avoid the area due to lack of cover. It is amazing how in a heavy masting year we can get bushels of acorns, yet they all disappear and almost none of them sprout the next spring. I can also confirm that the mouse and vole population is very large here. One only has to run a tractor across a fallow field and watch the ground to see that. The mice panic and scatter in hordes, leaving me to wonder where they all were hiding.

Feral cats, foxes, dogs, and other predators do catch mice, of course. I note, though, that our local foxes prefer domestic chickens, which are often readily available. Feral cats and dogs would not be frequent in the study area, and any found within the park are promptly trapped and removed. Owl populations are not large, though they are hanging on with some tenacity.