30 August 2006

The master of its domain


During one of our mountain field trips in Turkey last July, we had a tractor pull us up in its wagon to a high-altitude plateau. On our way up, we saw this goat stationed on an outcrop above the road. It watched us motionlessly as the tractor passed by. We were certainly intruders in its territory.

Herds of domesticated goats are quite common in the mountains of Turkey. Even at the steepest cliffs we had climbed with utmost difficulty, we saw the characteristic droppings of goats; they had already been there. Frequently, we would hear their distant, almost-mournful, bleats. We would look up and there would be goats casually browsing way above us on steep slopes we wouldn’t dare climb.

The livelihood it provides to the generally impoverished villagers notwithstanding, the domesticated goat is a very destructive animal. When they are present in large numbers, they probably constitute the dominant force that determines the composition of the flora where they browse.

"Many trees, when browsed, turn into maquis shrubs, which persist indefinitely in a shrubby form and, given the opportunity, turn back into trees…Browsing animals have their likes and dislikes. Goats devour prickly-oak despite the prickles, but prefer not to eat pine and cypress with their strong flavours. They thus encourage some trees and discourage others." (Rackham, 2001)

This sort of evidence implies to me that the present day plant species compositions in Greece, Turkey and other neighboring countries are drastically different than what they were before domesticated goats were introduced. But Rackham seems to disagree:

"Greece has hundreds of endemic plants…Nearly all endemics are plants of open ground, not of forests; this tells against any theory that on an evolutionary time-scale forest is the ‘normal’ vegetation of Greece."

This is faulty reasoning for at least 2 reasons. First, if most forests were cleared, then most endemics of forests must have gone extinct. Second, open spaces, and open-space endemics, would have existed even when the dominant plant cover was of forest type. A more likely scenario is that after the dominant forests of Greece and Turkey were cleared, the forest endemics disappeared, but the open-space plants expanded their ranges.

Not everyone seems to think that the present dominant plant cover in eastern Mediterranean countries is necessarily bad:
"Grazing alone, even heavy grazing, cannot eliminate the woody species…, but it creates and maintains open patches and gradations between dense and open areas, thus reducing uniformity and increasing habitat diversity.
The development of a dense overstory of woody species reduces the diversity of the understory species…The reduced understory diversity cannot be compensated for by the overstory diversity because the number of overstory species is invariably much smaller than the number of understory species." (Perevolotsky & Seligman, 1998)

One problem I see in this line of reasoning is that it emphasizes the plant species and ignores all other species (fungi, arthropods, birds, etc) that can only survive in dense forests.

High plant biodiversity may be a good thing even if it may not have been the original state of the land and provided that most or all contributing species are natives. Ultimately, though, if we want to return at least some of the land to its original, pre-grazing, pre-human state, the goats must go.

Rackham, O. 2001. Trees, wood, and timber in Greek history. Leopard’s Head Press.
Perevolotsky & Seligman. 1998. Role of grazing in Mediterranean rangeland ecosystems. BioScience 48:1007-1017.

1 comment:

bev said...

I kept a herd of about 60 goats here at the farm for about 25 years and would agree that, in numbers, they can have a major impact on an ecosystem. In small numbers in an fairly lush ecosystem, I'd say that their impact would be minimal as they tend to browse (rip a few leaves off of this plant, then the next, etc...), unlike sheep which will practically graze vegetation down to the soil. However, goats are very efficient at killing trees and clearing brush, especially if they are traveling in large numbers. In that case, they can strip down almost everything in their path. At one time, we purposely allowed them to do just that to clear dense brush on certain areas of our farm. In a fragile ecosystem -- let's say, one with dry, rather poor soil, I would think goats would have an absolutely devastating impact on the diversity of flora and fauna.