Erosion

The most common results of deforestation in the Mediterranean basin are erosion of hillsides, flooding as the waters are no longer retarded and absorbed, interference with the water supply, and siltation of lowlands and coastlands. George Perkins Marsh (180182), who served in Constantinople, and in Rome for a period longer than any other American ambassador (1861-82), understood this form of environmental deterioration well: ‘‘Vast forests have disappeared from mountain spurs and ridges; the vegetable earth accumulated beneath the trees... the soil of alpine pastures... are washed away;... rivers famous in history and song have shrunk to humble brooklets: . . . harbors. . . are shoaled by the deposits of rivers at whose mouths they lie’’ (Marsh 1965 [1864]: 9).

Forests regulate the runoff of the precipitation they receive. Like a sponge, the plants and soil hold water, preventing floods and releasing a year-round supply to springs and streams. Ancient authors noted the connection between forests and water supply. Pausanias (7.26.4) visited a place ‘‘clothed with oak woods’’ and remarked of it, ‘‘No town in Greece is more abundantly supplied with flowing water than Phellai.’’ Ancients also noted the effects of deforestation in light of this relationship. As Plato observed (Critias 111B), the water that rushed unimpeded down mountainsides was no longer available to feed the springs. Perhaps for this reason, he portrayed his ideal Atlantis as having springs surrounded by plantations of appropriate trees. Without forests, streams that formerly flowed clear all year long became intermittent and muddy, existing only as dry courses during the summer, while hundreds of springs dried up. Most of the erosion that occurs takes place in brief periods during torrential rains.

As Helen Rendell notes (1997: 52), ‘‘A vegetation cover is the most effective protection against erosion.’’ Once the land was bare of trees, torrential rains washed away the unprotected earth. Erosion destroyed uplands that might have grown trees again, and the silt, sand, and gravel that reddened the rivers was deposited at their mouths along the shores of the virtually tideless Mediterranean Sea. This greatly altered coastlines, in some cases pushing them many kilometers farther out to sea, as is the case around the mouth of the Peneios River. The new wetlands were unhealthy to humans because they served as a breeding ground for malarial mosquitoes, but were useful as homes for water birds and other animals, and spawning places for some species of fish.

Erosion and siltation around the Mediterranean in ancient times were large in scale, although the amount of soil removed from the highlands is difficult to estimate. Deposits along the coasts and in valleys and lowlands can be measured, and dated from artifacts found in them or by radiocarbon analysis of organic materials. Such studies indicate that erosion was a complicated and highly localized process. Thermo-pylai, the famous pass between cliffs and sea near the mouth of the Spercheios River, was narrow enough in 480 to be defended by a small Greek army against a vastly superior Persian force. Subsequent accretion of river deposits has widened the land at least 8 km seaward from the battle site. Pausanias (8.24.5) compared the silt deposits laid down at the mouths of two rivers: the Achelcios, whose watershed was uninhabited and therefore forested, ‘‘does not wash down so much mud on the Echinadian islands as it would otherwise do,’’ but the Maiandros, whose valley had been cleared, ‘‘had turned the sea between Priene and Miletos into dry land.’’ Siltation clogged harbors at river mouths, as was true of Miletos in the case just mentioned, and Heraklean labors were needed in many places to retain them.