Howzabout I quote some of this janx verbatim?
[QUOTE="The Fall of the Roman Empire", Peter Heather (Oxford University Press, 2007) p.122-4]...In his explorations [which took place in the 1950s], Tchalenko came across the remains of a spread of villages, sturdily constructed from limestone blocks, which had been abandoned in the eighth to ninth centuries after the Arab conquest of the region.
The villages showed that these hills had once been the home of a flourishing rural population, which could afford not only to build excellent houses, but to endow their villages with sizable public buildings. This ancient population was much denser than anything the region has supported at any point since, and it clearly made its living from agriculture; Tchalenko believed it produced olive oil commercially. The really revolutionary bit was Tchalenko's discovery that prosperity first hit the region in the later third and early fourth centuries, then continued into the fifth, sixth, and seventh with no sign of decline. [...]
Further archaeological work, using field surveys, has made it possible to test levels of rural settlement and agricultural activity across a wide geographical spread and at different points in the Roman period. Broadly speaking, these surveys have confirmed that Tchalenko's Syrian villages were a far from unique example of late Roman rural prosperity. The central provinces of Roman North Africa (in particular Numidia, Byzacena, and Proconsularis) saw a similar intensification of rural settlement and production at this time. This has been illuminated by separate surveys in Tunisia and southern Libya, where prosperity did not even begin to fall away until the fifth century. Surveys in Greece have produced a comparable picture. And elsewhere in the Near East, the fourth and fifth centuries have emerged as a period of maximum rural development - not minimum, as the orthodoxy would have led us to expect. Investigations in the Negev Desert region of modern Israel have shown that farming also flourished in this deeply marginal environment under the fourth-century Empire. The pattern is broadly similar in Spain and southern Gaul, while recent re-evaluations of rural settlement in Roman Britain have suggested that its fourth-century population reached levels that would only be seen again in the fourteenth. Argument continues as to what figure to put on this maximum, but that late Roman Britain was remarkably densely populated by ancient and medieval standards is now a given. The only areas, in fact, where, in the fourth century, prosperity was not at or close to its maximum for the entire Roman period were Italy and some of the northern European provinces, particularly Gallia Belgica and Germania Inferior on the Rhine frontier. Even here, though, estimates of settlement density have been revised substantially upwards in recent years.
For the poverty of the latter two northern provinces, the explanation probably lies in third-century disruption. [Dachs' note: as well as disruptions of the fourth century...Julian had to repel the famous invasion of the Alemanni at Argentorate, and Valentinian sparred with them again a decade later.] The Rhine frontier region was being heavily raided at the same time as so much energy was being poured into solving the Persian problem, and it may be that rural affluence in parts of the region never recovered. A methodological problem may also provide at least part of the explanation. Roman-period surveys rely on datable finds of commercially produced pottery to identify and date settlements. If a population ceased to import these wares, reverting to undatable locally made ceramics, especially if at the same time they were also building more in wood than in the traditional Roman stone, brick, and tile - which surveys also find - then they would have become more archaeologically invisible. This was happening in several areas of northern Europe by at least the mid-fifth century, so it is far from impossible that the seeming lack of fourth-century inhabitants in parts of the northern Rhine frontier region was caused not by substantial population decline, but by the first appearance of these new habits. The jury is still out.[/QUOTE]
Since one of the primary methods of examining agricultural output in the Roman period is to measure the prosperity level (in terms of goods acquired and apparent population sizes) of the rural populace, and that prosperity, as measured by the increase in opulence (comparatively; we're not talking senators' villas here) of their abodes and the other effects acquired by the rural population, was growing during the relevant period. This would seem to be inconsistent with a drop in food quality.
Oh, by the way, preemptive comment on the so-called "agri deserti", "deserted lands" - this doesn't mean desertification of productive land. Basically all of the territory referred to as agri deserti is North African wilderness, not the productive territories in what is now Tunisia and eastern Algeria. This just means land from which no taxes were taken, too, and is thus further inappropriate for determining the size of any sort of ecological disaster area, were one to exist.
[QUOTE="The Fall of the Roman Empire", Peter Heather (Oxford University Press, 2007) p.122-4]...In his explorations [which took place in the 1950s], Tchalenko came across the remains of a spread of villages, sturdily constructed from limestone blocks, which had been abandoned in the eighth to ninth centuries after the Arab conquest of the region.
The villages showed that these hills had once been the home of a flourishing rural population, which could afford not only to build excellent houses, but to endow their villages with sizable public buildings. This ancient population was much denser than anything the region has supported at any point since, and it clearly made its living from agriculture; Tchalenko believed it produced olive oil commercially. The really revolutionary bit was Tchalenko's discovery that prosperity first hit the region in the later third and early fourth centuries, then continued into the fifth, sixth, and seventh with no sign of decline. [...]
Further archaeological work, using field surveys, has made it possible to test levels of rural settlement and agricultural activity across a wide geographical spread and at different points in the Roman period. Broadly speaking, these surveys have confirmed that Tchalenko's Syrian villages were a far from unique example of late Roman rural prosperity. The central provinces of Roman North Africa (in particular Numidia, Byzacena, and Proconsularis) saw a similar intensification of rural settlement and production at this time. This has been illuminated by separate surveys in Tunisia and southern Libya, where prosperity did not even begin to fall away until the fifth century. Surveys in Greece have produced a comparable picture. And elsewhere in the Near East, the fourth and fifth centuries have emerged as a period of maximum rural development - not minimum, as the orthodoxy would have led us to expect. Investigations in the Negev Desert region of modern Israel have shown that farming also flourished in this deeply marginal environment under the fourth-century Empire. The pattern is broadly similar in Spain and southern Gaul, while recent re-evaluations of rural settlement in Roman Britain have suggested that its fourth-century population reached levels that would only be seen again in the fourteenth. Argument continues as to what figure to put on this maximum, but that late Roman Britain was remarkably densely populated by ancient and medieval standards is now a given. The only areas, in fact, where, in the fourth century, prosperity was not at or close to its maximum for the entire Roman period were Italy and some of the northern European provinces, particularly Gallia Belgica and Germania Inferior on the Rhine frontier. Even here, though, estimates of settlement density have been revised substantially upwards in recent years.
For the poverty of the latter two northern provinces, the explanation probably lies in third-century disruption. [Dachs' note: as well as disruptions of the fourth century...Julian had to repel the famous invasion of the Alemanni at Argentorate, and Valentinian sparred with them again a decade later.] The Rhine frontier region was being heavily raided at the same time as so much energy was being poured into solving the Persian problem, and it may be that rural affluence in parts of the region never recovered. A methodological problem may also provide at least part of the explanation. Roman-period surveys rely on datable finds of commercially produced pottery to identify and date settlements. If a population ceased to import these wares, reverting to undatable locally made ceramics, especially if at the same time they were also building more in wood than in the traditional Roman stone, brick, and tile - which surveys also find - then they would have become more archaeologically invisible. This was happening in several areas of northern Europe by at least the mid-fifth century, so it is far from impossible that the seeming lack of fourth-century inhabitants in parts of the northern Rhine frontier region was caused not by substantial population decline, but by the first appearance of these new habits. The jury is still out.[/QUOTE]
Since one of the primary methods of examining agricultural output in the Roman period is to measure the prosperity level (in terms of goods acquired and apparent population sizes) of the rural populace, and that prosperity, as measured by the increase in opulence (comparatively; we're not talking senators' villas here) of their abodes and the other effects acquired by the rural population, was growing during the relevant period. This would seem to be inconsistent with a drop in food quality.
Oh, by the way, preemptive comment on the so-called "agri deserti", "deserted lands" - this doesn't mean desertification of productive land. Basically all of the territory referred to as agri deserti is North African wilderness, not the productive territories in what is now Tunisia and eastern Algeria. This just means land from which no taxes were taken, too, and is thus further inappropriate for determining the size of any sort of ecological disaster area, were one to exist.
Really, you should read the book. Mayan case is thoroughly examined there and when you learn what they did with their environment (twice!), you realize how stupid are all the people living today who believe the world can sustain another 5 million humans.