CONCLUSIONS

There is a relationship between dendrochronology and climate change.  There is a relationship between climate change and agricultural productivity.  There is a relationship between agricultural productivity and human sustainability, especially in ancient societies.  Granted these relationships are not one-to-one relationships, they are more fluid in nature.  They are still relationships and cannot be completely discounted.  The focus of climate studies tends to be on drought periods, but good periods can also contribute to motivation of tribal communities.

The high percentage of events that occur in drought periods is intriguing.  Over four-fifths of all the years in which an event occurs are in a drought period, which is defined by four consecutive years below the 21-year mean average of tree ring chronologies.  Historical reconstruction of the predominantly agricultural nature of the Germanic tribes, from individual tribes to generic overviews, based on primary source documentation is supportive of an agriculturally-based clansman culture.  Climate change would be an important factor in their decision making process.  With the evidence available in annual-resolution climate proxy indicators like tree rings, the yearly climates can be related to agricultural yields.  These changes in agricultural output could have easily forced the Germanic tribes to relocate or search for sustenance elsewhere.

There have been many climate-migration studies that approach the idea of climate change influencing human relocation.  These studies reconstruct paleoclimate and attempt to establish a migration-threshold to support a change in climate would provoke a migration.  The study of the Germanic tribes is of a complex society that is interacting with not only the Roman Empire but internally with other tribes in Germania. 

The large variety of agricultural and livestock of central Europe in the 3^rd and 4^th centuries AD is not necessarily conducive to the migration-threshold theories.  Ignoring the potential for bartering, these food sources would not be depleted unless there was an extreme, prolonged climate change.  There are long below mean periods in the 3^rd and 4^th centuries, but probably never extreme enough to completely halt all food production.  However, the productivity would have surely been reduced to a degree that is related the extent and severity of the droughts.  This reduction in productivity did not necessarily cross a migration-threshold but allowed for a conscious decision to be made by the chieftain to look for other areas of settlement or alternate means of nourishment.  These decisions are evident in the Roman documents and archaeological record and may be directly linked to climate change.  The indigenous tribes of Germania in the 3^rd and 4^th centuries AD were affected by both drought and rainfall adequate for agriculture, and in several cases these periods have been either directly documented or inferred.  Climate change as a major motivational factor in the movements and invasions of the Germanic tribes, unfortunately, can neither be proven nor can it be disproved.  However, attempting to removal of climate from the realm of a plausible factor in the Völkerwanderung is not only a poor choice but also probably an incorrect one.