Having described changes in the archaeological record of plant use in the North Carolina Piedmont during the Late Prehistoric and Historic periods, the task of explaining those changes remains. Although the following suggestions should be considered informal hypotheses rather than conclusions, they can be used to guide further research. Additionally, this discussion is intended to integrate archaeological information on plant use with consideration of other aspects of aboriginal Piedmont culture during the Historic period, including relationships with Europeans.
Cost-benefit models are derived mainly from microeconomic theory. However, ecologists have incorporated some economic concepts into their own models of diet choice, territoriality, and group organization. Optimal foraging theory has integrated economic and ecological concepts in attempting to model optimal subsistence and survival strategies for both human groups and non-human animals. Examples of the use of cost-benefit models in interpreting archaeological subsistence data include the work of Earle (1980) and of Keene (1981), who also uses an optimal foraging approach.
Cost-benefit and optimization models include the assumption that humans, like other animals, tend to exploit resources in such a way that costs are minimized and benefits maximized. Subsistence practices vary in their efficiency in terms of time and energy costs, and it is assumed that increased efficiency results in increased fitness (Winterhalder 1981). Although these assumptions are not always justified, they will be used here for heuristic purposes. The proximate cause of changing frequencies of different behaviors within a population (i.e., decision-making by individuals or groups) will not be discussed here. However, since cost-benefit relationships affect decision-making, it should be acknowledged that the selection of certain behaviors ultimately will be made at the expense of others.
Currencies, Cost and Benefits
The currency (i.e., measure of efficiency) most commonly used in cost-benefit assessments is energy (Winterhalder 1981). Complex currencies such as nutrients are sometimes used in linear programming approaches (Keene 1981). Time factors should also be taken into account, which allows for assessment of acquisition rates (E. Smith 1979). Since the non-quantitative approach used here eliminates the complexities of mathematical modeling, time, energetic, and nutritional factors will all be considered where appropriate.
Cost components of resource acquisition include search costs, pursuit and handling costs, and opportunity costs. Search costs, which are incurred while locating prey, vary according to technological resources and distribution of prey in space. For agricultural products, for instance, search time would be essentially zero, in contrast to that for mobile fauna. Pursuit and handling costs consist of prey capture, transport, processing, consumption, and other related activities. All of these costs reflect time spent as well as energy expended on a given task.
Time spent on one activity is necessarily lost for other activities. Therefore, the cost of procurement of a given resource can be seen to include the value of activities in which resources could have been alternatively invested, or what has been called its opportunity cost (Winterhalder 1983:15). This opportunity cost model can be especially useful for comparing activities that result in different types of material gain (e.g., hunting for trade purposes versus hunting or other procurement for subsistence purposes).
Returns exist in the form of both energy and nutrients. It is assumed that decisions on what resources to use are made in an effort to maximize at least short-term returns, even though people lack complete and perfect information about their environment. Non-material benefits may also be relevant, but will not be considered in detail here.
Applying the Model
Relationships between subsistence activities, environmental variability, group organization, and information flow in human groups are always complex. When Europeans arrived in the North Carolina Piedmont they brought with them new potential resources as well as epidemic disease and attendant changes in population (Dobyns 1984) and group organization. By the time of the Occaneechi occupation of the Fredricks site, there is evidence of ongoing trade between aboriginal and European groups. We know from historical sources that trade in deerskins was prevalent in this period and certainly must have affected the costs and benefits of other activities. This evidence is persuasive, despite the fact that studies of faunal remains from the Wall and Fredricks sites are inconclusive regarding changes in the frequency or kind of deer hunting. With this information in mind, we can begin to assess the relationships between the European presence (particularly in the form of trade networks) and changes in plant food use as reflected in the archaeological record.
Trade and Opportunity Cost. At the Hillsborough locality, use of acorns declined in the Historic period, whereas hickory nuts remained an important resource. In the East as a whole, acorn use seems to have declined prehistorically after a peak during the Early Woodland period in Tennessee (c. 500 B.C. to A.D. 1), reaching its lowest levels during the Historic period (Yarnell and Black 1983). Its decline may in part reflect an increasing importance of corn and other grain crops.
Some modern time and energy expenditure studies comparing nut processing techniques suggest that the costs of processing acorns for consumption may be higher than that for hickory nuts, depending on the techniques employed (Petruso and Wickens 1984; Talalay et al. 1984). Although acorns may actually yield more meat per unit time spent shelling, most types of acorns require leaching to render the meats palatable. Hickory nut meats, on the other hand, can be easily extracted by pulverizing whole nuts and boiling the mixture to extract oil and hickory "milk" (provided that appropriate containers are available), a practice documented for North Carolina Indians during the early eighteenth century (Lefler 1967). Put into a cost-benefit framework, a prehistoric scenario might be as follows. If acorn processing costs were in fact relatively high, other resources with lower associated costs, higher benefits, and similar nutritional content (such as corn) could have outranked acorns.
This scenario is not, however, adequate for explaining why acorn use declined even further during the Historic period. Trade may have played a role in decreasing acorn's ranking. As trade items exchanged for deerskins became, in effect, a new resource for aboriginal groups, the opportunity cost of procuring acorns (as well as certain other plant foods) might have risen. Increased opportunity cost induced by the introduction of trade goods might have acted to lower the rank of acorns still further.
A similar argument can be advanced to explain decreasing use of walnut in the same area. Except for a few time periods at a few locations, walnut has not been a primary resource in the East based upon available archaeological evidence. Its distribution in the Carolinas is scattered (Radford et al. 1968), resulting in higher pursuit costs (in the form of travel time) relative to other nut resources. With the advent of the deerskin trade, a shift to a focus on the highest-ranked nut resource (hickory) could have made more time available for trade-related activities, particularly during the fall, when the deer rut and the fruiting times of most nut-bearing species partly coincide.
In the case of corn, the change in cost-benefit ratio was probably less severe. As a crop, corn would have had negligible search costs, moderate handling costs (including garden maintenance), and probably high yield compared to other food crops. High energetic and nutritional gains would have compensated for any increased opportunity costs resulting from trade. The symbolic significance of corn and its prominence in ritual are non-material factors that perhaps acted to encourage its maintenance. Trade brought in ornaments, tools, and alcohol, none of which could have replaced a staple food such as corn except through further complication of trade networks.
If use of "cool-season" grasses did in fact become less common, trade could have similarly introduced scheduling conflicts and increased opportunity costs. However, it seems that maintenance of grass harvesting as a seasonal strategy would have had relatively low associated costs and high benefits during a period of relative resource scarcity. Another possibility is that information about using these resources was simply lost because of depopulation and reorganization of human groups. Discontinuities introduced into the path of information flow between generations could have led to loss of some traditional procurement techniques. This suggestion is highly speculative, but presents some possibilities for further research.
The adoption of peach is easily explained using a cost-benefit approach. All fleshy fruits represented at the three sites are somewhat weedy species that tend to be highly productive in disturbed habitats such as those around Indian settlements. Search costs would have been correspondingly low, and processing cost would have been negligible. The peach was simply a newly available fruit with similar qualities. In addition, peach fruits had the large size and perhaps the increased palatability often associated with selection under domestication. Even as a crop, the maintenance costs of peach use would have been low because of its ability to grow well with relatively little care. Processing costs for storage would not have been any higher than those associated with native fruits.
Division of Labor and Group Size. Up to this point, subsistence activities have been discussed as if they were participated in equally by all group members. It should at least be pointed out that sexual division of labor is a factor to be considered. For instance, if deer hunting and trade with Europeans were male activities, and plant procurement a female activity, there would not necessarily have been direct scheduling conflicts between trade-related activities and nut collection, grass collection, and corn harvesting and planting. However, if women were the processors of deerskins, their activities would have closely tracked those of the men, resulting in a similar overall effect of increased opportunity cost. Similarly, group size and population structure would have affected the efficiency ratios of different activities.