The Dynamic Contribution of New Crops to the Agricultural Economy: Is it Predictable?

The diversification of agriculture and the development of new crops are closely related. Although diversification is often justified by reference to practical experience, we know little about the theoretical basis for diversification or its causes and effects. Is it theoretically possible to feed the world on a fixed and unchangeable set of species and varieties? Empirical evidence suggests not, but are there fundamental system properties that make this impossible? This paper addresses the following questions: 1. What is the “life cycle” of an economic crop from development to decline? 2. Does “successful” have any objective meaning or threshold in regards to crops? 3. Should we group all crops together or are there distinct functional groups or guilds? Guilds is used as in the ecological literature to signify a group of species having similar ecological (in this case agricultural management) requirements and therefore having similar economic roles. 4. Are there repeatable patterns in the abundance distribution of crops allowing the prediction of future patterns? The actual abundance distribution patterns of crops in New Zealand is tested against three models: the average, the lognormal, and a resource attraction model (RAM). The first two models are top-down (i.e. inferred from the actual distribution pattern). The average distribution over 150 years approximates an exponential function and represents the null model of a return to the mean. The lognormal is one of the distributions which most closely fits many diverse plant and animal communities (Preston 1948, 1962; Sugihara 1980; May 1981). The lognormal is a middle ground approximation between a variety of distributions ranging from the exponential and power functions to the broken stick model (Magurran 1988; Wilson et al. 1998). Here it represents the null model for competing species. The RAM is a bottom-up model (as is the broken-stick), which leads to distributions in the lognormal to power range based on simple rules of competition (i.e. the pattern emerges from rules affecting the bottom level of system integration such as the individual species, Halloy 1998).