Rainfall Variability and California Mission Agriculture: An Analysis from Harvest and Tree Ring Data

Publisher Website
Google Scholar
Abstract
Rainfall Variability and California Mission Agriculture: An Analysis from Harvest and Tree Ring Data * Lester Rowntree and Robert Raburn As a wide range of precipitation variability affects California, the -LI. impact of drought and excessively wet winters on agricultural systems causes justifiable concern. We wonder how farm productivity might be affected by future droughts, what crops and activities are most vulnerable, what institutional framework is best able to adjust to precipitation fluctuations. We also wonder just how wide the range of rainfall variability might be and with what frequency extremes will occur.1 As climate historians turn to the past for insights into the future, cultural ecologists might learn more about human adjustments to rainfall variability through study of historic agricultural systems. We ask whether analysis of agricultural and population records from the Franciscan missions of California might, when coupled with precipitation-sensitive tree ring data, answer questions about the vulnerability of pre-industrial agriculture to annual rainfall variations. To be more precise, we seek answers to the following questions: 1. Can the high variability of annual crop yields at each mission be explained mainly by precipitation differences, or, * Dr. Rowntree is an Associate Professor of Geography, San Jose State University, San Jose, 95192. Robert Rabum is a graduate student in Geography at the University of California, Berkeley, 94027. A modified version of this article was presented at the annual meeting of the Association of Pacific Coast Geographers at Santa Barbara in June 1979. 1 See, for example, Orman Granger, "Secular Fluctuations of Seasonal Precipitation in Lowland California," Monthly Weather Review, Vol. 105 (1977), pp. 386-397. 31 32ASSOCIATION OF PACIFIC COAST GEOGRAPHERS 2.Might these variations be more a function of the cultural environment, such as changes in labor force or different agricultural technologies? 3.Might there be change through time, from the early to late mission period, demonstrating a decreasing susceptibility to rainfall variation with man's increasing sophistication resulting from experiences in the new environment? In other words, were adjustments made through time that made mission agriculture less vulnerable to excessively wet and dry years? 4.Finally, since agricultural records have been used successfully in other parts of the world to verify climate reconstructions, how reliable would the mission records be for this task?2 Do they accurately reflect rainfall variation in California, or are they better indicators of cultural variables? These fundamental questions about the human ecology of mission agriculture have not been investigated. Instead, one finds an unquestioned assumption that all mission agriculture was highly dependent on rainfall, and that variations in crop yields were primarily a result of annual precipitation differences.3 Research Design To answer these questions, we focused on two southern California missions, San Diego, founded in 1769, and San Luis Rey, located about 40 miles north of San Diego, and founded in 1798." 2 For an example of how mission records are used in the verification of climate reconstructions, see Harold Fritts, G. Robert Lofgren, and Geoffrey Gordon, "Variations in Climate Since 1602 as Reconstructed from Tree Rings," Quaternary Research, Vol. 12 (1979), pp. 18-46. 3 See, for example, R. Louis Gentilcore, "Missions and Mission Lands of Alta California," Annals, Association of American Geographers, Vol. 51 (1961), pp. 46-72. 4 Our analysis of mission agriculture was limited to field crops; we have not examined any aspect of livestock, nor have we included cattle and sheep in our three-stage model of mission agriculture. This is not oversight or ignorance. We are fully aware of the important role of livestock in the mission agricultural economy; however, we chose to exclude husbandry from this initial analysis. Information on this subect is found in Gentilcore, Annals, Association of American Geographers, op. cit. YEARBOOK · VOLUME 42 · 198033 Crop yields and population figures were analyzed over different 30-year periods for each mission. For San Diego, chosen to represent the early nonirrigated stage of mission agriculture, the data run from 1778 to 1807. San Luis Rey, representing a later, irrigated stage, is examined between 1801 and 1831. These data are examined in relation to precipitation variability inferred from tree ring growth indices from the nearby Santa Ana mountains. The relationships between crops, population, and...

This publication has 0 references indexed in Scilit: