Document: MIC-3-64-36

Relationships between edaphic factors and vegetation in a chronosequence of abandoned agricultural fields: A case study along the San Pedro River, Arizona .

OLEKSYSZYN, M.M.*, J.C.STROMBERG and D.M.GREEN

Arizona State University, Tempe, Arizona 85287 USA ¹

Abstract:
Over 2 million acres of farmland have been abandoned in Arizona since 1940. It is likely that this trend will continue, due to increasing urban expansion, municipal water demands and conservation interests. There is considerable interest in restoring native riparian vegetation to abandoned fields, most of which are in river flood plains or terraces. This study was designed to provide information of value to restorationists by: 1.) Describing changes in vegetation structure and composition (including native to exotic plant cover ratios N:E) and soils of abandoned fields over successional time; 2.) Determining whether soils differ between native and exotic plant stands and; 3.) Determining whether relationships between soils and vegetation are stable or dynamic through successional time. I hypothesized that recently abandoned fields would have higher exotic plant cover, pH, electrical conductivity, total C and N than older fields, yet lower bulk density and organic carbon. I collected soil and vegetation data from 14 abandoned fields of various ages along the San Pedro River, Arizona in the fall of 1998 and spring and fall of 1999. Herbaceous trends show N:E ratios increasing with time since abandonment and perennial exotics or natives replacing annual exotics. Vegetation trends vary between river reaches. Soils range from clay loam to loamy sand with bulk density values from 1.2 g cm-3 to 2.0 g cm-3, coarse fragments from 1 % to 29 %, and pH values from 7.6 to 8.9. Both bulk density and pH values were unrelated to time since abandonment.

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This abstract is being presented at: 3:30 PM in session:
AGROECOLOGY