Date of Award:

1985

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Advisor/Chair:

Brien E. Norton

Abstract

The purpose of this study was to describe and characterize the principal kinds of land in the mid-portion of the Acarau Valley, Ceara State, Northeast Brazil. The specific aims were: (1) to develop a specific-purpose soil classification; (2) to investigate vegetation-environment relationships; (3) to develop hypotheses about short-term vegetation dynamics; and (4) to evaluate the usefulness of computer processed multispectral-scanner (MSS) data for mapping rangeland resources in Northeast Brazil. Fifty-one soil profiles were described and ocular estimates of vegetation cover by species were made at each subjectively selected site. Two Landsat scenes were used to assess the usefulness of MSS data for mapping rangelands. A specific-purpose soil classification was intuitively derived from field experience and tested with a clustering algorithm, itself validated with profiles from independently conducted soil surveys. Detrended correspondence analysis was used to ordinate vegetation stands. Computer-processed MSS data subjected to a maximum-likelihood classifier generated a map of spectral classes, which was compared xvii with delineations of a conventionally produced soils map. Cluster analysis of profiles from the independently conducted soil surveys produced three distinct clusters: soils with a reddish argillic horizon, soils with clay-pan and soils lacking pedogenic horizons. Values of selected chemical and physical parameters for each cluster were concentrated in relatively narrow ranges, which corroborated the practical validity of the clustering algorithm. Clustering of soils from the study area produced similar results. Close agreement between cluster composition and grouping of soils by the specific-purpose classification validated the intuitively derived soi1 classes. Slash-and-burn cultivation results in the replacement of late-seral fire-sensitive species such as Auxemma oncocalyx, Mimosa caesalpiniaefolia and Caesalpinia pyramidalis by fire-tolerant early-seral species such as Croton hemiargyreus and Mimosa acutistipula. Impeded drainage restricts the growth of important woody species and gives rise to sparcely wooded surfaces. The areal distribution of computer-generated spectral classes and soils map delineations revealed considerable disagreement. This was attributed to the large proportion of boundary pixels associated with small soil-vegetation units.

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