Date of Award:

1984

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Ecology

Department name when degree awarded

Range Science

Advisor/Chair:

Frederick D. Provenza

Abstract

Clearing of trees from the so-called caatinga woodland that characterizes the vegetation of the semi-arid region of northeast Brazil offers possibilities for increasing forage production. This research analyzed the first-year effects of clearing caatinga on dry season forage for goats and sheep. In addition, factors affecting litter decomposition on cleared and uncleared caatinga were assessed to evaluate the viability of deferring grazing of forages during the wet season for use later in the dry season.

Removing the trees resulted in a sixfold increase in production of herbaceous vegetation, however, 88 percent of the increased yield on the cleared areas was in the form of stems from herbaceous vegetation. Seventy-two percent of the stems were unpalatable to goats and sheep because of the massive size of those stems. Leaf litter from trees was an important component of the diets of goats and sheep during the dry season and clearing reduced production of this forage threefold.

Clearing resulted in increased decomposition of leaf litter. Changes in microclimate played only a minor role in this difference. The reduction in the amount of leaf litter from trees relative to litter from herbs had the greatest effect on decomposition rates of dry season forage because tree litter decomposed less rapidly than did herbaceous litter. The slow decomposition of leaf litter during the dry season suggests that deferment. of cleared or uncleared caatinga for use as forage in the latter part of the dry season is feasible.

An analysis of the diets of esophageally fistulated goats and sheep indicated that clearing may be a viable alternative for improving the amount and the in vitro dry matter digestibility of the forage consumed during the dry season the first-year post-treatment. These increases were attributed to an absolute greater abundance of preferred herbaceous forages (i.e., foliage and leaf litter) and to the persistent green foliage on coppicing woody plants. Dietary nitrogen appeared to limit intake, and clearing did not improve availability of this nutrient to sheep and goats at the higher levels of grazing pressure applied in this study. Other ecosystem considerations such as watershed protection and long-term community stability must also be considered in decisions to remove the tree canopy of the caatinga.

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