TheImprovement ofTropical and Subtropical Rangelands
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TheImprovement ofTropical and Subtropical Rangelands

TheImprovement ofTropical and Subtropical Rangelands TheImprovement ofTropical and Subtropical Rangelands

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196 IMPROVEMENT OF TROPIOAL AND SUBTROPIOAL RANGELANDS drainage, the presence or absence of waterlogging, or a satisfactory water table, and 10 forth). A simple calculation would show, for example, that a northern slope with a 30° dip under 40° latitude N. would have a potential evapotranspiration equal to only one-third of a similar lOuthern slope, and therefore, if rainfall remains similar in both cues, the water budget would be three times greater in the former than in the latter (Le Houerou, 1972). The selection ofspecies to be planted is therefore likely to be different in the two cues, if optimum use of the sites is lOught. Physiography may also strongly affect local precipitation if the site is exposed to rain-bearing winds; is in a rain shadow; or is subject to descending, warm, dry winds, similar to the Fohn of the lOuthern Alps, the .am"n winds of Iran, the Santa Anu of California, the chinooks of the eutern Rockies, the berg winds of South Africa, the nor'westers of New Zealand, or the zontla of Argentina. Geomorphology and slope may also play an important role in determining rates of erosion or sedimentation and lOil depth, thus greatly afFecting lOil fertility and water budget. Hence, species selection and plant productivity calculations must be modified accordingly (see table 8-1 and figure 8-1). ABRITY 01 INTRODUCED SPECIES TO COMPETE WITH NATIVE VEGETATION Plant competition should be considered from the viewpoint of short-term establishment, long-term survival, and perpetuation of stands. Competition during the establishment stage may be reduced by the application of herbicides or mechanical treatments (mowing, plowing) to the native vegetation until the desired species become established. When high yields are desired, competition from weeds may be eliminated on a continuous buis by regular or periodic treatments. Long-term perpetuation of stands of introduced species will depend on their ability to reproduce either vegetatively (for example, by suckers, runners, stolons, or rhizomes) or by teed. Some futgrowing exotic species are not able to perpetuate themselves on the site and may need to be replanted after a number of years. However, some exotics have become invading pests (Opuntia spp., Pro.o,u spp., Nicotiana glauca, Parkin.onia spp., Euphorbia spp., Jatropha spp.).

CRITERIA FOR PLANT SICLECTION 197 Competition within mixtures, when mixtures are desired, can be reduced by using species with different root systems (for example, shallow-rooted BPecies mixed with deep-rooted ones) 88 well 88 including species that have different le880nal patterns of growth. Competition may also be reduced by selecting species according to their adaptability to microhabitats such 88 mounds, depre88iona, flat areas, or sloping areas. Divene topography will create diversity in the resulting vegetation composition. Doing this, however, requires skill and experience and is not always practical for large-scale progrUl18. USEUGIMES lor_ge Productlcm Revegetation for forage production is quite common either by range seeding (with or without water conservation techniques) or planting fodder shrubs and trees for fodder reserves. Sown pastures, also called "tame pastures," may be included in rangeland systems either for continuous grazing, for le880nal grazing, or for deferred standing hay to be used in periods of shortage. Range seedings are commonplace, and suitable species are well documented for Ule in a number of countries. The use of rhizobial inoculants with annual or perennial legumes for agricultural areas is well known. The Ule of well-adapted trees that can serve both 88 forage and to enhance nitrogen in the soil is an obvious need. Various shrubs and trees are not only excellent sources of nitrogen but also lerve larger roles in integrated land-use systems (National Research Council, 1979). Fodder Trees and Shrubs Fodder tree and shrub plantationa probably occupy over one million hectares in the arid and semiarid IOnes. Some particularly uaeful trees and shrub. include acaci88 (such as Acacia ,aligna, A. Seraegal, A. tortilu, A. alIIida, cacti (o,uratia jicu.indica), saltbushes (Atriplez raummularia, A. cane,cen" A. halimu,), salesauIs (Haloqlora perlicum, H. aph,llum), and mesquites (such as Pro,opu juliftora, P. glaradulo,a, P. chileraN, P. alba, P. cineraria). Some are managed 88 wooded grazing lands with evergreen oaks, such 88 QuercUl roturadilolia, Q. ilez, Q.•uher, and Q. lulitanica (for example, the circum-Mediterranean region and parts of California), with

CRITERIA FOR PLANT SICLECTION 197<br />

Competition within mixtures, when mixtures are desired, can<br />

be reduced by using species with different root systems (for example,<br />

shallow-rooted BPecies mixed with deep-rooted ones) 88 well 88<br />

including species that have different le880nal patterns of growth.<br />

Competition may also be reduced by selecting species according<br />

to their adaptability to microhabitats such 88 mounds, depre88iona,<br />

flat areas, or sloping areas. Divene topography will create diversity<br />

in the resulting vegetation composition. Doing this, however, requires<br />

skill <strong>and</strong> experience <strong>and</strong> is not always practical for large-scale<br />

progrUl18.<br />

USEUGIMES<br />

lor_ge Productlcm<br />

Revegetation for forage production is quite common either by<br />

range seeding (with or without water conservation techniques) or<br />

planting fodder shrubs <strong>and</strong> trees for fodder reserves. Sown pastures,<br />

also called "tame pastures," may be included in rangel<strong>and</strong> systems<br />

either for continuous grazing, for le880nal grazing, or for deferred<br />

st<strong>and</strong>ing hay to be used in periods of shortage. Range seedings are<br />

commonplace, <strong>and</strong> suitable species are well documented for Ule in a<br />

number of countries.<br />

The use of rhizobial inoculants with annual or perennial legumes<br />

for agricultural areas is well known. The Ule of well-adapted trees<br />

that can serve both 88 forage <strong>and</strong> to enhance nitrogen in the soil<br />

is an obvious need. Various shrubs <strong>and</strong> trees are not only excellent<br />

sources of nitrogen but also lerve larger roles in integrated l<strong>and</strong>-use<br />

systems (National Research Council, 1979).<br />

Fodder Trees <strong>and</strong> Shrubs<br />

Fodder tree <strong>and</strong> shrub plantationa probably occupy over one<br />

million hectares in the arid <strong>and</strong> semiarid IOnes. Some particularly<br />

uaeful trees <strong>and</strong> shrub. include acaci88 (such as Acacia ,aligna, A.<br />

Seraegal, A. tortilu, A. alIIida, cacti (o,uratia jicu.indica), saltbushes<br />

(Atriplez raummularia, A. cane,cen" A. halimu,), salesauIs<br />

(Haloqlora perlicum, H. aph,llum), <strong>and</strong> mesquites (such as Pro,opu<br />

juliftora, P. glaradulo,a, P. chileraN, P. alba, P. cineraria). Some<br />

are managed 88 wooded grazing l<strong>and</strong>s with evergreen oaks, such 88<br />

QuercUl roturadilolia, Q. ilez, Q.•uher, <strong>and</strong> Q. lulitanica (for example,<br />

the circum-Mediterranean region <strong>and</strong> parts of California), with

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