Livestock Browsing Research Articles

Leaf area allometry and evaluation of non-destructive estimates of total leaf area and loss by browsing in a silvopastoral system

Tree growth and competition with other vegetation are strongly affected by leaf area, which can be modified by livestock browsing in silvopastoral systems. We studied the relationship of leaf area to stem diameter and sapwood area of koa (Acacia koa), a valuable hardwood tree species native to Hawaii. Because browsing alters allometric relationships, we compared harvest data with two non-destructive optical techniques (LAI-2000 canopy analyzer and photographic estimation of projected crown area). Destructive harvests of 30 trees showed that leaf area was equally well correlated with the diameter at breast height (dbh) or sapwood area of trees ranging from 2 to 16 cm in diameter, 1.3 m above ground level. Both optical techniques correlated with the leaf areas obtained by destructive analysis, but the photographic estimation of projected crown area provided more reliable estimates than the canopy analyzer. The photographic method based on projected crown area provided reliable estimates of leaf area removal within the browse zone (less than 2 m height). this method provides a simple, low-cost means of obtaining non-destructive estimates of changes in leaf area in isolated trees.

Nutritional aspects in the development of Bruchidius sahlbergi (Coleoptera: Bruchidae) in seeds of Acacia erioloba

Seeds of Acacia erioloba, a savanna tree of great potential for forestry and an excellent browse for game and livestock, is heavily infested with the bruchid beetle Bruchidius sahlbergi. The development from egg to beetle, and the uptake and turnover of food by the various developmental stages were investigated. After oviposition, the first-instar larva developed outside the host seed, with the egg mass as the only energy source. From the second instar onwards, development took place inside the host seed: this was followed by a non-destructive gravimetric method. During development from the second to the fifth instar, the larva consumed only a small part of the embryonic seed tissue: in single-infested seeds this was between 9 and 38% depending on the seed mass, but 100% in very small seeds. With increasing larval instars the number of starch grains in the faeces strongly decreased, but the size of the remnant grains increased. From the mineral nutrients of the food, copper and zinc were highly concentrated and passed to the beetle with a nutrient use efficiency of >90%. The nutrient use efficiency of calcium, magnesium, manganese and potassium was below 20%. Nitrogen utilization was only of the order of 34–41%, with a high concentration of nitrogen present in the frass. The approximate digestibility of the food was between 85 and 98%. The efficiency of conversion of ingested and digested food was larva-specific and varied between 10 and 45%. The impact of seed tissue consumption is discussed in relation to multiple seed infestation by this bruchid beetle.

Conservation Practices at an Upper-Elevation Village of West Nepal

Chimkhola, an upper-elevation village located on the southeastern flank of Dhaulagiri Himal, has virtually no irrigated agricultural fields, but large areas of widely dispersed, rain-fed fields and large areas of forest and alpine pastures. Villagers fertilize agricultural fields by taking livestock onto fields for one to several weeks prior to planting so that manure falls directly on the soil. The movement of herds from field to field, and to forest when all fields are planted, determines and coordinates the village subsistence system. Of the 17,035 dry weight kg of forest products collected by the average household each year, 32.8 % is fuelwood for herders, 23.8% is livestock fodder, and 19.2% is fuel for houses. Shortages of forest products have relatively recently begun to affect Chimkhola, and villagers have established a series of regulations designed to conserve forests and needed forest products. These measures, however, seem inadequate to halt the forest degradation process. Unless villagers insure forest regeneration by managing livestock grazing and browsing, a change that seems unlikely, the current communally controlled agro-silvo-pastoral system will probably dissolve into one of individual action, with increasingly intensive agricultural production on fewer, more spatially concentrated holdings and with fewer livestock which are kept close to the house and fed fodder from private trees.

Fire-related recruitment in stagnant Quercusdouglasii populations

Quercusdouglasii H. & A. (blue oak) age structure, stem analysis, and fire-scar history from more than 500 individuals on two sites in central California, U.S.A., revealed (i) meager tree recruitment since the 1940s and few trees older than 150 years, (ii) increased fire frequency following Anglo-American settlement in 1848 until fire suppression efforts in the 1940s, (iii) a positive association between tree ages and fire dates, and (iv) superior vertical growth to 135 cm of postfire sprouts (trees with ground-level ages within 1 year after fires) on the site with less livestock browsing pressure. We suggest that the association between tree ages and fire dates may have resulted from temporal concentration of postfire seedling sprouts, and faster vertical growth of postfire sprouts compared with true seedlings. However, sampling from existing trees may dampen the difference in vertical growth rates between sprouts and true seedlings where there is heavy browsing, because only true seedlings that grew as fast as sprouts survived and were available for sampling. Our findings contradict previous assumptions of the negative role of fire in Q. douglasii recruitment, and suggest that low recruitment since the 1940s in partly due to fire suppression.

Pollarding for Multiple Benefits

Abstract Pollarding is a traditional method of producing fuelwood in agroforestry systems where livestock browsing restricts tree regeneration by seedlings or coppice sprouts. As in coppicing, pollarding produces successive crops of wood from the vegetative sprouts of repeatedly harvested trees, but in pollarding the dominant sprouts are formed near the top of permanent trunks above the reach of livestock. The unique structure of pollards also makes them suitable for use as short-rotation fuelwood trees where fire restricts tree regeneration at ground level. In addition to fuelwood, pollards produce other tree products, as well as soil, wildlife, and esthetic benefits. With this combination of benefits, pollarding has potential for ameliorating certain environmental problems in the midwestern United States and for meeting the multiple objectives of many woodland owners. To assess this potential, we measured biomass yields and sprouting characteristics of honey locust and pin oak pollards harvested on 15- and 11-year rotations, respectively. Both species produced moderate yields of biomass and responded vigorously to pollarding. Potential benefits and problems of the method are discussed and applications of pollarding in farm and nonfarm settings are proposed. North. J. Appl. For. 5:148-152, June 1988.

An Evaluation of the Impact of Anthropogenic Pressures on Woodland Regeneration in the New Forest, Hampshire

A wide range of human activites have an impact on the open woodlands of the new Forest, but many affect the regeneration system in particular. A field survey was carried out to measure the extent and severity of human activitities (including livestock browsing) in the woodlands. This information was compared with regeneration patterns, using canonical correlation analysis, to evaluate the links betweeen the two sets

Cultural Practices for Establishing Fourwing Saltbush within Perennial Grass Stands

Cultural Practices for Establishing Fourwing Saltbush within Perennial Grass Stands