机械措施控制加拿大萨斯克彻温草场丛生卷柏生长的经济分析

对加拿大萨斯克彻温省干旱棕色土壤带、湿润棕色土壤带及黑棕色土壤带上的沙土和壤土草场区所应用的挖鱼鳞坑和犁翻两种机械措施控制丛生卷柏侵蚀天然草场的效果进行了经济效益分析。分析结果表明 :当市场折扣率为 8%和 10 %时 ,犁翻处理在任何草场区实施均在 2 0 a内不能收回投入 ,说明该处理在经济上是不可行的 ;而挖鱼鳞坑在黑棕色土壤带实施分别需要10 a和 11a才能收回投入 ,在湿润棕色土壤带分别需 12 a和 14 a,而在干燥棕色土壤带则分别需 15 a和 2 2 a。但在实际中 ,这两种处理是否能发挥 2 0 a以上的经济效益还需进一步研究。草场管理者应根据两种处理控制丛生卷柏效果及饲草产量的增量来确定净现值和内部报酬率 ,估测收回投入的年限 ,最终作出合理的经济决策。当然 ,如果考虑到铲除丛生卷柏所带来的一些生态方面的争议 ,草场管理者应慎重考虑其他一些改良措施 ,如改进放牧管理 ,施化肥及播种目标草种等 ,以达到取得经济效益的目的

An economic analysis of clubmoss control with mechanical treatments in Saskatchewan rangeland, Canada

Clubmoss (Selaginella densa Rybd.) is a low, dense-matted, slow-growing perennial plant, which occupies large areas of the Northern Great Plains and is common on Saskatchewan rangelands. It rarely exceeds 2.5 cm in height and has an extensive mat of very fine roots penetrating to a depth of about 8 cm. The mat intercepts precipitation and holds it on the surface of the ground. Much of this moisture dose not penetrate this layer of mat and is unavailable to more desirable vegetation. The most common habitats for clubmoss growing are level areas and moderate slopes in plain topography. The plant prefers well developed soil of medium textured and nearly neutral reaction. Knowledge of the ecological role of clubmoss is limited. However, it dominates some native grassland stands, but has no forage value and increases with overgrazing and mismanagement of prairie pasture. The objective of this study was to complete an economic analysis of pitting and chisel plowing mechanical treatments that are commonly used to reduce clubmoss on rangelands in the Northern Great Plains. Cost and benefit analysis of pitting and chisel plowing were determined for the sandy on loamy range sites in the Dry and Moist Brown Soil Zones, and the Dark Brown Soil Zone in Saskatchewan. The levels of costs and benefits per hectare from mechanical range renovation depend upon the additional animal units (AU) raised and return to grazing per AU and the carrying capacity. Additional AU could reached on areas receiving each of the two treatments on loamy and sandy range sites in the three selected areas in Saskatchewan. Economic feasibility of treatment varies and a number of factors affect the final results,but weather is more important in determining forage productivity than mechanical disturbance. This study shows that net present values for chisel plowing were negative, indicating this treatment is not economically feasible on any range site at either 8% or 10% interest rate. Results for pitting suggest that it is more desirable on economic grounds than chisel plowing. Recovery of total costs of pitting on a loamy range site occurred at 10 and 11 years post-treatment in the Dark Brown Soil Zone, 12 and 14 years in the Moist Brown Soil Zone, and 15 and 18 years in the Dry Brown Soil Zone at discount rates of 8 and 10%, respectively. It is questionable whether beneficial effects of pitting or chisel plowing on herbage production exceed 20 years. Range managers considering pitting or chisel plowing to reduce clubmoss on rangeland and improve forage productivity will find the net present value, internal rate of return, and the predicted number of years to break even in making economically prudent decisions. Considering the questionable ecological value of removing a cover of clubmoss, it may be prudent for range managers to economic alternatives methods of range improvement, for instance, improved grazing management, fertilizing and/or interseeding on clubmoss dominated rangeland. Such decision may require more reason on rangeland productivity.