ecosystem services to and from north american arid ... - Conabio

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IV SIMPOSIO INTERNACIONAL DE PASTIZALES San Luis Potosí, S.L.P. México; 22 al 24 de agosto de 2007 Artículos in extenso Área temática: Transferencia de Tecnología activity (Zhu et al., 2005). Hence it is important to understand plant growth dynamics and utilization to achieve better rangeland conservation. The good news for extensive grazing producers are that the world beef demand will increase within the next years (Delgado, 2005) and this demand must be supplied by efficient and less polluting production systems (Kibblewhite, 2005), due to the fact that residue management increases costs as well as public pressure on intensive production systems. Cow-calf extensive systems will continue to be an important source for the beef cattle market (Bowman, 2005). Grazing animal production, dominant within arid rangelands, will render better results for farmers with the best rangeland condition; this can be attained through good management and rangeland improvement practices such as: grazing enterprise efficiency, marketing strategies, and lower production costs. Expected changes of land property in Mexico may be a higher source for financial certainty and support for productive enterprises; however, rain-fed systems primary productivity will continuously be conditioned by drought and winter temperatures. Despite any resultant, land property structure or the productive land organization, ecological principles must be observed in order to attain stable production systems under those constant premises. Hence, it is a pertinent action to achieve the integration of a solid grazing management scheme as fast as possible in order to promote that the grazing production systems do not affect the arid rangeland ecosystems in Mexico, whose stability has been put under risk (Briske, 1993). Rangeland productivity must become again a well-being generator (economic, educative, cultural, etc.), producing citizens technically qualified that look and take advantage of opportunities for the rural family integral development. RANGELAND AND GRAZING There are two equitable to the ecosystem grazing models: equilibrium model and dynamic model (Rowntree et al., 2004). The equilibrium model is based on the principle that vegetation is tied to long term conditions, mainly rain and physiography, pursuing toward climax conditions, according to water availability on the long term. The dynamic model is based on the high variability of rain as vegetation conditioner and hence the rangeland’s grazing carrying capacity. Optimal carrying capacity allows vegetation to achieve successive stages of climax. Grazers and vegetation will reach equilibrium through continuous adjustments within a dynamic relation. Overgrazing will maintain the vegetation under sub-climax conditions, dominated by pioneer plant species with low dry matter production and palatability. Optimal carrying capacity combines grazing (with long term data to define it), rest from grazing, livestock rotation, as well as a careful use of fire. Fixed carrying capacity under grazing will produce regular overgrazing events and hence, grazing population must be dynamically adjusted. As long as the vegetation recovers from drought or winter, the carrying capacity may increase. Plant condition determines the carrying capacity and the water precipitation defines vegetation condition (Rowntree et al., 2004). There have been emergency plans to support drought effects in Mexico’s arid rangelands, and these became eternal and inefficient palliatives, due to the fact that these support the inefficient herd maintenance and do not reduce grazing pressures for the rangeland within a due time. Under such circumstances, any normal recurrent drought is considered as extreme phenomenon, due to the dynamic relation among plant condition and carrying capacity, as well as the mismanagement of the communal rangeland. Any normal drought becomes an emergency under the lack of standards. On the other hand, no plans for forage abundance exist. 210
IV SIMPOSIO INTERNACIONAL DE PASTIZALES San Luis Potosí, S.L.P. México; 22 al 24 de agosto de 2007 Artículos in extenso Área temática: Transferencia de Tecnología The paradox: for Mexican arid ecosystems, production scarceness is a serious problem and production abundance too. There is a lack of preventive plans for both, as it has been proved during the last years with excellent precipitations (2002- 2007) in several Chihuahuan desert regions. The Worst Combination for Rangeland Condition Due to the fragility of the arid rangeland ecosystem, rain-fed agriculture is not recommended in these areas. The best way to support rangeland recovering is to allow the expansion of perennial species managed under minimum tillage, and this promotion will result in an increased plant productivity and rangeland ecosystem stability. Cropped lands left under secondary succession and grazing have shown higher erosion compared with the non-cropping areas only overgrazed even during long periods (Evans and Geerken, 2004; Rowntree et al., 2004). Rain-fed agriculture and grazing disturbed areas combination, strongly accelerates rangeland erosion. Crop production under rain-fed agriculture systems within arid rangelands must be avoided through annual tillage. Arid rangeland’s vegetation is well adapted to drought modalities; however, animal grazing pressure during the drought season, the most sensible phase for forages, results from the personal interest or the cattlemen’s experience as well as from human relations arranged for the administration of rangeland resources, through land property systems (Walker and Janssen, 2002). Unfortunately, poor development and spread of rangeland management techniques as well as a lack of basic rules focused on grassland conservation, has placed the rangeland ecosystem under risk giving as a result the desertification advancement. These aspects promote, through continuous recurrence, not only losses on money but on opportunities for economical development and ecosystem stability for future generations. Rangeland ecosystem degradation, as well as cattle production systems does not demand an immediate solution; however, these conditions reduce development opportunities and quality of life, generally on a gradual and continuous basis. When soil movements are noticed by the shareholders, the rangeland has already lost: plant cover, productivity, desirable species and it has been affected by animal and plant genetic resources erosion. Few weeks of intensive drought, even days, depending on the rangeland’s history of use, combined with a lack or delayed response on grazing pressure adjustments, promote all kind of economic and ecological damage: 1. Cutback of cattle productive parameters. 2. Reduction of cattle sale prices. Hence, cattlemen sustain the rangeland’s grazing pressure, in order to avoid a cheap price for their cattle, despite rangeland’s condition deterioration, even reinforcing cattle supplementation. 3. Soil particle size reduction due the combination of drought and trampling beyond piospheres: high impact areas under grazing, mainly on the water, food, and mineral sources (Nash et al., 2003). 4. Soil exposition to wind and water effects (Lobe et al., 2001; Su et al., 2004). 5. Lost of the rangeland’s production potential. 6. Productive and desirable species density reduction. 7. Toxic, thorny and less productive species increase, among other factors. Organic carbon and soil nutrients losses reduce rangeland’s water retention ability, modifying soil structure and its biological properties, as well as exposing these to desertification forces (Su et al., 2004). These changes occur with higher intensity during drought events even at low frequency or intensity, and its effect is strongly related to the rangeland site history of use. Rangeland abuse is difficult to overcome in the short term through natural plant succession in the time, as well as, improvement practices; and it becomes irretrievable without visionary management. Hence, it is very important the efficient detection of imminent drought events and the promotion of speedy activities to reduce its effect on rangeland condition. Opportune grazing 211
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