周喜

The creation of a “culture of prevention” can go a long way towards protecting drylands from the onset of desertification or its continuation. The culture of prevention requires a change in governments and peoples attitudes through improved incentives. Young people can play a key role in this process. Evidence from a growing body of case studies demonstrates that dryland populations， building on long-term experience and active innovation， can stay ahead of desertification by improving agricultural practices and enhancing pastoral mobility in a sustainable way. For example， in many areas of the Sahel region， land users are achieving higher productivity by capitalizing on improved organization of labor， more extensive soil and water conservation， increased use of mineral fertilizer and manure， and new market opportunities.

Integrated land and water management are key methods of desertification prevention. Sustainable land use can address human activities such as overgrazing， overexploitation of plants， trampling of soils， and unsustainable irrigation practices that exacerbate dryland vulnerability. Management strategies include measures to spread the pressures of human activities， such as transhumance （rotational use） of rangelands and well sites， stocking rates matched to the carrying capacity of ecosystems， and diverse species composition. Improved water management practices can enhance water-related services. These may include use of traditional water-harvesting techniques， water storage， and diverse soil and water conservation measures. Maintaining management practices for water capture during intensive rainfall episodes also helps prevent surface runoff that carries away the thin， fertile， moisture-holding topsoil. Improving groundwater recharge through soil-water conservation， upstream revegetation， and ?oodwater spreading can provide reserves of water for use during drought periods.

Maintaining vegetative cover to protect soil from wind and water erosion is a key preventive measure against desertification. Properly maintained vegetative cover also prevents loss of ecosystem services during drought episodes. Reduced rainfall may be induced if vegetation cover is lost due to overcultivation， overgrazing， overharvesting of medicinal plants， woodcutting， or mining activities. This is usually coupled with the effect of reduced surface evapotranspiration and shade or increased albedo.

In the dry subhumid and semiarid zones， conditions equally favor pastoral and cropping land use. Rather than competitively excluding each other， a tighter cultural and economic integration between the two livelihoods can prevent desertification. Mixed farming practices in these zones， whereby a single farm household combines livestock rearing and cropping， allows a more efficient recycling of nutrients within the agricultural system. Such interactions can lower livestock pressure on rangelands through fodder cultivation and the provision of stubble to supplement livestock feed during forage scarcity （and immediately after， to allow plant regeneration） due to within- and between-years climatic variability. At the same time， farmland benefits from manure provided by livestock kept on fields at night during the dry season. Many West African farming systems are based on this kind of integration of pastures and farmland.

Use of locally suitable technology is a key way for inhabitants of drylands at risk of desertification to work with ecosystem processes rather than against them. Applying a combination of traditional technology with selective transfer of locally acceptable technology is a major way to prevent desertification. Conversely， there are numerous examples of practices—such as unsustainable irrigation techniques and technologies and rangeland management， as well as growing crops unsuited to the agroclimatic zone—that tend to accelerate， if not initiate， desertification processes. Thus technology transfer requires in-depth evaluation of impacts and active participation of recipient communities.

Local communities can prevent desertification and provide effective dryland resource management but are often limited by their capacity to act. Drawing on cultural history and local knowledge and experience， and reinforced by science， dryland communities are in the best position to devise practices to prevent desertification. However， there are many limitations imposed on the interventions available to communities， such as lack of institutional capacity， access to markets， and financial capital for implementation. Enabling policies that involve local participation and community institutions， improve access to transport and market infrastructures， inform local land managers， and allow land users to innovate are essential to the success of these practices. For example， a key traditional adaptation was transhumance for pastoral communities， which in many dryland locations is no longer possible. Loss of such livelihood options or related local knowledge limits the communitys capacity to respond to ecological changes and heightens the risk of desertification.

Desertification can be avoided by turning to alternative livelihoods that do not depend on traditional land uses， are less demanding on local land and natural resource use， yet provide sustainable income. Such livelihoods include dryland aquaculture for production of fish， crustaceans and industrial compounds produced by microalgae， greenhouse agriculture， and tourism-related activities. They generate relatively high income per land and water unit in some places. Dryland aquaculture under plastic cover， for example， minimizes evaporative losses， and provides the opportunity to use saline or brackish water productively. Alternative livelihoods often even provide their practitioners a competitive edge over those outside the drylands， since they harness dryland features such as solar radiation， winter relative warmth， brackish geothermal water， and sparsely populated pristine areas that are often more abundant than in non-drylands. Implementation of such practices in drylands requires institution building， access to markets， technology transfer， capital investment， and reorientation of farmers and pastoralists.

Desertification can also be avoided by creating economic opportunities in drylands urban centers and areas outside drylands. Changes in overall economic and institutional settings that create new opportunities for people to earn a living could help relieve current pressures underlying the desertification processes. Urban growth， when undertaken with adequate planning and provision of services， infrastructure， and facilities， can be a major factor in relieving pressures that cause desertification in drylands. This view is relevant when considering the projected growth of the urban fraction in drylands， which will increase to 60% by 2030.

建立一种“预防文化”对保护旱地免于发生荒漠化或持续荒漠化大有裨益。预防文化需要通过完善激励措施来转变政府和人民的态度。在这过程中，年轻人可以发挥至关重要的作用。越来越多的案例研究证据显示：以长期实践经验和积极创新为基础，通过可持续的方式改良农业生产模式、提高牧民流动性，旱地人口可以战胜荒漠化。例如，在萨赫勒地区的许多地方，土地使用者正在利用优化人力资源分配、大面积水土保持、增加矿物肥料和粪肥的利用率，以及新兴市场机遇来实现更高的生产力。

土地和水资源综合管理是荒漠化防治的重要措施。可持续的土地利用可以应对下列人类活动，诸如过度放牧、过度开发植物资源、践踏土壤，以及会给旱地雪上加霜的不可持续的灌溉方式。管理策略包括：采取措施分散人类活动造成的压力，如牧场和井场的季节性转场放牧（轮流利用）;载畜率要与生态承载力相匹配;以及物种组成多样化。加强水资源管理措施能改善水利服务。这其中可包括使用传统的水资源储集技术、蓄水，以及多种多样的水土保持措施。在强降雨期对雨水收集的养护管理措施也有助于防止地表径流带走保持土壤水分的肥沃表层薄土。水土保持、上游地区植被恢复和洪水漫流可改善地下水回灌，从而储水供干旱时期使用。

保持植被，保护土壤免遭風蚀和水蚀是防止荒漠化的关键措施。适当维护植被还可防止干旱期生态系统提供的惠益丧失。如果因过度耕作、过度放牧、过度采集药用植物、伐木或采矿活动致植被丧失，就可能导致降雨量减少。这通常会伴随地表蒸散和荫蔽减少或反射率增加的效应。

在干旱亚湿润区和半干旱区，自然条件使得土地既能用作牧场又能用于耕种。这两种生计并非相互排斥的竞争关系，它们在文化和经济层面更加紧密的融合可以防止荒漠化。这些地区的混合耕作方式，即家家户户将饲养牲畜和种植作物相结合，可以使农业系统内的养分更有效地循环利用。由于年内和年间气候的多变性，这种相互影响可以通过种植饲料，以及在饲料缺乏时（和饲料新获补充后，为给作物留出生长时间）提供秸秆补充牲畜饲料来降低牲畜对牧场造成的压力。与此同时，在旱季，在田地里过夜的牲畜提供的粪肥有利于提高农田肥力。西非的许多农业系统都是基于这种牧场和农田一体化。

对面临荒漠化风险的旱地居民来说，因地制宜地使用技术，是其与生态系统进程和谐相处而非与之对抗的关键。将采用传统技术与选择移用当地适用技术相结合是防止荒漠化的一个主要方法。相反，有许多实践案例，诸如不可持续发展的灌溉技术和牧场管理，以及种植不适合农业气候区的作物，往往会引发或加快荒漠化进程。因此，技术转移需要对其影响力进行深入评估，并且需要社区的积极参与。

地方社区能提供有效的旱地资源管理，预防荒漠化，但往往会受到其行动能力的限制。旱地社区运用文化历史和本地知识与经验，再加上科学的助力，最适合设计防止荒漠化的方案。然而，行政机构能力不足、市场准入机会缺乏、执行的资金不到位等重重限制束缚了社区可利用的干预措施。启用政策对成功实施方案至关重要，这些政策包括让地方和社区机构参与进来，普及交通和市场基础设施，向地方土地管理者通报情况，以及允许土地使用者创新。例如，转场曾是牧民社区一种重要的传统适应方式，但如今在许多旱地地区已绝无可能。这种生计选择的丧失，或相关本地知识的丧失限制了社区应对生态变化的能力，加剧了荒漠化风险。

通过转向不依赖传统土地使用、对地方的土地和自然资源利用要求更低，却能提供可持续收入的替代生计可以规避荒漠化。这些生计包括旱地水产养殖、温室农业和旅游相关活动，其中旱地水产养殖指出产鱼类、甲壳类水产及利用微藻生产工业化合物。在有些地方，按每单位土地和水的产出来看，这些生计的收益相对较高。举例来说，旱地大棚水产养殖可最大限度地减少蒸发，并提供了高效利用盐水或淡盐水的机会。与旱地以外的从业者相比，替代生计常常会为其从业者提供竞争优势，因为替代生计利用了旱地特征，如太阳辐射、冬季相对温暖、淡盐地热水，以及往往比非旱地更多的人口稀疏的未开发地区。在旱地实施这些措施需要进行体制建设、市场准入、技术转移、资金投入和农牧民的思想转变。

避免荒漠化的另一个办法是在旱地城市中心和旱地以外的区域创造经济出路。能为民生创造新机遇的总体经济和体制环境变化会有助于缓解目前荒漠化进程下的压力。在进行适当规划并提供服务、基础设施和设备的情况下，城市增长可成为缓解旱地荒漠化压力的一个主要因素——考虑到旱地中城市比例的增长情况，这一点非常重要，到2030年这一比例将增至60%。