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.

建立一種“預(yù)防文化”對(duì)保護(hù)旱地免于發(fā)生荒漠化或持續(xù)荒漠化大有裨益。預(yù)防文化需要通過完善激勵(lì)措施來轉(zhuǎn)變政府和人民的態(tài)度。在這過程中，年輕人可以發(fā)揮至關(guān)重要的作用。越來越多的案例研究證據(jù)顯示：以長期實(shí)踐經(jīng)驗(yàn)和積極創(chuàng)新為基礎(chǔ)，通過可持續(xù)的方式改良農(nóng)業(yè)生產(chǎn)模式、提高牧民流動(dòng)性，旱地人口可以戰(zhàn)勝荒漠化。例如，在薩赫勒地區(qū)的許多地方，土地使用者正在利用優(yōu)化人力資源分配、大面積水土保持、增加礦物肥料和糞肥的利用率，以及新興市場機(jī)遇來實(shí)現(xiàn)更高的生產(chǎn)力。

土地和水資源綜合管理是荒漠化防治的重要措施?？沙掷m(xù)的土地利用可以應(yīng)對(duì)下列人類活動(dòng)，諸如過度放牧、過度開發(fā)植物資源、踐踏土壤，以及會(huì)給旱地雪上加霜的不可持續(xù)的灌溉方式。管理策略包括：采取措施分散人類活動(dòng)造成的壓力，如牧場和井場的季節(jié)性轉(zhuǎn)場放牧（輪流利用）;載畜率要與生態(tài)承載力相匹配;以及物種組成多樣化。加強(qiáng)水資源管理措施能改善水利服務(wù)。這其中可包括使用傳統(tǒng)的水資源儲(chǔ)集技術(shù)、蓄水，以及多種多樣的水土保持措施。在強(qiáng)降雨期對(duì)雨水收集的養(yǎng)護(hù)管理措施也有助于防止地表徑流帶走保持土壤水分的肥沃表層薄土。水土保持、上游地區(qū)植被恢復(fù)和洪水漫流可改善地下水回灌，從而儲(chǔ)水供干旱時(shí)期使用。

保持植被，保護(hù)土壤免遭風(fēng)蝕和水蝕是防止荒漠化的關(guān)鍵措施。適當(dāng)維護(hù)植被還可防止干旱期生態(tài)系統(tǒng)提供的惠益喪失。如果因過度耕作、過度放牧、過度采集藥用植物、伐木或采礦活動(dòng)致植被喪失，就可能導(dǎo)致降雨量減少。這通常會(huì)伴隨地表蒸散和蔭蔽減少或反射率增加的效應(yīng)。

在干旱亞濕潤區(qū)和半干旱區(qū)，自然條件使得土地既能用作牧場又能用于耕種。這兩種生計(jì)并非相互排斥的競爭關(guān)系，它們?cè)谖幕徒?jīng)濟(jì)層面更加緊密的融合可以防止荒漠化。這些地區(qū)的混合耕作方式，即家家戶戶將飼養(yǎng)牲畜和種植作物相結(jié)合，可以使農(nóng)業(yè)系統(tǒng)內(nèi)的養(yǎng)分更有效地循環(huán)利用。由于年內(nèi)和年間氣候的多變性，這種相互影響可以通過種植飼料，以及在飼料缺乏時(shí)（和飼料新獲補(bǔ)充后，為給作物留出生長時(shí)間）提供秸稈補(bǔ)充牲畜飼料來降低牲畜對(duì)牧場造成的壓力。與此同時(shí)，在旱季，在田地里過夜的牲畜提供的糞肥有利于提高農(nóng)田肥力。西非的許多農(nóng)業(yè)系統(tǒng)都是基于這種牧場和農(nóng)田一體化。

對(duì)面臨荒漠化風(fēng)險(xiǎn)的旱地居民來說，因地制宜地使用技術(shù)，是其與生態(tài)系統(tǒng)進(jìn)程和諧相處而非與之對(duì)抗的關(guān)鍵。將采用傳統(tǒng)技術(shù)與選擇移用當(dāng)?shù)剡m用技術(shù)相結(jié)合是防止荒漠化的一個(gè)主要方法。相反，有許多實(shí)踐案例，諸如不可持續(xù)發(fā)展的灌溉技術(shù)和牧場管理，以及種植不適合農(nóng)業(yè)氣候區(qū)的作物，往往會(huì)引發(fā)或加快荒漠化進(jìn)程。因此，技術(shù)轉(zhuǎn)移需要對(duì)其影響力進(jìn)行深入評(píng)估，并且需要社區(qū)的積極參與。

地方社區(qū)能提供有效的旱地資源管理，預(yù)防荒漠化，但往往會(huì)受到其行動(dòng)能力的限制。旱地社區(qū)運(yùn)用文化歷史和本地知識(shí)與經(jīng)驗(yàn)，再加上科學(xué)的助力，最適合設(shè)計(jì)防止荒漠化的方案。然而，行政機(jī)構(gòu)能力不足、市場準(zhǔn)入機(jī)會(huì)缺乏、執(zhí)行的資金不到位等重重限制束縛了社區(qū)可利用的干預(yù)措施。啟用政策對(duì)成功實(shí)施方案至關(guān)重要，這些政策包括讓地方和社區(qū)機(jī)構(gòu)參與進(jìn)來，普及交通和市場基礎(chǔ)設(shè)施，向地方土地管理者通報(bào)情況，以及允許土地使用者創(chuàng)新。例如，轉(zhuǎn)場曾是牧民社區(qū)一種重要的傳統(tǒng)適應(yīng)方式，但如今在許多旱地地區(qū)已絕無可能。這種生計(jì)選擇的喪失，或相關(guān)本地知識(shí)的喪失限制了社區(qū)應(yīng)對(duì)生態(tài)變化的能力，加劇了荒漠化風(fēng)險(xiǎn)。

通過轉(zhuǎn)向不依賴傳統(tǒng)土地使用、對(duì)地方的土地和自然資源利用要求更低，卻能提供可持續(xù)收入的替代生計(jì)可以規(guī)避荒漠化。這些生計(jì)包括旱地水產(chǎn)養(yǎng)殖、溫室農(nóng)業(yè)和旅游相關(guān)活動(dòng)，其中旱地水產(chǎn)養(yǎng)殖指出產(chǎn)魚類、甲殼類水產(chǎn)及利用微藻生產(chǎn)工業(yè)化合物。在有些地方，按每單位土地和水的產(chǎn)出來看，這些生計(jì)的收益相對(duì)較高。舉例來說，旱地大棚水產(chǎn)養(yǎng)殖可最大限度地減少蒸發(fā)，并提供了高效利用鹽水或淡鹽水的機(jī)會(huì)。與旱地以外的從業(yè)者相比，替代生計(jì)常常會(huì)為其從業(yè)者提供競爭優(yōu)勢，因?yàn)樘娲?jì)利用了旱地特征，如太陽輻射、冬季相對(duì)溫暖、淡鹽地?zé)崴约巴确呛档馗嗟娜丝谙∈璧奈撮_發(fā)地區(qū)。在旱地實(shí)施這些措施需要進(jìn)行體制建設(shè)、市場準(zhǔn)入、技術(shù)轉(zhuǎn)移、資金投入和農(nóng)牧民的思想轉(zhuǎn)變。

避免荒漠化的另一個(gè)辦法是在旱地城市中心和旱地以外的區(qū)域創(chuàng)造經(jīng)濟(jì)出路。能為民生創(chuàng)造新機(jī)遇的總體經(jīng)濟(jì)和體制環(huán)境變化會(huì)有助于緩解目前荒漠化進(jìn)程下的壓力。在進(jìn)行適當(dāng)規(guī)劃并提供服務(wù)、基礎(chǔ)設(shè)施和設(shè)備的情況下，城市增長可成為緩解旱地荒漠化壓力的一個(gè)主要因素——考慮到旱地中城市比例的增長情況，這一點(diǎn)非常重要，到2030年這一比例將增至60%。