吕梁山沿黄红枣经济林退耕还林地生态调查研究

Ecological Investigation on Forestland Transformed from Farmland of Jujube Economic Forest along Yellow River in Lüliang Mountain

吕梁山沿黄坡耕地红枣经济林因经济效益低、放弃管理多,面临着生态林转换的命运。以吕梁市柳林县2000—2001年红枣经济林退耕还林地为研究对象,应用密度、郁闭度、地径、树高、枯落层、土壤养分等指标,综合评价红枣经济林退耕还林后的生态结构和生态效益。调查表明,4种退耕还林样地均达到了生态林造林密度要求(≥1600棵/hm^2);红枣经济林退耕还林后,乔木树种类型得到丰富(≥2种);红枣经济林退耕还林后乔木郁闭度大幅度增加,混交刺槐、油松的达到80%~90%,混交山杏、侧柏的达到50%~60%;林下开始形成2~3 cm枯落层、1~2 cm腐殖质层,土壤养分改善、土壤侵蚀防护能力提高;20 cm表层土壤的N和有机质含量比管护的坡耕地红枣经济林土壤养分高一二个等级。红枣经济林混交刺槐、侧柏、油松、山杏之后,红枣经济林的生态结构改善,生态服务功能提升;但另一方面,枣树竞争力弱,在混交林中面临被淘汰的可能性。

The jujube economic forest along the Yellow River in Lüliang Mountain may be conversed to ecological forest because its economic benefit is low and lots of jujube land is abandoned.Taking forestland transformed from farmland of jujube economic forest in Liulin county of Lüliang city from 2000 to 2001 as subject,the ecological structure and ecological benefits of forestland transformed from farmland of jujube economic forest were comprehensively evaluated using the indexes of density,canopy density,ground diameter,tree height,litter layer and soil nutrients.The results showed that the four plots all met the requirements of afforestation density of ecological forest(≥1600 trees/hm^2),and after returning farmland to forest,the types of tree species were enriched(≥2 kinds).After returning farmland to forest,the tree canopy density of jujube economic forest increased significantly,80%-90%of which were mixed with Robinia pseudoacacia and Pinus tabulaeformis,and 50%-60%of which were mixed with Prunus armeniaca and Platycladus orientalis.The litter layer above 2-3 cm and the humus layer above 1-2 cm were formed under the forest,which improved the soil nutrients and the soil erosion protection ability.The contents of N and the organic matter in the 20 cm surface soil were two grades higher than those in the managed and protected economic jujube forest on sloping farmland.The ecological structure and ecological service function of jujube economic forest were improved after mixed with Robinia pseudoacacia,Platycladus orientalis,Pinus tabulaeformis and Armeniaca sibirica.On the other hand,the competitiveness of jujube trees was weak and it was faced with the possibility of being eliminated in the mixed forest.