连栽第1和第2代杉木人工林养分循环的比较

森林生态系统的养分循环是生态系统的重要功能过程之一,直接影响着森林的生产力,很大程度上影响和制约着林地的肥力水平,而且人工林连栽地力衰退和生产力下降现象普遍存在,寻求杉木林连栽两代杉木人工林养分循环差异与连栽林分生产力下降的关系,无疑具有重要的现实意义。利用30多年连续定位的测定数据,分析了连栽第1、2代杉木人工林在物质生产养分利用有效性、生物地球化学循环、地球化学循环的差异。结果表明,杉木速生阶段,第2代林每生产1 t干物质需要的养分比第1代林多1.58-3.29 kg,干材生长阶段,第2代林每生产1t所需养分比第1代林多4.23-5.92kg;速生阶段生物地球化学循环的养分利用系数第2代林比第1代林分下降19.7%-22.8%,养分循环系数下降12.8%-15.6%,干材生长阶段养分利用系数比第1代林分下降35.3%-36.2%,养分循环系数下降23.2%-27.0%,养分周转利用的生物地球化学循环功能第2代林比第1代林差;由干材生长进入成熟阶段的生长期内,伴随水文学过程的养分地球化学循环中,第2代杉木人工林生态系统的养分积累的地球化学循环的能力下降,养分流失率是第1代林的2倍左右,养分的积累率还不到第1代林的60%,对森林地力的维持和林木生长都是不利的。从生态系统水平上定位研究,定量分析了杉木连栽两代人工林养分循环功能过程,研究成果为我国南方人工林持续经营措施的制定提供了理论指导和科学依据。

Characteristics of nutrient cycling in first and second rotations of Chinese fir plantations

Nutrient cycling is one of the most important functional processes in forest ecosystems. Nutrient contents and its biogeochemistry cycle directly affect forest productivity and soil fertility. It has been widely reported that timber yield was apparently declined and soil fertility was greatly degraded on the successive rotations of Chinese fir plantations. Therefore, it is a significance to examine the relationships between the characteristics of nutrient cycling and the decline of site productivity in the successive rotations of Chinese fir plantations. The pattern of nutrient biogeochemical cycle and nutrient utilizations efficiency were investigated and compared in the first and second rotations of Chinese fir plantations using the data collected from long term projects over past 30 years. The results showed that about 1.58-3.29kg and 4.23-5.92kg more nutrients were required to produce every one tons dry matter in the fast-growing stage and timbering stage, respectively, in the second rotations than in the first rotations. Nutrient utilizations coefficient and nutrient cycling coefficient reduced 19.7%-22.8%, 12.8%-15.6% and 35.3%-36.2%,23.2%-27.0%, respectively in the second rotations when comparing with those in the first rotations. When the stands reached in the mature stage, the ability of nutrient accumulation declined in the second rotations. The nutrient loss rate through runoff in the second rotations was about two times high as in the first rotations. The nutrient accumulation rate decreased about 40% in the second rotations than in the first rotations. The results suggest that the changes in nutrient biogeochemical cycling in the second rotations had negative effects on tree growth and site productivity. The research provides scientific references in making reasonable management practices and policies on the plantations in Southern China.