连栽杉木林林下植被生物量动态格局

用空间一致时间连续的定位研究方法,在湖南会同杉木林生态系统国家野外科学观测研究站试验基地的第2集水区,对连栽杉木林林下植被生物量进行了12 a的监测,研究了林下植被种类的变化、生物量动态特征、生物量的组成与分布变化格局。结果表明:连栽杉木林在14a生长发育过程中,林下植物种类呈现波动性的减少趋势,其中木本植物物种数下降率为40.0%,草本植物物种数下降率为47.1%。林下植被生物量由杉木林3年生29.48 t/hm²下降至14年生的2.53 t/hm²,其中木本植物生物量由7.07 t/hm²,下降至1.25 t/hm²,下降了82.3%;草本植物由22.41 t/hm²,下降至1.28 t/hm²,下降了94.3%。在此期间,木本与草本植物生物量的高低均出现波动现象。3年生杉木林下木本植物以乔木树种生物量6068.97 kg/hm²最高,占总生物量85.88%,藤本植物生物量736.97 kg/hm²为次,占10.44%,灌木植物生物量259.87 kg/hm²最低,仅占3.68%。14年生杉木林下木本植物以灌木植物生物量881.87 kg/hm²为首,占总生物量70.73%,藤本植物生物量247.07 kg/hm²为次,占19.82%,乔木树种生物量117.87 kg/hm²最少,只占9.45%。3年生杉木林下草本植物以蕨类植物生物量8391.44 kg/hm²最高,占总生物量的37.44%,过路黄生物量36.77 kg/hm²最低,仅占0.16%。杉木14年生时,以芒生物量573.00 kg/hm²最大,占总生物量44.78%,金毛耳草生物量2.93 kg/hm²最小,仅占0.23%。研究结果,可为研究杉木林养分循环、碳平衡、维护和提高林地地力及可持续经营管理提供科学依据。

Dynamics of understory vegetation biomass in successive rotations of Chinese fir (Cunninghamia lanceolata) plantations

Understory vegetation is an important component of forest ecosystems, and is known to have beneficial effects on soil fertility and nutrient cycling. Understory abundance and structure can be expected to change with forest development and understanding of dynamic properties of understory vegetation communities is of high significance in sustainable management of a forest ecosystem. However, quantitative assessment of understory dynamics in subtropical forests is lacking. The objective of this study was to examine how understory vegetation abundance, species composition and biomass production change with stand development after the second successive rotations of Chinese fir (Cunninghamia lanceolata) plantations were established at the same sites. This study has been carried out in Chinese fir forested small watersheds, located at the Huitong Ecosystem Research Station of the Central South University of Forestry and Technology in Hunan Province, one of the National Field Station for Scientific Observation and Experiment in China. The results showed that understory vegetation species was declined at 14 year after the establishment of the second rotation of Chinese fir plantations when compared with those at 3 year, of which woody plant species and herbaceous plant species decreased 40.0% and 47.1%, respectively. Understory vegetation biomass declined from 29.48 t/hm² at 3 year to 2.53 t/hm² at 14 year of the studied Chinese fir plantations, of which biomass of woody plant species and herbaceous plant species declined from 7.07 t/hm² to 1.25 t/hm² and from 22.41 t/hm² to 1.28 t/hm², respectively. In other words, understory biomass of woody and herbaceous plant species at 14-year old stands decreased by 82.3% and 94.3% compared that at 3-year old stands, respectively. Tree seedlings (6068.97 kg/hm²) dominated understory woody plant species biomass at 3 year of the studied stands, and the next was liana species biomass (736.97 kg/hm²) and shrubs species biomass (259.87 kg/hm²). Tree seedlings, liana and shrubs accounted for 85.9%, 10.4% and 3.7% of the total understory woody plant species biomass. In contrast, understory shrubs biomass was the highest (881.87 kg/hm²) at 14 year in the studied stands, and the second was liana biomass (247.07 kg/hm²), and the tree seedlings biomass was the lowest (117.87 kg/hm²). The three group accounted for 70.7%, 19.8% and 9.5% of the total understory woody plant biomass. Among understory herbaceous plant biomass at 3 year after the second rotation of Chinese fir stands were planted, biomass of fern (8391.44 kg/hm²) was the highest and accounted for 37.4% of the total herbaceous biomass, and Lysimachia christinae biomass was lowest (36.77 kg/hm²), only accounting for 0.16% of the total biomass. When the stands reached at 14 year old, biomass of Miscanthus sinensis (573.00 kg/hm²) was the highest and Hedyotis chrysotricha (2.93 kg/hm²) was the lowest among the understory herbaceous biomass components. The results demonstrated that understory biomass production and distribution change with stands development in the second successive rotations of Chinese fir plantations.