皆伐萌蘖更新是改造刺槐林的有效途径

刺槐是我国中西部重要的水土保持林树种。由于滥和管理问题致使大面积的刺槐人工林虽有生态效益，但经济效益很低。经我们在长武王东沟区多年试验研究表明：皆伐萌蘖更新是改造低产值刺槐林的有效途径。     

Forest recovery after clear-cutting in Chinese pine(Pinus tabuliformis) plantations of North China

In Hebei Province of North China, forest was recovered with natural recruitment in plantations with large area of clear-cutting Chinese pine(Pinus tabuliformis). This study was aimed to demonstrate the dynamic characteristics of recruits during the natural recruitment. Both plot survey and the spatial point-pattern analysis were performed. Five developmental stages of natural recruitment were selected and studied, including 1 year before and 2, 5, 8, and 11 years after clear-cutting. Different slope aspects were also included. Natural recruitment was always dominated by Chinese pine with a proportion of higher than 90%. For plots of 1 year before clear-cutting on east-and north-facing slopes, recruit densities were 7886 and 5036 stems/hm2, the average heights were 0.78(±0.85) and 1.06(±1.15) m, and the average diameters at breast height(DBH) were 3.21(±1.38) and 2.91(±1.38) cm, respectively. After clear-cutting, recruit density was initially increased, then it was gradually declined with time; however, the variation of average DBH was contrary to that of recruit density. Both of them were no longer varied between 8 and 11 years after clear-cutting. The average height of recruits continued to increase after clear-cutting. For the plots of 11 years after clear-cutting on east-and north-facing slopes, average heights of recruits reached 2.00(±1.14) and 2.24(±1.20) m, respectively. The statuses of recruits on north-facing slopes were better than those on east-facing slopes after clear-cutting. Meanwhile, recruits on east-facing slopes were always aggregated at small scales, while spatial pattern of recruits varied with time on north-facing slopes. Moreover, forest was recovered more quickly by natural recruitment than by artificial afforestation after clear-cutting. The structural diversity was higher in naturally regenerated forests than in plantations of the same age. Our results demonstrated that clear-cutting of Chinese pine plantations recovered by natural recruitment has the potential to be an effective approach for establishing multifunctional forest.     

皆伐方式对小兴安岭低质林土壤呼吸的影响

针对小兴安岭低质林分,采用不同的皆伐方式,利用LI-8100碳通量自动监测系统在春、夏、秋、冬4个季节对低质林分土壤呼吸进行观测,运用统计分析的方法,分析皆伐方式对土壤呼吸的影响和不同皆伐方式的土壤呼吸产生差异的原因.结果显示:试验区土壤呼吸夏季最大,冬季最低.春季和秋季因土壤温度和湿度差异不大使土壤呼吸相差较小;对于水平带同一条皆伐带,土壤呼吸并无显著性差异,并且不同的带宽对土壤呼吸的影响也不显著;垂直带随海拔升高土壤呼吸呈现波动性,总体趋势随海拔升高土壤呼吸逐渐降低,但是差距较小;水平带、垂直带和林窗的年土壤呼吸量分别为1.184,1.426,1.179 kgCO2·m-a-1,垂直带最高,水平带次之,林窗最低.影响垂直带土壤呼吸的关键因素是土壤温度,林窗则是土壤湿度,而水平带土壤温度和湿度的条件则介于垂直带和林窗之间.这说明在不同的皆伐方式条件下,影响土壤呼吸的关键因素并不完全相同.     

Methane consumption in a frequently nitrogen-fertilized and limed spruce forest soil after clear-cutting

Abstract. The effects of especially frequent nitrogen (N) additions (from 1959 to 1986, totalling 860 kg N ha⁻¹) and liming (in 1958 and 1980, totalling 6000 kg CaCO₃ ha⁻¹) on CH₄ uptake by a boreal forest soil were studied in a stand of Norway spruce. Except for a forested reference plot, the stand was clear-cut in January 1993 and the following year one-half of each clear-cut plot was prepared by mounding. Fluxes of CH₄ were measured with static chambers in the autumn before clear-cutting and during the following four summers. The average CH₄ uptake during 1993–96 in the forested reference plot was 82 μg CH₄ m⁻² h⁻¹(ranging from 10 to 147 units). In the first summer after clear-cutting, the cleared plot showed 42% lower CH₄ uptake rate than the forested reference plot, but thereafter the difference became less pronounced. The short-term decrease in CH₄ consumption after clear-cutting was associated with increases in soil NH₄⁺ and NO₃⁻concentrations. Mounding tended at first to stimulate CH₄ uptake but later to inhibit it. Neither liming nor N-fertilization had significant effects on CH₄ consumption. Our results suggest that over the long term, in N-limited upland boreal forest soils, N addition does not decrease CH₄ uptake by the soil.     

3种皆伐方式对毛竹林更新生长的影响

研究了不同面积规模的全面皆伐(2.0 hm²和3.33 hm²)、带状皆伐(带长均为60 m,带宽分别为3m、6 m和9 m)和块状皆伐(25 m²、100 m²和400 m²)对毛竹林更新生长的影响。结果显示:3种皆伐方式对竹林更新生长影响不同,其中全面皆伐后的竹林长势较差,生物量较低,且皆伐面积越大,竹林更新生长越差;带状皆伐,皆伐带宽为3 m和6 m的竹林更新生长状况均较好,以带宽为6 m时综合效果最好;在块状皆伐中,皆伐面积为25 m²的竹林更新生长最好。此外,皆伐后对毛竹伐桩进行施肥,能够促进竹林的恢复生长;竹林的坡向也影响林分的更新生长,阴坡林分通常在皆伐后2年即能恢复到皆伐前状态,而阳坡林分的恢复则需要3年以上。     

红松皆伐迹地更新红松的效果分析

为了探讨红松皆伐迹地更新红松的效果,对红松皆伐迹地更新的红松的生长情况进行了调查研究,结果表明：红松皆伐迹地更新红松效果不良,无论是胸径还是树高,其生长量都比较缓慢,荒山荒地更新的红松,胸径生长量比红松皆伐迹地高32%,树高生长量高62%;红松皆伐迹地的土壤理化性质均不如荒地,针叶N、P、K的含量和叶面积指数皆低于荒地,更新10年后根系的分布,无论是水平分布还是垂直分布,都远不如荒地的更新效果。建议对红松皆伐迹地应该培养人工阔叶林或人工针阔混交林。     

Long-term oscillation of drought conditions in the western China:an analysis of PDSI on a decadal scale

Water resource availability is one of the primary limiting factors with regard to ecosystems in the western China.Having a clear understanding of multi-scale drought patterns in this region is a key step for adaption and mitigation to climate change.The Palmer drought severity index(PDSI) is a widely applied index to assess drought conditions.In this study,long-term monthly self-calibrated PDSI data from 1951 to 2012 were examined for drought spatiotemporal variations in the western China.The results clearly indicated that apparent spatial heterogeneities were evidenced between two sub-regions(arid land with annual precipitation less than 200 mm and semiarid land with annual precipitation between 200 to 500 mm) as well as in the entire region of the western China.Ensemble empirical mode decomposition(EEMD) analyses on monthly PDSI and other atmospheric variable time-series obtained from the Department of Civil and Environmental Engineering,Princeton University revealed that all monthly time-series of variables could be completely decomposed into eight intrinsic mode functions(IMFs) and a trend(residual).This indicates that the monthly PDSI and atmospheric variables of the semiarid area in the western China contain eight quasi-period oscillations on various timescale spanning,seasonal to decadal cycles and a trend of a larger timescale from 1951–2012.The multi-scale drought patterns identified in this research could be powerful supports for decision-making regarding coping with droughts in this region.     

米槠人促更新林皆伐火烧后初期土壤CO2通量动态

[目的]为科学评价皆伐、火烧对中亚热带常绿阔叶林不同深度土壤有机碳吸存的影响,[方法]以福建省中亚热带36年生米槠人促更新林为研究对象,采用非散射红外CO₂浓度探测仪和Licor-8100土壤碳通量系统,并结合Fick扩散法计算并分析0~80 cm不同深度土层CO₂通量的日动态特征。[结果]表明:(1)火烧地(RB)和皆伐地(RR)不同土层CO₂浓度均出现明显下降,其中,对照(CK)地土壤CO₂浓度值(0~80 cm)分别是RB和RR的1.9、1.3倍;(2)各试验地土壤CO₂通量(0~80 cm)表现为RB(1.99 μmol·m²·s^-1)>RR(0.99 μmol·m²·s^-1)>CK(0.96 μmol·m²·s^-1),除2040 cm土层外,RB土壤各层CO₂通量均显著高于RR和CK(P<0.05);(3)试验地不同土层CO₂通量(0~80 cm)日变化幅度表现为RB>RR>CK,其中,RB土壤各层的变化幅度均显著大于RR和CK(P<0.05),而RR与CK间的差异表现在0~5、10~20、20~40 cm土层(P<0.05);(4)拟合分析表明,各试验地不同深度土壤CO₂通量与土壤温度呈显著相关,且 RB的决定系数(R²)显著高于RR和CK;不同试验地各土层温度、含水量的双因素模型拟合效果均优于单因素模型;Q₁₀值显示,皆伐、火烧后初期土壤各层的温度敏感性得到明显提高。     

杉木林采伐迹地连栽和撂荒对林地土壤养分与酶活性的影响

研究湖南会同连栽第2代杉木人工纯林和撂荒对第1代杉木人工林采伐迹地土壤养分与酶活性的影响.结果表明:0～30 cm和30～60 cm土层中,撂荒地土壤有机质、养分含量普遍高于连栽杉木人工林地,且腐殖质碳、有效磷含量的差异均达到极显著水平(P＜0.01),全磷含量在0～30 cm土层中的差异达到显著水平(P＜0.05).0～30 cm土层中,撂荒地过氧化氢酶活性极显著高于连栽杉木人工林地(P＜0.01),磷酸酶、脲酶、蔗糖酶活性均显著高于连栽杉木人工林地(P＜0.05),30～60 cm土层中,撂荒地过氧化氢酶、蔗糖酶活性也显著高于杉木人工林地(P＜0.05),磷酸酶和脲酶活性也高于连栽杉木人工林地,但差异不显著(P＞0.05).林地土壤过氧化氢酶、磷酸酶、脲酶、蔗糖酶活性与土壤有机质、养分含量之间均呈较好的正相关,而且与水解氮、速效磷、腐殖质碳的相关性高于其与有机质的相关性.主成分分析表明,土壤酶活性在林地土壤质量体系中扮演着重要角色,其中脲酶、蔗糖酶和磷酸酶可作为林地土壤质量评价的指标.撂荒具有更好地恢复土壤养分含量和酶活性的能力,对维持杉木人工林地持续生产力有着重要作用.     

不同清理方式下人工幼林地的水土流失规律

[目的]研究不同清理方式下人工幼林地的水土流失规律,为人工林科学经营和生态管理提供科学依据。[方法]在广西壮族自治区南部马尾松采伐迹地人工更新的林地上,基于2018—2020年野外径流小区定位观测数据,对比研究了炼山和不炼山两种林地清理方式下的水土流失规律。[结果](1)林地清理方式对水土流失的影响随炼山后林地恢复年限的增加急剧减小,但炼山后的前2 a,无论是按年、月统计的水土流失量,还是按场次降雨量统计的水土流失量,炼山均显著高于不炼山(p<0.05)。(2)炼山降低了发生地表径流的最小降雨量。且随次降雨量的增加,炼山区域水土流失量的增加幅度明显大于不炼山区域。[结论]在广西南部皆伐林地,炼山后的前2 a是水土流失发生的主要时期,也是防治水土流失的关键时期。