Tree productivity and water potential productivity in returning farmland to forest project in Datong County,Qinghai Province

From 2002 to 2003, based on the investigation of sample plots and stem analysis of remained plantation communities in the areas of returning farmland to forest in the 1980s in Datong County, Qinghai Province, this paper studies tree productivity and moisture potential productivity of six types of plantations on the land of returning farmland to forest, such as green poplar (Populus cathayana Rehd.) and shrub mixed forest, Asia white birch (Betula platyphylla) and China spruce (Picea asperata) mixed forest, Dahurian larch (Larix gmelinii) pure forest, China spruce pure forest and Asia white birch pure forest and so on. The results show that: in sub-humid region of Loess Plateau, 3 000 trees per hm² is a proper standard of planting density. Under current condition, the productivity index of green poplar and shrub mixed forest, Asia white birch pure forest, China spruce pure forest, and Asia white birch and China spruce mixed forest with the density of 2 100–3 333 trees per hm² can serve as potential productivity standard of actual biomass of arbor established forest. In sub-humid area, Thornthwaite Model is adopted to estimate plant climate potential productivity, which is about 8 462 kg•hm^–2•a^–1. The actual potential water productive efficiency of Purplecone spruce (Picea purpurea) and Asia white birch pure established forest are 17.22 and 22.14 kg•mm^–1•hm^–2•a^–1 respectively, and that of green poplar and shrub mixed established forest, and Asia white birch and China spruce mixed established forest are 21.14 and 19.09 kg•mm^–1•hm^–2•a^–1 respectively. The potential productivity of green poplar and shrub mixed forest, Asia white birch and China spruce mixed forest, China spruce pure forest and Asia white birch pure forest which have grown into forest with the density of 3 000 trees per hm² have attained or been close to that of local climax community, which is local maximum tree productivity at present. These types of forestation models are the developing direction of the returning farmland to forest project.     

红花尔基沙地樟子松天然林枯立木特征分析

[目的]了解沙地樟子松天然纯林中枯立木的数量及空间结构特征,探究枯立木形成的原因,为樟子松林的保护和经营提供依据。[方法]在沙地樟子松天然纯林中设置2块1 hm~2的大样地,用全站仪对样地中所有胸径大于5 cm的立木进行定位并进行全面调查;对调查样地的基本特征,枯立木的数量特征及径级分布进行了分析,提出了用于表达林分中枯立木微环境的活立木比的概念,并采用林分空间结构参数一元分布和二元分布分析方法,对枯立木与其最近4株相邻木的关系进行分析。[结果]2块不同密度的樟子松天然纯林下更新幼苗和枯立木数量相差较大,密度较小(样地1)的样地更新幼苗和枯立木较少,而密度较大的样地(样地2)中枯立木达到200棵,林下更新幼苗数量达到15 280株·hm~(-2);樟子松天然纯林样地内枯立木主要以小径级木为主,胸径集中在11 cm以下;样地1枯立木径级连续分布,幅度较窄;样地2中的枯立木径级幅度较宽,但在20 22 cm缺刻,有2株大于23 cm的枯立木;2块样地中枯立木的分布格局均为随机分布,样地1中枯立木周围的4株相邻立木大多为活立木,且胸径较枯立木大;样地2中,只有一半的枯立木周围的最近4株立木为活立木,且有三分之一以上的枯立木胸径不是最小的,枯立木有连续分布的现象。2块样地中枯立木的角尺度-大小比数二元分布特征的差异不明显,而角尺度-活立木比二元分布特征和大小比数-活立木比二元分布特征差异明显,样地1中枯立木的最近4株随机分布于其周围的相邻木为活立木且胸径大于枯立木的比例明显高于样地2,而枯立木最近4株随机分布于其周围的相邻木有枯立木的比例明显小于样地2。[结论]樟子松天然纯林枯立木以小径级林木为主,枯立木的数量与林分密度相关,林木竞争是林木死亡的主要原因,密度过大也会产生病虫害,因此,对天然樟子松纯林要进行适度经营,保持合理密度。     

近自然森林经营在德国的应用成效分析

[目的]分析德国推行近自然森林经营20年来的经营效果,总结德国推行近自然森林经营的经验。[方法]在明晰近自然森林经营原则的基础上,基于两期(间隔期10年)资源清查数据对比,对德国大面积推行近自然森林经营20年的经营效果进行分析。[结果]两期资源清查数据表明,德国采用近自然经营20年后,针叶林如挪威云杉和欧洲赤松的面积显著减少,阔叶林和针阔混交林面积持续增加;阔叶树种蓄积平均增长量约为15 m~3·hm~(-2),针叶树种蓄积平均增长4 m~3·hm~(-2),挪威云杉是唯一蓄积下降的树种,下降了5 m~3·hm~(-2);近自然度等级变化表明,人工林面积在减少,而近自然森林的面积在增加,甚至符合原始林等级的森林面积也在增加。[结论]实现近自然森林经营的目标是一个长期的过程,联邦政府促进和保护森林的政策以及林场主所采用的先进的森林经营技术也是德国森林每公顷蓄积达到336 m~3的重要原因;在近自然森林经营的原则下,德国森林中针阔混交林比例显著增加;将近自然程度不高的人工林经营转化为近自然的森林生态系统是德国森林经营所面临的主要问题。     

Biocycle of nitrogen in a Cyclobalanopsis glauca-dominated evergreen broad-leaved forest in East China

The nitrogen (N) cycling was elucidated in a 40-year-old subtropical evergreen broad-leaved forest dominated by Cyclobalanopsis glauca growing on red soil in Zhejiang Province, East China. The concentrations of N in the representative species ranged from 0.49% to 1.64%, the order of which in various layers was liana and herb layers > understory layer > tree and subtree layers; in various organs was leaf > branch > root > trunk; and aboveground parts > underground parts. The sequence of the concentrations of N in C. glauca was understory > tree > subtree layer; young and high-growing > old organs; reproductive > vegetative organs. Seasonal dynamics of the concentrations of N in C. glauca in the tree and subtree layers was comparatively stable. It was lower in autumn (October) in root, branch, and leaf in the tree layer, and low in January in the understory. There was no evident change in regularity of the concentrations of N in varying diameter classes. The concentrations of N in the litterfall, precipitation, throughfall, litter layer, and soil were 0.74%–2.30%, 0.000,038%, 0.000,09%, 1.94%, and 0.59%, respectively. The standing crop of N in the plant community was 1,025.28 kg/hm², accumulation in the litter layer was 224.88 kg/hm², and reserve in the soil was 55,151 kg/hm². Annual retention of N was 119.47 kg/hm², return was about 84.13 kg/hm², among which litterfall was 78.49 kg/hm² and throughfall, 5.64 kg/hm². Annual absorption of N was 203.60 kg/hm². Annual input of N through incident precipitation was 4.88 kg/hm². Compared with other forest types, cycling rate of N in the community was lower than in deciduous broad-leaved forests, rain forests, and mangroves, and was moderate in evergreen broad-leaved forests. N use efficiency of this forest was moderate among the forest types cited. According to the characteristics of the biocycle of phosphorous, it was concluded that N availability in the soil of this forest was not lower, and phosphorous not N was the limiting factor in the growth of plants in this community. __________ Translated from Acta Ecologica Sinica, 2005, 25(4): 740–748 [译自: 生态学报, 2005, 25(4): 740–748]     

甘肃兴隆山主要森林类型凋落物累积量及其影响因子

[目的]为了阐明森林凋落物累积量与主要影响因子的关系。[方法]2013-2014年,采用时空互代法和标准样地调查法,研究了兴隆山山杨-白桦-青杄林演替过程中山杨-白桦-青杄中龄林、青杄中龄林和青杄近熟林3种森林群落凋落物累积量及其主要影响因子。[结果]表明:1)随森林正向演替的进行,森林凋落物层厚度和总累积量先减小后增加,3种森林群落凋落物层厚度均值依次为5.26、5.03和5.59 cm,总累积量均值依次为57.08、51.44、56.34 t·hm^-2; 2)随海拔高度的升高,青杄近熟林凋落物总累积量不断增加,海拔2300、2400和2500 m均值依次为48.56、55.93和64.55 t·hm^-2;林分密度大的、坡度小的青杄中龄林凋落物总累积量较大,林分密度为2133、1705和1065株·hm^-2的均值依次为49.87、48.59和45.36 t·hm^-2,坡度为22°、32°和41°的均值依次为58.35、49.90和48.59 t·hm^-2; 3)凋落物未分解层与林分胸径、树高、针叶树密度呈显著相关性。[结论]森林凋落物累积量影响因子较多,其大小是众多因子共同作用的结果。在林分和立地因子中,海拔影响较为明显,随海拔高度的升高而不断增加;林分密度、坡度等因子均有影响,但作用不明显;林分胸径、树高、针叶树密度与未分解层累积量呈显著负相关性,而与已分解层呈显著正相关性。     

Effects of forest canopy gap on biomass of Abies faxoniana seedlings and its allocation in subalpine coniferous forests of western Sichuan

Using a strip transect sampling method, the density, height (≤ 100 cm), basal diameter and components of biomass of Abies faxoniana seedlings, living in a forest gap (FG) and under the forest canopy (FC) of subalpine natural coniferous forests in western Sichuan, were investigated and the relationships among different components of biomass analyzed. The results indicated that the density and average height (H) of A. faxoniana seedlings were significantly different in the FG and under the FC, with the values being 12903 and 2017 per hm², and 26.6 and 24.3 cm. No significant differences were found in the average basal diameter (D) and biomass. The biomass allocation in seedling components was significantly affected by forest gap. In the FG, the biomass ratio of branch to stem reached a maximum of 1.54 at age 12 and then declined and fluctuated around 0.69. Under the FC, the biomass ratio of branch to stem increased with seedling growth and exceeded 1.0 at about age 15. The total biomass and the biomass of leaves, stems, shoots and roots grown in the FG and under the FC were significantly correlated with D ² H. There were significant and positive correlations among the biomass of different components. __________ Translated from Chinese Journal of Applied Ecology, 2007, 18(4): 721–727 [译自: 应用生态学报]     

Carbon storage of artificial forests in rehabilitated lands in the upper reaches of the Yellow River

We studied 10-to 27-year-old artificial forests on rehabilitated lands in the upper reaches of the Yellow River with the objective of comparing the carbon densities of various artificial and natural forests. Under artificial plantations, the vegetation layer (including roots) had a mean carbon density of 111.3 t/hm², the litter layer a density of 5.1 t/hm², and the soil layer a density of 64.9 t/hm². These values accounted for 28.6%, 13.8%, and 61.0% of their respective counterparts in the natural secondary forests under the same site conditions in the region. The ratios of carbon density among vegetation, litter, and soil pools were 39.6:1.8:58.6 for artificial forests and 57.4:2.7:39.9 for natural forests. The carbon densities of the vegetation and litter layers increased exponentially with forest age. The total carbon density ratios were also increasing gradually. Although the mean total carbon density of the artificial forests in the rehabilitated lands was 281.2 t/hm² in the experimental area, it accounted for only 41.5% of the carbon density of the natural secondary forests (677.4 t/hm²). The annual increase in total carbon density of artificial forests was as high as 15.2 t/hm², which was 11.7% more than that of natural forests and 6.8 times higher than that (1.95 t/hm) of artificial forests in the entire country as measured during 1994–1998. This indicates that growth and carbon storage capacity of artificial forests in the rehabilitated lands were higher than those of forests on the barren hills and the secondary forests. We concluded that the conversion project from croplands to forests and grasslands based on scientific principles is very important in the formation of carbon sinks for reducing greenhouse effects. __________ Translated from Journal of Beijing Forestry University, 2005, 27(6): 1–8 [译自: 北京林业大学学报, 2005, 27(6): 1–8]     

Recovery process of a mountain forest after shifting cultivation in Northwestern Vietnam

The recovery process of fallow stands in the mountainous region of Northwestern Vietnam was studied, based on a chronosequence of 1–26-year-old secondary forests after intensive shifting cultivation. The number of species present in a 26-year-old secondary forest attained 49% of the 72 species present in an old-growth forest. Total stem density decreased gradually from 172,500 ha⁻¹ in a 3-year-old forest to 24,600 ha⁻¹ in the 26-year-old stand, but stem density of larger trees (diameter at breast height (D) ≥ 5 cm) increased from 60 ha⁻¹ in a 7-year-old to 960 ha⁻¹ in the 26-year-old forests, which was similar to that of an old-growth forest. Annual biomass increment of the 26-year-old stand was 4.2 Mg ha⁻¹ year⁻¹. A saturation curve was fitted to biomass accumulation in secondary forests. After an estimated time of 60 years, a secondary forest can achieve 80% of the biomass of old-growth forests (240 Mg ha⁻¹). Species diversity expressed by Shannon Index shows that it takes 60 years for a secondary forest in fallow to achieve a plant species diversity similar to that of old-growth forests.     

Aboveground biomass of three conifers in the Qianyanzhou plantation, Jiangxi Province, China

Regressive models of the aboveground biomass for three conifers in subtropical China—slash pine (Pinus elliottii), Masson pine (P. massoniana) and Chinese fir (Cunninghamia lanceolata)—were established. Regression analysis of leaf biomass and total biomass of each branch against branch diameter (d), branch length (L), d ³ and d ² L was conducted with functions of linear, power and exponent. A power law equation with a single parameter (d) was proved to be better than the rest for Masson pine and Chinese fir, and a linear equation with parameter (d ³) is better for slash pine. The canopy biomass was derived by adopting the regression equations to all branches of each individual tree. These kinds of equations were also used to fit the relationship between total tree biomass, branch biomass, foliage biomass and tree diameter at breast height (D), tree height (H), D ³ and D ² H, respectively. D ² H was found to be the best parameter for estimating total biomass. However, for foliage biomass and branch biomass, both parameters and equation forms showed some differences among species. Correlations were highly significant (P<0.001) for foliage biomass, branch biomass and total biomass, among which the equation of the total biomass was the highest. With these equations, the aboveground biomass of Masson pine forest, slash pine forest and Chinese fir forest were estimated, in addition to the allocation of aboveground biomass. The above-ground biomass of Masson pine forest, slash pine forest and Chinese fir forest was 83.6, 72.1 and 59 t/hm² respectively, and the stem biomass was more than the foliage biomass and the branch biomass. The underground biomass of these three forests which estimated with others’ research were 10.44, 9.42 and 11.48 t/hm², and the amount of carbon-fixed were 47.94, 45.14 and 37.52 t/hm², respectively. __________ Translated from Chinese Journal of Applied Ecology, 2006, 17(8): 1382–1388 [译自: 应用生态学报]     

Characteristics of leaf areas of plantations in semiarid hills and gully loess regions

The objectives of our study were to explore the relationship of leaf area and stand density and to find a convenient way to measure stand leaf areas. During the 2004 growing season, from May to October, we used direct and indirect methods to measure the seasonal variation of the leaf areas of tree and shrub species. The trees were from Robinia pseudoacacia stands of four densities (3333 plants/hm², 1666 plants/hm², 1111 plants/hm², and 833 plants/hm²) and Platycladus orientalis stands of three densities (3333 plants/hm², 1666 plants/hm², and 1111 plants/hm²). The shrub species were Caragana korshinskii, Hippophae rhamnoides, and Amorpha fruticosa. Based on our survey data, empirical formulas for calculating leaf area were obtained by correlating leaf fresh weight, diameter of base branches, and leaf areas. Our results show the following: 1) in September, the leaf area and leaf area index (LAI) of trees (R. pseudoacacia and P. orientalis) reached their maximum values, with LAI peak values of 10.5 and 3.2, respectively. In August, the leaf area and LAI of shrubs (C. korshinskii, H. rhamnoides, and A. fruticosa) reached their maximum values, with LAI peak values of 1.195, 1.123, and 1.882, respectively. 2) There is a statistically significant power relation between leaf area and leaf fresh weight for R. pseudoacacia. There are significant linear relationships between leaf area and leaf fresh weight for P. orientalis, C. korshinskii, H. rhamnoides, and A. fruticosa. Moreover, there is also a significant power relation between leaf area and diameter of base branches for C. korshinskii. There are significant linear relations between leaf area and diameter of base branches of H. rhamnoides and A. fruticosa. 3) In the hills and gully regions of the Loess Plateau, the LAIs of R. pseudoacacia stand at different densities converged after the planted stands entered their fast growth stage. Their LAI do not seem to be affected by its initial and current density. The same is true for P. orientalis stands. However, the leaf area of individual trees is negatively and linearly related with stand density. We conclude that, in the hills and gully regions of the Loess Plateau, the bearing capacity of R. pseudoacacia and P. orientalis stands we studied have reached their maximum limitation, owing to restricted access to soil water. Therefore, in consideration of improving the quality of single trees, a stand density not exceeding 833 and 1111 plants/hm² is recommended for R. pseudoacacia and P. orientalis, respectively. In consideration of improving the quality of the entire stands, the density can be reduced even a little more. __________ Translated from Journal of Plant Ecology (Chinese Version), 2008, 32 (2): 440–447 [译自: 植物生态学报]     

Gap formation in Danish beech (Fagus sylvatica) forests of low management intensity: soil moisture and nitrate in soil solution

Soil moisture content (0–90 cm depth) and nitrate-nitrogen (NO₃-N) concentrations in soil solution (90 cm depth) were monitored after gap formation (diameter 15–18 m) in three Danish beech-dominated forests on nutrient-rich till soils. NO₃-N drainage losses were estimated by the water balance model WATBAL for one of the sites. Two forests were non-intervention forests (semi-natural and unmanaged), the third was subject to nature-based management. The study was intended to assess the range of effects of gap formation in forests of low management intensity. In the unmanaged and the nature-based managed forest, soil solution was collected for 5 years and soil moisture measured in the fourth year after gap formation. Average NO₃-N concentrations were significantly higher in the gaps (9.9 and 8.1 mg NO₃-N l⁻¹, respectively) than under closed canopy (0.2 mg l⁻¹). In the semi-natural forest, measurements were carried out up to 29 months after gap formation. Average NO₃-N concentrations in the gap were 19.3 mg NO₃-N l⁻¹. Gap formation alone did not account for this high level, as concentrations were high also under closed canopy (average 12.4 mg NO₃-N l⁻¹). However, the gap had significantly higher N concentrations when trees were in full leaf, and NO₃-N drainage losses were significantly increased in the gap. No losses occurred under closed canopy in growing seasons. Soil moisture was close to field capacity in all three gaps, but decreased under closed canopy in growing seasons. In the semi-natural forest, advanced regeneration and lateral closure of the gap affected soil moisture levels in the gap in the last year of the study.     

六盘山主要植被类型的生物量及其分配

2009年,在宁夏六盘山南部林区香水河小流域,调查研究了主要森林类型的生物量及其层次和器官分配。结果表明:不同森林的活体植被总生物量(t·hm^-2)差别较大,依次为华山松(102.70)>桦木林(84.42)>山杨林(79.97)>华北落叶松人工林(58.37)>疏林(44.91),按各类森林面积加权平均为78.37,远高于灌丛(20.77)、草地(1.07)和草甸(2.29)。各类森林的枯落物现存量(t·hm^-2)为:华北落叶松人工林(18.21)>华山松林(11.99)>桦木林(10.90)>山杨林(7.67)>疏林(7.06),也都远高于灌木林(3.13)、草甸(0.82)和草地(0.49)。森林生物量集中在乔木层(占91.04%),灌木层仅占8.09%,草本层更低至0.87%。森林生物量的器官分配比例:乔木层为树干(54.06%)>枝(21.04%)>根(16.92%)>皮(5.34%)>叶(2.65%);灌木层为枝干(62.68%)>根(30.55%)>叶(6.77%);草本层为地上茎叶(58.82%)>根(41.18%)。乔木层地上与地下生物量比值的平均值为4.49,几种阔叶林都在4.0左右,但华北落叶松林为6.41,华山松林为5.80,都远大于灌木林的2.82、草地的1.89及草甸的1.20。不同林分的生物量均随林龄和林冠郁闭度的增大而几乎线性增加,并随林分密度的增加而增大,但在密度超过900株·hm^-2后生物量增速减缓并渐趋其最大值。     

Transfer characteristics of nutrient elements through hydrological process of a Pinus tabulaeformis stand in the West Mountain of Beijing

Forest precipitation chemistry is a major issue in forest hydrology and forest ecology. Chemical contents in precipitation change significantly when different kinds of external chemical materials are added, removed, translocated and transformed to or in the forest ecosystem along with precipitation. The chemistry of precipitation was monitored and analyzed in a 31-year-old Pinus tabulaeformis forest in the West Mountain of Beijing. Movement patterns of nutrient elements in hydrological processes can be discovered by studying this monitored data. Also, the information is useful for diagnosing the function of ecosystems and evaluating the impact of the environment on the ecosystem. Samples of rainfall, throughfall and stemflow were collected on the site. In the lab, Ca²⁺ and Mg²⁺ were analyzed by flame atomic absorption and K⁺ and Na⁺ by flame emission. NH₄ ⁺-N was analyzed by indophenol blue colorimetry and NO₃ ⁻-N was analyzed by phenoldisulfonic acid colorimetry. The results showed that: 1) The concentration gradient of nutrient elements clearly changed except for Na⁺. The nutrients in stemflow were significantly higher than those of throughfall and rainfall as the precipitation passed through the P. tabulaeformis forest. The monthly patterns showed distinct differentiation. There are indications that a large amount of nutrients was leached from the canopy, which is a critical function of intra-ecosystem nutrient cycling to improve the efficiency of nutrient use. 2) The concentrations of NO₃ ⁻-N and K⁺ changed more than those of the other nutrient elements. The concentration of NO₃ ⁻-N in throughfall and stemflow was 4.4 times and 9.9 times higher than those in rainfall, respectively. The concentration of K⁺ in throughfall and stemflow was 4.1 times and 8.1 times higher than those in rainfall, respectively. 3) The leaching of nutrient elements from the stand was an important aspect of nutrient return to the P. tabulaeformis forest, which returned a total amount of nutrient of 54.1 kg/hm², with the contribution of Ca²⁺ and K⁺ much greater than that of other elements. Also, K⁺ was the most active element in leaching intensity. 4) Nutrient input through precipitation was the main source in the West Mountain of Beijing and the amount of nutrient added was 66.4 kg/hm², of which Ca²⁺ and N contributed much more than the other nutrient elements. When precipitation passes through the P. tabulaeformis forest, 121 kg/hm² of nutrient is added to the forest floor. Ca²⁺ recorded the greatest nutrient increase, with 61.2 kg/hm², followed by N (NH₄ ⁺-N and NO₃ ⁻-N), K⁺ and Mg²⁺, with 31.3 and 16.5, and 8.11 kg/hm², respectively. The least was Na⁺, 3.34 kg/hm². Translated from Acta Ecologica Sinica, 2006, 26(7): 2,101–2,107 [译自: 生态学报]     

Biomass of a man-made forest of timber tree species in the humid tropics of West Java, Indonesia

Biomass of a mature man-made forest in West Java, Indonesia, was estimated to evaluate the carbon sequestration potential of plantation forest in the humid tropics. Twenty plots, each 0.25 ha in area and containing one to six planted species over 40 years of age and with closed canopies, were selected. Trunk dry mass was estimated from trunk diameter, tree height, and bulk density. Maximum trunk diameter (122 cm) was observed in a 46-year-old Khaya grandifoliola C. DC. tree, and the tallest tree (51 m) was a 46-year-old Shorea selanica (DC.) Blume. The largest trunk biomass (911 Mg ha⁻¹) was achieved in the plot composed of two Khaya spp. Among the plots composed of indigeneous Dipterocarpaceae species, the largest trunk biomass was 635 Mg ha⁻¹. These trunk biomasses were larger than those reported from primary rainforests in Southeast Asia (e.g., 403 Mg ha⁻¹ in East Kalimantan, 522 and 368 Mg ha⁻¹ in Peninsular Malaysia). The large biomass in this forest suggests that, given favorable conditions, man-made forests can accumulate the quantities of atmospheric carbon that were lost by the logging of primary forests in the humid tropics.     

Hydrological effects of forest litter and soil in the Simianshan Mountains in Chonging, China

A preliminary study of the hydrological effects of forest litter and soils in the Simianshan Mountains was carried out. Results indicate that the annual accumulation of different forest litters is about 6.80–20.21 t/hm² and the maximum water carrying capacity ranges from 1.8 to 4.6 mm. Among them the water carrying abilities of the litter of Lithocarpus glabra and natural deciduous forests are larger than that of Pinus massoniana. A power function relationship exists between the accumulated water-carrying volume and time. An investigation of the physical properties shows that forest soils, to a depth of 1 m, have a powerful water-carrying ability, varying from 7.84 to 18.87 mm. Non-linear regression analysis shows that the soil infiltration rate is significantly correlated with time. __________ Translated from Journal of Beijing Forestry University, 2005, 27(1): 33–37 [译自: 北京林业大学学报]     

Temperature sensitivity of soil CO2 production in a tropical hill evergreen forest in northern Thailand

Tropical forests, like boreal forests, are considered key ecosystems with regard to climate change. The temperature sensitivity of soil CO₂ production in tropical forests is unclear, especially in eastern Asia, because of a lack of data. The year-round variation in temperature is very small in tropical forests such that it is difficult to evaluate the temperature sensitivity of soil CO₂ production using field observations, unlike the conditions that occur in temperate and boreal forests. This study examined the temperature sensitivity of soil CO₂ production in the tropical hill evergreen forest that covers northern Thailand, Laos, and Myanmar; this forest has small temperature seasonality. Using an undisturbed soil sample (0.2 m diameter, 0.4 m long), CO₂ production rates were measured at three different temperatures. The CO₂ production (SR, mg CO₂ m⁻² s⁻¹) increased exponentially with temperature (T, °C); the fitted curve was SR = 0.023 e^0.077T, with Q₁₀ = 2.2. Although still limited, our result supports the possibility that even a small increase in the temperature of this region might accelerate carbon release because of the exponential sensitivity and high average temperature.     

Growth and population structure of the tree species Malouetia tamaquarina (Aubl.) (Apocynaceae) in the central Amazonian floodplain forests and their implication for management

The long-term success of forest management depends primarily on the sustainability of timber production. In this study we analyse the population structure, tree age and wood increment of Malouetia tamaquarina (Aubl.) (Apocynaceae) to define a species-specific minimum logging diameter (MLD) and felling cycle by modelling volume growth. Contrary to other timber species in the nutrient-rich white-water floodplains forests (várzea), M. tamaquarina grows in the subcanopy of old-growth várzea forests. The wood of this species is utilized by local inhabitants in the floodplains for handicraft. In 35 plots of 25 m × 50 m we measured diameter at breast height (DBH) and tree height of all trees taller than 150 cm height. From 37 individuals with DBH > 15 cm we sampled two cores by increment borers to determine the wood density, tree age and diameter increment rates. In the management area of a várzea settlement with about 150 ha recently harvested trees of M. tamaquarina have been recorded and DBH was measured. The species presents an inverse J-shaped diameter distribution indicating that the species is obviously regenerating in the old-growth forests. Tree-ring analysis indicates a mean age of 74.5 years for a DBH of 22.7 cm for a studied population comprising 37 trees with maximum ages of up to 141 years for an individual with a DBH of 45.7 cm. The tree species has low annual diameter increment rates (3.16 ± 0.6 mm) despite a low wood density (0.36 ± 0.05 g cm⁻³). The volume growth model indicates a MLD of 25 cm and a felling cycle of 32.4 years. In the management area 35 trees with a mean DBH of 24 cm were recorded, similar to the defined MLD. The abundance of trees above the MLD is 2.7 trees ha⁻¹, or 405 trees, when extrapolated to the whole management area. Considering a felling cycle of 32.4 years (annual production unit of 4.63 ha) this results in total of 12.5 harvestable trees, almost three times less than actually harvested. The actual practice of harvesting M. tamaquarina risks the overexploitation of this slow-growing species.     

Effect of density of trees on drag exerted on trees in river channels

Recently, riparian forests have attracted attention as they are effective for ecological preservation and landscape enhancement. Uses of such forests in flood prevention, sediment control, and erosion control works have been actively promoted. This study aims to clarify the effect of density of riparian trees on drag exerted on trees along river channels under the regime of bed load transport. Hydraulic model experiments were performed using a straight channel, and the methods to calculate the drag coefficient necessary for deriving drag exerted on trees were studied. Previous studies have stated that the drag coefficient of a cylinder is fairly constant when Reynolds number,R _e, is between 10³ and 10⁵ (e.g., Schlichting, 1979). This study clarified, however, that in cases of relatively dense arrangements of model trees (cylinders), the drag coefficient varies greatly with the density of the trees. As such, correlation between the drag coefficient and Reynolds number was found to be slight. Test results indicated that the drag coefficient of trees,C _d, correlates strongly with the coefficient of velocity,U′/U _* ′, friction factor of the channel bed,f′, and roughness concentration of trees × flow depth,aH′ or ratio of the area occupied by trees,λ. Furthermore, the drag coefficient,C _d, was also found to be slightly correlated with the gradient of the channel bed,I. Equations using either of the following parameters were obtained for deriving the drag coefficient,C _d, based on the experiment results:aH′; λ; U′/U _* ′; and Froude numberF _r. These equations allow fairly accurate calculation of drag exerted on trees.     

Forest biomass at Xiaolong Mountain in Gansu Province, China

In order to accurately estimate the size of the carbon pool and the capacity of the carbon sink in the forested areas of Xiaolong Mountain in Gansu Province, we have established regression equations of organ biomass of eight tree species. We measured and investigated the biomass of different forest stand types based on data from 1259 standard sample plots and 836 standard sample trees. The results show that stand biomass, expressed in t·hm⁻² for eight types of forest stands on Xiaolong Mountain, are as follows: Quercus aliena var. acuteserrata 84.05, Pinus tabulaeformis 62.44, Quercus variabilis 81.77, Populus sp. and Betula sp. combined 77.44, Larix sp. 69.00, Pinus armandii 70.07, Picea sp. 96.49 and Abies sp. 98.72. We also looked at other broad-leaved mixed forests. Our study shows that the biomass of a single tree of each tree species is closely related to the diameter at breast height (DBH) and to tree height. The biomass of single trees as well as stand volumes is closely related to average DBH, average tree height and to stand density. __________ Translated from Journal of Beijing Forestry University, 2007, 29(1): 31–36 [译自: 北京林业大学学报]     

阔叶红松林倒木贮量动态研究

本文研究了中国吉林省长白山区阔叶红松林倒木贮量的动态变化规律。阔叶红松林倒木贮量包括其现有倒木及其年输入量等贮量的变化规律。阔叶红松林现有倒木贮量开始为16.25 t·hm-2,以后随时间减少,到100年分解掉其干重的85%左右,300年后所剩无几。倒木年输入量平均约为0.6 t·hm-2,其贮量是随时间而增加,200年后稳定在31 t·hm-2,可保持到该群落的顶级时期。倒木总贮量的变化在初期呈增加趋势,而后随着现有倒木的完全分解,倒木贮量就与其倒木的年输入趋于一致,最后稳定在上述水平上。图4表2参9。