Effects of uprooting tree on herbaceous species diversity, woody species regeneration status and soil physical characteristics in a temperate mixed forest of Iran

We conducted a study to examine the pattern of development of herbaceous plant species, woody species regeneration and soil physical characteristics after tree uprooting in 20-ha areas of Experimental Forest Station of Tarbiat Modares University located in a temperate forest of Mazandaran province in the north of Iran. Soil bulk density, soil texture and moisture from pit and mound (PM) were measured in the laboratory. Results show that the soil bulk density was most in soil deeper layers at mound top, and the soil moisture content was most in soil deeper layers at Pit bottom. Our study supports that the micro-topography of PM (pit and mound) topography will create a mosaic of environmental conditions. This environmental heterogeneity could be responsible for the diversity of herbaceous plant species and regeneration of woody species. It is recommend that the fallen trees with PM structure should remain in the protected area without clearing as the best option for forest restoration. This information can be useful for forest management that attempts to emulate natural processes.     

额济纳胡杨空间分布格局及其与微生境异质性的关系研究

通过地统计学与方差分解等方法,对额济纳二道桥胡杨幼苗、幼树、成树以及微生境因子的分布格局进行研究。结果表明:受不同生活史阶段和微生境异质性的影响,胡杨幼苗趋于聚集分布,而幼树、成树则表现为随机分布;土壤全氮、含水率、全盐表现出显著的空间自相关结构,在空间上表现为聚集分布;胡杨幼苗的空间分布与土壤全盐含量呈负相关,而成树与土壤全氮、全盐显著正相关;环境因素与空间因素是影响胡杨种群分布格局的2个重要原因。     

Tree regeneration in gap-understory mosaics in a subtropical Shorea robusta(Sal) forest

Spatial variation in tree-regeneration density is attributed to the specialization of tree species to light availability for germination and growth. Light availability,in turn, varies across the gap-understorey mosaic. Canopy gaps provide an important habitat for the regeneration of tree species that would otherwise be suppressed in the understory. In subtropical forests, there is still a knowledge-gap relating to how canopy disturbances influence tree-regeneration patterns at local scale, and if they disproportionately favor regeneration of certain species. We aim to analyze whether canopy gaps promote tree regeneration, and tree species are specialized to gaps or understory for germination and growth. We sampled vegetation in 128 plots(0.01 ha), equally distributed in gaps and below canopy, in two subtropical Shorea robusta Gaertn.(Sal) forests in Nepal, recording the number of tree seedlings and saplings in each plot. We compared the regeneration density of seedlings and saplings separately between gaps and the understorey. The mean densities of seedlings and saplings were higher in the gaps at both sites;although there was no difference in the seedling density of the majority of the species between the habitats. No species were confined to either gap or understorey at the seedling stage. We conclude that gaps are not critical for the germination of tree species in Sal forests but these are an important habitat for enabling seedlings to survive into saplings. The classification of trees into regeneration guilds mainly based on germination does not apply to the majority of tree species in subtropical Sal forests. Our results reaffirm that gap creation promotes tree regeneration by favouring seedling survival and growth and can influence forest management for conservation, as well as for plantations.     

不同植被类型对沙地土壤理化性质的影响

为探讨不同植被类型与沙地土壤理化性质的影响,对我国辽西北沙地不同植被类型下土壤容重、土壤养分、水分含量进行了测定和分析。结果表明：辽西北沙地8种典型植被类型土壤容重大小依次为荒草地〉油松纯林〉弃耕地〉樟子松林〉山杏林〉榆树疏林〉松杨混交林〉杨树纯林;沙地经过人工固定后土壤的养分含量发生了变化,土壤有机质含量和全氮含量有不同程度的提高,全磷、全钾则有不同程度的下降。在雨季,针叶树林地土壤含水量高于其他植被类型,农业弃耕地在7月份和10月份中土壤表层含水量较高,山杏林地在不同时期含水量均表现为最低。     

不同经营措施对辽东红松林和杂木林土壤物理性质及土壤水分的影响

通过野外实地调查与室内分析,研究了不同经营措施下红松林和杂木林的土壤物理性质、土壤水分变化情况。结果表明:红松林择伐区土壤自然含水量、饱和含水量较杂木林高;土壤容重、总孔隙杂木林高于红松林;红松林内土壤的最大、最小、毛管持水量等指标皆高于杂木林。择伐上层林木栽植的红松林对土壤的改良效果较皆伐造林和直接林冠下造林者好。中度抚育间伐的森林经营措施改良土壤效果显著。     

Soil properties under a Pinus radiata – ryegrass silvopastoral system in New Zealand. Part I. Soil N and moisture availability, soil C, and tree growth

Understanding the changes in soil properties in silvopastoral systems is important in regulating the interactions between tree and understorey pastures. In this study, the effects of understorey management on soil mineral N and moisture availability, soil temperature, soil C, and tree growth were investigated in a seven-year-old silvopastoral agroforestry experiment in Canterbury, New Zealand. The systems included understorey treatments of bare ground and ryegrass (Lolium perenne) pasture. Soil mineral N, moisture content, and temperature were monitored from July 1997 to July 1998 in two positions (0.9 and 3.5 m north of tree rows) and two soil depths (0–10 and 10–20 cm). Soil C and N in the 0–10 cm depth were higher in the ryegrass than in the bare ground plots, reflecting the organic C and N input in the ryegrass plots, as well as greater N loss from the bare ground plots in the form of nitrate leaching and/or denitrification. Soil C was higher in the position 0.9 m than 3.5 m away from the tree rows, possibly caused by the greater C input from decomposing fine tree roots and needle litterfall at the 0.9 m position. Soil moisture availability was greater in the bare ground than in the ryegrass plots in the summer. No effect of understorey management on soil temperature was found. Soil nitrate levels were lower in the ryegrass plots and may be limiting when soil moisture supply was adequate. Tree volume growth from winter 1997 to 1998 was significantly greater in the bare ground treatment, reflecting better soil moisture and N supply conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Microclimate and soil moisture effects of three intercrops on the rows of a newly-planted intercropped plantation

Trees are grown in intercropping systems for a variety of purposes including wood products, fuelwood, fruit, forage or conservation purposes. No matter what end use, different tree/crop combinations interact differently resulting in differential growth rates of the trees during establishment. Preliminary work has shown that seedling growth and survival of trees are related to their intercrop and the results of this study help to explain these findings. Soil water potential, soil and air temperature, relative humidity, windspeed, and light (photosynthetic photon flux density — PPFD) were measured throughout the growing season in the clean-weeded treerows within crops of corn, soybeans and winter wheat. Crop height and biomass were also measured. This study was conducted during the 1992 growing season which was unusually cool and wet from mid June into the winter. The growth of winter wheat, measured by crop height and above-ground biomass, was earlier in the season than that of soybeans and corn, and this pattern affected the environmental conditions in the tree rows. Soil water potential was affected with associated effects on soil temperature (in combination with other factors). Crop height drastically reduced windspeed in the corn treatment from July through winter, also affecting PPFD and soil temperature later in the year. Although many microclimate differences were relatively small, data from subsequent years as well as associated soil moisture studies and additional years will help to further elucidate these relationships.     

Competition for nitrogen between adult European beech and its offspring is reduced by avoidance strategy

Plant growth, reproduction, and biomass allocation may be affected differently by nitrogen availability depending on tree size and age. In this context, competition for limited N may be avoided by different strategies of N acquisition between different vegetation components (i.e., seedlings, mature trees, other woody and herbaceous understorey). This study investigated in a field experiment whether the competition for N between different vegetation components in beech forests was prevented via seasonal timing of N uptake and affected by microbial N use. For this purpose, a removal approach was used to study the seasonal effects on N uptake and N metabolites in adult beech trees and beech natural regeneration, as well as soil microbial processes of inorganic N production and utilisation. We found that the competition for N between beech natural regeneration and mature beech trees was reduced by seasonal avoidance strategies (“good parenting”) of N uptake regardless of the N sources used. In spring, organic and inorganic N uptake capacity was significantly higher in beech seedlings compared to adult beech trees, whereas in autumn mature beech trees showed the highest N uptake rates. Removal of vegetation components did not result in changes in soil microbial N processes in the course of the growing season. Thus, N resources released by the removal of vegetation components were marginal. This consistency in soil microbial N processes indicates that competition between plants and soil microorganisms for N was not avoided by timing of acquisition during the vegetation period, but existed during the entire growing season. In conclusion, N nutrition in the studied forest ecosystem seems to be optimally attuned to European beech.     

半干旱黄土丘陵沟壑区人工林对土壤水分的适宜性分析

于2007～2010年生长季节,对侧柏、山杏、油松、柠条和山毛桃等林地土壤水分进行连续监测,并查阅相同树种和立地条件下的林分根系分布资料,以土壤水分对林木耗水满足程度作为评价指标,对半干旱黄土丘陵沟壑区小流域微地形条件下人工林对土壤水分的适宜性进行研究.结果显示:不同林分根系的垂直分布和土壤水分垂直变异相关性显著,水分...     

Seasonal pattern of nitrogen mineralization and soil moisture beneath Faidherbia albida (synAcacia albida) in central malawi

On fertile alluvial soils on the lakeshore plain of Malawi, maize (Zea mays L.) yields beneath canopies of large Faidherbia albida (synAcacia albida) trees greatly exceed those found beyound tree canopies, yet there is little difference in soil nutrients or organic matter. To investigate the possibility that soil nutrient dynamics contribute to increased maize yields, this study focused on the impact of Faidherbia albida on nitrogen mineralization and soil moisture from the time of crop planting until harvest. Both large and small trees were studied to consider whether tree effects change as trees mature.During the first month of the rainy season, a seven-fold difference in net N mineralization was recorded beneath large tree canopies compared to rates measured in open sites. The initial pulse beneath the trees was 60 g N g^–1 in the top 15 cm of soil. During the rest of the cropping cycle, N availability was 1.5 to 3 times higher beneath tree canopies than in open sites. The total production of N for the 4-month study period was 112 g N g^–1 below tree canopies compared to 42 g N g^–1 beyond the canopies. Soil moisture in the 0–15 cm soil layer was higher under the influence of the tree canopies. The canopy versus open site difference grew from 4% at the beginning of the season to 50% at the end of the cropping season.Both N mineralization and soil moisture were decreased below young trees. Hence, the impact of F. albida on these soil properties changes with tree age and size. While maize yields were not depressed beneath young F. albida, it is important to realize that the full benefits of this traditional agroforestry system may require decades to develop.     

武夷山不同类型毛竹林的土壤水分物理性质分析

调查分析了武夷山不同类型毛竹林的土壤水分物理性质状况。结果表明,不同类型毛竹林的土壤容重大小为对照地竹杉林竹阔林毛竹纯林;土壤总孔隙度大小为毛竹纯林竹阔林竹杉林对照地;各林地土壤最大持水量、毛管持水量大小为毛竹纯林竹阔林竹杉林对照;最小持水量大小为毛竹纯林竹杉林竹阔林对照;三项持水量依次是对照值的1.04~1.19倍、1.06~1.14倍、1.09~1.14倍。毛竹林分在0~60 cm土壤层的质地较为疏松,孔隙增多,透气性好,有利于水分的运输与贮存,适宜毛竹鞭根生长,因此,科学合理地经营毛竹林分,避免过度人为干扰可有效改善林分的水分物理状况,促进竹林丰产。     

Soil properties and nitrogen availability in silvopastoral plantings of Acacia melanoxylon in North Island, New Zealand

Acacia melanoxylon, a N₂-fixing timber tree occurring naturally in eastern Australia, is now promoted as a component of silvopastoral systems; but the interaction of the tree with pasture and soils has not been adequately studied. This study investigated the effects of Acacia melanoxylon on soil nitrogen (N) levels, N availability, soil pH, bulk density, organic carbon, C:N ratios and soil moisture in three separate silvopastoral sites with contrasting soil types in the North Island of New Zealand. At each site four tree stocking rates were studied (0, 500, 800, and 1700 stems ha^–1). The trees were nine years old at the time of the study. Soil samples from each study site were taken once at three depths (0 to 75 mm, 75 to 150 mm, and 150 to 300 mm), with three replicates per tree stocking rate. Soil analyses showed that although there were differences between soil types, few statistically significant differences occurred due to tree stocking rate. A greenhouse pot trial growing ryegrass (Lolium multiflorum L. cv. Concord) in soil from the A horizon of each soil type from under the trees and the open pasture found that ryegrass yield, N uptake and N supply increased with increasing tree stocking rate. Increased N supply under the trees, coupled with greater soil moisture compared to the open pasture may have accounted for the higher pasture yield under Acacia melanoxylon compared to non dinitrogen fixing tree species. This study suggested that Acacia melanoxylon in a silvopastoral system had the potential to increase soil N availability.This revised version was published online in November 2005 with corrections to the Cover Date.     

Effects of vegetation control on nutrient removal and Fagus orientalis, Lipsky regeneration in the western Black Sea Region of Turkey

Dense Rhododendron ponticum (L.) understories of eastern beech (Fagus orientalis Lipsky) stands in the Black Sea Region (BSR) of Turkey create challenging forest vegetation management problems relative to beech regeneration. Rhododendron traditionally is controlled in Turkish forests with grubbing and bulldozing. The effects of these practices on nutrient removal and natural beech regeneration have not been quantitatively studied. Two woody vegetation control treatments (bulldozing and hand-grubbing) were installed during late summer, 2002 in three mature beech stands with dense rhododendron understories in the Düzce Forest Management Directorate, in the Turkish western BSR. Aboveground biomass of each vegetation component, total aboveground vegetation biomass, nutrient concentrations, organic matter (OM) removal, and total amount of OM nutrients were determined for each woody vegetation control treatment. Soil bulk density and nutrient content, and beech seedling biomass, nutrient content, and natural regeneration also were studied. One year after treatment, the machine site preparation by bulldozing (MSP) that removed understory vegetation and attached roots, reduced mean forest floor OM content by about 84%, when compared to hand-grubbing. Mean soil C, N, K and Mg concentrations on the bulldozed sites were 36, 27, 50 and 55% less, respectively, than those on the grubbed sites. Total C and Mg amounts at the 5–10 cm soil depth were 24 and 47% lower, respectively, for mechanical site preparation (MSP) sites, when compared to grubbed sites. Overall, soil bulk density did not differ significantly between the grubbing and MSP treatments. Frequent passes on designated transects on MSP sites resulted in a significant (P < 0.01) one-third increase in bulk density of the first 20 cm soil depth, when compared to grubbed sites. No natural beech regeneration occurred on untreated control sites. Mineral soil exposure on the MSP sites increased beech seedling germination substantially. One year after treatment, the mean number of naturally regenerated seedlings for MSP sites was 2.5 times greater than for grubbed sites. Woody control treatments had significant effects upon beech seedling chemistry, with N, P, K, Ca and Mg concentrations averaging 35, 47, 12, 33 and 25% lower, respectively, for MSP sites, when compared to grubbed sites. However, mean seedling biomass and nutrient content were significantly greater (P < 0.05) on MSP sites. Long-term effects from windrowing on MSP site residues, associated topsoil and nutrients need to be evaluated.     

混农间作对兴安落叶松人工林土壤生态条件的影响

以落叶松人工纯林及落叶松与大豆混农间作人工林下土壤为研究对象,对不同林分下土壤物理性质和化学性质进行测定及比较分析,结果表明:混农林的土壤容重低于纯林,土壤总孔隙度和含水量大于纯林。另外,落叶松与大豆间作使土壤有机质含量增加,全N、速效N、P、K的含量增加,其中间作林土壤中N素含量增加尤为明显。     

Impact of soil drought on sap flow and water status of evergreen trees in a tropical monsoon forest in northern Thailand

Hill evergreen forest is the dominant vegetation type in northern Thailand. In this region, there is higher atmospheric evaporative demand and lower soil moisture during the 5- to 7-month dry season than in the rainy season under influences from Asian monsoons. In an earlier study we revealed that canopy-scale transpiration is actively maintained even during the latter part of the dry season in hill evergreen forest. However, the impact of soil drought on tree water use was not investigated. To clarify the ecohydrological processes at this site, we used individual tree-scale measurements during a 2-year period to base our examination of whether limited water use in individual trees is caused by soil drought in the latter part of the dry season. Sap flow and water potential measurements were conducted in four evergreen trees, two large emergent trees 29.8 and 25.4 m high, and two smaller understory trees 4.8 and 1.4 m high.The amount of rainfall preceding the late dry season of 2004 was significantly less than that preceding the late dry season of 2003. Although a distinct decrease in sap-flow velocities in individual trees due to soil water stress was not found in the late dry season of 2003, it did become comparatively apparent in the late dry season of 2004; ranging from 10 to 40% for a given atmospheric evaporative demand. Furthermore, the reductions in sap-flow velocities and predawn stem-water potential were most significant in the smallest tree. The recovery of sap-flow velocities and water potential in the smallest tree after irrigation confirmed that the reductions in sap-flow velocity and predawn stem-water potential in the smallest tree were caused by soil drought. These results suggest that shallower roots could be reason for the significant decrease in water use in the smallest trees. The deeper roots of larger trees could be the reason for the reduced impact of soil drought on water use in larger trees, and canopy-scale transpiration might be maintained by larger trees, even in an unusually severe drought. These possibilities provide a new insight for management of evergreen forests under Asian monsoon influences.     

Light,soil, and seedling characteristics associated with varying levels of competition in a red pine plantation

Red pine (Pinus resinosa Ait.) seedlings growing under differing levels of competition were evaluated during the fifth growing season following planting, and placed into low, moderate, or high tree classes, as a function of levels of competing vegetation. Tree growth, moisture status, and nutrition were monitored over the growing season. Additionally, site characteristics such as soil temperature and moisture, inorganic nitrogen concentration, mineralized soil nitrogen, and light were measured. Red pine seedlings growing under low competition had an absolute volume growth increase of 795% over the seedlings growing under the heaviest competition. The associated relative volume growth increase during the fifth growing season was 44%. Discriminant analysis was used to describe three classes of trees representing low, moderate, and high levels of competition. Trees growing under low competition had longer and heavier needles, but generally lower nutrient concentrations. Pre-dawn plant moisture status did not vary among competition levels. Soil variables indicated that, in general, the trees growing under low competition occupied warmer, drier, and less fertile microsites, as inorganic soil N and mean monthly mineralized NO₃-N and NH₄>-N tended to be lower on these microsites. The suite of independent variables was effective in classifying the model data into three tree competition classes, with percent correct classifications of 92, 75, and 100 for low (tree class one), moderate (tree class two), and heavy (tree class three) competition, respectively.     

巴山冷杉-牛皮桦混交林乔木更新及土壤化学性质对更新的影响

调查太白山巴山冷杉-牛皮桦混交林林下与林隙乔木更新及土壤化学性质,分析林隙及土壤化学性质对乔木更新的影响.结果表明:巴山冷杉-牛皮桦混交林乔木更新苗密度较小,为0.059株·m-2,但林下与林隙均以巴山冷杉更新苗为主;林下与林隙乔木更新苗密度差异不显著(P=0.160),但巴山冷杉幼苗密度表现为林隙内显著高于林下(P =0.012);相关分析表明,小林隙更利于巴山冷杉更新(r=- 0.397,P=0.030),而林隙大小对牛皮桦更新没有显著影响(r=0.125,P=0.511);在林下,土壤碱解N、全P含量和pH值与牛皮桦更新苗密度呈显著正相关;在林隙内,土壤全P和有效P含量与巴山冷杉更新苗密度呈显著负相关,全P含量与牛皮桦幼树密度呈显著负相关;林下土壤有机质含量、全N含量和有效P含量及林隙土壤pH值、有机质含量、全N含量和碱解N含量与牛皮桦和巴山冷杉更新苗密度均没有显著相关关系;林下土壤pH值显著高于林隙,而有机质、全N、碱解N、全P和有效P含量显著低于林隙.     

Using vector analysis to understand temporal changes in understorey-tree competition in agroforestry systems

Techniques to determine the respective effects of resource limitation or over supply on tree productivity are important for developing effective forestry and agroforestry management strategies. There is a need for a simple integrative measure of the understorey effect on soil nutrient and moisture competition on tree productivity in agroforestry systems during the time period before trees dominate understorey vegetation. For the first time, the little used, but potentially valuable tool of vector analysis was evaluated over 5 years by investigating nutrient and water competition in a Pinus radiata silvopastoral experiment which had 5 pastures and a nil-understorey control. The study, from ages 2 to 6 years, was on fertile arable soils in a temperate, sub-humid climate. Establishing permanent crops on this arable site increased soil pH, C, N, organic-P and C:N ratio. Vector analysis, an analysis based on fascicle nutrient concentrations, dry weights and nutrient contents, predicted nutrient and moisture competition until the trees dominated the site after year 5. Foliar critical nutrient levels were helpful where one of the vectors was unable to distinguish between nutrient and moisture stresses. While moisture and N were found to be the main competitive factors, vector analysis also detected foliar nutrient accumulation, particularly for P and Mg. Lucerne and phalaris understoreys were the most competitive pastures, followed by cocksfoot and the two ryegrass treatments. Foliage vector analysis enabled the relative competitive effects of soil nutrients and moisture on tree productivity to be determined. Soil nutrient concentrations and soil moisture measurements and the effects of competition on tree growth were consistent with predictions from vector analysis.     

石泥堆裸露山体植物绿化生态效应研究

通过石泥堆类型裸露山体植物绿化研究，结果表明，以巨尾按、台湾相思、马占相思和东南爬山虎容器苗为种植材料，在石泥堆中采用挖穴整地、下客土并拌少量过磷酸钙的造林措施，雨天在石泥堆中“见缝插针”栽种，3年生各种植物保存率达85％以上，高生长量达4．8～7．3m；土壤理化性质得到较大改善；土壤侵蚀量下降了72．53％～88．15％，提高了保持水土的功能。石泥堆选用巨尾桉、台湾相思、马占相思和东南爬山虎植物绿化可在短时间内恢复山体植被和生态系统。     

青海省湟水河流域退耕还林地土壤可蚀性研究

以青海湟水河流域2000—2009年退耕还林地为研究对象,基于野外定点观测和室内实验分析,测定土壤理化性质,采用EPIC模型中的算法求算土壤可蚀性K值,研究不同退耕还林年限和不同植被类型土壤可蚀性的变化情况。结果表明:1)随着退耕年限的增加,土壤孔隙度逐渐增大;砂粒含量略微增加;粉粒含量略有减少;黏粒含量则基本不变;有机质在退耕7年内逐渐减少,之后又开始增加;土壤可蚀性有降低的趋势,退耕9年后对土壤可蚀性有较明显的改善。2)相同退耕年限,退耕植被类型改善土壤可蚀性能力为乔木混交林>乔灌混交林>乔木林>灌木林,且退耕年限越长变幅越大,差别越明显。