Use of water stress integral to evaluate relationships between soil moisture,plant water stress and stand productivity in young Douglas-fir trees

Water stress integral (WSI) is a method of assessing cumulative plant water stress over a chosen period of time. While the technique has been used in other tree species, it has not been applied for reforestation projects. In this study we used the WSI approach for newly planted Douglas-fir in the Pacific Northwest (USA), where the Mediterranean climate, plant community development, and competition for water all play key roles in the success of establishment efforts. In this study, previously reported seedling growth, xylem water potential, and soil moisture data were utilized to provide direct correlations between Douglas-fir productivity, soil water availability and WSI. For each growing season, a strong relationship between WSI and volume growth as well as a strong linear relationship between WSI and soil moisture measured during mid-August was found. On average, for each reduction of 0.01 cm³ cm^?3 in soil moisture measured during mid-August, Douglas-fir seedling volume growth decreased by 5.6 and 7.7% in the first and second growing seasons, respectively. Preserving soil moisture until early-August through the judicial application of vegetation management regimes was critical for maximizing stand productivity. Based on these results, a single evaluation of soil volumetric water content during early-August can be used as a predictor of stand productivity during the initial two seasons of forest establishment.     

Influence of climate change,fire and harvest on the carbon dynamics of black spruce in Central Canada

The results of EFIMOD simulations for black spruce (Picea mariana [Miller]) forests in Central Canada show that climate warming, fire, harvesting and insects significantly influence net primary productivity (NPP), soil respiration (Rs), net ecosystem production (NEP) and pools of tree biomass and soil organic matter (SOM). The effects of six climate change scenarios demonstrated similar increasing trends of NPP and stand productivity. The disturbances led to a strong decrease in NPP, stand productivity, soil organic matter (SOM) and nitrogen (N) pools with an increase in CO₂ emission to the atmosphere. However the accumulated NEP for 150 years under harvest and fire fluctuated around zero. It becames negative only at a more frequent disturbance regime with four forest fires during the period of simulation. The results from this study show that changes in climate and disturbance regimes might substantially change the NPP as well as the C and N balance, resulting in major changes in the C pools of the vegetation and soil under black spruce forests.     

冀北沙荒地退化程度诊断及其短期封育效果评价

以冀北退化沙荒地为研究对象,以恢复生态学为研究理论基础,对冀北沙荒地各项指标进行权重赋值,诊断沙荒地的退化程度,并通过分析封育区、未封育区及其地带植被演替顶级群落的土壤理化性质和植被数量特征,评价5年封育效果。结果表明,沙荒地封育区及未封育区均属中度退化程度,沙荒地土壤状况尚未因为5年的封育得到明显改善;植被状况虽有明显改善,但还处在演替初期的草本植被阶段,与地带植被演替顶级群落仍存在很大差距,封育措施需要持续下去。     

全球气候变化及森林生态系统的适应性管理

人类活动所引起的温室效应及由此造成的全球气候变化对全球生态环境的影响正越来越引起人们的关注。森林作为全球陆地生态系统的一个重要组分, 对全球气候变化的响应较为敏感。文中系统总结了全球气候变化对物种和森林类型分布、森林生态系统结构和物种组成、森林生产力、森林土壤碳氮循环和森林灾害等几个方面的影响, 以及森林生态系统管理面临的挑战, 在此基础上提出了适应未来气候变化的森林生态系统管理策略。     

Assessing risks and uncertainties in forest dynamics under different management scenarios and climate change

Background: Forest management faces a climate induced shift in growth potential and increasing current and emerging new risks. Vulnerability analysis provides decision support based on projections of natural resources taking risks and uncertainties into account. In this paper we(1) characterize differences in forest dynamics under three management scenarios,(2) analyse the effects of the three scenarios on two risk factors, windthrow and drought stress, and(3) quantify the effects and the amount of uncertainty arising from climate projections on height increment and drought stress.Methods: In four regions in northern Germany, we apply three contrasting management scenarios and project forest development under climate change until 2070. Three climate runs(minimum, median, maximum) based on the emission scenario RCP 8.5 control the site-sensitive forest growth functions. The minimum and maximum climate run define the range of prospective climate development.Results: The projections of different management regimes until 2070 show the diverging medium-term effects of thinnings and harvests and long-term effects of species conversion on a regional scale. Examples of windthrow vulnerability and drought stress reveal how adaptation measures depend on the applied management path and the decision-maker's risk attitude. Uncertainty analysis shows the increasing variability of drought risk projections with time. The effect of climate projections on height growth are quantified and uncertainty analysis reveals that height growth of young trees is dominated by the age-trend whereas the climate signal in height increment of older trees is decisive.Conclusions: Drought risk is a serious issue in the eastern regions independent of the applied silvicultural scenario,but adaptation measures are limited as the proportion of the most drought tolerant species Scots pine is already high. Windthrow risk is no serious overall threat in any region, but adequate counter-measures such as species conversion, species mixture or reduction of target diameter can be taken. This simulation study of three silvicultural scenarios and three climate runs spans a decision space of potential forest development to be used for decision making. Which adaptation measures to counteract climate induced risks and uncertainty are to be taken is,however, a matter of individual risk attitude.     

Reforestation of degraded Kermes oak shrublands with planted pines: effects on vegetation cover, species diversity and community structure

This paper examines the results of plantings of the Mediterranean pine species, Pinus halepensis and Pinus pinea, in a degraded Mediterranean kermes oak (Quercus coccifera) shrubland in Northern Greece, which were accomplished in order to mitigate ecosystem degradation. Plant establishment and the vegetation differences between the degraded ecosystem’s previous state and the new state following reforestation were measured in order to evaluate the effect of reforestation. Monitoring of the seedling survival and growth of the planted species was carried out during the next five years. In the fifth year we conducted botanical inventories in 18 and 15 plots (50 m² in size) from the reforested and control area, respectively. Plant community parameters estimated were: vegetation composition, total plant cover, planted species cover, native woody, herb and grass species cover, plant species richness, Shannon-Weiner index, community structure and dominant plant height. P. halepensis exhibited higher survival and growth than P. pinea. The reforested area exhibited higher plant diversity, higher vegetation cover, taller plants and more complex community structures than the control area, which concludes that plantings of pines can be successfully used in degraded ecosystem reforestation projects, in areas with similar site conditions.     

城市绿地节水机制与技术研究

文中对城市植物节水机制和城市绿地节水技术进行了探讨。植物节水机制的研究主要包括植物抗旱以及节水的生理、遗传学基础等方面,可用于城市绿地的节水技术主要有中水回用和雨水利用、合理灌溉、选择乡土植物与节水耐旱植物进行合理配置、实施有机覆盖物的土壤养护和政策管理等。       

Intercropping system of tropical leguminous species and Eucalyptuscamaldulensis, inoculated with rhizobia and/or mycorrhizal fungi in semiarid Brazil

For the purpose of reforestation and wood supply the leguminous tree Anadenanthera peregrina, a native species, was intercropped with Eucalyptus camaldulensis in a degraded semiarid area of Brazil. Single and mixed stands of these species were inoculated with Rhizobium and/or arbuscular mycorrhizal fungi (AMF). The growth of all species in mixed stands did not differ from those cultivated in monoculture and land equivalent ratio (LER) exceeded unity in intercropped plots. Inoculated plants showed greater height and diameter growth and dry matter and nutrient concentration in plants of A. peregrina was higher in inoculated single plots. The distribution, composition and density of AMF species was related to the rhizosphere effect of plant species. The intercropped model where all the plants were inoculated achieved soil AMF diversity patterns similar to those of the preserved area and showed also higher soil organic matter, nutrient content as well as a reduction in soil macroporosity. This model of intercropping may be considered as an efficient system for reforestation under semiarid conditions.     

Water stress responses of two Mediterranean tree species influenced by native soil microorganisms and inoculation with a plant growth promoting rhizobacterium

Soil microorganisms, such as plant growth-promoting rhizobacteria (PGPR), play crucial roles in plant growth, but their influence on plant water relations remains poorly explored. We studied the effects of native soil microorganisms and inoculation with the PGPR strain Aur6 of Pseudomonas fluorescens on water stress responses of seedlings of the drought-avoiding Pinus halepensis Mill. and the drought-tolerant Quercus coccifera L. Plant growth, nutrient concentrations and physiology (maximum photochemical efficiency of photosystem II (PSII; F(v)/F(m)), electron transport rate (ETR), stomatal conductance (g(s)) and predawn shoot water potential (Psi(PD))) were measured in well-watered plants, and in plants under moderate or severe water stress. Inoculation with PGPR and native soil microorganisms improved tree growth, and their interactions had either additive or synergistic effects. Both F(v)/F(m) and ETR were significantly affected by PGPR and native soil microorganisms. Marked differences in g(s) and Psi(PD) were found between species, confirming that they differ in mechanisms of response to water stress. A complex tree species x treatment interactive response to drought was observed. In P. halepensis, F(v)/F(m) and ETR were enhanced by PGPR and native soil microorganisms under well-watered conditions, but the effects of PGPR on Psi(PD) and g(s) were negative during a period of water stress. In Q. coccifera, F(v)/F(m) and ETR were unaffected or even reduced by inoculation under well-watered conditions, whereas Psi(PD) and g(s) were increased by PGPR during a period of water stress. Our results indicate that microbial associates of roots can significantly influence the response of tree seedlings to drought, but the magnitude and sign of this effect seems to depend on the water-use strategy of the species.     

Environmental controls on sap flow in a northern hardwood forest

Our objective was to gain a detailed understanding of how photosynthetically active radiation (PAR), vapor pressure deficit (D) and soil water interact to control transpiration in the dominant canopy species of a mixed hardwood forest in northern Lower Michigan. An improved understanding of how these environmental factors affect whole-tree water use in unmanaged ecosystems is necessary in assessing the consequences of climate change on the terrestrial water cycle. We used continuously heated sap flow sensors to measure transpiration in mature trees of four species during two successive drought events. The measurements were scaled to the stand level for comparison with eddy covariance estimates of ecosystem water flux (Fw). Photosynthetically active radiation and D together explained 82% of the daytime hourly variation in plot-level transpiration, and low soil water content generally resulted in increased stomatal sensitivity to increasing D. There were also species-specific responses to drought. Quercus rubra L. showed low water use during both dry and wet conditions, and during periods of high D. Among the study species, Acer rubrum L. showed the greatest degree of stomatal closure in response to low soil water availability. Moderate increases in stomatal sensitivity to D during dry periods were observed in Populus grandidentata Michx. and Betula papyrifera Marsh. Sap flow scaled to the plot level and Fw demonstrated similar temporal patterns of water loss suggesting that the mechanisms controlling sap flow of an individual tree also control ecosystem evapotranspiration. However, the absolute magnitude of scaled sap flow estimates was consistently lower than Fw. We conclude that species-specific responses to PAR, D and soil water content are key elements to understanding current and future water fluxes in this ecosystem.     

物种入侵的生态学和进化生物学思考

物种入侵是指外来物种在自然状态或人类作用下,在异地生长、繁殖并建立种群的现象。目前,物种入侵已极为普遍,引起了全球性的关注。物种入侵产生了许多生态和环境问题,但是,它也为我们更好地了解自然界提供了大量的研究和实验的机会。来自于物种入侵研究(基础和应用性研究)的观点,对于理解正在形成的关于自然界的生态学、进化和生物地理学的一些观点非常重要。对于物种入侵的研究也可以支撑合理保护、管理和政策与对策的正常发展,这些对于阐述全球变化的许多方面包括物种灭绝、进化上的物种多样化以及生态系统功能都是必要的。本文从生态学和进化生物学的角度对物种入侵问题进行了分析,以期能使对物种入侵问题的认识更为全面。     

A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests

Greenhouse gas emissions have significantly altered global climate, and will continue to do so in the future. Increases in the frequency, duration, and/or severity of drought and heat stress associated with climate change could fundamentally alter the composition, structure, and biogeography of forests in many regions. Of particular concern are potential increases in tree mortality associated with climate-induced physiological stress and interactions with other climate-mediated processes such as insect outbreaks and wildfire. Despite this risk, existing projections of tree mortality are based on models that lack functionally realistic mortality mechanisms, and there has been no attempt to track observations of climate-driven tree mortality globally. Here we present the first global assessment of recent tree mortality attributed to drought and heat stress. Although episodic mortality occurs in the absence of climate change, studies compiled here suggest that at least some of the world's forested ecosystems already may be responding to climate change and raise concern that forests may become increasingly vulnerable to higher background tree mortality rates and die-off in response to future warming and drought, even in environments that are not normally considered water-limited. This further suggests risks to ecosystem services, including the loss of sequestered forest carbon and associated atmospheric feedbacks. Our review also identifies key information gaps and scientific uncertainties that currently hinder our ability to predict tree mortality in response to climate change and emphasizes the need for a globally coordinated observation system. Overall, our review reveals the potential for amplified tree mortality due to drought and heat in forests worldwide.     

Forest fire in India: a review of the knowledge base

Forest fire has profound impacts on atmospheric chemistry, biogeochemical cycling and ecosystem structure. This feedback interaction may be hastened in climate change scenarios. In view of this, the present day knowledge about the forest fire condition in India has been reviewed. Operational monitoring, geospatial modelling and climate change uncertainties are discussed. Indicators for forest fire assessment and the role of geoinformatics tools in developing those parameters are identified. The need for developing an adaptive management strategy from the existing experience is emphasized, and specific points are recommended sector-wise with short- and long-term visions.     

Drought and fire suppression lead to rapid forest composition change in a forest-prairie ecotone

Altered fire regimes and increased drought can lead to major vegetation changes, especially in ecotones. A decrease in fire can lead to woody species encroachment in prairies and increasing forest stand density. The threat of global climate change raises questions about potential increases in the length, severity, and incidence of droughts substantially altering species composition. Re-measured upland forests in south-central North America's midcontinent forest-prairie ecotone exhibited major changes in woody species composition and structure over fifty years and successional trajectories appeared to favor invasive Juniperus virginiana L. over the previous dominant Quercus species. The objective of this study was to determine whether climate and fire exclusion affected the recruitment history of dominant woody species in these upland forests located near the xeric western edge of the eastern deciduous forest biome of North America. We removed cores and cross-sections from 992 J. virginiana, Quercus marilandica Münchh. and Q. stellata Wangenh. trees from eleven forest stands located across central and northwest Oklahoma, and determined their ages using standard dendrochronological methods. Recruitment of all species increased following a severe mid-20th century drought, but a rapid increase in J. virginiana recruitment and decrease in Quercus recruitment appeared to be linked to a decrease in fire. Future fire regime changes and increased drought due to global climate change could lead to widespread shifts from Quercus- to Juniperus- dominated forests and cause substantial changes to ecosystem services.     

澳大利亚新南威尔士州台地上桉树的衰落

桉属植物是澳大利亚景观中的主要的乡土植物类群。在欧洲人定居澳大利亚以后,新南威尔士州台地的桉树急剧减少,桉树更新停滞,景观生态系统很难恢复到原初状态。本文介绍了桉树和乡土灌木减少的历史背景,分析了在这一地区幼苗更新减少的原因主要是由于开垦、放牧、火烧、外来物种竞争、枯萎、昆虫和干旱等,总结了桉树更新的可能条件,如幼苗存活的合适条件、充足的种子供应、避免捕食、适当的萌发条件、无放牧环境、机械处理、杂草控制、火烧系统和疾病控制等,借以建议在该地区应怎样保护和促进桉树的更新。参26。     

Species-site matching in mixed species plantations of native trees in tropical Australia

Mixed species plantations using native trees are increasingly being considered for sustainable timber production. Successful application of mixed species forestry systems requires knowledge of the potential spatial interaction between species in order to minimise the chance of dominance and suppression and to maximise wood production. Here, we examined species performances across 52 experimental plots of tree mixtures established on cleared rainforest land to analyse relationships between the growth of component species and climate and soil conditions. We derived site index (SI) equations for ten priority species to evaluate performance and site preferences. Variation in SI of focus species demonstrated that there are strong species-specific responses to climate and soil variables. The best predictor of tree growth for rainforest species Elaeocarpus grandis and Flindersia brayleyana was soil type, as trees grew significantly better on well-draining than on poorly drained soil profiles. Both E. grandis and Eucalyptus pellita showed strong growth response to variation in mean rain days per month. Our study generates understanding of the relative performance of species in mixed species plantations in the Wet Tropics of Australia and improves our ability to predict species growth compatibilities at potential planting sites within the region. Given appropriate species selections and plantation design, mixed plantations of high-value native timber species are capable of sustaining relatively high productivity at a range of sites up to age 10 years, and may offer a feasible approach for large-scale reforestation.     

退化林修复研究进展

退化林的基本内涵是森林生产力和生态服务功能出现逆向改变。国内外研究表明,过度采伐和外来树种干扰是引发森林退化的重要人为因素之一,而干旱是重要的自然因素之一。退化林修复技术研究主要集中在修复方式选择、乡土树种选育和土壤微生物利用等方面。自然恢复过程高度可变,人工辅助成本较高且效果良莠不齐,在景观水平上可将2种策略互补使用,以提高修复效果,降低实施成本;乡土树种比外来树种有更好的立地适应性且生态风险较小,在大多数情况下应采取自然修复和以乡土树种为主的人工修复相结合的综合修复措施;土壤微生物在增强土壤养分循环和促进植物生长方面具有重要作用,其中固氮微生物是最主要的成员,土壤真菌能够辅助细菌更好地发挥作用,充分利用土壤微生物可以有效促进退化林分的恢复。我国森林退化现状与世界各地森林退化情况基本一致,但退化林的成因有其特殊的历史性。在退化林修复工作中应因地制宜制定修复策略,及时调整抚育间伐措施和财政补贴政策,将森林经营系统化,确保退化林修复效果。     

Stomatal limitation to CO2 assimilation and down-regulation of photosynthesis in Quercus ilex resprouts in response to slowly imposed drought

Holm oak (Quercus ilex L.) is native to hot, dry Mediterranean forests where limited water availability often reduces photosynthesis in many species, and forest fires are frequent. Holm oaks resprout after a disturbance, with improved photosynthetic activity and water relations compared with unburned plants. To better understand the role of water availability in this improvement, watering was withheld from container-grown plants, either intact (controls) or resprouts after excision of the shoot, to gradually obtain a wide range of soil water availabilities. At high water availability, gas exchange rates did not differ between controls and resprouts. At moderate soil dryness, net photosynthesis of control plants decreased as a result of increased stomatal limitation, whereas gas exchange rates of resprouts, which had higher midday and predawn leaf water potentials, were unchanged. Under severe drought, resprouts showed a less marked decline in gas exchange than controls and maintained photosystem II integrity, as indicated by chlorophyll fluorescence measurements. Photosynthesis was down-regulated in both plant types in response to reduced CO2 availability caused by high stomatal limitation. Lower non-stomatal limitations in resprouts than in control plants, as evidenced by higher carboxylation velocity and the capacity for ribulose-1,5-bisphosphate regeneration, conferred greater drought resistance under external constraints similar to summer conditions at midday.     

气候变化与中国北方森林恢复和经营

全球气候变暖已经成为一个不争的事实。在全球气候变化背景下,我国的气温不断增高,降水和极端天气气候事件不断增多。根据气候变化现状和趋势,文章从陆地生态系统的可能响应、北方森林的分布变化、生产力、生物地球化学循环、火干扰等方面分析了气候变化对中国北方森林生态系统的可能影响,并提出了我国北方森林应对气候变化的适应性对策。