Photosynthetic responses to phosphorus nutrition in two-year-old maritime pine seedlings

We analyzed processes limiting photosynthesis in two-year-old, container-grown Pinus pinaster Ait. seedlings subjected to phosphorus (P) deficiency. After withholding P for 3 months, seedlings were supplied P at four relative addition rates (0, 0.005, 0.01 and 0.02 day(-1)) in a nutrient recycling system. At Weeks 12 and 22, responses of photosynthesis to CO(2) and irradiance were measured and the following parameters derived: maximal velocity of carboxylation by Rubisco, V(m); apparent quantum efficiency of electron transport, alpha maximal electron transport rate, J(m); stomatal conductance and relative stomatal limitation of photosynthesis. At Week 22, these measurements were combined with concurrent measurements of chlorophyll fluorescence to determine the quantum yield of PSII, and a theoretical partitioning of total light-driven linear electron flow between fractions used to regenerate carboxylated and oxygenated RuBP. After 12 weeks of treatment, needle P concentrations ranged from 0.04 to 0.15 x 10(-2) g g(DW) (-1), and then remained constant until Week 22. Values of J(m), alpha and V(m) increased with increasing needle P concentration (from 30 to 133 &mgr;mol m(-2) s(-1), 0.02 to 0.25 mol mol(-1) and 13 to 78 &mgr;mol CO(2) m(-2) s(-1) at the lowest and highest needle P concentrations, respectively). Under ambient conditions, net assimilation rates in P-deficient seedlings were limited by V(m) under saturating irradiance, and by J(m) under limiting irradiance, but not by triose-P regeneration. There was no detectable change in the partitioning of total light-driven linear electron flow between the fractions used for carboxylation and oxygenation. Predawn photochemical efficiency of PSII was significantly reduced in seedlings with low P concentrations. Although stomatal conductance tended to decrease with decreasing needle P concentration, relative stomatal limitation was not significantly affected. At Week 22, there was an attenuation of the effects of P nutrition on V(m) and an increase in alpha and J(m) that was probably related to cessation of growth and the seasonal decline in natural irradiance.     

Forest floor characteristics under longleaf-slash pine on two spodosols

Forest floor materials from a 45-year-old natural stand of Pinus palustris—P. elliottii growing on two coastal flatwood Spodosols (Electra and Wauchula fine sands), differing mainly in drainage characteristics, were similar except for total and organic matter weights and Al and Fe concentrations. The floors averaged 9.8 and 28.0 t/ha total dry weight in the 01(L) and 02(F + H) layers, respectively. Mineral soil represented 12 and 28% of the weights of these two layers. The 01 layer was equivalent to about 1.5 times and the 02 about 3.7 times the annual litter fall of the stands. The generally low nutrient concentrations, particularly of N (0.58 and 1.02% in 01 and 02 layers) and P (0.025 and 0.045%) are believed to influence decomposition rate of floor materials and result in a relatively heavy accumulation. This conclusion was supported by the wide C:N ratios of 92 (01 layer) and 53 (02 layer) and C:P ratios of 2116 and 1200 in these layers. Cation exchange capacity (CEC) at field pH averaged 32 and 45 meq/100 g of 01 and 02 material, on an ash-free basis. Grinding to pass a 20-mesh sieve significantly increased CEC of 01, but not of 02 materials. CEC increased linearly with decreasing acidity of the saturating solutions over the range of pH 4 to 7. The increase was from 35 to 75 meq/100 g in 01 materials and from 62 to 128 meq/100 g in 02 materials, over this pH range. The correlation between ash-free total N and CEC (pH 7) was highly significant (r² = 0.87), with 1.65 meq/100 g CEC associated with each meq/100 g N. The water-soluble organic materials contained similar types of chemical structures which differed only in numbers of functional groups.     

The contribution of wild plants to human nutrition in the Ferlo (Northern Senegal)

One aspect of agroforestry is the integration of indigenous species into appropriate land use systems. Some local trees and shrubs are particularly appreciated because of their value in human nutrition. The Ferlo is the most arid part of Senegal, covered by open woodland. The local population is using several indigenous plants for food. Most important are Adansonia digitata, Balanites aegyptiaca and Ziziphus mauritiana, as well as Boscia senegalensis and Cassia obtusifolia. Some 20 more species are consumed to a smaller extent. Their main function is to supply the vitamins A, B₂ and C, for which seasonal shortages occur. About 50% of all plants growing in the Ferlo have edible parts, but only the most common ones are consumed. Further exploitation of these natural resources and their conscious integration into agroforestry systems is economically and ecologically recommendable.     

Acid phosphatase activity and phosphorus nutrition in Scots pine needles

From March to October, acid phosphatase activity and phosphorus (P) concentration were measured in four needle age classes of the upper and lower crowns of fertilized and unfertilized Scots pine (Pinus sylvestris L.) trees. Negative correlations between acid phosphatase activity and P concentration were observed in current-year needles and in needles in the upper part of the crown, whereas there was a positive correlation between enzyme activity and P concentration in older needles and in needles in the lower part of the crown. In May and October, needles of all ages showed increased acid phosphatase activity. The most sensitive response of acid phosphatase activity to phosphate supply and phosphorus status of the whole tree was seen in current-year needles on the first whorl where a 300% increase in acid phosphatase activity was observed in response to a decrease in foliar P concentration of 1.7-1.8 mg P g(DW) (-1).     

The contribution of non-managed social bees to coffee production: new economic insights based on farm-scale yield data

Fruit set and quality of highland coffee (Coffea arabica) have been experimentally shown to be higher with bee-mediated or manual pollen supplementation than with autonomous self-pollination. Based on extrapolation from these small-scale experiments, very substantial monetary values for the pollination service have recently been suggested. However, previous research has not included direct measurement of coffee yield at a farm level in relation to pollinator activity, testing if pollinators are not only limiting fruit set and quality, but also coffee yield and farm profit. The extrapolations from small-scale experiments may be subject to error, because resource reallocation during fruit development, associated with enhanced pollination, was neglected, and many studies were restricted to a single coffee farm, limiting the validity of extrapolation. Here, we investigate the relationship between coffee yield and the community of coffee flower-visiting bees on 21 farms in Ecuador, where coffee is grown under tree shade. Our data show, for the first time on a farm-scale, that coffee yield was positively related to the density of non-managed, social flower-visiting bees per coffee shrub, but not to the number of inflorescences per shrub. Our data revealed that a fourfold increase in bee density was associated with an 80% increase in yield and an 800% increase in net revenues. Consequently, in our study higher yield associated with increased pollination generated higher revenues per hectare, so that farm profit was higher when bees were abundant.     

Forest floor vegetation plays an important role in photosynthetic production of boreal forests

We estimated gross photosynthetic production (GPP) of the forest floor vegetation in a 40-year-old Scots pine stand in southern Finland with three different methods: measurements of CO₂ exchange of single leaves of field and ground layer species, measurement campaigns of forest floor net CO₂ efflux at different irradiances with a manually operated soil chamber, and continuous measurements of forest floor net CO₂ efflux with an automatic transparent chamber system. We upscaled the measured light response curves from the manual soil chambers using the biomass distribution of the forest floor species, a modelled seasonal pattern of photosynthetic capacity and a model of light extinction down the canopy. Leaf gas exchange measurements as well as measurements of net CO₂ efflux with the manual chamber indicated saturation of photosynthesis at relatively low (50–400 μmol m⁻² s⁻¹) light levels. Leaf and patch level measurements gave similar rates of photosynthetic CO₂ fixation per unit leaf biomass suggesting that reduction in photosynthetic production due to within-patch shading was small. Upscaling of photosynthetic production to the stand level and continuous measurements with the automatic soil chambers indicated that momentary photosynthetic production by the forest floor vegetation in the summer was typically about 2 μmol m⁻² (ground) s⁻¹. Cumulative upscaled GPP over the period of no snow (from 20 April to 20 November) in year 2003 was 131 g C m⁻². Continuous measurements with the automatic soil chamber system were in line with the upscaling, the cumulative GPP being 83 g C m⁻² and the seasonal pattern of photosynthetic rate similar to that of the upscaled photosynthesis.     

Importance of soil extractable phosphorus distribution for mature Norway spruce nutrition and productivity

Phosphorus is an essential nutrient for forest growth. In this study, we assessed the impact of soil extractable phosphorus using two simple extraction methods on nutrition and productivity of Norway spruce in sixteen mature forest stands on different bedrocks and soils in Bavaria, Southern Germany. Representative trees were sampled for needles, twigs, branches, stem bark, and stem wood. Total phosphorus content in the tree parts and soil phosphorus stock extractable with citric acid and sodium bicarbonate up to a soil depth of 80 cm were determined. We found that easily soil extractable phosphorus is a suitable indicator for estimating phosphorus uptake and stand productivity in Norway spruce. In contrast, organic layer phosphorus showed no significant correlation with aboveground biomass phosphorus contents. In the biomass, the highest phosphorus contents were measured in young needles and twigs, but the highest correlation with soil phosphorus was detected for phosphorus contents in needles and bark. The stock of phosphorus extracted by citric acid down to 40 cm soil depth revealed the best correlation with phosphorus in needles and bark. Therefore, as a supplemental or alternative method to needle analysis, our study suggests the use of phosphorus contents in stem bark to evaluate tree phosphorus nutrition. These results highlight the suitability of the citric acid soil extraction method to characterize plant available phosphorus in Norway spruce ecosystems.     

Early frost damage on Sitka spruce seedlings and the influence of phosphorus nutrition

A frost on 8 September 1972 caused widespread damage to youngSitka spruce (Picea sitchensis (Bong.) Carr.) plantations. Inan experiment designed to examine the interaction of climateand P nutrition on the growth of young transplants in southScotland damage was greater on plants growing at low elevationand with high P content. This effect was attributed to theirextended growth period compared to those with low P supply.The lack of low temperatures prior to the frost resulted ininsufficient hardening of tissues to avoid damage from relativelyhigh temperatures. Damage and recovery were assessed by thereduction in height and dry weight increase compared to undamagedplants.     

Forest floor temperature and relative humidity following timber harvesting in southern New England,USA

Forest amphibians, especially salamanders, prefer forests with shaded, cool, and moist forest floors. Timber harvesting opens the forest canopy and exposes the forest floor to direct sunlight, which can increase forest floor temperatures and reduce soil moisture. These microclimatic changes can potentially degrade the harvested stand for amphibian habitat or affect other biotic resources or ecological processes at the forest floor and in the understory. The degree of forest floor disturbance is directly related to the intensity of harvesting, however, the duration of this effect is unknown. We conducted a study of forest floor temperature and relative humidity over a 12-year chronosequence (1993–2004) of timber harvests. We compared simultaneous, paired measurements of temperature and relative humidity at three positions (soil, forest floor, air) in harvested and control sites over three seasonal survey sessions. Vegetation composition and structure were measured at each survey location. Ambient weather conditions were recorded at three open-field locations across the study area.     

教学楼结构的综合加固

某教学楼钢筋混凝土现浇梁板、承重墙体严重开裂,梁板挠度大幅度超过规范允许值、刚度严 重不足,致使建筑物不能正常使用。教学楼的承重墙体及梁板的裂缝采用环氧树脂浆液压力灌浆补强,而梁 板的刚度不足则是通过增设组合钢梁的方法进行了加固,本文就其加固方法作了详细叙述。     

Auctioning the Forest: A Qualitative Approach to Exploring Stakeholder Responses to Bidding on Forest Ecosystem Services

The loss of private forestland diminishes ecosystems, including wildlife habitat, carbon sequestration and clean water. The emergence of new markets for forest ecosystem services offers one solution for private forestland financing while having the potential to increase the provision of forest ecosystem services. The general public’s willingness to participate in an auction mechanism for private forest ecosystem services was assessed for a regionally representative forest in Washington State using focus group methodology. The auction mechanism utilizes cost-effective management scenarios that stakeholders competitively bid on. Participants exhibited preferences for specific management plans while also making trade-offs in order to ensure that a plan would win. Participants expressed clear preferences for recreational access, mature forest habitat, aesthetic amenities, and improved water quality. Participants were receptive to the auction mechanism while maintaining concerns over viability, transparency, and local stakeholder involvement.     

近自然森林经营是提高我国森林质量的可行途径

尽管我国森林资源数量位居世界前列,但存在着森林质量较低、人工林树种单一等问题。由于继续增加森林面积的潜力有限,我国发展森林资源的重点应该从面积的增加转移到质量的提高上来。起源于德国的近自然林业理论,体现了"天人合一"的哲学思想,强调人与自然的和谐相处,符合当今世界的发展潮流。用它来指导我国的森林经营实践,可以兼顾森林三大效益,平衡林业利益分配,有利于提高森林整体质量。应该调整和改进我国现有的森林经营模式,对天然林实施择伐经营和结构调控,对人工林进行近自然化改造,从而不断提高森林质量,逐步实现森林资源的可持续发展。     

退耕还林与森林经营管理

在总结退耕还林工程具有建设任务重、政策性强、参与部门多、操作复杂、涉及面广5个显著特点的基础上,分析了在退耕还林工程实施管理过程中与森林经营管理密切相关的规划布局、作业设计、检查验收、林权证发放、抚育管护、采伐利用、效益监测、档案管理8个环节,提出了加强基础数据工作,完善检查验收方法,开发和推广应用工程管理信息系统,研究采伐利用政策和技术4条提高退耕还林经营管理水平的具体建议。     

基于高分二号遥感数据的森林自然度等级划分

以地面样点为基础的森林自然度评价方法很难获得区域范围森林自然度等级,针对该问题,提出了利用高分遥感卫星影像数据,划分区域范围森林自然度等级的方法。以湖北竹山县九华山林场为试验区域,在选取研究区典型样地的基础上,结合高分二号(GF-2)遥感影像数据的特点,从GF-2影像上提取遥感光谱、纹理等特征并结合地形特征,采用随机森林算法在大尺度范围对九华山林场森林自然度等级进行分类研究。结果发现:以GF-2数据为基础提取的植被指数、光谱、纹理等特征与地形特征结合,采用随机森林算法可较好地划分森林自然度等级,总体分类精度高达93.97%,Kappa系数为0.91。对森林自然度等级影响最重要的6个特征因子为高程、坡向、坡度、纹理均值、光谱主成分变化分量和归一化植被指数(NDVI)。结果表明,基于遥感影像提取的特征和地形特征结合进行森林自然度等级划分的研究方法具有可行性,为大面积区域的森林自然度等级划分奠定基础。     

森林的价值、效益与森林经营之关系概述

文章阐述了森林价值、效益的概念,相互关系,各类不同森林的价值、效益概述及森林价值最大化之森林经营措施等内容.     

加强森林资源保护 保障森林生态安全

森林法修订按照尊重自然、顺应自然,坚持生态优先、保护优先、保育结合、可持续发展的原则,对原森林法"森林保护"一章进行了补充完善。修订后的森林法"森林保护"一章共14条,是本法篇幅较大、分量较重的一章。在具体内容上,包含了公益林补偿、重点林区转型发展、天然林保护、护林组织和护林员、森林防火、林业有害生物防治、林地用途管制、古树名木和珍贵树木保护、林业基础设施建设等方面,明确了政府、林业主管部门以及林业经营者各自承担的森林资源保护职责。第一,关于天然林保护。     

Olevi Kull's lifetime contribution to ecology

In this article dedicated to Olevi Kull (June 22, 1955-January 31, 2007), we draw on his writings (in English and translated) to outline his thoughts on the relationship between scientists and science. We provide a brief synthesis of his most important work, give a short account of his career and, to bring the man into focus, share some personal stories of interactions with him. Kull considered that for a personal understanding to become scientific knowledge it must be explained convincingly based on theory and empirical support, and then taught to others in both spoken and written words. He saw the last step as the main distinction between learning and science. Olevi Kull's approach to science relied on two principles: first, linking theory and experiments in challenging settings, e.g., to test the generality of his ideas he often challenged them in multi-layered, mixed-species canopies. Second, he insisted on setting experiments to test assumptions used in quantitative analyses or in explaining an observed outcome; this, at times, led to falsification of commonly held ideas, thus enhancing ecophysiological understanding. After describing Kull's application of these principles, we give a brief synthesis of his most important work, in which he demonstrated through experimentation and modeling how the vertical distribution of leaves in canopies is consistent with the acclimation of the photosynthetic apparatus. We also review some of his findings on the interactive effects of carbon dioxide and ozone on canopy photosynthesis.     

林火对森林演替动态的影响及其应用

森林火灾是危害森林的一个重要的自然因子,但中等强度的林火干扰又是森林生态系统的一个建设因子,林火与森林演替动态的关系密切相关.通过查阅国内外有关林火与森林演替之间相互关系的资料,阐述了林火对森林演替动态的影响,分析了林火与原生演替、次生演替、进展演替和逆行演替的相互关系,列举了林火在维持偏途演替顶极群落和火顶极群落中的作用.