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1.
Increasing incidences of drought-induced tree mortality are being recorded worldwide, including Africa. African forests cover a significant proportion of the continent, which implies that African forest sustainability is threatened from a climate-change perspective. This is especially problematic in a developing nation context, because forest ecosystems such as plantation forestry provide important goods and services that sustain human well-being and economic growth. Disentangling the likely triggers of tree mortality (including those linked to drought) in landscapes would not only explain the mechanisms underlying local die-offs, but also better predict future mortality events. Methods applied in the field of ecophysiology are particularly useful to study in situ plant responses to an environment. We consider the status quo of global peer-reviewed publication outputs during the past century that have made use of key ecophysiological research approaches, specifically studies concerning ‘tree xylem anatomy’, ‘tree xylem cavitation’, ‘tree leaf gas-exchange’ and ‘tree xylem hydraulic conductivity’. We highlight the growth and applicability of this research field in understanding tree ecology. We also assess the role that the forestry sector has had in promoting such research to ensure future-proof forest products. Most importantly, we consider how Africa with its vast forested landscapes fits within this research spectrum. The last decade saw an increase of up to 60% in the total number of articles published, particularly with a focus on tree xylem cavitation and conductivity. Although forest research contributed greatly to the global tally of ecophysiological studies, and such studies in Africa have also increased by up to 88% in the past decade, there remains a general lack of this research topic in the continent. It is clear an optimisation of applied ecophysiological concepts and techniques will promote an improved understanding of tree mortality patterns. We argue that ecophysiological data will be crucial to future-proof tree improvement strategies in African commodity production landscapes, especially given future drier climates. 相似文献
2.
We used a combination of eddy flux, canopy, soil and environmental measurements with an integrated biophysical model to analyze the seasonality of component carbon (C) fluxes and their contribution to ecosystem C exchange in a 50-year-old Scots pine forest (Pinus sylvestris L.) in eastern Finland (62 degrees 47' N, 30 degrees 58' E) over three climatically contrasting years (2000-2002). Eddy flux measurements showed that the growing Scots pine forest was a sink for CO2, with annual net C uptakes of 131, 210 and 258 g C m-2> year-1 in 2000, 2001 and 2002, respectively. The integrated process model reproduced the annual course of daily C flux above the forest canopy as measured by the eddy covariance method once the site-specific component parameters were estimated. The model explained 72, 66 and 68% of the variation in daily net C flux in 2000, 2001 and 2002, respectively. Modeled annual C loss by respiration was 565, 629 and 640 g C m-2 year-1, accounting for 77, 77 and 65% of annual gross C uptake, respectively. Carbon fluxes from the forest floor were the dominant contributors to forest ecosystem respiration, with the fractions of annual respiration from the forest floor, foliage and wood being 46-62, 27-44 and 9-10%, respectively. The wide range in daily net C uptake during the growing season was largely attributable to day-to-day fluctuations in incident quantum irradiance. During just a few days in early spring and late autumn, ecosystem net C exchange varied between source and sink as a result of large daily changes in temperature. The forest showed a greater reduction in gross C uptake by photosynthesis than in C loss by respiration during the dry summer of 2000, indicating that interannual variability in ecosystem net C uptake at this site was modified mostly by summer rainfall and vapor pressure deficit. 相似文献
3.
Net CO2 exchange in a 35-year-old boreal Norway spruce (Picea abies (L.) Karst.) forest in northern Sweden was measured at the shoot (NSE), tree (NTE) and ecosystem levels (NEE) by means of shoot cuvettes, whole-tree chambers and the eddy covariance technique, respectively. We compared the dynamics of gross primary production (GPP) at the three levels during the course of a single week. The diurnal dynamics of GPP at each level were estimated by subtracting half-hourly or hourly model-estimated values of total respiration (excluding light-dependent respiration) from net CO(2) exchange. The relationship between temperature and total respiration at each level was derived from nighttime measurements of NSE, NTE and NEE over the course of 1 month. There was a strong linear relationship (r2 = 0.93) between the hourly estimates of GPP at the shoot and tree levels, but the correlation between shoot- and ecosystem-level GPP was weaker (r2 = 0.69). However, the correlation between shoot- and ecosystem-level GPP was improved (r2 = 0.88) if eddy covariance measurements were restricted to periods when friction velocity was > or = 0.5 m s(-1). Daily means were less dependent on friction velocity, giving an r2 value of 0.94 between shoot- and ecosystem-level GPP. The correlation between shoot and tree levels also increased when daily means were compared (r2 = 0.98). Most of the measured variation in carbon exchange rate among the shoot, tree and ecosystem levels was the result of periodic low coupling between vegetation and the atmosphere at the ecosystem level. The results validate the use of measurements at the shoot and tree level for analyzing the contribution of different compartments to net ecosystem CO2 exchange. 相似文献
4.
5.
The effects of plant diversity on ecosystem functioning have been mainly studied for fast growing systems such as grassland. These studies have stressed the context dependence of aboveground and belowground relationships (e.g. soil fertility, field vegetation or soil biota). Over the last few years, with the growing need for indicators for sustainable forest management, there has been a considerable increase in studies on AG–BG relationships within forest ecosystems. Nevertheless, given the specific characteristics of forest systems (long-term dynamics, the single tree effect) our mechanistic understanding of these relationships remains poor. 相似文献
6.
Law BE Goldstein AH Anthoni PM Unsworth MH Panek JA Bauer MR Fracheboud JM Hultman N 《Tree physiology》2001,21(5):299-308
We investigated key factors controlling mass and energy exchange by a young (6-year-old) ponderosa pine (Pinus ponderosa Laws.) plantation on the west side of the Sierra Nevada Mountains and an old-growth ponderosa pine forest (mix of 45- and 250-year-old trees) on the east side of the Cascade Mountains, from June through September 1997. At both sites, we operated eddy covariance systems above the canopy to measure net ecosystem exchange of carbon dioxide and water vapor, and made concurrent meteorological and ecophysiological measurements. Our objective was to understand and compare the controls on ecosystem processes in these two forests. Precipitation is much higher in the young plantation than in the old-growth forest (1660 versus 550 mm year-1), although both forests experienced decreasing soil water availability and increasing vapor pressure deficits (D) as the summer of 1997 progressed. As a result, drought stress increased at both sites during this period, and changes in D strongly influenced ecosystem conductance and net carbon uptake. Ecosystem conductance for a given D was higher in the young pine plantation than in the old-growth forest, but decreased dramatically following several days of high D in late summer, possibly because of xylem cavitation. Net CO2 exchange generally decreased with conductance at both sites, although values were roughly twice as high at the young site. Simulations with the 3-PG model, which included the effect of tree age on fluxes, suggest that, during the fall through spring period, milder temperatures and ample water availability at the young site provide better conditions for photosynthesis than at the old pine site. Thus, over the long-term, the young site can carry more leaf area, and the climatic conditions between fall and spring offset the more severe limitations imposed by summer drought. 相似文献
7.
Environmental controls on the carbon isotope composition of ecosystem-respired CO2 in contrasting forest ecosystems in Canada and the USA 总被引：1，自引：0，他引：1
We compared the carbon isotope composition of ecosystem-respired CO2 (delta13C(R)) from 11 forest ecosystems in Canada and the USA and examined differences among forest delta13C(R) responses to seasonal variations in environmental conditions from May to October 2004. Our experimental approach was based on the assumption that variation in delta13C(R) is a good proxy for short-term changes in photosynthetic discrimination and associated shifts in the integrated ecosystem-level intercellular to ambient CO2 ratio (c(i)/c(a)). We compared delta13C(R) responses for three functional groups: deciduous, boreal and coastal forests. The delta13C(R) values were well predicted for each group and the highest R2 values determined for the coastal, deciduous and boreal groups were 0.81, 0.80 and 0.56, respectively. Consistent with previous studies, the highest correlations between delta13C(R) and changes in environmental conditions were achieved when the environmental variables were averaged for 2, 3 or 4 days before delta13C(R) sample collection. The relationships between delta13C(R) and environmental conditions were consistent with leaf-level responses, and were most apparent within functional groups, providing support for our approach. However, there were differences among groups in the strength or significance, or both, of the relationships between delta13C(R) and some environmental factors. For example, vapor pressure deficit (VPD) and soil temperature were significant determinants of variation in delta13C(R) in the boreal group, whereas photosynthetic photon flux (PPF) was not; however, in the coastal group, variation in delta13C(R) was strongly correlated with changes in PPF, and there was no significant relationship with VPD. At a single site, comparisons between our delta13C(R) measurements in 2004 and published values suggested the potential application of delta13C(R) measurements to assess year-to-year variation in ecosystem physiological responses to changing environmental conditions, but showed that, in such an analysis, all environmental factors influencing carbon isotope discrimination during photosynthetic gas exchange must be considered. 相似文献
8.
Li Zhang Guirui Yu Fengxue Gu Honglin He Leiming Zhang Shijie Han 《Journal of Forest Research》2012,17(3):268-282
The uncertainty in the predicted values of a process-based terrestrial ecosystem model is as important as the predicted values themselves. However, few studies integrate uncertainty analysis into their modeling of carbon dynamics. In this paper, we conducted a local sensitivity analysis of the model parameters of a process-based ecosystem model at the Chaibaishan broad-leaved Korean pine mixed forest site in 2003?C2005. Sixteen parameters were found to affect the annual net ecosystem exchange of CO2 (NEE) in each of the three?years. We combined a Monte Carlo uncertainty analysis with a standardized multiple regression method to distinguish the contributions of the parameters and the initial variables to the output variance. Our results showed that the uncertainties in the modeled annual gross primary production and ecosystem respiration were 5?C8% of their mean values, while the uncertainty in the annual NEE was up to 23?C37% of the mean value in 2003?C2005. Five parameters yielded about 92% of the uncertainty in the modeled annual net ecosystem exchange. Finally, we analyzed the sensitivity of the meteorological data and compared two types of meteorological data and their effects on the estimation of carbon fluxes. Overestimating the relative humidity at a spatial resolution of 10?km?×?10?km had a larger effect on the annual gross primary production, ecosystem respiration, and net ecosystem exchange than underestimating precipitation. More attention should be paid to the accurate estimation of sensitive model parameters, driving meteorological data, and the responses of ecosystem processes to environmental variables in the context of global change. 相似文献
9.
作为环境因子,风与树木的关系较其他因子复杂,树木对风胁迫的响应与适应是植物逆境生理生态学研究的热点和难点。本文综述了不同叶形树种叶片气体交换对风胁迫的响应差异,总结发现风对不同叶形树种叶片气体交换影响的研究结论差异较大,有的甚至截然相反,表明了不同叶形树种叶片气体交换对风胁迫响应的复杂性。同时分析了由叶形引起的微环境、边界层导度和理化特征对叶片气孔交换的影响。 相似文献
10.
森林土壤酶的研究进展 总被引：79，自引：4，他引：79
土壤酶在土壤生态系统的物质循环和能量流动方面扮演重要的角色。目前 ,在几乎所有的森林生态系统研究中 ,土壤酶活性的监测似乎成为必不可少的研究内容。森林凋落物分解过程中的酶活性动态 ,植被特征与土壤酶活性的关系 ,土壤微生物与土壤酶的关系 ,植物 -土壤界面的土壤酶 ,森林土壤质量评价指标的土壤酶及人类活动干扰对森林土壤酶活性的影响等是当前森林土壤酶学的研究重点。由于土壤酶的功能和生态重要性 ,森林土壤酶研究可能包括 :(1 )土壤酶系统分异 ;(2 )作为森林土壤质量综合评价指标的土壤酶活性 ;(3)植被动态与土壤酶的关系 ;(4 )退化森林生态系统的土壤酶活性特征 ;(5 )人工林土壤酶活性特征 ;(6 )人类活动对森林土壤酶系统的影响。本文从土壤酶系统分异和生态系统的角度对土壤酶在森林生态系统中的作用和地位进行了综述 ,这对于加深理解森林生态系统中的物质循环、土壤酶的生态重要性以及森林生态系统退化机理有重要作用 相似文献
11.
Ryan MG 《Tree physiology》2002,22(15-16):1035-1043
The forest canopy regulates the exchange of carbon, water and energy between the ecosystem and the atmosphere, and provides a habitat for a wide variety of species. Understanding canopy processes is important for modeling forest production and carbon sequestration, and for predicting the effects of global changes in climate and atmospheric chemistry on the functioning of forest ecosystems. The Canopy Processes Working Group of the International Union of Forest Research Organizations has provided a forum for researchers working on forest canopies for nearly 20 years, principally through international meetings held every 2-3 years. In this paper, I review the history of the Canopy Processes Group, show how the research focus has changed and broadened, and provide a brief overview of some of the problems that remain to be solved. These include the topic of our 2001 meeting (Linking the Complexity of Forest Canopies to Ecosystem and Landscape Function), integration of canopy and respiratory processes, carbon allocation, physiological changes with tree age, predicting the response of forests to global change, understanding the genetic control of canopy structure and function, and scaling ecophysiological processes and modeling. Determining how forests will respond to global change and understanding the physiology of forest production will require increased attention to canopy processes and an increased focus on the interactions of canopy processes with other components of the ecosystem. 相似文献
12.
Turbulent fluxes of carbon, water and energy were measured at the Wind River Canopy Crane, Washington, USA from 1999 to 2004 with eddy-covariance instrumentation above (67 m) and below (2.5 m) the forest canopy. Here we present the decomposition of net ecosystem exchange of carbon (NEE) into gross primary productivity (GPP), ecosystem respiration (R(eco)) and tree canopy net CO(2) exchange (DeltaC) for an old-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco)-western hemlock (Tsuga heterophylla (Raf.) Sarg.) forest. Significant amounts of carbon were recycled within the canopy because carbon flux measured at the below-canopy level was always upward. Maximum fluxes reached 4-6 micromol m(-2) s(-1) of CO(2) into the canopy air space during the summer months, often equaling the net downward fluxes measured at the above-canopy level. Ecosystem respiration rates deviated from the expected exponential relationship with temperature during the summer months. An empirical ecosystem stress term was derived from soil water content and understory flux data and was added to the R(eco) model to account for attenuated respiration during the summer drought. This attenuation term was not needed in 1999, a wet La Ni?a year. Years in which climate approximated the historical mean, were within the normal range in both NEE and R(eco), but enhanced or suppressed R(eco) had a significant influence on the carbon balance of the entire stand. In years with low respiration the forest acts as a strong carbon sink (-217 g C m(-2) year(-1)), whereas years in which respiration is high can turn the ecosystem into a weak to moderate carbon source (+100 g C m(-2) year(-1)). 相似文献
13.
Applications of biotechnology for forest regeneration 总被引：4，自引：0，他引：4
The Forest Biotechnology Centre is an interdisciplinary research group dedicated to the development and application of advanced technology for the enhancement of forest regeneration. The Centre carries out contracts on behalf of clients in forest-related industries and government agencies. In addition, there are a number of long-term, in-house projects aimed at the development of proprietary technologies in genetics and propagation, and seedling production and establishment. Technical capabilities include: tissue culture, molecular genetics, pathology and microbial inoculants, and ecophysiology. These techniques are also being used to improve nursery culture regimes, disease assessment, planting regimes, and new product development for a variety of conifer species. Additional programs relate population genetics to adaptive traits, and develop clonal testing within elite families from tree-breeding programs. 相似文献
14.
What the towers don't see at night: nocturnal sap flow in trees and shrubs at two AmeriFlux sites in California 总被引：2，自引：0，他引：2
At the leaf scale, it is a long-held assumption that stomata close at night in the absence of light, causing transpiration to decrease to zero. Energy balance models and evapotranspiration equations often rely on net radiation as an upper bound, and some models reduce evapotranspiration to zero at night when there is no solar radiation. Emerging research is showing, however, that transpiration can occur throughout the night in a variety of vegetation types and biomes. At the ecosystem scale, eddy covariance measurements have provided extensive data on latent heat flux for a multitude of ecosystem types globally. Nighttime eddy covariance measurements, however, are generally unreliable because of low turbulence. If significant nighttime water loss occurs, eddy flux towers may be missing key information on latent heat flux. We installed and measured rates of sap flow by the heat ratio method (Burgess et al. 2001) at two AmeriFlux (part of FLUXNET) sites in California. The heat ratio method allows measurement and quantification of low rates of sap flow, including negative rates (i.e., hydraulic lift). We measured sap flow in five Pinus ponderosa Dougl. ex Laws. trees and three Arctostaphylos manzanita Parry and two Ceanothus cordulatus A. Kellog shrubs in the Sierra Nevada Mountains, and in five Quercus douglasii Hook and Arn. trees at an oak savanna in the Central Valley of California. Nocturnal sap flow was observed in all species, and significant nighttime water loss was observed in both species of trees. Vapor pressure deficit and air temperature were both well correlated with nighttime transpiration; the influence of wind speed on nighttime transpiration was insignificant at both sites. We distinguished between storage-tissue refilling and water loss based on data from Year 2005, and calculated the percentage by which nighttime transpiration was underestimated by eddy covariance measurements at both sites. 相似文献
15.
作为陆地生态系统的主体,森林生态系统的碳循环与碳蓄积对研究陆地生态系统碳循环起着重要作用.生物量、生产力、土壤有机质以及凋落物量及其分解等相互关系决定了森林生态系统的碳库量和碳交换量.本文简单地介绍了在碳蓄积研究中森林生物量和生产力的几种研究方法,并对研究过程中的问题(大尺度生物量的精确估算,地下生物量的研究,森林生态系统土壤碳库估算)进行了探讨. 相似文献
16.
森林生态系统碳通量是判定森林是CO2源/汇的标准, 其准确估算对碳循环研究具有重要的意义。针对森林生态系统碳通量的遥感研究处于起步阶段, 还有很多问题值得我们去探索。文中较系统地总结了有关碳通量的3种主要研究方法——样地清查法、通量观测法和模型模拟法; 重点分析了碳通量遥感估算中存在的问题, 主要有模型的全遥感化、尺度扩展和模型的不确定性等, 并对如何解决这些问题提出了粗浅的看法, 展望了一个全遥感化的森林生态系统碳通量模型, 希望对相关研究的开展有一些促进作用。 相似文献
17.
Dawson TE Burgess SS Tu KP Oliveira RS Santiago LS Fisher JB Simonin KA Ambrose AR 《Tree physiology》2007,27(4):561-575
It is commonly assumed that transpiration does not occur at night because leaf stomata are closed in the dark. We tested this assumption across a diversity of ecosystems and woody plant species by various methods to explore the circumstances when this assumption is false. Our primary goals were: (1) to evaluate the nature and magnitude of nighttime transpiration, E(n), or stomatal conductance, g(n); and (2) to seek potential generalizations about where and when it occurs. Sap-flow, porometry and stable isotope tracer measurements were made on 18 tree and eight shrub species from seven ecosystem types. Coupled with environmental data, our findings revealed that most of these species transpired at night. For some species and circumstances, nighttime leaf water loss constituted a significant fraction of total daily water use. Our evidence shows that E(n) or g(n) can occur in all but one shrub species across the systems we investigated. However, under conditions of high nighttime evaporative demand or low soil water availability, stomata were closed and E(n) or g(n) approached zero in eleven tree and seven shrub species. When soil water was available, E(n) or g(n) was measurable in these same species demonstrating plasticity for E(n) or g(n). We detected E(n) or g(n) in both trees and shrubs, and values were highest in plants from sites with higher soil water contents and in plants from ecosystems that were less prone to atmospheric or soil water deficits. Irrespective of plant or ecosystem type, many species showed E(n) or g(n) when soil water deficits were slight or non-existent, or immediately after rainfall events that followed a period of soil water deficit. The strongest relationship was between E(n) or g(n) and warm, low humidity and (or) windy (> 0.8 m s(-1)) nights when the vapor pressure deficit remained high (> 0.2 kPa in wet sites, > 0.7 kPa in dry sites). Why E(n) or g(n) occurs likely varies with species and ecosystem type; however, our data support four plausible explanations: (1) it may facilitate carbon fixation earlier in the day because stomata are already open; (2) it may enhance nutrient supply to distal parts of the crown when these nutrients are most available (in wet soils) and transport is rapid; (3) it may allow for the delivery of dissolved O(2) via the parenchyma to woody tissue sinks; or (4) it may occur simply because of leaky cuticles in older leaves or when stomata cannot close fully because of obstructions from stomatal (waxy) plugs, leaf endophytes or asymmetrical guard cells (all non-adaptive reasons). We discuss the methodological, ecophysiological, and theoretical implications of the occurrence of E(n) or g(n) for investigations at a variety of scales. 相似文献
18.
Luiz O. Moras Filho Railma P. Moraes Dalmo A. De Barros José A. A. Pereira Luís A. C. Borges 《Journal of Sustainable Forestry》2017,36(3):304-307
Due to impacts on Campos de Altitude vegetation, new environmental management strategies that consider regional ecophysiological information are being requested. Information was sought on the reproductive and propagation aspects of the species with higher importance value in Serra da Mantiqueira (Poços de Caldas, Minas Gerais State), in order to guide the embellishment of a state regulation regarding Campos de Altitude. The state of Minas Gerais does not have minimum criteria of richness and diversity for species selection in ecological restoration projects. Therefore, it is necessary to expand the ecophysiological studies in Campos de Altitude, as well as a greater interaction between scientists, legislators, and community through environmental education instruments, seeking greater effectiveness of legal mechanisms for conservation. 相似文献
19.
Forest conservation contributes to climate change mitigation, adaptation, and biodiversity/ecosystem conservation. To enhance the co-benefits of forest conservation, it is important to promote synergies among the three measures—mitigation, adaptation, and biodiversity/ecosystem conservation—in the forest sector and eliminate the overlaps among the three measures. However, limited research exists on the analysis of their synergies. This study explores the potential for synergy among the three forest sector measures, utilizing: 1) indicators that assess enabling conditions for synergies among the three measures at the different institutional levels of policies and strategies, institutional arrangements, and financing and programs/projects; and 2) case studies of five countries in Southeast Asia: Thailand, Indonesia, Vietnam, Lao PDR, and Cambodia.This analysis shows that the five countries all require various changes at different institutional levels in order to enhance their synergy potentials. The findings indicate the importance of national actors, financial mechanisms, programs, and projects in addressing the three measures. In terms of national actors, Thailand has the highest synergy potential due to its national-level committees and a single ministry that addresses all three measures. To enhance their synergy potentials, the other countries need to create national-level committees that address the three measures, and/or they need to enhance collaboration between the various ministries that represent the environment and forestry issues. At the financing and program/project aspects, Vietnam has the highest synergy potential. The other four countries need to develop common national funds that finance the three measures and/or develop joint programs and projects that address the three measures simultaneously. 相似文献
20.
Yasuko Mizoguchi Akira Miyata Yoshikazu Ohtani Ryuichi Hirata Satoko Yuta 《Journal of Forest Research》2009,14(1):1-9
Aggregating and sharing the metadata of flux observation sites results in a strong collaboration among various fields of study.
Such data sharing will also be a part of the future design of a tower flux observation network in Asia. The aim of this review
is to comprehend the state of tower flux observation sites in Asia. There are 109 tower flux observation sites in Asia including
51 forest sites. There are more new sites under construction in Asia than in America and Europe. These sites range from the
taiga in Siberia to the rainforest in Southeast Asia, and from the equatorial to polar Koeppen climate zones. There are many
highly humid areas in Asia, not only at low latitudes but also at middle latitudes. This climate condition has developed unique
vegetation such as lucidophyllous (evergreen broadleaf) forest, which is distributed in warm areas with high precipitation
in the growing season. However, there are only a few observations taking place in lucidophyllous forest. Rice paddy fields
are also unique land cover in Asia. It is important to accumulate long-term data for rice fields with their management records,
because plant activity depends highly on both climate conditions and land-use management. Flux data, especially net ecosystem
exchange and related elements, are used for widespread studies not only within the flux-research community but also in other
fields of study, for example remote sensing. At present, however, both the quantity and quality of the data are not sufficient
for these studies. Regarding the quantity, there are many recently established sites that have not published data yet; regarding
quality, flux data include uncertainties caused by methodological problems. Flux researchers are required not only to obtain
flux data but also to improve their quality. Meanwhile, data users must understand there are still uncertainties in flux data.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献