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LAI
Selected AbstractsImpact of the invasive alien grass Melinis minutiflora at the savanna-forest ecotone in the Brazilian CerradoDIVERSITY AND DISTRIBUTIONS, Issue 2 2004William A. Hoffmann ABSTRACT Exotic grasses are a serious threat to biodiversity in the cerrado savannas of central Brazil. Of particular concern is the possible role they may have in impeding tree regeneration at gallery (riverine) forest edges and increasing fire intensity, thereby driving gallery forest retreat. Here we quantify the effect of roads and distance from gallery forests on the abundance of the African grass Melinis minutiflora Beauv. and test for an effect of this species on woody plant regeneration and leaf area index. Melinis was present at approximately 70% of the sites near gallery forest edges, with its frequency declining sharply at greater distances from the edge. Melinis frequency was 2.8 times greater where roads were present nearby. Leaf area index (LAI) of the ground layer was 38% higher where Melinis was present than where it was absent. LAI was strongly correlated to fine fuel mass (r2 = 0.80), indicating higher fuel loads where Melinis was present. The abundance of tree and shrub species in the ground layer was negatively related to LAI and to the presence of Melinis. The greater fuel accumulation and reduced tree regeneration caused by Melinis may cause a net reduction in forest area by increasing fire intensity at the gallery forest edge and slowing the rate of forest expansion. [source] Wide-area estimates of saltcedar (Tamarix spp.) evapotranspiration on the lower Colorado River measured by heat balance and remote sensing methods,,ECOHYDROLOGY, Issue 1 2009Pamela L. Nagler Abstract In many places along the lower Colorado River, saltcedar (Tamarix spp) has replaced the native shrubs and trees, including arrowweed, mesquite, cottonwood and willows. Some have advocated that by removing saltcedar, we could save water and create environments more favourable to these native species. To test these assumptions we compared sap flux measurements of water used by native species in contrast to saltcedar, and compared soil salinity, ground water depth and soil moisture across a gradient of 200,1500 m from the river's edge on a floodplain terrace at Cibola National Wildlife Refuge (CNWR). We found that the fraction of land covered (fc) with vegetation in 2005,2007 was similar to that occupied by native vegetation in 1938 using satellite-derived estimates and reprocessed aerial photographs scaled to comparable spatial resolutions (3,4 m). We converted fc to estimates of leaf area index (LAI) through point sampling and destructive analyses (r2 = 0·82). Saltcedar LAI averaged 2·54 with an fc of 0·80, and reached a maximum of 3·7 with an fc of 0·95. The ranges in fc and LAI are similar to those reported for native vegetation elsewhere and from the 1938 photographs over the study site. On-site measurements of water use and soil and aquifer properties confirmed that although saltcedar grows in areas where salinity has increased much better than native shrubs and trees, rates of transpiration are similar. Annual water use over CNWR was about 1·15 m year,1. Copyright © 2008 John Wiley & Sons, Ltd. [source] Increased leaf area dominates carbon flux response to elevated CO2 in stands of Populus deltoides (Bartr.)GLOBAL CHANGE BIOLOGY, Issue 5 2005Ramesh Murthy Abstract We examined the effects of atmospheric vapor pressure deficit (VPD) and soil moisture stress (SMS) on leaf- and stand-level CO2 exchange in model 3-year-old coppiced cottonwood (Populus deltoides Bartr.) plantations using the large-scale, controlled environments of the Biosphere 2 Laboratory. A short-term experiment was imposed on top of continuing, long-term CO2 treatments (43 and 120 Pa), at the end of the growing season. For the experiment, the plantations were exposed for 6,14 days to low and high VPD (0.6 and 2.5 kPa) at low and high volumetric soil moisture contents (25,39%). When system gross CO2 assimilation was corrected for leaf area, system net CO2 exchange (SNCE), integrated daily SNCE, and system respiration increased in response to elevated CO2. The increases were mainly as a result of the larger leaf area developed during growth at high CO2, before the short-term experiment; the observed decline in responses to SMS and high VPD treatments was partly because of leaf area reduction. Elevated CO2 ameliorated the gas exchange consequences of water stress at the stand level, in all treatments. The initial slope of light response curves of stand photosynthesis (efficiency of light use by the stand) increased in response to elevated CO2 under all treatments. Leaf-level net CO2 assimilation rate and apparent quantum efficiency were consistently higher, and stomatal conductance and transpiration were significantly lower, under high CO2 in all soil moisture and VPD combinations (except for conductance and transpiration in high soil moisture, low VPD). Comparisons of leaf- and stand-level gross CO2 exchange indicated that the limitation of assimilation because of canopy light environment (in well-irrigated stands; ratio of leaf : stand=3.2,3.5) switched to a predominantly individual leaf limitation (because of stomatal closure) in response to water stress (leaf : stand=0.8,1.3). These observations enabled a good prediction of whole stand assimilation from leaf-level data under water-stressed conditions; the predictive ability was less under well-watered conditions. The data also demonstrated the need for a better understanding of the relationship between leaf water potential, leaf abscission, and stand LAI. [source] Vegetation structure characteristics and relationships of Kalahari woodlands and savannasGLOBAL CHANGE BIOLOGY, Issue 3 2004J.L. Privette Abstract The Kalahari Transect is one of several International Geosphere,Biosphere Programme (IGBP) transects designed to address global change questions at the regional scale, in particular by exploiting natural parameter gradients (Koch et al., 1995). In March 2000, we collected near-synoptic vegetation structural data at five sites spanning the Kalahari's large precipitation gradient (about 300,1000 mm yr,1) from southern Botswana (,24°S) to Zambia (,15°S). All sites were within the expansive Kalahari sandsheet. Common parameters, including plant area index (PAI), leaf area index (LAI) and canopy cover (CC), were measured or derived using several indirect instruments and at multiple spatial scales. Results show that CC and PAI increase with increasing mean annual precipitation. Canopy clumping, defined by the deviation of the gap size distribution from that of randomly distributed foliage, was fairly constant along the gradient. We provide empirical relationships relating these parameters to each other and to precipitation. These results, combined with those in companion Kalahari Transect studies, provide a unique and coherent test bed for ecological modeling. The data may be used to parameterize process models, as well as test internally predicted parameters and their variability in response to well-characterized climatological differences. [source] Canopy structure in savannas along a moisture gradient on Kalahari sandsGLOBAL CHANGE BIOLOGY, Issue 3 2004Robert J. Scholes Abstract Measurements of tree canopy architecture were made at six savanna sites on deep, sandy soils, along a gradient of increasing aridity. There was substantial variation in the leaf area estimated within each site, using the same sample frame, but different measurement techniques. The trends in canopy properties in relation to the aridity gradient were consistent, regardless of the technique used for estimating the properties. The effective plant area index for the tree canopy (the sum of the stem area index and the leaf area index (LAI)) declined from around 2 to around 0.8 m2 m,2 over a gradient of mean annual rainfall from 1000 to 350 mm. Stems contributed 2,5% of the tree canopy plant area index. Since the tree canopy cover decreased from 50% to 20% over this aridity range, the leaf area index within the area covered by tree canopies remained fairly constant at 3,4 m2 m,2. Tree leaves tended from a horizontal orientation to a more random orientation as the aridity increased. On the same gradient, the leaf minor axis dimension decreased from around 30 mm to around 3 mm, and the mean specific leaf area decreased from 14 to 5 m2 kgha,1. There was good agreement between LAI observed in the field using a line ceptometer and the LAI inferred by the MODIS sensor on the Terra satellite platform, 2 months later in the same season. [source] Vegetative growth and development of irrigated forage turnip (Brassica rapa var. rapa)GRASS & FORAGE SCIENCE, Issue 4 2008J. E. Neilsen Abstract Field and greenhouse experiments were conducted to identify visual markers and predictors of changes in the vegetative growth rate of forage turnip (Brassica rapa var. rapa) as a potential tool to improve the timing of inputs of N and irrigation to periods of maximum demand. The onset of root expansion, which was associated with a colour change and the death of cotyledons, was identified as a critical marker for the beginning of the rapid growth of the crop and the accumulation of starch in the storage root but indicators of subsequent changes in vegetative growth rate were not identifiable. The results suggested that management inputs can be more readily targeted to the beginning of the exponential growth phase but targeting of later vegetative growth stages will remain arbitrary. The vegetative growth and development of the crop was also studied to elucidate the process of leaf emergence and senescence (turnover) as they affected both leaf and root yield. The sequential senescence of leaves, which began immediately after cotyledon death, and translocation of carbohydrate to the storage root, coupled with high leaf area index (LAI), probably account for the high growth rates of 220 kg ha,1 day,1 maintained for periods of 10 weeks after the onset of root expansion. High yields can be expected if high LAI is maintained by ensuring that leaf emergence rates are not limited by nutrient or water deficiencies and leaves are protected from insect pests. Forage turnip is particularly robust because new leaf continues to emerge as older and damaged leaves senesce and carbohydrate is stored as starch in the storage root. [source] Spatial variations in throughfall in a Moso bamboo forest: sampling design for the estimates of stand-scale throughfallHYDROLOGICAL PROCESSES, Issue 3 2010Yoshinori Shinohara Abstract We investigated the spatial and seasonal variations in throughfall (Tf) in relation to spatial and seasonal variations in canopy structure and gross rainfall (Rf) and assessed the impacts of the variations in Tf on stand-scale Tf estimates. We observed the canopy structure expressed as the leaf area index (LAI) once a month and Tf once a week in 25 grids placed in a Moso bamboo (Phyllostachys pubescens) forest for 1 year. The mean LAI and spatial variation in LAI did have some seasonal variations. The spatial variations in Tf reduced with increasing Rf, and the relationship between the spatial variation and the Rf held throughout the year. These results indicate that the seasonal change in LAI had little impact on spatial variations in Tf, and that Rf is a critical factor determining the spatial variations in Tf at the study site. We evaluated potential errors in stand-scale Tf estimates on the basis of measured Tf data using Monte Carlo sampling. The results showed that the error decreases greatly with increasing sample size when the sample size was less than ,8, whereas it was near stable when the sample size was 8 or more, regardless of Rf. A sample size of eight results in less than 10% error for Tf estimates based on Student's t -value analysis and would be satisfactory for interception loss estimates when considering errors included in Rf data. Copyright © 2009 John Wiley & Sons, Ltd. [source] Estimating the evolution of vegetation cover and its hydrological impact in the Mekong River basin in the 21st centuryHYDROLOGICAL PROCESSES, Issue 9 2008Hiroshi Ishidaira Abstract The terrestrial biosphere plays a key role in regional energy and water cycles. Thus, for long-term hydrological predictions, possible future changes in vegetation cover must be understood. This study examined the evolution of vegetation cover in the 21st century and its estimated impact on river discharge in the Mekong River basin. Based on climatic predictions (TYN SC 2·03) under the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC SRES) A1FI, A2, B1, and B2, changes in vegetation type and the leaf area index (LAI) were simulated using a Lund-Potsdam-Jena-Dynamic Global Vegetation Model (LPJ-DGVM) and Terrestrial Biogeochemical Cycle Model (BIOME-BGC). The estimated LAI was then used in the rainfall-runoff analysis in the Yamanashi Distributed Hydrological Model (YHyM). The simulation results indicated a significant change in vegetation type mainly on the Tibetan Plateau and in mountainous areas, with the degree of change differing for each SRES scenario; LAI increases around the edge of the Tibetan Plateau and decreases in the lower reaches of the basin; and more conspicuous changes in river discharge in upstream areas than in the middle to lower reaches, mainly due to increases in precipitation in the plateau region. After the 2050s, the results suggested changes in river discharge will be slowed due to changes in evapotranspiration. Copyright © 2008 John Wiley & Sons, Ltd. [source] What is the best way to represent surface conductance for a range of vegetated sites?HYDROLOGICAL PROCESSES, Issue 9 2007Hikaru Komatsu Abstract Surface conductance Gs is a significant parameter for indicating the evaporative and photosynthetic properties of a vegetated surface. When comparing Gs values between different observation sites, some studies have used Gsmax and others have used ,smax (where Gsmax is the maximum Gs value measured during the measurement period, and ,smax is the maximum Gs value obtained with a vapour pressure deficit (VPD) of , 1·0 kPa during the measurement period). In this study, we demonstrate a clear justification for using ,smax instead of Gsmax when comparing Gs values between different sites. We examined whether both ,smax and Gsmax lead to the same conclusions in classifying vegetated sites. Komatsu (2003b) [Hydrological Processes 17: 2503,2512] reported a clear relationship between canopy height h and ,smax for coniferous forests with a projected leaf area index (LAI) of , 3·0. We examined not only the relationship between h and ,smax but also the relationship between h and Gsmax for coniferous forests with a projected LAI of , 3·0. Both ,smax and Gsmax decreased with increasing h. However, the relationship between h and Gsmax was less well defined than the relationship between h and ,smax because of biased Gsmax data. Consequently, we conclude that ,smax is a more appropriate index than Gsmax to represent Gs for sites with different vegetation. Copyright © 2007 John Wiley & Sons, Ltd. [source] Rainfall interception in a lower montane forest in Ecuador: effects of canopy propertiesHYDROLOGICAL PROCESSES, Issue 7 2005Katrin Fleischbein Abstract Rainfall interception in forests is influenced by properties of the canopy that tend to vary over small distances. Our objectives were: (i) to determine the variables needed to model the interception loss of the canopy of a lower montane forest in south Ecuador, i.e. the storage capacity of the leaves S and of the trunks and branches St, and the fractions of direct throughfall p and stemflow pt; (ii) to assess the influence of canopy density and epiphyte coverage of trees on the interception of rainfall and subsequent evaporation losses. The study site was located on the eastern slope of the eastern cordillera in the south Ecuadorian Andes at 1900,2000 m above sea level. We monitored incident rainfall, throughfall, and stemflow between April 1998 and April 2001. In 2001, the leaf area index (LAI), inferred from light transmission, and epiphyte coverage was determined. The mean annual incident rainfall at three gauging stations ranged between 2319 and 2561 mm. The mean annual interception loss at five study transects in the forest varied between 591 and 1321 mm, i.e. between 25 and 52% of the incident rainfall. Mean S was estimated at 1·91 mm for relatively dry weeks with a regression model and at 2·46 mm for all weeks with the analytical Gash model; the respective estimates of mean St were 0·04 mm and 0·09 mm, of mean p were 0·42 and 0·63, and of mean pt were 0·003 and 0·012. The LAI ranged from 5·19 to 9·32. Epiphytes, mostly bryophytes, covered up to 80% of the trunk and branch surfaces. The fraction of direct throughfall p and the LAI correlated significantly with interception loss (Pearson's correlation coefficient r = ,0·77 and 0·35 respectively, n = 40). Bryophyte and lichen coverage tended to decrease St and vascular epiphytes tended to increase it, although there was no significant correlation between epiphyte coverage and interception loss. Our results demonstrate that canopy density influences interception loss but only explains part of the total variation in interception loss. Copyright © 2004 John Wiley & Sons, Ltd. [source] Effects of land-cover changes on the hydrological response of interior Columbia River basin forested catchmentsHYDROLOGICAL PROCESSES, Issue 13 2002James R. VanShaar Abstract The topographically explicit distributed hydrology,soil,vegetation model (DHSVM) is used to simulate hydrological effects of changes in land cover for four catchments, ranging from 27 to 1033 km2, within the Columbia River basin. Surface fluxes (stream flow and evapotranspiration) and state variables (soil moisture and snow water equivalent) corresponding to historical (1900) and current (1990) vegetation are compared. In addition a sensitivity analysis, where the catchments are covered entirely by conifers at different maturity stages, was conducted. In general, lower leaf-area index (LAI) resulted in higher snow water equivalent, more stream flow and less evapotranspiration. Comparisons with the macroscale variable infiltration capacity (VIC) model, which parameterizes, rather than explicitly represents, topographic effects, show that runoff predicted by DHSVM is more sensitive to land-cover changes than is runoff predicted by VIC. This is explained by model differences in soil parameters and evapotranspiration calculations, and by the more explicit representation of saturation excess in DHSVM and its higher sensitivity to LAI changes in the calculation of evapotranspiration. Copyright © 2002 John Wiley & Sons, Ltd. [source] Exogenous Glycinebetaine and Salicylic Acid Application Improves Water Relations, Allometry and Quality of Hybrid Sunflower under Water Deficit ConditionsJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2009M. Hussain Abstract Limited water availability hampers the sustainability of crop production. Exogenous application of glycinebetaine (GB) and salicylic acid (SA) has been found very effective in reducing the adverse effects of water scarcity. This study was conducted to examine the possible role of exogenous GB and SA application in improving the growth and water relations of hybrid sunflower (Helianthus annuus L.) under different irrigation regimes. There were three levels of irrigation, viz. control (normal irrigations), water stress at budding stage (irrigation missing at budding stage) and water stress at flowering stage (FS) (irrigation missing at FS). GB and SA were applied exogenously at 100 and 0.724 mm respectively, each at the budding and FS. Control plants did not receive application of GB and SA. Water stress reduced the leaf area index (LAI), leaf area duration (LAD), crop growth rate (CGR), leaf relative water contents, water potential, osmotic potential, turgor pressure, achene yield and water use efficiency. Nevertheless, exogenous GB and SA application appreciably improved these attributes under water stress. However, exogenous GB application at the FS was more effective than other treatments. Net assimilation rate was not affected by water stress as well as application of GB and SA. The protein contents were considerably increased by water stress at different growth stages, but were reduced by exogenous GB and SA application. The effects of water stress and foliar application of GB were more pronounced when applied at FS than at the budding stage. Moreover, exogenous GB application was only advantageous under stress conditions. [source] Impact of Water Stress on Maize Grown Off-Season in a Subtropical EnvironmentJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 4 2007C. M. T. Soler Abstract During the last decade, the production of off-season maize has increased in several regions of Brazil. Growing maize during this season, with sowing from January through April, imposes several climatic risks that can impact crop yield. This is mainly caused by the high variability of precipitation and the probability of frost during the reproduction phases. High production risks are also partially due to the use of cultivars that are not adapted to the local environmental conditions. The goal of this study was to evaluate crop growth and development and associated yield, yield components and water use efficiency (WUE) for maize hybrids with different maturity ratings grown off-season in a subtropical environment under both rainfed and irrigated conditions. Three experiments were conducted in 2001 and 2002 in Piracicaba, state of São Paulo, Brazil with four hybrids of different maturity duration, AG9010 (very short season), DAS CO32 and Exceler (short season) and DKB 333B (normal season). Leaf area index (LAI), plant height and dry matter were measured approximately every 18 days. Under rainfed conditions, the soil water content in the deeper layers was reduced, suggesting that the extension of the roots into these layers was a response to soil water limitations. On average, WUE varied from 1.45 kg m,3 under rainfed conditions to 1.69 kg m,3 under irrigated conditions during 2001. The average yield varied from 4209 kg ha,1 for the hybrids grown under rainfed conditions to 5594 kg ha,1 under irrigated conditions during 2001. Yield reductions under rainfed conditions were affected by the genotype. For the hybrid DKB 333B with a normal maturity, yield was reduced by 25.6 % while the short maturity hybrid Exceler was the least impacted by soil water limitations with a yield reduction of only 8.4 %. To decrease the risk of yield loss, the application of supplemental irrigation should be considered by local farmers, provided that this practice is not restricted by either economic considerations or the availability of sufficient water resources. [source] Effects of Plant Population Density and Intercropping with Soybean on the Fractal Dimension of Corn Plant Skeletal ImagesJOURNAL OF AGRONOMY AND CROP SCIENCE, Issue 2 2000K. Foroutan-pour Three-year field experiments were conducted to determine whether the temporal pattern of fractal dimension (FD) for corn (Zea mays L.) plant structure is altered by plant population density (PPD) or intercropping with soybean [Glycine max. (L.) Merr.], and how changes in the FD are related to changes in other canopy characteristics. Plants in monocropped corn and intercropped corn,soybean plots were randomly sampled and labelled for later identification. Corn plant structure was photographed from the side that allowed the maximum appearance of details (perpendicular to the plane of developed leaves) and from two fixed sides (side 1: parallel to the row and side 2: perpendicular to the row). Images were scanned and skeletonized, as skeletal images provide acceptable information to estimate the FD of plant structure two-dimensionally by the box-counting method. Differences in the FD estimated from images taken perpendicular to the plane of developed leaves were not significant among competition treatments. An adjustment of corn plants to treatments, by changing the orientation of the plane of developed leaves with respect to the row, was observed. Based on overall FD means, competition treatments were ranked as: high > normal , intercrop , low for side 1 and intercrop > low , normal > high for side 2. Leaf area index (LAI) and plant height had a positive correlation with FD. In contrast, light penetration had a negative correlation with FD. In conclusion, FD provides a meaningful and effective tool for quantifying corn plant structure, measuring the structural response to cultural practices, and modelling corn plant canopies. Zusammenfassung Folgende Ziele der Untersuchungen wurden berücksichtigt: 1) Eine geeignete Methode für die Abschätzung der Anteile (FD) 2-dimensional für Pflanzen mit einer einfachen dreidimensionalen Vegetationsstruktur wie z. B. Mais (Zea mays L.) zu bestimmen; 2) der Frage nachzugehen, ob die zeitlichen Muster von FD bei der Maispflanzenstruktur durch die Bestandesdichte verändert wird (PPD: low, normal und hoch) oder in Mischanbau mit Sojabohnen (Glyzine max. L.) Merr.); und 3) in welcher Beziehung Änderungen in der FD in der Maispflanzenstruktur zu Änderungen in anderen Bestandeseigenschaften stehen. Pflanzen im Reinanbau von Mais und im Mischanbau in Mais-Sojabohnen-Parzellen wurden randomisiert gesammelt und für die spätere Identifikation gekennzeichnet. Die Maispflanzenstruktur wurde von der Seite fotografiert, so dai eine maximale Darstellung der Details (perpendiculär zu der Ebene der entwickelten Blätter) und von zwei festgelegten Seiten (Seite 1: parallel zur Reihe und Seite 2 perpendikulär zur Reihe) verfügbar war. Die Abbildungen wurden gescannt und skelettiert; Skelettabbildungen geben eine akzeptierbare Information zur Abschätzung von FD Pflanzenstrukturen in zweidimensionaler Form über die Box-counting-Methode. Unterschiede in der FD, die sich aus Bildern mit einer perpendikulären Aufnahme zu der Ebene der entwickelten Blätter ergaben, waren nicht signifikant innerhalb der Konkurrenzbehandlungen. Eine Anpassung der Maispflanzen an die Behandlungen durch Änderungen der Orientierung zur Ebene der entwickelten Blätter im Hinblick auf die Reihe, wurde beobachtet. Auf der Grundlage von gesamt FD-Mittelwerten ergab sich, dai Konkurrenzbehandlungen in folgender Reihe auftraten: Hoch (1,192) > (1,178) , zu Mischanbau (1,177) , zu gering (1,170) für Seite 1 und bei Mischanbau (1,147) > gering (1,158) , (1,153) > hoch für Seite 2. Der Blattflächenindex (LAI) und die Pflanzenhöhe hatten eine positive Korrelation zu FD. Im Gegensatz dazu wies die Lichtpenetration eine negative Korrelation zu FD auf. Es kann festgestellt werden, dai FD eine aussagekräftige und zweckmäiige Methode ist, die Maispflanzenstruktur zu quantifizieren, Strukturreaktionen zum Anbauverfahren zu messen und Maispflanzenbestände zu beschreiben. [source] Photon flux partitioning among species along a productivity gradient of an herbaceous plant communityJOURNAL OF ECOLOGY, Issue 6 2006ANNE AAN Summary 1We studied light partitioning among species along the natural productivity gradient of herbaceous vegetation with an above-ground dry mass of 150,490 g m,2. The aim was to investigate how the light capturing ability per above-ground biomass and leaf nitrogen changes in an entire community and to reveal whether different species respond similarly to changes in soil conditions and competition. 2Species becoming dominant at high soil resources have intrinsically low leaf area ratios (LAR) and lower tissue nitrogen concentration, and hence relatively high nitrogen use efficiency. These traits lead to dominance when soil resources allow rapid growth so that benefits arising from the ability to locate leaves above neighbours and thereby increasing asymmetry of competition, become more crucial. 3In contrast to our expectations, above-ground efficiency of nitrogen use on the community level (aNUE) increased along the productivity gradient. Species level nitrogen use efficiency was unaffected by variation in site productivity; the increase in community aNUE was solely as a consequence of changes in species composition. 4Light absorption per unit of above-ground mass, ,M, declined significantly at the community level and also in most species, indicating that light use efficiency increased with increased site productivity and LAI. 5Light absorption per unit of leaf nitrogen, ,N, as an indicator of the ratio NUE/LUE showed no clear pattern on the community level because both NUE and LUE tend to increase with increased productivity. At the species level, ,N tends to decrease because NUE did not change with stand productivity. 6Some subordinate species responded by enlarging their LAR to increased competition. Additionally, these species were the most responsive in their leaf chlorophyll/nitrogen ratio to changes in light conditions, which shows that physiological plasticity is important for species that are unable to compete for light with the ability to position their leaves above those of other species. 7This study shows how plasticity in above-ground growth pattern and nitrogen allocation differs between species with respect to increased soil fertility and competition, leading to distinctive strategies of survival. Light partitioning analysis reveals that increased competition for light, resulting in changes in species composition, is the key factor that leads to decoupling of species and community level acclimation. [source] Seedling regeneration, environment and management in a semi-deciduous African tropical rain forestJOURNAL OF VEGETATION SCIENCE, Issue 5 2009Edward N. Mwavu Abstract Questions: How is seedling regeneration of woody species of semi-deciduous rain forests affected by (a) historical management for combinations of logging, arboricide treatment or no treatment, (b) forest community type and (c) environmental gradients of topography, light and soil nutrients? Location: Budongo Forest Reserve, Uganda. Methods: Seedling regeneration patterns of trees and shrubs in relation to environmental factors and historical management types were studied using 32 0.5-ha plots laid out in transects along a topographic gradient. We compared seedling species diversity, composition and distribution patterns along topographic gradients and within types of historical management regimes and forest communities to test whether environmental factors contributed to differences in species composition of seedlings. Results: A total of 85 624 woody seedlings representing 237 species and 46 families were recorded in this rain forest. Cynometra alexandri C.H. Wright and Lasiodiscus mildbraedii Engl. had high seedling densities and were widely distributed throughout the plots. The most species-rich families were Euphorbiaceae, Fabaceae, Rubiaceae, Meliaceae, Moraceae and Rutaceae. Only total seedling density was significantly different between sites with different historical management, with densities highest in logged, intermediate in logged/arboricided and lowest in the nature reserve. Forest communities differed significantly in terms of seedling diversity and density. Seedling composition differed significantly between transects and forest communities, but not between topographic positions or historical management types. Both Chao-Jaccard and Chao-Sørensen abundance-based similarity estimators were relatively high in the plot, forest community and in terms of historical management levels, corroborating the lack of significant differences in species richness within these groups. The measured environmental variables explained 59.4% of variance in seedling species distributions, with the three most important being soil organic matter, total soil titanium and leaf area index (LAI). Total seedling density was positively correlated with LAI. Differences in diversity of >2.0 cm dbh plants (juveniles and adults) also explained variations in seedling species diversity. Conclusions: The seedling bank is the major route for regeneration in this semi-deciduous tropical rain forest, with the wide distribution of many species suggesting that these species regenerate continuously. Seedling diversity, density and distribution are largely a function of adult diversity, historical management type and environmental gradients in factors such as soil nutrient content and LAI. The species richness of seedlings was higher in soils both rich in titanium and with low exchangeable cations, as well as in logged areas that were more open and had a low LAI. [source] Light partitioning among species and species replacement in early successional grasslandsJOURNAL OF VEGETATION SCIENCE, Issue 5 2002Marinus J.A. Werger Makino (1962); Ohwi (1965) Abstract. We studied canopy structure, shoot architecture and light harvesting efficiencies of the species (photon flux captured per unit above-ground plant mass) in a series of exclosures of different age (up to 4.5 yr) in originally heavily grazed grassland in N Japan.Vegetation height and Leaf Area Index (LAI) increased in the series and Zoysia japonica, the dominant in the beginning, was replaced by the much taller Miscanthus sinensis. We showed how this displacement in dominance can be explained by inherent constraints on the above-ground architecture of these two species. In all stands light capture of plants increased with their above-ground biomass but taller species were not necessarily more efficient in light harvesting. Some subordinate species grew disproportionally large leaf areas and persisted in the shady undergrowth. Some other species first grew taller and managed to stay in the better-lit parts of the canopy, but ultimately failed to match the height growth of their neighbours in this early successional series. Their light harvesting efficiencies declined and this probably led to their exclusion. By contrast, species that maintained their position high in the canopy managed to persist in the vegetation despite their relatively low light harvesting efficiencies. In the tallest stands ,later successional' species had higher light harvesting efficiencies for the same plant height than ,early successional' species which was mostly the result of the greater area to mass ratio (specific leaf area, SLA) of their leaves. This shows how plant stature, plasticity in above-ground biomass partitioning, and architectural constraints determine the ability of plants to efficiently capture light, which helps to explain species replacement in this early successional series. [source] Cultivation of medicinal isabgol (Plantago ovata) in alkali soils in semiarid regions of Northern IndiaLAND DEGRADATION AND DEVELOPMENT, Issue 3 2006J. C. Dagar Abstract There is growing global demand for medicinal drugs including isabgol (Plantago ovata). With increasing demand of food for an ever-increasing population in India, it is not possible to bring arable lands under cultivation for aromatic and medicinal plants. Salt-affected lands (both saline and alkali) occupy about 8·6 million ha. Due to poor physical properties and excessive exchangeable Na+, most of these lands do not support good vegetation cover. The marginal and salt-affected lands could be successfully utilized for the cultivation of aromatic and medicinal plants. We achieved almost complete germination of isabgol seeds using up to 5000,ppm salt-solution. Grain yield (including husk) was 1·47 to 1·58,t,ha,1 at pH 9·2 showing no significant yield reduction as compared to normal soil. At pH 9·6 the grain yield was 1·03 to 1·12,t,ha,1. At higher pH there was significant reduction in yield. Sowing in good moisture (at field capacity) of soil was found best, but to save time sowing at shallow depth in dry soil, followed by irrigation was also suitable as compared to broadcasting seeds. The chlorophyll content was greater 70 days after sowing compared to younger stages (50 days after sowing). The total chlorophyll and plant biomass were lower from crops grown by broadcasting methods of sowing as compared to two other methods of sowing. The leaf area index (LAI) was higher for the broadcasting method of sowing as compared to the other two methods. Na+ absorption increased and K+ and K+/Na+ ratio decreased with increase in pH. Results reported in this paper clearly indicate that isabgol can successfully be grown on moderately alkali soils up to pH 9·6 without the application of any amendment. Copyright © 2006 John Wiley & Sons, Ltd. [source] Predicting moisture dynamics of fine understory fuels in a moist tropical rainforest system: results of a pilot study undertaken to identify proxy variables useful for rating fire dangerNEW PHYTOLOGIST, Issue 3 2010David Ray Summary ,The use of fire as a land management tool in the moist tropics often has the unintended consequence of degrading adjacent forest, particularly during severe droughts. Reliable models of fire danger are needed to help mitigate these impacts. ,Here, we studied the moisture dynamics of fine understory fuels in the east-central Brazilian Amazon during the 2003 dry season. Drying stations established under varying amounts of canopy cover (leaf area index (LAI) = 0 , 5.3) were subjected to a range of water inputs (5,15 mm) and models were developed to forecast litter moisture content (LMC). Predictions were then compared with independent field data. ,A multiple linear regression relating litter moisture content to forest structure (LAI), ambient vapor pressure deficit (VPDM) and an index of elapsed time since a precipitation event (d,1) was identified as the best-fit model (adjusted R2 = 0.89). Relative to the independent observations, model predictions were relatively unbiased when the LMC was , 50%, but consistently underestimated the LMC when the observed values were higher. ,The approach to predicting fire danger based on forest structure and meteorological variables is promising; however, additional information to the LAI, for example forest biomass, may be required to accurately capture the influence of forest structure on understory microclimate. [source] Seed removal in two coexisting oak species: ecological consequences of seed size, plant cover and seed-drop timingOIKOS, Issue 9 2008Ignacio M. Pérez-Ramos Seed predation and dispersal can critically influence plant community structure and dynamics. Inter-specific differences arising at these early stages play a crucial role on tree recruitment patterns, which in turn could influence forest dynamics and species segregation in heterogeneous environments such as Mediterranean forests. We investigated removal rates from acorns set onto the ground in two coexisting Mediterranean oak species ,Quercus canariensis and Q. suber, in southern Spain. We developed maximum likelihood estimators to investigate the main factors controlling probabilities of seed removal and to describe species-specific functional responses. To account for inter-specific differences in seed-drop timing, two experiments were established: a simultaneous exposure of acorns of the two species (synchronous experiments) and a seed exposure following their natural seed-drop phenology (diachronic experiments). A total of 1536 acorns were experimentally distributed along a wide and natural gradient of plant cover, and removal was periodically monitored for three months at two consecutive years (with contrasting differences in seed production and thus seed availability on the ground). The probability of seed removal increased with plant cover (leaf area index, LAI) for the two oak species. Inter-specific differences in acorn removal were higher in open areas and disappeared in closed microhabitats, especially during a non-mast year. Despite later seed-drop, Q. suber acorns were removed faster and at a higher proportion than those of Q. canariensis. The higher probability of seed removal for this species could be attributed to its larger seed size compared to Q. canariensis, as inter-specific differences were less pronounced when similar sized acorns were exposed. Inter-specific differences in seed removal, arising from seed size variability and microsite heterogeneity, could be of paramount importance in oak species niche separation, driving stand dynamics and composition along environmental gradients. [source] On the Role of Iron and one of its Chelating Agents in the Production of Protoporphyrin IX Generated by 5-Aminolevulinic Acid and its Hexyl Ester Derivative Tested on an Epidermal Equivalent of Human SkinPHOTOCHEMISTRY & PHOTOBIOLOGY, Issue 4 2006Pascal Uehlinger ABSTRACT Photodynamic therapy (PDT) with 5-aminolevulinic acid (ALA) or its derivatives as precursors of protoporphyrin IX (PPIX) is routinely used in dermatology for the treatment of various pathologies. However, this methodology suffers to some extent from a limited efficacy. Therefore, the main goal of this study was to investigate the modulation and pharma-cokinetics of PPIX buildup after a 5 h incubation with ALA (1.5 mM) and one of its derivatives, the hexyl ester of ALA (h-ALA) (1.5 mM), on the human epidermal equivalent EpidexÔ. PPIX production was modulated with (L+) ascorbic acid iron (II) salt (LAI) or the iron (II)-specific chelating agent deferoxamine (DFO). PPIX fluorescence from the EpidexÔ layers was measured up to 150 h after the precursor administration using a microspectrofluorometer (,ex: 400 ± 20 nm; ,det: 635 nm). The maximum PPIX fluorescence intensity induced by h-ALA was about 1.7x larger than that induced by ALA. The addition of DFO resulted in a more than 50% increase in PPIX fluorescence for both precursors. The decay half life measured for PPIX fluorescence is 30 and 42.5 h, respectively, for ALA and h-ALA. These half lives are doubled when the samples contain DFO. In the samples with the highest fluorescence intensity, a modified fluorescence spectrum was observed after 10 h, with the emergence of a peak at 590 nm, which is attributed to zinc protoporphyrin IX (Zn PPIX). [source] Evidence from Amazonian forests is consistent with isohydric control of leaf water potentialPLANT CELL & ENVIRONMENT, Issue 2 2006ROSIE A. FISHER ABSTRACT Climate modelling studies predict that the rain forests of the Eastern Amazon basin are likely to experience reductions in rainfall of up to 50% over the next 50,100 years. Efforts to predict the effects of changing climate, especially drought stress, on forest gas exchange are currently limited by uncertainty about the mechanism that controls stomatal closure in response to low soil moisture. At a through-fall exclusion experiment in Eastern Amazonia where water was experimentally excluded from the soil, we tested the hypothesis that plants are isohydric, that is, when water is scarce, the stomata act to prevent leaf water potential from dropping below a critical threshold level. We made diurnal measurements of leaf water potential (,l), stomatal conductance (gs), sap flow and stem water potential (,stem) in the wet and dry seasons. We compared the data with the predictions of the soil,plant,atmosphere (SPA) model, which embeds the isohydric hypothesis within its stomatal conductance algorithm. The model inputs for meteorology, leaf area index (LAI), soil water potential and soil-to-leaf hydraulic resistance (R) were altered between seasons in accordance with measured values. No optimization parameters were used to adjust the model. This ,mechanistic' model of stomatal function was able to explain the individual tree-level seasonal changes in water relations (r2 = 0.85, 0.90 and 0.58 for ,l, sap flow and gs, respectively). The model indicated that the measured increase in R was the dominant cause of restricted water use during the dry season, resulting in a modelled restriction of sap flow four times greater than that caused by reduced soil water potential. Higher resistance during the dry season resulted from an increase in below-ground resistance (including root and soil-to-root resistance) to water flow. [source] Potential contribution of selected canopy traits to the tolerance of foliar disease by spring barleyPLANT PATHOLOGY, Issue 6 2009I. J. Bingham A model of canopy photosynthesis and above-ground growth rate was used to investigate the potential impact of several canopy traits on tolerance of foliar disease by barley. Disease tolerance was defined as the reduction in predicted crop dry-matter growth rate per unit of visible disease symptoms. The traits were canopy area (leaf area index, LAI), light extinction coefficient (k) and the ratio of virtual to visible lesion size (,). The effects of altering the area of the healthy flag leaf and its light-saturated rate of photosynthesis (Pmax) in response to disease elsewhere on the plant were also investigated. The model was parameterized for spring barley and run with a solar radiation and temperature regime typical of north-east Scotland. Predicted reductions in growth rate per unit increase in disease were greatest at high disease severity and when disease was distributed relatively uniformly through the canopy. Tolerance was increased by increasing LAI to >3 and k to >0·3, but the beneficial effects depended on the severity and, to a lesser extent, the distribution of disease. Tolerance was reduced by increasing ,. A sensitivity analysis performed at a single disease severity and distribution showed that tolerance was most sensitive to variations in , and compensatory adjustments in area and Pmax of the flag leaf, and least sensitive to whole canopy LAI and k. Future research should quantify the genetic variation in these traits within barley germplasm to evaluate the scope for improving the disease tolerance of spring barley. [source] Detection of orientation-specific anti-gp120 antibodies by a new N-glycanase protection assayAPMIS, Issue 2 2002G. J. Gram Several functions have been assigned to the extensive glycosylation of HIV-1 envelope glycoprotein gp120, especially immune escape mechanisms, but the intramolecular interactions between gp120 and its carbohydrate complement are not well understood. To analyse this phenomenon we established a new microwell deglycosylation assay for determining N-linked glycan accessibility after binding of gp120-specific agents. Orientation-specific exposition of gp120 in ELISA microplates was achieved by catching with either anti-C5 antibody D7324 or anti-V3 antibody NEA-9205. We found that soluble CD4 inhibited the deglycosylation of gp120 only when gp120 was caught by D7324 and not by NEA9205. In contrast, antibodies from HIV-infected individuals inhibited the deglycosylation best when gp120 was caught by NEA9205. These results demonstrated that both the CD4-binding site and the epitopes recognised by antibodies from HIV-infected individuals have N-glycans in the close vicinity. However, the difference in gp120 orientation indicates that antibodies in HIV-infected individuals, at least partly, bind to epitopes different from the CD4-binding site. Finally, we determined the structural class of the glycan of one V1 glycosylation site of prototype HIV-1 LAI gp120, which remained unsolved from previous studies, and found that it belonged to the complex type of glycans. [source] Low-resolution remotely sensed images of winegrape vineyards map spatial variability in planimetric canopy area instead of leaf area indexAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 1 2008A. HALL Abstract Background and Aims:, Knowledge of the spatial variability of grapevine canopy density is useful in managing the variability of grape composition and yield. Rapid assessment of the characteristics of vineyards by remote sensing offers distinct advantages over ground-based measurements. In an effort to capture such advantages, this study aimed to assess the relative contribution to LAI of grapevine canopy density and grapevine canopy area derived from high-spatial-resolution airborne digital imagery. Methods and Results:, High-spatial-resolution airborne NDVI imagery of minimally pruned, unconfined (i.e. not confined by trellising) grapevines was used to partition image pixels into grapevine-only and non-grapevine groupings. An evaluation of the relative contributions of grapevine planimetric area (number of grapevine pixels across a single row) and leaf layers (NDVI of grapevine-only pixels) found that the variability observed across the vineyard was dominated by changes in canopy area rather than grapevine-only NDVI. Conclusion:, The primary predictive variable of grapevine LAI is canopy area. Low-spatial-resolution NDVI imagery of minimally pruned, unconfined vineyards is therefore effective in mapping spatial variability in planimetric canopy area, rather than LAI. Significance of the Study:, The process of estimating grapevine LAI from mixed pixels has incorrectly assumed that both components of LAI within a pixel's footprint, namely the number of leaf layers and planimetric canopy area, produce a consistent response in NDVI. Correlations between NDVI and LAI reported in previous studies based on low-resolution imagery most likely relied on the proxy relationship between NDVI and canopy area. [source] Temporal stability of an NDVI-LAI relationship in a Napa Valley vineyardAUSTRALIAN JOURNAL OF GRAPE AND WINE RESEARCH, Issue 2 2003LEE F. JOHNSON Abstract Remotely sensed values for normalised difference vegetation index (NDVI) were derived periodically from high-resolution Ikonos satellite images during the 2001 growing season, and compared with ground measurements of vineyard leaf area index (LAI) during that same period. These two derived variables were strongly related in six vineyard blocks on each of four occasions (R2= 0.91 to 0.98). Linear regression equations relating these two derived variables did not differ significantly by time-step, and a single equation accounted for 92 per cent of the variance in the combined dataset. Such temporal stability in that relationship opens the possibility of transforming NDVI maps to LAI units, at least on a localised basis, and minimising (or even eliminating) subsequent ground calibration. This reduction in fieldwork would then decrease information cost for viticulturists who wish to monitor LAI sequentially within season, or who wish to track year-to-year changes in climax LAI with a single image collected annually. To take advantage of this cost reduction, temporal consistency in spectral data values comprising NDVI must be assured. This present paper addresses that issue. [source] Effects of Season and Successional Stage on Leaf Area Index and Spectral Vegetation Indices in Three Mesoamerican Tropical Dry Forests,BIOTROPICA, Issue 4 2005Margaret E. R. Kalacska ABSTRACT We compared plant area index (PAI) and canopy openness for different successional stages in three tropical dry forest sites: Chamela, Mexico; Santa Rosa, Costa Rica; and Palo Verde, Costa Rica, in the wet and dry seasons. We also compared leaf area index (LAI) for the Costa Rican sites during the wet and dry seasons. In addition, we examined differences in canopy structure to ascertain the most influential factors on PAI/LAI. Subsequently, we explored relationships between spectral vegetation indices derived from Landsat 7 ETM+ satellite imagery and PAI/LAI to create maps of PAI/LAI for the wet season for the three sites. Specific forest structure characteristics with the greatest influence on PAI/LAI varied among the sites and were linked to climatic differences. The differences in PAI/LAI and canopy openness among the sites were explained by both the past land-use history and forest management practices. For all sites, the best-fit regression model between the spectral vegetation indices and PAI/LAI was a Lorentzian Cumulative Function. Overall, this study aimed to further research linkages between PAI/LAI and remotely sensed data while exploring unique challenges posed by this ecosystem. RESUMEN En este estudio comparamos el índice de área de plantas PAI, el índice de área foliar (LAI), y la apertura de dosel para diferentes etapas sucesionales en tres sitios del bosque seco tropical: Chamela, México; Santa Rosa, Costa Rica y Palo Verde, Costa Rica en la estación lluviosa y seca. Además, examinamos las diferencias en la estructura de dosel para indagar los factores que más influyen en el PAI/LAI. En forma adicional, exploramos las relaciones entre los índices espectrales de vegetación derivados de imágenes satelitales Landsat 7 ETM+ y el PAI/LAI para así crear mapas de PAI/LAI de la estación lluviosa para los tres sitios. En este estudio encontramos que las características específicas de la estructura del bosque con mayor influencia en PAI/LAI varían entre sitios y las mismas están asociadas a diferencias climáticas. Las diferencias en el PAI/LAI y la apertura del dosel entre los sitios son explicadas tanto por el historial de uso del suelo y asi como las prácticas de manejo del bosque. Para todos los sitios el mejor modelo de regresión entre los índices espectrales de vegetación y el PAI/LAI es la función Cumulativa Lorentziana. En general, este estudio tiene como objetivo estudiar más a fondo las relaciones entre el PAI/LAI y los datos colectados de manera remota, mientras se exploran otros retos particulares que plantea este ecosistema. [source] Remote Sensing Research Priorities in Tropical Dry Forest EnvironmentsBIOTROPICA, Issue 2 2003G. A. Sánchez-Azofeifa ABSTRACT Satellite multi, and hyper-spectral sensors have evolved over the past three decades into powerful monitoring tools for ecosystem processes. Research in temperate environments, however, has tended to keep pace with new remote sensing technologies more so than in tropical environments. Here, we identify what we consider to be three priority areas for remote sensing research in Neotropical dry forests. The first priority is the use of improved sensor capabilities, which should allow for better characterization of tropical secondary forests than has been achieved. Secondary forests are of key interest due to their potential for sequestering carbon in relatively short periods of time. The second priority is the need to characterize leaf area index (LAI) and other biophysical variables by means of bidirectional reflectance function models. These biophysical parameters have importance linkages with net primary productivity and may be estimated through remote sensing. The third priority is to identify tree species using hyper-spectral imagery, which represents an entirely new area of research for tropical forests that could have powerful applications in biodiversity conservation. RESUMEN En las últimas tres decadas, los sensores satelitales multi e hiper-espectrales han evolucionado hasta convertirse en importantes herramientas para el monitoreo de los ecosistemas. La investigación en los ecosistemas templados y boreales ha seguido el paso de los avances en los sistemas de percepción remota, mientras que en los sistemas tropicales existe un desface significative. En este articulo identificamos y revisamos tres prioridades básicas en la investigación basada en sensores remotos de las regiones neotropicales del bosque seco. Estas prioridades están relacionadas con el monitoreo de bosques secundarios, el desarrollo de estudios relacionados con la cuantificación del área foliar por médio de métodos ópticos y finalmente el desarrollo de técnicas, que ligadas a información hiper-espectral, puedan ser utilizadas para la identificación de especies de árboles en zonas tropicales. Esta última prioridad representa una nueva área de investigación en los bosques tropicales con importantes connotaciones para la conservación de la biodiversidad boilógica. [source] Cluster Disorder and Ordering Principles in Al-Stabilized "LaI"CHEMINFORM, Issue 39 2005Oliver Oeckler Abstract For Abstract see ChemInform Abstract in Full Text. [source] Design of change detection algorithms based on the generalized likelihood ratio testENVIRONMETRICS, Issue 8 2001Giovanna Capizzi Abstract A design procedure for detecting additive changes in a state-space model is proposed. Since the mean of the observations after the change is unknown, detection algorithms based on the generalized likelihood ratio test, GLR, and on window-limited type GLR, are considered. As Lai (1995) pointed out, it is very difficult to find a satisfactory choice of both window size and threshold for these change detection algorithms. The basic idea of this article is to estimate, through the stochastic approximation of Robbins and Monro, the threshold value which satisfies a constraint on the mean between false alarms, for a specified window size. A convenient stopping rule, based on the first passage time of an F -statistic below a fixed boundary, is used to terminate the iterative approximation. Then, the window size which produces the most desirable out-of-control ARL, for a fixed value of the in-control ARL, can be selected. These change detection algorithms are applied to detect biases on the measurements of ozone, recorded from one monitoring site of Bologna (Italy). Comparisons of the ARL profiles reveal that the full-GLR scheme provides much more protection than the window-limited GLR schemes against small shifts in the process, but the modified window-limited GLR provides more protection against large shifts. Copyright © 2001 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||||||||||||||