bluuebunny/crossref_metadata_2025_split huggingface dataset:
Hierarchical subdivision of Arctic tundra based on vegetation response to climate, parent material and topography
Authors: Walker D. A. 
Published: March 2003

SummaryCurrent land‐cover classifications used for global modelling portray Arctic tundra as one or two classes. This is insufficient for analysis of climate–vegetation interactions. This paper presents a simple three‐level vegetation‐map legend system useful for modelling at global, regional, and landscape scales. At the highest level (global scale: 107−108 km2) the Tundra Zone is divided into four subzones based on vegetation response to temperature along the latitudinal temperature gradient from north to south: (1) Cushion‐forb, (2) Prostrate Dwarf‐shrub, (3) Erect Dwarf‐shrub, and (4) Low Shrub subzones. The boundaries follow a modification of Yurtsev's phytogeographic subzones. Parent material and topography are also major considerations at global, regional, and landscape scales. Soil pH is a key variable for many ecosystem responses, and a division into acidic (pH 5.5 or less) and nonacidic soils is used. A conceptual mesotopographic gradient is used to characterize the influence of soil‐moisture and snow regimes. The example legend framework focuses on the Northern Alaska floristic subprovince, and could be expanded to other floristic provinces using local expert knowledge and available literature. Dominant plant functional types within each habitat type within the four subzones are also presented. Modellers could include or ignore different levels of resolution depending on the purpose of the model. The approach resolves conflicts in terminology that have previously been encountered between the Russian, North American, and Fennoscandian approaches to Arctic zonation.
Biotic disturbance agents in the boreal forest: considerations for vegetation change models
Authors: Malmström Carolyn M. , Raffa Kenneth F. 
Published: March 2003

SummaryDisturbance regimes strongly determine vegetation patterns and succession in the boreal landscape. One of the current challenges for boreal vegetation modellers is to represent disturbance agents as dynamic factors that can respond to climate change. Outbreak species of insects and plant pathogens can cause marked changes in vegetation patterns and should be incorporated into vegetation change models. This introduction to the ecology of boreal biotic disturbance agents is designed as a brief overview for global change researchers and modellers. We discuss the importance of biotic disturbance agents in the boreal forest, offer an overview of their ecology, and review modelling approaches. We illustrate these issues with examples from different systems, drawing largely from our experience with bark beetles.
An empirical model of carbon fluxes in Russian tundra
Authors: Zamolodchikov Dmitri G. , Karelin Dmitri V. 
Published: March 2003

SummaryThis study presents an empirical model based on a GIS approach, which was constructed to estimate the large‐scale carbon fluxes over the entire Russian tundra zone. The model has four main blocks: (i) the computer map of tundra landscapes; (ii) data base of long‐term weather records; (iii) the submodel of phytomass seasonal dynamics; and (iv) the submodel of carbon fluxes. The model uses exclusively original in situ diurnal CO2 flux chamber measurements (423 sample plots) conducted during six field seasons (1993–98). The research sites represent the main tundra biome landscapes (arctic, typical, south shrub and mountain tundras) in the latitudinal diapason of 65–74°N and longitudinal profile of 63°E−172°W. The greatest possible diversity of major ecosystem types within the different landscapes was investigated. The majority of the phytomass data used was obtained from the same sample plots. The submodel of carbon fluxes has two dependent [GPP, Gross Respiration (GR)] and several input variables (air temperature, PAR, aboveground phytomass components). The model demonstrates a good correspondence with other independent regional and biome estimates and carbon flux seasonal patterns. The annual GPP of Russian tundra zone for the area of 235 × 106 ha was estimated as −485.8 ± 34.6 × 106 tC, GR as +474.2 ± 35.0 × 106 tC, and NF as −11.6 ± 40.8 × 106 tC, which possibly corresponds to an equilibrium state of carbon balance during the climatic period studied (the first half of the 20th century). The results advocate that simple regression‐based models are useful for extrapolating carbon fluxes from small to large spatial scales.
Interactive effects of elevated CO2 and temperature on the leaf‐miner Dialectica scalariella Zeller (Lepidoptera: Gracillariidae) in Paterson's Curse, Echium plantagineum (Boraginaceae)
Authors: Johns Caitlin V. , Hughes Lesley 
Published: March 2003

Doubling of the current atmospheric CO2 concentration, and an increase in global mean annual temperatures of 1.5–6 °C, have been predicted to occur by the end of this century. Whilst the separate effects of CO2 and temperature on plant–insect interactions have been examined in a number of studies, few have investigated their combined impact. We carried out a factorial experiment to explore the effect of a doubling of CO2 concentration and a 3 °C temperature increase on the development of a complete generation of the leaf‐miner, Dialectica scalariella, in the host plant Paterson's Curse, Echium plantagineum.Elevated CO2 increased biomass, reduced leaf N and increased C:N ratios in the host plants. Leaf thickness also increased under elevated CO2, but only in the high‐temperature treatment. Female D. scalariella did not discriminate between plants grown at the different CO2 levels when ovipositing, despite the reduction in foliage quality under elevated CO2. Overall, the negative response of D. scalariella to elevated CO2 was greater than for many species of free‐living insects, presumably because of the limited mobility imposed by the leaf‐mining habit. Development was accelerated at the high temperature and slowed under elevated CO2. The net result was a reduction in development time of ∼14 days in the elevated CO2/high temperature treatment, compared to the ambient CO2/low temperature treatment. Larval survivorship and adult moth weight were both affected by a significant interaction between CO2 and temperature. At the low temperature, CO2 had little effect on survivorship, but at the high temperature, survivorship was significantly reduced under elevated CO2. Similarly, elevated CO2 had a stronger negative effect on adult moth weight when combined with the high‐temperature treatment. A possible explanation for these results is that the high temperature accelerated insect development to such an extent that the larvae did not have sufficient feeding time to compensate for the poorer quality of the foliage.The frequency with which interactions between CO2 and temperature affected both plant and insect performance in this study highlights the need for caution when predicting the effects of future climate change on plant–insect interactions from single‐factor experiments.
Elevated atmospheric CO2 in open top chambers increases net nitrification and potential denitrification
Authors: Carnol Monique , Hogenboom Laure , Jach M. Ewa , Remacle Jean , Ceulemans Reinhart 
Published: March 2003

AbstractThe control of soil nitrogen (N) availability under elevated atmospheric CO2 is central to predicting changes in ecosystem carbon (C) storage and primary productivity. The effects of elevated CO2 on belowground processes have so far attracted limited research and they are assumed to be controlled by indirect effects through changes in plant physiology and chemistry. In this study, we investigated the effects of a 4‐year exposure to elevated CO2 (ambient + 400 µmol mol−1) in open top chambers under Scots pine (Pinus sylvestris L) seedlings on soil microbial processes of nitrification and denitrification. Potential denitrification (DP) and potential N2O emissions were significantly higher in soils from the elevated CO2 treatment, probably regulated indirectly by the changes in soil conditions (increased pH, C availability and NO3– production). Net N mineralization was mainly accounted for by nitrate production. Nitrate production was significantly larger for soil from the elevated CO2 treatment in the field when incubated in the laboratory under elevated CO2 (increase of 100%), but there was no effect when incubated under ambient CO2. Net nitrate production of the soil originating from the ambient CO2 treatment in the field was not influenced by laboratory incubation conditions. These results indicate that a direct effect of elevated atmospheric CO2 on soil microbial processes might take place. We hypothesize that physiological adaptation or selection of nitrifiers could occur under elevated CO2 through higher soil CO2 concentrations. Alternatively, lower microbial NH4 assimilation under elevated CO2 might explain the higher net nitrification. We conclude that elevated atmospheric CO2 has a major direct effect on the soil microbial processes of nitrification and denitrification despite generally higher soil CO2 concentrations compared to atmospheric concentrations.
Changes in microclimate induced by experimental warming and clipping in tallgrass prairie
Authors: Wan S. , Luo Y. , Wallace L. L. 
Published: March 2003

AbstractIn order to facilitate interpretation and comparison of warming effects on ecosystems across various habitats, it is imperative to quantify changes in microclimate induced by warming facilities. This paper reports observed changes in air temperature, soil temperature and soil‐moisture content under experimental warming and clipping in a tallgrass prairie in the Great Plains, USA. We used a factorial design with warming as the primary factor nested with clipping as the secondary factor. Infrared heater was used in order to simulate climatic warming and clipping to mimic mowing for hay or grazing. The warming treatment significantly increased daily mean and minimum air temperatures by 1.1 and 2.3 °C, respectively, but had no effect on daily maximum air temperature, resulting in reduced diurnal air‐temperature range. Infrared heaters substantially increased daily maximum (2.5 and 3.5 °C), mean (2.0 and 2.6 °C) and minimum (1.8 and 2.1 °C) soil temperatures in both the unclipped and clipped subplots. Clipping also significantly increased daily maximum (3.4 and 4.3 °C) and mean (0.6 and 1.2 °C) soil temperatures, but decreased daily minimum soil temperature (1.0 and 0.6 °C in the control and warmed plots, respectively). Daily maximum, mean and minimum soil temperatures in the clipped, warmed subplots were 6.8, 3.2 and 1.1 °C higher than those in the unclipped, control subplots. Infrared heaters caused a reduction of 11.0% in soil moisture in the clipped subplots, but not in the unclipped subplots. Clipping reduced soil‐moisture content by 17.7 and 22.7% in the control and warmed plots, respectively. Experimental warming and clipping interacted to exacerbate soil‐moisture loss (26.7%). Overall, infrared heaters simulated climate warming well by enhancing downward infrared radiation and by reducing the diurnal air‐temperature range.
The long way from Kyoto to Marrakesh: Implications of the Kyoto Protocol negotiations for global ecology
Authors: Schulze E.‐D. , Valentini R. , Sanz M.‐J. 
Published: March 2003

AbstractThe Sixth and Seventh Conference of the Parties (COP 6 and 7) at The Hague, Bonn and Marrakesh came to a final Agreement on the Kyoto Protocol, which is thus ready for ratification by the individual nations. The Agreement was only achieved by allowing countries to offset their fossil fuel emission targets (on average 95% of the 1990 emissions) by increasing biological carbon sequestration, and by trading carbon credits. Activities that would count as increasing biological carbon sequestration include afforestation and reforestation, and changes in management of agriculture and forestry. According to the Agreement reached in Marrakesh, biological carbon sequestration may reach an offset of up to 80% of the required reduction in fossil fuel emissions (4% of the 5% reduction commitment). We explain why the allowable offset rose as high during the course of the negotiations. It is highlighted that major unintended consequences may be a result of the policy as it stands in the Marrakesh Accord. Major losses of biodiversity and primary forest are expected. We present scientific concerns regarding verification, which lead to scientific doubts that the practices encouraged by the Agreement can actually increase sequestration under a full carbon accounting scheme. We explain that there is a ‘win‐win’ option that would protect high carbon pools and biodiversity in an economically efficient way. But, this is not supported by the Agreement. Despite the very positive signal that most nations of the United Nations will devote major efforts towards climate protection, there remains a most urgent need to develop additional rules to avoid unintended outcomes, and to promote the ‘win‐win’ options that we explain.
Spatial distribution of phytomass carbon in Indian forests
Authors: CHHABRA ABHA , PALRIA S. , DADHWAL V. K. 
Published: March 2003

AbstractA spatial analysis of phytomass carbon (C) in Indian forests for the period (1988–94) at the district‐level is reported. District‐level forest phytomass C (1988, 1994) was computed by combining remote sensing‐based forest area inventories on 1:250 000 scale, field inventories of growing stock volume by the Forest Survey of India (FSI), and crown density‐based biomass expansion factors. The estimates of forest area inventory, forest phytomass C density, and forest phytomass C pools (1988–94) were linked to the district boundary coverage of India in ARC/INFO Geographic Information System (GIS). Of the total 386 districts examined, only 17 districts had more than 75% forest cover (as percent of their geographic area) in 1988. Estimated district‐level forest phytomass C densities ranged from 4.3 to 206.8 MgC ha−1*. At the national level, forest phytomass C pool was estimated to be 3871.2 and 3874.3 TgC# in 1988 and 1994, respectively. Although the aggregated national estimates were similar, the district‐level change analysis indicated a decrease of 77.8 TgC and an increase of 81 TgC (1988–94). The highest decrease of 10.4 TgC was observed in Vishakapatnam district (Andhra Pradesh) while largest increase of 9.8 TgC in Bastar district (Madhya Pradesh) resulting from deforestation and afforestation activities, respectively. At the national level, the total forest cover decreased by ∼0.6 Mha, however, the district‐level spatial analysis indicated an increase of 1.07 Mha, and decrease of 1.65 Mha forest cover during 1988–94 period. Although, this is the first district level phytomass C analysis of Indian forests, the aggregated results at state‐level were close to the earlier estimates. The spatial analysis identified the districts that have undergone significant changes in their forest phytomass C during the study period. This improved understanding of forest phytomass C pools is important to sustainable development and conservation of forests, mitigation strategies for C sequestration, and accurate estimation of contribution of land use changes to C emission in India.
P uptake by arbuscular mycorrhizal hyphae: effect of soil temperature and atmospheric CO2 enrichment
Authors: Gavito Mayra E. , Schweiger Peter , Jakobsen Iver 
Published: March 2003

AbstractMycorrhizas are ubiquitous symbioses that may have an important role in the movement of C from air to soil. Studies on the effects of climate change factors on mycorrhizas have been concentrated on the effects of atmospheric [CO2] whereas temperature effects have been neglected. Based on previous results showing no effect of varying atmospheric [CO2] on the development and P uptake of the arbuscular mycorrhizal fungi (AMF) colonizing plants growing in controlled conditions, we hypothesized that soil temperature would have a higher impact on AMF development and nutrient uptake than the effects of [CO2] on the host plant. Pea plants were grown in association with either a single isolate of Glomus caledonium or AMF from field soil in factorial combination with the corresponding current (10 °C) or elevated (15 °C) soil temperatures at current (350 p.p.m) or elevated (700 p.p.m) atmospheric [CO2]. 33P uptake by extraradical AMF hyphae was measured independently from root P uptake in a root exclusion compartment. Intraradical colonization developed well at both soil temperatures and almost duplicated from 10 to 15 °C. Extraradical mycelium developed only at 15 °C in the root exclusion compartment and hyphal P uptake could therefore be studied at 15 °C only. Hyphal P uptake differed markedly between inoculum types, but was not altered by growing the host plants at two atmospheric [CO2] levels. No significant [CO2] × soil temperature interactions were observed. The results suggested that, in the system tested, AMF development and function is likely more influenced by the temperature component of climate change than by its [CO2] component. We suggest that much more attention should be paid to temperature effects in future studies.
Simulation of biomass, carbon and nitrogen accumulation in grass to link with a soil nitrogen dynamics model
Authors: Wu  , McGechan  
Published: March 2003

In order to represent nitrogen and carbon cycling in the soil–plant–atmosphere continuum, a previously developed weather‐driven grass growth model has been adapted to become the crop growth component of the soil nitrogen dynamics model SOILN. This provides a means of simulating nitrogen uptake by the grass crop, an important component of the overall nitrogen balance in grassland.Grass growth is represented by a photosynthesis equation adjusted to take account of respiration as well as constraints due to lack of water and nitrogen in the soil. Water shortage is represented by linked simulations with the soil water and heat model SOIL, and nitrogen shortage by links with the
SOILN model. Accumulated biomass and the nitrogen component of biomass are allocated to leaf, stem and root pools, and flows from live biomass pools to those representing above‐ and below‐ground senescent material are also represented. The model is tested by comparing simulated cut grass yields and nitrogen contents of cut material with measured data at a test site. Soil nitrogen processes in the model are tested by comparing simulated and measured nitrate in drainflows. Agreement is reasonable, indicating that the combined model gives a␣realistic representation of carbon and nitrogen processes in grassland.The use of the combined model in a predictive manner has been demonstrated in a comparison of nitrogen balances with a number of alternative slurry and mineral nitrogen fertilizer application scenarios.
Influence of pH and aluminium on nitrogen partitioning in defoliated grasses
Authors: Thornton B. 
Published: March 2003

AbstractReduced inputs of fertilizer and lime to grasslands can result in decreased soil pH, increased aluminium concentration in the soil solution and, consequent upon these, inhinition of nitrogen acquisition by plannts. This study tested the hypothesis that under conditions of low pH and high aluminium concentrations a grass species more tolerant of acid conditions (Deschampsia flexuosa) maintains a greater total supply of nitrogen to growing leaves after defoliation from both root uptake and mobilization of stores than a less tolerant species (Lolium perenne). The grasses were grown without alumimium at pH values 3.5, 4.0, 5.0 or 5.5 and at a range of aluminium concentrations (0, 20, 100, 200 or 1000 mmol m−3) at pH 4.5. Labelling with 15NH415NO3 after defoliation allowed estimation of both root uptake and mobilization of stores in supplying nitrogen to growing leaves. The total amount of nitrogen supplied to the growing the leaves after defoliation by the combination of current root uptake and mobilization was maximal when aluminium was in the range 20–20 mmol m‐3. The total nitrogen supplied to growing leaves the both species after defoliation was greater when the grasses were grwon at pH 5.0 and 5.5 than when grown at pH 4.0. L. perenned and D. flexuosa were affected similarly by both aluminium and pH with respect to the total nitrogen supplied to the leaves. The effects of aluminium an dpH upon the supply of nitrogen to growing leaves after defoliation my not be a dominant factor in the vegetation dynamics of grazed swards.
Simulation of nitrogen uptake, fixation and leaching in a grass/white clover mixture
Authors: Wu  , McGechan  
Published: March 2003

To represent nitrogen cycling in a low input grass/legume pasture system, a previously developed, weather‐driven grass/white clover growth model has been adapted to become the crop growth component of the soil nitrogen dynamics model SOILN. This provides a means of simulating nitrogen uptake by a grass/white clover crop, an important component of the overall nitrogen balance in low‐input grassland systems.Crop growth is represented by a photosynthesis equation adapted to take account of competition between the two crops for resources of light, water and nitrogen in the soil. Water shortage is represented by linked simulations with the soil water and heat model SOIL, and nitrogen shortage by links with the SOILN model. Nitrogen fixation has been introduced according to an equation for potential fixation reduced by environmental factors, particularly temperature. Transfer of nitrogen‐rich clover plant material to the soil nitrogen pools of SOILN (from where it becomes available as a nutrient for grass) is also represented. The model is tested by comparing simulated cut crop yields and nitrogen content of cut material with measured data from perennial ryegrass/white clover at a test site. Soil nitrogen processes in the model are tested by comparing simulated and measured nitrate in drainflows. Apart from some discrepancies between simulated and measured results attributable to the inherent instability of a mixed crop system, agreement is reasonable by the standards of biological system models, indicating that the combined model gives a realistic representation of carbon and nitrogen processes in grassland with a grass, legume mixed crop.
The effect of herbage allowance on daily intake by Creole heifers tethered on natural Dichanthium spp. pasture
Authors: Boval  , Cruz  , Peyraud  , Penning  
Published: March 2003

Two experiments were carried out in Guadeloupe to estimate the organic matter intake (OMI) and digestibility (OMD) of a Dichanthium spp. sward, grazed by tethered Creole heifers [mean live weight (LW) 202 ± 2·0 kg], at three daily herbage allowances. Experiment 1 examined herbage allowances of 16, 25 and 31 kg of dry matter (DM) d–1 on a fertilized sward at 21 days of regrowth whereas, in experiment 2, lower allowances of 11, 15 and 19 kg DM d–1 were examined on the same sward, which was unfertilized and grazed at 14 days of regrowth. In each experiment, the herbage was grazed with three groups of two heifers in a 3 × 3 Latin square design. Sward characteristics were described before grazing. OMI was calculated from total faecal output, and OMD was predicted from the crude protein (CP) content of the faeces. The amount of herbage defoliated by the heifers was also estimated on tillers selected at random.Organic matter intakes were on average 26 g and 19 g OM kg–1 LW, and OMD values were 0·740 and 0·665 for Experiments 1 and 2, respectively, and were not affected by allowance. In Experiment 1, the herbage quality was high [0·50 of leaf and 116 g CP kg–1 organic matter (OM)] for a tropical forage, whereas in Experiment 2, the quality of the herbage (0·27 of leaf and 73 g CP kg–1 OM) was lower. These differences were reflected in differences in intake and digestibility in the two experiments.The experimental tropical Dichanthium spp. swards can have intake characteristics similar to those of a temperate sward.