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1

Electronic Resource

CO2 stabilization, climate change and the terrestrial carbon sink (2000)

White, Andrew ; Cannell, Melvin G. R. ; Friend, Andrew D.

Oxford, UK : Blackwell Science Ltd

Global change biology 6 (2000), S. 0

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ISSN: 1365-2486

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography

Notes: A nonequilibrium, dynamic, global vegetation model, Hybrid v4.1, with a subdaily timestep, was driven by increasing CO2 and transient climate output from the UK Hadley Centre GCM (HadCM2) with simulated daily and interannual variability. Three IPCC emission scenarios were used: (i) IS92a, giving 790 ppm CO2 by 2100, (ii) CO2 stabilization at 750 ppm by 2225, and (iii) CO2 stabilization at 550 ppm by 2150. Land use and future N deposition were not included. In the IS92a scenario, boreal and tropical lands warmed 4.5 °C by 2100 with rainfall decreased in parts of the tropics, where temperatures increased over 6 °C in some years and vapour pressure deficits (VPD) doubled. Stabilization at 750 ppm CO2 delayed these changes by about 100 years while stabilization at 550 ppm limited the rise in global land surface temperature to 2.5 °C and lessened the appearance of relatively hot, dry areas in the tropics.Present-day global predictions were 645 PgC in vegetation, 1190 PgC in soils, a mean carbon residence time of 40 years, NPP 47 PgC y−1 and NEP (the terrestrial sink) about 1 PgC y−1, distributed at both high and tropical latitudes. With IS92a emissions, the high latitude sink increased to the year 2100, as forest NPP accelerated and forest vegetation carbon stocks increased. The tropics became a source of CO2 as forest dieback occurred in relatively hot, dry areas in 2060–2080. High VPDs and temperatures reduced NPP in tropical forests, primarily by reducing stomatal conductance and increasing maintenance respiration. Global NEP peaked at 3–4 PgC y−1 in 2020–2050 and then decreased abruptly to near zero by 2100 as the tropical source offset the high-latitude sink. The pattern of change in NEP was similar with CO2 stabilization at 750 ppm, but was delayed by about 100 years and with a less abrupt collapse in global NEP. CO2 stabilization at 550 ppm prevented sustained tropical forest dieback and enabled recovery to occur in favourable years, while maintaining a similar time course of global NEP as occurred with 750 ppm stabilization. By lessening dieback, stabilization increased the fraction of carbon emissions taken up by the land. Comparable studies and other evidence are discussed: climate-induced tropical forest dieback is considered a plausible risk of following an unmitigated emissions scenario.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2486.2000.00358.x

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Environmental impacts of forest monocultures: water use, acidification, wildlife conservation, and carbon storage (1999)

Cannell, Melvin G. R.

Springer

New forests 17 (1999), S. 239-262

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ISSN: 1573-5095

Keywords: planted forests ; sustainability

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract A broad assessment is given of the contentions that plantation forests are high consumers of water, increase acidification, sustain a low diversity of wildlife, and store more carbon than do unmanaged forests. The following conclusions are drawn: (1) Evapotranspiration from planted forest monocultures is greater than from short vegetation, as a result of greater interception loss. Water loss from conifer forests is usually greater than from deciduous hardwoods, but evapotranspiration from Eucalyptus in the dry tropics is often no greater than from native hardwoods. (2) Compared to short vegetation, forests can significantly increase the transfer of acidifying pollutants from the air to the soil and surface waters, and conifers are more likely to enhance acidification than are hardwoods. (3) There are normally sufficient plantation management options available to make most plantation landscapes the homes of a rich diversity of flora and fauna. (4) An area covered with a plantation managed for maximum volume yield will normally contain substantially less carbon than the same area of unmanaged forest.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1006551018221

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Dynamics of mineral N availability in grassland ecosystems under increased [CO2]: hypotheses evaluated using the Hurley Pasture Model (2000)

Thornley, John H. M. ; Cannell, Melvin G. R.

Springer

Plant and soil 224 (2000), S. 153-170

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ISSN: 1573-5036

Keywords: climate change ; immobilisation ; mineralisation ; N-turnover ; nitrogen ; soil organic matter

Source: Springer Online Journal Archives 1860-2000

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Notes: Abstract The following arguments are outlined and then illustrated by the response of the Hurley Pasture Model to [CO2] doubling in the climate of southern Britain. 1. The growth of N-limited vegetation is determined by the concentration of N in the soil mineral N pools and high turnover rates of these pools (i.e., large input and output fluxes) contribute positively to growth. 2. The size and turnover rates of the soil mineral N pools are determined overwhelmingly by N cycling into all forms of organic matter (plants, animals, soil biomass and soil organic matter — `immobilisation' in a broad sense) and back again by mineralisation. Annual system N gains (by N2 fixation and atmospheric deposition) and losses (by leaching, volatilisation, nitrification and denitrification) are small by comparison. 3. Elevated [CO2] enriches the organic matter in plants and soils with C, which leads directly to increased removal of N from the soil mineral N pools into plant biomass, soil biomass and soil organic matter (SOM). ‘Immobilisation’ in the broad sense then exceeds mineralisation. This is a transient state and as long as it exists the soil mineral N pools are depleted, N gaseous and leaching losses are reduced and the ecosystem gains N. Thus, net immobilisation gradually increases the N status of the ecosystem. 4. At the same time, elevated [CO2] increases symbiotic and non-symbiotic N2 fixation. Thus, more N is gained each year as well as less lost. Effectively, the extra C fixed in elevated [CO2] is used to capture and retain more N and so the N cycle tracks the C cycle. 5. However, the amount of extra N fixed and retained by the ecosystem each year will always be small (ca. 5–10 kg N ha-1 yr-1) compared with amount of N in the immobilisation-mineralisation cycle (ca. 1000 kg N ha-1 yr-1). Consequently, the ecosystem can take decades to centuries to gear up to a new equilibrium higher-N state. 6. The extent and timescale of the depletion of the mineral N pools in elevated [CO2] depends on the N status of the system and the magnitude of the overall system N gains and losses. Small changes in the large immobilisation—mineralisation cycle have large effects on the small mineral N pools. Consequently, it is possible to obtain a variety of growth responses within 1–10 year experiments. Ironically, ecosystem models — artificial constructs — may be the best or only way of determining what is happening in the real world.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1004640327512

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Competition for light: detection, measurement, and quantification (1993)

Cannell, Melvin G. R. ; Grace, John

Canadian Science Publishing

In: Canadian Journal of Forest Research. 1993; 23(10): 1969-1979. Published 1993 Oct 01. doi: 10.1139/x93-248.

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Publication Date: 1993-10-01

Description: A broad review is presented of (i) indirect and direct methods of detecting and measuring competition for light in plant communities and (ii) simple methods of quantifying light interception by components in a mixture. Competition for light in plant stands may be inferred from the presence of "one-sided" competition, bimodal distributions of plant size, and even (nonrandom) spatial dispersion of plants. However, the outcome depends on the species' response to shadelight. Experimental methods are reviewed for detecting light limitation, distinguishing aboveground and belowground competition, and determining the light "foraging" capacity of plants. Dry matter production by each component in a mixture may be roughly proportional to the amount of light it intercepts. The simple Beer–Lambert equations for light interception are given for monocultures, vertically separated mixtures, and intimate two-component mixtures. These equations emphasize the penalty of being overshadowed. A survey is given of the main methods used to directly measure irradiance and interception in plant canopies.

Print ISSN: 0045-5067

Electronic ISSN: 1208-6037

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Published by Canadian Science Publishing

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Branch development on leaders of Piceasitchensis (1978)

Baxter, Shelagh M. ; Cannell, Melvin G. R.

Canadian Science Publishing

In: Canadian Journal of Forest Research. 1978; 8(1): 121-128. Published 1978 Mar 01. doi: 10.1139/x78-020.

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Publication Date: 1978-03-01

Description: The top whorl of branches on each year's leader on mature P. sitchensis (Bong.) Carr. had more needles and longer needle internodes than branches lower down on the leader. All branches developed as buds for similar periods of time from April to October, but top branch buds developed larger apical meristems which generated needle primordia more rapidly than lower branch buds. In mid-August, top branch buds produced at least 13 primordia per day compared with only 5 per day in basal buds. In the next year, when these preformed buds extended, top branches produced about one and a half times as many cells per needle internode as basal branches, as judged by observing the pith. In both years, cell division was the important growth process affected by 'dominance' mechanisms between branch buds.

Print ISSN: 0045-5067

Electronic ISSN: 1208-6037

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Published by Canadian Science Publishing

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Shoot apical growth and cataphyll initiation rates in provenances of Pinusconforta in Scotland (1976)

Cannell, Melvin G. R.

Canadian Science Publishing

In: Canadian Journal of Forest Research. 1976; 6(4): 539-556. Published 1976 Dec 01. doi: 10.1139/x76-074.

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Publication Date: 1976-12-01

Description: The dynamics of terminal bud development on seven 3-year-old nursery-grown provenances of Pinuscontorta Dougl. were monitored by sampling buds at 1- to 3-weekly intervals during one growing season. Differences in rates of cataphyll initiation occurred which were analysed in terms of (a) the projected areas of the apical domes, which changed over the season, (b) the relative rates at which the apical domes expanded radially during a plastochrone (square millimetres per square millimetre), as shown by the extent to which the new cataphyll primordia receded away from the domes, and (c) the projected areas of the tissues used to form new cataphyll primordia. Component a was a measure of the size of the apical dome meristems and b was a measure of their rates of 'activity.' A model-matching method is described to measure b.Those provenances which produced most cataphylls during the growing season developed and maintained large apical domes (component a above). There were unexpectedly small provenance differences in the apical dome 'activity' in midsummer (component b defined above), although differences occurred in spring and autumn. Differences in the projected areas of the new cataphyll primordia (component c) were inversely related to cataphyll initiation rates. Apical dome tissue doubling times in midsummer were estimated to be less than 120 h, irrespective of provenance.Inland provenances had small but relatively 'active' apical domes in spring, but they produced cataphyll primordia as products of this growth rather than reinvesting in apical dome 'capital.' Consequently, their apical domes remained small. Coastal Alaskan provenances, on the other hand, developed large apical domes, but these domes ceased to be very 'active' after the end of August. The apical domes on south coastal provenances did not become 'active' until early summer, but their domes were relatively large even in spring, became much larger by late summer, and they remained 'active' until mid-September.Implications are noted regarding cross-breeding of complementary genotypes to increase needle production and height growth.

Print ISSN: 0045-5067

Electronic ISSN: 1208-6037

Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition

Published by Canadian Science Publishing

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