Papers by Terry Callaghan
Forest ecosystems in the Alaskan Taiga, a synthesis of structure and function : Van Cleve, K., Chapin III, F. S., Flanagan, P. W., Viereck, L. A. & Dyrness, C. T. (Eds). Ecological Studies. Analysis and Synthesis, Volume 57. Springer Verlag, Berlin, 1986, 82 Figs, 20 Tabs, Approx. 235 pp. DM 128 ...
Agricultural Systems, 1989
The Journal of Ecology, 1984
(1) Uncinia meridensis is a Southern Hemisphere sedge showing a clonal growth habit. Leaf develop... more (1) Uncinia meridensis is a Southern Hemisphere sedge showing a clonal growth habit. Leaf development and dry weight accumulation in each tiller show periodicity and this has enabled the construction of an age-based life cycle for the tillers. (2) Individual tillers may live for 6 years and their rhizomes may persist after the death of the above-ground tissues. The rate of leaf production on a tiller decreases from eight per year in year 0 to three per year in year 5. Individual leaves persist for more than 1 year and the longest leaves are produced in year 3. (3) Flowering becomes possible during year 2 but flowering structures are a small part of the total dry weight of a flowering tiller. A mean of about ten seeds per inflorescence is produced in all age classes of flowering tiller, but the probability of seeds germinating to form year 0 tillers within the study area was zero. In contrast, vegetatively produced tillers had a high probability of surviving: 0 56 in year 0 and 0 94 in year 1. (4) Young vegetative offspring without leaves and roots are totally parasitic on older tillers; they receive 14C labelled photoassimilate from parent vegetative tillers and from photosynthetic inflorescences (which export 52% of their photoassimilate) on flowering tillers of older tiller generations. (5) The success of vegetative reproduction appears to result from the physiological interdependence of tillers within a clone where patterns of reciprocal translocation are evident between older tillers bearing leaves. The flowering tiller exports 10% of its carbon to its vegetative offspring while the offspring export 2% of their carbon to the parent flowering tiller. Translocation also occurs between tillers connected indirectly by older leafless tillers. (6) It is suggested that the vegetative reproduction, clonal growth and conservation of energy and nutrients exemplified by U. meridensis should be particularly important in the adverse tundra environment where clonal perennial plants predominate.
Agroforestry is a term which describes systems in which trees, animals and/or crops are grown tog... more Agroforestry is a term which describes systems in which trees, animals and/or crops are grown together in intimate mixtures. The term does not include farm woodlands which do not involve significant biological or environmental interactions between the woodland and agricultural components. A number of papers in this volume have discussed the possibility of increasing timber production in Cumbria, in response to Britain's present high rate of timber imports and excess agricultural production. Agroforestry could contribute to this increased timber production in a manner which would be attractive to the farming community because land would sustain a significant agricultural income whilst the trees were maturing. There are several types of agroforestry. Silvoarable systems are mixtures of trees and crops, while silvopastoralism describes intimate mixtures of trees and animals. Agrenforestry is a term used here to emphasize the co-production of bioenergy crops with agricultural and ti...
General Comments This paper presents an unusually detailed picture of nitrogen isotope compositio... more General Comments This paper presents an unusually detailed picture of nitrogen isotope compositions in mangrove systems as it seeks to explain very high variability in d15N in mangrove leaves. Explaining unusually low d15N (-10 to-20per mille) in P-limited mangroves is one focus of the work. Although leaf d15N ranged from-21.6per mille to 2.4per mille, the means among different tree types sampled only ranged from-6.8per mille (dwarf trees) to-0.6per mille (fringe trees). The authors make a good case for ammo-S123
1FWO Flanders Research Foundation, Geography Department, Ghent University, Belgium 2Institute of ... more 1FWO Flanders Research Foundation, Geography Department, Ghent University, Belgium 2Institute of Arctic Biology, University of Alaska Fairbanks, Fairbanks, AK 3Institute of Atmospheric Physics, Chinese Academy of Science, Beijing, China 4Plant Biology Department, Unit of Botany, University of Barcelona, Catalonia, Spain 5Institute for Botany and Landscape Ecology, Ernst-Moritz-Arndt-University Greifswald, Greifswald, Germany 6Geography Department, Ghent University, Belgium 7Abisko Scientific Research Station, Abisko, Sweden 8Department of Physical Geography, Stockholm University, S-106 91 Stockholm, Sweden 9Sheffield Centre for Arctic Ecology, Department of Plant and Animal Sciences, University of Sheffield, UK
The Population Structure of Vegetation, 1985
Selective forces of the physical environment are particularly strong in the tundra: positive plan... more Selective forces of the physical environment are particularly strong in the tundra: positive plant interactions tend to replace the competition or self-thinning typical in warmer latitudes. Tundra areas are young and evolution is slow because of long life spans, low reproductive rates and a predominance of vegetative proliferation. However, recruitment from seed is important in open habitats such as fell-fields, but early mortality rates are high and recruitment is intermittent. Age class distributions resulting from vegetative reproduction show low recruitment levels but high survival rates due to the physiological interdependence of modules. The dynamic equilibrium of forest tundra plant populations is regulated by interactions between fluctuating populations of animals and plants.
Oikos, 1976
... ac-ciieAoBaHHA OTAeJTbHbIX opraHoB pacTeH4lV1. PacTeHHrq TYH,PbpI oco6eHHO LIOAXO)jAT AJI.q T... more ... ac-ciieAoBaHHA OTAeJTbHbIX opraHoB pacTeH4lV1. PacTeHHrq TYH,PbpI oco6eHHO LIOAXO)jAT AJI.q TaKi4x pa6oT. ... Communities range from erect willow scrub through herb fields and dwarf shrub heaths to fell-field communities of mat and cushion plants. ...
Oikos, 1978
Photosynthesis, growth and reproduction of Hylocomium splendens and Polytrichum commune in Swedis... more Photosynthesis, growth and reproduction of Hylocomium splendens and Polytrichum commune in Swedish Lapland. Strategies of growth and population dynamics of tundra plants. 4.
The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar wind... more The annually averaged Arctic Oscillation index (AO, a measure of the strength of circumpolar winds) was slightly positive in 2006, continuing the trend of a relatively low and fluctuating index which began in the mid-1990s (Figure A1). This follows a strong, persistent positive pattern from 1989 to 1995. The current characteristics of the AO are more consistent with the characteristics of the period from the 1950s to the 1980s, when the AO switched frequently between positive and negative phases. Initial data from 2007 shows a positive AO pattern. Figure A1. Time series of the annually-averaged Arctic Oscillation Index (AO) for the period 1950- 2006 based on data from the website www.cpc.ncep.noaa.gov. (Courtesy of I. Rigor) Surface Temperatures and Atmospheric Circulation In 2006 the annual surface temperature over land areas north of 60 ° N was 1.0°C above the mean value for the 20th century (Figure A2). The surface temperature in this region has been consistently above the mean s...
Oikos, 1995
The aim of this study was to investigate how UV-B radiation will affect 1) the quality of plant l... more The aim of this study was to investigate how UV-B radiation will affect 1) the quality of plant litter grown under different UV-B levels in the Subarctic and 2) decomposition under different UV-B levels. The deciduous dwarf shrubs Vaccinium uliginosum and V myrtillus grew under ...
A catchment scale process study of carbon and greenhouse gas exchange in a subarctic landscape.
Philosophical Transactions of the Royal Society B: Biological Sciences, 1976
A summary is given of comparative work carried out within the I.B.P. Tundra Biome at an Arctic st... more A summary is given of comparative work carried out within the I.B.P. Tundra Biome at an Arctic station (Greenland) and a sub-Antarctic station (South Georgia). The investigations covered many aspects of plant ecology, primary production and adaptation to polar environments. The work was extended by an international synthesis of results. General conclusions are reported and the current continuation of the studies is discussed.
Global Change Biology, 2011
Extreme weather events can have negative impacts on species survival and community structure when... more Extreme weather events can have negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (2-10°C for 2-14 days), but returning to cold winter climate exposes the ecosystem to lower temperatures by the loss of insulating snow. Soil animals, which play an integral part in soil processes, may be very susceptible to such events depending on the intensity of soil warming and low temperatures following these events. We simulated week-long extreme winter warming eventsusing infrared heating lamps, alone or with soil warming cablesfor two consecutive years in a sub-Arctic dwarf shrub heathland. Minimum temperatures were lower and freeze-thaw cycles were 2-11 times more frequent in treatment plots compared with control plots. Following the second event, Acari populations decreased by 39%; primarily driven by declines of Prostigmata (69%) and the Mesostigmatic nymphs (74%). A community-weighted vertical stratification shift occurred from smaller soil dwelling (eu-edaphic) Collembola species dominance to larger litter dwelling (hemi-edaphic) species dominance in the canopy-with-soil warming plots compared with controls. The most susceptible groups to these winter warming events were the smallest individuals (Prostigmata and eu-edaphic Collembola). This was not apparent from abundance data at the Collembola taxon level, indicating that life forms and species traits play a major role in community assembly following extreme events. The observed shift in soil community can cascade down to the micro-flora affecting plant productivity and mineralization rates. Short-term extreme weather events have the potential to shift community composition through trait composition with potentially large consequences for ecosystem development.
The Journal of Applied Ecology, 1989
ABSTRACT
Research on nutrient dynamics concentrates on direct or indirect measurement of processes with li... more Research on nutrient dynamics concentrates on direct or indirect measurement of processes with little definition of populations involved, mainly because of technical difficulties and lack of interdisciplinary understanding. As the young science of nutrient dynamics evolves and management of species and systems becomes more sophisticated, there is a need for the science to draw on both population and process ecology.
Biogeosciences Discussions, 2015
Large amount of organic carbon is stored in high latitude soils. A substantial proportion of this... more Large amount of organic carbon is stored in high latitude soils. A substantial proportion of this carbon stock is vulnerable and may decompose rapidly due to temperature increases that are already greater than the global average. It is therefore crucial to quantify and understand carbon exchange between the atmosphere and subarctic/arctic ecosystems. In this paper, we combine an arctic-enabled version of the process-based dynamic ecosystem model, LPJ-GUESS (version LPJG-WHyMe-TFM) with comprehensive observations of terrestrial and aquatic carbon fluxes to simulate long-term carbon exchange in a subarctic catchment comprising both mineral and peatland soils. The model is applied at 50 m resolution and is shown to be able to capture the seasonality and magnitudes of observed fluxes at this fine scale. The modelled magnitudes of CO 2 uptake generally follow the descending sequence: birch forest, non-permafrost Eriophorum, Sphagnum and then tundra heath during the observation periods. The catchment-level carbon fluxes from aquatic systems are dominated by CO 2 emissions from streams. Integrated across the whole catchment, we estimate that the area is a carbon sink at present, and will become an even stronger carbon sink by 2080, which is mainly a result of a projected densification of birch forest and its encroachment into tundra heath. However, the magnitudes of the modelled sinks are very dependent on future atmospheric CO 2 concentrations. Furthermore, comparisons of global warming potentials between two simulations with and without CO 2 increase since 1960 reveal that the increased methane emission from the peatland could double the warming effects of the whole catchment by 2080 in the absence of CO 2 fertilization of the vegetation. This is the first processbased model study of the temporal evolution of a catchment-level carbon budget at high spatial resolution, integrating comprehensive and diverse fluxes including both terrestrial and aquatic carbon. Though this study also highlights some limitations in modelling subarctic ecosystem responses to climate change including aquatic system flux dynamics, nutrient limitation, herbivory and other disturbances and peatland 935 BGD 12, 933-980, 2015 C budget estimation of a subarctic catchment J. Tang et al.
Journal of Ecology, 2001
provides a review of synonyms for the C. bigelowii complex (listed as C. rigida) throughout its g... more provides a review of synonyms for the C. bigelowii complex (listed as C. rigida) throughout its geographical range, giving details of physiological variation between races. The original type for C. bigelowii was a specimen collected from the mountains of New Hampshire, North America, and is probably a member of the northern circumpolar ssp. Carex bigelowii ssp. bigelowii (Hultén 1964). In this account we will consider, unless otherwise stated, information on C. bigelowii sensu stricto , including ssp. rigida (UK and Ireland) and ssp. bigelowii (Northern Europe, North America and Greenland). Carex bigelowii is a common sedge species of open upland and arctic communities, often growing within carpets of moss. Its foraging clonal habit can produce high, dense coverage over large areas and it is often a target species for grazers. I. Geographical and altitudinal distribution Carex bigelowii is a native species of the British Isles, with the stronghold of its UK range in Scotland (Fig. 1) both within the main Highland region (Fraser Darling & Morton Boyd 1964), and in the Western and Northern Isles (Jermy & Crabbe 1978; Scott & Palmer 1987). However, it is also found at upland sites within the Pennines and Lake District of northern England (Fig. 1). In Wales its distribution is extremely localized, occurring only in the mountainous parts of Merioneth and Caernarvonshire (Ellis 1983). It occurs at sites throughout Ireland, in 16 out of the 40 Irish botanical divisions (Bot. Irl.). Preston & Hill (1997) classify C. bigelowii as a Circumpolar Arctic-Montane species. It occurs throughout much of Europe where its distribution has a distinct northerly bias, being found in Austria, the Czech Republic, the Faeroes,
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Papers by Terry Callaghan