Robert Lenthall Jefferies Collection
Permanent URI for this collection
When Bob Jefferies died unexpectedly in 2009, Canada lost one of its most important Arctic biologists at a vital and significant time. Bob was a professor at the University of Toronto from 1974 to 2009 in the Botany Department, which later became the Ecology and Evolutionary Biology Department.
This sub-community in the Churchill Communities of Knowledge digital archive celebrates Bob's life and research legacy. From 1978 to 2009, Bob and his students carried out field research on the effects of herbivory on salt-marsh vegetation by lesser snowgeese at La Pérouse Bay, on the shores of Hudson Bay, east of Churchill, Manitoba. Bob is seen above, at Camp Finney (Nestor 2) during spring melt in June 1983. Bob also did research with his students in other parts of the Churchill region, and elsewhere in the Arctic.
Bob not only worked in northern Canada. He carried out research in California, where he was a post-doc with Emmanuel Epstein, at University of California at Davis, from 1962-64, and a Distinguished Visiting Professor at the Bodega Marine Laboratory (UC Davis) in 2002-03. Bob also studied salt-marshes in the United Kingdom and Europe.
Digitized versions of many of Bob's research accomplishments can be found in this collection, including his students' theses and dissertations, along with images and other forms of media.
Correspondence and information relating to Bob's participation in the Intergovernment Panel on Climate Change is also lodged here.
The programme from Bob's Memorial Celebration, held on November 9th 2009, can be found here
Browse
Recent Submissions
Item Open Access Taxonomic status of diploid Salicornai europaea (s.L.) (Chenopodiaceae) in northeastern North America.(01/03/2013) Wolff, S.L.; Jefferies, Robert L.The taxonomic status of diploid Salicornia europaea L. (s.1.) in northeastern North America has been evaluated based on morphological and electrophoretic variation within and between populations. Populations of two European diploid micro- species, S. ramosissima J. Woods and S. europaea (s.s.), and populations of the midwestern diploid, S. rubra A. Nels., were also examined, affording a comparison between North American S. europaea (s.1.) and recognized species. Anther length, width of the scarious border of the fertile segment, and floral perianth shape were used to subdivide North American diploid populations into two groups. These groups were morphologically distinct from S. rubra and the European microspecies. The electrophoretic profile was unique in each morphologically distinct group of populations of S. europaea (s.1.) in northeastern North America. Based on morphological, geographical, and electrophoretic differences, diploid populations of S. europaea (s.1.) from this region are assigned to one of the following two new species: S. maririma Wolff & Jefferies, sp.nov., and S. borealis Wolff & Jefferies, sp.nov. The tetraploids are retained in S. europaea (s.1.).Item Open Access Robert Jefferies with a baby Arctic Fox(21/02/2013) Kotanen, Peter M.Item Open Access Researchers on the top of the McConnell esker(21/02/2013) Kotanen, Peter M.Item Open Access The biology of the annual Salicornia europaea agg. at the limits of its range in Hudson Bay.(NRC Research Press, 1983) Jefferies, Robert L.; Jensen, A.; Bazely, Dawn R.The biology of a marginal population of the annual Salicornia europaea agg. has been examined at La Pérouse Bay, Manitoba, on the shores of Hudson Bay. Plants were confined to south-facing sites which became hypersaline in summer, but which were not covered by tides. The difference in temperature of surface sediments between south- and north-facing slopes was as much as 7°C. Although most seedlings emerged in June, germination continued throughout the summer, but plants that appeared late in the season failed to set seed. Mortality of both seedlings and adult plants was low. Seeds or seedlings from a south-facing slope were transplanted during a 2-year period within the same site, into another south-facing site, to a north-facing site, and to an intertidal site. Germination either failed to occur or else was poor at the latter two sites. In addition, seed production of mature plants was low compared with that for individuals transplanted within south-facing sites. Additions of nitrogen to north-facing slopes increased overall seed output per plant, but the ratio of unripened to ripened seeds remained the same as that in plants from untreated plots. The results are discussed in relation to the ecology of marginal populations.Item Open Access Seasonal partitioning of resource use and constraints on the growth of soil microbes and a forage grass in a grazed Arctic salt-marsh(Springer Verlag, 2009) Hargreaves, Sarah K.; Horrigan, Emma J.; Jefferies, Robert L.Seasonal growth responses of plants and soil microorganisms to additions of nitrogen (N), phosphorus (P) and carbon (C) were examined in goose-grazed and exclosed plots in an Arctic salt marsh. Plants showed strong growth responses to N and NP additions but not to P. Nitrogen levels in the shoots and roots of Puccinellia phryganodes declined as summer progressed. Microbial biomass was low in spring in spite of N and P additions, likely due to C limitation, but values rose in autumn, independent of nutrient treatment, as dissolved organic carbon (DOC) increased. Glucose addition (C source) elicited a transitory increase in microbial biomass. Multiple plant defoliations by geese had a negative effect on microbial biomass, in spite of the presence of DOC and added N and P, possibly because hypersalinity restricted growth. Plants appear to limit soil inputs of C in summer and compete effectively for resources in contrast to autumn, indicating a temporal partitioning of resources.Item Open Access Soil microbial and nutrient dynamics in a wet Arctic sedge meadow in late winter and early spring(Elsevier, 2006) Edwards, Kate A.; McCulloch, Jennifer; Kershaw, Peter G.; Jefferies, Robert L.Microbial activity is known to continue during the winter months in cold alpine and Arctic soils often resulting in high microbial biomass. Complex soil nutrient dynamics characterize the transition when soil temperatures approach and exceed 0 °C in spring. At the time of this transition in alphine soils microbial biomass declines dramatically together with soil pools of available nutrients. This pattern of change characterizes alpine soils at the winter–spring transition but whether a similar pattern occurs in Arctic soils, which are colder, is unclear. In this study amounts of microbial biomass and the availability of carbon (C), nitrogen (N) and phosphorus (P) for microbial and plant growth in wet peaty soils of an Arctic sedge meadow have been determined across the winter–spring boundary. The objective was to determine the likely causes of the decline in microbial biomass in relation to temperature change and nutrient availability. The pattern of soil temperature at depths of 5–15 cm can be divided into three phases: below 10 °C in late winter, from 7 to 0°C for 7 weeks during a period of freeze–thaw cycles and above 0 °C in early spring. Peak microbial biomass and nutrient availability occurred early in the freeze–thaw phase. Subsequently, a steady decrease in inorganic N occurred, so that when soil temperatures rose above 0 °C, pools of inorganic nutrients in soils were very low. In contrast, amounts of microbial C and soluble organic C and N remained high until the end of the period of freeze–thaw cycles, when a sudden collapse occurred in soluble organic C and N and in phosphatase activity, followed by a crash in microbial biomass just prior to soil temperatures rising consistently above 0 °C. Following this, there was no large pulse of available nutrients, implying that competition for nutrients from roots results in the collapse of the microbial pool.Item Open Access Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?(Elsevier, 2010) Jefferies, Robert L.; Walker, Alan; Edwards, Kate A.; Dainty, JackDuring winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles. Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.Item Open Access A comparison of the growth responses of three sedges to foraging by lesser snow geese.(1987) Kotanen, Peter M.SUMMARY:Item Open Access The role of lesser snow geese in positive, degenerative feedback processes resulting in the destruction of salt-marsh swards.(1993) Srivastava, Diane SheilaA positive feedback cycle between soil salinity and graminoid growth, triggered by intensive grazing and grubbing by geese, is proposed to account for the loss of graminoid vegetation in an arctic salt marsh (La Pérouse Bay, Manitoba, Canada) based on the results of experimental field studies. Decreases in above-ground biomass, caused by goose herbivory, increase soil salinity. High soil salinities further reduce graminoid growth, both in the salt marsh and under controlled conditions, causing additional decreases in above-ground biomass. Graminoid growth is also reduced by intraspecific competition. The implications of this positive feedback on vegetation dynamics and the size of the goose colony at La Perouse Bay are discussed.Item Open Access Item Open Access RESPONSES OF SALT-MARSH VEGETATION TO GRAZING BY LESSER SNOW GEESE (Anser caerulescens caerulescens).(1984) Bazely, Dawn R.SUMMARY:Item Open Access Allochthonous inputs: integrating population changes and food-web dynamics(Elsevier, 2004) Jefferies, Robert L.Most ecosystems are recipients of allochthonous materials that enhance in situ productivity. Recent theoretical and empirical studies suggest that low to moderate inputs can stabilize food webs. However, depending on the trophic levels that use the resource, food webs can become unstable as inputs increase. Where large amounts of agricultural resources are transferred to natural habitats, trophic dynamics change: trophic cascades can occur and rare or uncommon species can become invasive. Rates of change in species abundances can also be amplified by the effects of changes in legislation and management practices on subsidized consumers.Item Open Access Robert L Jefferies Virtual Issue(12/11/2012) Jefferies, Robert L.Item Open Access Soluble carbohydrate content of shoots of Arctic wetland plants that are consumed by lesser snow geese(NRC Research Press, 2008) Jefferies, Robert L.; Edwards, Kate A.We recorded seasonal changes in the total amounts of soluble carbohydrates in shoots of salt- and fresh-water coastal plants at La Pérouse Bay, northern Manitoba, to determine whether adult snow geese and their goslings selected forage rich in soluble carbohydrates during the breeding season. The selection of forage plants in spring and summer by adults and goslings was strongly linked to the presence of high amounts of soluble carbohydrates in tissues: on the order of 100 mgg–1 dry mass. When the content fell as a result of shoot development or leaf senescence, the geese switched to alternative sources of forage. The extent to which individual shoots rich in soluble carbohydrates of the primary freshwater forage species are grazed depends on the local density of breeding geese at the study site, which has fallen in the last decade as a result of the earlier destruction of much of the coastal vegetation by foraging geese.Item Open Access Goose-induced Changes in Vegetation and Land Cover between 1976 and 1997 in an Arctic Coastal Marsh(Institute of Arctic and Alpine Research (INSTAAR), University of Colorado, 2005) Abraham, Kenneth F.; Jefferies, Robert L.; Rockwell, Robert F.Since the 1970s, a breeding colony of lesser snow geese (Chen caerulescens caerulescens L.) at La Pérouse Bay, Manitoba, has grown 8% annually. This increase has led to significant loss of plant cover in all major salt- and freshwater coastal habitats between 1976 and 1997. A series of transects established in 1976 was resurveyed in 1997. Exposed sediment, extent and type of vegetative cover, and aquatic areas were recorded along transects using a classification of 12 a priori classes. Five regions within the colony were identified, and changes in vegetation cover differed among these and depended on unique combinations of vegetation class and year. Grubbing by geese has led to loss of graminoid plants, especially in intertidal and supratidal marshes. Exposed sediments have largely replaced previously vegetated areas since 1976. Species characteristic of disturbed sites have colonized exposed sediment with the most abundant species varying according to soil conditions. In intertidal marshes, willow cover declined in association with the development of hypersalinity after loss of the graminoid mat, but willow cover increased at the base of well-drained beach ridges and in a river delta with ample winter snow accumulation and freshwater flow in spring that protected ground vegetation. Most of the expected successional trends associated with isostatic uplift and changes in soil organic matter failed to occur because of intense goose foraging throughout the 20 years. The likelihood of sustained recovery of plant communities in the immediate coastal zone is very low, as long as goose numbers continue to increase. Indirect effects of vegetation loss (e.g., hypersalinity) and subsequent erosion of exposed sediments following grubbing will delay plant colonization and retard succession.Item Open Access Patterns and Processes of Species Diversity in Fragmented Northern Hardwood Forests.(Toronto : University of Toronto, 2001) Draper, William B.Twenty-four upland hardwood forests were examined to determine the influence of plant dispersal and environmental heterogeneity on the composition and richness of species in the forest understory. Patterns in the dispersal attributes of established plants were evaluated in relation to associated plant traits, micro-habitats on the forest floor, and measured or inferred gradients in the availability of moisture, nutrients and light. Plant attributes that maximally explained differences in species richness were mode of dispersal, habitat affinity, life form, shade tolerance, and moisture affinity. Environmental variables that maximally explained species richness were stand structure. soil moisture and soil parent material. Species richness was strongly influenced by sugar maple abundance and declined sharply on mesic, calcium-rich soils. In this study, modes of dispersal were strongly correlated with plant traits and habitat factors that govern germination, establishment and persistence. The contribution of dispersal and environmental processes to species richness could not be distinguished, statistically.Item Open Access Dawn Bazely digging drainage ditches at Camp Finney(Jun-84) Bazely, Dawn R.Item Open Access Item Open Access Soil Microbial and Nutrient Dynamics During Late Winter and Early Spring in Low Arctic Sedge Meadows(Toronto : University of Toronto, 2010) Edwards, Kate A.Microbial activity occurs year-round in Arctic soils, including during the winter when soils are frozen. From 2004 to 2008 I monitored soil microbial and nutrient dynamics in low Arctic wet and dry sedge meadows near Churchill, Manitoba. I documented a consistent annual pattern in which soil microbial biomass (MB) and soil nutrients peak in late winter, and decrease during the early stages of spring thaw, remaining in low abundance during the summer. Based on a series of experiments, resource shortages do not appear to be the cause of the microbial decline, as has been hypothesized. Observations and theoretical considerations regarding soil physical properties indicate that this decrease is driven by the influx of liquid water at thaw that brings about a rapid change in the chemical potential of water, leading to cell lysis. I have used 15N isotope tracing to show that inorganic nitrogen is taken up very quickly at thaw by the roots of the dominant plant, Carex aquatilis. This represents a critical window of opportunity for these plants, as nitrogen remains abundant only for a short time. The described annual pattern was pronounced in wet sedge sites, but some inter-annual variation is evident, for example a post-thaw soil nitrogen pulse in 2006, and low winter MB in 2008. In the dry sedge meadow, fluctuations in MB and nutrients were dampened relative to wet sites, and the annual pattern was variable, particularly after 2006. Over four years, peak winter values of soil MB and nutrient variables declined in both wet and dry sites, and this could be related to a drying trend. This work improves our understanding of the controls on decomposition and primary productivity in a system that is experiencing climate warming and increased precipitation. Changes to hydrology, carbon and nitrogen cycling, and primary productivity will have further effects on vegetation communities and higher trophic levels, including several species of migratory birds.Item Open Access Seed and vegetation dynamics in undamaged and degraded coastal habitats of the Hudson Bay lowlands.(Ottawa : National Library of Canada = Bibliotheque nationale du Canada, 2000) Chang, Esther R.Grubbing and grazing by increasing numbers of lesser snow geese (Anser caerulescens caerulescens) have led to loss of vegetation and soil degradation in salt marshes and on beach ridges. These changes have had a deleterious effect on the soil seed bank by reducing density of seeds and shifting the composition from species present prior to the disturbance to invasive species. In the salt marsh, more recently degraded plots had greater revegetation potential from the remaining seed bank than plots where loss of vegetation was of long standing. Seed banks in beach-ridge soils were less affected by degradation due to the greater proportion of weedy species present in the original vegetation. Studies of the seed and vegetation dynamics in the supratidal marsh indicated that while there were no systematic differences between the seed rain in undamaged and degraded sites, degradation processes constrain recruitment at the entrapment, germination and establishment stages.