Gregory H Henry

Professor

Research Classification

Biodiversity and Biocomplexity
Biogeography
Ecological and Ecophysiological Processes
Climate Changes and Impacts
Environment and Habitats
Plants
Genotype and Phenotype

Research Interests

tundra ecosystems
experimental climate change
plant-animal interactions
Arctic environments
vegetation change
plant traits

Relevant Degree Programs

 

Research Methodology

Long-term experimental warming studies in tundra ecosystems using passive warming devices (open-top chambers (OTCs)).
Syntheses of responses to experimental and observed climate change in the International Tundra Experiment (ITEX).
Plant-animal interaction studies incuding grazing effects of muskox and caribou, insect foraging and pollination.
Ecosystem carbon fluxes using closed chamber and eddy covariance methods.
Ecosystem nutrient dynamics using ion exchange membranes and studies of nitrogen fixation using field gas chromatographs.

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Master's students
Doctoral students
Postdoctoral Fellows
2019
2020

1. Synthesis of tundra plant community changes to nearly 30 years of experimental warming using a suite of plant traits, including ecophysiology. PhD or postdoctoral study to involve 2-3 years of fieldwork and working with long-term data sets from an experimental study established in the Canadian High Arctic in 1992. 2. Ecological relaxation response of tundra after 30 years of experimental warming. PhD or postdoctoral study of the removal of experimental warming conditions on tundra plants and soils. 3. Landsape phenology patterns in tundra systems in relation to biological and physical conditions. Combination of plot studies and remote sensing using UAV technology for high resolution (temporal and spatial) analysis of plant phenology across a high Arctic landscape. 4. Phenology, growth and reproductive responses of southern populations in warmed high Arctic conditions: a common garden study. A PhD or MSc project involving the continuation of a common garden experiment established in 2011 with local and southern populations of two common forb species. The studies would involve using the Arctic Tundra controlled environment chamber at UBC. 5. Dendroecological studies using Arctic shrub species. Examination of the growth (and reproduction) patterns in up to four shrub species in response to: a) experimental climate change; b) landscape position, snow conditions and climate. The dendrochronological data can be used to reconstruct climate conditions over the past century.

I support public scholarship, e.g. through the Public Scholars Initiative, and am available to supervise students and Postdocs interested in collaborating with external partners as part of their research.
I support experiential learning experiences, such as internships and work placements, for my graduate students and Postdocs.
I am open to hosting Visiting International Research Students (non-degree, up to 12 months).
I am interested in hiring Co-op students for research placements.

Graduate Student Supervision

Doctoral Student Supervision (Jan 2008 - May 2019)
Importance of berries in the Inuit biocultural system : a multidisciplinary investigation in the Canadian North (2017)

In the Canadian North, the fruits of berry producing species are a highly nutritious source of food available to both animals and humans. Although relatively well-documented in boreal and subarctic environments, little information on the ecology and cultural importance of berry species is available for the Arctic. This research aims to fill that gap using archives, interviews, ecological monitoring as well as remote sensing tools. An overview of the different uses and roles of berry plants and berry picking as reported in close to 200 interviews conducted with Elders and active land users across Inuit Nunangat since the 1980s was compiled. Through extensive fieldwork and remote sensing analyses, local availability and animal consumption of berries were investigated in detail in the vicinity of Arviat, Nunavut. Finally, an overall assessment of berry productivity in the Canadian North was conducted using berry productivity data collected between 2007 and 2015 at 10 sites from Nain, Nunatsiavut, and Kugluktuk, Nunavut, to Alexandra Fiord, Ellesmere Island, Nunavut. Results showed the extensive and intimate knowledge of berry plants throughout Inuit Nunangat; berries were and remain culturally and nutritionally important for Inuit. Detailed landscape analyses in Arviat, revealed the large number of berries produced and the relatively large amount consumed by animals, mainly geese. Nevertheless, animals only eat a marginal portion of the total production at the site. Perceived competition for the resource may be linked to the small number of productive and accessible patches in the vicinity of the community. The analysis of inter-annual and regional variations in berry productivity illustrated that the abundance of berries in the Arctic is comparable or greater to certain forested areas in North America and Fennoscandia. The most productive sites were located in the low Arctic, in dry-mesic sites dominated by semi-prostrate dwarf shrubs. Inter-annual productivity analyses showed the complex interaction of winter and spring precipitation as well as summer temperature on productivity. Overall, this research demonstrates the cultural and ecological importance of berry species across Inuit Nunangat and suggests ongoing impacts of community development, pollution and recent climate change on the quality and availability of this important resource.

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The impacts of High Arctic permafrost disturbances on vegetation and carbon flux dynamics (2016)

Changing climate and disturbance regimes can have widespread ecosystem impacts, especially in the Arctic. Vegetation recovery and carbon flux dynamics were examined to determine the impacts of thermokarst disturbance on patterns and processes in High Arctic tundra ecosystems. Ecosystem responses to two forms of permafrost disturbance, active layer detachment slides and retrogressive thaw slumps, were studied on the Fosheim Peninsula, Ellesmere Island, Canada during the 2012, 2013, and 2014 growing seasons. The impacts of disturbance on vegetation and recovery were determined by sampling active retrogressive thaw slumps and recovered active layer detachment slides that were investigated nearly 20 years ago. Comparison of historic and modern data indicates distinct vegetation communities exist in differently aged disturbances with unique vascular plant species defining various zones and ages of disturbance. Differences were also found in site characteristics (including soil moisture, temperature, active layer depth, and soil nutrient concentrations) indicating the impacts of permafrost disturbance on the landscape. In addition, four active layer detachment slides measured in 1994 had transitioned to active retrogressive thaw slumps, which may be a response to the progressively warming climate. Carbon dioxide fluxes between the surface and the atmosphere were measured using a static chamber system and the eddy covariance technique at three sites on the Fosheim Peninsula. Over the studied growing seasons, disturbed landscapes sequestered significantly less carbon than their surrounding undisturbed tundra. In some sites, this resulted in the shift of the system from a net sink of CO₂ to a net source. A dual eddy covariance sampling approach was found to be preferable over a single tower setup with separation of fluxes based on wind partitioning as disturbed and undisturbed fluxes were simultaneously measured throughout the growing season using this method. Overall, active layer detachments and retrogressive thaw slumps alter vegetation and carbon flux dynamics, and these changes may persist over many years. With predicted increases in the frequency and magnitude of these permafrost disturbances, impacts on tundra ecosystems will be evident at the landscape scale.

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Ecological and evolutionary consequences of experimental and natural warming in the high Arctic tundra (2015)

Recent increases in global temperatures are having substantial and often unpredictable consequences for the earth’s biota. Species’ responses to environmental change depend on 1) the ability of individuals to adjust in situ through phenotypic plasticity, 2) the rate at which evolutionary adaptation can occur, and 3) the ability of individuals to colonize newly suitable habitat through migration or propagule dispersal. Temperatures in the Arctic are increasing faster than anywhere else, yet our understanding of the consequences of climate change in the Arctic lags behind that of temperate ecosystems. In this thesis, I ask whether plant phenology has advanced in response to 21 years of experimental and ambient warming at Alexandra Fiord, Ellesmere Island, Canada. While experimental warming led to earlier flowering in three out of four species, flowering dates in the control plots were unchanged or delayed despite more than 1 °C of ambient warming over the 21-year period, likely due to concurrent delays in snowmelt. This suggests that the effects of altered snowmelt patterns can counter the effects of warmer temperatures, even generating phenological responses opposite to those predicted by warming alone. I then use reciprocal transplant experiments to test for evidence of evolutionary adaptation in two plant species to differing environmental conditions between two spatially proximate habitat types and in response to 18 years of experimental warming treatments. Results were consistent both with substantial phenotypic plasticity in response to site-to-site and year-to-year variability, and with evolutionary adaptation to site and treatment conditions. Differences across natural habitats were stronger than those across experimental treatments. This indicates that plastic and genetic responses to climate change are likely to play an important role in structuring future Arctic plant communities. Finally, I test the hypothesis that warming will confer a fitness advantage to “pre-adapted” southern immigrants relative to native populations. Despite experimental conditions 3-5 °C warmer than the historical average, local populations leafed-out earlier and attained greater maximum size than foreign populations in two of three species, suggesting that the success of southern immigrants may be limited by a lack of adaptation to novel non-climatic environmental conditions even when temperatures are suitable.

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An evaluation of Waterless Human Waste Management Systems at North American public remote sites (2013)

The absence of sewers and roads at backcountry sites makes the management of humanexcreta offensive, intensive, and expensive. Proper management is essential in order toprevent deleterious pathogen and nutrient discharge. The dearth of resources, vaguecertification standards, absence of monitoring, and erroneous popular perception have causedmisapplication of systems and mismanagement of end products. Elevated environmentalimpacts, human health risks, and management costs have resulted.The diversion of urine from urinals and by urine diversion seats significantly reduced themass of helicopter extracted excrement. However, until a more robust urine diversion systemis developed that does not clog, only urine from urinals should be diverted.Composting toilets failed to produce safe, stable, and mature end-product at all sites surveyed.They should be re-named sawdust toilets, following European nomenclature, to avoid furtherconfusion. Performance was dramatically improved with urine diversion, elimination ofbulking agent, and optimization for vermicomposting. Despite improving mineralization andreduction of volatile solids, operating costs, exposure risk, and E. coli, Eisenia fetidaearthworms did not reduce Ascaris suum ova concentration or viability. Vermicompostingtoilets, unlikely to produce residuals approved for unrestricted discharge, should be designedto minimize waste, costs, hazards, and environmental impacts. This approach is seeminglyopposite from sawdust toilets, which at considerable cost, strive against unfavorablebiochemistry and thermodynamics to produce ‘compost’ for onsite disposal despiteprecautionary federal regulations.Solvita® test paddles, useful in the assessment of end-product, could be used withvermicomposting toilets, to ensure low ammonia is present in feedstock (values 4-5) and toensure stability (values 7-8) prior to disposal. Pit toilets, commonly excavated to depths greater than seasonal high ground water, carried thegreatest risk of pollution. These were conceptually redesigned to prevent diseasetransmission and treat nutrients with septic fields. In order to reduce the risks ofeutrophication and ammonia toxicity, fields should: be oversized by at least a factor of 10based on daily urine output; maximize the depth of unsaturated soil with curtain drains wherenecessary; lie >60m from surface water; and where appropriate use natural wetlands such asmoist, acidic, productive and phenotypically plastic graminoid meadows.

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Effects of simulated and actual caribou grazing on low-Arctic tundra vegetation (2011)

Barren-ground caribou have been grazing and trampling the tundra for thousands of years.Because the timing of grazing and trampling is episodic, it has been theorized that their impactsat any given site are weak or absent. This study investigated if this could be verifiedobservationally and experimentally. I conducted an experiment to examine the effects ofsimulated grazing and lichen removal on birch hummock - lichen heath tundra in the low-Arctic.I also examined the effects of trampling and grazing by the Bathurst Caribou Herd on thebiomass of three low-Arctic plant communities.In general, the simulated grazing at intermediate and high intensities did not cause changes invascular plants biomass or species diversity, or carbon dioxide flux. However, lichen removalcaused significant reductions in lichen biomass, lichen diversity, and net ecosystem production.Ecosystem respiration rates and biomass were much lower on than off the caribou migratorytrails in each of the habitats studied, due to the low amounts of biomass on migratory trailscompared to off the trails.These studies show that the effects of grazing were not easily detected, but the migratory trailsthat have been used by caribou for thousands of years were distinctly different than thesurrounding areas. The results indicate that some habitats may be resistant to change, but oncethey are altered, they may not readily recover.

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Master's Student Supervision (2010 - 2018)
Plant succession in the High Arctic: patterns and mechanisms (2018)

No abstract available.

The productivity of culturally important berry species in the Kugluktuk region of Nunavut, and their use in land-based education programs connecting Elders and youth (2017)

Communities in the Canadian Arctic are experiencing the effects of a rapidly changing environment. The development of appropriate policies to increase resilience and adaptation potential to these changes can only be gained with the inclusion of communities in research. This community-supported research was initiated to better understand how the changing environment affects the productivity of culturally important berry species by connecting Kugluktukmiut youth and Elders through place-based programming. The study took place during the Career and Technology Studies program offered by Kugluktuk High School in late August of 2011-2013. The place-based programming developed aimed to integrate Inuit Qaujimajatuqangit and science. The production of berries from samples collected by students in Kugluktuk, NU and from Kugluk/Bloody Falls Territorial Park was compared to those collected by researchers at the Tundra Ecology Research Station at Daring Lake, NT. Berry production was highest in coastal regions of Kugluktuk compared to inland sites. Vegetation at Kugluk/Bloody Falls differed from the other two sites due to the presence of Equisetum arvense and tall erect shrubs. Program evaluation is key to understanding how to build meaningful capacity for Inuit youth to connect to the environment. This critical evaluation showed that Inuit youth believe that learning about the environment is important. By providing place-based outreach programming youth are given the opportunity to exercise wellbeing by feeling a sense of identity, freedom and respect. The Berry Book was published to give back to the community for supporting the project and to contribute collection of Inuinnaqtun content.

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Insect pollination and experimental warming in the High Arctic (2014)

As climate change causes retreats in Arctic glaciers, it is important to understand the mechanics of growth and community change in Arctic plant communities. Arctic plants have been shown to respond to observed and experimental changes in temperature by altering their reproductive strategies, growth, and phenology. Researchers have used open-top chambers (OTCs) to experimentally alter the near-surface air temperatures of tundra plant communities over long periods of time, but these devices may exclude insect pollinators to flowers during crucial periods of pollen reception. Insect pollination in the context of OTCs and Arctic plants is therefore important to understand, but has been poorly researched. I altered pollination of Salix arctica, Dryas integrifolia, and Papaver radicatum inside and outside of OTCs in a High Arctic shrub community, and conducted targeted insect netting to understand the dynamics of the visiting insect community. I also conducted bowl trapping inside and outside of OTCs to gauge their effect on insect availability to receptive flowers. OTCs altered the timing of flowering in Arctic plants, and significantly reduced the availability of pollinators to available flowers. However, I found that while both warming and pollination can alter flower and seed production in the study species, pollination is largely independent of OTC warming. Early-flowering species have the potential to be most affected by OTC-induced insect exclusion. The most common visiting insects were flies of the families Syrphidae and Muscidae, with occasional bumblebees (Bombus polaris). Papaver radicatum was by far the most heavily-visited flower, and I showed that the Syrphidae visit the flower preferentially at low temperatures, likely for warmth as well as pollen. I discuss these results in context with the current literature on Arctic plant and insect communities, and make recommendations for future research.

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The use of repeat colour digital photography to monitor high Arctic tundra vegetation (2013)

High Arctic ecosystems are experiencing some of the earliest and most extreme changes in climate as a result of global climate change. Temperature increases twice the hemispheric average are initiating changes to terrestrial systems including shifts in timing of phenology, aboveground biomass and community composition of Arctic vegetation. Satellite imagery from the last 30 years has shown a greening across tundra ecosystems with increases in peak productivity and growing season length. A few plot scale field studies support these large-scale trends but overall validation at the plot scale is still lacking. Current manual and automated methods for monitoring vegetation at the community and plot scale is both time consuming and employs expensive, sensitive multispectral instrumentation that can be cumbersome to use in Arctic field sites. In this thesis I examine the utility of colour digital photography in monitoring tundra vegetation across four different vegetation communities, inside and outside of passive warming chambers. Colour and infrared photos were taken on one day peak season in 2010. Relationships between a greenness index derived from colour photographs and biomass data were compared to relationships with NDVI derived from infrared photographs. Results suggest that colour photographs can be used as a proxy for productivity and aboveground biomass in multiple tundra vegetation communities. These data were then used to infer phenological signals at multiple spatial scales from a set of colour photographs taken on six days during the 2012 growing season. Results show higher greenness values due to treatment at the plot scale but not at the individual scale suggesting greater green biomass in warmed plots. At the individual scale site differences emerged for two study species (Salix arctica, Dryas integrifolia) suggesting a difference in vegetation vigor due to differences in soil moisture and perhaps competition. The phenological signal was strongest at the species scale due to reduced interference from bare soil, litter and standing water. Overall, these results show the potential for this methodology for measuring vegetation in the Arctic. Its simplicity, affordability and efficiency has great potential for use in a vegetation monitoring network in the Arctic.

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Effects of long-term experimental warming on three High Arctic plant communities (2012)

Arctic regions are experiencing faster rates of atmospheric warming than any other biome. Increasing temperatures will affect the biomass, phenology, and composition of Arctic vegetation, which in turn will alter ecosystem functions such as greenhouse gas flux and nutrient cycling. These functional changes are likely to affect feedbacks to terrestrial and atmospheric systems. Responses are expected to occur at a range of scales and are likely to show close coupling to environmental conditions. In this thesis I compare ecosystem response in three plant communities after 18 years of experimental warming on Ellesmere Island, Canada. Warming response was measured at peak season in a dry, mesic and wet community. Biomass, height, and composition were measured using a point-intercept method and CO₂ flux was measured using an infrared gas analyzer and a custom made chamber. Environmental and NDVI data were collected from all three communities as well as being sampled across the entire lowland to map environmental heterogeneity and identify predictors of NDVI. All three plant communities showed structural responses to warming. Total above-ground biomass and height did not show significant changes but growth form composition shifted in all cases. Increases were observed for graminoids and forbs at the dry site; graminoids, deciduous shrubs and bryophytes at the mesic site; and deciduous shrubs and bryophytes at the wet site. Lichen abundance decreased at all sites. CO₂ flux responses were largely explained by compositional changes. All sites were CO₂ sinks at peak season and the dry and wet sites became stronger sinks as a result of warming. Landscape scale mapping successfully displayed the variation in environmental variables and NDVI across the landscape. Soil moisture was identified as an important determinant of NDVI signal and NDVI showed potential as a predictor of CO₂ flux. These results support the prediction that climate change response will be ecosystem specific. While some general trends existed across multiple communities, each community had a unique response to warming. Large scale climate change predictions will have to account for such variability.

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The reproduction, establishment, and growth of white spruce in the forest tundra ecotone of the Inuvik-Tuktoyaktuk region (2011)

Climate is considered one of the most important factors controlling tree reproduction, establishment, and growth at the treeline. As climate change continues the latitudinal treeline is expected to shift northwards. The main objective of this research was to characterize the ecological patterns and processes of Picea glauca (Moench.) Voss. (white spruce) in the Tuktoyaktuk region of the Northwest Territories, Canada. In particular, this study aims to determine how climate influences white spruce tree reproduction, establishment, and growth throughout the forest-tundra transition zone. A total of four forest stand sites and eight tree island sites, examined in the early 1990s, were located and re-examined in the summer of 2009. Cone production has increased since the early 1990s and cone production decreases northward across the forest-tundra. Germination rates significantly decrease with increasing latitude but have not significantly changed since they were last examined 15 years ago. In June 1994 seedlings were transplanted at three tree island sites, survivorship of these seedlings ranged from 3 to 20%. A search for true seedlings was also completed, however, none were found. Basal cores were obtained from numerous individuals within each of the sites and an age structure was developed. Establishment of individuals coincided with decades classified as cool and wet. The yearly diameter growth of each tree was determined via ring width measurements and using principal component analysis two chronologies were built, one for forest stands and one for tree islands. The chronologies were correlated to climate data of temperature and precipitation from the Inuvik airport. In general, growth was negatively correlated to previous growing season temperature and positively correlated to current season temperature.Results from this study indicate that tree islands are not likely to be important in supplying viable seed for the infilling of trees in the forest tundra, rather infilling will more likely occur from increased seed production in trees at or just south of treeline. Under proposed climate change scenarios the establishment of new seedlings will likely be negatively affected by the warmer and drier conditions, whereas the radial growth of individuals will likely increase with warming temperatures.

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