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Creators/Authors contains: "Henry, Greg H."

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  1. ; ; ; ; ; ( , Annals of Botany)
    Abstract Background and Aims

    The Arctic is warming at an alarming rate, leading to earlier spring conditions and plant phenology. It is often unclear to what degree changes in reproductive fitness (flower, fruit and seed production) are a direct response to warming versus an indirect response through shifting phenology. The aim of this study was to quantify the relative importance of these direct and indirect pathways and project the net effects of warming on plant phenology and reproductive fitness under current and future climate scenarios.

     Methods

    We used two long-term datasets on 12 tundra species in the Canadian Arctic as part of the International Tundra Experiment (ITEX). Phenology and reproductive fitness were recorded annually on tagged individual plants at both Daring Lake, Northwest Territories (64° 52' N, - 111° 35' W) and Alexandra Fiord, Nunavut (78° 49' N, - 75° 48' W). The plant species encompassed a wide taxonomic diversity across a range of plant functional types with circumpolar/boreal distributions. We used hierarchical Bayesian structural equation models to compare the direct and indirect effects of climate warming on phenology and reproductive fitness across species, sites and years.

     Key Results

    We found that warming, both experimental and ambient, drove earlier flowering across species, which led to higher numbers of flowers and fruits produced, reflecting directional phenotypic selection for earlier flowering phenology. Furthermore, this indirect effect of climate warming mediated through phenology was generally about two to three times stronger than the direct effect of climate on reproductive fitness. Under future climate predictions, individual plants showed a ~2- to 4.5-fold increase in their reproductive fitness (flower counts) with advanced flowering phenology.

     Conclusions

    Our results suggest that, on average, the benefits of early flowering, such as increased development time and subsequent enhanced reproductive fitness, might outweigh its risks. Overall, this work provides important insights into population-level consequences of phenological shifts in a warming Arctic over multi-decadal time scales.

     
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  2. ; ; ; ; ; ; ; ; ; ; et al ( , Nature Communications)
    null (Ed.)
    Abstract Rapid climate warming is altering Arctic and alpine tundra ecosystem structure and function, including shifts in plant phenology. While the advancement of green up and flowering are well-documented, it remains unclear whether all phenophases, particularly those later in the season, will shift in unison or respond divergently to warming. Here, we present the largest synthesis to our knowledge of experimental warming effects on tundra plant phenology from the International Tundra Experiment. We examine the effect of warming on a suite of season-wide plant phenophases. Results challenge the expectation that all phenophases will advance in unison to warming. Instead, we find that experimental warming caused: (1) larger phenological shifts in reproductive versus vegetative phenophases and (2) advanced reproductive phenophases and green up but delayed leaf senescence which translated to a lengthening of the growing season by approximately 3%. Patterns were consistent across sites, plant species and over time. The advancement of reproductive seasons and lengthening of growing seasons may have significant consequences for trophic interactions and ecosystem function across the tundra. 
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  3. ; ; ; ; ; ; ; ; ( , Global Change Biology)
    Abstract

    The Arctic is undergoing dramatic environmental change with rapidly rising surface temperatures, accelerating sea ice decline and changing snow regimes, all of which influence tundra plant phenology. Despite these changes, no globally consistent direction of trends in spring phenology has been reported across the Arctic. While spring has advanced at some sites, spring has delayed or not changed at other sites, highlighting substantial unexplained variation. Here, we test the relative importance of local temperatures, local snow melt date and regional spring drop in sea ice extent as controls of variation in spring phenology across different sites and species. Trends in long‐term time series of spring leaf‐out and flowering (average span: 18 years) were highly variable for the 14 tundra species monitored at our four study sites on the Arctic coasts of Alaska, Canada and Greenland, ranging from advances of 10.06 days per decade to delays of 1.67 days per decade. Spring temperatures and the day of spring drop in sea ice extent advanced at all sites (average 1°C per decade and 21 days per decade, respectively), but only those sites with advances in snow melt (average 5 days advance per decade) also had advancing phenology. Variation in spring plant phenology was best explained by snow melt date (mean effect: 0.45 days advance in phenology per day advance snow melt) and, to a lesser extent, by mean spring temperature (mean effect: 2.39 days advance in phenology per °C). In contrast to previous studies examining sea ice and phenology at different spatial scales, regional spring drop in sea ice extent did not predict spring phenology for any species or site in our analysis. Our findings highlight that tundra vegetation responses to global change are more complex than a direct response to warming and emphasize the importance of snow melt as a local driver of tundra spring phenology.

     
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  4. ; ; ; ; ; ; ; ; ; ; et al ( , Nature Ecology & Evolution)
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