Wookey Philip A.

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Wookey
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Philip A.
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  • Preprint
    Ecosystem feedbacks and cascade processes : understanding their role in the responses of Arctic and alpine ecosystems to environmental change
    ( 2008-09-11) Wookey, Philip A. ; Aerts, Rien ; Bardgett, Richard D. ; Baptist, Florence ; Bråthen, Kari Anne ; Cornelissen, Johannes H. C. ; Gough, Laura ; Hartley, Iain P. ; Hopkins, David W. ; Lavorel, Sandra ; Shaver, Gaius R.
    Global environmental change, related to climate change and the deposition of airborne N-containing contaminants, has already resulted in shifts in plant community composition among plant functional types in arctic and temperate alpine regions. In this paper, we review how key ecosystem processes will be altered by these transformations, the complex biological cascades and feedbacks that may result, and some of the potential broader consequences for the earth system. Firstly, we consider how patterns of growth and allocation, and nutrient uptake, will be altered by the shifts in plant dominance. The ways in which these changes may disproportionately affect the consumer communities, and rates of decomposition, are then discussed. We show that the occurrence of a broad spectrum of plant growth forms in these regions (from cryptogams to deciduous and evergreen dwarf shrubs, graminoids and forbs), together with hypothesized low functional redundancy, will mean that shifts in plant dominance result in a complex series of biotic cascades, couplings and feedbacks which are supplemental to the direct responses of ecosystem components to the primary global change drivers. The nature of these complex interactions is highlighted using the example of the climate-driven increase in shrub cover in low arctic tundra, and the contrasting transformations in plant functional composition in mid-latitude alpine systems. Finally, the potential effects of the transformations on ecosystem properties and processes which link with the earth system are reviewed. We conclude that the effects of global change on these ecosystems, and potential climate-change feedbacks, can not be predicted from simple empirical relationships between processes and driving variables. Rather, the effects of changes in species distributions and dominances on key ecosystem processes and properties must also be considered, based upon best estimates of the trajectories of key transformations, their magnitude and rates of change.
  • Article
    Slowed biogeochemical cycling in sub-arctic birch forest linked to reduced mycorrhizal growth and community change after a defoliation event
    (Springer, 2016-08-25) Parker, Thomas C. ; Sadowsky, Jesse ; Dunleavy, Haley ; Subke, Jens-Arne ; Frey, Serita D. ; Wookey, Philip A.
    Sub-arctic birch forests (Betula pubescens Ehrh. ssp. czerepanovii) periodically suffer large-scale defoliation events caused by the caterpillars of the geometrid moths Epirrita autumnata and Operophtera brumata. Despite their obvious influence on ecosystem primary productivity, little is known about how the associated reduction in belowground C allocation affects soil processes. We quantified the soil response following a natural defoliation event in sub-arctic Sweden by measuring soil respiration, nitrogen availability and ectomycorrhizal fungi (EMF) hyphal production and root tip community composition. There was a reduction in soil respiration and an accumulation of soil inorganic N in defoliated plots, symptomatic of a slowdown of soil processes. This coincided with a reduction of EMF hyphal production and a shift in the EMF community to lower autotrophic C-demanding lineages (for example, /russula-lactarius). We show that microbial and nutrient cycling processes shift to a slower, less C-demanding state in response to canopy defoliation. We speculate that, amongst other factors, a reduction in the potential of EMF biomass to immobilise excess mineral nitrogen resulted in its build-up in the soil. These defoliation events are becoming more geographically widespread with climate warming, and could result in a fundamental shift in sub-arctic ecosystem processes and properties. EMF fungi may be important in mediating the response of soil cycles to defoliation and their role merits further investigation.
  • Article
    Plant community responses to experimental warming across the tundra biome
    (National Academy of Sciences of the USA, 2006-01-20) Walker, Marilyn D. ; Wahren, C. Henrik ; Hollister, Robert D. ; Henry, Greg H. R. ; Ahlquist, Lorraine E. ; Alatalo, Juha M. ; Bret-Harte, M. Syndonia ; Calef, Monika P. ; Callaghan, Terry V. ; Carroll, Amy B. ; Epstein, Howard E. ; Jonsdottir, Ingibjorg S. ; Klein, Julia A. ; Magnusson, Borgbor ; Molau, Ulf ; Oberbauer, Steven F. ; Rewa, Steven P. ; Robinson, Clare H. ; Shaver, Gaius R. ; Suding, Katharine N. ; Thompson, Catharine C. ; Tolvanen, Anne ; Totland, Orjan ; Turner, P. Lee ; Tweedie, Craig E. ; Webber, Patrick J. ; Wookey, Philip A.
    Recent observations of changes in some tundra ecosystems appear to be responses to a warming climate. Several experimental studies have shown that tundra plants and ecosystems can respond strongly to environmental change, including warming; however, most studies were limited to a single location and were of short duration and based on a variety of experimental designs. In addition, comparisons among studies are difficult because a variety of techniques have been used to achieve experimental warming and different measurements have been used to assess responses. We used metaanalysis on plant community measurements from standardized warming experiments at 11 locations across the tundra biome involved in the International Tundra Experiment. The passive warming treatment increased plant-level air temperature by 1-3°C, which is in the range of predicted and observed warming for tundra regions. Responses were rapid and detected in whole plant communities after only two growing seasons. Overall, warming increased height and cover of deciduous shrubs and graminoids, decreased cover of mosses and lichens, and decreased species diversity and evenness. These results predict that warming will cause a decline in biodiversity across a wide variety of tundra, at least in the short term. They also provide rigorous experimental evidence that recently observed increases in shrub cover in many tundra regions are in response to climate warming. These changes have important implications for processes and interactions within tundra ecosystems and between tundra and the atmosphere.