Responses of boreal vegetation to recent climate change

Barichivich, J (2014) Responses of boreal vegetation to recent climate change. Doctoral thesis, University of East Anglia.

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    The high northern latitudes have warmed faster than anywhere else in the globe during
    the past few decades. Boreal ecosystems are responding to this rapid climatic change
    in complex ways and some times contrary to expectations, with large implications for the
    global climate system. This thesis investigates how boreal vegetation has responded to recent
    climate change, particularly to the lengthening of the growing season and changes in
    drought severity with warming. The links between the timing of the growing season and
    the seasonal cycle of atmospheric CO2 are evaluated in detail to infer large-scale ecosystem
    responses to changing seasonality and extended period of plant growth. The influence of
    warming on summer drought severity is estimated at a regional scale for the first time using
    improved data. The results show that ecosystem responses to warming and lengthening of
    the growing season in autumn are opposite to those in spring. Earlier springs are associated
    with earlier onset of photosynthetic uptake of atmospheric CO2 by northern vegetation,
    whereas a delayed autumn, rather than being associated with prolonged photosynthetic uptake,
    is associated with earlier ecosystem carbon release to the atmosphere. Moreover, the
    photosynthetic growing season has closely tracked the pace of warming and extension of the
    potential growing season in spring, but not in autumn. Rapid warming since the late 1980s
    has increased evapotranspiration demand and consequently summer and autumn drought
    severity, offsetting the effect of increasing cold-season precipitation. This is consistent with
    ongoing amplification of the hydrological cycle and with model projections of summer drying
    at northern latitudes in response to anthropogenic warming. However, changes in snow
    dynamics (accumulation and melting) appear to be more important than increased evaporative
    demand in controlling changes in summer soil moisture availability and vegetation
    photosynthesis across extensive regions of the boreal zone, where vegetation growth is often
    assumed to be dominantly temperature-limited. Snow-mediated moisture controls of vegetation
    growth are particularly significant in northwestern North America. In this region,
    a non-linear growth response of white spruce growth to recent warming at high elevations
    was observed. Taken together, these results indicate that net observed responses of northern
    ecosystems to warming involve significant seasonal contrasts, can be non-linear and are
    mediated by moisture availability in about a third of the boreal zone.

    Item Type: Thesis (Doctoral)
    Faculty \ School: Faculty of Science > School of Environmental Sciences
    Depositing User: Mia Reeves
    Date Deposited: 09 Jul 2014 12:52
    Last Modified: 09 Jul 2014 12:52

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