Heathland responses to nitrogen deposition : exploring the role of habitat management and soil biochemistry
Author(s)
Jones, Alan Glyn
Type
Thesis
Abstract
Elevated levels of nitrogen deposition are altering the normal functioning of seminatural
ecosystems around the world. Of concern in Europe are the nitrogen driven
changes occurring to (semi)-natural ecosystems such as obrotrophic bogs, upland
moors and lowland heathland. Lowland heathland is a particularly vulnerable
oligotrophic habitat, with a narrow climatic optimum that restricts the remaining
fragmented patches to a small corner of highly populated northwestern Europe.
Increased nitrogen availability reduces the competitiveness of characteristic heathland
plants, such as Calluna vulgaris, that are adapted to situations where nitrogen is the
limiting nutrient. Resulting changes such as accelerated productivity, increased
herbivore and frost damage, and changes in the nutrient limitation status of heathlands
can lead to invasion by nitrophilous graminoid species, but this process may be
dependent on (1) the intensity and duration of elevated nitrogen inputs, (2) the relative
availability of other nutrients and (3) conservation management intended to reduce
overall nutrient levels.
The present study investigated the effects of nitrogen deposition in N and P limited
vegetation, and in heathlands around the UK that are experiencing anthropogenically
enhanced background levels of nitrogen deposition. Physical and biochemical
parameters of vegetation, litter and soil were used as indicators. A long-term fieldscale
manipulation study at Thursley Common, Surrey was used to quantify the effect
of nitrogen inputs to an N limited system and, in particular, determine how these
effects were modified by a gradient of management intensity, and an unplanned
wildfire. The process of vegetation recovery, following a cessation of nitrogen inputs was also investigated. The effects of nitrogen deposition to P limited heathland were
investigated using heathland mesocosms. Two nationwide heathland surveys
investigated how the effect of nitrogen deposition within a gradient of background
deposition in England was modified by environmental factors, such as geology or soil
type. The first survey examined the effect of stand age (and management) on
responses to nitrogen deposition. The second survey focused on the physical and
biochemical responses to nitrogen deposition in Calluna, litter, bryophytes and soil to
quantify its impact on heathlands across England.
The Thursley nitrogen manipulation investigation showed clear ongoing responses in
rates of canopy development and shoot growth to nitrogen deposition, which were
reduced by increasing levels of management intensity. Historical nitrogen inputs in
the recovery experiment continued to significantly increase rates of Calluna canopy
development 9 years after inputs had ceased. These effects were re-invigorated by the
unplanned wildfire. The mesocosm experiment indicated that P limited heathlands are
susceptible to the detrimental effects of nitrogen deposition, particularly, altering
shoot phenology and increasing drought stress. Both the nationwide surveys indicated
that, at a national scale, heathland vegetation and soil biochemical indices are
responsive to background nitrogen deposition levels within (and exceeding) the
critical load range, despite environmental influences, such as geology and soil type
which were also found to have significant effects on these parameters.
ecosystems around the world. Of concern in Europe are the nitrogen driven
changes occurring to (semi)-natural ecosystems such as obrotrophic bogs, upland
moors and lowland heathland. Lowland heathland is a particularly vulnerable
oligotrophic habitat, with a narrow climatic optimum that restricts the remaining
fragmented patches to a small corner of highly populated northwestern Europe.
Increased nitrogen availability reduces the competitiveness of characteristic heathland
plants, such as Calluna vulgaris, that are adapted to situations where nitrogen is the
limiting nutrient. Resulting changes such as accelerated productivity, increased
herbivore and frost damage, and changes in the nutrient limitation status of heathlands
can lead to invasion by nitrophilous graminoid species, but this process may be
dependent on (1) the intensity and duration of elevated nitrogen inputs, (2) the relative
availability of other nutrients and (3) conservation management intended to reduce
overall nutrient levels.
The present study investigated the effects of nitrogen deposition in N and P limited
vegetation, and in heathlands around the UK that are experiencing anthropogenically
enhanced background levels of nitrogen deposition. Physical and biochemical
parameters of vegetation, litter and soil were used as indicators. A long-term fieldscale
manipulation study at Thursley Common, Surrey was used to quantify the effect
of nitrogen inputs to an N limited system and, in particular, determine how these
effects were modified by a gradient of management intensity, and an unplanned
wildfire. The process of vegetation recovery, following a cessation of nitrogen inputs was also investigated. The effects of nitrogen deposition to P limited heathland were
investigated using heathland mesocosms. Two nationwide heathland surveys
investigated how the effect of nitrogen deposition within a gradient of background
deposition in England was modified by environmental factors, such as geology or soil
type. The first survey examined the effect of stand age (and management) on
responses to nitrogen deposition. The second survey focused on the physical and
biochemical responses to nitrogen deposition in Calluna, litter, bryophytes and soil to
quantify its impact on heathlands across England.
The Thursley nitrogen manipulation investigation showed clear ongoing responses in
rates of canopy development and shoot growth to nitrogen deposition, which were
reduced by increasing levels of management intensity. Historical nitrogen inputs in
the recovery experiment continued to significantly increase rates of Calluna canopy
development 9 years after inputs had ceased. These effects were re-invigorated by the
unplanned wildfire. The mesocosm experiment indicated that P limited heathlands are
susceptible to the detrimental effects of nitrogen deposition, particularly, altering
shoot phenology and increasing drought stress. Both the nationwide surveys indicated
that, at a national scale, heathland vegetation and soil biochemical indices are
responsive to background nitrogen deposition levels within (and exceeding) the
critical load range, despite environmental influences, such as geology and soil type
which were also found to have significant effects on these parameters.
Date Issued
2010
Date Awarded
2010-07
Advisor
Power, Sally
Creator
Jones, Alan Glyn
Publisher Department
Biology
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)