2.3 Periodicity, Regularity
The impact of environmental conditions on biota relates to regularity and irregularity. For example, in landscapes of SW Australia or the Cerrado of Brazil, where
fires occur more or less regularly, the risk of ecosystem damage and the extinction
risk for certain species is very low since the biodiversity of most habitats in these
regions is well adopted to regular wildfires. Fires with devastating effects and
damages to the natural world most likely occur where they are severe and unexpected. One example of this comes from the California deserts where the invasion of
annual grasses creates a fuel layer that did not previously exist and allows fire to
carry across deserts. The lack of fire in the evolutionary history, due to the spacing
between individuals and the ephemeral nature of annual wildflowers, means that
fire-tolerance has not evolved in the native species found there (Minnich 2008).
2.4 Susceptibility of Ecosystems
The same cause may have different effects depending on the susceptibility of the
ecosystem. For example, global warming leads to rising sea levels. However, many
coastal regions on earth are uplifting due to geological processes. Therefore,
coastal regions of Scandinavia, Scotland, parts of the Mediterranean, or some of
the Caribbean Islands, for example, are little affected by relative sea level rise.
An introduced species might have a small effect if a native species with a similar
niche is already present. The effect may be dramatic if the introduced species
represents a new guild (predator, for example). This is the reason why the Brown
Tree Snake (Boiga irregularis) from Australia and Indonesia had dramatic effects
on the biodiversity of Guam and caused the extirpation of a dozen bird species on
this island (Savidge et al. 2007).
2.5 Date of Event
The longer the time since a catastrophe occurred, the lesser the memory which
means both human memory and aftermath that can still be recognized on the
landscape. If all individuals of a natural forest are of the same age then most likely
a fire or another catastrophe destroyed the forest during a special event. Mucina and
Wardell-Johnson (2011) distinguished three groups of temporal scales: short-term
(e.g., flash-floods, landslides, tsunamis, earthquakes, extensive fires), mid-term
(e.g. glacial scouring, marine transgressions and regressions, drought-pluvial
cycles, desiccation of lakes), and long-term (e.g., drift of continental plates, isostatic
and epirogenic uplift, continental scale erosion).
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C. Hobohm and S. E. Vanderplank
The impact of environmental conditions on biota relates to regularity and irregularity. For example, in landscapes of SW Australia or the Cerrado of Brazil, where
fires occur more or less regularly, the risk of ecosystem damage and the extinction
risk for certain species is very low since the biodiversity of most habitats in these
regions is well adopted to regular wildfires. Fires with devastating effects and
damages to the natural world most likely occur where they are severe and unexpected. One example of this comes from the California deserts where the invasion of
annual grasses creates a fuel layer that did not previously exist and allows fire to
carry across deserts. The lack of fire in the evolutionary history, due to the spacing
between individuals and the ephemeral nature of annual wildflowers, means that
fire-tolerance has not evolved in the native species found there (Minnich 2008).
2.4 Susceptibility of Ecosystems
The same cause may have different effects depending on the susceptibility of the
ecosystem. For example, global warming leads to rising sea levels. However, many
coastal regions on earth are uplifting due to geological processes. Therefore,
coastal regions of Scandinavia, Scotland, parts of the Mediterranean, or some of
the Caribbean Islands, for example, are little affected by relative sea level rise.
An introduced species might have a small effect if a native species with a similar
niche is already present. The effect may be dramatic if the introduced species
represents a new guild (predator, for example). This is the reason why the Brown
Tree Snake (Boiga irregularis) from Australia and Indonesia had dramatic effects
on the biodiversity of Guam and caused the extirpation of a dozen bird species on
this island (Savidge et al. 2007).
2.5 Date of Event
The longer the time since a catastrophe occurred, the lesser the memory which
means both human memory and aftermath that can still be recognized on the
landscape. If all individuals of a natural forest are of the same age then most likely
a fire or another catastrophe destroyed the forest during a special event. Mucina and
Wardell-Johnson (2011) distinguished three groups of temporal scales: short-term
(e.g., flash-floods, landslides, tsunamis, earthquakes, extensive fires), mid-term
(e.g. glacial scouring, marine transgressions and regressions, drought-pluvial
cycles, desiccation of lakes), and long-term (e.g., drift of continental plates, isostatic
and epirogenic uplift, continental scale erosion).
184
C. Hobohm and S. E. Vanderplank