459
ecosystem condition. Vegetation condition is the measurement of the vegetation
response to stress (Liu and Kogan 1994). High or good condition corresponds to
green, photosynthetically active vegetation, while stress such as water and nutrient
limitations, pest outbreaks, and fire results in low or poor condition, after accounting
for seasonal changes.
Physiologically, plants respond to stress by reducing chlorophyll activity and
subsequently expressing other pigments. Plants also respond to stress by closing
their stomata and reducing gas and water exchanges, which results in cells becoming turgid under water stress. These responses can be measured in the RS signal in
both the visible and near infrared (NIR). In the visible the signal switches from a
weak to a stronger reflectance signal due to chlorophyll absorption of red and blue
wavelengths. Water stress can be measured in the NIR because as cells become
turgid, they increase scattering of NIR radiation and therefore change the measured
signal. One advance toward systematic measurements of vegetation condition is the
Australian BioCondition (Lawley et al. 2016). This approach provides a framework
to systematically assess terrestrial biodiversity condition—“[t]he similarity in key
features of the regional ecosystem being assessed with those of the same regional
ecosystem in its reference state”—using attributes like fraction of large trees, tree
canopy height, recruitment of canopy species, native plant richness, size of patch,
and connectivity. Thus, such in-situ measurements of vegetation condition can be
linked to RS estimates to better provide an assessment of an ecosystem’s stress level
and ability to function and to provide services like habitat provisioning. In the next
section, we will cover the later issue.
17.3.3 Habitat Intactness and Critical Transitions
Habitat intactness may be defined temporally or spatially as either (i) the degree to
which the condition of the vegetation that forms habitat has not changed beyond
what is expected from natural processes such as phenology and other dynamics or
(ii) the spatial pattern of a given habitat, its degree of connectivity or fragmentation,
and its edge extent. An active area of research on the potential of RS for conservation
is the assessment of habitat intactness. Nagendra et al. (2013) employed RS to estimate how habitat has been changing in several regions of the Western Ghats in
India. Coops et al. (2008, 2009) developed a dynamic habitat index using time series
satellite data and showed its potential to monitor habitat condition in Canada. Later
the approach was expanded to other regions, and dynamic habitat indices have been
used as predictors of the richness of other taxa (Hobi et al. 2017). Coops et al.
(2018) have now expanded it globally and have shown how these data sets mimic
global biodiversity patterns. These data sets are currently available at http://silvis.
forest.wisc.edu/data/DHIs-clusters/ and can be very useful to monitor protected
area performance.
RS data are increasingly applied across large spatial scales to study stable state
conditions of habitats and assess early warning signals for catastrophic shifts.
17 Integrating Biodiversity, Remote Sensing, and Auxiliary Information for the Study…
ecosystem condition. Vegetation condition is the measurement of the vegetation
response to stress (Liu and Kogan 1994). High or good condition corresponds to
green, photosynthetically active vegetation, while stress such as water and nutrient
limitations, pest outbreaks, and fire results in low or poor condition, after accounting
for seasonal changes.
Physiologically, plants respond to stress by reducing chlorophyll activity and
subsequently expressing other pigments. Plants also respond to stress by closing
their stomata and reducing gas and water exchanges, which results in cells becoming turgid under water stress. These responses can be measured in the RS signal in
both the visible and near infrared (NIR). In the visible the signal switches from a
weak to a stronger reflectance signal due to chlorophyll absorption of red and blue
wavelengths. Water stress can be measured in the NIR because as cells become
turgid, they increase scattering of NIR radiation and therefore change the measured
signal. One advance toward systematic measurements of vegetation condition is the
Australian BioCondition (Lawley et al. 2016). This approach provides a framework
to systematically assess terrestrial biodiversity condition—“[t]he similarity in key
features of the regional ecosystem being assessed with those of the same regional
ecosystem in its reference state”—using attributes like fraction of large trees, tree
canopy height, recruitment of canopy species, native plant richness, size of patch,
and connectivity. Thus, such in-situ measurements of vegetation condition can be
linked to RS estimates to better provide an assessment of an ecosystem’s stress level
and ability to function and to provide services like habitat provisioning. In the next
section, we will cover the later issue.
17.3.3 Habitat Intactness and Critical Transitions
Habitat intactness may be defined temporally or spatially as either (i) the degree to
which the condition of the vegetation that forms habitat has not changed beyond
what is expected from natural processes such as phenology and other dynamics or
(ii) the spatial pattern of a given habitat, its degree of connectivity or fragmentation,
and its edge extent. An active area of research on the potential of RS for conservation
is the assessment of habitat intactness. Nagendra et al. (2013) employed RS to estimate how habitat has been changing in several regions of the Western Ghats in
India. Coops et al. (2008, 2009) developed a dynamic habitat index using time series
satellite data and showed its potential to monitor habitat condition in Canada. Later
the approach was expanded to other regions, and dynamic habitat indices have been
used as predictors of the richness of other taxa (Hobi et al. 2017). Coops et al.
(2018) have now expanded it globally and have shown how these data sets mimic
global biodiversity patterns. These data sets are currently available at http://silvis.
forest.wisc.edu/data/DHIs-clusters/ and can be very useful to monitor protected
area performance.
RS data are increasingly applied across large spatial scales to study stable state
conditions of habitats and assess early warning signals for catastrophic shifts.
17 Integrating Biodiversity, Remote Sensing, and Auxiliary Information for the Study…