169
million years ago, during the last stage of the Cretaceous period (Yan et al. 2015;
Irving and Hebda 1993). This attests to the durability of this genus to survive and
adapt to the changes at the Earth’s surface (Milne et al. 2004; Irving and Hebda
1993). R. ponticum is an aggressive, allelopathic, evergreen coloniser that threatens
biodiversity. Once established, it is difficult and costly to remove (Edwards 2006).
R. ponticum thrives in milder, wet climatic conditions, favouring acidic ground but
capable of colonising very poor soil and cliff faces, growing from 5 to 8 m in height
and 4 to 6 m in width to form dense impenetrable areas within seven to ten years
(Edwards 2006; FC 2016; Milne and Abbott 2000).
Furthermore, and not insignificantly, R. ponticum is a key sporulation host for the
emerging virulent tree-killing pathogen Phytophthora (ramorum and kernoviae
species). This is a high concern in the UK due to its rapid spread and diversification,
which has enabled it to infect a range of host tree species not previously known to
be vulnerable, including the English Oak (Quercus robur) (Purse et al. 2013; FC
2016). Infection control dictates that entering known infection sites, as well as areas
of surrounding forest, is kept to a minimum; this limits the potential for data collection in these priority areas. (FC 2016).
Remote Sensing Background
Light is measured in waves and the distance between each wave is typically measured in nano- meters (nm). The visible spectrum ranges from 400–700 nm, for
human eyes, and can be broken down into groups of colour called ‘bands’: blue (B),
green (G) and red (R) in order of increasing wavelength (nm). The wavelengths just
outside the visible spectrum are ultraviolet (UV) light at <400 nm and infrared (IR)
at >750 nm. Green plants reflect predominantly in the green band (around 500 nm)
and the Near Infrared (NIR, 700 + nm) portion of the spectrum (Heege 2015).
Differentiating plants from non-photosynthetic organisms and objects can be
achieved using many wavelengths but differentiating between plant groups and species most often requires reference to the visible green and NIR bands green and
infrared bands (Heege 2015).
Buschmann et al. (2012) determined, using high resolution 4-band (RGB + NIR)
imagery, that leaf reflectance is categorised by three basic parameters: Leaf pigment
content, i.e. the absorption of chlorophylls and carotenoids in the pigment protein
complexes; leaf tissue structure, i.e. the size of aerial interspaces between cells
(influence leaf optical properties); and structure of the leaf surface, e.g. waxes and
hairs.
Traditional cameras split the visible spectrum into three bands, as standard: Red,
Green, Blue (RGB, 700–400 to respectively). They are designed in this way to
mimic our own colour chemicals, present in our eyes, to then produce images that
mimic how we, as humans, visualise our surroundings (Pfundel et al. 2008). What
we and our traditional cameras. However, we and our traditional cameras cannot see
the energy reflected by an object in all wavelengths. Multispectral cameras typically
Mapping the Distribution of Understorey Rhododendron Ponticum Using…
million years ago, during the last stage of the Cretaceous period (Yan et al. 2015;
Irving and Hebda 1993). This attests to the durability of this genus to survive and
adapt to the changes at the Earth’s surface (Milne et al. 2004; Irving and Hebda
1993). R. ponticum is an aggressive, allelopathic, evergreen coloniser that threatens
biodiversity. Once established, it is difficult and costly to remove (Edwards 2006).
R. ponticum thrives in milder, wet climatic conditions, favouring acidic ground but
capable of colonising very poor soil and cliff faces, growing from 5 to 8 m in height
and 4 to 6 m in width to form dense impenetrable areas within seven to ten years
(Edwards 2006; FC 2016; Milne and Abbott 2000).
Furthermore, and not insignificantly, R. ponticum is a key sporulation host for the
emerging virulent tree-killing pathogen Phytophthora (ramorum and kernoviae
species). This is a high concern in the UK due to its rapid spread and diversification,
which has enabled it to infect a range of host tree species not previously known to
be vulnerable, including the English Oak (Quercus robur) (Purse et al. 2013; FC
2016). Infection control dictates that entering known infection sites, as well as areas
of surrounding forest, is kept to a minimum; this limits the potential for data collection in these priority areas. (FC 2016).
Remote Sensing Background
Light is measured in waves and the distance between each wave is typically measured in nano- meters (nm). The visible spectrum ranges from 400–700 nm, for
human eyes, and can be broken down into groups of colour called ‘bands’: blue (B),
green (G) and red (R) in order of increasing wavelength (nm). The wavelengths just
outside the visible spectrum are ultraviolet (UV) light at <400 nm and infrared (IR)
at >750 nm. Green plants reflect predominantly in the green band (around 500 nm)
and the Near Infrared (NIR, 700 + nm) portion of the spectrum (Heege 2015).
Differentiating plants from non-photosynthetic organisms and objects can be
achieved using many wavelengths but differentiating between plant groups and species most often requires reference to the visible green and NIR bands green and
infrared bands (Heege 2015).
Buschmann et al. (2012) determined, using high resolution 4-band (RGB + NIR)
imagery, that leaf reflectance is categorised by three basic parameters: Leaf pigment
content, i.e. the absorption of chlorophylls and carotenoids in the pigment protein
complexes; leaf tissue structure, i.e. the size of aerial interspaces between cells
(influence leaf optical properties); and structure of the leaf surface, e.g. waxes and
hairs.
Traditional cameras split the visible spectrum into three bands, as standard: Red,
Green, Blue (RGB, 700–400 to respectively). They are designed in this way to
mimic our own colour chemicals, present in our eyes, to then produce images that
mimic how we, as humans, visualise our surroundings (Pfundel et al. 2008). What
we and our traditional cameras. However, we and our traditional cameras cannot see
the energy reflected by an object in all wavelengths. Multispectral cameras typically
Mapping the Distribution of Understorey Rhododendron Ponticum Using…