106
Plants play a foundational role in establishing and maintaining ecosystem function,
biogeochemical cycling, hydrological cycling, and biodiversity (Mooney et al. 1996;
Schimel et al. 2013). More specifically, canopy plants (those that occupy the sunfacing portion of a landscape) serve as dominant primary producers through the capture and utilization of light. Their structures also provide habitat for vast numbers of
species living in the shadows. To maintain this premier position in a forest ecosystem,
plants have evolved a vast array of strategies for growth, defense, and longevity,
largely manifested as chemical and/or structural adjustments in their leaves (Reich
et al. 2003; Wright et al. 2004; Diaz et al. 2016). The molecular arrangement of these
foliar properties generates an optical reflectance spectrum that can be measured at a
variety of scales with spectroscopy (Curran 1989; Jacquemoud and Ustin 2001; Ustin
et al. 2009; Ustin and Jacquemoud, Chap. 14). The ultimate result is a massive number
of tree species coalescing into forest communities of varying complexity, with unique
taxonomic compositions and functional roles that can potentially be mapped across a
forested landscape (Reichstein et al. 2014 and others).
Despite understanding the important role different canopy species and communities of species play in creating and maintaining biodiversity, the measurement, mapping, and monitoring of forest canopy composition and functional diversity has
remained a challenge. Current Earth-observing satellite technology is limited to
detecting changes in vegetation cover as well as major differences in vegetation
type and photosynthesis (Running et al. 1994; Tucker and Townshend 2000) and
does not easily reveal compositional differences or changes over time (Turner et al.
2003). Tropical forest canopy diversity is especially underexplored because spatial
and temporal variation often exceeds our ability to adequately utilize field-based
approaches (Marvin et al. 2014). Airborne imaging spectroscopy can provide an
intermediate solution; however, a fundamental prerequisite for determining whether
species diversity or a particular species might be successfully mapped is an assessment of chemical uniqueness and diversity among plant taxa. This is important
because the spectroscopy of canopies is driven primarily by the chemical composition of the foliage (Curran 1989; Asner et al. 2015).
5.2 Spectranomics Approach
The Spectranomics approach was developed to link plant canopy functional traits to
their spectral properties with the objective of providing time-varying, scalable
methods for remote sensing (RS) of forest biodiversity (Asner and Martin 2009). In
the pool of potentially important plant functional traits, foliar chemicals stand out as
core physiologically based predictors of plant adaptation to environmental conditions (Díaz et al. 1998; Wright et al. 2010). We selected a suite of 23 canopy chemical traits based on their strong ecological and evolutionary relevance, spatial
variation in species and communities, and measurable spectral properties. These
traits consist of those that (i) mediate or are indicative of photosynthesis and carbon
uptake (chlorophyll a and b, carotenoids, nitrogen, δ
13
C, and δ
15
N; non-soluble carR. E. Martin
Plants play a foundational role in establishing and maintaining ecosystem function,
biogeochemical cycling, hydrological cycling, and biodiversity (Mooney et al. 1996;
Schimel et al. 2013). More specifically, canopy plants (those that occupy the sunfacing portion of a landscape) serve as dominant primary producers through the capture and utilization of light. Their structures also provide habitat for vast numbers of
species living in the shadows. To maintain this premier position in a forest ecosystem,
plants have evolved a vast array of strategies for growth, defense, and longevity,
largely manifested as chemical and/or structural adjustments in their leaves (Reich
et al. 2003; Wright et al. 2004; Diaz et al. 2016). The molecular arrangement of these
foliar properties generates an optical reflectance spectrum that can be measured at a
variety of scales with spectroscopy (Curran 1989; Jacquemoud and Ustin 2001; Ustin
et al. 2009; Ustin and Jacquemoud, Chap. 14). The ultimate result is a massive number
of tree species coalescing into forest communities of varying complexity, with unique
taxonomic compositions and functional roles that can potentially be mapped across a
forested landscape (Reichstein et al. 2014 and others).
Despite understanding the important role different canopy species and communities of species play in creating and maintaining biodiversity, the measurement, mapping, and monitoring of forest canopy composition and functional diversity has
remained a challenge. Current Earth-observing satellite technology is limited to
detecting changes in vegetation cover as well as major differences in vegetation
type and photosynthesis (Running et al. 1994; Tucker and Townshend 2000) and
does not easily reveal compositional differences or changes over time (Turner et al.
2003). Tropical forest canopy diversity is especially underexplored because spatial
and temporal variation often exceeds our ability to adequately utilize field-based
approaches (Marvin et al. 2014). Airborne imaging spectroscopy can provide an
intermediate solution; however, a fundamental prerequisite for determining whether
species diversity or a particular species might be successfully mapped is an assessment of chemical uniqueness and diversity among plant taxa. This is important
because the spectroscopy of canopies is driven primarily by the chemical composition of the foliage (Curran 1989; Asner et al. 2015).
5.2 Spectranomics Approach
The Spectranomics approach was developed to link plant canopy functional traits to
their spectral properties with the objective of providing time-varying, scalable
methods for remote sensing (RS) of forest biodiversity (Asner and Martin 2009). In
the pool of potentially important plant functional traits, foliar chemicals stand out as
core physiologically based predictors of plant adaptation to environmental conditions (Díaz et al. 1998; Wright et al. 2010). We selected a suite of 23 canopy chemical traits based on their strong ecological and evolutionary relevance, spatial
variation in species and communities, and measurable spectral properties. These
traits consist of those that (i) mediate or are indicative of photosynthesis and carbon
uptake (chlorophyll a and b, carotenoids, nitrogen, δ
13
C, and δ
15
N; non-soluble carR. E. Martin