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whereas foliar P and Ca are driven more by changes in site conditions than by phylogeny. In short, Spectranomics led us to understand that canopy functional traits
can be nested regionally by environmental setting but expressed locally within any
given environment by their evolutionary origin.
5.3.2 Spectral Properties of Humid Tropical Forest Canopies
In concert with chemical trait collections, we measured the spectral properties of
canopy foliage from thousands of humid tropical tree canopies and determined that
all 23 chemical traits can be remotely sensed to varying degrees (Asner et al. 2011;
Chadwick and Asner 2016; Martin et al. 2018). Utilizing leaf-level spectral- chemical
relationships, we discovered that the spectral properties of canopy foliage closely
tracked canopy functional trait responses to macro-environmental changes such as
broad differences in soil fertility (Asner and Martin 2011; Asner et al. 2012b).
Similar to the functional trait findings, we discovered that the spectral properties of
foliage within communities along elevation gradients were largely determined by
phylogenetic identity (Asner et al. 2014a). Consequently, canopy functional traits
and spectral properties tracked one another at nested ecological scales, a result that
suggests what we might find if we collected map-based spectral data over a much
larger geographic area using RS instrumentation.
When coupled with DNA analyses, Spectranomics data indicate that forest canopies show strong phylogenetic organization of their foliar spectral properties, particularly in the shortwave-infrared (1500–2500 nm) wavelength region (McManus
et al. 2016). This finding suggests that mapping of forest canopies with airborne
imaging spectroscopy may provide spatial insight to the genetic distribution and
genealogy of forest canopy taxa. Growth-form-specific studies using the
Spectranomics approach revealed that lianas (woody vines) maintain functional
traits and spectral properties unique from their host tree canopies (Asner and Martin
2012). Lianas are important drivers and limiters of biodiversity and carbon cycling
in tropical forests (Schnitzer and Bongers 2011), and these measured differences
predicted and underpinned the subsequent mapping of lianas in tropical forests
using airborne imaging spectroscopy (Marvin et al. 2016).
Spectranomics data have been collected and archived under stringent field and
analytical standards, which has facilitated the development new quantitative linkages between canopy foliar spectroscopy and canopy functional traits (Feilhauer
et al. 2010, 2015; Féret et al. 2011, 2017). Spectral modeling studies showed that
full-spectrum (350–3500 nm) data provided retrieval capability for three times the
number of chemicals as 350–1300 nm data from less expensive, more common visible to near-infrared spectrometers. These studies also pointed to the need for sampling fully sunlit foliage in higher-density portions of tree crowns to minimize the
effect of canopy structure on chemical trait retrievals. These findings were key guiding components in the development of laser-guided imaging spectroscopy that links
Spectranomics field surveys to remotely sensed spectra to generate consistent canopy chemical trait retrieval at multiple geographic scales.
R. E. Martin
whereas foliar P and Ca are driven more by changes in site conditions than by phylogeny. In short, Spectranomics led us to understand that canopy functional traits
can be nested regionally by environmental setting but expressed locally within any
given environment by their evolutionary origin.
5.3.2 Spectral Properties of Humid Tropical Forest Canopies
In concert with chemical trait collections, we measured the spectral properties of
canopy foliage from thousands of humid tropical tree canopies and determined that
all 23 chemical traits can be remotely sensed to varying degrees (Asner et al. 2011;
Chadwick and Asner 2016; Martin et al. 2018). Utilizing leaf-level spectral- chemical
relationships, we discovered that the spectral properties of canopy foliage closely
tracked canopy functional trait responses to macro-environmental changes such as
broad differences in soil fertility (Asner and Martin 2011; Asner et al. 2012b).
Similar to the functional trait findings, we discovered that the spectral properties of
foliage within communities along elevation gradients were largely determined by
phylogenetic identity (Asner et al. 2014a). Consequently, canopy functional traits
and spectral properties tracked one another at nested ecological scales, a result that
suggests what we might find if we collected map-based spectral data over a much
larger geographic area using RS instrumentation.
When coupled with DNA analyses, Spectranomics data indicate that forest canopies show strong phylogenetic organization of their foliar spectral properties, particularly in the shortwave-infrared (1500–2500 nm) wavelength region (McManus
et al. 2016). This finding suggests that mapping of forest canopies with airborne
imaging spectroscopy may provide spatial insight to the genetic distribution and
genealogy of forest canopy taxa. Growth-form-specific studies using the
Spectranomics approach revealed that lianas (woody vines) maintain functional
traits and spectral properties unique from their host tree canopies (Asner and Martin
2012). Lianas are important drivers and limiters of biodiversity and carbon cycling
in tropical forests (Schnitzer and Bongers 2011), and these measured differences
predicted and underpinned the subsequent mapping of lianas in tropical forests
using airborne imaging spectroscopy (Marvin et al. 2016).
Spectranomics data have been collected and archived under stringent field and
analytical standards, which has facilitated the development new quantitative linkages between canopy foliar spectroscopy and canopy functional traits (Feilhauer
et al. 2010, 2015; Féret et al. 2011, 2017). Spectral modeling studies showed that
full-spectrum (350–3500 nm) data provided retrieval capability for three times the
number of chemicals as 350–1300 nm data from less expensive, more common visible to near-infrared spectrometers. These studies also pointed to the need for sampling fully sunlit foliage in higher-density portions of tree crowns to minimize the
effect of canopy structure on chemical trait retrievals. These findings were key guiding components in the development of laser-guided imaging spectroscopy that links
Spectranomics field surveys to remotely sensed spectra to generate consistent canopy chemical trait retrieval at multiple geographic scales.
R. E. Martin