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3.1.1 Plant Traits and Functional Diversity
The importance of characterizing leaf and plant functional traits across scales is tied
to the crucial role these traits play in mediating ecosystem structure, functioning,
and resilience or response to perturbations (Lavorel and Garnier 2002; Reich et al.
2003; Wright et al. 2004; Reich 2014; Funk et al. 2017). The structural, biochemical, physiological, and phenological properties of plants regulate the growth and
performance or fitness of plants and their ability to propagate or survive in diverse
environments. As such, these traits are used to characterize the axes of variation that
define broad plant functional types (PFTs), which in turn describe global vegetation
patterns and properties (Ustin and Gamon 2010; Díaz et al. 2015), particularly in
ESMs (Bonan et al. 2002; Wullschleger et al. 2014). Our focus here will be on leaf
traits related to nutrition and defense that broadly fit within the concept of the leaf
economics spectrum (LES, Wright et al. 2004), because these are most amendable
to measurements using spectral methods. Other traits relating to reproductive strategies, hydraulics, physiology (though see Serbin et al. 2015), wood characteristics,
etc. may be inferred from the traits described here, especially when combined with
climate, soils, topography, or other data that generally are not directly detectable
using RS.
Leaf nutritional properties and morphology are strong predictors of the photosynthetic capacity, plant growth, and biogeochemical cycling of terrestrial ecosystems (Aber and Melillo 1982; Green et al. 2003; Wright et al. 2004; Díaz et al.
2015). With respect to litter turnover and nutrient cycling, leaf traits that correspond
to the distribution and magnitude of structural carbon and chemical compounds
such as lignin and cellulose are used to infer the recalcitrant characteristics of canopy foliage (Madritch et al., Chap. 8). Capturing the spatial variation in these traits
can therefore provide critical information on the nutrient cycling potential of ecosystems (Ollinger et al. 2002). On the other hand, leaf mass per area (LMA)—the
ratio of a leaf’s dry mass to its surface area—and its reciprocal, specific leaf area
(SLA), correspond to a fundamental trade-off of leaf construction costs versus lightharvesting potential (Niinemets 2007; Poorter et al. 2009). The amount of foliar
nitrogen within a leaf, on a mass (N mass , %) or area (N area , g/m
2
) basis, strongly regulates the photosynthetic capacity of leaves given its fundamental role in the lightharvesting pigments of leaves (chlorophyll a and b) and photosynthetic machinery,
namely, the enzyme RuBisCo (Field and Mooney 1986; Evans and Clarke 2018).
Other traits, such as the concentration or content of water and accessory pigments,
are important indicators of plant health and stress (Ustin et al. 2009). Moreover, the
covariation of traits is also a primary focus of ecological and biodiversity research
given strong trade-offs defining different leaf form and function (Díaz et al. 2015).
For example, across the spectrum of plant functional diversity (Wright et al. 2004),
foliar nitrogen and LMA form a key axis of variation that describes end-members
between “cheap” thinner, low-LMA leaves with high leaf nitrogen, higher photosynthetic rates and faster turnover versus thick, expensive leaves with high LMA,
low nitrogen, slower turnover, and longer leaf life spans. Other traits with strong
S. P. Serbin and P. A. Townsend
3.1.1 Plant Traits and Functional Diversity
The importance of characterizing leaf and plant functional traits across scales is tied
to the crucial role these traits play in mediating ecosystem structure, functioning,
and resilience or response to perturbations (Lavorel and Garnier 2002; Reich et al.
2003; Wright et al. 2004; Reich 2014; Funk et al. 2017). The structural, biochemical, physiological, and phenological properties of plants regulate the growth and
performance or fitness of plants and their ability to propagate or survive in diverse
environments. As such, these traits are used to characterize the axes of variation that
define broad plant functional types (PFTs), which in turn describe global vegetation
patterns and properties (Ustin and Gamon 2010; Díaz et al. 2015), particularly in
ESMs (Bonan et al. 2002; Wullschleger et al. 2014). Our focus here will be on leaf
traits related to nutrition and defense that broadly fit within the concept of the leaf
economics spectrum (LES, Wright et al. 2004), because these are most amendable
to measurements using spectral methods. Other traits relating to reproductive strategies, hydraulics, physiology (though see Serbin et al. 2015), wood characteristics,
etc. may be inferred from the traits described here, especially when combined with
climate, soils, topography, or other data that generally are not directly detectable
using RS.
Leaf nutritional properties and morphology are strong predictors of the photosynthetic capacity, plant growth, and biogeochemical cycling of terrestrial ecosystems (Aber and Melillo 1982; Green et al. 2003; Wright et al. 2004; Díaz et al.
2015). With respect to litter turnover and nutrient cycling, leaf traits that correspond
to the distribution and magnitude of structural carbon and chemical compounds
such as lignin and cellulose are used to infer the recalcitrant characteristics of canopy foliage (Madritch et al., Chap. 8). Capturing the spatial variation in these traits
can therefore provide critical information on the nutrient cycling potential of ecosystems (Ollinger et al. 2002). On the other hand, leaf mass per area (LMA)—the
ratio of a leaf’s dry mass to its surface area—and its reciprocal, specific leaf area
(SLA), correspond to a fundamental trade-off of leaf construction costs versus lightharvesting potential (Niinemets 2007; Poorter et al. 2009). The amount of foliar
nitrogen within a leaf, on a mass (N mass , %) or area (N area , g/m
2
) basis, strongly regulates the photosynthetic capacity of leaves given its fundamental role in the lightharvesting pigments of leaves (chlorophyll a and b) and photosynthetic machinery,
namely, the enzyme RuBisCo (Field and Mooney 1986; Evans and Clarke 2018).
Other traits, such as the concentration or content of water and accessory pigments,
are important indicators of plant health and stress (Ustin et al. 2009). Moreover, the
covariation of traits is also a primary focus of ecological and biodiversity research
given strong trade-offs defining different leaf form and function (Díaz et al. 2015).
For example, across the spectrum of plant functional diversity (Wright et al. 2004),
foliar nitrogen and LMA form a key axis of variation that describes end-members
between “cheap” thinner, low-LMA leaves with high leaf nitrogen, higher photosynthetic rates and faster turnover versus thick, expensive leaves with high LMA,
low nitrogen, slower turnover, and longer leaf life spans. Other traits with strong
S. P. Serbin and P. A. Townsend