1
Stand Structure in Terrestrial Ecosystems
Frank W. Davis and Dar Roberts
Introduction
This chapter provides a brief overview of instrumentation and methods for characterizing vegetation structure at the stand level, where a stand is
defined as an area of relatively uniform physical
environmental conditions, vegetation structure, and
plant community composition (Barbour et al.
1987). By vegetation structure we mean the threedimensional distribution of aboveground phytomass integrated over some period of time. We will
not consider the temporal components of stand
structure, such as diurnal variation in leaf orientation or seasonal phenology, focusing instead on
methods for estimating structural variables at a particular point in time.
Knowledge of vegetation structure is essential
for describing the exchange of energy and mass between vegetation and its environment. At leaf,
branch, and canopy scales, vegetation structure influences the interception of precipitation, absorption of photosynthetically active radiation, and the
turbulent exchange of momentum, heat, and mass.
At the stand or regional scale, the density, height,
and crown dimensions of canopies modify the
availability of light and moisture and thus influence
rates of plant establishment, growth, and succession. At all of these scales, vegetation structure influences the rates at which carbon is assimilated,
stored, and transported through ecosystems and
thus has a major impact on the cycling of carbon,
water, and other nutrients.
Stand structure is also of fundamental importance to many other disciplines, for example, wildlife biology, phytosociology, forestry, range science, and fire ecology. Not surprisingly, an
enormous array of qualitative and quantitative procedures has been developed to estimate different
stand structural properties, and those procedures
have tended to be tailored to the specific needs and
perspectives of the different disciplines. The focus
of this chapter is on recently developed procedures
of special interest to ecosystem ecologists. We do
not go into any detail on traditional, direct measurement methods, which are well described in reference works such as Ross (1981), Bonham (1989),
Husch et al. (1982), and Norman and Campbell
(1989). Instead, we emphasize indirect approaches
that make use of recent advances in remote sensing
and image analysis.
The chapter is organized as follows: First, we
summarize and contrast direct versus indirect approaches for measuring vegetation structure, followed by an overview of models of canopy architecture that guide the analysis of vegetation
structure and can form the basis for indirect approaches. Next, we describe some remote sensing
instruments of special importance for indirect measurement of vegetation structure. The final section
reviews some widely used direct and indirect methods for estimating common descriptors of vegetation structure at the stand level.
Methodological Approaches
Elements of stand structure include stems,
branches, twigs, leaves, and other specialized organs, whole plants, and groups of plants (e.g., cohorts, members of a stratum, etc.), which can be
7
Stand Structure in Terrestrial Ecosystems
Frank W. Davis and Dar Roberts
Introduction
This chapter provides a brief overview of instrumentation and methods for characterizing vegetation structure at the stand level, where a stand is
defined as an area of relatively uniform physical
environmental conditions, vegetation structure, and
plant community composition (Barbour et al.
1987). By vegetation structure we mean the threedimensional distribution of aboveground phytomass integrated over some period of time. We will
not consider the temporal components of stand
structure, such as diurnal variation in leaf orientation or seasonal phenology, focusing instead on
methods for estimating structural variables at a particular point in time.
Knowledge of vegetation structure is essential
for describing the exchange of energy and mass between vegetation and its environment. At leaf,
branch, and canopy scales, vegetation structure influences the interception of precipitation, absorption of photosynthetically active radiation, and the
turbulent exchange of momentum, heat, and mass.
At the stand or regional scale, the density, height,
and crown dimensions of canopies modify the
availability of light and moisture and thus influence
rates of plant establishment, growth, and succession. At all of these scales, vegetation structure influences the rates at which carbon is assimilated,
stored, and transported through ecosystems and
thus has a major impact on the cycling of carbon,
water, and other nutrients.
Stand structure is also of fundamental importance to many other disciplines, for example, wildlife biology, phytosociology, forestry, range science, and fire ecology. Not surprisingly, an
enormous array of qualitative and quantitative procedures has been developed to estimate different
stand structural properties, and those procedures
have tended to be tailored to the specific needs and
perspectives of the different disciplines. The focus
of this chapter is on recently developed procedures
of special interest to ecosystem ecologists. We do
not go into any detail on traditional, direct measurement methods, which are well described in reference works such as Ross (1981), Bonham (1989),
Husch et al. (1982), and Norman and Campbell
(1989). Instead, we emphasize indirect approaches
that make use of recent advances in remote sensing
and image analysis.
The chapter is organized as follows: First, we
summarize and contrast direct versus indirect approaches for measuring vegetation structure, followed by an overview of models of canopy architecture that guide the analysis of vegetation
structure and can form the basis for indirect approaches. Next, we describe some remote sensing
instruments of special importance for indirect measurement of vegetation structure. The final section
reviews some widely used direct and indirect methods for estimating common descriptors of vegetation structure at the stand level.
Methodological Approaches
Elements of stand structure include stems,
branches, twigs, leaves, and other specialized organs, whole plants, and groups of plants (e.g., cohorts, members of a stratum, etc.), which can be
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