The Leaf angle distribution (or LAD) of a plant canopy refers to the mathematical description of the angular
orientation
Orientation may refer to:
Positioning in physical space
* Map orientation, the relationship between directions on a map and compass directions
* Orientation (housing), the position of a building with respect to the sun, a concept in building de ...
of the
leaves
A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
in the
vegetation
Vegetation is an assemblage of plant species and the ground cover they provide. It is a general term, without specific reference to particular taxa, life forms, structure, spatial extent, or any other specific botanical or geographic character ...
. Specifically, if each leaf is conceptually represented by a small flat plate, its orientation can be described with the
zenith
The zenith (, ) is an imaginary point directly "above" a particular location, on the celestial sphere. "Above" means in the vertical direction (plumb line) opposite to the gravity direction at that location (nadir). The zenith is the "highest" ...
and the
azimuth
An azimuth (; from ar, اَلسُّمُوت, as-sumūt, the directions) is an angular measurement in a spherical coordinate system. More specifically, it is the horizontal angle from a cardinal direction, most commonly north.
Mathematicall ...
angles of the
surface normal
In geometry, a normal is an object such as a line, ray, or vector that is perpendicular to a given object. For example, the normal line to a plane curve at a given point is the (infinite) line perpendicular to the tangent line to the curve at ...
to that plate. If the leaf has a complex structure and is not flat, it may be necessary to approximate the actual leaf by a set of small plates, in which case there may be a number of leaf normals and associated angles. The LAD describes the statistical distribution of these angles.
Examples of leaf angle distributions
Different plant canopies exhibit different LADs: For instance, grasses and willows have their leaves largely hanging vertically (such plants are said to have an erectophile LAD), while oaks tend to maintain their leaves more or less horizontally (these species are known as having a planophile LAD). In some tree species, leaves near the top of the
canopy
Canopy may refer to:
Plants
* Canopy (biology), aboveground portion of plant community or crop (including forests)
* Canopy (grape), aboveground portion of grapes
Religion and ceremonies
* Baldachin or canopy of state, typically placed over an a ...
follow an erectophile LAD while those at the bottom of the canopy are more planophile. This may be interpreted as a strategy by that plant species to maximize exposure to light, an important constraint to growth and development. Yet other species (notably
sunflower
The common sunflower (''Helianthus annuus'') is a large annual forb of the genus ''Helianthus'' grown as a crop for its edible oily seeds. Apart from cooking oil production, it is also used as livestock forage (as a meal or a silage plant), as ...
) are capable of reorienting their leaves throughout the day to optimize exposure to the Sun: this is known as
heliotropism
Heliotropism, a form of tropism, is the diurnal or seasonal motion of plant parts (flowers or leaves) in response to the direction of the Sun.
The habit of some plants to move in the direction of the Sun, a form of tropism, was already known by t ...
.
Importance of LAD
The LAD of a plant canopy has a significant impact on the
reflectance
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. It is the fraction of incident electromagnetic power that is reflected at the boundary. Reflectance is a component of the response of the electronic ...
,
transmittance
Transmittance of the surface of a material is its effectiveness in transmitting radiant energy. It is the fraction of incident electromagnetic power that is transmitted through a sample, in contrast to the transmission coefficient, which is th ...
and
absorption
Absorption may refer to:
Chemistry and biology
* Absorption (biology), digestion
**Absorption (small intestine)
*Absorption (chemistry), diffusion of particles of gas or liquid into liquid or solid materials
*Absorption (skin), a route by which ...
of solar light in the vegetation layer, and thus also on its growth and development. LAD can also serve as a quantitative index to monitor the state of the plants, as
wilting
Wilting is the loss of rigidity of non-woody parts of plants. This occurs when the turgor pressure in non-lignified plant cells falls towards zero, as a result of diminished water in the cells. Wilting also serves to reduce water loss, as it m ...
usually results in more erectophile LADs.
Models
A model is an informative representation of an object, person or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin ''modulus'', a measure.
Models c ...
of
radiation
In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:
* ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...
transfer need to take this distribution into account to predict, for instance, the
albedo
Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
or the productivity of the canopy.
Measuring LAD
Accurately measuring the statistical properties of leaf angle distributions is not a trivial matter, especially for small leaves.
Clinometer
An inclinometer or clinometer is an instrument used for measuring angles of slope, elevation, or depression of an object with respect to gravity's direction. It is also known as a ''tilt indicator'', ''tilt sensor'', ''tilt meter'', ''slope ...
s can be used but may be rather bulky or inconvenient. Most leaves are quite light and tend to move with the slightest
breeze
Breeze often refers to:
* A gentle to moderate wind
* Sea breeze, an onshore afternoon wind, caused by warm air rising over the land in sunny weather
Breeze or The Breeze may also refer to:
* Breeze block a concrete masonry unit made from recovere ...
or air
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
. Nevertheless, when these environmental conditions are suitable or can be controlled, it is possible to acquire data on leaf orientation.
This may be done, for instance, with a Spatial Coordinate Apparatus, which is an articulated mechanical device capable or recording the position in three-dimensional space of three separate points forming a small triangle. The orientation of the triangle is computed from these coordinates.
Yet another approach is to use a
laser scanner
Laser scanning is the controlled Deflection (physics), deflection of laser beams, visible or invisible.
Scanned laser beams are used in some 3-D printers, in rapid prototyping, in machines for material processing, in laser engraving machines, i ...
: this instrument can record the angular and distance coordinates of the intersection of a laser beam with objects within its range. The LAD of canopy leaves can be derived from such measurements.
Extensive data sets of LAD have been recorded, especially during intensive field campaigns, such as the First ISLSCP Field Experiment (FIFE) or the SAFARI 2000 field campaign. See the external links below for getting access to these data.
LAD functions
In general, LAD are modelled with one- or two-parameters functions including ellipsoidal, rotated-ellipsoidal and Beta functions. Comparison between different LAD functions with in-situ measurements show that, two-parameter functions (especially Beta function) may perform better than one-parameter functions.
See also
*''
Orixa japonica
''Orixa japonica'', commonly called East Asian orixa or Japanese orixa, is a deciduous shrub growing to with an equal spread. Native to Japan and South Korea, it is found on forested, sunny slopes at elevations from 500 to 1300 m.
A recent ...
'', a plant with an unusual leaf angle distribution
References
* J. Ross (1981) ''The Radiation Regime and Architecture of Plant Stands'', 391 pp., W. Junk, Boston, Massachusetts.
* David M. Gates (1980) ''Biophysical Ecology'', Springer-Verlag, New York, 611 pp., {{ISBN, 0-387-90414-X (especially pages 379-381).
* Wang W. M., Li Z.-L. and Su H.-B., 2007, ''Comparison of leaf angle distribution functions: effects on extinction coefficient and sunlit foliage'', Agricultural and Forest Meteorology, 2007, Vol. 143, NO. 1-2, pp. 106-122.
External links
Leaf angle data (FIFE)
Radiation
Plant morphology
Leaves