In
ecologyEcology is the interdisciplinary scientific study of the interactions between organisms and the interactions of these organisms with their environment....
,
shade tolerance is a
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
's abilities to tolerate low
lightLight is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye ....
levels. The term is also used in
horticultureHorticulture is the industry and science of plant cultivation. Some would say that horticulture is the process of preparing soil for the planting of seeds, tubers, or cuttings. Horticulturists work and conduct research in the disciplines of plant propagation and cultivation, crop production, plant...
and
landscapingLandscaping refers to any activity that modifies the visible features of an area of land, including:# living elements, such as flora or fauna; or what is commonly referred to as gardening, the art and craft of growing plants with a goal of creating a beautiful environment within the landscape.#...
, although in this context its use is sometimes sloppy, especially with respect to labeling of plants for sale in
nurseriesA nursery is a place where plants are propagated and grown to usable size. There are retail nurseries which sell to the general public, wholesale nurseries which sell only to...
.
Shade tolerance is a relative term, and its use and meaning depends on context. One can compare large trees to each other, but when comparing
understoryUnderstory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...
trees and
shrubA shrub or bush is a horticultural rather than strictly botanical category of woody plant, distinguished from a tree by its multiple stems and lower height, usually less than 5-6 m tall. A large number of plants can be either shrubs or trees, depending on the growing conditions they experience...
s, or non-woody plants, the term takes on a different meaning.
In
ecologyEcology is the interdisciplinary scientific study of the interactions between organisms and the interactions of these organisms with their environment....
,
shade tolerance is a
plantPlants are living organisms belonging to the kingdom Plantae. They include familiar organisms such as trees, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The scientific study of plants, known as botany, has identified about 350,000 extant species of plants, defined as seed plants,...
's abilities to tolerate low
lightLight is electromagnetic radiation, particularly radiation of a wavelength that is visible to the human eye ....
levels. The term is also used in
horticultureHorticulture is the industry and science of plant cultivation. Some would say that horticulture is the process of preparing soil for the planting of seeds, tubers, or cuttings. Horticulturists work and conduct research in the disciplines of plant propagation and cultivation, crop production, plant...
and
landscapingLandscaping refers to any activity that modifies the visible features of an area of land, including:# living elements, such as flora or fauna; or what is commonly referred to as gardening, the art and craft of growing plants with a goal of creating a beautiful environment within the landscape.#...
, although in this context its use is sometimes sloppy, especially with respect to labeling of plants for sale in
nurseriesA nursery is a place where plants are propagated and grown to usable size. There are retail nurseries which sell to the general public, wholesale nurseries which sell only to...
.
Shade tolerance is a relative term, and its use and meaning depends on context. One can compare large trees to each other, but when comparing
understoryUnderstory is the term for the area of a forest which grows at the lowest height level below the forest canopy. Plants in the understory consist of a mixture of seedlings and saplings of canopy trees together with understory shrubs and herbs...
trees and
shrubA shrub or bush is a horticultural rather than strictly botanical category of woody plant, distinguished from a tree by its multiple stems and lower height, usually less than 5-6 m tall. A large number of plants can be either shrubs or trees, depending on the growing conditions they experience...
s, or non-woody plants, the term takes on a different meaning. Even in a specific context, shade tolerance is not a single variable or simple continuum, but rather a complex, multi-faceted property of plants, since different plants exhibit different
adaptationAdaptation is the process whereby a population becomes better suited to its habitat. This process takes place over many generations, and is one of the basic phenomena of biology....
s to
shadeShade is the blocking of sunlight by any object, and also the shadow created by that object. Shade also consists of the colors grey, black,white, etc...
.
Basic concepts
All but a few plants need sunlight to survive. However, in general, more sunlight does not always make it easier for plants to survive. Where
waterWater is an ubiquitous chemical substance that is composed of hydrogen and oxygen and is essential for all known forms of life.In typical usage, water refers only to its liquid form or state, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam. Water covers 71%...
is scarce, life can actually be easier in the shade. In direct sunlight, plants face
desiccationDesiccation is the state of extreme dryness, or the process of extreme drying. A desiccant is a hygroscopic substance that induces or sustains such a state in its local vicinity in a moderately-well sealed container.-Science:-Desiccator:...
and exposure to UV rays, and must expend energy producing
pigmentA pigment is a material that changes the color of reflected or transmitted light as the result of wavelength-selective absorption. This physical process differs from fluorescence, phosphorescence, and other forms of luminescence, in which a material emits light.Many materials selectively absorb...
s to block UV light, and waxy coatings to prevent water loss.
Plants in shade have the ability to absorb far-red light (730nm). Red light gets absorbed by the shade intolerant plants, but the far-red penetrate the canopy, reaching the understory. The shade tolerant plants found here have the ability to absorb light at this wavelength.
On the other hand, when less light is available, less
energyIn physics, energy is a scalar physical quantity that describes the amount of work that can be performed by a force, an attribute of objects and systems that is subject to a conservation law...
is available to the plant. Whereas in sunny and dry environments water can be a
limiting factorA factor or limiting resource is a factor that controls a process, such as organism growth or species population, size, or distribution. The availability of food, predation pressure, or availability of shelter are examples of factors that could be limiting for an organism...
in growth and survival, in shade, energy (in the form of sunlight) is usually the limiting factor.
The situation with respect to nutrients is often different in shade and sun. Most shade is due to the presence of a canopy of other plants, and this is usually associated with a completely different environment--richer in
soilSoil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics. It is composed of particles of broken rock that have been altered by chemical and...
nutrientA nutrient is a chemical that an organism needs to live and grow or a substance used in an organism's metabolism which must be taken in from its environment. Nutrients are the substances that enrich the body. They build and repair tissues, give heat and energy, and regulate body processes...
s--than sunny areas.
Shade tolerant plants are thus adapted to be efficient energy-users. In simple terms, shade-tolerant plants grow broader, thinner
leavesLeaves are an Icelandic five-piece alternative rock band who formed in 2001. Late in 2001 they played with Emiliana Torrini and drew early praise from the New York Times. They came to prominence in 2002 with their debut album, Breathe, drawing comparisons to groups such as The Verve and Doves...
, to catch more sunlight relative to the cost of producing the leaf. Shade tolerant plants are also usually adapted to make more use of soil nutrients than their sun-loving counterparts.
Non-woody plants
In temperate zones, many wildflowers and non-woody plants persist in the closed canopy of a forest by leafing out early in the spring, before the trees leaf out. This is partly possibly because the ground tends to be more sheltered and thus the plants are less susceptible to
frostFrost is the solid deposition of water vapor from saturated air. It is formed when solid surfaces are cooled to below the dew point of the adjacent air. Frost crystals' size differ depending on time and water vapor available. Frost is also usually translucent in appearance. There are many types of...
, during the period of time when it would still be hazardous for trees to leaf out. As an extreme example of this, winter annuals sprout in the fall, grow through the winter, and
flowerA flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to mediate the union of male sperm with female ovum in order to produce seeds...
and die in the spring.
Just like with trees, shade-tolerance in non-woody plants is diverse. Some early-leafing out plants will persist after the canopy leafs out, whereas others rapidly die back. In many species, whether or not this happens depends on the environment, such as water supply and sunlight levels.
Although most plants grow towards light, many tropical
vineThe term vine may refer to a climbing or trailing plant. The word, derived from Latin vīnea, in the original sense referred to the grapevines . The modern extended sense is mostly restricted to North American English, which uses "grapevine" to refer to the grape-bearing Vitis species...
s, such as
Monstera deliciosaMonstera deliciosa is a creeping vine native to tropical rainforests...
(and a number of other members of the
PhilodendronPhilodendron is a large genus of flowering plants in the Araceae family, consisting of close to 900 or more species according to TROPICOS . Other sources quote different numbers of species. According to S.J. Mayo there are about 400 formally recognized species whereas according to Croat there are...
genus) initially grow away from light; this helps them locate a tree trunk, which they then climb to regions of brighter light.
Trees
In forests where rainfall is plentiful and water is not the limiting factor to growth, shade-tolerance is one of the most important factors characterizing tree species. However, different species of trees exhibit different adaptations to shade.
The
Eastern HemlockTsuga canadensis, also known as Eastern or Canadian Hemlock, and in the French-speaking regions of Canada as Pruche du Canada, is a coniferous tree native to eastern North America. It ranges from northeastern Minnesota eastward through southern Quebec to Nova Scotia, and south in the Appalachian...
, considered the most shade tolerant of all North American tree species, is able to germinate, persist, and even grow under a completely closed canopy. Hemlocks also exhibit the ability to transfer energy to nearby trees through their
rootIn vascular plants, the root is the organ of a plant that typically lies below the surface of the soil. This is not always the case, however, since a root can also be aerial or aerating . Furthermore, a stem normally occurring below ground is not exceptional either...
system. In contrast, the
Sugar MapleAcer saccharum is a species of maple native to the hardwood forests of northeastern North America, from Nova Scotia west to southern Ontario, and south to Georgia and Texas....
, also considered to be highly shade tolerant, will germinate under a closed canopy and persist as an understory species, but only grows to full size when a gap is generated.
Shade-intolerant species such as
willowWillows, sallows, and osiers form the genus Salix, around 400 species of deciduous trees and shrubs, found primarily on moist soils in cold and temperate regions of the Northern Hemisphere...
and
aspenAspen is a common name for trees of the Salicaceae family, most of those in a section, Populus sect. Populus, of the Populus genus. Some of the species in the section are:...
cannot sprout under a closed canopy. Shade-intolerant species often grow in
wetlandA wetland is an area of land whose soil is saturated with moisture either permanently or seasonally. Such areas may also be covered partially or completely by shallow pools of water. Wetlands include swamps, marshes, and bogs, among others. The water found in wetlands can be saltwater, freshwater,...
s, along waterways, or in disturbed areas, where there is adequate access to direct sunlight.
In addition to being able to compete in conditions of low light intensity, shade bearing species, especially trees, are able to withstand relatively low daytime temperatures compared with the open, and above all high root competition especially with subordinate vegetation. It is very difficult to separate the relative importance of light and below ground competition, and in practical terms they are inextricably linked.