Crown shyness (also canopy disengagement, [1] canopy shyness, [2] or inter-crown spacing [3] ) is a phenomenon observed in some tree species, in which the crowns of fully stocked trees do not touch each other, forming a canopy with channel-like gaps. [4] [5] The phenomenon is most prevalent among trees of the same species, but also occurs between trees of different species. [6] [7] There exist many hypotheses as to why crown shyness is an adaptive behavior, and research suggests that it might inhibit spread of leaf-eating insect larvae. [8]
The exact physiological basis of crown shyness is uncertain. [6] The phenomenon has been discussed in scientific literature since the 1920s. [9] The variety of hypotheses and experimental results might suggest that there are multiple mechanisms across different species, an example of convergent evolution.[ citation needed ]
Some hypotheses contend that the interdigitation of canopy branches leads to "reciprocal pruning" of adjacent trees: trees in windy areas suffer physical damage as they collide with each other during winds; the abrasions and collisions induce a crown shyness response. Studies suggest that lateral branch growth is largely uninfluenced by neighbours until disturbed by mechanical abrasion. [10] If the crowns are artificially prevented from colliding in the winds, they gradually fill the canopy gaps. [11] This explains instances of crown shyness between branches of the same organism. Proponents of this idea cite that shyness is particularly seen in conditions conducive to this pruning, including windy forests, stands of flexible trees, and early succession forests where branches are flexible and limited in lateral movement. [6] [12] According to this theory, variable flexibility in lateral branches greatly influences the degree of crown shyness.
Similarly, some research suggests that constant abrasion at growth nodules disrupts bud tissue such that it is unable to continue with lateral growth. Australian forester M.R. Jacobs, who studied the crown shyness patterns in eucalyptus in 1955, believed that the trees' growing tips were sensitive to abrasion, resulting in canopy gaps. [13] Miguel Franco (1986) observed that the branches of Picea sitchensis (Sitka spruce) and Larix kaempferi (Japanese larch) suffered physical damage due to abrasion, which killed the leading shoots. [10] [14]
A prominent hypothesis is that canopy shyness has to do with mutual light sensing by adjacent plants. The photoreceptor-mediated shade avoidance response is a well-documented behavior in a variety of plant species. [15] Neighbor detection is thought to be a function of several unique photoreceptors. Plants can sense the proximity of neighbors by sensing backscattered far-red light, a task widely thought to be accomplished by the activity of the phytochrome photoreceptors. [16] Many species of plant respond to an increase in far-red light (and, by extension, encroaching neighbors) by directing growth away from the far-red stimulus and by increasing the rate of elongation. [17] Similarly, plants use blue light to induce the shade-avoidance response, likely playing a role in the recognition of neighboring plants, [18] though this was just starting to be recognised in 1988. [19]
The characterization of these behaviors might suggest that crown shyness is simply the result of mutual shading based on well-understood shade avoidance responses. [6] [20] Malaysian scholar Francis S.P. Ng, who studied Dryobalanops aromatica , suggested that the growing tips were sensitive to light levels and stopped growing when nearing the adjacent foliage due to the induced shade. [6] [20]
A 2015 study has suggested that Arabidopsis thaliana shows different leaf placement strategies when grown amongst kin and unrelated conspecifics, shading dissimilar neighbors and avoiding kin. This response was shown to be contingent on the proper functioning of multiple photosensory modalities. [21] A 1998 study proposed similar systems of photoreceptor-mediated inhibition of growth as explanations of crown shyness, [6] [20] though a causal link between photoreceptors and crown asymmetry had yet to be experimentally proven. This might explain instances of intercrown spacing that are only exhibited between conspecifics. [6] [7]
Trees that display crown shyness patterns include:
Eucalyptus is a genus of more than 700 species of flowering plants in the family Myrtaceae. Most species of Eucalyptus are trees, often mallees, and a few are shrubs. Along with several other genera in the tribe Eucalypteae, including Corymbia and Angophora, they are commonly known as eucalypts or "gum trees". Plants in the genus Eucalyptus have bark that is either smooth, fibrous, hard, or stringy and leaves that have oil glands. The sepals and petals are fused to form a "cap" or operculum over the stamens, hence the name from Greek eû ("well") and kaluptós ("covered"). The fruit is a woody capsule commonly referred to as a "gumnut".
In vascular plants, the roots are the organs of a plant that are modified to provide anchorage for the plant and take in water and nutrients into the plant body, which allows plants to grow taller and faster. They are most often below the surface of the soil, but roots can also be aerial or aerating, that is, growing up above the ground or especially above water.
In forestry and ecology, understory, or understorey, also known as underbrush or undergrowth, includes plant life growing beneath the forest canopy without penetrating it to any great extent, but above the forest floor. Only a small percentage of light penetrates the canopy so understory vegetation is generally shade-tolerant. The understory typically consists of trees stunted through lack of light, other small trees with low light requirements, saplings, shrubs, vines and undergrowth. Small trees such as holly and dogwood are understory specialists.
Pinus contorta, with the common names lodgepole pine and shore pine, and also known as twisted pine, and contorta pine, is a common tree in western North America. It is common near the ocean shore and in dry montane forests to the subalpine, but is rare in lowland rain forests. Like all pines, it is an evergreen conifer.
A liana is a long-stemmed woody vine that is rooted in the soil at ground level and uses trees, as well as other means of vertical support, to climb up to the canopy in search of direct sunlight. The word liana does not refer to a taxonomic grouping, but rather a habit of plant growth – much like tree or shrub. It comes from standard French liane, itself from an Antilles French dialect word meaning to sheave.
Silviculture is the practice of controlling the growth, composition/structure, as well as quality of forests to meet values and needs, specifically timber production.
An old-growth forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Nations defines primary forests as naturally regenerated forests of native tree species where there are no clearly visible indications of human activity and the ecological processes are not significantly disturbed. One-third of the world's forests are primary forests. Old-growth features include diverse tree-related structures that provide diverse wildlife habitats that increases the biodiversity of the forested ecosystem. Virgin or first-growth forests are old-growth forests that have never been logged. The concept of diverse tree structure includes multi-layered canopies and canopy gaps, greatly varying tree heights and diameters, and diverse tree species and classes and sizes of woody debris.
Fire ecology is a scientific discipline concerned with the effects of fire on natural ecosystems. Many ecosystems, particularly prairie, savanna, chaparral and coniferous forests, have evolved with fire as an essential contributor to habitat vitality and renewal. Many plant species in fire-affected environments use fire to germinate, establish, or to reproduce. Wildfire suppression not only endangers these species, but also the animals that depend upon them.
Forest ecology is the scientific study of the interrelated patterns, processes, flora, fauna, funga, and ecosystems in forests. The management of forests is known as forestry, silviculture, and forest management. A forest ecosystem is a natural woodland unit consisting of all plants, animals, and micro-organisms in that area functioning together with all of the non-living physical (abiotic) factors of the environment.
In biology, the canopy is the aboveground portion of a plant cropping or crop, formed by the collection of individual plant crowns. In forest ecology, canopy refers to the upper layer or habitat zone, formed by mature tree crowns and including other biological organisms. The communities that inhabit the canopy layer are thought to be involved in maintaining forest diversity, resilience, and functioning. Shade trees normally have a dense canopy that blocks light from lower growing plants.
Serotiny in botany simply means 'following' or 'later'.
In ecology, a disturbance is a temporary change in environmental conditions that causes a pronounced change in an ecosystem. Disturbances often act quickly and with great effect, to alter the physical structure or arrangement of biotic and abiotic elements. A disturbance can also occur over a long period of time and can impact the biodiversity within an ecosystem.
A treefall gap is a distinguishable hole in the canopy of a forest with vertical sides extending through all levels down to an average height of 2 m (6.6 ft) above ground. These holes occur as result of a fallen tree or large limb. The ecologist who developed this definition used two meters because he believed that "a regrowth height of 2 m was sufficient" for a gap to be considered closed, but not all scientists agree. For example, Runkle believed that regrowth should be 10–20 m (33–66 ft) above the ground. Alternatively, a treefall gap is "the smallest gap [that must] be readily distinguishable amid the complexity of forest structure."
In ecology, shade tolerance is a plant's ability to tolerate low light levels. The term is also used in horticulture and landscaping, although in this context its use is sometimes imprecise, especially in labeling of plants for sale in commercial nurseries.
The crown of a plant is the total of an individual plant's aboveground parts, including stems, leaves, and reproductive structures. A plant community canopy consists of one or more plant crowns growing in a given area.
An epicormic shoot is a shoot growing from an epicormic bud, which lies underneath the bark of a trunk, stem, or branch of a plant.
Gap dynamics refers to the pattern of plant growth that occurs following the creation of a forest gap, a local area of natural disturbance that results in an opening in the canopy of a forest. Gap dynamics are a typical characteristic of both temperate and tropical forests and have a wide variety of causes and effects on forest life.
In ecology, stratification refers to the vertical layering of a habitat; the arrangement of vegetation in layers. It classifies the layers of vegetation largely according to the different heights to which their plants grow. The individual layers are inhabited by different animal and plant communities (stratozones).
Fire adaptations are traits of plants and animals that help them survive wildfire or to use resources created by wildfire. These traits can help plants and animals increase their survival rates during a fire and/or reproduce offspring after a fire. Both plants and animals have multiple strategies for surviving and reproducing after fire. Plants in wildfire-prone ecosystems often survive through adaptations to their local fire regime. Such adaptations include physical protection against heat, increased growth after a fire event, and flammable materials that encourage fire and may eliminate competition.
The Milnthorpe Model describes a situation where fast-growing non-indigenous trees such as eucalypts, are used to colonise ex-pasture in order to establish a forested environment where indigenous canopy species can thrive.
Media related to Crown shyness at Wikimedia Commons