In ecology, a light gap is a break in forest canopy or similar barrier that allows young plants to grow where they would be otherwise inhibited by the lack of light reaching the seedbed. Light gaps form predominantly when a tree falls, and thus produces an opening in the forest canopy. Light gaps are important for maintaining diversity in species-rich ecosystems. [1]
There are many ways in which light gaps can form. A major occurrence is through previously mentioned treefall gaps. The death of a full-grown tree initiates a treefall gap, where light is exposed to the soil and creates resources for seeds and younger trees. Treefall gaps have been proven to maintain tree diversity by increasing stem density, which in turn can lead to species richness [2] . Juvenile stems, or saplings, do an exceptional job at increasing stem density which increases species diversity as a result. Species compete for resources in order to regenerate. Succession can begin when treefall occurs because the newly lit area provides an area for a new population to grow. Trees that will grow in a treefall gap are not necessarily the most suited for that particular environment, but rather, grow by chance. [3] Therefore, different organisms may experience a greater attraction to certain environments over others, which can also have an effect on the extent to which an area flourishes.
An interesting example of gap formation comes from Japanese Black Bears [4] and their effects on the forest canopy. When Japanese Black Bears are looking for fruit, they break off branches when climbing trees and as a result, small light gaps form in the canopies. Therefore, their search for food is improving the light conditions of understory plants, which in return benefits the bears, as this helps fruit they eat to grow more abundantly.
On a report done in a Neotropical forest, the process of gap-phase regeneration is studied. [5] Through conducted experiments, conclusions are confirmed about the gap-phase regeneration process. A tree fall forms a light gap, which stimulated growth, resulting in an increase in the stem density on the forest floor. Thus, in turn, allows multiple trees to grow back and ecosystems to prosper. Studies of gap dynamics have provided evidence for understanding many small disturbances in an ecosystem.
In a uniform and discontinuous conifer forest canopy, solar energy is projected at certain angles in the light gaps, which determine soil conditions and amount of snow accumulation. [6] Depending on the time of year, the variety of tree species and the size of the light gap will determine how much light hits the forest floor and what kind of temporal and spatial heterogeneity will form.
In the coastal areas of south-eastern Australia, large brown kelp, another kind of canopy, formed by Ecklonia radiata , dominates the existing temperate reefs. Climate change in the area poses a direct effect on the underwater canopy cover, reducing its overall quality. [7] Climate change is causing patches in the canopy layer and because of this loss of coverage, the understory becomes a prime place for benthic algae to grow. This affects other organisms, such a sponges and encrusting algae that are trying to grow on the reefs. This discovery has shown that although light gaps oftentimes produce positive outcomes, they can also negatively effect some members of the biotic community.
In the Amazon rainforest, light gaps are extensively studied. However, ways in which the understory is affected by light gaps there, remains mostly a mystery. Overall biomass in the light gap areas is directly impacted by the size of the light opening, the type of roots that pre-existed its formation, and the type of tree that fell to create the light gap. [8] The quality of biomass determines the level of regrowth in the environment.
All types of canopy structures rely on the quality that seeds experience when developing. Seeds can grow better when they are protected, however, they also flourish to a greater extent when they are not in a shaded environment. In fact, some seeds are so sensitive that even a slight change in light can prevent it from surviving. [9]
Light gap herbivores are animals that contribute to the creation of light gaps by feeding on the older plants. Some herbivorous animals include algae and bacteria in their diet. Insect herbivores target the shade-tolerant tree species. They cause a substantial amount of damage to the leaves of plants. There is more herbivory in tropical forests than in temperate forests. [10]
Many organisms are directly affected by the formation of light gaps. In a tropical forest, butterflies, which are great biodiversity indicators, exemplify this notion. [11] Out of twenty various species, each has ecological and behavioral requirements that can be found in both opened and closed canopy gaps. Males will claim certain gaps as their territory to protect the patch from other males, in hopes to attract their female counterpart. Twelve species of butterflies had a positive phototactic response, while four species had a negative response and the remaining four did not express any sort of preference. Overall, butterfly species in a tropical rainforest were, on average, occupying open canopy gaps more frequently. Butterfly assemblage is determined by the amount of light and temperature that penetrates the canopy.
Newly created light gaps are avoided in a lot of situations by species that would normally replenish them through seed dispersal. However, the aid of the wind for seed dispersal in the light gap has a positive effect on plants, taking them further from the parent plant and decreasing predation. [12] Frugivores such as birds and bats find recently created gaps dangerous because they pose a hazard on their overall well-being. Birds find no place to perch, and bats are more susceptible to predators when they fly in this area. Large monkeys, toucans, and guans perch in the tops of the canopy, and therefore release their seeds under the canopy and as a result, the seeds do not get dispersed where most needed. Wind initiates seed movement into the canopy gap. [13] As the gap matures, it begins to grow trees that bear fruit, and growth of shrubs draw in more animals as they provide better protection from the open canopy above.
Overall, there are many advantages and disadvantages of a light gap disturbance. Some species benefit, and others are threatened. Through more research and investigation, scientists hope to uncover all aspects of the occurrence. It is only then that laws may be implemented to reduce harmful outcomes and increase further ecological sustainability.
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.
The Tasmanian temperate rain forests are a temperate broadleaf and mixed forests ecoregion in western Tasmania. The ecoregion is part of the Australasian realm, which includes Tasmania and Australia, New Zealand, New Guinea, New Caledonia, and adjacent islands.
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.
Tropical rainforests are dense and warm rainforests that occur in tropical rainforest climate where there is no dry season – all months have an average precipitation of at least 60 mm. True rainforests are typically found between 10 degrees north and south of the equator ; they are a subset of the tropical forest biome that occurs roughly within the 28-degree latitudes. Tropical rainforests are a type of tropical moist broadleaf forest, that includes the more extensive seasonal tropical forests.
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.
In forestry, windthrow refers to trees uprooted by wind. Breakage of the tree bole (trunk) instead of uprooting is called windsnap. Blowdown refers to both windthrow and windsnap.
Forest dynamics describes the underlying physical and biological forces that shape and change a forest ecosystem. The continuous state of change in forests can be summarized with two basic elements: disturbance and succession.
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.
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."
Cocha Cashu Biological Station is a tropical biological research station located at 11° 54'S and 71° 22'W in Manú National Park, Peru. It was established in 1969-70, predating the founding of its containing national park. Though only 10 km2 in area, the site has provided valuable research. The station is situated on the shore of an oxbow lake, from which it takes its name. "Qucha" is the Quechua word for lake. "Cashu" is derived from the English word "cashew" and refers to the shape of the lake.
Simarouba amara is a species of tree in the family Simaroubaceae, found in the rainforests and savannahs of South and Central America and the Caribbean. It was first described by Aubl. in French Guiana in 1775 and is one of six species of Simarouba. The tree is evergreen, but produces a new set of leaves once a year. It requires relatively high levels of light to grow and grows rapidly in these conditions, but lives for a relatively short time. In Panama, it flowers during the dry season in February and March, whereas in Costa Rica, where there is no dry season it flowers later, between March and July. As the species is dioecious, the trees are either male or female and only produce male or female flowers. The small yellow flowers are thought to be pollinated by insects, the resulting fruits are dispersed by animals including monkeys, birds and fruit-eating bats and the seeds are also dispersed by leaf cutter ants.
Monodominance is an ecological condition in which more than 60% of the tree canopy comprises a single species of tree. Monodominant forests are quite common under conditions of extra-tropical climate types. Although monodominance is studied across different regions, most research focuses on the many prominent species in tropical forests. Connel and Lowman, originally called it single-dominance. Conventional explanations of biodiversity in tropical forests in the decades prior to Connel and Lowman's work either ignored monodominance entirely or predicted that it would not exist.
A várzea forest is a seasonal floodplain forest inundated by whitewater rivers that occurs in the Amazon biome. Until the late 1970s, the definition was less clear and várzea was often used for all periodically flooded Amazonian forests.
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.
Oxera splendida is an evergreen vine in the family Lamiaceae which produces white, fragrant flowers and white, egg-shaped fruit. It naturally is occurs in the tropical rain forests of tropical Asia and Australia and is often sighted along rain forest margins such as roads. Some common names include October Glory, Glory Vine, Potato Vine and Fragrant Faradaya. Australian indigenous names include Garanggal used from Cairns to Yarrabah, Buku used in the Tully River area, Koie-yan used at Dunk Island and Djungeen used by the Girramay clan.
Julie Sloan Denslow is an American botanist, ecologist and biologist. She grew up in South Florida, and always loved nature. She graduated from Coral Gables Senior High School in 1960. She has contributed to the field of ecology through her work with and research of tropical ecosystems. Earlier in her career, she spent significant time in the field in tropical locations such as Costa Rica and Panama, as well as in temperate locations in Louisiana. and later on in her career she worked more in the office and classroom, but still spent the occasional day in the field. She has focused on research involving the ecology of exotic invasive plant species, and on ecosystem reactions and recovery following disturbances. Denslow is also a strong supporter of gender equality in the natural sciences, pushing for equal representation of women involved in tropical research and leadership during a 2007 Gender Committee Meeting within the Association for Tropical Biology and Conservation (ATBC). Her most notable contribution to tropical research is her paper "Gap Partitioning among Tropical Rainforest Trees", published in 1980.
Robin B. Foster is a botanist studying tropical forests. He co-originated the "tropical forest dynamics plot".
Strephonema pseudocola is a species of flowering plant in the family Combretaceae. It is a tree found in the forests of tropical West Africa. It was first described from the Ivory Coast.
The Tropical Wet Forests are a Level I ecoregion of North America designated by the Commission for Environmental Cooperation (CEC) in its North American Environmental Atlas. As the CEC consists only of Mexico, the United States, and Canada, the defined ecoregion does not extend outside these countries to Central America nor the Caribbean.
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