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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.
Forest disturbances are events that cause change in the structure and composition of a forest ecosystem, beyond the growth and death of individual organisms. Disturbances can vary in frequency and intensity, and include natural disasters such as fire, landslides, wind, volcanic eruptions, rare meteor impacts, outbreaks of insects, fungi, and other pathogens, animal-caused effects such as grazing and trampling, and anthropogenic disturbances such as warfare, logging, pollution, the clearing of land for urbanization or agriculture, and the introduction of invasive species. Not all disturbances are destructive or negative to the overall forest ecosystem. Many natural disturbances allow for renewal and growth and often release necessary nutrients. [1]
Small-scale disturbances are the key to creating and maintaining diversity and heterogeneity within a forest. Small-scale disturbances are events such as single-tree blowdowns, which create gaps that let light through the canopy to the understory and forest floor. This available light allows early-successional shade-intolerant species to colonize and maintain a population within the dominant forest, leading to the complex spatial mosaic forest structure recognized as old-growth. This process is referred to as patch dynamics or gap dynamics and has been described across many types of forests, including tropical, temperate, and boreal. [2]
The sets and patterns of natural disturbances that characterize a particular area or ecosystem are referred to as the ecosystem's disturbance regime. A natural community is closely linked with its natural disturbance regime. [3] For example, temperate and boreal rainforests typically have a disturbance regime consisting of high-frequency but small-scale events, resulting in a highly complex forest dominated by very old trees. [4] In contrast, forests that have a disturbance regime consisting of high-severity stand-replacing events, such as frequent fires, tend to be more uniform in structure and have relatively young tree stands.
Forest succession is the process by which species recover and regenerate after a disturbance. The type of disturbance, the climate and weather conditions, the presence of colonizing species, and the interactions among species all influence the path that succession will take. Species diversity and composition fluctuate throughout succession. The classic model of succession is known as relay floristics and refers to a relay of dominant species. After a stand-replacing disturbance, shade-intolerant species colonize and grow into a dominant canopy, but due to their shade-intolerance they are unable to regenerate under their own canopy; the understory (composed of shade-tolerant species) gradually replaces the canopy, and due to its shade-tolerance it can regenerate under its own canopy and therefore becomes the dominant species. [5] Often succession is not so complete or directed as the relay floristics model describes. Species can be mid-tolerant of shade and survive by taking advantage of small amounts of light coming through the canopy, and further disturbances can create small gaps. These and other factors can lead to a mixture of dominant species and a not so obvious “end” to succession (climax community). [6]
Many successional trajectories follow a basic four-stage development pattern. The first of these stages, stand initiation, occurs after a major disturbance and involves many species arriving in the area of abundant light and nutrients. The second stage, stem exclusion, describes the growth and competition of these species as resources become less available; likely one or a few species outcompetes and becomes stand-dominating. The third stage, understory reinitiation, involves further disturbance and the creation of gaps; at this point stratification develops, with layers of canopy, midstory, and understory appearing. The final stage, known as old-growth, is the extension and completion of the understory reinititation; a complex multi-aged and multi-layered forest has developed. [7]
Forests are sensitive to climate, and so climate change can have a great effect on the dynamics of the ecosystem. Rising carbon dioxide levels can increase the productivity and growth of trees, which will then decrease as other nutrients become limiting. Changes in temperature and precipitation can affect the success of various species and the resulting species assemblage. [8] Many factors of climate change can also affect an ecosystem’s disturbance regime, making the forest more or less susceptible to different disturbances and altering or even preventing recovery after a disturbance. [9]
Forests offer many ecosystem services including timber, fresh water, carbon storage, and areas of recreation. To conserve these services, along with the natural habitat and biodiversity that forests provide, understanding the dynamics that are creating and maintaining the forests is a priority. Forestry and silviculture operations require a thorough comprehension of forest dynamics in order to implement effective management and conservation techniques.[ citation needed ]
Ecological succession is the process of change in the species that make up an ecological community over time.
Tropical rainforests are rainforests that occur in areas of tropical rainforest climate in which there is no dry season – all months have an average precipitation of at least 60 mm – and may also be referred to as lowland equatorial evergreen rainforest. True rainforests are typically found between 10 degrees north and south of the equator ; they are a sub-set of the tropical forest biome that occurs roughly within the 28-degree latitudes. Within the World Wildlife Fund's biome classification, tropical rainforests are a type of tropical moist broadleaf forest that also includes the more extensive seasonal tropical forests.
An old-growth forest, sometimes synonymous with primary forest, virgin forest, late seral forest, primeval forest, first-growth forest, or mature forest—is a forest that has attained great age without significant disturbance, and thereby exhibits unique ecological features, and might be classified as a climax community. 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. More than one-third of the world's forests are primary forests. Old-growth features include diverse tree-related structures that provide diverse wildlife habitat 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.
Clearcutting, clearfelling or clearcut logging is a forestry/logging practice in which most or all trees in an area are uniformly cut down. Along with shelterwood and seed tree harvests, it is used by foresters to create certain types of forest ecosystems and to promote select species that require an abundance of sunlight or grow in large, even-age stands. Logging companies and forest-worker unions in some countries support the practice for scientific, safety and economic reasons, while detractors consider it a form of deforestation that destroys natural habitats and contributes to climate change. Environmentalists, traditional owners, local residents and others have regularly campaigned against clearcutting, including through the use of blockades and nonviolent direct action.
A secondary forest is a forest or woodland area which has regenerated through largely natural processes after human-caused disturbances, such as timber harvest or agriculture clearing, or equivalently disruptive natural phenomena. It is distinguished from an old-growth forest, which has not recently undergone such disruption, and complex early seral forest, as well as third-growth forests that result from harvest in second growth forests. Secondary forest regrowing after timber harvest differs from forest regrowing after natural disturbances such as fire, insect infestation, or windthrow because the dead trees remain to provide nutrients, structure, and water retention after natural disturbances. Secondary forests are notably different from primary forests in their composition and biodiversity; however, they may still be helpful in providing habitat for native species, preserving watersheds, and restoring connectivity between ecosystems.
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 ecology is the scientific study of the interrelated patterns, processes, flora, fauna 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 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."
Management of Pacific Northwest riparian forests is necessary because many of these forests have been dramatically changed from their original makeup. The primary interest in riparian forest and aquatic ecosystems under the Northwest Forest Plan (NWFP) is the need to restore stream habitat for fish populations, particularly anadromous salmonids. Some of these forests have been grazed by cattle or other livestock. The heavy hooves of these animals compact the soil. This compaction does not allow the water to be absorbed into the ground, so the water runs off into the stream carrying topsoil along the way.
Spruce–fir forests are type of forest found in the Northern Hemisphere dominated by spruce and fir trees. These forests are often considered to be climax forests, with the two main tree genera able to reproduce in their own shade.
Even-aged timber management is a group of forest management practices employed to achieve a nearly coeval cohort group of forest trees. The practice of even-aged management is often pursued to minimize costs to loggers. In some cases, the practices of even aged timber management are frequently implicated in biodiversity loss and other ecological damage. Even-aged timber management can also be beneficial to restoring natural native species succession.
FORECAST is a management-oriented, stand-level, forest-growth and ecosystem-dynamics model. The model was designed to accommodate a wide variety of silvicultural and harvesting systems and natural disturbance events in order to compare and contrast their effect on forest productivity, stand dynamics, and a series of biophysical indicators of non-timber values.
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.
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.
The Japanese temperate rainforest is well sustained and maintains a high biodiversity. One method that has been utilized in maintaining the health of forests in Japan has been afforestation. The Japanese government and private businesses have set up multiple projects to plant native tree species in open areas scattered throughout the country. This practice has resulted in shifts in forest structure and a healthy temperate rainforest that maintains a high biodiversity.
In ecology regeneration is the ability of an ecosystem – specifically, the environment and its living population – to renew and recover from damage. It is a kind of biological regeneration.
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.
The relationships between fire, vegetation, and climate create what is known as a fire regime. Within a fire regime, fire ecologists study the relationship between diverse ecosystems and fire; not only how fire affects vegetation, but also how vegetation affects the behavior of fire. The study of neighboring vegetation types that may be highly flammable and less flammable has provided insight into how these vegetation types can exist side by side, and are maintained by the presence or absence of fire events. Ecologists have studied these boundaries between different vegetation types, such as a closed canopy forest and a grassland, and hypothesized about how climate and soil fertility create these boundaries in vegetation types. Research in the field of pyrogeography shows how fire also plays an important role in the maintenance of dominant vegetation types, and how different vegetation types with distinct relationships to fire can exist side by side in the same climate conditions. These relationships can be described in conceptual models called fire–vegetation feedbacks, and alternative stable states.
Forests play a crucial role as valuable repositories of biodiversity, eradicating the habitat that supports numerous plant and animal species. In Nigeria, this phenomenon has resulted in the endangerment of various trees, shrubs, and animals, with some species facing depletion.