thumb|right|The [[Daintree Rainforest in Queensland, Australia]]
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 (biotic components) in that area functioning together with all of the non-living physical (abiotic) factors of the environment.
Importance
Forests have an enormously important role to play in the global ecosystem, as they cover almost a third of all land. They produce approximately 28% of the Earth's oxygen (the vast majority being created by oceanic plankton), and serve as crucial carbon sinks. Forests drive the hydrological cycle through a biotic pump, which draws moisture from the ocean in order to replace natural water losses. Without forests, erosion and sediment production intensifies. Forests also host 80% of all terrestrial organisms. and provide services for humans as well. People depend directly on forests for fuel, wood products, and enrichment. Forest ecology therefore has a great impact upon the whole biosphere and human activities that are sustained by it.
Threats to forest ecology
Deforestation
A significant threat to forest ecology is deforestation as it removes large areas of forest for timber and land development. As trees are cleared, forest habitat become fragmented into smaller patches, making it harder for forest-dependent species to find resources such as food, shelter and mates. Mining activities are also a significant driver of deforestation as they involve the clearing of native forests for the access to and extraction of minerals. The combination of logging and smelting involved in mining have also resulted in both soil erosion and acidification, hindering the ability of forests to naturally recover from the effects of mining. Mining activities also alter pollinator-plant interactions. Heavy metal contamination impacts the quality of nectar and thus the growth, reproduction and survival of plants and their pollinators. Over time the hostile environmental conditions may lead to a plant population with more stress tolerant traits, but abiotic stressors could also decrease the functional diversity of plants, disrupting the ecosystems. Microbial soil and tree biodiversity loss from mining has been remedied by liming and phytoremediation technology; which has a significant improvement to soil microbial biomass. Organic matter also plays a significant role in alleviating negative metal contamination effects.
Urbanization and agriculture
Urbanization fragments habitats into roads, cities, and infrastructure development. This displaces wildlife and exposes forests to human disturbances. Likewise, agricultural activities transform forests into farmland and monocultures, This impacts forest ecology by altering nutrient cycles degrading ecosystem health.
Approaches
thumb|right|[[Sequoia sempervirens|Redwood tree in northern California forest, where many trees are managed for preservation and longevity]]
Forests are studied at a number of organizational levels, from the individual organism to the ecosystem. However, as the term forest connotes an area inhabited by more than one organism, forest ecology most often concentrates on the level of the population, community or ecosystem. Logically, trees are an important component of forest research, but the wide variety of other life forms and abiotic components in most forests means that other elements, such as wildlife or soil nutrients, are also crucial components.
Forest ecology shares characteristics and methodological approaches with other areas of terrestrial plant ecology, however, the presence of trees makes forest ecosystems and their study unique in numerous ways due to the potential for a wide variety of forest structures created by the uniquely large size and height of trees compared with other terrestrial plants.
The emergence of machine learning(ML) has allowed for new methods of approaching forest ecology, as it can process larger and more complex data. Since the 1990s, machine learning is increasingly used to improve the accuracy of species distribution models, predict carbon flux, and in hazard assessment procedures. Drones are also heavily used in forest ecology research. The use of drones allows for easier mapping of forest landscapes, and surveying large sections of land. Using drones, information such as tree height, diameter, species, and plant stress can be acquired with fewer expensive, labour intensive methods. They also aid in the identification of wildfires, especially when drones are equipped with thermal cameras.
Climate Change and Carbon Cycling
Climate change has an effect on forests from wildfires, droughts, soil erosion, and heat stress effects on vegetation. The world resource institute summarizes the IPCC AR6 report and anthropogenic effects on global warming. The IPCC covers carbon removal and reforestation; loss of vegetation impacts carbon cycling, and these effects can vary among canopy structures .
Forest pathology
Community diversity and complexity
thumb|upright=1.35|Overall decline in a forest-specialist index for 268 forest vertebrate species (455 populations), 1970–2014, from the [[Food and Agriculture Organization publication The State of the World's Forests 2020. Forests, biodiversity and people – In brief]]
Since trees can grow larger than other plant life-forms, there is the potential for a wide variety of forest structures (or physiognomies). The infinite number of possible spatial arrangements of trees of varying size and species makes for a highly intricate and diverse micro-environment in which environmental variables such as solar radiation, temperature, relative humidity, and wind speed can vary considerably over large and small distances. In addition, an important proportion of a forest ecosystem's biomass is often underground, where soil structure, water quality and quantity, and levels of various soil nutrients can vary greatly. Thus, forests are often highly heterogeneous environments compared to other terrestrial plant communities. This heterogeneity in turn can enable great biodiversity of species of both plants and animals. Some structures, such as tree ferns may be keystone species for a diverse range of other species.
A number of factors within the forest affect biodiversity; primary factors enhancing wildlife abundance and biodiversity was the presence of diverse tree species within the forest and the absence of even aged timber management. For example, the wild turkey thrives when uneven heights and canopy variations exist and its numbers are diminished by even aged timber management.
Forest management techniques that mimic natural disturbance events (variable retention forestry) can allow community diversity to recover rapidly for a variety of groups, including beetles.
Types of forest ecosystems
Boreal forests
The boreal forest, also referred to as the taiga is found at high polar latitudes around the globe. As one of the largest biomes, the taiga provides an exceptional amount of value to human populations including lumber and paper production. Dominant tree species is influenced by lumbering activities within plots of the boreal forest however, the most significant factor in forest composition is wildfires. Dominant boreal conifers include fir, pines and spruce dependent on the time elapsed since the last wildfire. Deciduous trees play an important role in boreal forests, mainly as successional species. Parts of the boreal forest are of mixed wood composition or entirely deciduous however these plots are only frequent at the southern border of the taiga. Common Deciduous species include birch, aspen, alder and willow. These species can sometimes be found in old growth coniferous forests as snags or stunted specimens of a transitional stage.
Temperate forests
Temperate forests account for nearly 25% of forest habitats. The temperate zone is generally attributed to latitudes between tropical and polar regions however, forests in these zones can have significant differences in weather. Temperate forests vary depending on the climate of the region, they can be coniferous, deciduous or mixed in composition. Regardless of composition, plant species have adapted to the constraints of the temperate zone, most notably drought. Unlike tropical environments, water is not consistently available in temperate forests and is dependent on annual weather trends. A common adaptation involves highly responsive stomata that are able to rapidly respond to dry conditions, preventing water loss. Variable leaf budding in deciduous species is another common trait that allows plants to avoid freezing conditions based on yearly weather opposed to an average climate. Water scarcity is not a factor in temperate rainforests, a biome that typically occurs along the west coast of the Americas, and Australasia, though other instances exist. This biome is characterized by cool and wet conditions, where precipitation may be rain snow or sleet. They have lower evaporation rates compared to tropical rainforests. Temperate rainforests in the northern hemisphere are generally dominated by conifers as opposed to broad-leafed species, and support many lichens.
Tropical forests
thumb|Paca the South American rodent species that has shared features with the African chevrotain due to convergent evolution.
thumb|The African chevrotain an ungulate that shares convergently evolved features with the South American paca.
Tropical forests are some of the most diverse ecosystems in the world. Although there are many different tree species present per acre of forest, many share similar appearances due to the similar environmental pressures. Some of these shared traits, possessed by many tropical trees, include thick and leathery leaves that are elongated and ovular with mid-ribs and drip-tips.
Mycorrhizal symbiosis
thumb|The benefits of mycorrhizal fungi interacting with plant roots to improve nutrient absorption among other benefits compared to a plant without this symbiotic relationship.
An important interaction in forest ecosystems is the mycorrhizal network, which consists of fungi and plants that share symbiotic relationships. Mycorrhizal networks have been shown to increase the uptake of important nutrients, especially ones which disperse slowly into the soil like phosphorus. The fine hypha of the mycelium is able to reach farther into the soil than the roots of the plant, allowing it to better access phosphorus and water. These interactions can help provide drought resistance to their symbiotic plants, helping protect them through the progression of climate change. He takes three groups of parameters:
- Related to site requirements: Tolerance to low temperatures, tolerance to dry climate, frugality.
- Specific qualities: Shade tolerance, height growth, stability, longevity, regeneration capacity.
- Specific risks: Resistance to late freezing, resistance to wind/ice storm, resistance to fire, resistance to biotic agents.
Every parameter is scored between 0 and 5 for each considered species, and then a global mean value calculated. A value above 3.5 is considered high, below 3.0 low, and intermediate for those in between. In this study Fagus sylvatica has a score of 3.82, Fraxinus excelsior 3.08 and Juglans regia 2.92; and are examples of the three categories.
Competition
Forest ecosystem interactions consist of not only symbiotic relationships, but also competition. Competition can either be in forms of intraspecific or interspecific competition. Intraspecific competition can occur between members of the same species for resources, whereas interspecific competition occurs between different species in a population. For example, in order to fulfil nutritional needs decomposing organic matter in soils is a sought after resource by plants, microbes and fungi. Invasive species in forest ecosystems also play a role in interspecific competition. They often compete with native species for resources and may conquer these resources successfully due to low intraspecific competition. The hemlock woolly adelgid and the emerald ash borer are examples of well known invasive species that colonize an area and create disturbances in forest ecology by killing host trees and reducing forest vegetation.
Matter and energy flows
Energy flux
thumb|upright=1.1|Forest ecologists are interested in the effects of large disturbances, such as [[wildfires. Montana, United States.]]
Forests accumulate large amounts of standing biomass, and many are capable of accumulating it at high rates, i.e. they are highly productive. Such high levels of biomass and tall vertical structures represent large stores of potential energy that can be converted to kinetic energy under the right circumstances.
The world's forests contain about 606 gigatonnes of living biomass (above- and below-ground) and 59 gigatonnes of dead wood.
Two such conversions of great importance are fires and treefalls, both of which radically alter forest structure and ecosystem processes and the physical environment where they occur. Also, in forests of high productivity, the rapid growth of the trees themselves induces biome and environmental changes, although at a slower rate and lower intensity than relatively instantaneous disturbances such as fires.
Water
Forest trees store large amounts of water because of their large size and anatomical/physiological characteristics. They are therefore important regulators of hydrological processes, especially those involving groundwater hydrology and local evaporation and rainfall/snowfall patterns.
An estimated 399 million ha of forest is designated primarily for the protection of soil and water, an increase of 119 million ha since 1990. Trees growing in arid and/or cold environments do so especially slowly. Thus, tree trunks and branches can remain on the forest floor for long periods, affecting such things as wildlife habitat, fire behaviour, and tree regeneration processes.
Some trees leave behind eerie skeletons after death. In reality these deaths are actually very few compared to the amount of tree deaths that go unnoticed. Thousands of seedlings can be produced from a single tree but only a few can actually grow to maturity. Most of those deaths are caused from competition for light, water, or soil nutrients, this is called natural thinning. Singular deaths caused by natural thinning go unnoticed, but many deaths can help form forest ecosystems.