Tree ecology
Trees are an important part of the terrestrial ecosystem,[86] providing essential habitat for a community of organisms. Epiphytic plants such as ferns, some mosses, liverworts, orchids and some species of parasitic plants (e.g., mistletoe) hang from branches; these along with arboreal lichens, algae, and fungi provide micro-habitats for themselves and for other organisms, including animals. Leaves, flowers and fruits are seasonally available. On the ground underneath trees there is shade, and often there is undergrowth, leaf litter, fallen branches and/or decaying wood that provide other habitat. Trees stabilise the soil, prevent rapid run-off of rain water, help prevent desertification, have a role in climate control and help in the maintenance of biodiversity and ecosystem balance.[87] Many species of tree support their own specialised invertebrates. In their natural habitats, 284 different species of insect have been found on the English oak (Quercus robur) [88] and 306 species of invertebrate on the Tasmanian oak (Eucalyptus obliqua).[89] Non-native tree species provide a less biodiverse community, for example in the United Kingdom the sycamore (Acer pseudoplatanus), which originates from southern Europe, has few associated invertebrate species, though its base rich bark[clarification needed] does support a wide range of lichens, bryophytes and epiphytes.[90] Trees can play a role in the development of an ecosystem,[clarification needed] for example in mangrove swamps the roots of the mangrove trees reduce the speed of flow of tidal currents and hence trap water-borne sediment, leading over time to a reduction in water depth and the creation of suitable conditions for further mangrove colonisation. Thus mangrove swamps tend to extend seawards in suitable locations.[91] Mangrove swamps also provide an effective buffer against the more damaging effects of cyclones and tsunamis. An ecosystem is a community of living organisms (plants, animals and microbes) in conjunction with the nonliving components of their environment (things like air, water and mineral soil), interacting as a system.[2] These components are regarded as linked together through nutrient cycles and energy flows.[3] As ecosystems are defined by the network of interactions among organisms, and between organisms and their environment,[4] they can come in any size but usually encompass specific, limited spaces[5] (although some scientists say that the entire planet is an ecosystem).[6] Energy, water, nitrogen and soil minerals are other essential abio ic components of an ecosystem. The energy that flows through ecosystems is obtained primarily from the sun. It generally enters the system through photosynthesis, a process that also captures carbon from the atmosphere. By feeding on plants and on one another, animals play an important role in the movement of matter and energy through the system. They also influence the quantity of plant and microbial biomass present. By breaking down dead organic matter, decomposers release carbon back to the atmosphere and facilitate nutrient cycling by converting nutrients stored in dead biomass back to a form that can be readily used by plants and other microbes.[7] Ecosystems are controlled both by external and internal factors. External factors such as climate, the parent material which forms the soil and topography, control the overall structure of an ecosystem and the way things work within it, but are not themselves influenced by the ecosystem.[8] Other external factors include time and potential biota. Ecosystems are dynamic entities—invariably, they are subject to periodic disturbances and are in the process of recovering from some past disturbance.[9] Ecosystems in similar environments that are located in different parts of the world can end up doing things very differently simply because they have different pools of species present.[8] The introduction of non-native species can cause substantial shifts in ecosystem function. Internal factors not only control ecosystem processes but are also controlled by them and are often subject to feedback loops.[8] While the resource inputs are generally controlled by external processes like climate and parent material, the availability of these resources within the ecosystem is controlled by internal factors like decomposition, root competition or shading.[8] Other internal factors include disturbance, succession and the types of species present. Although humans exist and operate within ecosystems, their cumulative effects are large enough to influence external factors like climate.[8] Biodiversity affects ecosystem function, as do the processes of disturbance and succession. Ecosystems provide a variety of goods and services upon which people depend; the principles of ecosystem management suggest that rather than managing individual species, natural resources should be managed at the level of the ecosystem itself. Classifying ecosystems into ecologically homogeneous units is an important step towards effective ecosystem management, but there is no single, agreed-upon way to do this.