1. Ecosystems and Silviculture
"Although trees are the most dominate woody vegetation (both visually and in terms of biomass) they represent only a small portion of the total number of species present in the forest. There are thousands, perhaps millions, of different type of plants and animals in the forest. Shrubs, herbs, ferns, mosses, lichens, and fungi are present beneath forest canopy and in the gaps of forest cover. Large animals (such as deer and bear) coexist with smaller birds, insects and tiny micro-organisms. Each component contributes to the flow of energy and materials throughout the system" (Young 1982, 3).
Being terrestrial and highly visible, forests are clearly the most accessible plant community and resource. They provide diverse resources, which are then conceptualized or defined in different ways via science and professional fields that are related to forests.
In botany, the forest is considered as the "main formation of plant communities, where trees are the most dominant species". In ecology, this can be briefly defined "as an ecosystem, where trees are the most significant biotic component". Landscape architecture may regard the forest as a "state of landscape, where trees are the major visible element" and urban planning may see it simply as a "green area characterized by trees". Whatever the scientific or professional description of forests, the role of trees is emphasized and simply put - there cannot be forests without trees.
In forest sciences, the forest in general is seen as "a totality composed of trees and forest land" and in the financial calculation of forest economics the concept of forest refers to "trees and land." Forest economics may also see the forest as an economic resource or "as a property" thus representing a part of capital. Both forest economics and forest policy see forests as natural resources, which can be allocated for different purposes. Forest policy emphasizes the relationship between society and forests.1
Forest ecosystems and related concepts
Ecosystems are communities of plants and animals within a physical environment or habitat characterized by a wide variety of complex interactions and interdependencies. Biological communities compose the living part of the ecosystem and the physical and chemical factors make up the non-living environment. Some examples of ecosystems are: forests, grasslands, estuaries, lakes, and even deserts.
Energy transformation and biogeochemical cycling are the main processes of ecosystems. They link the living, or biotic, components to the non-living, or abiotic, components. The transformation of energy in an ecosystem, such as a forest ecosystem, starts with the input of energy from the sun. Energy from the sun is captured by the process of photosynthesis by green plants. Green plants (i.e.,trees, grasses) are called the "primary producers" since virtually all the energy available to these organisms originates in plants. The "primary consumers" are herbivores (i.e., a moose or insects) obtain their energy by consuming plants or plant products. Carnivores (i.e., birds or wolves) eat herbivores and are called "secondary consumers". Detritivores (i.e., scavengers, crows, and ultimately bacterian and fungi) consume the droppings and the carcasses and are called "decomposers".
The manifold significance of trees is due to their role as the "primary producer" of major photosynthetic plants in the forest ecosystem. This largely defines the characteristics of the structure and functions of the forest ecosystem itself.
Forest ecosystems are also characterized by the same functional processes as other ecosystems. Solar energy is transformed into chemical energy by photosynthesis and it flows through the ecosystem via a food web. Some energy is always lost in each transfer from a higher trophic level via respiration and as heat.
The "internal" processes of forest ecosystems are dynamic and complicated since they occur at different levels. First, there are numerous "individuals" (i.e., trees, other plants, animals, fungi etc..) that each have their own physiology, reproduction and developmental traits. The second level is the "population" of each "individual" species, that includes their habitat, resource needs and population growth. At the "community" level populations of many species interact with one another, even populations of different tree species can compete on space and nutrients.
"Energy flows, elements cycle" is one of the key phrases of ecology.
What are open & closed systems?
During decomposition or mineralization, such elements as carbon, nitrogen, and phosphorus (which have entered living organisms in a variety of ways) are not destroyed or lost. These elements are cycled endlessly between their biotic and abiotic states. The earth as a whole is considered a "closed system" with respect to these elements.
The energy entering this biological system is ultimately converted to heat energy and lost. It cannot be recycled. Without the continued input of solar energy, biological systems would quickly shut down. With regards to energy, the earth is an "open system" and so are single ecosystems such as forests.
The principal energy input does not come from green plants but from dead organic matter (i.e., dead wood or leaves on the forest floor). This is called the "detritus food chain".2
Nutrients are the elements whose supply tends to limit biological activity. The amount and availability of nutrients, water and solar radiation varies greatly from place to place, and causes large differences in the amount of primary production. This variation is particularly seen in the primary production that forests represent.
Biotic and abiotic components
The "living or biotic components" of the forest ecosystem are trees, shrubs, herbs and grasses. Herbivores and carnivores are made up from a wide variety of fauna that range from large mammals to small insects. In the living layers of soil, one can find mushrooms, beetles, worms and microscopic organisms. (Figure F1). Forests are the most complex communities (both with animals and plants on the earth's surface) and they can be briefly defined as ecosystems, where the trees themselves are the most significant biotic component of the system.
Figure F1: The forest ecosystem and its individual components and the environmental factors affecting the ecosystem (Hannelius & Kuusela 1995)
The non-living or abiotic components of the forest ecosystem consist of : solar or radiation energy, macro and microclimates, the water cycle, nutrients and other particles found in the soil and soil parent materials ( i.e., bedrock). The energy that is needed to support the biological production and hydrological cycle of forest ecosystems is obtained from solar radiation. However, only about 2% of this energy is bound in the gross biological production of trees. Half of this is used in respiration and the other half is bound in the biomass as net production. The energy bound in biomass is transferred to other components in the nutrient and food web and through them, gets gradually lost in outer space.
Material elements such as carbon, phosphorus, nitrogen, and potassium are among the nutrients captured by trees and other minor "primary production" plants in the forest ecosystem. These elements are needed for growth and are used by various consuming organisms. In photosynthesis carbon dioxide is combined with hydrogen (derived from the splitting of water molecules) to produce carbohydrates.
Forests influence the micro-climate, wind, soil, stream flow, water quality, fish and wildlife populations. They serve as a critical source of biological diversity on which humankind depends on and will increasingly depend on for a variety of purposes (including food production and the development of new medicines). In other words - the industrial wood that is used for making paper and wood products, the local wood used for farming and construction, and the use of wood for energy will provide a multiplicity of human benefits (including environmental services and natural beauty) that will continue to grow in number and importance.
Our knowledge about forest ecosystems - as a science called forest ecology - provides us with a basic understanding of forests which can be applied to many purposes (such as understanding the protective functions of forests, and the issues related to forest biodiversity or carbon sequestration). Forest ecology provides an important basis for "silviculture" - which is the art and science of maintaining natural forests for wood production and any other purposes. Silviculture also deals with forest plantations. The development of a more productive and sustainable forest plantation, could take on a greater role in world wood supply without compromising environmental impacts (thus easing pressure on natural forests).
Silviculture is the art and science of controlling the establishment, growth, composition, health and quality of forest and woodlands to meet the targeted diverse needs and values of landowners and society on a sustainable basis. (FRA 2005).
2. The ecosystem is composed of many food links and chains (such as the forest that composes the food web).