FOREST DYNAMICS: THE BACKGROUND AND THE APPROACH

Goal: to place the content and approach of this course into the broader contexts of ecology and vegetation science.

The subject matter of Ecology includes:

1. individual organisms in relation to other organisms and the nonliving (abiotic) environment;

2. groups of organisms of the same species (populations);

3. natural assemblages of populations of different species (communities);

4. entire natural systems composed of communities and their physical environment (ecosystems).

SUBDIVISIONS OF ECOLOGY (with particular reference to forest ecology)

1. Autecology

Plant autecology is the study of the influence of the environment on a single individual or species. It is concerned with explaining environmental controls on a species distribution by considering physiological, phenological and genetic traits that allow a species to be successful in a particular habitat. (Phenology = the timing of behavior in relation to environmental cues; for example, timing of pollination, flowering, seed dispersal, leaf growth, stem growth, etc.)

Subdivisions of autecology include evolutionary ecology (genecology, demecology), population ecology (plant demography), and physiological ecology (ecophysiology).

2. Synecology

Plant synecology is the study of plant communities and the interaction of the organisms which compose them.

Approximate synonyms for synecology include Vegetation Science and Vegetation Ecology.

Non-mutually exclusive approaches to synecology include:

a. Phytosociology, geobotany, plant community description and classification.

b. Paleoecology.

c. Plant geography, vegetation geography.

d. Community dynamics (emphasized in this course)

3. Ecosystem ecology

An ecosystem includes "not only the organism-complex, but the whole complex of physical factors forming what we call the environment." (A. Tansley 1935).

"An ecosystem is a functional system that includes an assemblage of interacting organisms and their environment, which acts on them and on which they act." (R. Whittaker 1962).

Emphasis in an ecosystem approach is on exchange of matter and energy between the physical environment and the living environment.

FOREST DYNAMICS or FOREST STAND DYNAMICS (the emphasis of this course)

"Forest stand dynamics is the study of changes in forest stand structure with time, including stand behavior during and after disturbances" (Oliver and Larson 1990).

A stand is a spatially continuous group of trees and associated plants having a similar structure and growing under similar environmental conditions. Can be any size but must be relatively homogeneous.

Stand structure is the spatial arrangement of and size differentiation (or age differentiation) of plants (but especially trees) within a stand. Can be characterized by tree diameters, ages, heights, crown densities, stem volumes, understory vegetation, etc.

"Disturbances are any relatively discrete events that disrupt the stand structure and/or change resource availability." (Pickett and White 1985). Includes both natural and anthropogenic disturbance, and abiotic and biotic disturbance.

Study of forest dynamics includes both:

a. succession (directional change in species composition), and

b. regeneration dynamics or maintenance dynamics (e.g. changes in population structures occur even though there is no significant change in the species composition).