GEOGRAPHY 4371: FOREST GEOGRAPHY
I. INTRODUCTION
Note: Read chapters 2 and 3 of Kimmins (2004).
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).
I.A. Brief overview of silviculture
Silviculture is the theory and practice of controlling forest establishment, composition
and growth. It is the manipulation of forests to enhance certain forest values or
products.
Two extremes of silviculture are:
1. Arboriculture is intensive management of planted forests.
2. Naturalistic silviculture is the manipulation of natural processes of stand
dynamics.
A silvicultural system is a long range harvest and management scheme designed
to optimize growth, regeneration and other forest values (e.g. wood quality, tree health,
wildife habitat, watershed protection, etc.). In practice, silvicultural systems are largely
harvesting systems.
Harvesting or silvicultural systems are appropriate for two different types of forest
structure determined by the regeneration ecology of the tree species. These two types
of forest structure are:
a. Even-aged--trees of the same age, shade-intolerant, dependent on large-scale
openings for regeneration.
b. Uneven-aged-- trees of different ages, shade-tolerant, not dependent on large
openings for regeneration.
Even-aged methods include:
1. Clearcutting and patch cutting.
2. Seed tree method.
3. Shelterwood.
4. Coppice method.
Uneven-aged methods include:
1. Single-tree selection.
2. Group selection.
II. Introduction to ecosystem-based management
Definitions of “ecosystem-based” or “ecosystem management” vary widely and will be
discussed later in the course. Initially, we will adopt the following definition:
Ecosystem management “… is management that acknowledges the importance of
human needs while at the same time confronting the reality that the capacity of our
world to meet those needs in perpetuity has limits and depends on the functioning of
ecosystems.” — Christensen et al. 1996 (Ecological Society of America).
.
Guiding Principles of Ecosystem Management:
1. Intergenerational sustainability
2. Explicit goals
3. Sound ecological models and understanding
4. Ecosystem complexity and connectedness
5. Recognition of the dynamic character of ecosystems
6. Context and scale
7. Humans as ecosystem components
8. Adaptability and accountability
Historic Range of Variability (HRV) of Ecosystems
What is HRV and what is its role in ecosystem-based management?
For resource managers, it is important to know the range of critical ecological
processes and conditions that have characterized particular ecosystems over specified time
periods and under varying degrees of human influences. An understanding of how
ecosystems functioned and sustained themselves in the absence of major human
modification of ecological patterns and processes provides a concrete model of ecosystem
integrity.
As a practical matter, understanding of natural variability in ecosystem conditions and
processes provides operational flexibility for management actions and protocols.
Incorporating historical ecosystem patterns into management goals provides a coarse-filter
strategy for dealing with sustainability of diverse and often unknown species requirements.
Managing within boundaries of site variability and history is also probably easier and less
expensive to achieve than trying to manage outside of constraints imposed by driving
factors of the system. Historical patterns of ecosystem conditions provide what may be the
only viable model for how ecosystems have evolved and perpetuated themselves in the
absence of significant human impacts.
Some key HRV issues for discussion
1. What are equilibrium versus non-equilibrium views of ecosystems?
2. What is the appropriate time period for describing “reference conditions” of
forests in Colorado?
3. How have climatic variation and impacts of Native Americans affected the HRV
of forests in Colorado?
4. To what extent can and do modern forest management practices mimic natural
disturbances?
5. What is a “healthy forest”? What are suitable measures of forest health?