Forest Ecology

INTRODUCTION

Rainforests, semi-arid forests, cold boreal forests, British Columbia has them all and many more. B.C.'s forests have this diversity because the land itself is an assortment of mountains, plateaus and deep river gorges. As the landscape changes from place to place, so does the climate. It is these different climates that have led to the development of so many types of forest ecosystems in British Columbia.

In order to understand these forests, scientists and foresters have to look at all of the parts, from soil to squirrels. Forest ecology is the study of the interactions between the living and non-living parts of a forest ecosystem. That is, the relationship between plants or animals and the climate, topography, soil, and micro-organisms of the surrounding environment.

Forest ecosystems are complex, but we are starting to understand more about how they function. After over 40 years of research in forest ecology in British Columbia, it is now possible to identify and classify the various forest ecosystems found here. This research has also led to a solid understanding of how forest ecosystems work and how they respond to change.

Why is this important to forestry? Every day in B.C., foresters and other land managers make decisions that affect ecosystems. They want to be sure that, in the long term, those decisions are the right ones for both people and forests. Sustainable choices follow or complement the natural processes of each area. Studying nature will help us to design our work to be in harmony with the ecosystem.

By understanding forest ecology and gathering specific ecological information, foresters can make predictions about how different forestry activities will affect each ecosystem. By building this information into a computer modelling system, foresters can run computer simulations to estimate the long term effects of different forestry actions. For example, they can analyse the impact of clearcutting vs. selection harvesting. They are then able to make choices as to the best actions for each specific type of ecosystem.

Forest ecology is the basis for good forest management. The essential elements to examine in exploring how forest management and ecology connect are: ecosystem characteristics, disturbance and succession, and ecosystem classification.

ECOSYSTEM CHARACTERISTICS

There are many types of forest ecosystems. The characteristics that help differentiate one ecosystem from another have to do with both structure and function. "Structure" is the physical nature of the environment such as slope, elevation, and climate, as well as the kind of plants and animals that live there. This, of course, can vary widely and leads to the many types of ecosystems we see here in British Columbia. "Function" is the interaction between the living and non-living parts. This involves energy flow and nutrient cycling. All ecosystems have these processes, although they do vary in speed and efficiency.

Structure

The plant community within the ecosystem has a distinctive vertical structure. Think of the layers you would go through starting with the tallest tree tops and moving down:

• Tree canopy layer
• Shrub canopy layer
• Herb layer
• Moss layer

There may be more than one layer at each level or entire layers may be missing. This variety once again adds to the diversity of forest ecosystems. The structure can also vary as you move across the landscape. For example:

• Is the vertical layering uniform over large areas or is it patchy?
• Are there frequent gaps in the canopy?
• Are there wildlife trees and large logs on the ground?

Certain combinations of these layers can be characteristic for specific ecosystems.

Energy

Green plants play a critical role in fuelling all the processes in an ecosystem. They provide the entrance into the ecosystem for the sun's energy. The process of photosynthesis stores this energy in new plant tissues. Plants in turn become the energy source for the growth of animals. There is less and less energy stored at each level of the food chain because each living thing uses some for its own life processes. This is why we see a decrease in the total mass of organisms at each level of the food chain. The largest mass is at the plant level, a smaller mass of herbivores and the smallest mass at the predator level. For an ecosystem to keep operating, solar energy must be continuously available.

Nutrients

Plants can only capture the sun's energy if they get the proper nutrients. Ecosystems continuously receive and lose nutrients. Plants take in nutrients from the air and the soil, use them for life processes, and then eventually return them during respiration or when the plants decay. Some nutrients will be washed out of the ecosystem by rain, but most will be recycled many times. The speed at which nutrients circulate in a forest ecosystem influences the rate of plant growth. The slower the cycling, the slower the growth. The efficiency of this cycling will also determine how quickly an ecosystem can "bounce back" after logging, fire or other disturbances.

Link to Forestry

The nature of the structure, energy flow and nutrient cycling found in an ecosystem will produce a set of characteristics that controls what species of plants and animals will be found there. Plants themselves can be very selective about where they grow. The very presence of some plants tells a great deal about the characteristics of that ecosystem. These "indicator" plants only grow where there are specific levels of soil nutrients, soil moisture, light, elevation and a particular climate. The direct link between ecosystem characteristics and indicator plants can be used as a very useful tool for forestry. A quick look at the species present will produce a wealth of information about the ecosystem characteristics.

The set of characteristics that make an ecosystem unique is also the basis for decisions about forest management.

Examples:

The structure of the plant community can affect the choice of forestry activities:

• a multi-layered tree canopy, indicating an uneven aged stand, is suited to a selection harvest system.
• If the forest has fast nutrient cycling, weeds will probably be a problem for reforestation.

One option is to plant large sized seedlings quickly after logging.

Foresters use the solar energy in the ecosystem to produce the kind of plants and plant structure preferred.

Examples:

• If the goal is wood production, the forester will divert a larger portion of the solar energy into tree production through such actions as weeding or stand tending.
• If the goal is wildlife management, the forester will divert more energy into shrubs for animal browsing through such actions as pruning and selection harvest.

The ability of a forest to recover after a disturbance such as fire or harvesting activities is due to these energy and nutrient processes as well. Understanding the sensitivity of a specific forest ecosystem to disturbance is critical when making decisions as to what kind of harvest system to use and how often to use it. Clearly, forest ecology is central to sustainable forest management.

DISTURBANCE AND SUCCESSION

All ecosystems change constantly: nutrients are cycling, plants and animals are growing, dying and new generations are being started. Periodically, the changes to ecosystems can be more dramatic due to disturbances from fire, windstorms, floods, diseases or insects.

The history of disturbance varies for different forest ecosystems. Some ecosystems are affected frequently while others have had few large-scale changes. Disturbances change the forest's structure and dynamics temporarily. Given enough time before the next disturbance, an ecosystem will return to its previous condition. This process of recovery is called ecological succession. Succession produces a series of living communities, one gradually replacing another, until a stable self-replacing community called the "climax" condition is reached. A typical progression of sucessional stages would be:

herb/grasses > sun loving shrubs > sun loving trees > shade loving trees (climax)

All disturbances, whether human or natural, affect the ecosystem characteristics of the forest.

These charateristics include:

• structure
• level of photosynthesis,
• nutrient cycling,
• microclimate,
• soil,
• plants, animals and microbial life.

All disturbances initiate a new sequence of succession. Different disturbances such as fire or clearcut logging will lead to initial differences in the successional patterns. However, given enough time, these differences diminish as succession returns the forest to its pre-disturbance condition. Forest ecosystems overall are very resilient.

Links to Forestry

Foresters manage succession. They move succession back with harvest and then speed it up by planting and stand tending (weeding, fertilizing, thinning, etc.). By understanding how each ecosystem will react to disturbance, the forester can predict the response to a planned disturbance. Understanding how the ecosystem will respond leads to selecting the type of logging, the size of the blocks and frequency of harvest that will be sustainable for each specific ecosystem.

ECOSYSTEM CLASSIFICATION

In order to make good management decisions based on ecosystem principles, we need to to be able to predict how forests will respond to different management practices. To make these predictions we need to be able to identify and classify the forest landscape. The ecosystem characteristics and responses to disturbance produce identifiable qualities that can be used in a classification system.

Many individual ecosystems occur within a forest. We group those ecosystems that have similar vegetation and soil characteristics. Grouped ecosystems usually occupy similar places in the landscape. We expect that these ecosystems will respond to the same forestry treatment in the same way. Because there are sites with recurring properties and predictable "behavior," the development of a classification system for British Columbia was possible. This tool is the Biogeoclimatic System of Ecosystem Classification. The classification system assists managers in making management decisions and provides a common language in assessing forest sites.

Climate is the principle factor influencing ecosystem development in BC. The Biogeoclimatic system divides the province into 14 broad climatically distinct zones. Within these zones, ecosystems vary because of differences in topography and soil. Vegetation patterns will reflect these physical differences. So, by identifying some key indicator plants and gathering some basic information about the soil, a forester can use the classification system to identify an ecosystem quickly. Once identified, the accumulated data about that particular ecosystem, its characteristics, its disturbance history and its responses to management practices, are available to the forester to aid in decision making.

To see the 14 zones, we have provided links to the B.C. Forest Service Research Branch's maps.

Links to Forestry

The ecological classification system is the basis for selecting the following forestry options:

• species for reforestation
• harvest methods
• site preparation methods
• stand tending methods
• rotation length

Ecosystem classification is a tool that uses the accumulated knowledge of ecosystem characteristics and responses to disturbance to predict the best management option for each individual forest stand.

FORESTRY ECOLOGY SUMMARY

Forest ecology is the basis for good forest management. If the goal is to manage a forest ecosystem to produce products such as timber, water, viewscapes and wildlife habitat, then it is essential to have an understanding of how the living and non-living components of that ecosystem interact.

All events occurring in the woods, from logging to camping, have some kind of an effect on the forest ecosystem. To design forestry activities to function with the natural ecosystem processes is part of what sustainable forestry is all about. Ecosystem characteristics and their responses to disturbance are used as the basis for a classification tool that helps to connect forestry decisions to the ecosystem.

Forest ecology provides a critical base of understanding for the land manager. However, due to the complex nature of ecosystems, our knowledge is incomplete. To improve the knowledge base, more research into ecological processes is required. Another essential factor is the gathering of ecological inventory information. As improvements are made in understanding ecological processes and as more complete data is gathered in the forest, the predictions forest managers make will be more accurate, resulting in better management decisions.

References:

Balancing Act - Environmental Issues in Forestry. Hamish Kimmins UBC Press 1992 Biogeoclimatic Zones of British Columbia (map). Province of British Columbia 1988 Biology. L Johnson 1983 WC Brown Publishers Field Guide For Site Interpretation for the Vancouver Region. Land Management Handbook 28, 1994 Forestry Handbook for B.C. The Forest Club UBC 1971 Indicator Plants of Coastal B.C. K. Klinka 1989 Government of Canada, Province of B.C. Investigating Terrestrial Ecosystems. W. Andrews. 1986 Prentice Hall