Forest Ecology

Population

a group of organisms of the same species occupying a particular space at a particular time

Albedo:

the reflective nature of surfaces; Light Coloured Soils - reflect a lot of radiation and therefore have a High Albedo. Dark Coloured Soils - absorb lots of radiation (reflect little radiation) and therefore have a Low Albedo

subdivisions of ecology

Autecology: The life history and response of an organism to its environment (i.e. silvics). Population Ecology: The study of the abundance, distribution, productivity and dynamics of a single species. Community Ecology: The study of the assemblage of different species. Ecosystem Ecology: The study of both the biotic community and it's abiotic environment and their interactions. Ecophysiology: The study of how plants grow in their natural environment. Landscape Ecology: The study of ecosystems across landscapes.

Sources of Energy:

Autotrophs (producers): - plants (photoautotrophs) - some bacteria (chemoautotrophs) Heterotrophs (consumers): - herbivores - carnivores - omnivores - saprotrophs (decomposers)

*

By far the nutrient "bank" and the availability of nutrients are the most easily changed by management practices. e.g. - harvesting methods - manipulation of species composition - burning - fertilization

ecology

The focus is on the interrelationships between the living (biotic) and the non-living (abiotic) environment.

carbon...

Carbon enters the biogeochemical cycle primarily as gaseous CO2 (via photosynthesis). 6CO2 + 6H2O + light energy = C6H12O6 + 6O2 Carbon is lost from plants as respiratory CO2. Carbon is also "returned" back into the atmosphere as methane gas (CH4). Carbon fixed in "permanent" plant structures (i.e. wood of trees) will remain in an ecosystem for a longer period of time (i.e. "old-growth forest").

Types of Nutrient Cycling

Geochemical Cycle (between ecosystems) Biogeochemical Cycle (within an ecosystem) Biochemical Cycle or Internal Cycle (within an organism)

nitrifcation

"the conversion of nitrogen in ammonia into nitrites and nitrates by the oxidizing action of nitrobacteria"

Ecosystem Stability

'the tendency of a system to remain in its present condition or return to that condition following a disturbance. However, the term stability has many meanings. The following is a partial list of different types of stability: - -Constancy - Inertia or Resilience - Elasticity - Amplitude - Cyclic stability - Trajectory stability

lithosere

(ecological succession originating on bare rock).

halosere

(ecological succession within saline habitats; i.e. salt ponds within semi arid climates).

psammosere

(ecological succession within sand environments; i.e. sand dunes).

The Characteristic Features of Cold Climates

(i) Temperature (air and soil) - Very low temperatures during the winter months. - Summer temperatures are usually low as well. (ii) Water relations - Plants are subjected to summer drought conditions due to: - Frozen soil moisture - unavailable for plant uptake. - Low precipitation - many cold climates are desert like. - High transpiration rates caused by high winds. - Direct sublimation of snow into the dry air. (iii) Persistent high winds (iv) Inorganic nutrition - Low supply of inorganic nitrogen. (v) Frost heaving (mechanical effects) - May cause the uprooting of plants. (vi) Reproductive problems - Scarcity of insects.

nudum stage

***stage before old growth forests dominate

• Stand models

- Builds upon the Markov models but with greater detail. These models may include descriptions of: - seed supply - growth rates - competition for: - moisture - nutrients - light - spatial distribution - structure

c) Biomes

- Characteristic bands of vegetation that occur along altitudinal and latitudinal temperature gradients.

Relay Floristics

- Described as waves of plants successively colonizing, occupying an area and eventually being replaced by the subsequent wave of new species (may be an important mechanism in primary succession as well as in xerarch and hydrarch succession). - The idea is that plants of subsequent stages cannot occupy a site until the previous stage of vegetation has altered a site for the next stage.

secondary succession

- Ecosystem development in environments that have been modified by living organism (i.e. post clearcutting or post wildfire).

• Climax pattern hypothesis

- Idea of vegetation as a complex pattern of integrating communities (as opposed to a mosaic

• Polyclimax theory

- In any one geographical area there may be many factors which will prevent an area from reaching the climatic climax condition: i.e. - fire (pyral climax) - soil conditions (edaphic climax) - animals (biotic climax) - Therefore, the vegetation of a region is viewed as a mosaic of communities at different stages of succession.

Distribution Limitations of Organisms: Cold environments

- Low winter temperatures - can determine the upper (elevation) and poleward limits of a species, - severe (cold) temperatures during early fall and late spring. - Low summer temperatures - short growing season - lack of enough gross photosynthesis.

g) Autogenic succession

- Plants can change their environment to such a point that the environment becomes unfavourable (or less favourable) to them and more favourable to the species that replace them.

b) Primary succession

- Primary succession is the development of ecosystems within environments that lack organic matter or put more simply, environments that have not been altered by living organisms (i.e. fresh landslides or post glaciation).

a) Sere

- Product of succession - characteristic sequence of biotic communities that successively occupy and replace each other (halosere, psamosre, etc.).

Initial floristics

- Representatives of various seral stages are always present (may be important in mesarch and secondary succession).

• Markov models

- Stochastic (random) processes of plant replacement (i.e. the use of probability in species replacement).

biogenic succession

- The influence of animals on succession (i.e. high grazing pressure by certain animals will maintain grasslands or meadow environments).

• Monoclimax theory

- The monoclimax theory states that the climax community of all seres (i.e. xerosere, mesosere, hydrosere) is determined by the regional macroclimate. - This is also referred to as ecological or successional convergence. We rarely see this occurring mainly due to the frequency of disturbances across the landscape.

f) Seral stage

- The various communities that make up a sere.

Distribution Limitations of Organisms: Temperate Environments

- high summer temperatures, - lack of winter chilling period

fecundity

- maximum potential rate (i.e. humans have a fecundity of one birth per 9-10 months

types of succession based on nutrient availability:

- oligotrophic succession (succession within nutrient poor environments). - mesotrophic succession (succession within nutrient medium environments). - eutrophic succession (succession within nutrient rich environments).

Logistic growth

- populations do not increase indefinitely - they are limited by environmental resistance. - This type of growth has an S or sigmoidal shape. Curve can be described as: Nt = K 1 + e a - r·t

Regulation of Population Size: "• Natality"

- process of producing new individuals - a function of fertility (i.e. # offspring/female/time) or fecundity

objectives for maintaining biodiversity within the units may be set for the following characteristics:

- seral stage distribution - temporal and spatial distribution of the cut and leave area patch size distribution - old seral retention and representativeness - landscape connectivity - stand structure - species composition.

The following is a partial list of different types of stability:

-Constancy - Inertia or Resilience - Elasticity - Amplitude - Cyclic stability - Trajectory stability

allogenic succession

-The change in the biota is influenced by changes in the physical environment by geological processes (i.e. the filling in of a lake with sediment).

f) Intraspecific competition

...

g) Carrying capacity

...

h) Carrying capacity

...

Attributes of Ecosystems

1) Structure. 2) Function - exchange of matter and energy between the non-living and living community. 3)Complexity - multiply determined. 4) Interaction and interdependency. 5) Spatial boundaries not defined. 6) Change over time - ecosystems are not static

Nitrogen Cycle - Consists of 6 major processes:

1. Nitrogen fixation 2. Ammonium assimilation 3. Ammonification 4. Nitrification 5. Nitrate reduction 6. Denitrification

LAR

Leaf Area Ratio (cm2g-1) - Leaf area per weight of whole plant. Measurement of how much leaf there is.

LWR

Leaf Weight Ratio (gg-1) - Ratio of leaf weight to total plant weight.

Example of specific functions of some nutrients within plants:

N (nitrogen) - chlorophyll; photosynthesis - proteins P (phosphorus) - membranes - ATP synthesis Fe (iron) - photosynthesis Mg (magnesium) - part of the chlorophyll molecule; photosynthesis B (boron) - membrane integrity Zn - enzyme component

Five natural disturbance types (NDTs):

NDT1 - Ecosystems with rare stand-initiating events NDT2 - Ecosystems with infrequent stand-initiating events NDT3 - Ecosystems with frequent stand-initiating events NDT4 - Ecosystems with frequent stand-maintaining fires NDT5 - Alpine Tundra and Subalpine Parkland ecosystems

Geometric growth: can be described as:

Nt +1 = Ro·Nt Nt = population size at generation t Nt +1 = population size in the subsequent generation Ro = net reproductive rate

Life Zones

Regions they (biomes) occupy.

SLA

Specific Leaf Area (cm2g-1) - Ratio of leaf area to leaf weight. SLA is a much more variable parameter (i.e. leaf area is more plastic than leaf weight) and therefore is a better morphological indicator of plant response to low light conditions.

• Succession

The process of change over time. Within ecology, succession refers to changes within both the biotic and abiotic environment over some time period.

• Cardinal Temperature

There are three basic cardinal temperatures which affect plants: Minimum - Minimum temperature at which growth ceases entirely. Maximum - Maximum temperature at which growth ceases entirely. Optimum - Range of temperatures over which the highest growth rate can be maintained.

Survivorship Curves:

Type I - Low mortality until the end of the physiological life span (i.e. humans). Type II: - Mortality is constant per unit time (i.e. birds). Type III: - Constant percentage of the survivors die in each time interval (i.e. fish and maritime invertebrates). Type IV: - High juvenile mortality. (i.e. insects, plants).

h) Ecosystem

a unit or portion of the landscape and the life on and in it, which is relatively uniform in the composition, structure and the properties of both the biotic and abiotic environments, and in their interactions over time

Leaf Area Index (LAI)

area of foliage projected per area of ground surface (m2/m2). Most terrestrial ecosystems have an LAI of between 1 and 6.

disclimax

communities are maintained at an early stage by biotic factors (i.e. animals).

Mechanisms of Successional Change

i) Colonization - this will depend on invasion and survival. - In 1954, F.E. Egler proposed two major patterns of plant succession; Relay Floristics & Initial Floristics ii) Alteration of the environment - Species will eventually alter their environment to a point where it is unsuitable for their offspring (i.e. post glaciation).

biodiversity

is the diversity of plants, animals and other living organisms in all their forms and levels of organization, and includes the diversity of genes, species and ecosystems, as well as the evolutionary and functional processes that link them."

Population ecology

is the study of the abundance and dynamics of species populations.

direct nutrient cycling

litter is rapidly invaded by the mycelium of mycorrhizal fungi, - start decomposing the fresh litter. Results in nutrients never entering into soil solution, - eliminates (or greatly reduces) nutrient loss via leaching. A very efficient method of conserving nutrients within an ecosystem. Direct nutrient cycling is important in areas with nutrient poor soils, - i.e. some tropical forests

K - strategist

produce few offspring - A function of: - predictable environment

• r - strategist

produce large numbers of offspring. - A function of: - unpredictable environment - high mortality

i) Specific Leaf Area

ratio of leaf area to leaf weight cm2/g

provenance

refers to the geographical location in which the genotype has evolved

sereclimax

succession is arrested at an early stage

subclimax

succession is delayed (i.e. fire, wind, human disturbance - timber management).

the bacteria Rhizobium forms root nodules on leguminous plants for n-fixation

the bacteria Rhizobium forms root nodules on leguminous plants for n-fixation

Succession and Ecological Rotation

the time taken for an ecosystem to recover to its pre-disturbance condition after a some disturbance. This will depend, in part, on: - Type of disturbance (i.e. clearcut, fire, wind throw, etc.). - Intensity of disturbance (i.e. hot fire vs. a cool fire, severe soil compaction vs. minimal soil disturbance, etc.). - Extent of disturbance.

Advantages and Disadvantages of Aggregation

• Advantages - protection - reproduction - genetic diversity - intraspecific competition (i.e. selection of the fittest) • Disadvantages - intraspecific competition (members of the same species tend to compete for the same resources) - alteration of the environment (i.e. overgrazing can result in an overall shortage of food for a population) - disease transmission i.e. Mountain Pine Beetle

Rates of Successional Change depend on:

• Climate and soil condition. • The degree of environmental change that must occur before one community is replaced by another (i.e. xerarch succession). • The productivity and efficiency of the organism (i.e. thallophytes vs. herbs and shrubs). • The longevity of the organism dominating each seral stage. • The degree to which communities resist invasion by other species. • Frequency and severity of disturbance.

Population Growth

• Geometric growth - Often defined as the increase (or decrease) in a population in which the growth increment is proportional to the original number of individuals (

In nature, populations rarely reach and maintain a level near the carrying capacity. Why?

• Lack of response to K (carrying capacity) - for some species, there is little evidence to suggest that the growth rate of a population decreases as density (N) increases. • Reduction of K by high population density (i.e. overgrazing). • Time lags

Factors determining clumping:

• Seed dispersal - This may be due to wind action or by animals storing seed for future use. • Reproduction - Some species produce seed or propagules which fall near the parent plant. • Physical environment - i.e. proper seed bed. • Modification of the environment • Biotic factors - i.e. the elimination of certain plants from grassland ecosystems due to grazing by animals.

Types of Succession

• Xerarch succession - Succession in a (very) dry environment. • Mesarch succession - Succession in a moist environment. • Hydrarch succession - Succession in a wet environment. The resulting seres are called: - xeroseres - mesoseres - hydroseres

Reproductive Strategies:

• r - strategist - produce large numbers of offspring. - A function of: - unpredictable environment - high mortality • K - strategist - produce few offspring - A function of: - predictable environment • Mortality • Immigration & Emmigration