Forest Ecology

A change in ecosystem structure and function resulting from in following formation of barren land () or a disturbance (___).
Occurs when a community exists and is disrupted by a disturbance, and then replaced by another community type.

Occurs when a community exists and is disrupted by a disturbance, and then replaced by another community type.
Secondary Succession In Abandoned Agricultural Land
Time
- Agricultural land kept in an artificial seral stage
- Crops like wheat act as a grassland
- After being abandoned wild grasses from wind-blown and dormant seed in the ground take over
- With time small shrubs start to colonize the grassland
- Eventually trees establish leading to the development of a climax community on mature soils
A predictable shift in plant community composition following field abandonment, with horseweed (Erigeron canadense) dominating fields one year after abandonment, white aster (Aster pilosis) dominating in year two, and broomsedge (Andropogon virginicus) dominating in year three.

Study of change in forest structure over time, including stand development after disturbance
- Once a forest is established, no plant starts or accelerates growth unless something dies, freeing up resources
  - Space, light, nutrients, water, CO_2
- All silvicultural procedures are in part a simulation of natural processes
- Stand development stages MUST BE RECOGNIZED in order to use silviculture to imitate, guide, or alter natural processes

Natural forest
- Stand initiation stage (Herb/brush stage)
Plantation
- Stand initiation stage
- (Stem exclusion stage) (Understorey reinitiation stage)
Gap dynamics stage
Regeneration by non-clearcutting
Regeneration by clearcutting

Cohort –An aggregation (group) of trees starting as a result of a single (i.e. same) disturbance.
Age Class –A range of tree ages within a stand
- 3 basic age-class defined stand types:
  - Even aged or single cohort
  - Two aged or double-cohort
  - Uneven aged or multiple cohort (3+ age classes)

After sufficient time, the growing space has become occupied, crowns become closed forming a continuous canopy, base of crowns begin to rise up due to death of lower branches due mainly to shading from upper foliage.
More vigorous trees seize the growing space of weaker; weaker trees die from lack of light, moisture, suppression.
Shade-tolerant trees survive
Cover of grasses and herbs mostly shaded out

Trees that have been previously successful in competition with other trees begin to be lost by pests, other damaging agents, cutting operations; crowns do not fully close again.
Gaps created are filled by new plants – shrubs and herbaceous vegetation along with advance regeneration of shade tolerant species – but grow little or slowly.
Total biomass (living + dead) begins to decline from its peak during stem exclusion stage.

Overstory trees die in irregular fashion, some understory or lower canopy trees begin growing into overstory.
Living trees are comprised of a variety of sizes.
Large old snags present, as well as large fallen trees (logs).
Fewer than half of trees in original cohort remain; one or more new age classes (cohorts) compose parts of the top canopy.
Biomass remains fairly constant: fluctuates little around the area mean.
May continue past the death of the last original trees … likely to be unbalanced, production gains = losses to death and decay.

Oak savannah (left) with a sparse oak overstory and lush, herbaceous understory and an oak woodland (right) with a substantial herbaceous ground layer under greater canopy cover

Evaluates the production, transfer, and storage of energy in ecosystems
- “Energy is what life is all about, and everything about life is associated with energy” Kimmins (2004)
- “Energy, ecology, and economics form a single, unified system” H.T. Odum (1973)
What is the ENERGY source in an ecosystem?

Light is the primary source of energy in all ecosystems.
- Photoautotrophs (aka primary producers) – use the process of photosynthesis to capture solar energy and store it in organic molecules (i.e., sugars, carbon).
- Gross Primary Productivity (GPP) is the RATE that expresses photosynthetic carbon production per unit area and time measured at the ecosystem scale.