FORS 330 - Forest Ecology Final

Janzen - Connell Hypothesis

depends on a special kind of CNDD caused by host specific tree enemies

CNDD (Conspecific Negative Density-Dependent)

When the population growth rate decreases with increasing local population density

Under the Janzen-Connell hypothesis, who experiences more CNDD?

Rare species due to simplification in biodiversity

Trophic Cascades

A situation where predators suppress their herbivore prey, releasing the next lower trophic level (Predators → Herbivores → Food)

Example of Trophic Cascade

Less elk herbivory leads to high levels of aspen shoots

Green World Hypothesis

Idea that predators reduce the abundance of herbivores, allowing plants to flourish

Ecosystem Engineer

Organisms that create, modify, or maintain habitats

Examples of Ecosystem Engineers

Woodpeckers, coral reefs

Symbiosis

A close, long-term interaction between two or more species

Example of Symbiosis

Mycorrhizal fungus and plant root in physical relationship

Mutualism

Symbiotic relationship in which both species benefit (+/+)

Commensalism

Symbiotic relationship in which one species benefits and the other has no cost of the relationship (+/ ..)

Parasitism

Symbiotic relationship in which one species benefits and the other is harmed (+/-)

Epiphytic Plants

Plants grow on surface of another plant

Example of Epiphytic Plants

Mosses, Ferns, Mushrooms

Ectomycorrhiza

Does not penetrate cell wall, penetrates between cells, and forms a mantle sheet [] (happens outside cell wall)

Endomycorrhiza

Fungi penetrates root cell wall

Common Mycorrhizal Networks

Tree A and tree B are integrated by their mycorrhizal fungi, roots are connected through belowground network

Root Nodule

A structure on the root where nitrogen-fixing bacteria live (NOT MYCORRHIZAL)

Biological Nitrogen Fixation

Taking nitrogen from the air and breaking up the triple bond so plants/animals can consume

Nitrogen

Most frequently limiting nutrient in terrestrial ecosystems

Primary Succession

Starting from nothing, forest grows after

Secondary Succession

Following a disturbance, new establishment

Keystone Species

(Rare or uncommon species but take away = ecosystem whole reorganizes) Affects whole ecosystem

Fluvial Wood

Wood in the river

How is fluvial wood deposited?

Input through trees fall, landslides, channel migration, bank erosion

Key Piece

Big enough, not flushed through the system, forming log jams

Woody Debris - Stable Deposition

Piece of wood that’s deposited, unlikely to be moved by river

Woody Debris - Unstable Deposition

Flow has dropped, river can’t move log

What are pathways for internal nutrient cycling?

Through Fall and Stem Flow

Through Fall

Precip goes through canopy

Stem Flow

Precip goes down the stem into the ground

Edaphic Factors and Temperature

Limiting factors on tree establishment and growth on Alpine treeline

Krumholz

trees grow horizontally rather than vertically, forced into shrubby-like growth down, close to the ground

Stress-gradient Hypothesis

Low stress environments - dominant interaction is competition

High stress environments - beneficial interactions become more important