The Forest Ecosystem – Exam I Study Guide

Vocabulary practice flashcards based on the Exam I Study Guide for The Forest Ecosystem course, covering tree architecture, regeneration mechanisms, plant interactions, stand dynamics, environmental history, and gradient analysis.

Primary growth

Growth originating from apical meristems at buds and root tips that causes elongation of shoots and roots.

Secondary growth

Growth originating from lateral meristems (vascular cambium and cork cambium) that results in the thickening of roots, stems, and branches.

Meristems

Tissues composed of undifferentiated, actively dividing cells that facilitate plant elongation, thickening, and branching.

Primordia

Embryonic tissues within buds that develop into leaves, scales, and shoots.

Fascicle

A bundle of pine needles held together at the base.

Pre-form growth

Fixed or determinate growth where next year's shoot is entirely preformed as primordia in the bud the prior season, reflecting the previous year's environmental conditions.

Neoform growth

Sustained or indeterminate growth where primordia form and expand within the same season, directly reflecting current-year growing conditions.

Recurrent growth

A growth pattern characterized by multiple sequential flushes in a single season from telescoped preformed shoots, producing false growth rings.

Lammas growth

A late-summer second flush of growth originating from buds that would normally remain dormant until the following spring, often leading to a crooked stem.

Apical dominance

The physiological mechanism by which the active shoot tip uses auxin to inhibit the outgrowth of nearby lateral buds along a young shoot.

Apical control

The suppression exerted by the central leader over the subsequent growth and elongation of existing lateral branches across the entire crown.

Excurrent crown

A tree growth form characterized by strong apical control, resulting in a single dominant central leader and a conical crown.

Decurrent crown

A tree growth form characterized by weak apical control, resulting in multiple competing leaders and a broad, rounded crown.

Reaction wood

Specialized wood produced by leaning stems to counteract gravity, formed as compression wood in conifers and tension wood in hardwoods.

Leaf mass per area (LMA)

The ratio of dry leaf mass to leaf area ($\text{g/m}^2$), reflecting a fundamental tradeoff between leaf construction costs and leaf lifespan.

Phenotypic plasticity

The degree to which a single genotype can alter its morphological or physiological traits in response to different environmental conditions.

Fundamental niche

The full theoretical range of physical and environmental conditions in which a species can persist in the absence of competition.

Realized niche

The restricted range of conditions in which a species actually persists after accounting for biological interactions such as competition.

Competitive exclusion principle

The ecological concept stating that two species competing for the exact same limiting resource cannot coexist indefinitely.

Resource partitioning

The differentiation of ecological niches that allows coexisting species to utilize different resources, locations, or time intervals.

Ecological amplitude

The range of environmental conditions along a gradient across which a particular species is capable of surviving and persisting.

Site-sensitive species

A species that grows exceptionally well on high-quality sites but performs very poorly on unproductive or stressful sites.

Growing space

The combination of light, water, nutrients, and physical room accessible to vegetation in an ecosystem, which is vacated by disturbance.

Cohort

An age class of trees that established concurrently following a disturbance event.

Advance regeneration

Seedlings or saplings that establish in the understory under intact canopies and wait to be released by subsequent disturbance.

Soil seed bank

A reserve of viable, dormant seeds stored within the forest floor and mineral soil that germinate when triggered by disturbance.

Serotiny

An ecological adaptation where seed release from cones or fruits is delayed until triggered by an environmental event, typically heat or fire.

Coppice

A silvicultural system where trees are cut near the ground to intentionally stimulate regeneration from dormant stump sprouts.

Genet

A genetically distinct individual originating from sexual reproduction and recombination between two parents.

Ramet

A physiologically independent, vegetatively produced module that is genetically identical to its single parent.

Stand initiation

The first phase of stand development during which newly arriving individuals occupy the available growing space vacated by a disturbance.

Stem exclusion

The second stand development phase where growing space becomes fully utilized, initiating intense competition, canopy differentiation, self-thinning, and preventing new individuals from establishing.

Understory reinitiation

The third stand development phase in which the overstory loses canopy integrity as large trees die, creating gaps that permit a new cohort to establish.

Old growth (phase)

The terminal stage of stand development reached when all trees from the initial post-disturbance cohort have died and been completely replaced by trees that developed beneath them.

Self-thinning

Density-dependent tree mortality driven by competitive exclusion as surviving stems expand, causing population density to decline predictably relative to stem diameter.

Crown differentiation

The vertical divergence of competing trees into distinct canopy classes (emergent, dominant, co-dominant, intermediate, suppressed) during stem exclusion.

Crown shyness

A phenomenon where tree crowns avoid physical contact through mutual branch abrasion, allowing light penetration down to the forest floor.

Mesophication

The shift of forests toward shade-tolerant, fire-sensitive mesophytic species following fire exclusion, creating cooler, moister, less flammable understory conditions that further impede fire and pyrophyte regeneration.

Resilience

The capacity of a forest ecosystem to absorb disturbances and reorganize while maintaining its fundamental structure, composition, and processes.

Resilience debt

The accumulated erosion of an ecosystem's recovery capacity caused by altered disturbance regimes, increasing the risk of abrupt conversion to an alternate state.

Ecological memory

The network of biological legacies, adaptations, seed banks, and structural features that provide the foundation for recovery following disturbance.

Natural Range of Variability (NRV)

The baseline spectrum of ecological conditions, structures, and disturbance regimes that characterized an ecosystem under historical processes prior to major modern alteration.

Biological legacies

Organisms, organic structures, and biological patterns (such as live canopy trees, snags, logs, and seed banks) that survive a disturbance event.

Ordination

A statistical dimension-reduction technique that arranges ecological sample plots and species along axes representing gradual gradients in composition.

Topoedaphic

Pertaining to the combined, interacting influences of topography (aspect, elevation, slope position) and soil characteristics on plant communities.

Ecotone

A boundary or transitional zone existing between two distinct ecological communities or vegetation types.

Topographic Relative Moisture Index (TRMI)

A relative scalar index ranging from 0 (xeric) to 60 (hydric) calculated from topographic position, slope aspect, slope steepness, and slope configuration.

Importance value (IV)

A composite ecological index for a species within a plot, calculated as the sum of its relative basal area and relative density (totaling 200 per plot).

Autogenic change

Successional environmental modifications brought about directly by the organisms living within the community, such as litter accumulation or light reduction.

Allogenic change

Environmental shifts in an ecosystem caused by external abiotic forces or disturbances, such as climate variations, storms, or wildfires.

Relay floristics

A successional model where distinct groups of species replace each other sequentially, with earlier colonists modifying conditions to facilitate later species.

Initial floristic composition

A successional model proposing that most species of later successional stages are already present at or immediately after disturbance, with succession unfolding via differences in growth rate and lifespan.

Facilitation

A positive interspecific interaction in which early colonizing species modify habitat conditions in ways that make the site more suitable for subsequent species.

Inhibition

A successional mechanism where early colonizing individuals preempt space and resources, directly suppressing or preventing colonization by subsequent species.

RAD framework

A strategic management framework under accelerating environmental change outlining three options: Resist ecological change, Accept the trajectories, or Direct change toward desired states.