Understanding Ecological Disturbances: Types, Impacts, and Factors
Ecological Disturbances: An Overview
Disturbance: A relatively discrete event in time, causing a disruption in ecosystems, changing the substrate and availability of resources, and creating opportunities for the establishment of new individuals. Disturbances are partly allogenic and autogenic because their impact is the result of both the magnitude of the disturbance and the resilience of the community to the particular type of alteration.
Key Temporal and Spatial Attributes of Disturbances
- Type: Agents of disturbance (natural or anthropogenic)
- Area (Scale): Size of the area altered
- Frequency: Average number of events per unit time
- Return Interval: The average time between disturbances (1 / Frequency)
- Intensity: The physical strength of the event by area and time
- Severity: Impact on organisms or community
- Timing and Seasonality: When the disturbance occurs
- Interaction: How disturbances interact with each other
Wind Disturbances: Factors Influencing Susceptibility
Wind x Wind: Increased Susceptibility
- Mature trees dominant in the canopy, exposed in the stand or gap edges, and those that grow in shallow soils with shallow rooting are more susceptible.
- The impact of the wind is accentuated when accompanied by snow (mass) and rain (weakens the roots to soil).
- Trees weakened by insect and fungi attacks or damaged by lightning, or an abundant epiphyte biomass (> 0.5 ton) are also more vulnerable.
Types of Winds
- Hurricane (200-250 km / hr): Can cause great damage to the landscape (50 km-wide with Andrew 1992)
- Tornadoes (> 430 km / hr): Damage more localized
- Wind gusts associated with thunderstorms (90-200 km / hr): Affects surface size variable as uprooted trees or breaking speed
- Barrage: Heavy rain, rough and windy
Stands most affected by the wind are those within 600m of the summit with the N-EAST exposure.
Conclusions on Wind Disturbance
- Topographic position and fire history influence wind patterns.
- Young forests were less affected than mature forests (especially with severity <80%).
- Stands at higher altitudes, near the summits and exhibitions that were most affected.
- Legacies earlier unrest, several centuries ago, about the effects of subsequent disturbances.
- Interactions between disturbances and physical environment determine the dynamics of the ecosystem.
Fire Disturbances: Conditions and Types
Conditions: Accumulation of organic matter, dry weather, landscape conducive to propagation, ignition source (lightning and humidity).
Types of Fires
Underground Fires
Fires without flames that consume the organic matter in the soil. It spreads slowly, burning the roots and killing all species. These fires produce little smoke and are therefore difficult to detect. Fens or bogs can be very dangerous because they are not seen on the surface.
Surface Fires
Common in open woods, with long dry season during the year. Kills most of the herbaceous stratum, shrub, and young trees and eat the litter layer, humus and dead woody material. Usually does not damage the roots, bulbs, rhizomes plants or the trunks of trees. The rapid spread and depending on fire intensity and thickness of crust leads to death or scars on trees.
Crown Fires
Common in dense forests where fire travels from top to top. Fire severity and speed of propagation resulting in high mortality.