Disturbance & Succession Flashcards
Define disturbance
a discrete event changing the structure and resource availability or environment, severe disturbances initiate successional sequences
Direct disturbances
killing disturbance, increases space and resources for survivors
Indirect disturbances
individuals not killed, changes resource availability to individuals
3 forms of disturbance
1) abiotic
2) biotic
3) anthropogenic
Spatio-temporal-severity variation in disturbance regimes
how often is the community impacted (reproduction?), how sever is the damage (populations recover?), how big are the disturbance patches (recolonize?)
2 types of wind disturbance
hurricanes in large areas with low frequency or tornadoes in small areas with high frequency
Avalanche disturbance
subalpine forest is restricted to slopes that are stable and not prone to snow slides or avalanches
FIRE :)))) and fire tolerant tree adaptations
a source of fuel, lightning ignition, low precipitation and strong wind dries biomass, sever fires remove forest canopy and increase light level, destroy organic layers on forest floor which increases nutrient availability on the short run, fire scars indicate thermal damage to the cambial layer/rings indicate the age of event
Fire tolerant tree adaptations: thick bark, regrowth from epicormic shoots, stimulation of seed dispersal in serotinous cones
Define succession
changes in species composition, vegetation structure, and environment over time is an ongoing process
Primary succession: community change on a substrate with no former plant community, generally long-term slow process
Secondary succession: community change at a site with a previous plant community and relatively intact soil, fast relative to primary succession, but takes years/decades/centuries to reach maturity
Classic succession model: facilitative succession
seres evolve in a highly predictable sequence, is controlled by facilitation where later seres depend on earlier invading plants/animals
Define climax community
the predictable end product of succession, and is self-perpetuating in the absence of disturbance
Successional change/modification of the environment
Modification of the environment by plants: microenvironment or microclimate, light availability, temperature, humidity, change in nutrients from leaf litter, soil development from addition of leaf litter
Modification of the environment by animals: litter decomposition and other soil processes, grazing, seed dispersal
Differences between species: seed dispersal, juvenile rates of growth, maximum size, lifespan, life history traits
Modification of the environment by new disturbances: add complexity, continuation of succession
3 problems with the climax concept
1) Natural disturbances are common, disturbance is the rule not the exception
2) environmental change is always occurring = environment is not stable
3) “Climax” vegetation is extremely rare because disturbances are so frequent that it basically never exists
Alternative models of succession
Tolerance model for succession: species of both early and late seral stage are established very quickly following disturbance, early seral plants grow faster and late seral plants grow slowly, and as succession progresses, some of the early seral plants cannot tolerate the competition for light and moisture
Inhibition model for succession: proximity to seed sources and chance factors related to seed dispersal play a major role in determining which species occupy the site, once the sight is occupied, the presence of the early invaders inhibits establishment of other species
Random model of succession: random arrival and survival of species at a disturbed site, there is no facilitation or inhibition
Succession is a stochastic process
forest succession is a lottery that can be modelled by a Markov chain process (which assigns probabilities to competing outcomes in a sequence
Ideas primarily developed by Henry Horn in the 1970s based on his observations in the Princeton Research Forest (a mixed hardwood forest) in NE USA
