E4 Flashcards
Succession
the temporal change in community structure through time, begins with disturbance
Henry Chandler Cowles
he studied ecological succession in the Indiana dunes of northwest Indiana
led to efforts to preserve the Indiana dunes
FE Clements
described plant succession
characteristics of disturbance
four factors
1. the magnitude of the physical force, such as the strength of the wind, or the heat of the fire
2. morphological characteristics of the organisms that influence their response to disturbance
3. the nature of the substrate (soil). Is the soil wet or dry, clay or sand
4. the amount of aboveground biomass accumulation and height of vegetation
frequency
the mean number of disturbances that occur within a particular time interval
return interval
the interval between disturbance events
if intervals are long or frequency is low, biomass accumulates and the intensity of the disturbance can be high
what is the impact of return interval
in some communities the return interval of disturbance is roughly proportional to the life span of the dominant organisms
in forest communities with trees that potentially live for several hundred years, return intervals of disturbance are shorter than the life span of the trees
framework for examining community dynamics
- The fundamental niche of a species acts as a primary constraint on its distribution and abundance
- species vary in their fundamental niches (environmental tolerances)
- Environmental conditions change in time and space
- the fundamental niche is modified by species interactions (realized niche)
logging began in Michigan in 1880s
logs were sent down rivers to be milled
the land was nude
-following the logging era farmers tired and failed on the land
-fires in the early 20 century burn up slash
-causing further soil loss
-clements viewed succession as a process involving several phases, to each of which he gave his own terminology
-succession began with the development of a bare site called nudation (disturbance)
-nudation was followed by migration, the arrival of propagules onto the area
-migration was followed by the establishments and the initial growth of vegetation
-the outcome of the process was the replacement of one plant community by another reaching a phase called stabilization
-ice contact stratified outwash
-impact on streams: without forest cover streams heated up and sand eroded into the streams. the gravel bottoms of the streams were smothered in sand
trout were introduced
the grayling went extinct
-most trees in Michigan today are managed maple/beech forests
dominance shift of overstay and understory pine, to hardwood
in the early stages of plant succession, shade-intolerant species come to dominant as a result of their high growth rates
shade-intolerant species overtop and shade the slower-growing, shade tolerant species
as time progresses and light levels decline below the canopy, seedlings of the shade-intolerant species cannot grow and survive in the shaded conditions
at this time, although shade-intolerant species dominate the canopy, no new individuals are being recruited into the populations
hardwood (shade tolerant species) are able to grow and take over
climax community
according to classical ecology theory, succession stops when the sere has arrived at an equilibrium or steady sate with the physical and biotic environment
at this point the community is stable and self-replicating
barring major disturbances, it will persist indefinitely
the end point of succession is climax
characteristics of climax
- the vegetation is tolerant of the environmental conditions it has imposed upon itself
- it has a wide diversity of species
- complex food chains
- well-developed spatial structure
- individuals in the climax stage are supposedly replaced by others of the same kind. Thus the species composition maintains equilibrium
- The climax view of succession was later modified by tansley and whittaker
serotiny
jack pine have seeds that remain in the cone for years awaiting a fire
the fire melts the resins that kept the cone sealed up
then the pine seeds are ready for the newly repaired ground of ash
frequency rolling plains
how frequently a fire burns over a given area, and its return rate is influenced by the occurrence of droughts, accumulation and flammability of fuel, the resulting intensity of the burn, and human interference
in NA, grasslands have fires every 3 years
the time was needed for sufficient mulch, dead stems, and leaves to accumulate
wind as a force of succession
wind shapes the canopies of trees exposed to prevailing winds, affects their growth, and uproots them from the ground
trees weakened by fungal disease, insect damage, lightning strikes and tropical forests trees carrying a heavy load of epiphytes in their crowns are candidates for wind throw
hurricanes
a powerful recurring event of high intensity but low frequency
hurricanes, especially those with wind speeds of 166km/hr and rainfall of 200mm have a devastating impact
impacts of wind is accentuated when strong winds accompany heavy snowfall that weighs down trees or heavy rains that soften the soil about the roots
cyclic replacement in an old-field community in Michigan
the bare areas at the bottom are invaded by moss
mosses are invaded by Canada bluegrass and dock
the accumulated dead leaves of these plants are covered by lichens that crowd out the grass
rain, frost, and wind destroy the lichens to start the cycle with bare ground again
“return to the same place in the same cycle”
chronoseres/ chronosequences
patterns of diversity through succession have been investigated by comparing datable sites within an area that are in a different stages of succession
allogenic environmental change
purely abiotic environmental (allogenic) change can produce patterns of succession over time scales ranging from days to millennia or longer
annual fluctuations in temp and precipitation will influence the relative growth responses of different species in a forest community, but they will have little influence on the general patterns of secondary succession
in contrast, shifts in environmental conditions that occur at periods as long or longer than the organism’s life span are likely to results in shifts in species dominance
primary succession
begins on sites that have never supported life
ex: rock outcrops and cliffs, sand dunes, and newly exposed glacial till
diversity increases with
age
secondary succession
where life has been before
soil and nutrients are present
type of ecological succession in which plants and animals recolonize a habitat after a major disturbance—such as a devastating flood, wildfire, landslide, lava flow, or human activity (e.g., farming or road or building construction)—significantly alters an area but has not rendered it completely lifeless.
secondary succession- farmer
old-field succession in the Piedmont of North Carolina
-a famed crop land is abandoned, the ground in claimed by crabgrass, whose seeds lying dormant in the soil, respond to light and moisture and germinate
-in late summer seeds horse weed ripen
-the following spring horse weed, claims the field over crabgrass
-by the third summer broomsedge a perennial bunchgrass, invades the field
about this pine seedlings, find room to grow in open places among the clumps of broomsedge invade the field
-within five years the pines are tall enough to shade out the broomsedge
-eventually hardwood species, such as oaks and ash, grow up through the pines and the pines die
-development of the hardwood forest continues as shade tolerant trees and shrubs fill the understory
autogenic change (self-generated)
one feature common to all plant succession is autogenic environmental change. In both primary and secondary succession, the colonization of an area by plants alters the environmental conditions
one clear example is the alteration of the light environment
