disturbance and succession of habitats Flashcards
examples of habitat disturbance
- migration of animals e.g. geese
- engineering a system for human benefit e.g. golf courses
- wildfire events (crucial for some ecosystems)
- insect disturbance
- deforestation
- droughts (often related to deforestation)
- flooding (river straightening in UK)
- pathogens e.g. ash dieback
- volcanic activity
- soil erosion (especially coastlines)
succession
= the change in vegetation over time/ the directional change in ecosystems over time
- Clements coined term (1916)
- suggested it was ordered and predictable to a single climax community determines by the macroclimate of the area
- development of a ‘superorganism’ (predictable climax group of cooperating organisms)
Balsam fir, Abies balsamea
- North American boreal forests
- fire/ wind damage important in system
- once forest system reaches 300yrs old it burns
- regeneration then succession, process repeats
- in the intervening period there are different species that exploit the gap; species that are more tolerant of higher light intensities than you would normally find in a forest ground layer = spatial heterogeneity before it is replaced by Balsam fir
Calluna Vulgaris (heather) heath
- example of a plagioclimax in the UK
- fire artificially used around every 30yrs
- creates right cover for game fowl in the UK for the shooting industry
- the ‘building phase’ is artificially created and maintained, mostly heather, least diverse successional stage (pioneer to building to mature to degenerate community)
Plagioclimax community
= an area or habitat in which the influences of the humans have prevented the ecosystem from developing further
boreal forest, E. autumnata moth attacks
- 10yr cycle, peaks every 100yrs
- regeneration and succession between attacks
- concerns cycle is shortening due to climate change
Dendochronology
- study of tree rings
- reveals climate history of the area
e.g. Mesa Verde Colorado, native Americans moved to caves from 1300+, collected wood, can see history of species and climate
tracing and tracking succession
- difficult as very slow, longer than a human lifetime
- soil samples, fossil history, dendochronology
tracing succession Netherlands
- land was drained for agriculture
- peat cores taken
- history of organic matter follows history of vegetation
- DNA and chemical analysis (FT-IR) showed willow = wetland ecosystem
- marine sediment found Roman times, underwater
primary succession
- development on new substrates
- dry substrates = xeroseres, on rock, sand etc
- wet substrates = hydroseres, in lakes, ponds, estuaries etc
primary succession, volcanic eruptions
- e.g. Hawaii, 1986
- eruption site still solidified lava in 2002
- vegetation blew in and colonised cracks
- no seed bank left due to very high temperature of eruption
- seeds washed in in troughs, more water
- trees, palms, low shrubs
succession on a morraine
- glacial retreat leaves exposed xerosere
- seeds unlikely to have survived time and low temperature
- difficult to study due to human influence, tourists carrying seeds on hiking boots
- terminal moraine = most recently released
succession on cliffs
- xerosere exposed on cliff face as rocks fall off leaving bare rock
- e.g. Milford sound New Zealand
hydrosere succession
- primary coloniser often duckweed (Lemnacea)
- organic matter builds up over time and clogs wetland, climax is often terrestrial ecosystem
secondary succession
= those that evolve on partially developed substrates such as subsoil
secondary succession on a landslip
- substrate with seeds still there after a landslip
e.g. Cwm Cletr, moss and bilberry spp.
chronosequence
- areas of different ages on the same sort of substrate
- indicates possible evolution/succession
- diversity increases with time
- glacial moraine, sand dunes, uplift from sea following earthquakes (Alaska)
the climax community
= mature phase of succession
- not always predictable, system specific
- usually trees
- e.g. in Dutch dune slack systems, climax can either be trees or Pragmites depending on substrate and environmental conditions (presence of water)
three theories of succession
- facilitation
- tolerance
- inhibition
facilitation theory
- species in the sequence improve the environment for subsequent species
tolerance theory
- initial environment become less favourable for species initially present by no better or worse for subsequent species
inhibition theory
- species present at any time inhibits the establishment/performance of subsequent species, long lived species later outlive others
