Influences on the Vegetation of an Area
1. Geologic and geographic context
a. Location on the globe
i. Influences of global position on weather and climate as described under #2.b.
ii. Effects on the natural ranges of species and possible speciation (see #4.a. and #5)
b. Forces affecting geologic conditions
i. Tectonic forces resulting in lateral and/or vertical movements of parts of the Earth’s crust, e.g., uplift
(orogeny), subsidence, lateral plate tectonic movements
ii. Forces responsible for erosion, transport, and deposition of earth materials
Materials so moved are termed colluvium
- Flowing liquid water (fluvial transport):
The term for materials deposited by flowing water is
Aeolian deposits include materials such as loess and dune sands
- Glaciers (Flowing ice):
Glacial drift is the general term, while much of that drift, which is
heterogeneous and unstratified is specifically referred to as glacial till; recurrent Pleistocene
Epoch glaciers significantly reshaped extensive portions of higher latitude and higher elevation
portions of the Earth
- Modern humans, with all of their construction and other earth-moving endeavors, have now
also become a prominent geologic force
iii. Most lakes and wetlands are relatively transitory features of landscapes, with lifespans ranging from
a few thousand years to several tens of thousands of years.
Those are long time intervals compared to
human lifespan, yet brief on a geological time scale.
Lakes and wetlands tend to disappear because of
two primary causes: infilling by sediments, and, in some cases, self drainage, as occasional
overtopping of a shoreline results in downcutting of an outlet.
Parts of the world having an abundance
of lakes and wetlands have two common features: a precipitation-evaporation regime offering an
abundance of water to keep basins filled, and geologic processes, such as glaciation, dissolution of
bedrock, river channel shifts, which create(d) new basins.
c. Episodic geologic events, e.g., landslides, avalanches, earthquakes, tsunamis, while limited in frequency,
can obviously have great effects on ecosystems when they occur.
d. Terrain: Topographic features, i.e., physical configuration of land surfaces, with effects on the following:
i. Macroclimate (see #2.b.i. and ii) and microclimate (see #2.c.ii)
ii. Movement of water (see #1.f.ii)
iii. Pedogenesis (see #1.e.ii) as affected by movement and storage of water and inorganic and organic
iv. Biological productivity, which is related to the above conditions
v. Spread of fire, e.g., fires can spread readily across plains, while hilly or mountainous terrain provides
e. Geologic substrate
i. In some areas, bedrock is exposed at or near the surface, while in other areas bedrock is buried