Comparing Slope, Aspect, Solar Radiation & Elevation Preferences In Plant Species
The
first map that I created with ArcGIS shows the vegetation distribution in the Santa Monica Mountains.The second map shows topography (slope & aspect) of the region as well as solar radiation changes by season. The third map shows
the correlation between topography and vegetation distribution for each of the four main
vegetation types using statistical graphs about slope, aspect, elevation and solar radiation. The data sets utilized for this analysis
are the National Elevation Data (NED) 1 Arc Second (30 m resolution) and
California Vegetation data from USGS.
The
third map of charts and graphs contains a lot of interesting information. The
information was calculated using a zonal statistics tool which overlays the
vegetation info on top of the slope, aspect, elevation and solar radiation maps
and then computes a statistical breakdown for each vegetation type. The urban
agriculture data lends itself to what intuition already tells us; it is most
likely to be found in flat areas with low elevation, it also in places where it
consistently receives the most amount of sunlight from season to season. The
most interesting piece of information on the third map is the “Aspect
Preferences” compass. All four of the main vegetation types are most likely to
be found of the south facing side of the mountain. This potentially has
something to do with sun exposure or the rain shadow effect.
There
is a 1:1 correlation between slope and elevation preference for each plant
type; the higher the plant is in elevation, the steeper the slope is that it’s found
on. (In descending order from highest elevation and steepest slope:
chamise-redshank chaparral, coastal scrub, annual grass and urban-agriculture).
Definitions:
Slope
- the steepness of an angle represented in degrees
Aspect - the
direction that the slope is facing (e.g. North)
Elevation - meters above
sea-level
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