Distribution of Plants on Terrain
Possible ways to describe plant distribution
- Using a coverage bitmap
- discretely - type information per element of the elevation grid, or
any overlapping grid
- pro: easy to draw in a paint program, easy to vary density
- con: doesn't work well for fine boundaries, e.g. along the edge of a
road
- Polygonal areas
- structured - polygonal bounding regions indicate areas of plant
coverage
- pro: more precise placement, works well for crops
- con: would have to create graphical tool for defining the areas, or
rely entirely on existing polygonal data sources
- also need the ability to place individual trees, and/or lines of trees
(e.g. along a road or fence)
- many academic papers cover the subject of producing plant distributions,
such as with algorithms which simulate ecosystems - see
Plant Papers
Sources of Data
- USGS LULC (land use
and land cover) files
- includes classification code such as "Herbaceous Rangeland" and
"Evergreen Forest Land" which very roughly description vegetation type
- U.S. only
-
USGS
Global Land Cover
Characterization
- huge raster files, in a raw format, with 1km coverage of the whole
earth
- has much better classification than LULC, example of a single type:
"Needleleaf Forest (Western Hemlock, Sitka Spruce, Douglas Fir)"
- the main drawback is the very low resolution (1km) which makes it
useless for visualization at a human scale
- The GLCF has global
vegetation data
- USGS NLCD
(National Land Cover Database)
- WWF
Ecoregions
is an amazing global map of ecoregions
- the map data is available (25 MB zipped Shapefile), only requires
submitting an email address
- a great many people in the GIS field use
polygonal areas with attributes (e.g. in a Shapefile) to describe vegetation
coverage
- unfortunately, there are no standards for the number and meaning of
the attributes
- therefore, there is no consistent way to exploit these data sources,
or to exchange data
- USDA vegetation maps? 7.5-Minute DLG Vegetation Overlay?
Classification of Vegetation
- there is very little standardization
- some people treat classification of vegetation as a subset of general
land-use classification (e.g. the USGS and USDA) but this does not well
describe either the physical appearance or the scientific
description, e.g. species
- one fairly common physical measure of trees in the forestry industry is
their radius
- "There are some standards, but surprisingly few, and almost always
non-visual. Some ecologists have worked on structural vegetation
classifications, since it turns out that structure is very important to
birds, for instance. But from what I've seen, this is usually for trees
only, mostly based on age, "site class" (soils/slope/aspect), and
DBH. I've
never seen anything which would cross-walk a meadow from Siberia to Florida.
You might get part of the way there with a structural description of
vegetation form ranges (bounding sphere x age?), plus geographic range (by
bioregion?). You could then pick the closest vegetation form from the
closest broad bioregion. If you are in a forest in the NE but have no trees
for that area, fallback might be trees of same size from a Michigan forest."
- Michael Flaxman
Descriptions of Plant Distribution
Game Programming:
- "We simply have the artists create a density map for the terrain and
then randomly (with a seed) place/ render vegetation depending on the
density map. Then between min and max distance we either shrink objects to
size 0 or fade them out using alpha. This approach works fine for small
stuff like grass or ferns." - Daniel Vogel, Epic Games
