Geoscience Reference
In-Depth Information
Table 6-3.
Example of the 50/20 rule for the tree stratum of vegetation.
Relative contribution
(%)
Cumulative
dominant total
Species
Total basal area
Yes/No
Category
Acer rubrum
80
80/200
=
40
40
Y
FAC, FACW
Taxodium distichum
60
60/200
=
30
70
Y
OBL
Quercus virginiana
40
40/200
=
20
90
Y
FACU
Pinus elliotti
10
10/200
=
5
95
N
UPL, FACW
Ulmus americana
5
5/200
=
2.5
97.5
N
FAC, FACW
Carpinus caroliniana
5
5/200
=
2.5
100
N
FAC
Totals
200
100
Table 6-4.
Plant hardiness zones of the U.S.
Department of Agriculture based on average annual
minimum low temperature. In Canada, zone 0
represents the harshest growing conditions.
data from the 1940s and 50s. The map was
updated in 1990 using climatic data from 1974
to 1986; the revised map showed a signii cant
shift toward colder zones (Fig. 6-33). On this
version, Kansas is split between zone 5 (
−
10 to
Temperature
Hardiness
zone
−
20 °F) in the north and zone 6 in the south.
The Arbor Day Foundation subsequently revised
the map in 2006 toward warmer zones; once
again most of Kansas is in zone 6 (Arbor Day
2006). These changes rel ect real climatic shifts,
affecting primarily winter conditions. Minimum
low temperatures decreased during the 1970
and 80s then rebounded in the 1990s and early
2000s.
Celsius
Fahrenheit
1
<
−
46
<
−
50
2
−
40 to
−
46
−
40 to
−
50
3
−
34 to
−
40
−
30 to
−
40
4
−
29 to
−
34
−
20 to
−
30
5
−
23 to
−
29
−
10 to
−
20
6
−
18 to
−
23
0 to
−
10
7
−
12 to
−
18
10 to 0
8
−
7 to
−
12
20 to 10
9
−
1 to
−
7
30 to 20
10
4 to
−
1
40 to 30
11
>
4
>
40
6.5 Invasive plant species
An invasive species can be dei ned as “an alien
species whose introduction does or is likely to
cause economic or environmental harm or harm
to human health” (National Invasive Species
Information Center 2008). This dei nition applies
to both plants and animals in all types of habi-
tats. Introduced wetland plants may become
invasive if they possess some competitive advan-
tage compared with pre-existing (native) plants.
Invasive plants tend to grow fast, disperse
rapidly, and reproduce quickly, which may lead
to replacement of the native l ora and substan-
tial changes in habitat conditions.
Such invasions may take place quite naturally
in the course of plant migrations, but human
intervention has accelerated the rate of plant
movements over long distances. When people
carry a plant species from one continent or
island to another, for purposes of agriculture or
within a colder zone, for example on a pro-
tected, sun-facing slope or within a large urban
area.
In North America, the harshest growing con-
ditions (zones 0-2) are found in the far north
of Canada and Alaska; the mildest zones (10-11)
are located in southern parts of California, Texas
and Florida, as well as much of Mexico. Similar
plant hardiness zone maps have been developed
for South America, Europe, China, and Australia
(BackyardGardener 2010).
It is most interesting to note how the plant
hardiness zones have changed over the past half
century in North America. The state of Kansas,
in the center of the coterminous United States,
is a good example. In the original USDA map
of 1965, nearly all of Kansas was shown in zone
6 (0 to
−
10 °F). This map was based on climatic
