TheImprovement ofTropical and Subtropical Rangelands

ORITERIA FOR PLANT SELEOTlON
189
Latitude, Day Length, Photoperiodlan
Some species may have a wide area of distribution, such as:
Atriplez C4neecene
Atriplez 1&aJimu
EucaJJ/ptu c4maJtlulenm
Oenc1&ru cili4r"
OJ/notlon tl4ctJ/lon
20C' Lat. N. to 45° Lat. N.
25° Lat. N. to 55° Lat. N.
15° Lat. S. to 45° Lat. S.
35° Lat. N. to 35° Lat. S.
50C' Lat. N. to 40° Lat. S.
Each degree in latitude results in a difference in day length of
12 minutes at the time of the solstice. Thus, the day-length requir~
ments between the extreme northerly and southerly populations of
Atriplez C4neecene or A. 1&aJimue may differ by as much as five
hours, making southerly populations unfit for the northern part of
the geographic area of distribution and vice versa. For this reason,
most species of Atriplez do not produce flowers under intertropical
latitudes, even though they can still thrive vegetatively under these
conditions. Therefore, in photoperiodically sensitive species, care
must be taken to address latitudinal compatibility between the zone
or origin of the plant material and the site to be revegetated.
Rab"'aD aDd B.a1n-U.. Efficiency
The amount, distribution, and variability of precipitation must
be as similar as poaible from the sites of origin to the revegetation
site. For example, plant material from areas with a predominantly
summer rainfall regime should not be expected to perform well in
sites with a winter rainfall regime. Within a given rainfall regime,
it is usually safer to take plants from dry areas to more humid
sites, rather than from humid to dry sites. There are some exceptions,
however: AC4Ci4 eaJi"'4, for example, thrives on sand dunes
in southwestern Australia under a Mediterranean climatic regime
with rainfall ranging from 700 to 1,200 mm per annumj yet, in the
Mediterranean Basin, it grows successfully when annual rainfall is
as low as 200-300 mm. Similar cases are known with some Euc41,lPtu
species. Such situations, however, are the exception rather than
the rule. Rain-use efficiency (kg of dry matter per ha per year per
mm) may be a good general indicator for evaluating environmental
suitability (Le Houerou, 1984).