More info for the terms:
density,
fire management,
fire suppression,
frequency,
shrub,
shrubsBrushfield expansion: During the past century, shrubs such as mesquite
(Prosopis spp.) and algerita have been increasing on Texas rangelands
[
2,
3,
10,
39]. An estimated 736,744 acres (1.82 million ha) of Texas
rangeland is now "infested" with algerita. The situation is particularly
pronounced on the Edwards Plateau where algerita density can reach up to
121 plants per acre (300/ha) [
19]. Possible causes of this shrub
expansion include fire suppression, overgrazing, and/or climatic change
[
2,
10].
Grazing: In semiarid grasslands of Texas, heavy grazing apparently
favors the spread of redberry juniper (Juniperus pinchotii) which in
turn facilitates the establishment of algerita. Frequency of algerita is
typically highest on grazed sites occupied by redberry juniper, as
illustrated below [
39]:
high plains rolling plains
grazed sites ungrazed sites redberry redberry
present absent present absent j. present j. absent
(percent frequency)
29 0 63 20 25 0
Mechanical removal: Ranchers commonly view algerita as a nuisance [
24],
and numerous studies have focused on various means of mechanical removal
[
19,
22,
23]. Soil penetration to a depth of 4 to 6 inches (10-15 cm) is
generally necessary to sever the taproot from the crown and to uproot
all lateral roots capable of resprouting. Resprouting often occurs
where blade penetration is insufficient. Small plants with shallow
roots are most readily killed by mechanical means [
19].
On the Edwards Plateau of Texas, various types of mechanical grubbing
have produced erratic mortality [
19]. Grubbing, using a modified blade
with fins on top, killed up to 93 percent of the plants where
pretreatment densities had ranged from 17 to 79 plants per acre
(42-195/ha). Consequently, this method of control was judged both
effective and economical [
19]. On rocky outcrops with shallow soil, the
blade was prevented from eliminating all of the lateral roots. An
estimated 88 percent of algerita was killed on these sites. Root plowing
is also effective, although often prohibitively expensive.
Posttreatment burning, when used in combination with mechanical removal,
can also aid in reducing algerita density [see Fire Management
Considerations].
Chemical control: Algerita is resistant to many herbicides including
2,4,5-T and picloram [
14,
19,
22]. Although canopies were reduced by 24
to 30 percent 13 months after large amounts of picloram were applied to
the soil, plants recovered within 24 months [
33]. No plants were
actually killed by the herbicide. Details on response to various rates
of herbicide application are available [
14,
29,
22].
Damage/disease: Algerita is susceptible to black stem rust [
52].
However, roots contain large amounts of the alkaloid berberine, a
substance known to inhibit some root fungi. Roots may, therefore, be
relatively resistant to a number of pathogens [
24].
Biomass: Models have been developed for predicting biomass estimates of
algerita. Current growth is primarily leaves and includes little twig
elongation. Studies indicate that new growth on young plants is greater
per unit volume than is growth on older plants [
16].