52
can no longer support large populations of grazers and a pastoral economy (Campbell
et al. 1997 ; Reynolds et al. 2007 ). Management has changed in many southwestern
North American arid and semiarid grasslands from cattle and other grazing animals
to white-tailed deer and other browsing ungulates (Doughty 1983 ).
However, there is some evidence that shrub or woody plant cover has started to
stabilize, with little continued temporal expansion (Browning et al. 2008 ). The
encroachment of some of these woody plants into grasslands appears to have slowed
(Miller et al. 2005 ), suggesting that the period of greatest encroachment may be past
but evidence is limited. Perhaps the majority of grasslands that could be encroached
have been encroached. However, there are many ongoing encroachment studies.
Past woody plant or brush encroachment was treated as a problem associated
with the encroaching woody species. What was not recognized was the effect of
constant, long-term, high levels of herbivory by domestic herbivores on the grass
plants. Grass plants can tolerate some herbivory but not a lot. With the loss of
aboveground parts due to herbivory, roots and other belowground parts are reduced,
and the ability of the grasses to obtain soil resources including water is reduced.
This is followed by a reduction in aboveground carbon fi xation and production (Van
Auken and Bush 1989 , 1997 ; Bush and Van Auken 1995 ). Encroaching woody species were considered aggressors, aliens, and invaders. Using anthropogenic terms
suggested, these species were special. In fact they were growing extremely well in
disturbances or gaps without competition and without fi re. These are areas or conditions where these species normally grow very well with the niche requirements
needed for their typical growth. The biology and ecology of what was happening
was not considered or it was ignored. What was happening to the grass in these
grassland or rangeland was not deemed important except that it appeared to be
declining and the woody plants were the cause. This decline appeared to be very
important to ranchers and cattle or domestic animal production. Thus, grassland and
rangeland managers used various techniques including both mechanical and chemical to try unsuccessfully to control the perceived problem (Scifres 1980 ; Heitschmidt
and Struth 1991 ; Taylor 2008 ; Taylor et al. 2012 ).
Unfortunately, the mature woody legumes or other mature woody plants were
targeted, not the newly germinated or the newly emerged woody plant seedlings
(Fig. 8.3 ). Healthy grass competitors can reduce and slow the growth of the woody
legumes, but they do not seem to be able to totally prevent their growth (Fig. 8.4 ).
Combinations of burning and biological control were tried without a lot of apparent
success, probably because of little light, fl uffy fuel remaining after years of heavy
grazing. Woody plant mortality is size and fi re dependent, and large plants in these
encroached grasslands are fi re resistant (Collins and Wallace 1990 ). In these managed, manipulated communities, the domestic animals were usually put back on the
treated area as soon as the grasses started to regrow after mechanical, chemical, or
other treatment. This was usually after one or more rains. This type of treatment
would reset the grassland-woodland succession with an approximate 20-year cycle
of treatment, grass regrowth, and woody plant encroachment followed by retreatment. This kind of procedure or treatment is very expensive, not very practical,
and really not ecologically sound.
8 Management and Community Restoration
can no longer support large populations of grazers and a pastoral economy (Campbell
et al. 1997 ; Reynolds et al. 2007 ). Management has changed in many southwestern
North American arid and semiarid grasslands from cattle and other grazing animals
to white-tailed deer and other browsing ungulates (Doughty 1983 ).
However, there is some evidence that shrub or woody plant cover has started to
stabilize, with little continued temporal expansion (Browning et al. 2008 ). The
encroachment of some of these woody plants into grasslands appears to have slowed
(Miller et al. 2005 ), suggesting that the period of greatest encroachment may be past
but evidence is limited. Perhaps the majority of grasslands that could be encroached
have been encroached. However, there are many ongoing encroachment studies.
Past woody plant or brush encroachment was treated as a problem associated
with the encroaching woody species. What was not recognized was the effect of
constant, long-term, high levels of herbivory by domestic herbivores on the grass
plants. Grass plants can tolerate some herbivory but not a lot. With the loss of
aboveground parts due to herbivory, roots and other belowground parts are reduced,
and the ability of the grasses to obtain soil resources including water is reduced.
This is followed by a reduction in aboveground carbon fi xation and production (Van
Auken and Bush 1989 , 1997 ; Bush and Van Auken 1995 ). Encroaching woody species were considered aggressors, aliens, and invaders. Using anthropogenic terms
suggested, these species were special. In fact they were growing extremely well in
disturbances or gaps without competition and without fi re. These are areas or conditions where these species normally grow very well with the niche requirements
needed for their typical growth. The biology and ecology of what was happening
was not considered or it was ignored. What was happening to the grass in these
grassland or rangeland was not deemed important except that it appeared to be
declining and the woody plants were the cause. This decline appeared to be very
important to ranchers and cattle or domestic animal production. Thus, grassland and
rangeland managers used various techniques including both mechanical and chemical to try unsuccessfully to control the perceived problem (Scifres 1980 ; Heitschmidt
and Struth 1991 ; Taylor 2008 ; Taylor et al. 2012 ).
Unfortunately, the mature woody legumes or other mature woody plants were
targeted, not the newly germinated or the newly emerged woody plant seedlings
(Fig. 8.3 ). Healthy grass competitors can reduce and slow the growth of the woody
legumes, but they do not seem to be able to totally prevent their growth (Fig. 8.4 ).
Combinations of burning and biological control were tried without a lot of apparent
success, probably because of little light, fl uffy fuel remaining after years of heavy
grazing. Woody plant mortality is size and fi re dependent, and large plants in these
encroached grasslands are fi re resistant (Collins and Wallace 1990 ). In these managed, manipulated communities, the domestic animals were usually put back on the
treated area as soon as the grasses started to regrow after mechanical, chemical, or
other treatment. This was usually after one or more rains. This type of treatment
would reset the grassland-woodland succession with an approximate 20-year cycle
of treatment, grass regrowth, and woody plant encroachment followed by retreatment. This kind of procedure or treatment is very expensive, not very practical,
and really not ecologically sound.
8 Management and Community Restoration