15
O.W. Van Auken and J.K. Bush, Invasion of Woody Legumes, SpringerBriefs in Ecology 4,
DOI 10.1007/978-1-4614-7199-8_4, © Springer Science+Business Media New York 2013
Apparently many former grasslands and savannas have changed because of anthropogenic disturbances caused by the introduction of numerous domestic grazing animals (cattle and other species), the reduction of light, fl uffy fuel (grasses by
herbivory), and a concomitant reduction of fi re frequency (Van Auken 2000 , 2009 ).
In southwestern North America, these changes have led to encroachment of various
woody species including species of Prosopis , Senegalia, and Vachellia (the latter
two previously acacias). The conditions required for the establishment (encroachment), growth, and dominance of the woody plants in many of these former grasslands have been diffi cult to understand. Global change phenomena including
increased levels of atmospheric CO 2 and concomitant elevated temperature do not
seem to be the main cause of the encroachment, which appears to be a management
problem or phenomena (Van Auken 2000 , 2009 ).
One of the most well-studied species of the former genus Acacia s. l. in the New
World is Vachellia farnesiana (Fig. 4.1 ). It was reported on more that 1.1 million ha
in south Texas alone with more than 20 % cover in many places (Smith and
Rechenthin 1964 ) and probably 100 % cover in mid-successional, dense, woodland
thickets or communities (Van Auken and Bush 1985 ; Bush et al. 2006 ). Although it
is widespread and has a high density in places, there are still relatively few papers
concerning its basic ecology (Van Auken and Bush 1985 ). Various management
strategies have been used to try to control it because it is encroaching into many C 4
grasslands (Scifres 1980 ).
Prosopis ( P. glandulosa, P. velutina, P. torreyana, or P. julifl ora ) another genus
of woody legume has been reported on more that 38 million ha in the American
southwest and northern Mexico (Van Auken 2000 ). Some arid or semiarid communities have relatively low Prosopis cover and density (Fig. 4.2 ) (Smith and
Rechenthin 1964 ), but there are many apparent mid-successional, dense, woodland
thickets where the cover approaches 100 % (Smith and Rechenthin 1964 ; Simpson
1977 ; Scifres 1980 ; Archer et al. 1988 ). It is a widespread genus and has a high
density in places, and there is considerable concern about its increase in density in
grasslands or former grasslands (Scifres 1980 ; Heitschmidt and Struth 1991 ).
Chapter 4
Woody Legume Community Structure
O.W. Van Auken and J.K. Bush, Invasion of Woody Legumes, SpringerBriefs in Ecology 4,
DOI 10.1007/978-1-4614-7199-8_4, © Springer Science+Business Media New York 2013
Apparently many former grasslands and savannas have changed because of anthropogenic disturbances caused by the introduction of numerous domestic grazing animals (cattle and other species), the reduction of light, fl uffy fuel (grasses by
herbivory), and a concomitant reduction of fi re frequency (Van Auken 2000 , 2009 ).
In southwestern North America, these changes have led to encroachment of various
woody species including species of Prosopis , Senegalia, and Vachellia (the latter
two previously acacias). The conditions required for the establishment (encroachment), growth, and dominance of the woody plants in many of these former grasslands have been diffi cult to understand. Global change phenomena including
increased levels of atmospheric CO 2 and concomitant elevated temperature do not
seem to be the main cause of the encroachment, which appears to be a management
problem or phenomena (Van Auken 2000 , 2009 ).
One of the most well-studied species of the former genus Acacia s. l. in the New
World is Vachellia farnesiana (Fig. 4.1 ). It was reported on more that 1.1 million ha
in south Texas alone with more than 20 % cover in many places (Smith and
Rechenthin 1964 ) and probably 100 % cover in mid-successional, dense, woodland
thickets or communities (Van Auken and Bush 1985 ; Bush et al. 2006 ). Although it
is widespread and has a high density in places, there are still relatively few papers
concerning its basic ecology (Van Auken and Bush 1985 ). Various management
strategies have been used to try to control it because it is encroaching into many C 4
grasslands (Scifres 1980 ).
Prosopis ( P. glandulosa, P. velutina, P. torreyana, or P. julifl ora ) another genus
of woody legume has been reported on more that 38 million ha in the American
southwest and northern Mexico (Van Auken 2000 ). Some arid or semiarid communities have relatively low Prosopis cover and density (Fig. 4.2 ) (Smith and
Rechenthin 1964 ), but there are many apparent mid-successional, dense, woodland
thickets where the cover approaches 100 % (Smith and Rechenthin 1964 ; Simpson
1977 ; Scifres 1980 ; Archer et al. 1988 ). It is a widespread genus and has a high
density in places, and there is considerable concern about its increase in density in
grasslands or former grasslands (Scifres 1980 ; Heitschmidt and Struth 1991 ).
Chapter 4
Woody Legume Community Structure