25
O.W. Van Auken and J.K. Bush, Invasion of Woody Legumes, SpringerBriefs in Ecology 4,
DOI 10.1007/978-1-4614-7199-8_5, © Springer Science+Business Media New York 2013
The chronological appearance and function of the woody legumes in many of the C 4
grassland communities is still not completely understood or accepted by all ecologists or rangeland scientists. Vachellia , particularly V. farnesiana and V. rigidula, as
well as Senegalia berlandieri and Prosopis glandulosa appear to be early successional species that establishes on low nutrient or low nitrogen soils (Van Auken
et al. 1985 ) or in grassland communities that have had high levels of disturbances
via extensive continuous domestic grazing and no or few fi res or probably both
(Archer et al. 1988 ; Van Auken 2009 ). Two factors or conditions that may be limiting and that are very important for the establishment and growth of these species or
community are surface light levels and soil nitrogen levels. These are factors suggested by Tilman as potentially responsible for the sequence of species in the
resource ratio theory of community development in succession (Tilman 1985 ).
The growth of V. farnesiana w as not promoted by nitrogen addition to the soil,
but its growth was promoted by the addition of other nutrients (Fig. 5.1 ) (Van Auken
et al. 1985 ; Van Auken 1994 ). If we are truly demonstrating secondary succession,
then there should be a species that takes the place of V. farnesiana during secondary
succession. In this south central Texas successional sequence, we have shown that
the species is Celtis laevigata (hackberry or sugar hackberry). If the resource ratio
hypothesis is true and represents what is occurring in this successional sequence,
C. laevigata should respond differently to added soil resources. Celtis laevigata was
not stimulated by additional added soil nutrients, but its growth increased 5.6 times
with added soil nitrogen (Fig. 5.1 ).
A second environmental factor that seems to be important in secondary succession is light level. During succession light levels near the surface of the soil will
decrease with the development of a community and a canopy (Fig. 3.1 ). This is part
of the resource ratio theory of succession. Early successional species would be high
light requiring species or sun species, while late successional species would be low
light requiring species or shade species. Light requirements of V. farnesiana, a proposed early successional sun species, and C. laevigata, a proposed late successional
shade species, were tested and compared.
Chapter 5
Factors that Determine Growth Rates
O.W. Van Auken and J.K. Bush, Invasion of Woody Legumes, SpringerBriefs in Ecology 4,
DOI 10.1007/978-1-4614-7199-8_5, © Springer Science+Business Media New York 2013
The chronological appearance and function of the woody legumes in many of the C 4
grassland communities is still not completely understood or accepted by all ecologists or rangeland scientists. Vachellia , particularly V. farnesiana and V. rigidula, as
well as Senegalia berlandieri and Prosopis glandulosa appear to be early successional species that establishes on low nutrient or low nitrogen soils (Van Auken
et al. 1985 ) or in grassland communities that have had high levels of disturbances
via extensive continuous domestic grazing and no or few fi res or probably both
(Archer et al. 1988 ; Van Auken 2009 ). Two factors or conditions that may be limiting and that are very important for the establishment and growth of these species or
community are surface light levels and soil nitrogen levels. These are factors suggested by Tilman as potentially responsible for the sequence of species in the
resource ratio theory of community development in succession (Tilman 1985 ).
The growth of V. farnesiana w as not promoted by nitrogen addition to the soil,
but its growth was promoted by the addition of other nutrients (Fig. 5.1 ) (Van Auken
et al. 1985 ; Van Auken 1994 ). If we are truly demonstrating secondary succession,
then there should be a species that takes the place of V. farnesiana during secondary
succession. In this south central Texas successional sequence, we have shown that
the species is Celtis laevigata (hackberry or sugar hackberry). If the resource ratio
hypothesis is true and represents what is occurring in this successional sequence,
C. laevigata should respond differently to added soil resources. Celtis laevigata was
not stimulated by additional added soil nutrients, but its growth increased 5.6 times
with added soil nitrogen (Fig. 5.1 ).
A second environmental factor that seems to be important in secondary succession is light level. During succession light levels near the surface of the soil will
decrease with the development of a community and a canopy (Fig. 3.1 ). This is part
of the resource ratio theory of succession. Early successional species would be high
light requiring species or sun species, while late successional species would be low
light requiring species or shade species. Light requirements of V. farnesiana, a proposed early successional sun species, and C. laevigata, a proposed late successional
shade species, were tested and compared.
Chapter 5
Factors that Determine Growth Rates