30
patches probably because of lower light levels below its canopy (Bush and Van
Auken 1987 ; Archer 1995 ). Replacement species would be any number of trees or
shrubs capable of growth in the higher nitrogen soil and the low light environment of
the canopy understory. Species identifi ed in older or mature Prosopis communities
included Zanthoxylum fagara (lime prickly ash), Celtis pallida (desert hackberry),
Diospyros texana (Texas persimmon), Condalia obovata (blue wood), Berberis trifoliolata (agarito), and a few others (Archer et al. 1988 ). However, the growth
requirements especially the light requirements of these species are not well defi ned
at this time. In drier areas of the American southwest, canopies would be more open,
but there would still be higher levels of soil nitrogen below the canopies.
Apparently many if not all of these arid land, subtropical, or tropical woody
legumes can or have been able to encroach and establish in area grasslands that have
been disturbed by heavy and continuous domestic grazing and a reduced fi re frequency. Once the woody plants are established, the communities would go through
secondary succession responding to soil resource levels and surface light levels. The
temporal sequence of species change in the communities would be from grassland to
savanna to woodland with the late stage or stages undefi ned. The temporal sequence
will be governed by the amount of annual rainfall and probably other factors. The
time it takes to reach a late stage in succession will vary by approximately 150 years
in fairly wet areas (75 cm/year) to an unknown number of years in drier regions.
References
Archer S (1994) Woody plant encroachment into southwestern grasslands and savannas: rates,
patterns and proximate causes. In: Vavra M, Laycock WA, Pieper RD (eds) Ecological implications of livestock herbivory in the West. Society for Range Management, Denver, pp 13–69
Archer S (1995) Tree-grass dynamics in a Prosopis -thronscrub savanna parkland: Reconstructing
the past and predicting the future. Ecoscience 2:83–99
Archer S, Scifres C, Bassham CR, Maggio R (1988) Autogenic succession in a subtropical
savanna: conversion of grassland to thorn woodland. Ecol Monogr 52:111–127
Bush JK (2008) Soil nitrogen and carbon after twenty years of riparian forest development. Soil
Sci Soc Am J 72:815–822
Bush JK, Van Auken OW (1986) Light requirements of Acacia-smallii and Celtis-laevigata in relation to secondary succession on fl oodplains of south Texas. Am Midl Nat 115:118–122
Bush JK, Van Auken OW (1987) Light requirements for growth of Prosopis-glandulosa seedlings.
Southwestern Nat 32:469–473
Lohstroh RJ, Van Auken OW (1987) Comparison of canopy position and other factors on seedling
growth in Acacia Smallii . Texas J Sci 39:233–239
Schlesinger WH, Raikes JA, Hartley AE, Cross AF (1996) On the spatial pattern of soil nutrients
in desert ecosystems. Ecology 77:364–374
Taylor FB, Hailey RB, Richmond DL (1966) Soil survey of Bexar County, Texas. USDA, Soil
Conservation Service, Washington
Tilman D (1985) The resourse-ratio hypothesis of plant succession. Am Nat 125:827–852
Van Auken OW (1994) Changes in competition between a C 4 grass and a woody legume with
differential herbivory. Southwestern Nat 39:114–121
5 Factors that Determine Growth Rates
patches probably because of lower light levels below its canopy (Bush and Van
Auken 1987 ; Archer 1995 ). Replacement species would be any number of trees or
shrubs capable of growth in the higher nitrogen soil and the low light environment of
the canopy understory. Species identifi ed in older or mature Prosopis communities
included Zanthoxylum fagara (lime prickly ash), Celtis pallida (desert hackberry),
Diospyros texana (Texas persimmon), Condalia obovata (blue wood), Berberis trifoliolata (agarito), and a few others (Archer et al. 1988 ). However, the growth
requirements especially the light requirements of these species are not well defi ned
at this time. In drier areas of the American southwest, canopies would be more open,
but there would still be higher levels of soil nitrogen below the canopies.
Apparently many if not all of these arid land, subtropical, or tropical woody
legumes can or have been able to encroach and establish in area grasslands that have
been disturbed by heavy and continuous domestic grazing and a reduced fi re frequency. Once the woody plants are established, the communities would go through
secondary succession responding to soil resource levels and surface light levels. The
temporal sequence of species change in the communities would be from grassland to
savanna to woodland with the late stage or stages undefi ned. The temporal sequence
will be governed by the amount of annual rainfall and probably other factors. The
time it takes to reach a late stage in succession will vary by approximately 150 years
in fairly wet areas (75 cm/year) to an unknown number of years in drier regions.
References
Archer S (1994) Woody plant encroachment into southwestern grasslands and savannas: rates,
patterns and proximate causes. In: Vavra M, Laycock WA, Pieper RD (eds) Ecological implications of livestock herbivory in the West. Society for Range Management, Denver, pp 13–69
Archer S (1995) Tree-grass dynamics in a Prosopis -thronscrub savanna parkland: Reconstructing
the past and predicting the future. Ecoscience 2:83–99
Archer S, Scifres C, Bassham CR, Maggio R (1988) Autogenic succession in a subtropical
savanna: conversion of grassland to thorn woodland. Ecol Monogr 52:111–127
Bush JK (2008) Soil nitrogen and carbon after twenty years of riparian forest development. Soil
Sci Soc Am J 72:815–822
Bush JK, Van Auken OW (1986) Light requirements of Acacia-smallii and Celtis-laevigata in relation to secondary succession on fl oodplains of south Texas. Am Midl Nat 115:118–122
Bush JK, Van Auken OW (1987) Light requirements for growth of Prosopis-glandulosa seedlings.
Southwestern Nat 32:469–473
Lohstroh RJ, Van Auken OW (1987) Comparison of canopy position and other factors on seedling
growth in Acacia Smallii . Texas J Sci 39:233–239
Schlesinger WH, Raikes JA, Hartley AE, Cross AF (1996) On the spatial pattern of soil nutrients
in desert ecosystems. Ecology 77:364–374
Taylor FB, Hailey RB, Richmond DL (1966) Soil survey of Bexar County, Texas. USDA, Soil
Conservation Service, Washington
Tilman D (1985) The resourse-ratio hypothesis of plant succession. Am Nat 125:827–852
Van Auken OW (1994) Changes in competition between a C 4 grass and a woody legume with
differential herbivory. Southwestern Nat 39:114–121
5 Factors that Determine Growth Rates