Soil enrichment by Acacia mellifera subsp. detinens on nutrient poor sandy soil in a semi-arid southern African savanna

Abstract The study was conducted in a semi-arid savanna of South Africa, dominated by an almost pure stand of Acacia mellifera subsp. detinens (Black Thorn). Due to its invasive habits and suppression of the herbaceous layer, this woody species is viewed by land owners as a serious threat. Clearing of all A. mellifera trees in order to restore the production potential of the herbaceous layer is thus a well-established practice. In view of possible beneficial effects of A. mellifera, a study was undertaken with the objective of quantifying differences in soil nutrient status under A. mellifera canopies (canopied subhabitat) in comparison to the open areas (uncanopied subhabitat). The results of the study confirmed the existence of differences in the soil nutrient status between the various subhabitats, which occurred in a specific spatial gradient from the stem base of the plants towards the open, uncanopied areas. These differences were statistically significant ( p 0.05 ) for total N, % organic matter and Ca, with the highest values recorded in the area surrounding the stem base. Though statistically non-significant ( p > 0.05 ) the P and K contents, and to a lesser extent Mg, were also higher under the tree canopies, while pH was lower. No differences ( p > 0.05 ) were established for Na. Some notable differences to similar studies in other areas were established, of which the reduction of soil pH is an example. The practical significance of these results in terms of land management practices is discussed, which will invariably necessitate a change in attitude of land owners in their approach to the management of A. mellifera.

[1]  N. Smart,et al.  The effect of long‐term exclusion of large herbivores on soil nutrient status in Murchison Falls National Park, Uganda , 1984 .

[2]  C. Delwiche,et al.  Natural 15N abundance of presumed N2-fixing and non-N2-fixing plants from selected ecosystems , 1982, Oecologia.

[3]  G. N. Smit,et al.  Relations between woody and herbaceous components and the effects of bush‐clearing in southern African savannas , 1992 .

[4]  G. N. Smit.  An approach to tree thinning to structure southern African savannas for long-term restoration from bush encroachment. , 2004, Journal of environmental management.

[5]  G. N. Smit,et al.  Influence of leguminous and non-leguminous woody plants on the herbaceous layer and soil under varying competition regimes in Mixed Bushveld. , 1994 .

[6]  C. Donaldson,et al.  An investigation of the veld problems of the Molopo area: I. early findings , 1970 .

[7]  Robert J. Scholes,et al.  The influence of soil fertility on the ecology of southern African dry savannas , 1990 .

[8]  R. Mead,et al.  Statistical Methods in Agriculture and Experimental Biology , 1994 .

[9]  P. Werner,et al.  Savanna ecology and management : Australian perspectives and intercontinental comparisons , 1991 .

[10]  P. Felker,et al.  Position of mesquite (Prosopis spp) nodulation and nitrogen fixation (acetylene reduction) in 3-m long phraetophytically simulated soil columns , 1982, Plant and Soil.

[11]  N. Smit.  Guide to the acacias of South Africa. , 1999 .

[12]  C. Potter.  Stemflow nutrient inputs to soil in a successional hardwood forest , 1992, Plant and Soil.

[13]  R. Lubke,et al.  Aspects of the vegetation and soil relationships in the Andries Vosloo Kudu Reserve, Cape Province , 1988 .

[14]  S. Singh,et al.  Microbial C, N and P in dry tropical savanna: effects of burning and grazing , 1991 .

[15]  G. Schroth,et al.  Mulch decomposition under agroforestry conditions in a sub-humid tropical savanna processes and influence of perennial plants , 1992, Plant and Soil.

[16]  M. Kvarnström,et al.  Nitrogen fixation by the woody legumeLeucaena leucocephala in Tanzania , 1982, Plant and Soil.

[17]  P. Högberg.  Nitrogen-fixation and nutrient relations in savanna woodland trees (Tanzania) , 1986 .

[18]  H. Elwell.  Determination of erodibility of a subtropical clay soil: a laboratory rainfall simulator experiment , 1986 .

[19]  H. Snyman,et al.  The influence of tree density on the grass layer of three semi-arid savanna types of southern Africa , 2001 .

[20]  R. Ruess.  Savanna Ecology and Management , 1988 .

[21]  Y. Hirabuki.  Heterogeneous dispersal of tree litterfall corresponding with patchy canopy structure in a temperate mixed forest , 1991, Vegetatio.

[22]  G. Stuart-Hill,et al.  The influence of an Acacia karroo tree on grass production in its vicinity , 1987 .

[23]  J. Holt,et al.  Nutrient cycling in Australian savannas. , 1990 .

[24]  M. Kent,et al.  Quantity and quality of bracken throughfall, stemflow and litterflow in a Dartmoor catchment , 1987 .

[25]  G. Oba,et al.  Dynamics of Acacia tortilis litter in the Turkwel River floodplain woodlands, Kenya , 1993 .

[26]  M. C. Rutherford,et al.  The vegetation of South Africa, Lesotho and Swaziland. , 2006 .

[27]  G. N. Smit,et al.  THE INFLUENCE OF TREE THINNING ON THE REPRODUCTION DYNAMICS OF COLOPHOSPERMUM MOPANE , 1998 .

[28]  R. H. Westfall,et al.  Biomes of Southern Africa: An objective categorization , 1994 .

[29]  T. O’Connor,et al.  Rate and pattern of bush encroachment in Eastern Cape savanna and grassland , 1999 .

[30]  B. Walker,et al.  Relationships between tree canopy cover and Panicum maximum in the vicinity of Fort Victoria , 1973 .

[31]  A. J. Belsky,et al.  Influences of Trees on Savanna Productivity: Tests of Shade, Nutrients, and Tree-Grass Competition , 1994 .

[32]  N. M. Tainton.  Veld Management in South Africa , 1999 .

[33]  R. Bell.  The Effect of Soil Nutrient Availability on Community Structure in African Ecosystems , 1982 .

[34]  Fulco Ludwig,et al.  The influence of savanna trees on nutrient, water and light availability and the understorey vegetation , 2004, Plant Ecology.

[35]  John Phillip Harison. Acocks,et al.  Veld types of South Africa. , 1955 .

[36]  S. Shapiro,et al.  A Comparative Study of Various Tests for Normality , 1968 .

[37]  A. Tietema,et al.  Abiotic factors regulating nitrogen transformations in the organic layer of acid forest soils: Moisture and pH , 1992, Plant and Soil.