Introduction 1998 2002 1989 1993 1995 2001 2004a) 1997 2001 2001 2004b 1998 2003 1995 2001 1997 2004a 1994 1998 2002 Acacia 1992 Eucalyptus 1998 1979 1989 1997 2000 1999 2002 1990 2000 2001 2002 Acacia tortilis Materials and methods Site description 2 1999 2 1987 Equus burchelli Connochaetes taurinus Syncerus caffer 1999 Loxodonta africana Acacia A. tortilis 1999 Combretum Commiphora Acacia 1997 1999 A. tortilis 1999 1999 Grass sample collection and chemical analyses Acacia 2004a 1993 2004a 1982 1 Cynodon Cynodon dactylon, Cynodon nlemfluensis and Cynodon plectostachius 1982 Table 1  in parentheses n Acacia tortilis Location Species Cover of vegetation at specific zone (%) Live stem (%) Live leaf (%) Dead stem (%) Dead leaf (%) Leaf/stem ratio Data Under tree canopy Panicum maximum 9 33.1 (5) 51.1 (13) 4.5 (6) 11.3 (4) 1.81 (0.73) Cynodon 62 47.4 (7) 42.0 (8) 4.4 (2) 6.2 (3) 0.95 (0.24) Cenchrus ciliaris 9 40.8 (15) 28.3 (9) 6.8 (3) 24.0 (13) 1.22 (0.54) Around tree canopy Cynodon 7 50.4 (6) 25.4 (3) 5.4 (3) 18.8 (7) 0.80 (0.14) Cenchrus ciliaris 6 40.9 (19) 27.2 (3) 15.4 (10) 16.5 (10) 0.83 (0.37) Digitaria macroblephera 14 39.0 (15) 25.2 (8) 7.9 (15) 27.8 (3) 0.70 (0.24) Chloris virgata 9 43.7 (7) 30.7 (8) 9.0 (6) 16.6 (6) 1.14 (0.12) Urochloa mosambicencis 21 52.4 (3) 34.7 (11) 4.9 (5) 8.0 (10) 0.91 (0.20) Heteropogon contortis 17 43.8 (6) 27.2 (9) 15.9 (4) 13.1 (3) 0.77 (0.25) Open grassland H. contortis 38 48.3 (4) 32.9 (7) 8.4 (5) 10.4 (5) 0.77 (0.11) Sehima nervosum 36 50.1 (12) 29.2 (9) 12.0 (7) 8.7 (14) 0.62 (0.16) a  df      Location F 2 ,38 1.76 6.57** 1.86 1.84 8.60*** Tree (block) F 3, 38  1.60 0.42 1.18 0.08 1.15 P P a 1995 1983 1970 1963 2004a A. tortilis A. tortilis 2004a Linear model 1978 1999 1999 1997 1993 1995) 1 \documentclass[12pt]{minimal}
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$$ C \ge {\text{or}} \le \sum c_i \times I_i $$\end{document} C I i  i c i I i C 1995 1994 1969 2 \documentclass[12pt]{minimal}
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$$ 22.32({\text{MJ}}/{\text{day}}) \le \sum 19({\text{MJ}}/{\text{kg}}\,{\text{DW}}) \times {\text{DOM}}_i ({\text{g}}/{\text{g}}) \times 0.82\,I_i $$\end{document} I  i 1999 3 \documentclass[12pt]{minimal}
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$$ {\text{DP}}\,({\text{g}}/{\text{day}})\, = \,3.150 \times W^{{0.75}} $$\end{document} W 1993 1987 4 \documentclass[12pt]{minimal}
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$$ {\text{DP}}\,({\text{mg}}/{\text{g}})\, = \,0.91 \times {\text{CP }}({\text{mg}}/{\text{g}}) - 32.2 $$\end{document} 5 \documentclass[12pt]{minimal}
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$$ 130\,{\text{g}}\,{\text{DP}}/{\text{day}} \le \sum {\text{DP}}_i \times I_i.$$\end{document} 1999 1994 1988 4 6 \documentclass[12pt]{minimal}
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$$ {\text{NDF}}\,{\text{intake}}\,({\text{kg}})\, = \,66.7 \times 10^{{ - 3}} \times W^{{0.75}} $$\end{document} 7 \documentclass[12pt]{minimal}
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$$ 2.76\,{\text{kg}}\,{\text{NDF}}/{\text{day}}\, = \,\sum {\text{NDF}}_i \times I_i $$\end{document} 1995 8 \documentclass[12pt]{minimal}
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$$ 5.75\,{\text{g}}\,{\text{P}}/{\text{day}} \le \sum {\text{P}}_i \times I_i $$\end{document} 9 \documentclass[12pt]{minimal}
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$$ 3.59\,{\text{g Ca}}/{\text{day}} \le \sum {\text{Ca}}_i \times I_i $$\end{document} 1999 Statistical analysis Percentages of dead and live leaves and stems, nutrient concentrations, NDF and DOM of grass samples were analysed with a general linear model (GLM) with vegetation zone (under and around tree canopies, and open grassland) as fixed factors and trees as a random factor. Differences in NDF, DOM and protein concentrations of grasses from different tree stages (open grassland, bushes and small, large and dead trees) were analysed with a GLM with tree stage as a fixed factor. All data were statistically analysed with SPSS 11.0. Results Cynodon 1 Panicum maximum Cenchrus ciliaris 1 Heteropogon contortis Sehima nervosum 2 1 Cynodon 1 H. contortis Cynodon . H. contortis S. nervosum Cynodon  Cenchrus ciliaris 1 Table 2  in parentheses DOM NDF A. tortilis Location Species DOM (%) NDF (%) Protein (mg/g) P (mg/g) K (mg/g) Ca (mg/g) Mg (mg/g) Data Under tree canopy P. maximum 65.7 (6.5) 70.6 (3.3) 141 (19.7) 1.77 (0.17) 40.6 (2.2) 4.12 (0.26) 3.25 (0.79) Cynodon 70.3 (7.2) 61.5 (4.9) 165 (8.4) 1.80 (0.32) 38.4 (2.4) 6.91 (0.71) 2.44 (0.57) Cenchrus ciliaris 59.8 (3.2) 70.1 (5.0) 137 (5.0) 1.74 (0.18) 44.8 (3.8) 4.34 (2.19) 1.95 (0.43) Around tree canopy Cynodon 65.1 (12.4) 66.5 (8.6) 127 (26.2) 2.38 (0.42) 36.1 (11.2) 6.70 (2.18) 2.58 (0.38) Cenchrus ciliaris 58.0 (9.0) 71.5 (6.1) 106 (15.4) 2.43 (0.07) 41.9 (7.0) 3.30 (0.65) 1.87 (0.38) D. macroblephera 62.6 (8.0) 72.9 (6.2) 75 (13.5) 2.85 (0.52) 38.6 (1.5) 3.75 (0.76) 2.26 (0.55) Chloris virgata 66.8 (5.9) 70.4 (4.1) 105 (5.0) 2.59 (0.61) 37.6 (1.8) 4.91 (0.30) 3.03 (0.45) U. mosambicencis 69.1 (5.4) 64.8 (3.5) 104 (10.3) 3.59 (0.78) 44.3 (3.9) 5.28 (0.56) 4.00 (0.40) H. contortis 57.0 (4.8) 70.2 (3.0) 82 (11.8) 1.46 (0.13) 17.2 (0.5) 3.30 (0.3) 1.64 (0.18) Open grassland H. contortis 51.7 (2.2) 74.0 (2.2) 68 (9.3) 1.65 (0.19) 15.1 (0.7) 3.31 (0.31) 1.22 (0.15) S. nervosum 54.7 (1.0) 74.6 (1.0) 61 (9.7) 1.46 (0.13) 12.0 (0.8) 4.67 (0.36) 1.47 (0.06) a Location F 10.4*** 5.55** 49.9*** 11.7*** 28.2*** 1.34 7.77** Tree (block) F 7.08*** 5.45*** 1.36 1.07 1.36 0.64 0.71 P P a Fig. 1 Acacia tortilis NDF Bars  same letter P >  P  1 Acacia Acacia 1 2 2 Fig. 2  lines 2 5 7 8 9 shaded part DW  Discussion Cynodon  Acacia 2 2001 2004a 1994 1997 2001 . 1999 P. maximum . 1996 2000 Acacia 2004a Acacia Acacia 2003 2004a 1993 1994 2006 2006 1985 2006 . 2004a 2004a 2004a . 1999 . 2000 . 2004 . 2000 P. maximum 1994 1990 1993 1997 . 2000 . 2007 . 1999 . 2000 . 2002