5 the state of science in south africa
B I O L O G I C A L S C I E N C E S
suitable for forests, and it is probably fre- The costs and benefits of changes in woody
quent fires that restrain the growth of cover in the tropical grassy biomes vary, de-
woody vegetation. Mean annual rainfall, pending on ecological and socio-economic
and fire, are the most important correlates contexts, and spatial scale. Carbon seques-
of tree cover, with African megafauna, par- tration projects have become a source of in-
ticularly elephants (where they still exist) come in some regions where increased tree
contributing to open grassy structure. The cover is a desirable goal. Elsewhere, tree in-
advent of satellite imagery has led to an crease is undesirable, as in African savanna
increased appreciation of fire in impacting parks and livestock farming areas. Forest
on both vegetation structure and global cli- spread into grasslands could cause casca-
mate change. ding changes in biodiversity. Holistic studies
of the consequences of changes in savanna
The future of savannas and grasslands is landscapes are needed to evaluate fully the
uncertain. The direct effects of increasing social and economic impacts on society
atmospheric CO
2
are likely to be consider- and on nature; this is an area that requires
able, given that C3 woody vegetation is further directed research in South Africa.
likely to respond more than the C4 grasses.
A consequence of this is that woody spe- Grassland science
cies may grow sufficiently rapidly to escape Grassland science is an applied form of
the flame zone and thus become well es- plant science in South Africa referring to
tablished. The overall effect of increasing the ecology and management of natural
CO
2
in grassy ecosystems is to promote grassland and cultivated pasture. The term
woody plants within savannas, leading to can be somewhat misleading in that grass-
increased woody cover. Indeed, in South dominated vegetation occurs in many of
Africa, scrub forest has invaded savannas the biomes (other than the grassland bi-
in conservation, commercial ranching and ome) occurring in South Africa. Internation-
communally farmed areas. Acting against ally, ‘rangeland’ is a more commonly used
CO
2
-induced increases in woody cover are term to describe natural, grass-dominated
climate-induced increases in tree mortality vegetation.
from drought or high-severity burns.
In South Africa, grassland science originat-
Changes in woody cover have many con- ed out of a need to understand and man-
sequences, both positive and negative, age the vast natural veld used primarily for
for pastoralists, timber-use, biodiversity, livestock production. The origins can be
and ecosystem function. Changes in tree traced to the Drought Investigation Commis-
cover can have important ecosystem con- sion Report of 1923, in which many recom-
sequences with feedbacks to the earth- mendations pointed to the development
atmosphere system, including the role of of a focused attempt to improve veld and
trees as carbon sinks and their influence on livestock management and soil conserva-
energy budgets and hydrology. tion. At the time, vegetation management
in conservation areas was considered to
144
TWAS book_Chap1-6.indd 144 2009/10/06 12:03:55 PM
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52 |
Page 53 |
Page 54 |
Page 55 |
Page 56 |
Page 57 |
Page 58 |
Page 59 |
Page 60 |
Page 61 |
Page 62 |
Page 63 |
Page 64 |
Page 65 |
Page 66 |
Page 67 |
Page 68 |
Page 69 |
Page 70 |
Page 71 |
Page 72 |
Page 73 |
Page 74 |
Page 75 |
Page 76 |
Page 77 |
Page 78 |
Page 79 |
Page 80 |
Page 81 |
Page 82 |
Page 83 |
Page 84 |
Page 85 |
Page 86 |
Page 87 |
Page 88 |
Page 89 |
Page 90 |
Page 91 |
Page 92 |
Page 93 |
Page 94 |
Page 95 |
Page 96 |
Page 97 |
Page 98 |
Page 99 |
Page 100 |
Page 101 |
Page 102 |
Page 103 |
Page 104 |
Page 105 |
Page 106 |
Page 107 |
Page 108 |
Page 109 |
Page 110 |
Page 111 |
Page 112 |
Page 113 |
Page 114 |
Page 115 |
Page 116 |
Page 117 |
Page 118 |
Page 119 |
Page 120 |
Page 121 |
Page 122 |
Page 123 |
Page 124 |
Page 125 |
Page 126 |
Page 127 |
Page 128 |
Page 129 |
Page 130 |
Page 131 |
Page 132 |
Page 133 |
Page 134 |
Page 135 |
Page 136 |
Page 137 |
Page 138 |
Page 139 |
Page 140 |
Page 141 |
Page 142 |
Page 143 |
Page 144 |
Page 145 |
Page 146 |
Page 147 |
Page 148 |
Page 149 |
Page 150 |
Page 151 |
Page 152 |
Page 153 |
Page 154 |
Page 155 |
Page 156 |
Page 157 |
Page 158 |
Page 159 |
Page 160 |
Page 161 |
Page 162 |
Page 163 |
Page 164 |
Page 165 |
Page 166 |
Page 167 |
Page 168 |
Page 169 |
Page 170 |
Page 171 |
Page 172 |
Page 173 |
Page 174 |
Page 175 |
Page 176 |
Page 177 |
Page 178 |
Page 179 |
Page 180 |
Page 181 |
Page 182 |
Page 183 |
Page 184 |
Page 185 |
Page 186 |
Page 187 |
Page 188 |
Page 189 |
Page 190 |
Page 191 |
Page 192 |
Page 193 |
Page 194 |
Page 195 |
Page 196 |
Page 197 |
Page 198 |
Page 199 |
Page 200 |
Page 201 |
Page 202 |
Page 203 |
Page 204 |
Page 205 |
Page 206 |
Page 207 |
Page 208 |
Page 209 |
Page 210 |
Page 211 |
Page 212 |
Page 213 |
Page 214 |
Page 215 |
Page 216 |
Page 217 |
Page 218 |
Page 219 |
Page 220 |
Page 221 |
Page 222 |
Page 223 |
Page 224 |
Page 225 |
Page 226 |
Page 227 |
Page 228 |
Page 229 |
Page 230 |
Page 231 |
Page 232 |
Page 233 |
Page 234 |
Page 235 |
Page 236 |
Page 237 |
Page 238 |
Page 239 |
Page 240 |
Page 241 |
Page 242 |
Page 243 |
Page 244 |
Page 245 |
Page 246 |
Page 247 |
Page 248 |
Page 249 |
Page 250 |
Page 251 |
Page 252 |
Page 253 |
Page 254 |
Page 255 |
Page 256 |
Page 257 |
Page 258 |
Page 259 |
Page 260 |
Page 261 |
Page 262 |
Page 263 |
Page 264 |
Page 265 |
Page 266 |
Page 267 |
Page 268 |
Page 269 |
Page 270 |
Page 271 |
Page 272 |
Page 273 |
Page 274 |
Page 275 |
Page 276 |
Page 277 |
Page 278 |
Page 279 |
Page 280 |
Page 281 |
Page 282 |
Page 283 |
Page 284 |
Page 285 |
Page 286 |
Page 287 |
Page 288 |
Page 289 |
Page 290