Garbon sequestration in urylana tcosystems

Drylands occupy 6 15 billion hectares (Bha) or 47 2% of the world's land area Of this, 3 5 to 4 0 Bha (57%65%) are e~ther deserl~fied or prone to deserlificat~on Desp~te the low soil organic carbon (SOC) concentratlon, total SOC pool of soils of the drylands IS 241 Pg (1 Pg = petagram = 10" g = I billion metrlc ton) or 15 5% of rhe world's rota1 of 1550 Pg to 1 -meter depth Desertification has caused historic C loss of 20 to 30 Pg Assuming that two-th~rds of the hlstoric loss can be resequestered, the total potent~al of SOC sequestration is 12 to 20 Pg C over a 50-year period Land use and management practices to sequester SOC include afforestation Dryland ecosystems are defined as regions in which the ratio of total annnal precipitation to potelltial evapotranspiration (P:E'I' or the Aridity Index, AI) ranges from 0.05 to 0.65, and include dry sub-humitl regions (A1 = 0.50-0.65) covering 9.9%; semi-arid regions (A1 = 0.20-0.50) covering 17.7%; arid regions (A1 = 0.05-0.20) covering 12.0%; and hyperarid regions (A1 = < 0.05) covering 7.5% of the earth's la1-1~1 area (Dregne 1983, Glenn and others 1993, lieyllolds and Snlith 2002). 'I'hese regions cover about 47.2% ol' the earth's land area or al,out 6.15 billion hectares (1Sha) ('Fable 1 ) , predomiiiantly in northern and southwestern Africa, southwestern anti central Asia, northwestern India and l'akistai~, southwestern U~lited States ,it-td Mexlco, westeln South America, and Australia (F11llc.l antl Koscnr.\~etg 2002, WKI 2000, Middleton and I horllas 1992, N a n and Clarke 1097). I'he wor lcl's dryland 5011s corltaln 241 Pg ol sot1 organlc cat bon (SCIC) (I.,\wnr an and others 2000), wll~ctl 1s r ~ b ~ j ~ ~ t 4