To date, most studies on the effectiveness of geotextiles on soil erosion rates were conducted in laboratory experiments for <1 h. Hence, at Hilton, East Shropshire, UK, this study investigated the effectiveness of palm-mat geotextiles (Borassus and Buriti mats) in reducing rainsplash erosion, runoff and soil loss and changing selected soil properties under field conditions over two years (January 2007-January 2009). Mat-cover effects on rainsplash erosion were studied in two sets on a loamy sand soil (0o slope). In both sets, six randomly-selected plots (each 1 m2) were completely matcovered and six were bare. Unlike Buriti mats, Borassus mat-cover on bare soil significantly (P<0.001) decreased rainsplash erosion (by ~89%). Duplicate runoff plots (10 x 1 m on a 15o slope) had five treatments (bare, permanent grass, Borassus completely-cover, Borassus buffer strip and Buriti buffer strip). Using Borassus buffer strips (area coverage ~10%) on bare soil decreased runoff by ~71% (P>0.05) and soil erosion by ~92% (P<0.001). Borassus buffer strip, Buriti buffer strip and Borassus completely-covered plots had similar effects in decreasing runoff and soil loss. However, the longevity of Borassus mats was ~twice that of Buriti mats. Despite physical protection, runoff control and sediment entrapment, biomat buffer zones may considerably alter and protect flow direction by presenting barriers and creating several cross-drains. Except Borassus completely-covered plots, all plots had significant (P<0.05) increases in topsoil (0-5 cm) bulk density and decreased aggregate stability. However, buffer strips were more effective in trapping fine particles than Borassus completely-covered plots. No treatments had significant (P>0.05) effects on changes in pH, soil organic matter, total soil carbon or N. Plots with Borassus mats significantly (P<0.05) increased total P and decreased total Ca. Treatments had no significant effects on changes in total S, Mg, Zn, Cu, Fe, Mn, Mo or Cl concentrations. Borassus buffer strips can effectively conserve soil and water and improve and maintain selected soil properties, with results similar to Borassus completely-covered plots. The mechanisms explaining the effectiveness of buffer zones require further studies under varied pedo-climatic conditions.

Made available in DSpace on 2016-04-28T20:13:51Z (GMT). No. of bitstreams: 1 2008 Marie Therese Yaba Ndiaye.pdf: 7814625 bytes, checksum: d4eab4a0a17148cd52fe0a71238c8c15 (MD5) Previous issue date: 2008-08-21 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In 1998 Senegal passed laws that transferred authority over the management of forests to local communities. This dissertation studies the impact of this decentralization on the health of the Samba Dia and Sambande forests and the livelihoods of forest-dependent populations. I use this analysis to reflect on the broader question of the impact of decentralization on conservation and poverty alleviation. I employ temporal and spatial modes of comparison in this study with qualitative research methods. Decentalization has contained forest degradation in both areas. But while people in Samband? forest report benefits to all from the forest, in Keur Samba Dia members of one village report benefits while others decry a reduction in their benefits from the forest. I argue that the transfer of authority from a largely absent and incapable state to well-organized and knowledgeable local communities account for the containment of environmental degradation in both forests. But while the uniform use of the forest by community members has helped people in Samband? solve distributive conflicts and so universally benefit from the forest, a significant divergence in how the two villages in Keur Samba Dia exploit the forest has worsened distributive conflicts allowing the more powerful people of Yayem to benefit more but exclude the less powerful people of Samba Diallo from these new benefits. The impact of decentralization on poverty alleviation and forest health is mediated by important local factors and we should not expect it to have good effects in all areas in which it is pursued. / A descentraliza??o florestal no Senegal constitui o tema desta pesquisa. Em 1998, o Senegal promoveu novas leis florestais que transferiam as compet?ncias de gest?o das florestas para as comunidades rurais, para frear a pobreza e a degrada??o ambiental. Neste contexto, a tese investiga os impactos destas reformas nas vidas das popula??es e nas florestas. A tese tentou lidar com as duas perguntas, se ap?s a descentraliza??o: - as popula??es locais seriam capazes de manejar efetivemente as florestas e o manejo florestal comunit?rio participaria na redu??o da pobreza rural. Fiz um estudo com varia??o espacial e temporal, comparando duas florestas: Keur Samba Dia e Samband? durante dois per?odos diferentes: antes e ap?s a descentraliza??o. Antes de 1998, a gest?o das duas florestas estava sob a responsabilidade do Servi?o Florestal Nacional. Depois de 1998, as comunidades rurais se tornaram as novas autoridades na floresta Samband? enquanto que a floresta Keur Samba Dia permaneceu sob um sistema de co-manejo entre as comunidades rurais e o Estado. A pesquisa deparou com o fato de que, em ambas as florestas, os impactos ecol?gicos da descentraliza??o foram positivos, pois houve uma regenera??o florestal. Todavia, os impactos econ?micos resultantes da descentraliza??o, foram diferentes de uma floresta para outra. Na floresta de Samband?, todos os vilarejos foram beneficiados pela descentraliza??o, enquanto que na floresta de Keur Samba Dia, um vilarejo se sentiu mais prejudicado do que o outro. Estes resultados nos informam, que a participa??o popular foi ben?fica ? sa?de das florestas, mas n?o foi suficiente para que as popula??es se aproveitassem economicamente de uma floresta regenerada. A distribui??o eq?itativa, dos benef?cios econ?micos da descentraliza??o, ? mediada pela uniformidade ou formas conflituosos do uso florestal e por fatores s?cio - hist?ricos.