Soil organic carbon (SOC) stocks and fluxes in forest ecosystems are influenced by natural and human disturbances. In the Tropical regions the highest impacts on disturbance in forest C cycles are related to human activities such as conversion of natural lands to cropland and pasture areas and to forest plantations. The disturbances in the forest C cycles will release CO2 emissions to the atmosphere triggering global warming. In this study the focus was set in subTropical soils in Brazil, south extreme region of Bahia. The aim of the study was to investigate whether reforestation of Eucalyptus plantations under former pasture areas will help mitigate climate change through carbon sequestration.

As the world´s population increases and people's living conditions are improving, larger areas are needed for houses as well as food production. This means that new areas are exploited and that people, livestock, blood sucking insects and wild animals are forced to live close together. In combination with the global warming, leading to extreme weather such as floods and storms, this allows both new and old pathogens to emerge. The number of "emerging infectious diseases", EIDs, has increased in recent years and many of them have their origin in poor, Tropical countries. Moçambique is therefore considered to be a high risk area for EIDs. Schmallenberg virus, SBV, was discovered in 2011 as an "emerging infectious disease" in dairy cows in Germany.

The study was performed in southwest of Colombia in close collaboration with the interna-tional centre of Tropical agriculture, CIAT and supervised from the university of Valle, Uni-valle, Cali, Colombia and from the Department of Landscape Management and Horticultural Technology, SLU, Alnarp, Sweden. The main purpose of this thesis was to evaluate six different non-conventional insecticides and their ability to control whitefly Aleurotrachelus socialis in cassava Manihot esculenta. The aim was also to evaluate the most appropriate application technique for these products which were: Agronim, Biomel, Bioneem, EcoSwing, Coco soap + chilli and L´Ecomix. The products are mainly based on vegetable oil, soap and plant extract and cause primarily a physical contact effect which affirm that it is fundamental to obtain a high coverage of the underside of the leaves, where A. socialis is present.

Large areas of forests in the Tropical region have during the last decades been lost and converted to new land uses while other areas have been degraded into secondary forests. These secondary forests need to be restored and rehabilitation through enrichment planting and liberation may help to speed up the recovery process. The objective of this thesis was to evaluate a rehabilitation method that includes enrichment planting, slashing of weeds and girdling of unwanted trees. The site for the project is situated in Sabah, Borneo in a secondary forest which had been logged and burnt by a wildfire. The project?s goal is to rehabilitate and increase biodiversity through enrichment planting of seedlings mainly belonging to the family Dipterocarpeaceae (dipterocarps).

The rainforests of the world are important not only to the countries in which they grow but to the world as a whole. They influence oxygen and water circulation as well as carbon sequestration which in turn affect global radiation and global warming. The forest also have great value and in Malaysia as in many other Tropical countries large volumes are harvested which leaves great areas of degraded forest with little growth and biological diversity. Due to their low financial value these forests are often transformed and used for other purposes than forestry such as oil palm plantations. The trees are often transported out of the forest using large bulldozers. They are heavy which causes compaction of the forest floor and during transport the top soil layers are moved to improve mobility.