This study investigated the implications of the presence of migrant-tenant-farmers in natural forest reserves of Ondo State, Nigeria. It also examined the contributions of the forest reserves to rural livelihood. To achieve these, multistage sampling technique was used for the study. A well-structured questionnaire was employed to elicit information from 180 household heads. The data collected were analyzed using descriptive statistics analysis. According to the results, the majority of the migrant-tenant-farmers were in their productive age of 41-50 years, most of them had low level of education. Chi-square test (p<0.05) confirmed that there is significant association between age and gender of migrant-tenant-farmers and the effects of their livelihood activities on natural forest in the study area. More than 80% of them had been farming for over ten years. And this had positive effects on their productivity. The results showed that majority of the respondents derived their livelihoods from yam, cassava, maize, and cocoa production as well as palm oil and cassava processing. They also collect various types of Non-timber forest products (NTFPs) in the study areas for their livelihoods. The results further revealed that these migrant-tenant-farmers preferred virgin land which are natural forest or abandon land occupied by trees due to its huge deposition of organic manures and the essential soil minerals for crop production. Consequently, it leads to deforestation and fragmentation of forests, loss of unique habitats, biodiversity and atmospheric deterioration of the study areas. The results further showed that on-farm tree, with 37.2% of the respondents was the major method of tree conservation by the migrant-tenant-farmers in the study areas. Practicable suggestions that could reduce the current pressure on this fragile forest such as provision of subsidized fertilizer to boost agricultural productivity, and continuous campaign against deforestation in Ondo State were recommended.