The study was carried out in West Matogoro Catchment Area (WMCA) of Songea, Tanzania, to establish whether for the period between intercensal periods 1978-1988 and 1988-2002, and between 2002 and 2005 characteristics of human population of the area had changed in terms of size, age structure and sex composition. In case it did, then the study had to establish whether such changes may be used to explain the observed forest cover change that occurred in the area. Establishing whether the observed changes were proportionate was important in linking the relationship among factors at hand. The study partly tested the thesis by Liu and others which linked human population changes and their implications to the panda habitat [1] . The findings indicated existence of changes in human population characteristics for the period under review. Variations in terms of population size, age structure and sex composition were realized. While growth was measured by the total population and size of age group of the environmentally active population as identified by the study by Haule, sex composition was determined by sex ratios [2] . The environmentally active age group included males aged 20 to 44 and females aged 10 to 44, i.e. the key actors in felling trees for farm expansion and for firewood respectively. Geographic Information System (GIS) evidence indicated progressive forest cover deterioration. When compared, the changes in human population characteristics and those of the forest cover were noted to be un- proportional. Variations were in terms of increase in human population size and expansion of age group of the “actors” thus attributed to the augmenting deforestation. A positive relationship was demonstrated between population growth, expansion of age segment of the key actors and expanded deforestation. We reiterate that any sustainable measures to address the environmental issues should take into account changes in demographic characteristics of the in Situ population which forms the locus of the interface between population and environment. These factors signify the intensity and duration of the involved forces that characterize forest cover quality.