Forest fragments in Arid and Semi-Arid Lands are key water catchment areas and provide important ecosystem services. However, uncontrolled human activities are fast altering their stem density basal area and diameter structure resulting into forest degradation. Besides, information regarding tree density and diameter size-class distribution of dryland forest fragments such as Museve and Mutuluni is lacking. Thus, the purpose of this study was to document key human activities in Museve and Mutuluni forest fragments in Kitui, Kenya and comparatively investigate their influences on stem density, basal area and stem diameter size-class distribution. Two belt transect of 20 m wide and 500 m long, with contiguous sample plots of 20 m by 20 m and subplots of 10 m by 10 m were established in each forest. Evidence of human activities, abundances and diameter measurements for mature trees were assessed in the 20 m by 20 m plots while abundances and diameter measurements for saplings were in the subplots. Mann-Whitney, t-test and logistic regression were used for data analysis. Mutuluni forest exhibited significantly (p<0.05) high stem density compared to Museve however, basal area density was not different (p<0.05). Introduction of exotic species enhanced basal area and stem density (p<0.05) in Museve forest. Tree cutting reduced both basal area and stem density in Museve forest and only stem density in Mutuluni. Stem-density diameter distribution in both forests followed a reverse J-curve but with more fluctuations and irregularities observed in Museve compared to Mutuluni forest. Diameter size-class distribution did not differ (p<0.05) across the two forests. Therefore human activities significantly impacted on tree density in both forest fragments with high impacts in Museve. This study recommends formulation of appropriate protection and conservation strategies, especially for Museve, to control tree cutting and increase tree density.