Abstract: Humancaused landscape fragmentation is a primary driving force for global biodiversity loss, and a major threat to nature reserves (NRs). However, studies on the effectiveness of NRs in preventing landscape fragmentation are still limited. Based on four phases of land cover data in 1990, 2000, 2010, and 2015 in Southwest China, we constructed a landscape index to quantitatively analyze the effectiveness of 102 NRs in the region in preventing landscape fragmentation. We assessed the impacts of different administrative levels, establishing years and categories of NRs on conservation effectiveness. Finally, we established a human disturbance index in each NR to reveal the impacts of human disturbances on landscape fragmentation. The results showed that: (1) During the past 25 years, the number of NRs with decreased fragmentation was greater than that with increased fragmentation, indicating that NRs were effective in habitat conservation. However, the overall increasing trend of average fragmentation showed that some NRs had lower ability on protecting habitat intactness; (2) There were no significant differences in the conservation effectiveness of four categories of NRs. The administrative levels and their establishing years influenced the effectiveness of these NRs. Before 2000, the effectiveness of provincial NRs and NRs established in 1981-1990 was better than that of national NRs and NRs established in 1958-1980 (P<0.01), respectively. After 2000, the effectiveness between NRs at different levels and established in different years was similar (P>0.05); (3) The relationship between human disturbance index and landscape fragmentation varied in different periods. From 1990 to 2000, there was no significant correlation between them, and NRs demonstrated a strong effect of offsetting human disturbances. From 2000 to 2010, there was a significant correlation between them, and human disturbances were probably the dominant factor increasing landscape fragmentation. From 2010 to 2015, the correlation was no longer significant. It is noteworthy that the influence of natural disturbances should be considered for those NRs with decreased human disturbance index but increased landscape fragmentation.

Key words: nature reserve, landscape fragmentation, habitat protection effectiveness, human disturbance, Southwest China.