In publications on tropical forest fragmentation, regrowing secondary forests (SF) on abandoned agricultural land are often overlooked. These forests represent highly fragmented components in the landscape matrix which are generally less than 100 ha in size. SF are found on privately owned land where they are contributing to on-farm income through logging and/or use of non-timber products. Hence, defining pure conservation goals for this forest type seems to be unrealistic. In this paper, we used the process-based model FORMIX3-Q to simulate successional processes and logging scenarios in SF exposed to different degrees of fragmentation (either facing non-forest land on only one side or totally surrounded by agricultural land) in the subtropical eastern part of Paraguay. We compared results with primary forest embedded in a similar matrix. Under light fragmentation, bole volume of SF approached primary forest values after about 50 years of succession. Species composition, however, was clearly distinct from primary forest over the first 200 years of succession. The development of bole volume and species composition in severely fragmented SF was similar to the less fragmented SF over the initial 50 years. However, limited seed input, largely confined to on-site seed sources in the severely fragmented SF, led to a decline in bole volume by about one-third compared to the reference value over the simulation period of 400 years. By applying a minimum felling diameter (MFD) of 35 cm in the lightly fragmented SF, first logging was only possible after 30 years, resulting in a mere 3.7 m3 ha-1 harvest. Highest timber yields were obtained with 10 yr cutting cycles and a maximum removal of 20 stems ha-1, though sustainable yields only resulted from lowering the MFD to 30 cm. Logging in severely fragmented SF accelerated the decline of bole volume. Overall, results suggest that timber production in SF without silvicultural treatments is low and hence does not constitute a viable option to diversify farm income. Only managed SF may serve this function. Research focusing on the elaboration of management options for SF, integrating as much as possible of the original vegetation, is needed. © 2002 Elsevier Science B.V. All rights reserved.