A legacy of past agriculture continues to shape many current forests in north-eastern North America and Europe, where the understorey flora of postagricultural stands shows reduced diversity and altered composition for hundreds of years. Effective management of forests recovering from human disturbance requires an understanding of the mechanisms that produce these patterns. Here we discuss forest regeneration on abandoned agricultural land in Tompkins County, New York. USA, in comparison with other regions that share a broadly similar history. Using data from vegetation surveys of primary and secondary forests, we assessed the relationship between land-use history and forest herb diversity; the effects of time since abandonment, distance from primary forest and type of agricultural use, whether cultivation or pasture, on the species-richness of secondary stands; and the influence of dispersal mechanism on individual species' distributions. Secondary forests 70-100 years old contained, on average, 65% the number of forest herb species in primary forests. Among all secondary stands, forest herb species-richness increased with time since abandonment, and decreased with distance from primary forest; type of agricultural use did not affect species-richness directly, but the relationship with distance was weaker for former pastures. Dispersal mechanism did not influence species' relative frequency in the two forest types. While landscape-level patterns indicate that the process of dispersal largely controls forest herb diversity in postagricultural stands, unexplained variation among species with similar dispersal mechanisms suggests that other processes, such as recruitment, may also affect the distributions of some species.

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Several threatened forest species are currently associated with semi-open, wood-pasture conditions and do not thrive in present-day, non-intervention temperate forests of north-western Europe. We assess the changing importance through time of five disturbance agencies that open forest canopies and induce the past structure of these forests. The influence of browsing and grazing animals has varied through time, but was most intense from domestic animals during recent centuries. The role of large ungulates on forest structure during the early Holocene was negligible. Fires of both natural and anthropogenic origin have been of importance in the past, but have now virtually ceased. Past effects of waterlogging have been severely reduced by drainage schemes. Windthrow has been a relatively constant factor through time, while anthropogenic influence has dominated forest structure, particularly during recent centuries. Natural forest structure is probably more open and varied than found in present-day, non-intervention, reference forests, due to variable combinations of these disturbance agencies.

Degradation and regeneration of tropical forests can strongly affect gene flow in understorey species, resulting in genetic erosion and changes in genetic structure. Yet, these processes remain poorly studied in tropical Africa. Coffea canephora is an economically important species, found in the understorey of tropical rainforests of Central and West Africa, and the genetic diversity harboured in its wild populations is vital for sustainable coffee production worldwide. Here, we aimed to quantify genetic diversity, genetic structure, and pedigree relations in wild C. canephora populations, and we investigated associations between these descriptors and forest disturbance and regeneration. Therefore, we sampled 256 C. canephora individuals within 24 plots across three forest categories in Yangambi (DR Congo), and used genotyping-by-sequencing to identify 18,894 SNPs. Overall, we found high genetic diversity, and no evidence of genetic erosion in C. canephora in disturbed old-growth forest, as compared to undisturbed oldgrowth forest. In addition, an overall heterozygosity excess was found in all populations, which was expected for a selfincompatible species. Genetic structure was mainly a result of isolation-by-distance, reflecting geographical location, with low to moderate relatedness at finer scales. Populations in regrowth forest had lower allelic richness than populations in old-growth forest and were characterised by a lower inter-individual relatedness and a lack of isolation-by-distance, suggesting that they originated from different neighbouring populations and were subject to founder effects. Wild Robusta coffee populations in the study area still harbour high levels of genetic diversity, yet careful monitoring of their response to ongoing forest degradation remains required.