Abstract

AbstractWe investigated seed dispersal phenology of bird‐dispersed and encroaching woody species in the Free State National Botanical Garden (FSNBG), South Africa, over a 12‐month period. Results from defecated seeds' collection in 17 roosting sites show that a total of 22,161 seeds belonging to 14 woody species under 11 families were eaten and dispersed by foraging birds with seeds of six species being frequently dispersed. The native species had a larger number of dispersed bird‐ingested seeds than the alien and invasive species. Seeds' collection suggested that out of five fruiting species, birds mostly preferred the red (Ziziphus mucronata, Ehretia rigida and Viscum rotundifolium) and black fruits (Olea europaea subsp. africana and Diospyros lyciodes). Ziziphus mucronata and O. subsp. africana seeds were dispersed in significantly higher numbers between March and July (mean ± SE: 47.1 ± 11.6; 51.4 ± 9.0), while Searsia lancea and E. rigida were mostly dispersed between August and December (221.6 ± 74.1; 373.6 ± 91.5)—a dichotomy that could minimise competition for dispersal agents while sustaining the resident bird species. Over 480 h of camera trapping, 22 bird species were captured, of which seven displayed high foraging frequency, and were resident in behaviour, while six species were migratory and colonial avian frugivores, including two alien bird species. We conclude that the reported bush encroachment is a likely result of high propagule pressure by resident frugivorous birds and colonial wintering birds in FSNBG, together with low fruit diversity in the grassland habitat.

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