Seed banks of subtropical grassland patches within an urban matrix in South Africa: reflecting the past and foretelling the future

Urban grasslands often exist as fragmented patches with varying threat levels. These patches are generally inappropriately managed due to limited data on their responses to disturbance and seed bank regenerative potential. This study compared seed banks between non-naturally disturbed and undisturbed patches of South African subtropical grasslands in an urban environment. Standing vegetation was characterised via year-round quadrat and monthly transect sampling. The seed banks were sampled after the two main dispersal periods and assessed for species composition and density. The seed bank species (24) represented a subset (9%) of the standing vegetation, with forbs being the most speciose lifeformandgrasses themostabundant. Disturbancehada moderate impactonseedbankdensity but significantly affected species composition and ordering. Clustering and ordination analyses separated seed banks based on disturbance history. However, seed banks in disturbed patches maintained the general character of the grassland type. Diagnostic, rare and threatened taxa were absent from seed banks, irrespective of disturbance history. Consequently, restoration will possibly require seed enrichment and species reintroduction rather than exploitation of natural seed banks. Identifying disturbance-sensitive species through seed bank surveys can inform grassland conservation and restoration strategies. Key words: disturbance, grassland, seed banks, urban environment. Les prairies urbaines existent souvent sous forme de parcelles fragmentees, menacees a des degres variables. Ces parcelles sont generalement gerees de facon inappropriee a cause des donnees limitees quant a leurs reponses aux perturbations et au potentiel regenerateur des banques de graines. Cette etude a compare des banques de graines issues de parcelles perturbees de facon non naturelle et de parcelles non perturbees de prairies subtropicales d'un environnement urbain en Afrique du Sud. La vegetation sur pied a ete caracterisee au moyen d'echantillonnage tout au long de l'annee de quadrats et d'un echantillonnage mensuel de transects. Les banques de graines ont ete echantillonnees apres deux periodes principales de dispersion et evaluees quant a la composition et la densite des especes. Les especes des banques (24) representaient une sous-categorie (9 %) de la vegetation sur pied, les herbes non gramineennes constituant la forme de vie la plus diversifiee alors que les graminees etaient les plus abondantes. La perturbation avait un impact modere sur la densite des banques de graines, mais elle affectait significativement la composition et le classement des especes. Les analyses par segmentation et d'ordination separaient les banques de graines sur la base de leur historique de perturbations. Cependant, les banques de graines des parcelles perturbees conservaient le caractere general de la prairie. Les taxons diagnostiques, rares et menaces etaient absents des banques de graines, nonobstant l'historique de perturbations. En consequence, la restauration necessitera possiblement un enrichissement en graines et la reintroduction d'especes plutot que l'exploitation des banques de graines naturelles. L'identification d'especes sensibles aux perturbations par le suivi des banques de graines peut guider les strategies de conservation et de restauration des prairies. [Traduit par la Redaction] Mots-cles : perturbation, prairie, banques de graines, environnement urbain.
Introduction Tropical and subtropical grasslands are ancient, with high levels of plant endemism and many specialised plant taxa (Bond 2016). In South Africa, subtropical grasslands occur along the eastern seaboard, [...]