The effects of woody plant encroachment and wildfire on plant species richness and composition: Temporal changes in a forest–steppe mosaic

Abstract

AbstractQuestionsWoody plant encroachment and wildfire may both have major effects on species richness and composition, yet studies that assess these two factors in combination are rare. We asked the following specific questions: (1) how did juniper cover change over a decade in the study area; what are the effects of juniper encroachment and subsequent wildfire on(2) plant species richness; and (3) vegetation composition?LocationSand forest–steppe in Kiskunság, Central Hungary.MethodsWe studied a juniper‐encroached grassland hit by a wildfire. We assessed changes in plant species richness and composition in burnt and unburnt grassland and juniper plots for 11 years following the wildfire. Yearly vegetation sampling was performed in permanent quadrats of 1 m2 and 25 m2 using visual cover estimation. Temporal changes in juniper cover and species richness were evaluated with generalized linear mixed‐effects models. Compositional changes were analysed by non‐metric multidimensional scaling and fidelity analysis.ResultsAt the beginning of the study, the presence of individual juniper shrubs increased species richness, and did not alter species composition. However, microsites covered by junipers were extremely species‐poor. Juniper growth during the study period caused a sharp decline in species richness at the edge of juniper shrubs and a shift in species composition compared to grassland plots. Wildfire increased species richness both in grassland and juniper plots. It caused only transient compositional responses in grasslands, but converted juniper habitats back to the grassland state.ConclusionsWe conclude that neither moderate juniper encroachment nor wildfire have negative effects on plant species richness in the studied ecosystem. However, as juniper thickening may cause species loss and devastating fires, conservation management should prevent the development of dense juniper stands.