Effects of woody species encroachment and fire on vegetation and the soil seed bank in dry grasslands of Transylvania

Abstract

Questions: (a) In which ways do woody species encroachment and fire affect vegetation and seed bank composition, structure and diversity in Transylvanian dry grassland; (b) do native and non-native woody species differ with respect to their impact on grassland community composition and structure; (c) is burning useful to control woody species encroachment; and (d) can soil seed banks contribute to the restoration of grasslands in Transylvania? Location: Transylvania, Romania. Methods: We collected data on vegetation and seed bank composition in 4 m 2 plots in 16 shrub-encroached grasslands and adjacent open grassland. Data were analyzed with regard to the impact of woody species encroachment (native vs non-native) and fire on grassland vegetation and the seed bank using NMDS and LME models combined with ANOVA and Tukey contrast tests.Results: Encroachment was accompanied by a decrease in plant species diversity and altered microclimatic conditions. There was a lack of sufficient evidence for a difference in effect size between native and non-native woody species on tested vegetation or seed bank parameters. While the effects of fire on vegetation were weak compared to encroachment, burning failed to reduce the cover of woody species sustainably. Grassland vegetation and the seed bank differed significantly in species composition and diversity, indicating a limited potential for restoration from the seed bank alone. Conclusions:To halt secondary succession in Transylvanian grassland sustainably, we suggest the establishment of a post-fire management regime including the cutting of woody species and/or re-introduction of grazing and mowing. Grassland restoration from the seed bank may be supported by the introduction of species from surrounding intact grassland. K E Y W O R D S dry grassland, fire, Hippophae rhamnoides, invasive shrub, native and non-native woody species, plant species composition, plant species diversity, restoration and management, seed bank, Transylvania, vegetation, woody species encroachment 410 | Applied Vegetation Science GÖRZEN Et al.

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

“…Overall, our results indicate that shrub encroachment influenced vegetation composition more than wildfire (see also Görzen et al, 2019). Grassland recovery in burnt juniper plots following the wildfire was surprisingly fast and took place within the timeframe of our study.…”

“…Our results support considerable and long‐lasting effects of juniper encroachment on species composition during the transformation of grasslands into woodlands (Gehring & Bragg, 1992; Linneman & Palmer, 2006; Ganguli et al, 2008). Furthermore, invasions of native shrubs have been reported to induce substantial compositional changes in several ecosystems, such as in Southwestern Australian heathlands (Shackelford et al, 2015), in South American savanna wetlands (Barbosa da Silva et al, 2016), in Indian montane grasslands (Srinivasan, 2011), and also in European dry grasslands (Maestre et al, 2009; Görzen et al, 2019). We also showed that the expansion of juniper patches led to an increase in the number of plant species associated with Juniper plots.…”

Using UAV Imagery to Detect and Map Woody Species Encroachment in a Subalpine Grassland: Advantages and Limits

“…In the last few decades, socio-economic transformations in the Alps have led, in some areas, to the decline of livestock farming and agriculture and consequently to land abandonment [7,8]. This process opened the way to woody shrub and tree encroachment, which, in turn, has the potential to modify the ecosystem structure and function, with both negative and positive consequences for ecosystem services [9][10][11] and biodiversity [12,13]. Generally, the woody encroachment of grasslands causes an alteration of microclimatic conditions and a reduction of herbaceous cover, which contribute to the consequent decrease of species richness in the long-term, e.g., [12][13][14].…”

“…This process opened the way to woody shrub and tree encroachment, which, in turn, has the potential to modify the ecosystem structure and function, with both negative and positive consequences for ecosystem services [9][10][11] and biodiversity [12,13]. Generally, the woody encroachment of grasslands causes an alteration of microclimatic conditions and a reduction of herbaceous cover, which contribute to the consequent decrease of species richness in the long-term, e.g., [12][13][14]. Nevertheless, this observation depends on the encroachment stage and the relative woody cover.…”

Grassland management and land use history shape species composition and diversity in Transylvanian semi‐natural grasslands

“…C. Craioveanu​, I. Muntean, E. Ruprecht, R. I. Băncilă, R.I., A. Crișan, L. Rákosy (unpublished) pointed out that spatio‐temporal changes in land use type and intensity in Transylvanian basiphilous dry grasslands affect plant and animal diversity as well, and that butterfly diversity is the highest in mown grasslands. Numerous studies showed that abandonment is linked with diversity loss compared to grazing and mowing (e.g., Wahlman & Milberg, 2002; Bossuyt et al, 2006; Enyedi et al, 2008; Görzen et al, 2019). In contrast, our results suggest that in some cases short‐term abandonment may not be as detrimental in terms of species richness.…”