Where does the community start, and where does it end? Including the seed bank to reassess forest herb layer responses to the environment

Abstract

Question Below‐ground processes are key determinants of above‐ground plant population and community dynamics. Still, our understanding of how environmental drivers shape plant communities is mostly based on above‐ground diversity patterns, bypassing below‐ground plant diversity stored in seed banks. As seed banks may shape above‐ground plant communities, we question whether concurrently analysing the above‐ and below‐ground species assemblages may potentially enhance our understanding of community responses to environmental variation. Location Temperate deciduous forests along a 2000 km latitudinal gradient in NW Europe. Methods Herb layer, seed bank and local environmental data including soil pH, canopy cover, forest cover continuity and time since last canopy disturbance were collected in 129 temperate deciduous forest plots. We quantified herb layer and seed bank diversity per plot and evaluated how environmental variation structured community diversity in the herb layer, seed bank and the combined herb layer–seed bank community. Results Seed banks consistently held more plant species than the herb layer. How local plot diversity was partitioned across the herb layer and seed bank was mediated by environmental variation in drivers serving as proxies of light availability. The herb layer and seed bank contained an ever smaller and ever larger share of local diversity, respectively, as both canopy cover and time since last canopy disturbance decreased. Species richness and β‐diversity of the combined herb layer–seed bank community responded distinctly differently compared to the separate assemblages in response to environmental variation in, e.g. forest cover continuity and canopy cover. Conclusions The seed bank is a below‐ground diversity reservoir of the herbaceous forest community, which interacts with the herb layer, although constrained by environmental variation in e.g. light availability. The herb layer and seed bank co‐exist as a single community by means of the so‐called storage effect, resulting in distinct responses to environmental variation not necessarily recorded in the individual herb layer or seed bank assemblages. Thus, concurrently analysing above‐ and below‐ground diversity will improve our ecological understanding of how understorey plant communities respond to environmental variation.

Buffering effects of soil seed banks on plant community composition in response to land use and climate

“…Dormant life‐history stages such as persistent seeds accumulated in soil seed banks have also been shown to contribute towards the persistence of plant species in communities undergoing environmental change, for example through lower extinction rates following habitat isolation and climate change (Estrada et al., 2015; Stöcklin & Fischer, 1999), and demographic recovery after a drought spell (LaForgia et al., 2018). Seed banks are therefore likely to be able to buffer environmental change, both through the maintenance of species richness and through effects on community composition (Hopfensperger, 2007; Plue et al., 2017). Despite this, the seed bank’s functional importance has been much debated, likely because the imposed methodological challenges and difficulties may have hampered ecologically meaningful interpretations of the underlying data (Jabot & Pottier, 2017; Vandvik et al., 2016).…”

“…At the same time, a successional series of land‐cover types from managed grassland to old‐growth forest uses a space‐for‐time approach to address a currently important shift in land use due to land abandonment in many parts of the Northern Hemisphere, and Europe in particular (Buitenwerf et al., 2018; Kuemmerle et al, 2016; Song et al., 2018). To test how climate and land cover interact to affect plant community diversity, we relate climate and land‐cover variables to species richness of the herb layer, seed bank and combined community (seed bank and herb layer combined), where the latter species assemblage may help unveil the potential buffering effect of soil seed banks on plant community diversity (Plue et al., 2017). We also calculate the compositional similarity of the herb layer and the seed bank in all plots, to capture both the extent to which species extirpations in the herb layer may be offset by their potential re‐introduction from the seed bank (Hopfensperger, 2007), as well as the likelihood that established populations can rely on banked seeds to maintain population demographics and dynamics (Hille Ris Lambers et al., 2005).…”

A study of soil seed banks across one complete chronosequence of secondary succession in a karst landscape

“…The study of seed banks in global karst regions can predict the future of degraded ecosystem restoration, considering that aboveground vegetation is often established from the germination and growth of seeds in soil seed banks ( Shen et al, 2007 ; Plue et al, 2017 ). Moreover, the data from the study on seed banks can be applied to quantify the relationships between species diversity in seed banks and aboveground vegetation.…”

Is there more than meets the eye? Seed bank analysis of a typical novel ecosystem, the extensive green roof

“…Furthermore, while one can expect that EGR ecosystems will develop as other vegetated ecosystems, aspects such as seed banks have not been investigated in the past. Seed banks can however provide an important biodiversity reservoir (Vandvik, Klanderud, Meineri, Måren, & Töpper, ), which, apart from contributing to the overall biodiversity and population dynamics of a habitat or ecosystem (Plue et al., ), can also be used for restoration (Bossuyt & Honnay, ).…”