Abundance response of western European forest species along canopy openness and soil pH gradients
Highlights
► We model abundance patterns of plant species by canopy openness and soil gradients. ► Regional patterns with local precision are established. ► Differences between low and high abundance patterns are analyzed. ► Optimal requirements are quantified for low and high abundance responses. ► The species-specific reactions illustrate the need for species-specific management.
Introduction
The understory layer has a key role in maintaining the structure and functions of forests, (Gilliam, 2007, Whigham, 2004). Among all temperate forest strata, the understory layer has the highest species diversity (Gilliam, 2007), and as such, it influences the direction and the magnitude of vegetation dynamics (Pickett et al., 2009, Royo and Carson, 2006). In addition, the understory layer is a main component of macro- and microfauna habitat (Bowen et al., 2007) and strongly influences soil properties (Gilliam, 2007). In forest management practices, the dynamics of understory vegetation must be managed to preserve plant species diversity, ensure the regeneration of desired tree species, protect fauna habitat, and more generally, maintain various functions of the forest ecosystem (Gilliam, 2007, Wagner et al., 2010).
A large body of studies has shown that understory composition, structure, and development vary according to soil fertility, acidity, moisture, air temperature, and light (Ellenberg et al., 1992, Landolt, 1977) in managed temperate forests. It is also admitted that management practices strongly affect understory composition and cover through their effects on the above-mentioned factors (Balandier et al., 2006, Barbier et al., 2008). Besides these abiotic factors, understory plant communities may also vary locally due to historical heritage (Dupouey et al., 2002), dispersal limitation (Bossuyt et al., 1999), biotic interactions (Desteven, 1991), and landscape features (Dufour et al., 2006).
Overstory characteristics are among the most visible factors affecting understory development. They result from the combined effects of progressive stand development, natural disturbance, and silvicultural thinning, and show important small-scale spatial variations. Many studies have shown that overstory composition, structure, and density influence the dynamics of understory species on the forest floor through modification of resource availability such as light, water, and soil nutrients (Barbier et al., 2008, Wagner et al., 2010). Particularly, the effect of overstory light transmittance on vegetation cover and richness has been largely studied (Barbier et al., 2008). A general increase in herbaceous layer diversity in response to canopy openness appears (Ares et al., 2009, Degen et al., 2005, Tinya et al., 2009). Shifts in species composition also appear, with a higher proportion of light-demanding species or of species with high dispersal abilities observed in open canopy conditions (Ares et al., 2009, Degen et al., 2005). From a silvicultural perspective, it has been shown that adjustment of light availability through thinning may be used to control the development of fast growing opportunistic species (Barbier et al., 2008, Royo and Carson, 2006, Wagner et al., 2010). However, plant light requirements have not been precisely quantified for most taxa growing in the understory. Only a few studies exist where species-specific approaches were used and restricted canopy openness ranges were taken into consideration. In addition, most of these studies were carried out in small study areas, which strongly restricts the scope of the results, with individual species development being site dependent (Gaudio et al., 2008; Moola and Mallik, 1998, Ricard and Messier, 1996, Shields and Webster, 2007, Tinya et al., 2009). Furthermore, most of these studies considered only small openings and consequently rather closed-canopy conditions.
Besides stand characteristics, site factors are major determinants of understory development (Van Couwenberghe et al., 2010, Wagner et al., 2010). More specifically, soil factors have been shown to be important drivers of community composition. Soil pH, ranging from acidic soil to calcareous soil conditions, is known to strongly influence plant communities (Marage and Gégout, 2009, Salisbury, 1920). However, only few quantitative models of individual species responses to soil pH exist (Coudun and Gégout, 2007, Van Couwenberghe et al., 2010). In addition, most studies separately analyzed the effects of stand structure and site factors, with the exception of Van Couwenberghe et al. (2010) and Grogan et al. (2003) who clearly showed how stand characteristics and site factors interact in their effects on plant species distribution.
In most studies, species distribution patterns are derived from presence–absence data. Alternatively, when the required data are available, it is possible to model abundance distribution (Van Couwenberghe et al., 2010). Abundance models are likely to predict more accurately the habitat quality than occurrence models and indicate more precisely the direction and magnitude of vegetation dynamics (Pearce and Ferrier, 2001).
The general objective of this study was to analyze the combined effects of soil pH and canopy openness on the presence and abundance of forest understory species. The specific objectives are: (i) to quantify individual understory species presence and abundance distribution along canopy openness and soil pH gradients; (ii) to identify optimal soil pH and canopy openness for presence and abundance for each species; (iii) to identify the most abundant species for different soil pH and canopy openness conditions. The study focuses on 12 species potentially reaching high coverage in the understory of western European forests. Furthermore, we established habitat-based models for quantifying the species realized niche (Kearney, 2006). More particularly ordinal regression models correlating species responses to their environment were developed on the basis of data extracted from a national forest database and from a regional long-term experimental project.
Section snippets
Databases, records, and site description
In order to assess species responses across large canopy openness and soil pH gradients, two databases with similar floristic inventory protocol were used. Records were extracted from: (1) EcoPlant, a phytoecological forest site database (Gégout et al., 2005); (2) the gap-project, a long-term project on vegetation dynamics in gaps created by the 1999 storms Lothar and Martin (Van Couwenberghe et al., 2008, Van Couwenberghe et al., 2010). EcoPlant records were taken in various forest
Plot description
A total of 847 species, excluding bryophytes, were observed in the understory layer. Minimum number of species in any plot was one and maximum was 71. The average number of species per plot increased with increasing pH (Fig. 2). Species richness estimated per Braun-Blanquet abundance category showed similar responses to pH, with a smaller increase for the high-abundance scores. An increasing number of species were also observed from closed-canopy to open field conditions for all abundance
Discussion
As initially expected, canopy openness and soil pH determine the development of most highly covering species present in the understory of temperate European forests. Although there variability is defined at different spatial scales (regional scale for soil pH and local scale for canopy openness), the combination of the two variables allowed the prediction of species presence and species abundance classes. The strong observed effects of the explanatory factors are in agreement with previous
Acknowledgements
We thank Jean-Claude Pierrat and anonymous reviewers for their helpful comments on the manuscript. This study was part of the projects Observatoire de Peuplements Dévastés (OPD), Observatoire de Peuplement Mités (OPM), and EcoPlant. OPD and OPM are supported by the Direction Régionale de l’Agriculture et de la Forêt de la Lorraine and Centers Régionaux de la Propriété Forestière Lorraine-Alsace. The EcoPlant database is financed by the Agence de l’ Environnement et la Maîtrise de l’ Energie and
References (55)
- et al.
The effects of disturbance intensity on temporal and spatial patterns of herb colonization in a southern New England mixed-oak forest
For. Ecol. Manage.
(2007) - et al.
Influence of tree species on understory vegetation diversity and mechanisms involved – A critical review for temperate and boreal forests
For. Ecol. Manage.
(2008) - et al.
Regrowth forests on abandoned agricultural land: a review of their habitat values for recovering forest fauna
Biol. Conserv.
(2007) - et al.
Big-leaf mahogany (Swietenia macrophylla) seedling survival and growth across a topographic gradient in southeast Para, Brazil
For. Ecol. Manage.
(2003) - et al.
Local and regional trends in the ground vegetation of beech forests
Flora
(2010) - et al.
Morphological plasticity and regeneration strategies of velvet leaf blueberry (Vaccinium myrtilloides Michx.) following canopy disturbance in boreal mixed wood forests
For. Ecol. Manage.
(1998) - et al.
The practical value of modelling relative abundance of species for regional conservation planning: a case study
Biol. Conserv.
(2001) - et al.
Abundance, growth and allometry of red raspberry (Rubus idaeus L.) along a natural light gradient in a northern hardwood forest
For. Ecol. Manage.
(1996) - et al.
Gap partitioning among temperate tree species across a regional soil gradient in windstorm-disturbed forests
For. Ecol. Manage.
(2010) - et al.
Regression models for ordinal responses: a review of methods and applications
Int. J. Epidemiol.
(1997)
Understory vegetation response to thinning disturbance of varying complexity in coniferous stands
Appl. Veg. Sci.
Designing forest vegetation management strategies based on the mechanisms and dynamics of crop tree competition by neighbouring vegetation
Forestry
Migration of herbaceous plant species across ancient-recent forest ecotones in central Belgium
J. Ecol.
Plant Sociology: The Study of Plant Communities
Quantitative prediction of the distribution and abundance of Vaccinium myrtillus (L.) with climatic and edaphic factors
J. Veg. Sci.
Soil nutritional factors improve models of plant species distribution: an illustration with Acer campestre (L.) in France
J. Biogeogr.
Gaps promote plant diversity in beech forests (Luzulo-Fagetum), North Vosges, France
Ann. For. Sci.
Experiments on mechanisms of tree establishment in old-field succession – seedling emergence
Ecology
Plant species richness and environmental heterogeneity in a mountain landscape: effects of variability and spatial configuration
Ecography
Irreversible impact of past land use on forest soils and biodiversity
Ecology
Zeigerwerte von Pflanzen in Mitteleuropa
Scr. Geobot.
The calcareous riddle: why are there so many calciphilous species in the central European flora?
Folia Geobot.
Light-dependent development of two competitive species (Rubus idaeus, Cytisus scoparius) colonizing gaps in temperate forest
Ann. For. Sci.
Light-mediated influence of three understorey species (Calluna vulgaris, Pteridium aquilinum, Molinia caerulea) on the growth of Pinus sylvestris seedlings
Eur. J. For. Res.
EcoPlant: a forest site database linking floristic data with soil and climate variables
J. Veg. Sci.
Cited by (27)
Herbaceous vegetation under planted woody species on coal mine spoil acts as a source of organic matter
2022, Acta OecologicaCitation Excerpt :Stand characteristics such as tree density, volume, height, basal area, and canopy structure influence the amount of light reaching the plantation floor. Also, stand characteristics regulate below canopy microclimate and vegetation dynamics by modifying belowground resources such as soil, water, and nutrients (Barbier et al., 2008; Van Couwenberghe et al., 2011; Hedwall et al., 2019). For example, a study conducted by Pensa et al. (2008) on reclaimed oil shale in Estonia reported maximum herb layer biomass (142.7 g m−2) under canopies of Alder tree and lowest (23.6 g m−2) under Larch plantation.
Responses of competitive understorey species to spatial environmental gradients inaccurately explain temporal changes
2018, Basic and Applied EcologyCitation Excerpt :and R. idaeus developed higher cover on sites with low humus quality, which indicates their association as acidophytes with oligotrophic site conditions. This is largely in agreement with previous studies (Taylor, Rowland, & Jones, 2001; Coudun & Gégout, 2007; Van Couwenberghe et al., 2011). It should be noted that R. fruticosus agg.
A comparison of ground-based methods for estimating canopy closure for use in phenology research
2018, Agricultural and Forest MeteorologyCitation Excerpt :Growing season extensions have been observed for many European tree species, most notably due to canopies coming into leaf earlier (Menzel and Fabian, 1999; Menzel et al., 2006; Thompson and Clark, 2008). The phenology of dominant canopy trees exerts strong influence on the understorey environment, as canopy openness is highly related to available photosynthetically active radiation (PAR) (Brusa and Bunker, 2014; Gonsamo et al., 2013; Promis et al., 2012), influencing microclimate, soil respiration (Giasson et al., 2013; Yuste et al., 2004) and understorey plant dynamics (Van Couwenberghe et al., 2011). Therefore, earlier canopy closure and later senescence is likely to have wide-ranging impacts on the phenology and life processes of understorey plants and wider forest biodiversity.
Drivers of regeneration dynamics following salvage logging and different silvicultural treatments in windthrow areas in Slovenia
2018, Forest Ecology and ManagementCitation Excerpt :The storm was followed by a bark beetle outbreak that claimed almost the same amount of wood. Besides damage to existing stands, disturbances, especially windthrows, create large openings where different successional stadia develop (Fischer et al., 2002; Wohlgemuth et al., 2002; Jonasova and Prach, 2004; Van Couwenberghe et al., 2011). They may be beneficial for early successional flora and fauna on the one hand, but forest protection functions may be negatively affected on the other (Brang, 2001).
Effects of forest patch type and site on herb-layer vegetation in a temperate forest ecosystem
2013, Forest Ecology and ManagementCitation Excerpt :The effect of the overstory has been well-researched (Beatty, 1984; Augusto et al., 2003; Thomsen et al., 2005) and it is widely accepted that an increase in the number of species in the overstory tends to increase understory diversity (Gilliam, 2007). Overstory characteristics are among the most visible factors controlling understory development (Van Couwenberghe et al., 2011), resulting from the combined effects of stand dynamics, natural disturbance, and small-scale spatial variations (Van Couwenberghe et al., 2011). Canopy structure can have a particularly important influence on understory through the effects of canopy trees competing with the understory for resources both above- (light) and below-ground (water and nutrients) (Riegel et al., 1992; Okland et al., 1999).