Rationale for grounded theory methodology

Juan M. Arenas1 *_{, Adrián Escudero}2_{, Ignacio Mola}3_{, Miguel A. Casado}1_.

Arenas, J. M. ([email protected]) 1 _*

Escudero, A. ([email protected] ) 2

Mola, I. ([email protected]) 3

Casado, M. A. ([email protected]) 1

1 Departamento de Ecología, Universidad Complutense de Madrid, 28040 Madrid, Spain

2 Unidad de Biodiversidad y Conservación, Departamento de Biología y Geología, Universidad Rey Juan Carlos, Móstoles, 28933 Madrid, Spain 3 Research, Development and Innovation (R&D) Service, Obrascón Huarte Lain, S.A. (OHL), 28046 Madrid, Spain

*Author for correspondence:

[email protected]

ARTICLE INFO:

Received: 11 Octubre 2016

Received in revised form: 7 March 2017

Keyword: Drylands; Green infrastructure; Gypsum habitats; Emergent habitats; Partial RDA; Perennial vegetation; Plant reservoir; Roadslopes; Road verges.

Nomenclature: Castroviejo et al. (1986–2016) except for Compositae and Gramineae, which follow the Euro+Med PlantBase (ww2.bgbm.org/EuroPlusMed, accessed

on 18 Sep 2015).

ABSTRACT

Questions

How do roadsides interact with patches of natural vegetation in shaping perennial plant communities in fragmented agricultural areas? Are the observed differences due to the type of roadside (i.e., roadcuts, embankments or road verges) or are there other factors driving community structure and composition?

Location

Stretch of motorway A3 and its surrounding area, in central Spain.

Methods

We analysed the variation in perennial plant species composition and diversity among 92 plots (400 m2_{). The}

plots were located in five different environmental scenarios, three of them in a fragmented landscape (patches of natural vegetation, embankments, and roadcuts) and two in an unfragmented landscape (natural vegetation and road verges). In each plot, the cover of each perennial plant species and eight soil variables were assessed. We used phi coefficient of correlation to determine the scenario preferences of each species, Kruskal-Wallis tests to compare the soil variables between landscape scenarios and eight descriptive variables of the community, and RDA and partial RDA analysis to evaluate the relative importance of the type of environmental scenario on the floristic community.

Results

We identified 130 species, with only 16 species never appearing on roadsides. Perennial total cover, species richness, inverse Simpson’s index and number of protected species showed no significant differences between the five scenarios considered. In contrast, the number of nutrient-demanding species and restricted-range diversity showed lower values in natural vegetation plots. Soil variables and the type of scenario together explained 28.5% of the species composition variation. Of this percentage, 6.8% was explained by soil variables, 12.1% by the type of scenario and 10.0% of the variation was shared between the two datasets.

Conclusions

Our results show that almost all perennial species occurring in natural vegetation patches were also able to reach and settle in the roadsides. However, soil conditions and other specific roadside variables generate different plant communities. In spite of the differences found between the perennial plant community of roadsides and their surrounding area, roadsides are excellent reservoirs of biodiversity.

INTRODUCTION

Transport infrastructure is generally perceived as having negative impacts on ecosystems (Forman & Alexander 1998). Habitat fragmentation, mortality from road construction and collision with vehicles, modification of animal behaviour, alterations of the physical and chemical environment and the spread of exotic species, among other impacts, have been described (for a review, see Trombulak & Frissell 2000). However, linear infrastructures may provide habitats that strengthen ecosystem services, especially those that are particularly weak in humanized landscapes (Millennium Ecosystem Assessment 2005). Thus, minimizing these adverse effects or placing them in a broader ecological context, for instance considering these emergent positive opportunities, may help to draw a more precise picture of the impact of linear transport infrastructures in the territory.

In recent decades, intensification of agricultural activities has triggered the loss of critical landscape elements for diversity (e.g. fallow land, borders, marginal lands, etc.), which has led to a decrease in biodiversity and ecosystem services (Benton et al. 2003; Karp et al. 2012). Within these intensive modified farming areas, road margins can be a management

priority and an opportunity for biodiversity conservation, increasing landscape heterogeneity and providing refuge for certain species (Tikka et al. 2000; Helden & Leather 2004; Spooner & Smallbone 2009; Zeng et al. 2011). In this context infrastructure margins can play an important role in ecosystem dynamics, since they can generate ecological flows to and from these areas reinforcing the connectivity among remnants (Lugo & Gucinski 2000). For instance, understanding the role of linear infrastructures and how they interact with a fragmented agricultural landscape is critical to determining their net effect on diversity from a global perspective. More specifically, determining whether linear infrastructures can serve as an opportunity for conservation management should be a priority, especially in high-income countries.

The role of roadsides in acting as reservoirs of biodiversity can be expressed differently for each species, biological group and community type (Auffret & Cousins 2013). Here we focused our study on perennial vegetation because it contains a number of advantages over other biological guilds, such as annual plants. First, perennials are more persistent over time, which makes their population dynamics less dependent on weather conditions in a given year (Polis et al. 1997;

Gutiérrez et al. 2000; Caballero et al. 2008). Second, biotic interactions (e.g., facilitation, competition) between species can be extended over years, allowing more structured and stable communities. Moreover, perennial vegetation, such as woody plants and tussock grasses, are well-known as facilitators for the establishment of other species by improving abiotic conditions, such as enhanced soil nutrients, water availability and microclimatic heterogeneity, especially in harsh environments (Jones et al. 1994; Perelman et al. 2003; Gómez-Aparicio et al. 2004; Wilby & Shachak 2004; Luzuriaga et al. 2012).

The aim of this study is to analyse the composition and structure of communities of perennial plants on the roadsides of a highway in central Spain, comparing them with those of their surrounding areas at a landscape scale. The territory dissected by this highway is mainly agricultural with small patches of natural vegetation. These patches are a mosaic of gypsum (calcium sulfate) soil habitats, which are characteristic of arid and semi-arid environments and are widespread with over 100 million ha worldwide (Verheye & Boyadgiev, 1997). Gypsophiles are dependent on the special physical and chemical features of this type of soil (Escudero et al. 2014). Gypsum plant communities shelter an unusual flora very rich in narrow endemic and endangered species. For this reason, it is critical to determine if these roadside margins can contribute to conserving some of the most remarkable biodiversity hotspots in terrestrial European ecosystems (see European Directive for Conservation of Habitats and Wild Fauna and Flora; Directive 92/43/CEE, 1992). Unfortunately, the synergic effect of global change drivers operating simultaneously in the territory, such as climate warming, landscape fragmentation and human-driven degradation, are positioning these habitats at a critical point (see Escudero et al. 2014). Therefore, knowing if these roadsides can alleviate this pressure and how they can strengthen biodiversity conservation in gypsum habitats is of special interest, particularly

to developing proper ecological restoration and conservation measures.

Specifically, we try to answer the following question: How do roadsides interact with patches of natural vegetation in shaping perennial plant communities in fragmented agricultural landscapes? We compare natural vegetation and road margins at the species and community levels, including structural, functional and species conservation indices. We also examine whether the observed differences are caused by the type of roadside (roadcuts, embankments or road verges), given their different soil characteristics generated by road construction. By addressing these questions, we seek to contribute to understanding whether adequate interventions in roadsides can promote their ability to generate or encourage certain ecosystem services. Specifically, we focus on the creation of refuges for species and plant communities of interest, and its implications for biodiversity conservarion.