How does roadside vegetation management affect the diversity of vascular plants and invertebrates? A systematic review

Abstract

Background: With appropriate management, based on vegetation removal that reverses late-successional vegetation stages, roadsides can support high levels of biodiversity. However, current recommendations for roadside management to conserve or restore biodiversity are largely based on research on non-roadside grassland habitats, and much of the evidence on how roadside management practices affect biodiversity is found in non-peer-reviewed grey literature. Therefore, based on suggestions from key stakeholders and an initial systematic map that identified 97 studies on how biodiversity is affected by vegetation removal on roadsides, we conducted a full systematic review of the effects on plant and invertebrate diversity of disturbance-based maintenance of roadsides. Methods:The review was restricted to effects of non-chemical interventions such as mowing, burning, grazing and mechanical shrub removal. Studies were selected from the systematic map and from an updated search for more recent literature using a priori eligibility criteria. Relevant articles were subject to critical appraisal of clarity and susceptibility to bias, and studies with low or unclear validity were excluded from the review. Data on species richness, species diversity and abundance of functional groups were extracted together with metadata on site properties and other potential effect modifiers. Results from the 54 included studies were summarised in a narrative synthesis, and impacts of mowing practices on the total species richness and diversity of plants and on the abundance of forbs, graminoids and woody plants were quantitatively analysed using t tests of study-level effect ratios.Results: Nearly all of the 54 studies included in the review were conducted in Europe (29) or North America (24). The vast majority of studies (48) examined impacts of mowing. Effects on vascular plants were reported in 51 studies, whereas 8 of the studies reported on invertebrates. Quantitative analysis of plant species richness and species diversity showed that mowing effects were dependent on the interplay between mowing frequency and hay removal. Thus, there were no statistically significant overall effects of mowing vs. no mowing, frequency of mowing, timing of mowing or hay removal. However, species richness was higher in roadsides mowed once or twice per year with hay removal than in unmown roadsides, and positively affected by mowing twice compared to once per year. Similar, but less pronounced, effects were found for plant species diversity. In addition, mowing had a negative impact on woody plant abundance, and increased mowing frequency had a negative impact on graminoid abundance. The few studies on invertebrates showed effects that diverged across taxon groups, and there was not enough data for quantitative analysis of these results. Conclusions:The results provide evidence on the effects of mowing on plant species richness. To increase plant species richness, roadsides should be mowed each year, preferably twice per year, and hay should be removed a...

Road verges support pollinators in agricultural landscapes, but are diminished by heavy traffic and summer cutting

“…Existing studies suggest that removing verge cuttings benefits plant and insect diversity (Jakobsson et al, 2018), and flower abundance (Noordijk et al, 2009 Another limitation of our findings of the impacts of verge cutting is that the weather in the study year was particularly hot and dry, which may have accentuated the slow recovery of plant and flower communities. Our findings suggest that multiple cuts would be detrimental to flower production in drought years, at least if cuttings were not removed.…”

“…Road verge management affects their conservation value, though research has mostly focused on plants (Jakobsson, Bernes, Bullock, Verheyen, & Lindborg, 2018). A plot experiment along a single road verge found that cutting twice a year resulted in more flowers and insects than cutting once or no management (Noordijk, Delille, Schaffers, & Sýkora, 2009).…”

Ecosystem service provision by road verges

“…Piepenschneider, Bühle, Hensgen, & Wachendorf, ; Appendix ), which are often a by‐product of routine road verge management. The diversity of plants and insects benefits from cuttings being removed from road verges, which reduces soil nutrients and provides gaps for seedlings (Jakobsson et al, ). Currently, cuttings are rarely removed due to the financial costs of collection and disposal but using cuttings for biogas might make their removal financially viable and even profitable.…”

“…However, both the financial and environmental costs of management must be considered. For example, management frequency and the machinery required will affect the amount of noise pollution and fossil fuel emissions, and therefore the net benefits of the ES provided (Säumel et al, 2016), though also the demand for mitigating ES Mowing twice per year and removing hay is optimal for plant diversity (reviewed in Jakobsson et al, 2018) and insect pollinators (Noordijk et al, 2009) Leaving areas uncut reduces water flow and improves water filtration (Henderson et al, 2016) (Continues) species richness (reviewed in Jakobsson, Bernes, Bullock, Verheyen, & Lindborg, 2018), flower species richness, flower abundance and pollinator abundance (Noordijk, Delille, Schaffers, & Sýkora, 2009), which are likely to benefit pollination services and a range of other ES (Schwarz et al, 2017).…”

Management effects on plant community and functional assemblages in Chicago’s vacant lots

“…For example, the data do not indicate whether clippings were left on-site or removed. While we observed mulched clippings in some recently-mowed vacant lots, we were unable to examine the effects of this practice, which other studies have found to be important in nitrogen cycling and plant community dynamics (Maron & Jeffries, 2001;Kopp & Guillard, 2002;Schippers & Joenje, 2002;Qian et al, 2003;Jakobsson et al, 2018). Furthermore, an examination of urban soils and the characteristics shaping the below-ground biotic and abiotic profiles of the area is necessary to truly understand the drivers of plant diversity in vacant lots.…”