A tale of two green walls: a functional trait approach to assess vegetation establishment on restored steep slopes

Abstract

Green walls (GWs) have been increasingly recognized as an important restoration technique for steep slopes resulting from quarrying activities or major infrastructure construction projects. In practice, GW irrigation is considered essential, although studies evaluating vegetation establishment under different irrigation regimes are lacking. Besides taxonomic metrics, functional diversity measures were used to compare the diversity and composition of plant communities of two hydroseeded GWs, with different irrigation regimes (irrigated vs. low-irrigated). The studied GWs were installed in Peneda-Gerês National Park (NW Portugal) to minimize the visual impact of shotcrete walls, along a road infrastructure, and promote their ecological restoration. Species' cover was recorded 3 years after installation. Species were classified according to their growth form, life form, and life strategy. Despite hydroseeding approximately 57 species, GW vegetation was dominated by spontaneous species, particularly acrocarpous mosses, regardless of irrigation regime. Species and functional richness were higher under irrigated conditions, while no differences were observed for species diversity and functional dispersion. Functional trait composition did not differ between GWs, indicating that both systems potentially provide the same ecosystem functions and services. Our results also suggest that spontaneous species colonizing GWs are highly adapted to local environmental conditions, given their dominance in both irrigated and low-irrigated communities. Overall, irrigation did not affect the structure and functioning of GW communities, only their redundancy, since more species exhibiting similar traits were established in the irrigated GW. Therefore, our findings suggest that low-irrigated GWs, hydroseeded with native species, represent a more cost-effective solution to reduce the ecological impacts of steep slopes. Implications for Practice• Green wall irrigation promotes the establishment of plant communities with higher (species and functional) richness, without changes in functional composition. • Practitioners should consider hydroseeding green walls with native species (both vascular plants and bryophytes), in order to promote the provision of multiple ecosystem services and the conservation of local diversity. • On green wall systems, spontaneous colonization is a key component of community assembly, especially in areas surrounded by natural vegetation. As such, under favorable environmental conditions, the use of hydroseeding can be minimized. • Extensive, low-irrigated green walls represent an innovative solution for the ecological restoration of steep slopes.

Do plant traits influence primary succession patterns for bryophytes and vascular plants? Evidence from a 33‐year chronosequence on bare chalk

“…The bryophyte searches did not yield useful information, although several of the returned papers used Ellenberg indicator values (e.g., Rajandu et al, 2021;Rola et al, 2021); however, these are considered to be ecological preferences rather than plant traits and we did not consider these further (Violle et al, 2007). Instead, we selected traits based on similar studies investigating succession found using alternate search terms in Google Scholar (Fernández-Martínez et al, 2019;Laine et al, 2018;Monteiro et al, 2020). The selected traits, length, perennation, life form, sporophyte frequency and maximum spore diameter, were extracted from BRYOATT (Hill et al, 2007).…”

Enhancing biodiversity and ecosystem services in quarry restoration – challenges, strategies, and practice

“…An innovative technique that has been proposed consists of vertical greening systems, or Green Walls (Medl et al ). Monteiro et al () studied the effectiveness of green walls in steep slopes under different conditions, by assessing vegetation establishment and spontaneous colonization. Their results validate the use of geotextiles to retain the substrate.…”

“…Even under different environmental constraints, the vegetation evolved similarly, benefiting spontaneous colonization by native species, more adapted to local conditions. Monteiro et al () further explored the compositional and functional diversity of vegetation community and found that alleviating limiting conditions (e.g. using irrigation) would only increase functional redundancy.…”

El papel de las plantaciones y la regeneración natural en la recuperación inicial de la cobertura vegetal en una cantera en Morelos, México

“…Sin embargo, hay poca información sobre la contribución de las especies introducidas y las reclutadas de forma natural en la recuperación de canteras, probablemente porque la sucesión espontánea se produce con mayor frecuencia y facilidad en sitios cuyas condiciones ambientales no son muy extremas (Prach y Hobbs, 2008). A pesar de ello, se ha reportado el éxito de la revegetación natural en canteras de caliza (Tropek et al, 2010), minas de arena y de grava (Šebelíková et al, 2020), y muros verdes colocados en paredes verticales de canteras (Monteiro et al, 2020). En otros casos, sin embargo, los parches en regeneración pueden resultar en "desiertos de pioneras", en los que están ausentes las especies características del bosque maduro (De la Peña-Domene et al, 2013), por lo que si estas no se reclutan de manera natural es necesario introducirlas mediante plantaciones que no solo permiten recuperar especies, sino también funciones ecológicas.…”