Environmental filtering of agroforestry systems reduces the risk of biological invasion

Abstract

Prevention is the most effective way of mitigating the negative impacts of exotic species invasions on biodiversity. Preventative measures include inhibiting the further dispersal and recruitment of established invasive species. We expect coffee production in agroforestry systems to reduce the recruitment of exotic species relative to monoculture stands because intercropped trees function as environmental filters that select for individuals with traits such as shade tolerance. If ecologically similar species are also closely related phylogenetically, such environmental filters should reduce phylogenetic diversity, supporting the coexistence of closely related species. Here, we test whether the taxonomic and phylogenetic diversity of native and exotic species in agroforestry systems is lower than in monocultures. We sampled the understory in 180 plots distributed in both habitats in three study sites within the Araponga municipality, Brazil, and measured understory light availability. Phylogenetic diversity was calculated as the net relatedness index (NRI) and the nearest taxon index (NTI). Understory light availability was lower in agroforestry systems. Of the 48 species found, 25 occurred in agroforestry systems, three of which were exotics. Forty-two species were found in monoculture stands (including 13 exotics). As expected, NRI and NTI indicated lower phylogenetic diversity in agroforestry systems than in monoculture stands. Agroforestry systems provide less favorable habitats for exotic species, filtering them from the understory. The mechanisms that select against exotic species remain unknown; however, shading might exclude predominantly heliophytic exotic species from the agricultural matrix. Therefore, agroforestry systems may function as buffer zones preventing invasion into sensitive ecosystems.

The community ecology of invasive species: where are we and what's next?

“…Patterns such as thesewhich are consistent with the signature of competitive interactions -have been observed much more commonly at local scales, where invasive species have generally been found to have higher establishment success when they were functionally (Petermann et al 2010, Price andPärtel 2013) or phylogenetically distant from natives (e.g. for invasive plants and bacteria, Jiang et al 2010, Davies et al 2011, Ramos et al 2014, Li et al 2015a). In summary, though there have been exceptions (Procheş et al 2015), the results from local scale studies relying on species-based absolute similarity indices generally suggest that competitive interactions and resource opportunities are important in limiting invasions within local communities.…”

Using revegetation to suppress invasive plants in grasslands and forests

“…The ability (or more often, inability) of many native plants to compete with IPS for diverse resources is well-documented. Competition for light can exclude some shade-intolerant species from grasslands (Blumenthal, Jordan, & Svenson, 2005;Hautier, Niklaus, & Hector, 2009) and strongly regulates community assembly, canopy regeneration and invasion in forests (Kunstler et al, 2012;Ramos, Gastauer, de Cordeiro, & Meira-Neto, 2015). In Hawaiian forests, shading by native canopy suppresses invasive grasses Pennisetum clandestinum (Kikuyu grass) and Ehrharta stipoides (Meadow ricegrass) more than it suppresses native shrubs and trees (Funk & McDaniel, 2010).…”

Invasão de palmeira australiana no sub-bosque de uma floresta plantada, Viçosa, MG

“…A maioria das espécies exóticas introduzidas que se tornaram invasoras são heliófitas e intolerantes ao sombreamento e, dessa forma, invadem predominantemente ecossistemas abertos (ex: savana, campo) e ambientes perturbados (ex: pasto abandonado), onde a disponibilidade de luz não é limitante (Martin et al, 2009). Logo, a restauração florestal, plantios florestais e sistemas agroflorestais são práticas de uso da terra que podem prevenir a invasão de espécies exóticas pelo estabelecimento de um filtro ambiental, como o sombreamento, que seleciona as espécies vegetais regenerantes por meio de suas preferências e características ecofisiológicas (Ramos et al, 2014).…”