The impact of naturalized legumes on plant communities in Northern Taiwan: are we worrying too much?

Abstract

Habitat transformation caused by naturalized legumes has been considered as a profound environmental threat worldwide. However, the weight of the impact on species diversity of local native and naturalized flora has yet to be revealed. In order to gain a better understanding of the phenomenon, we developed and tested the following hypotheses: (1) naturalized legumes promote local species diversity; (2) naturalized legumes increase local naturalized species diversity rather than native biodiversity; and (3) the impact of naturalized legumes varies with habitat type. Four counties in Northern Taiwan were selected to form the study site. Nine major habitat types were identified in 100 sampling sites (1 km 2 /each site) in northern Taiwan, and a total of 2,242 plots (1 m 2 /each plot) were sampled. Species, cover, and biodiversity indices of both native and naturalized floras were obtained, and soil samples were collected from plots with and without naturalized legumes analyzed. The biodiversity and cover of the whole and naturalized flora were increased significantly by naturalized legumes, while no effects on native flora were found. The significant increase in the species diversity and cover of the whole flora and naturalized flora disappeared when naturalized legumes were excluded from the data set; the same trend was observed when habitat type was considered. Soil nitrogen was marginally significantly higher in the plots with naturalized legumes. The effects of naturalized legumes on native and naturalized floristic composition are divergent. Although species diversity and cover were increased by naturalized legumes, the additional species were naturalized legumes per se, which were the only beneficiaries of the enriched soil. The naturalized legumes did not facilitate further invasion by other exotic species, nor did they have an impact upon the native community in terms of cover, species diversity, or composition.

A synthesis of plant invasion effects on biodiversity across spatial scales

“…At broader biogeographic scales, the effects of an invader are diffi cult to evaluate since these studies typically use presence/absence data for both the invader and the native species from large, national or global databases such as the IUCN Red List ( Atkinson and Cameron, 1993 ;Lonsdale, 1999 ;Vi é et al, 2008 ; but see, Maskell et al, 2006 ;Vil à et al, 2010 ). From such data, studies often conclude that many naturalized invaders are present, but no native species have gone extinct from the introduction of plant competitors ( Sax et al, 2002 ;Davis, 2003 ;Maskell et al, 2006 ;Sax and Gaines, 2008 ;Tsai et al, 2010 ), even in locations that are infamous for being devastated by species invasions, such as remote oceanic islands (e.g., Hawai'i; Denslow et al, 2009 ). However, the presence and effects of the invader are likely to only occur in a subset of the spatial scales under consideration.…”

Livestock grazing promotes legume abundance under increased nutrient loads: Mechanistic evidence from a temperate grassland

“…The outcomes of this study have profound implications for the optimization of rangeland management practices, not only within our study area but also for similar rangelands worldwide. First, they can contribute to design strategies to manage exotic legume species, many of which are planted as forage and can trigger invasion processes (Tsai et al., 2010). Second, knowing the controls of legume abundance can promote sustainable management practices, aimed to jointly improve the conservation and productivity of grasslands.…”

“…Sowing of forage species and fertilization with different nutrients are common practices in rangelands dedicated to livestock production (Hu et al., 2020). In addition, the introduction of forage species, many of which are legumes, can also trigger invasion processes (Tsai et al., 2010), with harmful consequences for the conservation of rangelands and nearby natural areas (Paynter et al., 2003).…”

“…First, they can contribute to design strategies to manage exotic legume species, many of which are planted as forage and can trigger invasion processes (Tsai et al, 2010). Second, knowing the controls of legume abundance can promote sustainable management practices, aimed to jointly improve the conservation and productivity of grasslands.…”