Rapid recovery of soil arthropod assemblages after exotic plantation tree removal from hydromorphic soils in a grassland‐timber production mosaic

Abstract

Many wetland systems are being lost or degraded by human activities such as plantation forestry. Therefore, efforts to restore these wetland systems are important for biodiversity recovery. We assess the recovery of arthropod assemblages that occupy hydromorphic grassland topsoil and leaf litter after the removal of exotic pine trees. We sampled arthropods in three biotopes (natural untransformed hydromorphic grasslands, restored hydromorphic grasslands, and commercial pine plantations) replicated across a large‐scale timber‐grassland mosaic in the KwaZulu‐Natal Midlands, South Africa. In the restored sites, overall species richness, as well as species richness of spiders, ants, and orthopterans, was significantly higher than in plantations, and was as high as in natural, untransformed sites. Additionally, overall assemblage structure along with spider, beetle, ant, and orthopteran assemblages showed no significant differences between restored and natural grasslands. Therefore, pine tree removal enables recovery of these arthropod taxa to levels similar to those in natural hydromorphic grassland. Recovery was rapid, with the assemblages in some restored sites resembling those in untransformed sites after only 6 years, indicating a high level of resilience and recovery in these systems. Contrary to expectations, time since pine removal had a negative effect on arthropod recovery. This was due to the strongly negative effect of alien invasive American bramble (Rubus cuneifolius), which was most common in older restored sites, causing deviation from their restoration trajectory. The potential for arthropod recovery in these hydromorphic grasslands is high, but successful restoration is dependent on ongoing appropriate grassland management, especially removal of bramble.

Impacts of the removal of invasive Carpobrotus on spider assemblage dynamics

“…Bars not sharing letters were significantly different between years (p < 0.05) (Bell et al 2001). Similar rapid changes in spider assemblages after invasive plant removal was also observed by Eckert et al (2019) and Gratton and Denno (2005) only 6 years after the removal of invasive Pinus spp. and Phragmites australis respectively.…”

Identifying managerial legacies within conservation corridors using remote sensing and grasshoppers as bioindicators

“…Score is the score-test statistic from the manyglm model. impacts on birds (Reynolds and Symes 2013), dragonflies (Kietzka et al 2015), flower-visiting insects (Hansen et al 2018), as well as topsoil and leaf litter arthropods (Eckert et al 2019). We add to this by showing that bramble negatively impacts larger-sized grasshopper species (especially Pyrgomorphinae), as well as species of conservation concern (mainly Thericleinae).…”

“…Where bramble invades, the local plant communities become more characteristic of woodlands, thereby threatening specialist grassland taxa (Henderson 2007). Furthermore, bramble within the corridors has severe negative impacts on biodiversity, with previous research indicating negative impacts on birds (Reynolds and Symes 2013), dragonflies (Kietzka et al 2015), flower‐visiting insects (Hansen et al 2018), as well as topsoil and leaf litter arthropods (Eckert et al 2019). We add to this by showing that bramble negatively impacts larger‐sized grasshopper species (especially Pyrgomorphinae), as well as species of conservation concern (mainly Thericleinae).…”

“…We add to this by showing that bramble negatively impacts larger‐sized grasshopper species (especially Pyrgomorphinae), as well as species of conservation concern (mainly Thericleinae). Fortunately, the removal of bramble can enhance bird diversity (Reynolds and Symes 2013), positively influence pollination networks (Hansen et al 2018), and promote grassland restoration success (Eckert et al 2019).…”

“…For example, prescribed burning used to reduce grassland fuel load for protecting timber compartments against wildfires helps maintain stable grassland plant populations within this fire adapted ecosystem (Joubert et al 2014) and promote grasshopper and butterfly diversity (Joubert et al 2016, Gaigher et al 2019). However, invasion of the alien invasive plant Rubus cuneifolius (American bramble) into grasslands, has severe negative impacts on grassland bird diversity (Reynolds and Symes 2013), flower visiting insects (Hansen et al 2018), as well as on the restoration success of grasslands (Eckert et al 2019). Furthermore, domestic cattle roam throughout these corridors, causing some excessive grazing of the landscape, as manifested by changes in grasshopper assemblage composition (Joubert‐van der Merwe and Pryke 2018).…”