Hahn Philip G, Orrock John L
Department of Zoology, University of Wisconsin-Madison, Madison, WI, 53706, USA.
J Anim Ecol. 2015 May;84(3):745-754. doi: 10.1111/1365-2656.12311. Epub 2014 Nov 23.
Past land use can create altered soil conditions and plant communities that persist for decades, although the effects of these altered conditions on consumers are rarely investigated. Using a large-scale field study at 36 sites in longleaf pine (Pinus palustris) woodlands, we examined whether historic agricultural land use leads to differences in the abundance and community composition of insect herbivores (grasshoppers, families Acrididae and Tettigoniidae). We measured the cover of six plant functional groups and several environmental variables to determine whether historic agricultural land use affects the relationships between plant cover or environmental conditions and grasshopper assemblages. Land-use history had taxa-specific effects and interacted with herbaceous plant cover to alter grasshopper abundances, leading to significant changes in community composition. Abundance of most grasshopper taxa increased with herbaceous cover in woodlands with no history of agriculture, but there was no relationship in post-agricultural woodlands. We also found that grasshopper abundance was negatively correlated with leaf litter cover. Soil hardness was greater in post-agricultural sites (i.e. more compacted) and was associated with grasshopper community composition. Both herbaceous cover and leaf litter cover are influenced by fire frequency, suggesting a potential indirect role of fire on grasshopper assemblages. Our results demonstrate that historic land use may create persistent differences in the composition of grasshopper assemblages, while contemporary disturbances (e.g. prescribed fire) may be important for determining the abundance of grasshoppers, largely through the effect of fire on plants and leaf litter. Therefore, our results suggest that changes in the contemporary management regimes (e.g. increasing prescribed fire) may not be sufficient to shift the structure of grasshopper communities in post-agricultural sites towards communities in non-agricultural habitats. Rather, repairing degraded soil conditions and restoring plant communities are likely necessary for restoring grasshopper assemblages in post-agricultural woodlands.
过去的土地利用方式会造成土壤条件和植物群落的改变，这些改变会持续数十年，不过这些改变的条件对消费者的影响却很少被研究。我们在长叶松（Pinus palustris）林地的36个地点进行了一项大规模的实地研究，调查历史上的农业土地利用是否会导致食草昆虫（蝗虫，蝗科和螽斯科）的数量和群落组成产生差异。我们测量了六个植物功能组的覆盖度以及几个环境变量，以确定历史上的农业土地利用是否会影响植物覆盖度或环境条件与蝗虫群落之间的关系。土地利用历史具有特定分类群的影响，并与草本植物覆盖度相互作用，从而改变蝗虫数量，导致群落组成发生显著变化。在没有农业历史的林地中，大多数蝗虫类群的数量随草本植物覆盖度的增加而增加，但在农业后的林地中则没有这种关系。我们还发现蝗虫数量与落叶覆盖度呈负相关。农业后的地点土壤硬度更大（即压实程度更高），且与蝗虫群落组成有关。草本植物覆盖度和落叶覆盖度都受火灾频率影响，这表明火灾可能对蝗虫群落具有潜在的间接作用。我们的研究结果表明，历史土地利用可能会使蝗虫群落组成产生持续差异，而当代干扰（如规定火烧）可能对确定蝗虫数量很重要，这主要是通过火灾对植物和落叶的影响实现的。因此，我们的研究结果表明，当代管理制度的变化（如增加规定火烧）可能不足以使农业后地点的蝗虫群落结构向非农业栖息地的群落转变。相反，修复退化的土壤条件和恢复植物群落可能是恢复农业后林地蝗虫群落的必要条件。
