The Impact of Animal Trampling on Free-living Nematode Abundance, Genera, and Trophic Diversity was Attenuated by Tree Canopies

Livestock grazing and trampling is an important factor in the formation and development of different terrestrial ecosystems. However, despite numerous studies on soil compaction, there is still no consensus as to which kind of effect (positiveornegative) animal trampling exerts on soil nematodes. The main goal of this study was to evaluate the animal trampling effect onfree-living nematode abundance and diversity, and to define the attenuating effect of the tree canopies (Cupressus sempervirens, Eucalyptus camaldulensis, and Tamarix aphylla) during wet and dry periods. The nematodes were extracted from100 g aliquotsofsoil samples (brown-red sandy soils) during cold-wet (CW), warm-wet (WW), and hot-dry (HD) periods during 2013-2014, inaman-made safari-zoo habitat, using the Baermann funnel procedure. Our results revealed the impact of trampling on both free-livingnematode abundance and diversity, and their soil habitat. It was found that trampling, along with seasonal fluctuation andthetree-species attenuating effect on the soil medium, resulted in the creation of the spatial-temporal heterogeneity of soil propertiesinthe study area. In turn, variation in soil properties was reflected in soil nematode abundance and diversity, revealing tight correlationwith the observed soil properties. Animal trampling had an overwhelming, mostly negative impact on soil nematode abundance, genera, and trophic diversity in the open, bare area. However, the protective effect of the tree canopies, as well as seasonal
fluctuations, attenuated this negative impact. The trees had a significant attenuating effect on trampling compared with the open, barearea. However, different tree species during the wet and dry periods had a variable impact on nematode abundance, genera, andtrophic diversity. During the hottest period of the year, when external adverse factors dominated the trampling effect, the abilityofthe trees to protect nematode communities was significantly reduced. Of all the colonizer-persister (cp) continuumof nematodefunctional guilds, only bacteria-feeding nematodes belonging to the cp-1 guild were positively affected by trampling. In general, nematodes belonging to the r-life-strategy group (colonizers tolerant to environmental disturbance), mainly bacteria-feedingnematodes, were the most numerous (61 and 44% at the trampling and undisturbed sites, respectively). In contrast tothebacteria-feeding group, fungi-feeding nematodes were the smallest group in the study area (8 and 4%in the tramplingandundisturbed sites, respectively). The undisturbed sites were a more favorable habitat for the plant-parasite nematodes (9 and26%inthe trampling and undisturbed sites, respectively). Surprisingly, the omnivore-predator nematodes belonging to the K-life strategygroup and that are characterized by hypersensitivity to disturbance, were relatively numerous at the trampling (22%) and relativelyundisturbed (26%) sites. The results showed that 62% of the nematode species were affected (48% negatively and 14%positively) byeither direct trampling or changes in soil properties. The ecological indices confirmed that animal trampling had a negative impact onthe soil biota in the study area. Our results suggested that animal trampling exerts significant a direct and indirect effects (throughchanges in soil properties) on soil free-living nematodes. Moreover, the wet-dry seasonal periods along with the tree canopiesprotective effect may significantly change the extent of animal trampling impact