Consistent response of nematode communities to management of coniferous plantations

Abstract

Crop-tree thinning (CTT) is a forest management practice aiming at enhancing the growth of target trees in plantations by harvesting neighboring trees. Along with the positive effect on tree growth, thinning represents a disturbance, which likely affects belowground organisms and may feed back to stand productivity. However, the impact of CTT on the belowground food web is poorly understood. Since nematodes are species-rich and abundant belowground organisms, occupying a variety of trophic positions in soil food webs and being sensitive to disturbances, they serve as ecological indicators of ecosystem disturbance. We studied the effect of CTT on the soil nematode community structure in pine ( Pinus massoniana Lamb.), Chinese fir ( Cunninghamia lanceolata (Lamb.) Hook.) and cypress ( Cupressus funebris Endl.) plantations in the Sichuan Basin three years after applying CTT. Crop-tree thinning significantly increased the abundance of soil nematodes in each of the plantations. Moreover, CTT significantly increased the relative abundance of herbivorous nematodes in each of the plantations. Furthermore, CTT increased the proportion of stress tolerators (c-p 1) and enrichment opportunists (c-p 2) and reduced the maturity, structure and enrichment indices of nematodes in Chinese fir and cypress plantations, while only subtle changes were observed in pine plantations. Interestingly, across plantations, the effects of CTT on soil nematode communities were mainly due to changes in microbial biomass nitrogen and understory vegetation diversity. Forest management practices resulting in more open canopies uniformly affect soil food webs by changing the quantity and quality of resources associated with increased understory cover and diversity as well as microbial food. These insights increase our understanding of the impacts of forest management on the structure and functioning of belowground communities, which may contribute to management and conservation policies for more sustainable forestry.