Consistent response of nematode communities to management of coniferous plantations

Background: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.Results: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.Conclusions: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.

Soil carbon and nutrient stocks under Scots pine plantations in comparison to European beech forests: a paired-plot study across forests with different management history and precipitation regimes

Background:Organic carbon stored in forest soils(SOC)represents an important element of the global C cycle.It is thought that the C storage capacity of the stable pool can be enhanced by increasing forest productivity,but empirical evidence in support of this assumption from forests differing in tree species and productivity,while stocking on similar substrate,is scarce.Methods:We determined the stocks of SOC and macro-nutrients(nitrogen,phosphorus,calcium,potassium and magnesium)in nine paired European beech/Scots pine stands on similar Pleistocene sandy substrates across a precipitation gradient(560–820mm∙yr−1)in northern Germany and explored the influence of tree species,forest history,climate,and soil pH on SOC and nutrient pools.Results:While the organic layer stored on average about 80%more C under pine than beech,the pools of SOC and total N in the total profile(organic layer plus mineral soil measured to 60 cm and extrapolated to 100 cm)were greater under pine by about 40%and 20%,respectively.This contrasts with a higher annual production of foliar litter and a much higher fine root biomass in beech stands,indicating that soil C sequestration is unrelated to the production of leaf litter and fine roots in these stands on Pleistocene sandy soils.The pools of available P and basic cations tended to be higher under beech.Neither precipitation nor temperature influenced the SOC pool,whereas tree species was a key driver.An extended data set(which included additional pine stands established more recently on former agricultural soil)revealed that,besides tree species identity,forest continuity is an important factor determining the SOC and nutrient pools of these stands.Conclusion:We conclude that tree species identity can exert a considerable influence on the stocks of SOC and macronutrients,which may be unrelated to productivity but closely linked to species-specific forest management histories,thus masking weaker climate and soil chemistry effects on pool sizes.