Impacts of leaf-litter addition on carabids in a conifer plantation

Published source details Magura T., Tóthmérész B. & Elek Z. (2005) Impacts of leaf-litter addition on carabids in a conifer plantation. Biodiversity and Conservation, 14, 475-491.
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Summary

In Hungary, as in many other European countries, large areas of native deciduous forests have been cleared and reforested with conifers during the 20th century. Non-native Norway spruce Picea abies is a preferred species because of its quick growth and high productivity. However, even-aged conifer monocultures drastically alter the microclimatic, abiotic and biotic conditions compared to that of original woodlands, and generally support an impoverished flora and fauna within a homogeneous habitat.

In this study, leaf litter was added in plots to increase habitat heterogeneity within a 50-year-old Norway spruce plantation, established after the clear-cutting of a native beech Fagus sylvatica forest, in the Hungarian Mountain Range. Pitfall trap catches of carabid beetles from leaf-litter plots were compared with those from control plots to explore the effect of leaf-litter addition.

Study site: The study was performed in a 50 year old non-native Norway spruce Picea abies plantation (12 ha of former beech forest) in the North Hungarian Mountain Range. The shrub layer was almost entirely missing and the herbaceous ground flora sparse.

Leaf litter addition: Three treated and three control plots (each 5 m x 5m) were established randomly in the study area. Distances between the plots and to the forest edge were at least 30 m. In the treated plots, leaf litter from a neighbouring beech forest was added in a 15 cm thick layer at the beginning of November 1999. More leaves were added in late November 2000 to imitate autumn leaf fall. Prior to litter addition samples were checked for presence of ground beetles; none were found.

Sampling: In each plot, nine pitfall traps (plastic cups diameter 10 cm, volume 500 ml partly filled with 70% ethyleneglycol and detergent) were placed 2 m apart to collect carabids. Trapped beetles were collected monthly from 2 April to 30 November in 2000 and 2001. This was considered to give a sampling period long enough to cover most beetle species seasonal activity period.

Data on eight environmental factors that may affect the carabid distribution was also collected: temperature at 2 cm depth; temperature at the substrate surface; relative humidity on the surface (each measured monthly by each trap); estimate of cover of leaf litter; herb, shrub and canopy cover around within a 1 m diameter circle around traps; the number of other invertebrates (i.e. other Coleoptera, Chilopoda, Collembola, Diplopoda, Gastropoda, and Isopoda) in the traps which could be taken as potential carabid prey.

A total of 1,656 individual carabids representing 24 species were caught over the 2 years; the total number of trapped individuals was nearly the same in both years (virtually 50% in each year), although the dominance order of the species varied slightly between years. The commonest species were Pterostichus oblongopunctatus, Abax parallelepipedus, Molops piceus, Carabus glabratus and Carabus hortensis, which made up 72.5% of the total catch. Three species were caught exclusively in the leaf-litter plots (Bembidion properans, Harpalus distinguendus and Leistus piceus - one individual of each), and Zabrus tenebrioides (5 individuals) was caught only in the control plots.

Differences in abundance, species richness and Shannon diversity were not significant between the control and litter plots, but carabid catch was higher in the litter plots in both years. The most numerous species P.oblongopunctatus was significantly more abundant in the leaf-litter plots.

In leaf-litter plots the ground temperature was lower, there was significantly more prey, and carabid larvae were significantly more numerous, compared to the control plots.

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