Comparison of the interest of four types of organic mulches to reclaim degraded areas: a field study based on their relative attractiveness for soil macrofauna

ACLThe study focused on the attractiveness of mulches (consisting of the addition of a layer material to the soil surface) and their efficiency to promote recolonization by pedofauna of isolated and degraded areas. The experimental study was set up in the former coal mining area of Northern France. This area is particularly disturbed and fragmented by land-use change, urbanization, industry, intensive agriculture and metal pollution. To examine the movements of pedofauna, four kinds of mulches were applied: (i) Ramial Chipped Wood (RCW), (ii) chopped Miscanthus, (iii) dead leaves and (iv) wheat straw as well as plastic sheeting, a material often used in green spaces. A negative control consisted in soil without mulch addition. The experimental set-up consisted of a set of 18 bands of mulch (6 m long x 0.5 m width x 8 cm thick, i.e. a volume of 0.04 m3 per band) installed on three adjacent plots on a surface area which stretch on 4400 m2: (i) plot F1, a mixed plantation, (ii) plot M consisted of three rows of maples (both considered to be the reservoir of biodiversity) and (iii) plot BF, an ash plantation (with lower biodiversity). Faunistic communities of soil present within the mulches were monitoring using pitfall traps for four months (April to July), at a rate of eight surveys for each of the 90 traps installed, i.e. 720 samples. Different life traits and indices of diversity were studied, more specifically on carabid beetles. The main objective of the study was first to check whether mulches could or not reconnect different planted plots in a peri-urban landscape highly modified by human activities. The second aim was to find which type of mulch had the best efficiency in the recovery of the connectivity between plots. The last questions were which type of zoological groups could be favoured by the use of mulches and which benefits for ecosystem functioning. The main hypotheses of this study were: (i) Organic mulches would act as dispersal corridors and refuge zones to the soil organisms; (ii) organic mulches would be attractive to many organisms with various ecological needs. This study highlighted the potential benefits of using the mulching technique to support ecological connectivity in disturbed environment since this method highlighted the presence of individuals with different diets (saprophagous, predators, phytophagous and so forth), small and large size species which do not have the same dispersal capacities as well as species that are more dependent on forest environments and others that depend on more open environments. The study concluded that organic mulches are more favourable to pedofauna than soil without mulch or plastic sheeting. With regard to organic mulches, no difference was noted, either in terms of cumulative abundance or monthly monitoring. However, for carabids, it should be noted that dead leaves and wheat straw have higher specific richness than Miscanthus and RCW