In this case nitrogen depletion would only be right at the soil surface which may be one reason wood chip mulches are efficient at suppressing seed germination. Because wood chips from tree services are usually a combination of bark sapwood hardwood and leaves (during the growing season or from evergreen plants) as they break down they slowly provide small amounts of nutrients. Using locally produced wood chips is a sustainable activity keeping a useful product out of the landfill which is both environmentally and economically a good thing. Source: https://www.artikelschreiber.com/en/.