The invasive Asian clam, Corbicula fluminea, can enhance conditions needed for denitrification, but the effects of C. fluminea on denitrification in streams have not been measured. In summer 2012, we incubated sandand gravel-filled boxes in the North Branch of the Chicago River, Illinois (high nutrient), and Eagle Creek, Michigan, USA (low nutrient). One side of the box contained no clams (control), and the other contained C. fluminea. After 6 wk in situ, we measured inorganic N and dissolved-gas fluxes using a continuous-flow approach. At both sites, live C. fluminea significantly increased NH 4 + and N 2 flux out of sediments and O 2 consumption (i.e., respiration) relative to control sediment. Clams did not affect NO 3 − flux. Clams probably increased NH 4 + flux via direct NH 4 + excretion or mineralization of clam wastes and increased N 2 flux through either increased coupled nitrification-denitrification or enhanced exchange of nutrients between water column and sediment via bioturbation (i.e., burrowing). We used benthic clam density in each stream to scale up effects of live C. fluminea on in situ N fluxes. In the low-nutrient stream, live clams increased NH 4 + flux more than N 2 production. However, in the highnutrient stream, live clams enhanced N 2 production more than NH 4 + flux. The influence of dense assemblages of burrowing bivalves on denitrification may be an overlooked and potentially significant component of lotic N uptake in low-and high-N streams.

Small mammals cause serious damage to forests but there is only little knowledge of their ecology and possibilities of plantation protection. The objective of our study was to collect information on the damage caused by rodents to plantations of forest tree species. Data were obtained from a survey conducted in 2008 that was aimed at damage caused by small mammals. Questionnaires were sent mostly to foresters engaged in the Lesy CR state enterprise. We obtained usable data from 316 foresters. The response rate was 81%. It was confirmed that rodents cause significant damage all over the Czech Republic and that the occurrence of damage cannot be easily predicted with certainty as significant damage may appear perhaps in a small part of the threatened plantations where the key conditions for small mammals have been fulfilled. The main factors which affected probability of damage include: presence of a woody species attractive to rodents; suitable structure of ground vegetation enabling the pest species to breed sufficiently during the vegetation period; and also long-lasting snow cover. The current approach of forestry practice to damage by small mammals is considerably passive and we are missing an alert system of threat to stands and a methodology of dealing with problematic situations. Most of the foresters are uninterested in small mammals and many have only very smattering knowledge of the dangerousness of individual species and their ecological requirements. The use of rodenticides is expensive and the most effective and economic measure to lower damage by small mammals is to support forest management favouring natural regeneration of forest stands.

Conversion of coniferous monocultures to more stable mixed stands is one of the crucial tasks of present forestry in the Czech Republic. One of the factors hampering this process is the activity of small rodents that can cause severe damage to young plantations in winter. Little knowledge is still available of the ecology of small mammals in the forest environment and of the factors influencing their distribution and extent of damage. In order to acquire relevant information on rodent impacts on forest regeneration, we mapped the cumulated damage to forest plantations in 13 regions within the Czech Republic in 2007 and 2008. We checked 19,650 trees of eight species on 393 plots. Broadleaves were affected by browsing much more than conifers (20% and 4%, respectively). Of the monitored species, beech was damaged the most frequently (26% individuals). Browsing intensity differed among the regions (6-60% browsed individuals). The least damaged were the plantations at the altitudes below 400 m a.s.l.; on higher located plots the browsing intensity showed no trend. The proportion of damaged trees increased with plantation age up to 6 years, then it did not vary significantly. This study has confirmed that rodents are an important factor with a negative influence on the regeneration of broadleaves. Bark browsing in young trees is affected by several factors and the prediction of damage is complicated. Further research should improve the prediction of the bark browsing threat to young plantations and at the same time the efficiency of protection against rodent-caused damage.

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