Future climate scenarios for the boreal zone project increasing temperatures and precipitation, as well as extreme weather events such as heavy rain during the growing season. This can result in more frequent short-term waterlogging (WL) leading to unfavorable conditions for tree roots. In addition, it is decisive whether short-term WL periods during the growing season occur continuously or periodically. We assessed the effects of short-termed WL on 4-year-old Scots pine (Pinus sylvestris L.) saplings after shoot elongation started. Waterlogging (WL) lasted either continuously for 2.5 weeks (ContWL) or noncontinuously for 5 weeks, consisting of three repeated 1-week-interval WL periods (IntWL). Both treatments resulted in the same duration of soil anoxia. We studied soil gases, root and shoot growth and physiology, and root survival probability and longevity during the experiment. In the final harvest, we determined shoot and root biomass and hydraulic conductance and electrical impedance spectra of the root systems. Soil CO2 and CH4 concentrations increased immediately after WL onset and O2 decreased until anoxia. Waterlogging decreased fine root survival probability, but there was no difference between WL treatments. Shoot growth suffered more from ContWL and root growth more from IntWL. Needle concentrations of pinitol increased in the WL saplings, indicating stress. No WL effects were observed in photosynthesis and chlorophyll fluorescence. Increased starch concentration in needles by WL may be due to damaged roots and thus a missing belowground sink. Electrical impedance indicated suffering of WL saplings, although root hydraulic conductance did not differ between the treatments. Oxidative stress of short-term and interval WL can have long-lasting effects on shoot and root growth and the physiology of Scots pine. We conclude that even short-term WL during the growing season is a stress factor, which will probably increase in the future and can affect carbon allocation and dynamics in boreal forests.

Capsule We examined intraspecific variation in the nest size of open cup nesting Blackbirds Turdus merula and found that of seven variables considered, nest size variation was determined by the length of the nest construction period, nest height and the experience of the building female. Aims We tested seven hypotheses to investigate the influence of the following factors on nest size: (A) speed of construction: smaller nests are constructed faster; (B) nest height: nests placed higher up are smaller; (C) experience: inexperienced females construct smaller nests; (D) predation pressure: predation is less on smaller nests; (E) clutch size: larger nests contain larger clutches; (F) nest placement: nests constructed in open areas are larger than those situated in well-concealed sites and (G) incubation: larger and thicker nests are constructed during colder periods. Methods We used data from 54 Blackbird females nesting (73 nests) in two urban parks. Results Our data supported the speed, nest height and experience hypotheses. With respect to predation pressure, our data indicated that breeding failure occurred later in smaller nests. We found no evidence for the placement and incubation hypotheses. Conclusion Nest size may be determined by predator avoidance and the energy used during building. The negative relationship between nest size and time of nest failure suggests that nest size parameters are adjusted to avoid predation.

Wood ants are common in coniferous, mixed and deciduous forests of the Palaearctic ecozone. We conducted a survey of wood-ant mounds in an area of 1400 ha in the Białowieża Forest (NE Poland) and related physical mound characteristics to the surrounding forest properties. The overall density of inhabited wood-ant mounds was 0.13 per ha. Formica polyctena and F. rufa were the most abundant species, and the highest densities of their mounds were found in fresh mixed deciduous and fresh mixed coniferous forests. The physical mound properties, such as direction of the longest mound slope and the distance to the closest tree did not differ significantly between these two ant species. Amount of light significantly affected mound size and the distance to the closest tree distance: mound diameter, height and volume increased with increasing shade; and the distance to the closest tree with increasing amount of light. The results of our study suggest that coniferous forests with an admixture of deciduous trees are ...

The wild boar is an omnivorous animal, and by foraging (rooting) disturbs the top soil layer. In some regions of Poland and Europe seasonal fluctuations in rooting have been observed. Wild boars not only eat plants, but also strongly modify their habitat. In Białowieża National Park wild boar most frequently visit oak-hornbeam forests on fertile soil. On sites where the forest floor is covered with dense vegetation the germination of seeds is difficult, and wild boar rooting can promote the removal of diaspores from deeper layers of the soil seed bank. Within a 3-year observation on 30 subplots about 10,000 seedlings emerged representing 38 species. Our study revealed that rooted patches are characterised by a very rich and diverse flora of seedlings representing mostly forest species, but their density is low. The dominant species germinating in the disturbed ground vegetation is Urtica dioica, a species forming the persistent soil seed bank. There is a possibility that seedlings of herbaceous plants emerging on permanently rooted patches are of exogenous origin, since the seeds germinating there were in many cases damaged by repeatedly rooting animals and had no chance for further growth and reaching the generative phase. However, the soil seed bank in the rooted area has to be analysed to confirm this theory, that they have exogenous or endogenous origin. Seedling density in a repeatedly rooted oak-hornbeam forest is determined by factors other than those related to rooting. In this context the present study did not demonstrate a negative impact of rooting intensity on seedling emergence.