The Bialowieza Primeval Forest (BF) is one of the well-known forests in Central Europe. The most common tree species in BF was Norway spruce (Picea abies (L.) H. Karst), comprising 26%. However, a mass dieback of spruce has occurred during recent years. The spruce dieback in Bialowieza Forest is directly caused by the spruce bark beetle. However, the mass appearance of this pest can be a consequence of global warming and drought. Changes in air temperature were presented and drought indices were calculated as follows: standardized precipitation index, Palmer drought severity index, climatic water balance and soil water storage deficit. The warming of the climate of Bialowieza from 1950 to 2015 is comparable to that observed throughout central Europe. The temperature increased by 1.27 °C. The occurrence of drought from 1950 to 1966 and from 1985 to 2015 had a similar frequency. From 1963 to 1966, the volume of removed deadwood from the managed part of Bialowieza Forest was 27 thousand m3 but from 2012 to 2016, the volume was more than one million m3.
Abstract. Despite the importance of vegetation uptake of atmospheric gaseous elemental
mercury (Hg(0)) within the global Hg cycle, little knowledge exists on the
physiological, climatic, and geographic factors controlling stomatal uptake
of atmospheric Hg(0) by tree foliage. We investigate controls on foliar
stomatal Hg(0) uptake by combining Hg measurements of 3569 foliage samples
across Europe with data on tree species' traits and environmental conditions.
To account for foliar Hg accumulation over time, we normalized foliar Hg
concentration over the foliar life period from the simulated start of the
growing season to sample harvest. The most relevant parameter impacting daily foliar stomatal Hg uptake was
tree functional group (deciduous versus coniferous trees). On average, we
measured 3.2 times higher daily foliar stomatal Hg uptake rates in deciduous
leaves than in coniferous needles of the same age. Across tree species, for
foliage of beech and fir, and at two out of three forest plots with more
than 20 samples, we found a significant (p<0.001) increase in
foliar Hg values with respective leaf nitrogen concentrations. We therefore
suggest that foliar stomatal Hg uptake is controlled by tree functional
traits with uptake rates increasing from low to high nutrient content
representing low to high physiological activity. For pine and spruce
needles, we detected a significant linear decrease in daily foliar stomatal
Hg uptake with the proportion of time during which water vapor pressure
deficit (VPD) exceeded the species-specific threshold values of 1.2 and
3 kPa, respectively. The proportion of time within the growing season during
which surface soil water content (ERA5-Land) in the region of forest plots
was low correlated negatively with foliar Hg uptake rates of beech and pine.
These findings suggest that stomatal uptake of atmospheric Hg(0) is
inhibited under high VPD conditions and/or low soil water content due to the
regulation of stomatal conductance to reduce water loss under dry
conditions. Other parameters associated with forest sampling sites (latitude
and altitude), sampled trees (average age and diameter at breast height), or
regional satellite-observation-based transpiration product (Global Land Evaporation Amsterdam Model: GLEAM) did not
significantly correlate with daily foliar Hg uptake rates. We conclude that
tree physiological activity and stomatal response to VPD and soil water
content should be implemented in a stomatal Hg model to assess future Hg
cycling under different anthropogenic emission scenarios and global warming.
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