Ground Vegetation in Pinus sylvestris Forests at Different Successional Stages following Clear Cuttings: A Case Study.

The impact of intensive forestry on various components of ecosystems has become the main subject of public and scientific debate in many regions in recent years. Forest ground vegetation is considered one of the most consistent and biodiversity-rich indicators of a certain stage of successional forest development. Therefore, changes in this forest component can potentially show the risks of forest damage due to clear-cutting and recovery trends. This study was carried out to identify the ground vegetation species diversity, including species composition and cover, also ground vegetation species relations with organic layer (forest floor) and upper mineral soil parameters at the different successional stages of the Pinus sylvestris L. stand development, including 1-2-year-old clear-cuts, and 6-130 years old stands. This study identified that the herb and dwarf shrub species were more light-demanding in the 2-year-old clear-cuts, as well as in the 6-year and 10-year old P. sylvestris stands compared to the middle-aged and mature forest stands. The dominant ground vegetation species, characteristic for the Pinetum vaccinio-myrtillosum forest type, were negatively dependent on the forest floor mass; they also had negative correlations with the concentrations of total P, K, Ca, and Mg in the forest floor and upper mineral soil but had positive correlations with the soil pH values and total N. The developed regression models of the percentage cover of mosses, herbs and dwarf shrubs according to the P. sylvestris stand age highlight the stabilization of the increase in the moss cover about 30 years after clear-cutting, with no clear trend for vascular species. The herbs and dwarf shrub species were highly variable during the stand rotation due to the species-specific characteristics and random factors rather than due to the influence of stand age. In this study, relatively short-term changes in ground vegetation species composition and percentage cover were determined after clear-cutting, but an important aspect is that new ground vegetation species appeared in the open areas, creating the potential for increasing species diversity. The clear-cutting system supports different species and numbers of herbs and mosses at different stages of stand development, which potentially increases the overall vegetation species diversity of the ecosystem.

Evaluation of the anthropogenic black carbon emissions and deposition on Norway spruce and silver birch foliage in the Baltic region.

This study investigates potential influence of urban trees on black carbon (BC) removal by Norway spruce and silver birch along with the BC formation, mass concentration in air, and source apportionment. The main sources of BC in urban areas are transport, household and industry. BC concentrations monitored in urban background station in Vilnius (Lithuania) showed that biomass burning was a significant contributor to BC emissions even during warm period of the year. Therefore, BC emission levels were determined for the most common biomass fuels (mixed wood pellets, oak, ash, birch and spruce firewood) and two types of agro-biomass (triticale and rapeseed straw pellets) burned in modern and old heating systems. The highest emissions were obtained for biomass fuels especially birch firewood. BC aerosol particles produced by the condensation mechanism during the combustion processes were found in all samples taken from the leaf surface. The short-term effect of BC exposure on photosynthetic pigments (chlorophyll a and b; and carotenoids) in the foliage of one-year-old Norway spruce and silver birch seedlings was evaluated by the experiment carried out in the phytotron greenhouse. The seedlings showed different short-term responses to BC exposure. All treatments applied in the phytotron greenhouse resulted in lower chlorophyll content in spruce foliage compared to natural conditions but not differed for birch seedlings. However, the exposure of BC particles on the spruce and birch seedlings in the phytotron increased the content of photosynthetic pigments compared to the control seedlings in the phytotron. Overall, urban trees can help improve air quality by reducing BC levels through dry deposition on tree foliage, and needle-like trees are more efficient than broad-leaved trees in capturing BC. Nevertheless, a further study could assess the longer-term effects of BC particles on tree biochemical and chemical reactions.

Trends and inter-relationships of ground-level ozone metrics and forest health in Lithuania.

Lithuania is representative of maritime to continental climate, no water limitation, and moderate ground-level ozone (O3) pollution. We investigated the trends of meteorological variables and O3 and how these environmental conditions associate with tree health from 2001 onward. Ozone metrics for forest protection, based on Accumulated O3 exposure Over a Threshold of X ppb (AOTX) or on Phytotoxic O3 Dose over a Y threshold (PODY), were modeled at nine ICP-Forests plots over the time period 2001-2014. Tree-response indicators, i.e. crown defoliation and visible foliar O3 injury, were assessed during annual field surveys carried out at each ICP-Forests plot over the time period 2007-2017. Mann-Kendall and Sen statistical tests were applied to estimate changes over time of meteorological variables, response indicators and O3 metrics. Finally, the O3 metrics were correlated (Spearman test) to the response indicators over the common period 2007-2014. Over this time period, trend analyses revealed an increasingly hotter (+0.27 °C decade-1, on average) and drier climate (rainfall, -48 mm decade-1). A reduction was found for O3 annual mean (-0.28 ppb decade-1, on average) and AOT40 (-2540 ppb·h decade-1, on average) whereas an increase was found for POD0 (+0.40 mmol m-2 decade-1, on average). Visible foliar O3 injury increased (+0.17% decade-1), while an improvement of the crown conditions (-5.0% decade-1) was observed. AOT40 was significantly associated with crown defoliation while PODY and soil water content were correlated with visible foliar O3 injury. As visible foliar O3 injury was negligible in all the studied species, the results suggest that moderate O3 pollution (approximately 30 ppb as annual average) does not induce biologically significant effects on this forest vegetation under the current conditions, however the overall O3 risk (POD0) is expected to increase in the future under a hotter and drier climate.