Wind disturbance and climate change increase the risk of major European spruce bark beetle (ESBB) outbreaks. In order to understand the drivers behind the spread, we used a combination of the Random Forest algorithm and logistic regression mixed modelling to generate robust results. We analysed tree and stand characteristics, level of infestation, and nearness to eight major blowdown areas from a summer storm in 2016 in two conservation areas in south-eastern Estonia, Karula National Park and Otepaa Nature Park. The two areas differ in forest site quality (tree growth conditions) and topographical features, spatial distribution of protected and managed patches, and management history, and were therefore analysed separately. Data collection, in 2020, was based on a network of transect-based circular plots surrounding the blowdowns. By the time of the inventory, four years after the storm, the wind-induced spread had largely come to a halt, with only a few freshly infested Norway spruce trees recorded. The study revealed that, besides the often-mentioned factors tree diameter and share of Norway spruce, intensity of initial infestation in the first 10 m outside the storm area was positively correlated with ESBB infestation probability in the surrounding forest in Karula, where forest cover is more contiguous and under more severe management restrictions. Conversely, distance to any type of open area and tree species diversity decreased infestation probability in Otepaa. Furthermore, trees in patches with average site quality class had a significantly higher infestation risk, compared to those in a low site quality class. Distance to the storm area was not a driver behind the outbreak, and neither did the number of infested trees in the initial storm area affect surrounding stands, at this stage. Differences in significance of factors for infestation probability between the two conservation areas were considerable, which hints at even higher complexity of Norway spruce vigour-bark beetle-climate relations at an international level. Since storm area infestation levels and vicinity did not directly affect spatial distribution of ESBB, but infestation levels in our study were nonetheless high, this suggests that research should focus on early detection and prevention strategies at the landscape scale. In that respect, further investigation is required into the role of tree species diversity, stand structural heterogeneity and growth conditions in reducing outbreak risk and favouring a fast recovery from disturbances.

Wind disturbance and climate change increase the risk of major European spruce bark beetle (ESBB) outbreaks. In order to understand the drivers behind the spread, we analysed tree and stand characteristics, level of infestation and position relative to eight major blowdown areas from a summer storm in 2016 in two conservation areas in south-eastern Estonia. The two areas differ in site quality and topographical features, spatial distribution of protected and managed patches, and management history. Data collection was based on a network of transect-based circular plots surrounding the blowdowns. By the time of the inventory, four years after the storm, the wind-induced spread had largely come to a halt, with only a few freshly infested Norway spruce trees recorded. Logistic regression mixed modelling revealed that, besides the often-mentioned factor tree diameter, intensity of initial infestation in the first 10 meters outside the storm area was also positively correlated with ESBB infestation probability in the surrounding forest. Furthermore, trees in patches with average site quality class had significantly highest infestation risk, compared to those in a low site quality class. Tree species diversity was negatively correlated with infestation probability. Distance to the storm area did not show up as a driver behind the outbreak. Differences in significance of factors for infestation probability between the two conservation areas were considerable, which hints at even higher complexity of Norway spruce health – bark beetle – climate relations at an international level. Research should focus on early detection and prevention strategies at the landscape scale. Tree species diversity and stand heterogeneity at different scales may help keep away or control outbreaks, or at least support a faster recovery from disturbances. Furthermore, establishment of pure Norway spruce stands should be avoided in areas susceptible to drought or with a high storm risk.

Since fire frequency is expected to increase globally due to climate change, it is important to understand its effects on forest ecosystems. We studied the long-term patterns in species diversity, cover and composition of vascular plants and bryophytes after forest fire and the site-related factors behind them. Research was carried out in northwestern Estonia, using a chronosequence of Scots pine ( L.) stands, located on nutrient poor sandy soils, where fires had occurred 12, 23, 38, 69, 80 and 183 years ago. In every stand three 100 m vegetation plots were established to collect floristic and environmental information. The effects on floristic characteristics of time since fire, light, and soil variables were evaluated with linear mixed models, followed by backward variable selection. Compositional variation was analysed with non-metric multidimensional scaling, Multi-response Permutation Procedures, and Indicator Species Analysis. Altogether, 31 vascular plant and 39 bryophyte species were found in vegetation plots. The cover of the vascular plant and bryophyte layers increased with a longer time since fire. Soil and light variables impacted the richness of several vascular plant and bryophyte groups, whereas only the richness of liverworts and dwarf-shrubs correlated with time since fire. Considerable compositional differences were observed in vascular plant and bryophyte assemblages between recently vs. long-time ago burned stands. To conclude, time since fire significantly impacted compositional patterns of vascular plants and bryophytes in pine forests on nutrient poor soils, although time-related trends in species richness were less evident.Pinus sylvestris2

We studied long-term effects of forest fires on the dynamics of soil fungal community along a post-fire chronosequence in hemiboreal Scots pine stands in north-western Estonia. Effects of fire on soil and fungi were studied on six sites that differed in time since fire (10, 21, 36, 67, 78 and 181 years ago), without further management interventions. Soil fungal communities along the chronosequence were dominated by soil saprotrophs and ectomycorrhizal (EcM) fungi. Across the chronosequence, the most dominant phylum was Ascomycota. The most abundant OTUs were identified as Umbelopsis sp., Hyaloscyphaceae sp. and Pezoloma ericae with relative abundances of 9.5, 8.9 and 6.8 %, respectively. Fungal species richness was similar among sample areas except in the area where fire occurred 36 years ago, where it was significantly lower. There were considerable differences in EcM fungal species composition along the chronosequence. The most recently burned site had Piloderma sphaerosporum, Pseudotomentella sp. and Clavulinaceae sp. as most abundant EcM OTUs while in three oldest burned areas Clavulinaceae sp. and Cortinarius sp. were abundant. Soil C and N stocks were lower in the most recently burned area but differences with other areas were not statistically significant. Soil pH had a significant effect on fungal species composition. Older areas had substantially lower pH compared to more recently burned areas.

In this article, we introduce an alternative solution for forest regeneration based on unmanned ground vehicles (UGV) and describe requirements for external data, which could significantly increase the level of automation. Over the past few decades, the global forested area has decreased, and there is a great need to restore and regenerate forests. Challenges such as the lack of labor and high costs demand innovative approaches for forest regeneration. Mechanization has shown satisfactory results in terms of time-efficient planting, although its usage is limited by high operational costs. Innovative technologies must be cost-efficient and profitable for large scale usage. Automation could make mechanized forest regeneration feasible. Forest regeneration operations can be automated using a purpose built unmanned platform. We developed a concept to automate forest planting operations based on mobility platform. The system requires external data for efficient mobility in clear-cut areas. We developed requirements for external data, analyzed available solutions, and experimented with the most promising option, the SfM (structure from motion) technique. Earth observation data are useful in the planning phase. A DEM (digital terrain model) for UGV planter operations can be constructed using ALS (airborne laser scanning), although it may be restricted by the cost. Low-altitude flights by drones equipped with digital cameras or lightweight laser scanners provided a usable model of the terrain. This model was precise (3–20 cm) enough for manually planning of the trajectory for the planting operation. This technique fulfilled the system requirements, although it requires further development and will have to be automated for operational use.

Fire is the most important natural disturbance in boreal forests, and it has a major role regulating the carbon (C) budget of these systems. With the expected increase in fire frequency, the greenhouse gas (GHG) budget of boreal forest soils may change. In order to understand the long-term nature of the soil-atmosphere GHG exchange after fire, we established a fire chronosequence representing successional stages at 8, 19, 34, 65, 76 and 179 years following stand-replacing fires in hemiboreal Scots pine forests in Estonia. Changes in extracellular activity, litter decomposition, vegetation biomass, and soil physicochemical properties were assessed in relation to carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. Soil temperature was highest 8 years after fire, whereas soil moisture varied through the fire chronosequences without a consistent pattern. Litter decomposition and CO2 efflux were still lower 8 years after fire compared with pre-fire levels (179 years after fire). Both returned to pre-fire levels before vegetation re-established, and CO2 efflux was only strongly responsive to temperature from 19 years after fire onward. Recovery of CO2 efflux in the long term was associated with a moderate effect of fire on enzyme activity, the input of above- and below-ground litter carbon, and the re-establishment of vegetation. Soil acted as a CH4 sink and N2O source similarly in all successional stages. Compared with soil moisture and time after fire, soil temperature was the most important predictor for both GHGs. The re-establishment of overstorey and vegetation cover (mosses and lichens) might have caused an increase in CH4 and N2O effluxes in the studied areas, respectively.

We compared the changes in aboveground biomass and initial recovery of C pools and CO2 efflux following fire disturbances in Scots pine (Pinus sylvesteris L.) stands with different time since stand-replacing fire. The study areas are located in hemiboreal vegetation zone, in north-western Estonia, in Vihterpalu. Six areas where the last fire occurred in the year 1837, 1940, 1951, 1982, 1997, and 2008 were chosen for the study. Our results show that forest fire has a substantial effect on the C content in the top soil layer, but not in the mineral soil layers. Soil respiration showed a chronological response to the time since the forest fire and the values were lowest in the area where the fire was in the year 2008. The respiration values also followed seasonal pattern being highest in August and lowest in May and November. The CO2 effluxes were lowest on the newly burned area through the entire growing season. There was also a positive correlation between soil temperature and soil respiration values in our study areas.