BG3.11

In 2018, an extreme drought affected large parts of Europe and led to the worst fire season in over a century in Sweden. We investigated the impacts of the Ljusdal fire, the largest fire complex that year, on soil CO₂ and CH₄ fluxes, nutrient concentrations and microclimate in a Scots pine forest. The measurements were conducted during the first growing season after the fire. In three separate analyses, we compared stands that differed in terms of burn severity (unburnt, low and high burn severity), salvage-logging (logged or unlogged) and stand age (young: 12 years old or mature: ~100 years old at the time of the fire).

A mature stand affected by a high severity burn (100% tree mortality) had significantly lower soil respiration compared to a stand affected by a low severity burn (nearly 100% tree survival), but there was no difference in soil respiration between the low burn severity and unburn stands. These results indicate that autotrophic respiration plays a key role in determining post-fire soil respiration. After a high severity burn, salvage logging had no significant effects on forest soils compared to a stand where the dead trees had been left standing, although differences between these two stands are likely to become significant in the future. Stand age had a clear impact on most of the soil properties tested. Despite mean soil temperature being 5 °C warmer at a young site compared to a mature site after a high severity burn, soil respiration was lower at the young site. The young site had been clear-cut and undergone soil scarification and replanting 12 years before the fire, which is likely to have contributed to the lower nutrient availability and thinner soil organic layer there compared to the mature site. Short return intervals between disturbances such as harvesting and wildfire that remove part of the soil organic layer can thus have significant and long-term impacts on nutrient cycling and carbon exchange in the boreal forest. The boreal forest is thus vulnerable to becoming a carbon source, especially in regions where climate change is increasing the frequency of high severity wildfire and commercial timber production is expanding.

How to cite: Kelly, J., Ibáñez, T., Santín, C., Doerr, S., Nilsson, M.-C., Holst, T., Lindroth, A., and Kljun, N.: Boreal soil carbon fluxes one year after a forest wildfire: impacts of burn severity and forest management, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2097, https://doi.org/10.5194/egusphere-egu21-2097, 2021.

Key words: forest regeneration, Conniflex, Trico, mechanical site preparation

Forest regeneration is crucial stage in commercial forest management because actions during this stage impact future forest productivity and value. Scots pine is one of the main tree species in forestry of the northern part of Europe. Foresters have to overcome different risk factors during regeneration process and two of them are seedling damage by Pine weevil (Hylobius abietis L) and browsing by herbivores of Cervidae family. Pine weevil is one of the main forest pests in Europe that damage regenerated coniferous stands. Damage caused by this pest can produce 70% mortality of planted seedlings. Another significant risk factor is browsing. With increase of deer (Cervidae) population the damaged forest area also increases to the extent that foresters choose other tree species for regeneration. The mitigation of these risks is possible with appliance of forest management practices.  There are used different repelents against Cervidae animals.  Regarding Pine weevil, due to restrictions on insecticide use in EU, different protective coating materials have been developed, and several studies show that soil preparation before planting reduce amount of damaged Pine seedlings and increase possibility of successful regeneration.  We evaluated if and how forest management methods - soil preparation techniques (spot mounding, disc trenching) in combination with different plant protection products (Conniflex, Trico) - affects the degree of damage caused by pine weevil and Cervidae animals to Scots pine seedlings one and two years after outplanting in four forest stands in Latvia. The results from this study shows that application of Conniflex reduce number of damaged trees by 16.8% first and 20.3% second year after outplanting compared to untreated seedlings. Soil preparation has significant impact on reduction of pine weevil damage. The best results have been achieved by planting with Conniflex treated seedlings on spot mounds (2.4% damaged trees compared to 48.9% in unprepared soil without treatment). Repellent Trico do not provide additional protection against Pine weevil and do not have long term protection effect against browsing. Overall conclusion is that combination of soil preparation and use of appropriate coating material (Conniflex) can provide sufficient protection without usage of insecticides, and Trico has to be applied before winter season to achieve effect of protection.

How to cite: Dūmiņš, K., Timma, S., and Lazdiņa, D.: Forest management practices in reduction of damage caused by Pine weevil (Hylobius abietis L.) and Cervidae animals in newly planted Scots pine forests., EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-14555, https://doi.org/10.5194/egusphere-egu21-14555, 2021.

In the December 2017, 211 000 ha of Slovenian forests or 2 201 000 m³ were severely damaged by the windstorm. The damage was greatest in the adult beech-silver fir forest stands. In each management district (FMD) with different share of damaged forested area - Kočevje (69%), Postojna (22%) and Ljubljana (19%), research location were established to evaluate soil properties, root characteristics and ecophysiological regeneration response of predominating tree species in damaged stands as well as the economic effect of the windstorm on sensitive high karst sites. The restoration and regeneration efficiency of latest disaster (2017) was also compared with restoration efficiency of areas damaged in 2008, identifying possible specifics / differences and providing guidelines for their optimal recovery.

Timber database from Slovenian Forest Service with data about felling and felling reasons between Dec. 2017 and the end of 2019 was used to evaluate economic losses. The total amount from the database was multiplied by the shares of individual quality category, obtaining the quantitative assortment structure according to the actual felling. We used tables of assortment losses caused by wind to estimate the actual assortment loss and multiplied those with 2018 roundwood market prices. Estimated cumulative biomass loss amounted 205 855 m³ - 5.6% less, compared to regular felling, or 16.1 million €.

Physical soil properties between plots damaged by wind and control areas without damage did not confirm any significant difference in relation to weather and microsite conditions (rootstock, exposition, altitude, species structure of stands, microrelief). Characteristics of root systems of the most affected tree species - fir, spruce and beech did not differ between damaged and neighboring undamaged sites. An overview of fir and spruce windbreaks during the 1995 - 2018 period outlined the cumulative effect of multiple site conditions with strong wind, severely reducing the mechanical stability of fir and spruce; consequently, the following weather events with even mild wind intensities resulted in calamity.

Natural regeneration ability on all plots of recent windthrow shows successful regeneration of beech, maple, and fir in all light categories of damaged stands, but questionable regeneration of fir, which is in tight relation with ungulate browsing.  For comparison with regeneration after windthrow in 2017, we analyzed successional development in three windthrow areas from 2008. Seedling densities ranged from 5000 to 9000 ha-1, with the highest densities in the 150-300 cm height class. Within plots with natural regeneration, height and species diversity were better compared to planted plots. Shade-tolerant species increased in plots at lower elevations, while pioneer species still increased at higher elevations. Overall browsing was moderate, but silver fir and sycamore had difficulty establishing. The results indicate that regeneration spreads from areas that were covered with seedlings shortly after windthrow and that certain parts will not be covered with regeneration for a longer period.

How to cite: Čater, M., Marinšek, A., Ferlan, M., Alagić, A., Diaci, J., Fidej, G., Jevšenak, J., and Simončič, P.: Causes and effect of latest windthrow on further development of beech-fir stands in Slovenian forests, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7529, https://doi.org/10.5194/egusphere-egu21-7529, 2021.

Forest management and land use can strongly alter the forest ecosystem with long-lasting legacy effects by shaping e.g. species composition and age structure in stand and landscape scales. These changes may lead to changes in the local disturbance regime. In addition, forest management may directly affect the dynamics of disturbance agents. Heterobasidion root rot is one of the most important diseases of conifers in the Northern hemisphere. The epidemiology of the fungus relies heavily on the availability of fresh wood material which the spores need to cause an infection. In managed forests, fresh stump surfaces provide massive amounts of perfect growth media.  Once the fungus has infected a stand, the disease remains in there over tree generations slowly deteriorating the timber quality, killing trees and predisposing trees to subsequent disturbance agents such as wind. Thus, host availability in landscape scale, stand conditions and the management history all are assumed to play an important role in the epidemiology. The aim of this study was to analyze the drivers of current distribution of Heterobasidion root rot in Finland in order to understand the disease dynamics better and to manage the disease in the future. Specifically, we asked how important the legacies of different past management and land-use methods are. The National Forest Inventory (NFI) in Finland has recorded root rot observations since 1995 covering in total over 348 000 sample plots over four inventories. We combined that database with 20 different explanatory variables with a hypothetical relation to the biology and epidemiology of the fungus. The variables were categorized to three categories; (i) management legacies, (ii) landscape structure, and (iii) site conditions. Management legacies included for example the historical locations of sawmills and the share of forest pastures. Landscape structure combined structural characteristics, such as Norway spruce and old forest (120+ years) shares from different time periods. Site conditions were described with e.g. temperature sum and Shannon index for tree species richness. By using Boosted Regression Tree and Generalized Liner Models, we found that variables from all the three categories contributed to the presence of Heterobasidion root rot. The distance from an NFI plot to the nearest sawmill operating in 1910 (historical intensity of logging) and the distance to a waterway (timber rafting as main transportation methods) were shown to be one of the most important variables together with temperature sum and current Norway spruce share in landscape scale. This indicates that the management legacies, especially the past management intensity, has a significant effect on the epidemiology of Heterobasidion root rot.

How to cite: Honkaniemi, J., Heikkinen, J., Henttonen, H., and Peltoniemi, M.: Management legacies and forest structure shape the root rot risk of coniferous forests in Finland, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15536, https://doi.org/10.5194/egusphere-egu21-15536, 2021.

Extreme climatic events such as droughts threaten forests and their climate mitigation potential globally. Stability, the ability of forests to maintain functioning in periods of stress, is therefore expected to be a primary focus of forest management in the 21st century. A key management strategy suggested for enhancing stability may be to increase tree species richness in secondary and plantation forests. Here, we aim to understand the drivers that may promote forest stability in mixed-species tree communities. We use structural equation models to explain how tree species richness, asynchronous species dynamics and diversity in hydraulic traits affect the stability of yearly forest productivity along an experimentally manipulated biodiversity gradient ranging from monocultures up to mixtures of 24 tree species. Tree species richness improved stability by increasing species asynchrony. That is, at higher species richness, inter-annual variation in productivity among tree species buffered the community against stress-related productivity declines. This effect was mediated by diversity in species’ hydraulic traits in relation to drought tolerance and stomatal control within the community, but not by the community-weighted means of these hydraulic traits. The examined hydraulic traits may be used to select suitable tree species and design mixtures that stabilize productivity in an increasingly variable climate through diverse response strategies, while excluding those that would succumb to drought or competition. The identified mechanisms by which tree species richness stabilizes forest productivity emphasize the importance of hydraulically diverse, mixed-species forests to adapt to climate change.

How to cite: Schnabel, F., Liu, X., Kunz, M., Barry, K. E., Bongers, F. J., Bruelheide, H., Fichtner, A., Härdtle, W., Li, S., Pfaff, C.-T., Schmid, B., Schwarz, J. A., Tang, Z., Yang, B., Bauhus, J., von Oheimb, G., Ma, K., and Wirth, C.: Hydraulic diversity stabilizes forest productivity in a large-scale subtropical tree biodiversity experiment, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7113, https://doi.org/10.5194/egusphere-egu21-7113, 2021.

Growing evidence suggests that low-intensity anthropogenic activities affect ecological communities. The resultant changes in the forest structure and composition can also be influenced by elevational gradients. During foraging for food collection, humans can cover a wider spatially and elevational range compared to other high-intensity activities. These foraging activities can alter the species richness and evenness patterns either through preferential planting or intentionally or inadvertently influence the propagule pool. This study investigated the impact of foraging on forest composition and structure along an elevation gradient in Cross River National Park in the tropical rainforest zone of Nigeria. Fifteen permanent 40 x 40 m sample plots, covering an area of 2.4 hectares, were established in the forest located in the park along an elevational gradient of 120m to 460m. All trees of 10cm diameter at breast height (dbh) and above in all the plots were measured for dbh and identified to species level. Structured questionnaires on tree species utilization amongst forest-dependent rural communities were used to create edible and inedible tree species categories. Species abundance distributions were calculated at community level. Pairwise beta diversity between all plots along the elevational gradient was calculated using Sorensen’s dissimilarity index (β_sor) and the turnover component of β_sor using Simpson’s dissimilarity index (β_sim). A total of 35 edible species with a density of 128 stems/hectare and basal area of 11.99 m²/ha and 109 inedible species with a density of 364 stems/hectare and basal area of 22.42 m²/hectare were encountered. A reversed j-shaped function characteristic of a ‘natural’ uneven-aged tropical forest stand was observed in the diameter size distribution for all species categories. The pairwise beta diversity trend of inedible species showed that there was a positive trend between beta diversity and elevation, and this was driven by turnover; the replacement of species in the species pool along the elevational gradient. In comparison, edible species differed significantly from inedible species and showed a negligible trend indicating that the species turnover was not enough to cause a change in beta diversity with increase in elevation. These results suggest that low-impact activities such as foraging may be subtly but notably altering the composition of tropical forest, perhaps by preferential planting, or influencing the propagule pool along elevational gradients. Further tests across a wider range of sites are required to assess if this is a widespread phenomenon and to identify the driving mechanisms.

How to cite: Asuk, S., Kettridge, N., Sadler, J., Pugh, T., Matthews, T., Ebu, V., and Ifebueme, N.: Does foraging impact tropical forest composition?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8867, https://doi.org/10.5194/egusphere-egu21-8867, 2021.

Stand-replacing disturbances vary in their type, frequency and severity across regions, with consequent heterogeneity in their effects on forest stand age, structure and carbon cycling. These effects can be assessed using dynamic global vegetation models (DGVMs), but representations of disturbances in these models are generally limited to wildfire, with other major natural agents, such as windthrow and biotic outbreaks, typically neglected. Furthermore, human actions, such as harvest and forest management, may intensify or dampen disturbance regimes and modulate forest susceptibility to certain agents. Here, we assess the relative importance of non-fire-related disturbances in canopy turnover, as opposed to fire-related, accounting for human influence across the world. Using the Landsat-derived Global Forest Change product, we delineate contiguous patches of tree cover loss at 30m resolution for the period 2001-2016 and combine them with different global satellite-based data products to identify fire disturbances, land conversion and exposure to human activities. We then calculate disturbance rates by forest ecoregion, excluding land use change and differentiating by fire association and forest intactness. We find that the rate of non-fire-related disturbances in intact forests, mainly windthrow and biotic outbreaks, exceeds the rate of fire in most tropical regions, as well as in British Columbia’s coastal and mountain temperate conifer forests and West Scandinavian and Russian taiga, whereas wildfire dominates in remaining boreal regions. Outside intact forests, the rate of non-fire-related disturbances, with the addition of anthropogenic disturbances, mainly harvest, exceeds the rate of fire in most regions of the world, apart from the fire-prone boreal Siberia, Mediterranean Australia, boreal North America and West American mountain temperate conifer and Mediterranean forests. The dominant disturbance agent shifts from fire in intact forests to non-fire outside intact forests, mainly in West Siberian taiga, East Australian temperate broadleaf and mixed forests, and some North American boreal forests. This analysis shows the potential of leveraging satellite remote sensing for assessing disturbance regimes and provides a globally consistent dataset that can help achieve more realistic disturbance simulations in DGVMs and reduce uncertainties in projections appraising the future role of forests in global carbon cycling.

How to cite: Acil, N., Pugh, T., Sadler, J., and Senf, C.: Remotely sensed quantification of non-fire-related disturbances and their contribution to global forest dynamics, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9349, https://doi.org/10.5194/egusphere-egu21-9349, 2021.

Worldwide, forests provide natural resources and ecosystem services. However, forest ecosystems are threatened by increasing forest disturbance dynamics, caused by direct human activities or by altering environmental conditions. It is decisive to reconstruct and trace the intra- to transannual dynamics of forest ecosystems. Therefore, the monitoring of large and small scale vegetation changes such as those caused by natural events (e.g., pest infestation, higher mortality due to altering site conditions) or forest management practices (e.g., thinning or selective timber extraction) becomes more and more crucial. National to local forest authorities and other stakeholders request detailed area-wide maps that delineate forest disturbance dynamics at various spatial scales.

We developed a time series analysis (TSA) framework that comprises data download, data management, image preprocessing and an advanced but flexible TSA. We use dense Sentinel-2 time series and a dynamic Savitzky–Golay-filtering approach to model robust but sensitive phenology courses. Deviations from the phenology models are used to derive detailed spatiotemporal information on forest disturbances. In a first case study, we apply the TSA to map forest disturbances directly or indirectly linked to recurring bark beetle infestation in Northern Austria.

In addition to spatiotemporal disturbance maps, we produce zonal statistics on different spatial scales that provide aggregated information on the extent of forest disturbances between 2018 and 2019. The outcomes are (a) area-wide consistent data of individual phenology models and deduced phenology metrics for Austrian forests and (b) operational forest disturbance maps, useful to investigate and monitor forest disturbances, for example to facilitate sustainable forest management.

At a forest stand level, we reconstruct the origin date of forest disturbances (FDD – Forest Disturbance Date). Theses FDD outputs show the spatiotemporal patterns and the development of damages and indicate that most dynamics are caused by recurring and spreading bark beetle infestation. The validation results based on field data confirm a high detection rate and show that the derived temporal information is reliable. In total, 23400 hectares, i.e., on average 2.8% of the forest area in the study area, are found to be affected by forest disturbance. The zonal statistic maps point out hotspots of significant forest disturbances, where adequate forest management measures are highly needed. Furthermore, this study highlights the TSA’s potential to also depict and monitor minor human impacts on forests, such as thinning, selective timber extraction or other moderate forest management practices.

Keywords:  forest disturbance; forest monitoring; bark beetle infestation; forest management; time series analysis; phenology modelling; remote sensing; satellite imagery; Sentinel-2

How to cite: Löw, M. and Koukal, T.: Forest Disturbance Mapping with Sentinel-2 Time Series in Austria, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7795, https://doi.org/10.5194/egusphere-egu21-7795, 2021.

Predicted climate warming and increasing anthropogenic pressure on environmental resources are expected to increase wildfire risk in Central and Eastern Europe (including Romania) and thus may affect areas currently outside fire risk areas. Therefore, knowledge of the natural and anthropogenic variability of wildfire, as well as its long-term impacts on the environment can provide an important perspective and be used to enhance the environmental management of this region.

Our study aims to reconstruct fire history in relation to anthropogenic disturbances and climate variability, over the last 2000 years in a now forested but former mining area from Lăpuș Mts (Eastern Carpathians, Romania) based on an ombrotrophic peat sequence. To reconstruct past fire activity, we employed sedimentary macroscopic charcoal (counts and morphological characteristics), a widely used proxy for gaining insight into long-term fire history and vegetation burning. Ombrotrophic peat bogs are sensitive to local environmental changes and, given that the deposition of allochthonous material is exclusively atmospheric, they are ideal archives for recording charcoal fluxes resulted from vegetation burning. Past local soil/bedrock erosion and regional atmospheric pollution from (pre)historical mining were reconstructed on the basis of abiotic sediment properties such as elemental geochemistry, mineral magnetic characteristics, organic matter content and particle size. Published sources were used to extract information regarding regional climate variability and extra-local to regional vegetation history.

Results show that increases in macro-charcoal concentration, particularly the woody charcoal morphotype, were shortly followed by marked increases in heavy metal concentration and by enhanced soil and bedrock erosion, as inferred from geochemical, magnetic and grain-size proxies. This suggests increased local disturbance during intervals with mining activities and indicates the likelihood that humans used fire to clear the forests and open the access to the mining sites. Alternatively, humans could have deforested the landscape to obtain charcoal in kilns, for ore smelting. Such actions likely resulted in topsoil removal and exposed bedrock surfaces, which is supported by the increase in the concentration of detrital elements and small, topsoil-derived magnetic particles in our record. Over recent centuries, the recovery of the local environment is evident in the proxies, with low fire activity and decreased soil/bedrock erosion, which coincides with the abandonment of the mining sites. This multi-proxy study shows the impact of anthropogenic disturbances and the recovery of the local environment and can be used to predict future possible responses of the local environment to stressors.

How to cite: Petras, A., Florescu, G., Hutchinson, S. M., and Mindrescu, M.: Fire history and the relationship with late Holocene anthropogenic activity in Tăul Mare peat bog in the Lăpuș Mts (Eastern Carpathians). Romania, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-15609, https://doi.org/10.5194/egusphere-egu21-15609, 2021.

Forest roads are crucial to forest conservation. They can be perfect barriers against forest wildfires if they maintained appropriately and firefighting equipment were provided. This paper discusses the effect of forest roads in context of forest transportation and fire fighting in Czech Republic forestry. The results prove that, the wildfire sizes are reduced if the fire brigade can reach the fires more rapidly.  In other words, the wildfire sizes were evaluated from a function of the distances to roads. Increasing road density can decrease wildfire size. Enhancement of the road network can decrease the future wildfire problems as attack times strongly effects on wildfire sizes. This motivates the location of some firefighting stations close to the forest areas. Furthermore, the importance of road density, road quality and other infrastructure to attack time and efficiency, such as bridges and water reservoirs, may be enhanced. In case forest management methods, infrastructure and the capacities of fire brigades are not updated to the new climate, larger areas destroyed by wildfires can be predicted.

Keywords: attack time, forest roads, forest management, forest wildfires, Czech Republic forestry.

How to cite: Mohammadi, Z., Lohmander, P., Kašpar, J., and Marušák, R.: The effect of road networks on the forest wildfires ‘size, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-12000, https://doi.org/10.5194/egusphere-egu21-12000, 2021.

Forest restoration and afforestation on degraded lands are receiving tremendous research efforts globally as a climate change mitigation option. There is a growing interest in mixed species plantation to ensure sustainable ecosystem services and biodiversity. However, successful mixture of achieving these potential benefits is rare. We studied the polyculture of two pioneer fast growing species (i.e. B. pendula,  and A. glutinosa- of which A. glutinosa is N-fixing) and one shed tolerant species with slow juvenile growth (i.e. F. sylvatica) to examine the effects of species mixture on biomass production and quality of soil organic C stock following the replacement series approach. Standing woody biomass in polyculture demonstrated no over-yielding, presumably due to concurrent impacts of suppression of F sylvatica by two fast growing species and competitive reduction benefits in A. glutinosa. Similarly, standing fine root biomass production and turnover showed no significant mixture effect.  Although the quantity of soil organic C stock was unaffected by tree mixture, the vertical distribution of biodegradable C fractions was differed between mono and polyculture stands,  most probably due to slow decay rate of mixed litter. We found that species mixture decreased soil C lability in the upper soil layers, and increased recalcitrant C  in deep soil (>40 cm) that has enormous potential for long-term sequestration. We concluded that contrasting growth responses can result in no biomass over-yielding in polyculture stands but the mixed litter can affect soil C quality.

Key words: Mixture effects, Tree polyculture, biomass, over-yielding, C quality, recalcitrant C

How to cite: Ahmed, I., Smith, A., and Godbold, D.: Mixture-effects on tree biomass production and soil organic C quality in a temperate plantation forest, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-11964, https://doi.org/10.5194/egusphere-egu21-11964, 2021.