Windthrow Areas Research Articles

Automatic Windthrow Detection Using Very-High-Resolution Satellite Imagery and Deep Learning

Wind disturbances are significant phenomena in forest spatial structure and succession dynamics. They cause changes in biodiversity, impact on forest ecosystems at different spatial scales, and have a strong influence on economics and human beings. The reliable recognition and mapping of windthrow areas are of high importance from the perspective of forest management and nature conservation. Recent research in artificial intelligence and computer vision has demonstrated the incredible potential of neural networks in addressing image classification problems. The most efficient algorithms are based on artificial neural networks of nested and complex architecture (e.g., convolutional neural networks (CNNs)), which are usually referred to by a common term—deep learning. Deep learning provides powerful algorithms for the precise segmentation of remote sensing data. We developed an algorithm based on a U-Net-like CNN, which was trained to recognize windthrow areas in Kunashir Island, Russia. We used satellite imagery of very-high spatial resolution (0.5 m/pixel) as source data. We performed a grid search among 216 parameter combinations defining different U-Net-like architectures. The best parameter combination allowed us to achieve an overall accuracy for recognition of windthrow sites of up to 94% for forested landscapes by coniferous and mixed coniferous forests. We found that the false-positive decisions of our algorithm correspond to either seashore logs, which may look similar to fallen tree trunks, or leafless forest stands. While the former can be rectified by applying a forest mask, the latter requires the usage of additional information, which is not always provided by satellite imagery.

Успішність природного поновлення деревних порід на вітровальних ділянках в Українських Карпатах

Досліджено процес природного поновлення деревних порід на 42 вітровальних ділянках в Українських Карпатах, які розташовані на території 12 державних лісогосподарських підприємств та установ природно-заповідного фонду України у 15 типах лісу. Проаналізовано видовий склад і частоту трапляння самосіву та підросту окремих деревних порід на досліджених вітровальних ділянках: на пробних площах переважає ялина європейська, частка якої становить 23,7 % від загальної кількості самосіву і підросту, бук лісовий (21,1 %), ялиця біла (13,5 %) та клен-явір (11,3 %). Найрідше трапляється підріст дуба звичайного (0,03 %), дуба червоного (0,1 %), липи серцелистої (0,2 %), черешні (0,3 %), сосни звичайної (0,4 %), в'яза шорсткого (0,8 %) та клена гостролистого (0,8 %). На 24 досліджених вітровальних ділянках Українських Карпат виявлено добре природне поновлення деревних порід, на вісьмох – задовільне, на дев'ятьох – недостатнє і лише на одній – незадовільне.

Waldentwicklung und flachgründige Rutschungen: eine grossflächige GIS-Analyse

Forest dynamics and shallow landslides: a large-scale GIS-analysis Through continuous and abrupt changes in the forest and particularly in its root area, the disposition for shallow landslides also changes. The aim of this article is to learn more about the relationships between long-term forest dynamics and the risk of landslides with the help of large spatial data sets. A total of 6670 shallow landslides were selected from the natural event register StorMe, the event register of the Canton of Obwalden and the WSL database for shallow landslides and slope debris flows and overlaid with GIS data on the current and former forest situation (Siegfried maps of approx. 1880) and with windthrow areas (Vivian and Lothar). Shallow landslides occurred less frequently in the forest than outside of it at inclinations of less than 35 degrees. Higher landslide densities occurred in coniferous and mixed forests (compared to deciduous forests) and in relatively young forests (ingrown after 1880). Landslides in younger forests occurred on slopes less steep than in older forests. More shallow landslides occurred on former windthrow areas during the first 3 to 17 years after the event, however these landslides occurred on comparatively steep slopes. The analyses show that the disposition towards shallow landslides defined by slope inclination and subsoil can change strongly due to reforestation processes and natural disturbances. Silvicultural interventions may contribute to an improvement of the protective effect in the long term if they are carried out carefully and if they contribute to an increased adaptability to natural disturbances.

Rapid effects of windfall on soil microbial activity and substrate utilization patterns in the forest belt in the Tatra Mountains

The aim of the study was to compare the activity, functional diversity, and community-level physiological profiles of soil microorganisms in light of soil physical and chemical properties in areas where a forest was damaged by hurricane-force winds and in untouched spruce forests of the lower montane belt of the Tatra Mountains (the Carpathians). Foehn winds caused a huge windfall in December 2013. The studied valley was strongly affected by windthrow, but in some places, patches of mature forest did survive. In the studied windthrow area, the first stage of secondary succession can now be observed. Sampling sites were selected in places where the soil was not mechanically disturbed. Soil samples were taken from the organic O and humus A soil horizons and basic soil properties were measured, as were the microbial parameters. Overall microbial activity was determined via the soil respiration rate (R), whereas the microbial biomass was determined via the substrate-induced respiration rate (SIR). Bacterial and fungal catabolic activity, functional diversity (H′), and community-level physiological profiles (CLPP) were determined using Biolog® ECO and FF plates, respectively. Research has shown that 21 months following the studied windthrow, in Hypereutric Skeletic Cambisols developed on calcareous parent material, changes have occurred in some soil properties: soil field moisture in O and A horizons has increased, DOC concentration in O horizons has decreased, and the C/N ratio in A horizons has decreased. The effect of the windthrow episode on overall biological activity was observed in soil A horizons, where overall microbial respiration and SIR biomass decreased. In both O and A horizons, the ratio of bacterial and fungal functional activity (AUCbact/fungi) increased as a result of a fungal AUC decrease. Significant differences in substrate utilization by bacteria occurred between forest-covered soils and windthrow soils in O horizons, where the share of polymer-utilized bacteria activity increased. Rapid effects of windfall on soil microbial parameters expressed mostly in decrease overall microbial activity caused by breakdown in fungal activity. However, those differences are more pronounced in A than in O horizons. In spite of changes in those differences, windthrow did not produce a significant effect on the functional diversity index of microorganisms found in the studied soils.

Measurements of CO2 Fluxes at Non-Ideal Eddy Covariance Sites.

This protocol is an example of utilizing the eddy covariance (EC) technique to investigate spatially and temporally averaged net CO2 fluxes (net ecosystem production, NEP), in non-typical ecosystems, on a currently reforested windthrow area in Poland. After a tornado event, a relatively narrow "corridor" was created within surviving forest stands, which complicates such kind of experiments. The application of other measuring techniques, such as the chamber method, is even more difficult under these circumstances, because especially at the beginning, fallen trees and in general great heterogeneity of the site provide a challenging platform to perform flux measurements and then to properly upscale obtained results. In comparison with standard EC measurements carried out in untouched forests, the case of windthrow areas requires special consideration when it comes to the site location and data analysis in order to ensure their representativeness. Therefore, here we present a protocol of real-time, continuous CO2 flux measurements at a dynamically changing, non-ideal EC site, which includes (1) site location and instrumentation setup, (2) flux computation, (3) rigorous data filtering and quality control, and (4) gap filling and net fluxes partitioning into CO2 respiration and absorption. The main advantage of the described methodology is that it provides a detailed description of the experimental setup and measurement performance from scratch, which can be applied to other spatially limited ecosystems. It can also be viewed as a list of recommendations on how to deal with unconventional site operation, providing a description for non-specialists. Obtained quality-checked, gap filled, half-hour values of net CO2, as well as absorption and respiration fluxes, can be finally aggregated into daily, monthly, seasonal or annual totals.

Rapid Detection of Windthrows Using Sentinel-1 C-Band SAR Data

Storm events are capable of causing windthrow to large forest areas. A rapid detection of the spatial distribution of the windthrown areas is crucial for forest managers to help them direct their limited resources. Since synthetic aperture radar (SAR) data is acquired largely independent of daylight or weather conditions, SAR sensors can produce temporally consistent and reliable data with a high revisit rate. In the present study, a straightforward approach was developed that uses Sentinel-1 (S-1) C-band VV and VH polarisation data for a rapid windthrow detection in mixed temperate forests for two study areas in Switzerland and northern Germany. First, several S-1 acquisitions of approximately 10 before and 30 days after the storm event were radiometrically terrain corrected. Second, based on these S-1 acquisitions, a SAR composite image of before and after the storm was generated. Subsequently, after analysing the differences in backscatter between before and after the storm within windthrown and intact forest areas, a change detection method was developed to suggest potential locations of windthrown areas of a minimum extent of 0.5 ha—as is required by the forest management. The detection is based on two user-defined parameters. While the results from the independent study area in Germany indicated that the method is very promising for detecting areal windthrow with a producer’s accuracy of 0.88, its performance was less satisfactory at detecting scattered windthrown trees. Moreover, the rate of false positives was low, with a user’s accuracy of 0.85 for (combined) areal and scattered windthrown areas. These results underscore that C-band backscatter data have great potential to rapidly detect the locations of windthrow in mixed temperate forests within a short time (approx. two weeks) after a storm event. Furthermore, the two adjustable parameters allow a flexible application of the method tailored to the user’s needs.

Windthrows control biomass patterns and functional composition of Amazon forests.

Amazon forests account for ~25% of global land biomass and tropical tree species. In these forests, windthrows (i.e., snapped and uprooted trees) are a major natural disturbance, but the rates and mechanisms of recovery are not known. To provide a predictive framework for understanding the effects of windthrows on forest structure and functional composition (DBH ≥10cm), we quantified biomass recovery as a function of windthrow severity (i.e., fraction of windthrow tree mortality on Landsat pixels, ranging from 0%-70%) and time since disturbance for terra-firme forests in the Central Amazon. Forest monitoring allowed insights into the processes and mechanisms driving the net biomass change (i.e., increment minus loss) and shifts in functional composition. Windthrown areas recovering for between 4-27years had biomass stocks as low as 65.2-91.7Mg/ha or 23%-38% of those in nearby undisturbed forests (~255.6Mg/ha, all sites). Even low windthrow severities (4%-20% tree mortality) caused decadal changes in biomass stocks and structure. While rates of biomass increment in recovering vegetation were nearly double (6.3±1.4Mgha-1 year-1 ) those of undisturbed forests (~3.7Mgha-1 year-1 ), biomass loss due to post-windthrow mortality was high (up to -7.5±8.7Mgha-1 year-1 , 8.5years since disturbance) and unpredictable. Consequently, recovery to 90% of "pre-disturbance" biomass takes up to 40years. Resprouting trees contributed little to biomass recovery. Instead, light-demanding, low-density genera (e.g., Cecropia, Inga, Miconia, Pourouma, Tachigali, and Tapirira) were favored, resulting in substantial post-windthrow species turnover. Shifts in functional composition demonstrate that windthrows affect the resilience of live tree biomass by favoring soft-wooded species with shorter life spans that are more vulnerable to future disturbances. As the time required for forests to recover biomass is likely similar to the recurrence interval of windthrows triggering succession, windthrows have the potential to control landscape biomass/carbon dynamics and functional composition in Amazon forests.

The carbon balance of a Scots pine forest following severe windthrow: Comparison of reforestation techniques

Even though windthrows are the main disturbance type in European forests, their impact on forest carbon balance is generally understudied. In order to close this knowledge gap, we took advantage of a tornado event, which occurred in July 2012 in Trzebciny Forest District in northwest Poland. The main objective of this study was to determine how two completely different reforestation techniques in windthrow areas impact net ecosystem production (NEP) of this Scots pine forest ecosystem under similar meteorological conditions. The two techniques were: conventional (“Tlen I” site): uprooted stumps pulled out and removed from the site followed by ploughing, and non-conventional (“Tlen II” site): all stumps left on the site to decompose with no ploughing. Therefore, we measured carbon dioxide (CO2) fluxes using the eddy covariance (EC) technique for four continuous years. Our results indicate that both sites became significant carbon (C) sources after the windthrow (up to 575 ± 56 g C m−2 y-1 in the first year, Tlen I). However, the Tlen I (conventional technique) lost over 30% less C than Tlen II during the 2015–2016 observation period. In contrast to existing knowledge, ploughing as done at Tlen I, did not substantially increase CO2 emission, as compared to local soil ripping (non-conventional technique). The decrease in net C emission, estimated on the basis of linear model parameters, was almost five times greater at Tlen I than at Tlen II. We thus hypothesize that the annual NEP at conventionally reforested windthrow site will reach C neutrality (NEP = 0) six years after windthrow at most, while at the non-conventionally managed area it will probably take ca. 18 years. So far then, the currently widely applied conventional reforestation technique in wind-disturbed Polish forest appeared to be more effective in decreasing C losses than a technique that leaves stumps to decompose and avoids ploughing.

Drivers of regeneration dynamics following salvage logging and different silvicultural treatments in windthrow areas in Slovenia

Abstract We studied regeneration dynamics in forests disturbed by three different windthrow events in 2008 in Slovenia to assess the success of natural regeneration vs planting and subsequent silvicultural treatments. Fifty-three plots with planted saplings of Norway spruce and sycamore maple and 50 plots with dominant naturally regenerated saplings were selected in a randomly stratified manner. Sapling characteristics (height, height increment, root collar diameter, free-to-grow score, browsing and micro-site) were assessed in 2012 and 2014. Herbs and seedling establishment were studied in two subplots within each plot. Average seedling density was 13,074 and 14,674 ha−1 four and six years after the windthrows, respectively. Seedlings were irregularly distributed, which suggests micro-site differences in regeneration dynamics. The results indicated lower seedling success on sites that were southerly exposed, farther from the forest edge and seed trees, on undisturbed micro-sites and at higher altitudes. On such sites planting was justified. While seedling density indicated a positive relation to herb coverage, sapling survival was negatively associated with it as well as with browsing. Initial sapling height was the strongest predictor of survival. Spruce saplings had the lowest mortality, while shade-tolerant silver fir and beech experienced high mortality. The study indicated a high density and species diversity of naturally regenerated seedlings within windthrow areas, which was reduced by planting, mowing of competing vegetation and protection measures favouring planted saplings. Recommendations for the improvement of silvicultural operations for post windthrow restoration are given.

Sediment transport by uprooting in the forested part of the Tatra Mountains, southern Poland

The process of tree uprooting plays an important role in sediment transport within forested slopes. In this study we determine the intensity of sediment transport by uprooting and its dependencies. We use the Principal Component Analysis (PCA) to determine the most important factors influencing root plate sizes, and we calculate sediment flux by windthrow for the area of the Tatra National Park (211.6km2), for the year 2013, when an extreme windthrow event occurred. For this purpose we combine field data with the results of windthrow areas mapping based on satellite imagery. We also use data recorded by the Tatra National Park concerning the amount of destroyed wood in the forests of the Tatra National Park to calculate sediment flux by windthrow for the period between 1968 and 2015 (48years). To calculate the transport distance by the uprooting needed to compute sediment flux, we modified the Gabet et al.'s (2003) Eq. (11), which in our opinion gives results which are twice the actual size. The PCA identified two the most important factors influencing root plate sizes. The first factor shows that all root plate dimensions increase with increasing tree DBH (diameter at breast height), and, to a lesser degree, with an increase in the content of coarse material. The second factor shows that the depth of a root plate increases with the downslope angle of tree fall, decreasing slope inclination, and decreasing the content of coarse material. The sediment flux by windthrow in 2013 in the area of the Tatra National Park was 3.55×10−4m3m−1yr−1. Mean annual sediment flux for the period of the last 48years was 2.76×10−5m3m−1yr−1.

Early Stage Forest Windthrow Estimation Based on Unmanned Aircraft System Imagery

Strong wind disturbances can affect large forested areas and often occur irregularly within a forest. Due to this, identifying damaged sites and estimating the extent of these losses are crucial for the harvesting management of salvage logging. Furthermore, the location should be surveyed as soon as possible after the disturbance to prevent the degradation of fallen trees. A fixed-wing type of unmanned aircraft system (UAS) with a compact digital camera was used in this study. The imagery was acquired on approximately 200 hectares where five large windthrow areas had occurred. The objective of the study was to determine the location of the windthrow areas using a semi-automatic approach based on the UAS imagery, and on the combination of UAS imagery with airborne laser scanning (ALS). The results were compared with reference data measured by global navigation satellite system (GNSS) devices. At the same time, windthrow areas were derived from Landsat imagery to investigate whether the UAS imagery would have significantly more accurate results. GNSS measurements and Landsat imagery are currently used in forestry on an operational level. The salvage logging was estimated for each forest stand based on the estimated areas and volume per hectare obtained from the forest management plan. The results from the UAS (25.09 ha) and the combined UAS/ALS (25.56 ha) methods were statistically similar to the reference GNSS measurements (25.39 ha). The result from Landsat, at 19.8 ha, was not statistically similar to the reference GNSS measurements or to the UAS and UAS/ALS methods. The estimate of salvage logging for the whole area, from UAS imagery and the forest management plan, overestimated the actual salvage logging measured by foresters by 4.93% (525 m3), when only the most represented tree species were considered. The UAS/ALS combination improved the preliminary results of determining windthrow areas which lead to decreased editing time for all operators. The UAS imagery shows potential for application to early-stage surveys of windthrow areas in forests. The advantages of this method are that it provides the ability to conduct flights immediately after the disturbance, the foresters do not need to walk within the affected areas which decreases the risk of injury, and allows flights to be conducted on cloudy days. The orthomosaic of the windthrow areas, as a by-product of data processing in combination with forest maps and forest road maps, can be used as a tool to plan salvage logging.

Corrigendum

Functional EcologyVolume 31, Issue 8 p. 1669-1669 CorrigendumFree Access Corrigendum This article corrects the following: Increase in heterotrophic soil respiration by temperature drives decline in soil organic carbon stocks after forest windthrow in a mountainous ecosystem Mathias Mayer, Hans Sandén, Boris Rewald, Douglas L. Godbold, Klaus Katzensteiner, Katie Field, Volume 31Issue 5Functional Ecology pages: 1163-1172 First Published online: December 19, 2016 First published: 13 July 2017 https://doi.org/10.1111/1365-2435.12918AboutSectionsPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Mayer, M., Sandén, H., Rewald, B., Godbold, D.L. & Katzensteiner, K. (2017) Increase in heterotrophic soil respiration by temperature drives decline in soil organic carbon stocks after forest windthrow in a mountainous ecosystem. Functional Ecology, 31, 1163–1172. https://doi.org/10.1111/1365-2435.12805. In the paper by Mayer et al. (2017), Table 1 and Supporting Information Table S2 show data with incorrect units for Dissolved organic carbon, DOC and Dissolved N, DN. The units should read mg g soil−1 L−1. The errors occurred due to the neglect of entering conversion factors in the data file correcting for the amount of liquid extract (25 mL). Table 1. (corrected): Abiotic and biotic properties of the topsoil (mean ± SE) at the Höllengebirge control stand (HC; n = 10) and the windthrow areas from 2009 (HW09; n = 12) and 2007 (HW07; n = 11) in August 2013. Different letters indicate significant (P < 0·05) differences between areas (highlighted in bold). Trenched and clipped plots were excluded from statistics Topsoil properties Control Windthrow Windthrow Stand 2009 2007 Ground vegetation root biomass (kg m−2) 0·0 ± 0·0 a 0·3 ± 0·1 b 0·4 ± 0·1 b Tree root biomass (kg m−2) 0·6 ± 0·1 a 0·1 ± 0·1 b 0·2 ± 0·1 b Tree root necromass (kg m−2) 0·7 ± 0·1 a 0·4 ± 0·1 a 0·7 ± 0·1 a Ectomycorrhizal growth index 0·5 ± 0·1 a 0·1 ± 0·0 b 0·3 ± 0·1 ab Soil C content (kg m−2) 10·8 ± 1·8 a 8·0 ± 1·8 a 12·4 ± 2·3 a Soil N content (kg m−2) 0·6 ± 0·1 a 0·5 ± 0·1 a 0·7 ± 0·1 a C : N ratio 17·9 ± 0·8 a 16·7 ± 0·5 a 17·2 ± 0·7 a Dissolved organic C, DOC (mg g−1 L−1) 15·6 ± 2·0 a 21·2 ± 2·9 a 12·8 ± 1·7 a Dissolved N, DN (mg g−1 L−1) 3·1 ± 0·6 a 4·8 ± 0·6 a 4·1 ± 0·8 a DOC : DN ratio 5·9 ± 0·7 a 4·9 ± 0·6 a 4·2 ± 0·8 a pH (H2O) 4·3 ± 0·1 a 4·8 ± 0·2 ab 5·2 ± 0·3 b Table S2. (corrected): Summary statistics of variables used for structural equation modelling, and latent variables for which observed variables served as indicator Observed variable Mean ± SE Min–Max Latent variable Soil CO2 efflux (μmol m−2 s−1) 4·3 ± 0·2 0·7–7·7 – Soil temperature (°C) 16·7 ± 0·5 11·9–29·4 – Gravimetric soil moisture content (%) 65·1 ± 1·8 25·0–82·6 – Ground vegetation root biomass (kg m−2) 0·3 ± 0·0 0·0–1·9 Ground vegetation abundance Tree root biomass (kg m−2) 0·4 ± 0·1 0·0–2·1 Tree & EM abundance Ectomycorrhizal (EM) growth index 0·2 ± 0·0 0·0–1·0 Tree & EM abundance Tree root necromass (kg m−2) 0·8 ± 0·1 0·0–2·2 SOM quantity Soil carbon (C) content (kg m−2) 14·3 ± 1·1 3·3–49·7 SOM quantity C : N ratio 17·1 ± 0·3 13·6–23·1 SOM quality Dissolved organic C, DOC (mg g−1 L−1) 16·7 ± 0·9 4·8–45·2 SOM quality Dissolved N, DN (mg g−1 L−1) 4·8 ± 0·3 0·5–11·5 SOM quality DOC : DN ratio 4·2 ± 0·3 2·0–11·2 SOM quality pH (H2O) 4·8 ± 0·1 3·8–7·2 SOM quality The incorrect units did not affect the conclusions of this study as the results were used for relative comparisons of treatments only and absolute values were neither interpreted nor compared to other studies. The correct tables are listed below and Table S2 has been corrected in the Supporting Information file. Reference Mayer, M., Sandén, H., Rewald, B., Godbold, D.L., & Katzensteiner, K. (2017) Increase in heterotrophic soil respiration by temperature drives decline in soil organic carbon stocks after forest windthrow in a mountainous ecosystem. Functional Ecology, 31, 1163– 1172. Volume31, Issue8August 2017Pages 1669-1669 ReferencesRelatedInformation

Assessing forest windthrow damage using single-date, post-event airborne laser scanning data

One of many possible climate change effects in temperate areas is the increase of frequency and severity of windstorms; thus, fast and cost efficient new methods are needed to evaluate wind-induced damages in forests. We present a method for assessing windstorm damages in forest landscapes based on a two-stage sampling strategy using single-date, post-event airborne laser scanning (ALS) data. ALS data are used for delineating damaged forest stands and for an initial evaluation of the volume of fallen trees. The total volume of fallen trees is then estimated using a two-stage model-assisted approach, where variables from ALS are used as auxiliary information in the difference estimator. In the first stage, a sample of the delineated forest stands is selected, and in the second stage the within-stand damages are estimated by means of line intercept sampling (LIS). The proposed method produces maps of windthrown areas, estimates of forest damages in terms of the total volume of fallen trees, and the uncertainty of the estimates. A case study is presented for a large windstorm that struck the Tuscany Region of Italy the night of the 4th and the 5th of March 2015 and caused extensive damages to trees in both forest and urban areas. The pure field-based estimates from LIS and the ALS-based estimates of stand-level fallen wood were very similar. Our positive results demonstrate the utility of the single-date approach for a fast assessment of windthrow damages in forest stands which is especially useful when pre-event ALS data are not available.

Reforestation in Slovakia: History, current practice and perspectives

The history of reforestation in Slovakia is long and rich; from reforestation by seeding, through the small forest nurseries, reforestation of extreme degraded and high-mountain sites to the current The Act on forest reproductive material, nursery centers and reforestation of large windthrow areas. After brief introduction of the history, rather large part of this review is dedicated to the current nursery and especially reforestation practices – planning, pre-planting site preparation, seeding and planting techniques, post-planting care, monitoring of planting performance. Recent nursery and planting research activities are given very shortly. Perspective nursery (e.g. improvement of seedlings’ quality by inoculation with beneficial microorganisms, vegetative propagation) and reforestation treatments and practices (e.g. the use of larger amount of container-grown seedlings, application of hydrogels and ectomycorrhizal fungi, progressive seeding technique, underplanting) are relatively in detail but of course not comprehensively discussed finally. Despite of the lack of a complex reforestation strategy and current and possibly future financial sources and personnel limitations, the introduced perspective practices should contribute to successful solution of reforestation challenges following from endangering the forests by climate change.

Post-windthrow management in protection forests of the Swiss Alps

The two storms Vivian (1990) and Lothar (1999) left an area of roughly 9000 ha of fully damaged protection forests in Swiss mountain regions. Given this huge dimension, questions arose on how to manage these areas to keep the protection gap, i.e. the time period with reduced overall protection against natural hazards, short. Quantifications are presented for the stability of lying logs left in place, the frequency of post-disturbance mass movements, and the tree regeneration in windthrow areas. The average height above ground of unsalvaged lying logs decreased from 2.1 m shortly after disturbance to 0.8 m 20 years later. In the period 1990–2014, the number of avalanches in windthrow areas was markedly small, and annual rates of shallow landslides and debris flows in windthrow areas did not differ from rates in comparable undamaged forested areas. Regeneration density rarely exceeded 4000 stems ha−1 20 years post-windthrow at elevations above 1200–1500 m a.s.l. Mean height of tallest trees reached 5.6 m in areas that were cleared and 6.5 m in those left unsalvaged. Trees planted post-windthrow were 1.0–2.4 m taller than naturally regenerated ones. Practitioners rated the protective effect to be acceptable 24 years post-disturbance in only 5 out from 16 observed windthrow areas (31%), with planting trees as the main cause of success. We conclude that in protection forests the regeneration speed after disturbance rarely meets practitioner’s expectations in terms of both stem density and stand structure. However, leaving woody debris from wind disturbance in place proved to replace protective effects for an astonishingly long time. An intensive management with salvage logging, planting and even technical constructions seems therefore only inevitable on windthrown areas where risks seem too high based on hazard, damage potential and possible spread of bark beetles to nearby protection forests. A management alternative applicable to many other cases of windthrown protection forests is to plant trees between lying stems.

Die Brutvogelfauna eines Nadelwaldes der nördlichen Voralpen nach dem Sturm Lothar

Breeding bird fauna in a coniferous forest in the northern Prealps after storm Lothar In a 70-hectare large coniferous forest located on the northern edge of the Alps in central Switzerland, Canton of Obwalden, at an altitude of 1260 to 1550 metres above sea level, we surveyed the local breeding bird fauna in 2002 and 2013 by means of point counts as well as additional area searches for rare species. In December 1999, hurricane Lothar caused two large windthrow areas and several smaller areas with scattered throws in the survey range. We found a total of 48 breeding bird species, which is a very diverse species composition for a mountain forest. In the eleven years between surveys, a decline in distribution or abundance was recorded for four species, while seven species showed an increase; a further four species showed no change. For the remaining species, the data sets were too small to reliably estimate changes. A comparison with forest structure data provided by the Swiss Federal Institute of Forest, Snow and Landscape Research WSL revealed that for five bird species, the changes in distribution or abundance could be explained at least partially by forest succession. In order to obtain realistic distribution and abundance values in this kind of breeding bird survey, it is essential to collect large enough samples and to consider the detection probability of each individual species using appropriate statistical methods.

Windthrow Detection in European Forests with Very High-Resolution Optical Data

With climate change, extreme storms are expected to occur more frequently. These storms can cause severe forest damage, provoking direct and indirect economic losses for forestry. To minimize economic losses, the windthrow areas need to be detected fast to prevent subsequent biotic damage, for example, related to beetle infestations. Remote sensing is an efficient tool with high potential to cost-efficiently map large storm affected regions. Storm Niklas hit South Germany in March 2015 and caused widespread forest cover loss. We present a two-step change detection approach applying commercial very high-resolution optical Earth Observation data to spot forest damage. First, an object-based bi-temporal change analysis is carried out to identify windthrow areas larger than 0.5 ha. For this purpose, a supervised Random Forest classifier is used, including a semi-automatic feature selection procedure; for image segmentation, the large-scale mean shift algorithm was chosen. Input features include spectral characteristics, texture, vegetation indices, layer combinations and spectral transformations. A hybrid-change detection approach at pixel-level subsequently identifies small groups of fallen trees, combining the most important features of the previous processing step with Spectral Angle Mapper and Multivariate Alteration Detection. The methodology was evaluated on two test sites in Bavaria with RapidEye data at 5 m pixel resolution. The results regarding windthrow areas larger than 0.5 ha were validated with reference data from field visits and acquired through orthophoto interpretation. For the two test sites, the novel object-based change detection approach identified over 90% of the windthrow areas (≥0.5 ha). The red edge channel was the most important for windthrow identification. Accuracy levels of the change detection at tree level could not be calculated, as it was not possible to collect field data for single trees, nor was it possible to perform an orthophoto validation. Nevertheless, the plausibility and applicability of the pixel-based approach is demonstrated on a second test site.

First Steps into the Wild - Exploration Behavior of European Bison after the First Reintroduction in Western Europe.

Biodiversity is rapidly declining globally. One strategy to help to conserve species is to breed species in captivity and release them into suitable habitats. The way that reintroduced animals explore new habitats and/or disperse from the release site is rarely studied in detail and represents key information for the success of reintroduction projects. The European bison (Bison bonasus L. 1758) was the largest surviving herbivore of the post-glacial megafauna in Europe before it became extinct in the wild, surviving only in captivity since 1919. We investigated the exploration behavior of a herd of European bison reintroduced into the Rothaargebirge, a commercial forest in low range mountain intensively used and densely populated by humans, in the first six months after release. We focused on three questions: (1) how did the European bison move and utilize the habitat on a daily basis, (2) how did the animals explore the new environment, and (3) did their habitat preferences change over time. The European bison dispersed away from their previous enclosure at an average rate of 539 m/month, with their areas of daily use ranging from 70 to 173 ha, their movement ranging from 3.6 km to 5.2 km per day, and their day-to-day use of areas ranged between 389 and 900 m. We could identify three major exploration bouts, when the animals entered and explored areas previously unknown to them. During the birthing phase, the European bison reduced daily walking distances, and the adult bull segregated from the herd for 58 days. Around rut, roaming behavior of the herd increased slightly. The animals preferred spruce forest, wind thrown areas and grassland, all of which are food abundant habitat types, and they avoided beech forest. Habitat preference differed slightly between phases of the study period, probably due to phenological cycles. After six months, the complete summer home range was 42.5 km2. Our study shows that a small free-ranging herd of European bison can live in an area intensively used by humans and describes in detail the initial roaming behavior and habitat utilization of the animals.

Die Schutzfunktion in Windwurfflächen

Protection against natural hazards on windthrow areas We give an overview on natural hazard processes on windthrow areas during the first 20 years after the winterstorm Vivian (1990). This overview is based on 1) repeated pulling experiments and a long-term analysis of stem movements in the uncleared winthrow area Cavorgia/Disentis, 2) the assessment of avalanche protection function of 26 windthrow areas, and on (3) StorMe cadastral data of natural hazard events on windthrow areas. The effective heights and stem resistance of lying logs have been reduced to ca. 40% of the original values on average in the uncleared winthrow area Cavorgia/ Disentis. In particular on very steep (&amp;gt;45°) and rocky slopes, some of the stems have moved several meters. Most of the 26 investigated windthrow areas did not fulfill any of the considered criteria to effectively protect against avalanches. Nevertheless, very few avalanches and rockfall events were observed on Vivian areas. The relatively large number of shallow landslides in the years after the windthrow could, however, be a sign of a certain time with increased landslide susceptibility. Our results and observations suggest that the increased terrain roughness after Vivian largely compensated for the decreased protection effects against avalanche and rockfall of former stands structures during the first years after the storm. After 20 years, the terrain roughness effect has strongly decreased and reliable protection against mass movements depends in most cases on a sufficiently advanced natural forest regeneration or on additional post-windthrow plantations. It is important to consider specific conditions on the level of single slopes when planning measures against natural hazards in windthrow areas.

Lehren aus Vivian für den Gebirgswald – im Hinblick auf den nächsten Sturm

Lessons from Vivian for mountain forests – regarding the next storm The winter storm “Vivian” in February 1990 took Swiss forestry by surprise due to its enormous extent. It gave cause for entirely new and challenging questions for scientists and practitioners. Twenty-four years after the storm, the Swiss mountain forest tending group assessed in the frame of two workshops forest succession and the evolution of the protective effect against natural hazards in several well-documented Vivian storm areas at elevations between 1,500 and 1,700 m a.s.l. in the cantons of St. Gallen and Grisons. The decision to salvage the damaged timber or to leave it in place depends primarily on how the risk of bark beetle infestations is assessed. Lying stems can transiently reduce the risk created by natural hazards and favor stand establishment, by reducing snow movements and by serving as nurse logs in the long term. On several areas among those studied, forest succession has progressed so far that the protective effect is nearly restored. However, in the majority of the areas, this is not yet the case even 24 years after the storm. The presence of regeneration in the pre-storm stand, so-called advance regeneration, considerably accelerates forest succession in a windthrow area. If advance regeneration is absent, planting can considerably fasten succession in comparison to natural regeneration, which establishes often slowly. In summary, it is concluded that on large windthrow areas at high elevation the potential of natural regeneration is limited and that a more varied combination of the different treatment options should be envisaged in the case of future windthrow events.