634 Obstanlagen, Früchte, Forstwirtschaft
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With the development of new imaging and near field remote sensing UAV technologies, the field of forest canopy and tree crown investigations in the context of rainforest ecology gained new perspectives in recent years. This study demonstrates the feasibility of structural analysis of canopy for the assessment of succession states of tropical lowland rainforests using a consumer UAV and open access ground reference data. Therefore, the canopy of 22 small-scale forest plots in the Ecuadorian Andes and the Mata Atlântica were captured with an UAV between October 2017 and February 2018. The fully remote image acquisition used automated flight plans consisting of crossed flights with different incident camera angles and did not require ground control points (GCP) as further ground reference. Photogrammetric Point Clouds (PPC), image meshes and crown height models (CHM) were created with Structure from Motion (SfM), combined with a Digital Terrain Model from the Shuttle Radar Topography Mission (SRTM), in order to analyze structural parameters of the canopy. The standard deviation of the height values of the PPC and the CHM differs statistically significant between succession stages. Investigation plots in climax or late succession show a mean PPCSD of 6.7 m with a standard error of 0,3 m. Plots in early succession show a PPCSD of 4.8 m with a standard error of 0.3 m and degraded plots show 2.8m with a standard error of 0.2m. This result proves the applicability of the proposed workflow under typical NGO conditions and other applied science research with limitations in budget and access to sophisticated survey equipment.
Severe storm events are the biggest driving factor for biomass loss in European forests. Besides the damages caused by the storm itself, there are subsequent damages due to biotic, abiotic and market factors with far reaching implications for forestry and conservation. These subsequent damages can be minimized if the amount and spatial distribution of the windthrown trees is known and can be used to optimize salvage operations and calamity management.
Traditional methods and space born remote sensing can only provide estimations of the affected area, whereas remote sensing with aerial sensors is able to obtain the spatial distribution of the stems with detection rates up to 92% but not to quantify single logs due to an insufficient spatial resolution. Recent approaches utilizing UAVs are promising but a methodology for the quantification of windthrown trees is not published yet.
The presented work closes this gap by analyzing UAV-orthomosaics with Deep Learning techniques to obtain precise information of the spatial distribution and estimate the volume of the windthrown trees. Therefore, the U-Net was included in a bottom-up object detection based on a skeletonization algorithm including a reconstruction of occluded stem parts by a voting system based on morphological heuristics. For the subsequent quantification of the detected stems, the diameter is determined every 25 cm and the volume is calculated as sum of truncated cone volumes.
In the scope of this work, 21 orthomosaics of beech, spruce and mixed stands with a ground sampling distance of mostly less than 2 cm were used, on which 1747 windthrown tree stems were manually outlined for the training of the models “Spruce”, “Beech” and “General” for pure and mixed stands, respectively. Additionally, 710 trees were digitized and measured for the validation of the methodology.
It could be proven that the proposed methodology is able to detect windthrown tree stems with an average detection rate of 93.8% for spruce stands and with 93.3% for beech and mixed stans (error rates between 4.3% and 6.3%). Thereby, the detected volumes were overestimated by the specific models for spruce (11.8%) and beech stands (10.7%) while the “General” model was underestimating the volume by 5.8%, on average. Generally, specialization on certain tree species carries the risk of lower detection rates for unfamiliar scenes and species, while a general model is associated with a higher rate of classification errors. Further, it could be shown that the performance of the proposed methodology is affected by the quality of the used orthomosaics.
The quantification of the amount of windthrown wood and the reconstruction of occluded stem parts are unique features compared to other recently published approaches with far reaching implications for forestry, ecology, and biodiversity conservation. The proposed methodology provides additional information for decision-making in the planning of salvage loggings and for monitoring of biomass and carbon cycles. Further, it can contribute to a better understanding of windthrow dynamics and therewith, will support the development of sustainable management strategies which focus on resilient forest ecosystems.
To develop measures to reduce the vulnerability of forests to drought, it is necessary to estimate specific water balances in sites and to estimate their development with climate change scenarios. We quantified the water balance of seven forest monitoring sites in northeast Germany for the historical time period 1961–2019, and for climate change projections for the time period 2010–2100. We used the LWF-BROOK90 hydrological model forced with historical data, and bias-adjusted data from two models of the fifth phase of the Coupled Model Intercomparison Project (CMIP5) downscaled with regional climate models under the representative concentration pathways (RCPs) 2.6 and 8.5. Site-specific monitoring data were used to give a realistic model input and to calibrate and validate the model. The results revealed significant trends (evapotranspiration, dry days (actual/potential transpiration < 0.7)) toward drier conditions within the historical time period and demonstrate the extreme conditions of 2018 and 2019. Under RCP8.5, both models simulate an increase in evapotranspiration and dry days. The response of precipitation to climate change is ambiguous, with increasing precipitation with one model. Under RCP2.6, both models do not reveal an increase in drought in 2071–2100 compared to 1990–2019. The current temperature increase fits RCP8.5 simulations, suggesting that this scenario is more realistic than RCP2.6
Background: Over the last 25 years, the prominent forest certification system established by the Forest Stewardship Council (FSC) has used by many companies worldwide for claiming responsible forest management. The objectives of the Russian National FSC standard to decrease the size of clearcuts and the retention of forest elements such as residual seed trees need on-site validation to proof the effectiveness of FSC. To assess the ecological impacts of harvesting practices and benefits of FSC certification, we geospatially compared logging activities with and without FSC certification. Within a sample area covering approximately 3,000 km 2 in the east of the Russian Arkhangelsk Region, we used available data on tree cover loss and satellite images to assess secondary impacts of clearcuttings
on adjacent remnant forests and to quantify the logging intensity. Additionally, the size and structure as well as the density of skidding trails of ten specific clearcuttings located within the sample area were surveyed using satellite images and in the field observation to delineate the boundaries of clearcuts and forested remnants within the clearcuts.
Results: We found a significant increase of small-scale tree cover loss in the proximity of the clearcuts. Patchy dieback is possibly linked to the scale and intensity of logging in the surroundings. On the investigated clearcuts, FSC failed to reduce the size, to increase the retention of forest remnants including seed trees on logged areas, and to maintain larger tracts of undisturbed ground and soil compared to clearcuts that were logged before they received FSC-certification.
Conclusions: Trees and forest remnants remaining inside an increasingly stressed forest ecosystem matrix may not resist further harvesting-related and climate change-induced stresses and disturbances. Large-scale clearcuttings seem to have negative impacts even in adjacent forests and undermine the ecological effectiveness of FSC certification in the study area. The Russian FSC standard is not clearly setting effective guidelines that induce a change in clearcutting practices in order to reduce ecological risks.
The complexity of highly structured forests with multiple tree species, especially when coniferous and broadleaved tree species are mixed, as well as stands with extended machine operating trail spacing and inclined terrain, create challenging operational conditions for mechanized timber harvesting and extraction. Motor-manually felling trees within the midfield and bunching them at the machine operating trails, prior to the arrival of a harvester-forwarder system, is a complex operation. The aim of this study was to assess and compare tethered harvester productivities of a thinning operation, for felling and processing standing trees and for processing bunched trees, through a time study in forest stands with 40-m distances between machine operating trails. Total operational costs of the analyzed thinning operation were 69 €/m3o.b., including extraction using a multiple forwarder approach. Tree species, merchantable timber volume, and whether the trees were standing or presented as bunched logs all had a significant effect on the harvester time consumption. Moreover, harvester positioning time was significantly shorter when trees were already bunched at the machine operating trail. While the productivity of standing or bunched spruce trees did not differ significantly between the cases (approximately 18 m3o.b./productive machine hours excluding all delays (PMH0)), the productivity of standing broadleaved tree species (8.3 m3o.b./PMH0) was much lower than that of bunched trees (15.5 m3o.b./PMH0). Thus, the described timber harvesting and extraction system may be a valuable option for forest stands with high proportion of broadleaved trees.
The accurate estimation of timber volume is of the utmost importance. For industrial timber, the volume is often estimated as stacked cubic meters. In addition to manual measurements, volume estimation is possible with photo-optical systems. Over 100 piles of industrial timber of broadleaved tree species were analyzed. In the study, a standard manual measurement method for the estimation of wood pile volumes was compared with a smartphone based photo-optical application for the determination of woodpile volume. Mean gross volume of the piles was approximately 56 m3 and mean width of piles was 9.43 m. A strong correlation was found between the manual measurements and the photo-optical measurement. However, volume estimation of large volume piles seems to perform better in comparison to piles with small volumes. Further research is needed to determine the effects of variables such as log quality or quality of pile on volume estimation accuracy.
In terms of assessing economic impact, one of the most important elements in the wood supply chain is the measurement of round wood. Besides the one-by-one measurement of logs, logs are often measured when stacked at the forest road. The gross stacked volume includes the volume of the wood, bark and airspace and is widely used for industrial wood assortments. The increasing international attention given to photo-optical measurement systems for portable devices is due to
their simplicity of use and efficiency. The aim of this study was to compare the gross volumes of
hardwood log stacks measured using one widespread photo-optical app with two manual section-wise volume estimations of log stacks based on the German framework agreement for timber trade (RVR). The manual volume estimations were done starting from the left (RVRleft) and right (RVRright) sides of the log stacks. The results showed an average deviation of the photo-optical gross volume estimation in comparison to the manual estimation of –2.09% (RVRleft) and –3.66% (RVRright) while the deviation between RVRleft and RVRright was +2.54%. However, the log stack
gross volume had a highly significant effect on the deviation and better accuracy with smaller
deviation were reached for larger log stacks. Moreover, results indicated that the gross volume estimations of higher quality log stacks were closer for the three analyzed methods compared to estimations of poor-quality log stacks.
1. Forest management influences a variety of ecosystem structures and processes relevant to meso- and microclimatic regulation, but little research has been done on how forest management can mitigate the negative effects of climate change on forest ecosystems.
2. We studied the temperature regulation capacity during the two Central European extreme summers in 2018 and 2019 in Scots pine plantations and European beech forests with different management-related structural characteristics.
3. We found that the maximum temperature was higher when more trees were cut and canopy was more open. Logging 100 trees per hectare increased maximum temperature by 0.21–0.34 K at ground level and by 0.09–0.17 K in 1.3 m above ground. Opening the forest canopy by 10% significantly increased Tmax, measured 1.3 m above ground by 0.46 K (including pine and beech stands) and 0.35 K (only pine stands). At ground level, Tmax increased by 0.53 K for the model including pine and beech stands and by 0.41 K in pure pine stands. Relative temperature cooling capacity decreased with increasing wood harvest activities, with below average values in 2018 (and 2019) when more than 656 (and 867) trees per hectare were felled. In the pine forests studied, the relative temperature buffering capacity 1.3 m above ground was lower than average values for all sample plots when canopy cover was below 82%. In both study years, mean maximum temperature measured at ground level and in 1.3 m was highest in a pine-dominated sample plots with relatively low stand volume (177 m3 ha−1) and 9 K lower in a sample plot with relatively high stock volumes of Fagus sylvatica (>565 m3 ha−1). During the hottest day in 2019, the difference in temperature peaks was more than 13 K for pine-dominated sample plots with relatively dense (72%) and low (46%) canopy cover.
4. Structural forest characteristics influenced by forest management significantly affect microclimatic conditions and therefore ecosystem vulnerability to climate change. We advocate keeping the canopy as dense as possible (at least 80%) by maintaining sufficient overgrowth and by supporting deciduous trees that provide effective shade.
Comparison of different approaches to estimate bark volume of industrial wood at disc and log scale
(2021)
Within the wood supply chain, the measurement of roundwood plays a key role due to its high economic impact. While wood industry mainly processes the solid wood, the bark mostly remains as an industrial by-product. In Central Europe, it is common that the wood is sold over bark but that the price is calculated on a timber volume under bark. However, logs are often measured as stacks and, thus, the volume includes not only the solid wood content but also the bark portion. Mostly, the deduction factors used to estimate the solid wood content are based on bark thickness. The aim of this study was to compare the estimation of bark volume from scaling formulae with the real bark volume, obtained by xylometric technique. Moreover, the measurements were performed using logs under practice conditions and using discs under laboratory conditions. The mean bark volume was 6.9 dm3 and 26.4 cm3 for the Norway spruce logs and the Scots pine discs respectively. Whereas the results showed good performances regarding the root mean square error, the coefficient of determination (R2) and the mean absolute error for the volume estimation of the total volume of discs and logs (over bark), the performances were much lower for the bark volume estimations only.