Philipp Koal

Forests in temperate mountain regions are increasingly exposed to extreme heat. Near-surface microclimates, shaped by vegetation and topography, influence forest regeneration, fuel dynamics, and disturbance feedbacks. We examined how daily warming rates, maximum temperatures, and cooling rates differ between microsites contrasting in vegetation height, elevation, and slope orientation during summer, and whether these differences increase under higher summer temperatures. We deployed a network of temperature loggers in the Río Manso Valley (northern Patagonia), recording summer temperatures at 15-minute intervals. Using a paired sampling design, we compared six environmental contrasts representing forest versus shrubland, low versus high elevation, and north- versus south-facing slopes. Following a contrast-wise approach, we used linear mixed-effects models to quantify daily differences in thermal metrics between paired microsites and assessed how these differences scaled with maximum daily temperature at the warmer site within each pair. Summer thermal sensitivity varied strongly across environmental contrasts. Differences associated with vegetation height and elevation were larger and more consistent than those associated with slope orientation. Across all contrasts, differences in warming rates, maximum temperatures, and cooling rates increased with rising summer temperatures, indicating that microclimatic divergence among microsites amplifies under heat extremes. By quantifying near-surface thermal sensitivity across paired environmental contrasts, our study provides empirical information relevant for modelling microclimate-sensitive ecological processes under climate change, particularly in comparable temperate mountain systems.

Biomass ashes represent a promising secondary phosphorus (P) source, yet their agronomic performance depends on feedstock origin, processing, and crop-specific interactions. This study evaluated the P fertilizer efficacy of raw and processed biomass ashes derived from cereal straw and paludiculture biomass, compared with triple superphosphate (TSP), using two sequential greenhouse pot experiments with maize, amaranth, and blue lupine. Processed ash products, particularly compacted ashes and ash–straw mixtures, increased plant biomass and P uptake to levels comparable to or exceeding those achieved with TSP. The cumulative P uptake of the three crops reached up to 250–300 mg pot⁻¹ under processed ash treatments, exceeding the uptake under TSP (≈150–180 mg pot⁻¹) and the unfertilized control (≤80 mg pot⁻¹). However, crop-specific differences were observed: amaranth benefited most from the ash products, whereas combinations of ashes with lupine were less favorable. Beside acting as a P source, processed biomass ashes also increased soil pH by about 0.5 units, improved soil aggregation by increasing macroaggregates (>2 mm) to up to 20% compared with only about 7% in TSP and the control, and promoted favorable shifts in Hedley P fractions. Soil enzyme activities were governed primarily by crop species, with amaranth stimulating phosphatase activity the most. Further research should aim to refine crop-specific application strategies for processed biomass ashes and to elucidate their impacts on soil structure and P dynamics.

The impact of extreme weather events such as droughts, heatwaves, storms and the associated intensifcation of bark beetle outbreaks in Norway spruce forests in recent years, has led to a large-scale forest loss in Central Europe. There are various options for post-disturbance management, from complete clearing to no intervention, but their pros and cons - in the context of multifunctional forest management - are not resolved. The ResEt-Fi project ('Pioneering reforestation: Regional management for establishing multifunctional forests on post-disturbed Norway spruce areas') consortium implemented a cross-regional field trial to test how specific practices of deadwood retention affect the ecological conditions and subsequent reforestation dynamics of natural regeneration and planted trees. It aims at generating climate-stable mixed forests within an ecological valuable transition, balancing ecosystem functioning and socio-economic benefits. As an outcome for stakeholders and forest practitioners, guidelines and showcase scenarios for facilitating the selection of management procedures will be created. In this article, we provide insight into (i) the applied post-disturbance deadwood management practices and the rationale for their selection, (ii) the experimental setup of our cross-regional field trial, (iii) the initial post-disturbance status and perspective with respect to regional site conditions and deadwood treatment. While the setup and site conditions will primarily serve as a reference for subsequent studies in our joint project, this is the first systematic, cross-regional study on the effects of the management options standing deadwood, high stumps and clearing on microclimate, biodiversity, and tree regeneration in the critical early stages of forest regeneration after disturbance.

Prolonged drought and increased susceptibility to biotic stressors have led to a far-reaching calamity in forests dominated by Norway spruce (Picea abies (L.) Karst.) across Central Europe. European beech (Fagus sylvatica L.) has suffered from crown defoliation and increased mortality. The drastic consequences for forestry and ecosystems urge for comprehensive insights to guide future forest management. The recent drought represents an experimental setting for applying remote sensing-based anomaly detection to understand the role of site conditions for drought response. As quantitative information on soils is scarce and usually available at coarse spatial resolution, knowledge on the role of soil properties is limited. To close this gap, our study pioneers a fine-scale assessment on the role of soil properties based on satellite remote sensing-derived forest disturbance.We applied an existing forest disturbance modeling framework, based on Sentinel-2 time series data on 340 km² in Central Germany, representing hotspots of forest disturbance. Our approach allowed for a reconstruction of spatio-temporal-dynamics of forest disturbance at 10 m spatial resolution over the initial period (2019 to 2021) of the recent drought. Forest disturbance information was intersected with fine-scale soil information (1:10,000) based on roughly 2,870 soil profiles in three study areas. We investigated on how disturbed area varied among sites with different soil type, texture, stoniness, effective rooting depth and available water capacity (AWC).Our approach enabled to retrace where initial disturbance took place and how disturbance developed over time. For Norway spruce, we found that stands were most affected on deep Cambisols with medium to high AWC (90 to 160 mm) and rather low stone content, i.e., on soils usually considered as suitable in silviculture. However, these stands seemed to be more prone to suffer from unexceptional water scarcity. In contrast, we could not find evidence for pronounced disturbance on shallow soils or soils with high stone content, even though stands on soils with high AWC (> 160 mm) were least affected. Compared to spruce, the drought response of beech seemed less clearly directed to soil properties, but based on our results, we support the general concern on drought vulnerability of this species. In this regard, only stands on Luvisols with very high AWC (> 180 mm) remained undisturbed. Although long-term post-drought effects are unknown, stands initially affected did not necessarily develop the highest proportions of disturbed area, indicating recovery or adaptive mechanisms.We conclude that the integration of remote sensing-based forest disturbance monitoring with fine-scale soil information allowed us insights into soil-related drought risks. In view of the currently still high level of spruce die-back due to bark beetle infestation, disturbance in the hotspot regions we investigated will hardly to be stopped. Nevertheless, other areas with a high proportion of spruce could benefit from our findings, by identifying vulnerable stands and target in situ monitoring at an early stage of drought. For long-term strategies related to forest conversion and recovery, we consider fine-scale and quantitative information on soils crucial for implementing precision forestry.

It has become increasingly challenging to maintain "regular" forest management, as the pace and magnitude of climate-related changes exceeds the response of many forest ecosystems. This has led to large-scale disturbances in recent years. To limit impacts on soil structure, the loss of soil organic matter and soil nutrients and to restore forest climate and functions, the development of suitable reforestation strategies on disturbed areas must be prioritised. Alternative management measures are needed to point out further options for the extensive clearing. To draw conclusions about the site-specific selection of suitable management options for disturbed areas, this study monitored mid- to long-term effects on soil structural and soil chemical parameters of the humus layer and topsoil as well as microclimatic properties. Studies were carried out on large-scale Norway spruce (Picea abies (L.) Karst.) disturbance areas in low mountain regions in Thuringia. Different management variants were compared to vital spruce stands, ranging from standing deadwood to "high stumps", mulched and completely cleared areas. In addition to basic soil chemical and physical parameters, soil moisture and temperature of the topsoil and the organic layer as well as the surface temperature were recorded continuously over 30 months. The results revealed significant differences in surface and soil temperature between the variants. Clear-cut areas showed higher soil temperatures and greater variability during the vegetation period. Standing deadwood lowered the average temperature and, in particular, mitigated high and low temperature peaks. Soil moisture showed temporal changes depending on the status of decline of the spruce forests. Even within the first few months, effects on the soil structure of the cleared disturbed areas can be detected, as macroaggregates degrade and the size fraction of microaggregates increases. With a narrowing C/N ratio in the mineral soil along with increasing thinning on the plots and intensity of management, mid-term (>6 months) losses in plant-available and total phosphorus content in the organic layer and the upper mineral soil were observed. While mulching led to an increase in soil organic matter (SOM) in the surface layer, a significant loss of SOM was determined over time in all other variants compared to vital spruce stands. Overall, we conclude that the aggregate stability and nutrient availability of the soil decreased faster with more intensive management intervention so that characteristics of the microclimate moved away from forest interior climate. Prolonged monitoring is required to verify whether the results are mid-term occasional effects or on the way to an equilibrium.

Proper fertilizer management and applications could effectively reduce global warming potential (GWP) and improving soil fertility under cereal production. However, the effect of soil fertilizer management practices on GWP and soil fertility is less understood in the agricultural soils of Ethiopia. The present study evaluated the effects of fertilizer application strategy on GWP, and soil fertility in a Nitisol. Both field and laboratory incubation experiments were conducted with the same treatments. Seven treatments (Cont: no input; 100 min: 100% mineral fertilizer, 80 min: 80% mineral fertilizer + 1.4 t ha⁻¹ compost; 60 min: 60% mineral fertilizer + 2.8 t ha⁻¹ compost; 50 min: 50% mineral fertilizer + 3.5 t ha⁻¹ compost; 30 min: 30% mineral fertilizer + 4.9 t ha⁻¹ compost, and 100 comp: 100% compost) with four replications were applied on maize crop (Zea mays L. Bako hybrid 661) for two consecutive growing seasons. The laboratory incubation experiment was also carried out with two moisture levels (40% and 75% of water-filled pore space) to simulate the seasonal rainfall pattern. GWP was calculated by summing up the quantified gas emissions of nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄). The laboratory result for GWP shown that soil fertilized with mineral fertilizer alone was significantly (p < 0.05) increased by 27–34% of the average GWP compared to combined fertilizer treatments in the soil at a moisture level of 75%. From the field experiment, most plant nutrients were significantly increased in combined fertilizer treatments compared to sole mineral fertilizer application. For example, carbon, calcium, magnesium and potassium were increased by 26.2–39.8%, 73.2–168.8%, 146.6–251.5% and 47–99% respectively in combined fertilizer compared to 100 min treatment. The study revealed that combining 30 or 50 kg N ha⁻¹ of mineral fertilizer with biowaste compost (4.9 or 3.5 t ha⁻¹) would be a suitable combination to mitigate the GWP and improve soil quality in smallholder farming systems, due to a slow release of N during decomposition into the soil compared to mineral fertilizer alone. However, to evaluate GWP under the field conditions, future investigations are recommended.

The fraction of absorbed photosynthetic active radiation (FAPAR) is an essential climate variable for assessing the productivity of ecosystems. Satellite remote sensing provides spatially distributed FAPAR products, but their accurate and efficient validation is challenging in forest environments. As the FAPAR is linked to the canopy structure, it may be approximated by the fractional vegetation cover (FCOVER) under the assumption that incoming radiation is either absorbed or passed through gaps in the canopy. With FCOVER being easier to retrieve, FAPAR validation activities could benefit from a priori information on FCOVER. Spatially distributed FCOVER is available from satellite remote sensing or can be retrieved from imagery of Unmanned Aerial Vehicles (UAVs) at a centimetric resolution. We investigated remote sensing-derived FCOVER as a proxy for in situ FAPAR in a dense mixed-coniferous forest, considering both absolute values and spatiotemporal variability. Therefore, direct FAPAR measurements, acquired with a Wireless Sensor Network, were related to FCOVER derived from UAV and Sentinel-2 (S2) imagery at different seasons. The results indicated that spatially aggregated UAV-derived FCOVER was close (RMSE = 0.02) to in situ FAPAR during the peak vegetation period when the canopy was almost closed. The S2 FCOVER product underestimated both the in situ FAPAR and UAV-derived FCOVER (RMSE > 0.3), which we attributed to the generic nature of the retrieval algorithm and the coarser resolution of the product. We concluded that UAV-derived FCOVER may be used as a proxy for direct FAPAR measurements in dense canopies. As another key finding, the spatial variability of the FCOVER consistently surpassed that of the in situ FAPAR, which was also well-reflected in the S2 FAPAR and FCOVER products. We recommend integrating this experimental finding as consistency criteria in the context of ECV quality assessments. To facilitate the FAPAR sampling activities, we further suggest assessing the spatial variability of UAV-derived FCOVER to benchmark sampling sizes for in situ FAPAR measurements. Finally, our study contributes to refining the FAPAR sampling protocols needed for the validation and improvement of FAPAR estimates in forest environments.