The map shows selected points on the forest site map (centres of polygons of representative forest soil forms). The colour symbolises the level of soil water available to the plant to a depth of 40 cm on a daily basis. For each point, the water balance was simulated according to the specific soil properties and the main tree species suitable for the site. The main tree species are pine or oak in the Saxon lowlands, oak or beech in the hills and spruce or beech in the mountains.

The map shows the points of the Bundeswaldinventur (BWI) resp. the National Forest Inventory Network (not exactly in position for data protection reasons). Each point represents the soil properties present at the BWI points. The colour symbolises the daily amount of soil water available to plants, initially to a depth of 40 cm. Water balance simulations are provided for the four main tree species: spruce, beech, oak, pine and grass. Different soil depths (40 cm, 80 cm and 100 cm) and map backgrounds can also be selected using the icon in the top right-hand corner of the map.

The points of the forest climate stations appear on the map. These weather stations in open areas in or near forests are operated by the competence center for wood and forestry at the Public Enterprise Sachsenforst and complement the DWD monitoring network. After selecting the desired forest climate station, the current and past measured values of various climate parameters can be displayed, aggregated to different time periods or exported for your own applications.

The graph shows the progression of the soil water level to a depth of 40 cm from the beginning of the current year to the current date (red line). In comparison, statistical measures (quantiles) of the retrospective model results from 30 years are shown. The quantiles allow the current water level trend to be categorised in relation to average or particularly dry or wet soil moisture conditions over the course of the year.

The graph shows the soil moisture dynamics of the selected location one year back to the current date. The soil profile from 0cm - 100cm is shown. For each 10cm layer of soil, the changing colours indicate the depletion or replenishment of the plant available water. This shows the dynamics of soil moisture over time and at depth.

Soil water content refers to the current level (%) of soil water available to the crop down to a defined soil depth. The technical term is "plant available water" (PAW) or "relative extractable water" (REW).

Soil consists of solid soil particles and pores filled with water or air. The pore system and total pore volume depend on soil type, bulk density, rock content and structure. In coarse pores (> 50 μm), water percolates down very quickly. In micropores (< 0.2 μm), water is very strongly retained by capillary forces, so that even tree roots cannot absorb this water. A high proportion of medium pores (0.2-50 μm) is most favourable for plants because this is the area (suction tension approximately > 6.3 kPa and < 1585 kPa) where water can be stored most readily available to plants. Soils with different pore systems store water differently.

In the model, the plant-available soil water storage (PAW) or relative extractable water (REW) is determined for each soil profile according to its physical properties as the difference between the volumetric water content at field capacity (pressure head at -6.3 kPa or pF 1.8) and the permanent wilting point (PWP or WP at -1585 kPa or pF 4.2). The current soil water content (Theta, Θ in vol%) is calculated using the LWF-BROOK90 numerical simulation model optimised for forest ecosystems.

Where Θ_i is the volumetric water content of the fine soil in the i-th soil layer, c_i is the volume fraction of coarse soil (gravel and stones), and di is the layer thickness in mm. AWC is the plant-available water holding capacity of the soil, Θ_fci and Θ_wpi represent the water content at field capacity (-6.3 kPa or pF 1.8) and at wilting point (-1585 kPa or pF 4.2), respectively.

From the depth-discrete results of the LWF-BROOK90 modeling, the values for REW or PAW are aggregated for the following depth ranges of the soil profile: 0cm - 40cm, 0cm - 80cm, and 0cm - 100cm.

In the soil moisture traffic light system of ReKIS and Sachsenforst, the current-day soil moisture is utilized to describe the water supply of plants using the PAW. A menu for selecting soil depth (0cm - 40cm, 0cm - 80cm, or 0cm - 100cm) and vegetation type (spruce, beech, pine, oak, or grass) is available.

At field capacity, the plant-available water is fully filled (100%). During cool, wet periods with ongoing rainfall, some of the macropores also become filled with water. Hence, the plant-available water can exceed 100% and "overflow".

When values exceed 100% of field capacity, clay soils are particularly susceptible to deep rutting when machinery is used incorrectly. Surface runoff also forms very quickly, leading to soil erosion. During periods of > 100% field capacity, there is also less oxygen in the soil. If such periods continue for many weeks, root rot can occur.

No, the current version of the model can only represent vertical percolation (1D), ideally in freely draining soil profiles in flat terrain. Water flowing laterally into the soil profile through impervious layers (e.g. on slopes) or fluctuating groundwater levels are very poorly represented. The model results for mineral and organic wetlands (O and N sites) and waterlogged sites (W sites) on slopes or in depressions may therefore differ significantly from reality due to actual hydromorphological influences. Therefore, model results are not shown for some of these sites.

To simulate the soil water balance, real-time weather data are required as meteorological model inputs: air temperature, wind speed, precipitation, radiation and relative humidity. These data are measured daily by the German Weather Service (DWD). They are collected, processed and made available for water balance simulations via a SensorHub from Pikobytes GmbH.

• Kronenberg et al. (2022): "Die Bodenfeuchteampel – Ein webbasiertes Informationssystem für die tagaktuelle Bewertung der Wasserverfügbarkeit in Wäldern"
• Luong et al. (2023): "Toward reliable model-based soil moisture estimates for forest managers"