Method and sources

Last updated: 13 October 2026

This page describes how Treemulator determines the site conditions, the suitability of tree species, the number of plants and protection against deer, and where the data comes from. The calculation is a decision aid. It does not replace a site survey or advice from the forest service.

Each plan saves its basis and the calculation version, the date of the last change to the calculation. The report states both. What changed and when is listed under Changes to the calculation.

Data

For the planning, the app queries Open-Meteo and OpenStreetMap. Only the coordinate of the centre of the area leaves the device. Every value retrieved can be overwritten in the planning.

Terrain: elevation model Copernicus DEM GLO-90 via Open-Meteo. Five elevation points within a radius of 180 m give the slope and its aspect.
Climate today: ERA5 reanalysis via Open-Meteo, daily values for the years 2015 to 2024. These give the mean annual temperature, annual precipitation, precipitation from May to September, the temperature of the warmest and the coldest month, the growing days above 5 °C, the solar energy and the clear sunny days.
Climate around 2050: two high-resolution climate models from CMIP6, MRI-AGCM3-2-S and EC-Earth3P-HR, via Open-Meteo. The years 2041 to 2050 are compared with 2015 to 2024 of the same models. The change is applied to the measured climate, which removes the models’ error in the starting value. It applies separately to the whole year and to the summer from May to September. The planning shows the range between the two models.
Surroundings: OpenStreetMap via the Overpass interface. The app counts buildings within 150 m, forest within 100 m and 1 km and water within 40 m. From this it estimates how often game comes onto the area.
Soil: soil type, rooting depth, stone content, soil moisture and lime are entered by whoever knows the area. The planning includes instructions for determining them in the field. The app does not query soil maps.

The privacy policy states which services receive which data. The legal notice names the map providers.

Site

Water supply

Water supply is a level from 1 to 5, from extremely dry to wet. The starting point is the precipitation from May to September, weighted by the soil’s water store. This is set by soil type, rooting depth and stone content. The evaporative demand is subtracted from it. It is 150 mm for a warmest month of 18.5 °C and changes by 9 mm per degree. A surplus or deficit of 130 mm equals one level.

Rain alone does not make a soil wet. Without groundwater or seepage from the slope, the level therefore stays at 3.6 at most. A slope facing due south costs almost one level. Entering the soil moisture keeps the level within its range.

Soil moisture	Available water capacity in summer	Level
Extremely dry	below 10 %	1,0
Very dry	10 to 20 %	1.1 to 1.8
Dry	20 to 40 %	1.9 to 2.5
Fresh	40 to 80 %	from climate and soil
Moist	80 to 100 %	4.0 to 4.3
Wet	over 100 %	4.8 to 5.0
Alternately wet and dry	below 40 to over 100 %	from climate and soil, with a check of its own

Water around 2050

The same calculation runs with the climate around 2050, using the warming and the summer precipitation from the models. The difference from today is subtracted from today’s level. Moist and wet soils depend on groundwater or seepage from the slope and stay as they are. If the model values are missing, the app assumes 2 °C of warming.

Nutrients and lime

Nutrient supply is also a level from 1 to 5. Each soil type has its value, loam about 4, sand 1.5 and raised bog 1. Shallow rooting depth and many stones lower it. Whether the soil contains lime follows from the soil type or from the acid test.

Light and previous land use

The planning distinguishes open area, partial shade and shade under old trees. The previous land use shows whether fresh conifer stumps attract the large pine weevil and whether a former meadow harbours many voles.

Vegetation zone and vegetation belt

From the coordinate the app determines the floristic region, and from the climate the vegetation zone, such as the deciduous mixed broadleaved forest or the taiga. The zone is determined twice, for today and for 2050, and suggestions draw on both. The vegetation belt follows from the warmest month. The boundaries are calculated from climate values, not mapped. The app covers Eurasia.

Suitability of tree species

The app knows 342 tree and shrub species. For each species, a table records its requirements, including tolerance of drought and waterlogging, late-frost hardiness, light requirement, temperature range, minimum precipitation and nutrient requirement. Added to these are its behaviour on lime and on heavy soils, its tie to bogs or floodplains, its prospects under climate change, its distribution and known risks. The values summarise what the fact sheets of the forest research institutes WSL, FVA, LWF and BFW and the common tree species recommendations agree on. Where they differ, the more cautious assessment applies.

Every species starts with 100 points, and every objection costs points. The check covers today and the climate around 2050, and the less favourable result counts. From 70 points a species counts as well suited, from 45 as suitable with reservations, below that as unsuitable.

Objection	Deduction in points
Too dry, today or around 2050, or too wet	by the distance from the limit, at most 80
Soil alternately wet and dry	12 to 30
Soil too poor	by the gap to the requirement, at most 70
Lime for lime-avoiding species	35
Acidic soil for species of base-rich soils	15 to 30
Heavy, dense soil for species that avoid it	20
Temperature at the limit or beyond, today or around 2050	12 or 35
Annual precipitation slightly or clearly too low	12 or 30
Different vegetation zone	30, or 8 if the area moves into the species’ zone by 2050
Nearest natural occurrence more than 400, 1,200 or 3,000 km away	8, 22 or 35
Light-demanding species under a canopy, shade-tolerant species on open ground	30 or 10
Floodplain species without groundwater	22
Non-bog species on wet peat	30
Known risk, such as Dutch elm disease, ash dieback or invasiveness	per species
Loser of climate change	up to 12 or 25, the warmer the area lies within the species’ temperature range

In addition there are small deductions without an objection, at most 8 for temperature, 6 for water and 9 for a good soil that an undemanding species does not use. They rank species whose optimum lies here ahead of those that only just cope. On an area with dense competition such as bramble, species that quickly give shade get 18 extra points.

Sorting is by points only. The planting goal selects which species appear and gives no points. A production forest, for example, shows no small trees. Species that do not grow in the region appear only if their nearest occurrence is at most 1,200 km away and their vegetation zone fits. The others appear only on explicit request.

Counted survival on the area and nearby is shown next to the suitability and does not enter the points. A count is an observation at one place in one year.

Number of plants

How closely to plant depends on the purpose. Each planting goal comes with a space level as its default, and every level can be chosen for every goal.

Space level	Space per plant	Default for
Valuable timber	forestry guide value for the species	Production forest
Groups and clusters	groups of 20 or 25 plants, at the final spacing or twice the final spacing	Protection forest in the mountains
Quick canopy closure	geometric mean of guide value and final spacing	Protection forest
Final spacing	mature crown	–
Open woodland	final spacing plus 25 %	Nature conservation
Open landscape	final spacing plus 60 %	Food

The final spacing is the crown diameter of the mature species, when its crown just touches those of its neighbours. Light-demanding species get 5 or 10 % more spacing. Where water becomes scarce for a species, the area per plant increases up to double.

The guide values lie at the lower end of the German federal states’ recommendations for timber plantations, for example 6,000 plants per hectare for oak, 5,000 for beech and Scots pine, 1,600 for Douglas fir and 1,500 for wild cherry. “Valuable timber” and “Quick canopy closure” never plant wider than the final spacing, groups never denser than the guide value.

In a group, 20 plants stand 1.2 m apart, with the group centres at the final spacing. Each group is meant to produce a future crop tree, and natural regeneration grows in between. In the mountains, where the warmest month stays below 13.5 °C, they become clusters of 25 plants, 0.8 m apart. The cluster centres are twice the final spacing apart, so that at least one crown width stays free between the clusters.

The percentages of the mix are shares of the number of plants. The area divided by the mean space per plant gives the number. Wildflower areas, wet zones and small habitats are deducted first, by default 7 % of the area. Under a canopy there are 25 to 45 % fewer plants.

A reserve for losses is added to the number of plants, 10, 15 or 20 % depending on the site’s productivity. For valuable timber and in groups it is half as large, at least 5 %.

For a hedge, the app calculates in running metres. Length and width follow from area and perimeter, and the hedge type sets the rows and the planting distance.

Protection against deer

Only what needs protection is protected. The calculation has three steps.

The risk on the area follows from the game species and the browsing pressure. It is best judged by looking at the natural regeneration in the surroundings. Without this information, the app estimates it from the surroundings.
Each species’ need depends on how readily game eats it and whether bucks fray it. A plant that is already taller than game can reach when planted needs no protection against browsing.
The height of the protection depends on the largest animal, about 1.2 m for roe deer, 1.8 m for red deer and 60 cm for hares. It stays in place until the terminal bud has grown out of reach, at least 2 and at most 15 years. The duration follows from the species’ juvenile growth and the site’s productivity.

The time in place determines the material. Rotting material is chosen where it lasts long enough, plastic only where nothing else will do. For conifers the app suggests only free-standing or rotting protection, because their branches grow through nets and holes.

The app compares individual protection and fencing by the effort for material, installation, inspection and removal. One individual guard with a stake is one unit. One metre of roe deer fence counts as 2.5 units, one metre of red deer fence as 3.5. The fence is recommended if it costs less than 90 % of individual protection. Above a slope of 35°, the app does not suggest a fence.

Plastic and bioplastic must be collected, because bioplastic usually does not break down completely in cool forest soil. Wood, cellulose, jute, sheep’s wool, bamboo and woven rods stay in the forest.

Dates and tending

Planting is in autumn, from mid-October to the end of November. On wet or alternately wet and dry soils and above 1,000 m, spring applies. Inspection is due every 6 months, tending every 12 months. With dense competition such as bramble, weeding is every 6 months. The next date counts from the last time the task was done. Collection is due at the end of the time in place.

Comparison with the Tree App

In Switzerland, the Tree App by FOEN and WSL recommends tree species by site type, for the climate of 1961 to 1990 and for moderate and severe climate change towards the end of the century. It needs the site type, whereas Treemulator needs information on the soil, and Treemulator calculates up to 2050. On 12 October 2026, nine site types were compared, six on the Swiss Plateau, one near Davos and two in the Pfyn forest in Valais. The count was how many of the species recommended by the Tree App Treemulator rates as well suited.

Site type	Recommended by the Tree App	Of these well suited
1 Typical woodrush beech forest	Silver birch, hornbeam, sweet chestnut, beech, Scots pine	4 of 5
8a Typical wood millet beech forest	Norway maple, sycamore, beech, ash, sessile oak, pedunculate oak	5 of 6
12a Typical dog’s mercury beech forest	Norway maple, sycamore, beech, ash, wild cherry, sessile oak	5 of 6
14 Sedge beech forest with white sedge	Field maple, Italian maple, sycamore, beech, ash, Scots pine, sessile oak, whitebeam	4 of 8
29 Elm–ash forest	Silver fir, Norway maple, sycamore, ash, bird cherry, pedunculate oak, wych elm	5 of 7
44 Sedge black alder carr	Black alder	1 of 1
57V Alpine coltsfoot spruce forest with bilberry	Norway spruce, rowan	2 of 2
65* Restharrow pine forest	Scots pine, whitebeam	2 of 2
38S Soapwort downy oak forest	Italian maple, Scots pine, sessile oak, downy oak, whitebeam	4 of 5

The differences have four reasons.

Ash, wych elm and sweet chestnut are considered at risk from disease in both apps. The Tree App marks them with a symbol, Treemulator deducts points and so rates them as unsuitable or suitable with reservations.
On the shallow, dry limestone site (14), the soil becomes very dry by 2050 according to Treemulator. Beech and sycamore are unsuitable there, while the Tree App considers both suitable.
Treemulator does not know Italian maple.
In the Pfyn forest, Treemulator also suggests species from neighbouring regions that suit the warming, such as manna ash, hop hornbeam and Turkey oak. The Tree App limits itself to the species of Swiss forest sites.

The comparison revealed three errors in Treemulator, which have been fixed. Scots pine, silver birch, aspen and eleven other native species were missing from the warm-temperate zone, and Scots pine lost 30 points in the Pfyn forest, the largest pine forest in Switzerland. For sycamore, moist soil counted as too wet. Norway spruce received the full deduction for losers of climate change even in subalpine spruce forest. It now applies only in the warm part of its temperature range.

A fourth finding concerns the data. For the Pfyn forest, ERA5 gives an annual precipitation of 1,278 mm, while the MeteoSwiss station at Sion measures about 600 mm. A loam would thus come out as fresh instead of dry. The planning points out this limit.

Limits of the calculation

The calculation does not replace a site survey. Only a soil pit shows rooting depth, stone content and nutrients, and two areas on the same slope can differ.
Terrain and climate come from data grids. The elevation model has a mesh size of 90 m, the climate data 10 to 25 km. Cold-air hollows, springs and small hummocks are missing from them, and in mountain valleys precipitation deviates strongly.
Two climate models show a direction, not a certainty. The planning states their range.
The species’ requirements are best documented for Central Europe. For species from Asia they are based on their distribution and on provenance trials.
Protection forests have their own requirements, in Switzerland according to “Sustainability and success monitoring in protection forests” (NaiS).
The app does not know laws or funding conditions. Fences, non-native species and plantings in protection forests often need a permit.

Sources

Data

Open-Meteo, interfaces for elevation, weather history and climate models.
Hersbach et al. (2020): The ERA5 global reanalysis. Quarterly Journal of the Royal Meteorological Society 146. doi.org/10.1002/qj.3803
Haarsma et al. (2016): High Resolution Model Intercomparison Project (HighResMIP v1.0) for CMIP6. Geoscientific Model Development 9. doi.org/10.5194/gmd-9-4185-2016
OpenStreetMap contributors, queried via Overpass. Licence

Number of plants and planting pattern

Lower Saxony Ministry of Food, Agriculture and Consumer Protection: Pflanzenzahlen je Hektar (plants per hectare, in German).
State Forestry of Mecklenburg-Western Pomerania: Pflanzverbände (planting patterns, in German).
Bavarian State Institute of Forestry: LWF Wissen 59, Douglasie (Douglas fir, in German).
Doutaz and Gendre (2017): practice leaflet “Eichenpflanzung” (oak planting). Forest, Wildlife and Fisheries Office of the Canton of Fribourg. fr.ch
Kohnle, Saha, Kühne and Bauhus (2013): Eiche: Nester oder Trupp? (Oak: nests or groups?) AFZ-Der Wald 2/2013. waldwissen.net
Schönenberger (1986): Rottenaufforstung im Gebirge (cluster afforestation in the mountains). Schweizerische Zeitschrift für Forstwesen 137. waldwissen.net

Tree species, forest protection and provenance

Federal Office for the Environment and WSL: Tree App and NaiS.
Bavarian State Institute of Forestry: Merkblatt 44, Rüsselkäferbefall in Kulturen (pine weevil in plantations, in German).
Council Directive 1999/105/EC on the marketing of forest reproductive material. EUR-Lex
Ordinance on Forests (Forest Ordinance, ForO) of 30 November 1992, SR 921.01, Article 21.

Changes to the calculation

13.10.2026: Comparison with the Tree App. Warm-temperate zone for 14 native species, sycamore on moist soils, deduction for losers of climate change by their position in the temperature range. Note on the limits of the climate data in mountain valleys.
12.10.2026: Space levels per goal with valuable timber, “Quick canopy closure” and groups and clusters. Three dry levels of soil moisture. Water around 2050 with the summer values of the climate models. Previous land use for pine weevil and voles. Sliding nutrient deduction, raised bog and fen separated, deduction for heavy soils. Since then, each plan saves the calculation version.
14.09.2026: Number of plants by the final size of the species instead of density levels. Protection against deer by the need of each species.
10.09.2026: Floristic region and vegetation zone, today and around 2050.

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