The object

In every edition of WSL's magazine DIAGONAL we present an instrument, a tool, a machine - in short an object. Apart from the presentation in the magazine, there is always a video clip of the object.

Tree rings provide us with important information about the climate of the past, which is why the dendro-­researchers at WSL measure hundreds of thousands of them every year. Until now, they have had to do this ‘by hand’ with a click of the mouse on a ‘live’ image of an increment core or a stem disc. Recently, the photo robot known as ‘Skippy’ has made this work easier for them. The increment core or the stem disc is placed on the movable plate, which can be controlled by a computer and moved forward a few millimetres at a time. Each time it stops, a camera mounted on a bracket takes a photo. All the images are then stitched with the help of a computer programme. The resulting high-resolution panorama image is distortion free and each annual ring can then be measured very precisely.

The point dendrometer is a useful tool for finding out how dry periods affect forests. It measures a tree’s growth and water deficit by recording tiny fluctuations in the stem’s thickness. During the day, the stem shrinks because more water evaporates through the stomata in the leaves than is absorbed by the roots. At night, these openings are closed and the stem expands again. In addition, the stem becomes thicker during the growing season due to the newly formed wood and bark cells. The researchers from TreeNet (treenet.info), a research network under WSL management, have installed over 350 point dendrometers in the Swiss forest. The fine temporal resolution of the resulting data is unique.

Researchers at WSL have developed a small drone that can settle on tree branches. Attached to its protective housing are ‘hooks’ with undersides made of special material that adheres well to the branches. Once it reaches its destination, the propellers are turned off. This allows the drone, known as the "Hedgehog", to collect data silently over a long period of time without consuming much energy. Various measuring devices can be mounted on it, for example to make acoustic recordings or to observe wildlife in the treetops with a camera.

Satellites measure soil moisture on the Earth in order to better understand the global water cycle and to increase the reliability of weather forecasts. Radiometers, which were developed at WSL, among other places, are used for comparative recordings on the ground. They have been installed, for example, in Davos Laret (CH) and on the Tibetan plateau. The measurements of the microwave radiation provide the basis for calculating how much water is present in soils, vegetation and snow.

Tried and tested things hardly ever change: snow researchers still work with magnifying glasses and snow grids to examine snow crystals even today – just as they did eighty years ago. They take samples from the different layers of a snow profile and place them on the grid. Cells of different sizes in the grid serve as a reference for determining the size of the crystals. Once the shape and size of the snow crystals are known, conclusions can be drawn about the properties of the snow layer.

At WSL, seeds from about ninety different tree species are harvested, cleaned and stored. These seeds are then used for in-house experiments or made available to forest enterprises. To remove impurities, various seed-cleaning machines can be used. These machines separate the raw material according to weight, separating, for example, heavier spruce seeds from lighter impurities. The cleaned seeds are collected in a container for further use.

The spore trap sucks in air from the environment constantly, collecting the particles it traps, which include spores from fungi, in a small container. The spore samples are analysed genetically to determine the species they come from. The trap on the WSL site in Birmensdorf is part of the Global Spore Sampling Project. Up until now, only 150,000 species of fungi have been scientifically described, but it is assumed that there are actually between two and 13.2 million. The sampling project should help to obtain more accurate estimates.

WSL employees have developed an automatic insect trap that catches insects during specified time periods only, for example at night between 9pm and 5am. The insects fall into a collector filled with liquid. Between sunrise and sunset, however, the trap is set so that diurnal insects, such as bees, can immediately return to the open air through an opening. The turntable with the trapping collectors rotates one position further each night. This means that the trap only needs to be emptied once a week as it collects samples seven nights in a row. Automatic insect traps were developed to investigate how the light colour and light intensity of LED street lights influence nocturnal insects.

WSL staff are currently recording data on the Swiss forest for the fifth National Forest Inventory (NFI). On the NFI sample plots, they measure the trees, describe the tree stand and assess the site conditions. They carry all the instruments and tools they need in a rucksack to the plots, which are sometimes difficult to get to. The material includes several GPS instruments, a tool for measuring tree height, and a so-called Finnish calliper. This is used to measure a tree’s diameter at a height of seven metres. Using this diameter, together with the diameter at a height of 1.3 m and the tree height, the volume of the tree can be calculated.

Floods in torrents frequently transport large quantities of stones and sand down with them. In the Alptal (Canton Schwyz), WSL has been measuring how much material the Erlenbach transports. When a flood event occurs, metal baskets move automatically into the stream and collect the solid material. Along with the data from the acoustic sensors, the researchers can then determine the bedload transport for different particle sizes.

A debris flow is a fast-flowing and destructive mixture of water, fine sediments and pieces of rock. Researchers release model debris flows onto an eight-meter long slide in the mountain hydrology lab at WSL. This enables them to test the flow, impact and deposition behavior of different debris-flow mixtures.

The SnowMicroPen (Snow Micropenetrometer) was developed at SLF to measure snow-cover hardness without having to shovel snow. Such measurements allow conclusions to be drawn about the snow density and structure, and thus about the snow stratigraphy, which is an important factor in avalanche formation.

WSL harvests and kilns forest seed material, and operates the national seed agency, which offers seed material to forestry enterprises and tree nurseries. In a refrigerated storage room, WSL stores up to 60-year-old Norway spruce seeds from a variety of origins, as well as seed material from a further 50 tree species and shrubs.

Please find further videos on You tube.