What are Norway's forests doing today?

We measure stem growth continuously using point dendrometers. These instruments record the shrinkage and swelling of the stem as trees take up water at night and release water during the day. Permanent swelling (when the stem does not shrink back to its original level during the day) is considered growth, and is recorded at the micrometer level.

See the interactive diagram

Tree water deficit (TWD) is calculated daily using the dendrometers, as the difference between the stem's maximum and current radius, and is used as an indicator of the tree's water status and water stress.

Soil probes at each logger box report volumetric water content every hour, at several depths, alongside soil temperature.

A reading is compared with the same site's own last 28 days, never with another site. Soils differ enough between localities that an absolute number says little on its own. What is informative is a site drying out relative to how it has recently been.

Soil moisture is often what explains the stem: dry soil first, then trees that no longer rehydrate overnight.

Air temperature and humidity are measured at each logger box. Precipitation comes from MET Norway's observation network, from a public station near the site.

The station is chosen by which elements it actually reports, not by distance alone. The nearest stations are often road-weather stations that record no precipitation at all. Its name and its distance are shown beside the chart, because it is a nearby public station and not an instrument at the plot.

Weather is drawn on the same figure as the stem trace on purpose. A stem that has shrunk for four days reads very differently with rain on the fourth day than without it.

The observations are pulled nightly into our own store, so a number on the chart can still be reproduced later.