About BorealNet

A dendrometer band sits on the stem at 1.3 m and reads its radius to the micrometre, every ten minutes. It measures the stem, not the whole tree.

Wood only ever grows outward. Within a single day the stem still shrinks and swells, and that movement is water rather than growth. Growth is the part the stem does not give back: a new widest point that it reaches and holds.

From that trace we derive a daily growth increment for each tree, and from the trees at a plot a verdict over the last seven days: active growth, low growth, or dormant. Low growth can occur naturally during the growing season and does not by itself indicate water stress.

BorealNet has no long-term record yet, so the site never says whether growth is high or low for the time of year. It reports what the trees are doing now.

The chart, explained on the tree

Stem water deficit is the distance between the widest the stem has been this season and where it is right now, in micrometres. It is zero when the tree is fully hydrated.

On a warm day a tree loses water faster than its roots replace it, and the stem narrows. Overnight it usually refills and returns to zero. A tree that stops returning to zero is carrying a deficit it has not recovered.

How long that lasts is what decides the wording. Signs of water deficit means most reporting trees at a plot have not fully rehydrated for more than three days. Prolonged water deficit means it has passed a week and the daily maximum is still rising.

It comes from the same trace as growth. Nothing extra is installed to measure it.

Current conditions across the network

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.