Results

The surface area of ​​Dutch forests has decreased slightly compared to previous measurements in 2017 to 363,801 ha.

The decrease (1,925 ha) is a lot lower than in the period 2013-2017 (10,186 ha). Forests cover 11% of the land use in the Netherlands.

The forests are becoming increasingly mixed, predominantly to the expense of monotonous coniferous stands. For the first time since measurements began, we have now measured more deciduous then coniferous trees in this cycle of the NBI.

The Dutch forest is ageing since the Second World War and the number of large trees is increasing. Coniferous forest is now on average 71 years old, while deciduous forest is on average 60 years old. Young forest (<20 years old) has decreased compared to the first forest inventory in 1938-1942 from almost 40% to 9% now.

The amount of natural regeneration (trees with a diameter at breast height <5 cm, but with a height >50 cm) has also been estimated in the NBI-7. On the majority of the plots there was only regeneration of deciduous tree species, while only on 6% of the plots the regeneration consisted solely of coniferous species. It was striking that black cherry (Prunus serotina) was found on more than one third of all plots.

The standing stock of wood has increased from 198 m³/ha in 2001-2005 to 224 m³/ha in the NBI-7. Standing dead wood has increased from 4,6 to 10,0 m³/ha and lying dead wood has increased from 5,4 to 9,2 m³/ha. The share of almost all coniferous species has decreased in the growing stock, causing coniferous species to account for 46% of the growing stock now, compared to 55% in the MFV. An exception to the increase in deciduous trees is ash, which is declining.

The average increment has decreased slightly, from 7,2 m³ ha^-1 yr^-1 in NBI-6 to 6,6 m³ ha^-1 yr^-1 in NBI-7. The decline in Douglas fir and ash is particularly notable. Douglas fir probably suffered from drought stress, while in ash it is a direct result of ash dieback disease. Other conifer species also seem to suffer from drought, because in coniferous forest increment decreased from 8,1 m³ ha^-1 yr^-1in NBI-6 to 7,0 m³ ha^-1 yr^-1 in NBI-7.

An estimated 1.15 million m³ of wood is felled annually (from 3.4 m³ ha^-1 yr^-1 in NBI-6 to m³ ha^-1 yr^-1 in NBI-7). Of this, roughly two-thirds is felled in coniferous forests and one-third in deciduous forests. In general, deciduous tree species have a lower share in felling than would be expected based on their share in both basal area and increment. The opposite applies to coniferous tree species.