Fine root density and root biomass of two Douglas-fir stands on sandy soils in the Netherlands. 1. Root biomass in early summer

In two fully stocked, fast growing Douglas-fir plantations of the Dutch ACIFORN project, detailed studies were carried out on fine root biomass and fine root length to obtain informa tion on fine root densities.For three consecutive years, fine roots were sampled with a root corer in the early part of the growing season.The coarse root biomass was calculated from aboveground stand parameters.The vertical distribution of fine roots in these sites was simi lar.In the stand with less aboveground biomass the dry weight and density of the fine roots were higher.The fine root biomass agreed with values found in Douglas-fir stands in the Pac ific northwest of the USA.Up to 80 cm depth the fine root biomass varied from 3900 kg ha -1 in moist conditions to 900 kg ha -1 after dry periods.The fine root length varied accordingly, with a maximum of 27.10 6 m ha -1 and a minimum of 3.10 6 m ha" 1 .The fine root density in the mineral topsoil varied between 0.6 and 0.05 cm cm" 3 ; in the subsoil it varied between 0.3 and 0.04 cm cm" 3 .In 1989 there was some sudden root death during a dry period.