Effects of climate and management on the productivity of Dutch heathlands.
Effects of burning and turf-cutting treatments on the productivity of Calluna vulgaris heathlands were studied for a climatologically dry site (Strabrecht) as well as for relatively wet sites (Dwingelhoo/Hoge Veluwe) on podzol soils in the Netherlands. Productivity for specific site-treatment combinations was assessed from age-sequences (chronosequences) of the aboveground biomass in Calluna stands of different age-classes, and from indirect as well as direct estimates of the aboveground annual production. A two-parameters Mitscherlich curve is used to describe the relationship between aboveground biomass and age for various site-treatment combinations. The relationship is used to examine the effect of management and site on biomass. After correcting for age differences, biomass for plots subjected to turf-cutting was lower by a factor of 0.57 than in burned stands. The biomass in Strabrecht was lower by a factor of 0.81 than in Dwingelhoo/Hoge Veluwe. Maximum indirect estimates of the annual production for burned heathland at Dwingelhoo/Hoge Veluwe and at Strabrecht were 257 and 209 g m-2 year-1, respectively and, for stands subjected to turf-cutting, 147 and 119 g, respectively. Direct annual production estimates for various site-treatment combinations confirmed differences between site-treatment combinations obtained from indirect production estimates. The assumptions underlying the productivity estimates are discussed and possible causes of differences in productivity are indicated.