Changes in understorey vegetation and fine root quantity following thinning of 30-year Pinus radiata in central North island, New Zealand.
Describes a study in two-36-year-old stands of P. radiata to determine the effects of a heavy thinning in one of them at 30 years of age on the understorey vegetation of indigenous plants, and the dry weight of the fine roots of both P. radiata and understorey plants in the organic soil horizons (F,H, and A1). Fine roots were defined as roots of < 1 mm diameter plus mycorrhizae for P. radiata, and roots (undifferentiated as to species) of < ca. 1 mm diameter plus Coriaria arborea root nodules for the understorey. In the unthinned stand the understorey had a linear cover of 168% in all strata up to 5 m. The fine-root weight of P. radiata equalled that of the understorey. In the thinned stand the understorey, dominated by Coriaria arborea, had a cover of 249% and was 4 m high. Compared with the unthinned stand, P. radiata roots had halved in total weight and understorey fine roots had doubled. In work by Newhook in 25-year-old stands with no understorey, on the same soil type and with the same climate, it was found that the quantity of fine roots of P. radiata regained its pre-thinning equilibrium in the upper soil horizons only three years after thinning.