Effects of intensity of forest regeneration measures on stand development in a nationwide Swedish field experiment

The general belief that intense regeneration measures are financially viable and essential for high sustained yields of commercial forest products has been inadequately tested. This field experiment evaluates effects of three different regeneration intensities 24-27 years after clear-cutting of 14 sites across Sweden. The treatments, designated high (HI), normal (NI) and low (LI), respectively, consisted of: mechanical site preparation and planting of large seedlings at 2x2 m spacing, with supplemental planting and pre-commercial thinning (PCT) when deemed necessary; standard local practices; and natural regeneration with no site preparation, artificial regeneration or PCT. Average crop seedling densities were highest and lowest (3359 and 1662 ha(-1)) under the HI and LI treatments, respectively, 4-8 growing seasons after planting. After 24-27 years, HI also resulted in higher mean stem volume (90 m(3) ha(-1)) than LI (36 m3 ha 21) but was not significantly different from NI (65 m(3) ha(-1)) and increasing the regeneration intensity was not consistently positive. In some cases, high planted seedling mortality and generally abundant natural regeneration resulted in minor (or no) differences between the treatments. The results illustrate that current Swedish regeneration standards may need revision in order to reflect contemporary societal and commercial demands.