Vegetation management on grass-dominated clearcuts planted with Norway spruce in southern Sweden

Abstract

A field experiment was established between 1989 and 1993 to study the effects of competing vegetation on growth of planted Norway spruce (Picea abies (L.) Karst.) seedlings. Effects of clearcut age, scarification (mounding), herbicide treatment, and seedling stock type were investigated 5 years after planting. On fresh clearcuts, amounts of vegetation were negligible, whereas 2.1-3.7 Mg·ha-1 was found on 4-year-old and older clearcuts. Soil temperatures were about 10% higher in mounds than in undisturbed ground, while herbicide and clearcut age only marginally affected soil temperatures. Seedlings planted on old clearcuts showed significant reductions in growth due to interference from vegetation. Five years after planting, the reduction in growth corresponded to about 1 year's growth. Most of the interaction between seedlings and vegetation occurred during the first 2 years after planting. Thus, scarification was just as effective as repeated herbicide treatments in reducing competition from vegetation. Differences in periods of drought between years could largely explain variation in leading shoot length. However, leading shoot length was affected in the same way irrespective of vegetation control treatments. Five years after planting, the relative differences in diameter between bare-root and containerized seedlings were the same as at the time of planting.

Response of newly planted Norway spruce seedlings to fertilization, irrigation and herbicide treatments

“…The finding that competing vegetation reduce growth of planted Norway spruce and that herbicide treatment is an effective way to reduce this competition agrees with many other studies of Norway spruce [1,11,16]. However, we conclude that even though competing vegetation was removed by herbicides, availability of nutrients was still limiting seedling growth.…”

“…This conclusion agrees with earlier studies of competition between ground vegetation and planted Norway spruce in similar climate [15,16,18,20]. None of the years 1998-2000 was considered as a dry year, which is quite usual for the area.…”

“…For planted Norway spruce in southern Sweden, it has been shown that competition from field vegetation is most important during the two first years after planting and is less important for established seedlings [16]. However, it has been debated whether competition for light, water, nutrients or a combination of these factors is the most limiting factor for newly planted seedlings [12].…”

“…[3]. Mowing experiments has shown that competition for light is of minor importance when the field vegetation mainly consists of grass [16] and that is probably also true for more fertile sites where vegetation is more dense [1,14,17].…”

“…The availability of nutrients is usually high on clearcuts as a U. Nilsson, G. Örlander result of decreased competition from removed trees, and decomposition of slash that are retained during the logging operation [4,7]. However, despite the high nutrient availability, several studies have indicated that nutrients might restrict seedling establishment [1,12,16,18,19,20]. Nordborg [17] found that competition from field vegetation might restrain nitrogen uptake during the first months after planting.…”