The initial stocking (spacing) of Norway spruce plantations has continuously decreased from the XIXth century (10,000 trees/ha--1 x 1 m--or even more) until present days, when it reaches much lower levels (wide spacing) as follows (Table 1):
This lower stocking was chosen due to (i) the need to reduce the cost of plantation establishment as well as to (ii) the reality that the resistance of Norway spruce plantations to snow (early ages) or wind (middle and late ages) increases with the reduction of initial stocking as well as the reduction of slenderness (stability) index SI = h/d, dependant on both initial stocking and early silvicultural interventions (cleaning-respacing and first thinning) (Kramer, 1980).
In Romania, where Norway spruce is planted at narrow spacing (usually 5000 seedlings/ha but sometimes--in forest areas prone to snow-breaks 3300 plants/ha--2 x 1.
Under these circumstances, a long-term research project consisting of variable intensity cleaningrespacing interventions performed in dense, pure and even-aged Norway spruce plantations was launched back in 2004.
The stand consists of a pure and even-aged Norway spruce plantation, 2 x 1 m (5000 seedlings/ha), planted in 1994 using 2-year old plants brought in from Vama Forest District (Suceava County Branch of National Forest Administration-ROMSILVA).
As a result of this variable intensity cleaningrespacing as well as various remaining stand densities, the mean diameter of Norway spruce trees had increased in the 2004-2010 period as shown in Table 3.
Considering the mean diameter increment of Norway spruce trees since the establishment of plantation (1994 = trees 17 years old in 2010), its values per plot are extremely variable (from 0.
However, in case of all Norway spruce trees regardless their location in both very dense plots (e.
The same positive significant correlation was found between the dbh and mean crown diameter of individual Norway spruce trees as shown in Figure 4.
These values confirm the positive effect of early started and high intensity cleaning-respacing on Norway spruce stand stability, the present level (2010) of slenderness index (between 0.
Taking into account the preliminary outputs of this case-study, one may conclude that, in dense, young and pure Norway spruce plantations:
When the initial stand density is as high as the one used traditionally in Romanian plantations of Norway spruce, such reduction of density is possible and necessary through cleaning-respacing, any delayed intervention leading to even more unstable stands to snow damages.
The inner accessibility of young and crowded Norway spruce plantations can be improved by opening silvicultural racks during the early stages of development.
Obviously, for a more profitable trade-off between the economic and stability constraints of early Norway spruce silviculture, would be better: