Ingrowth, survival and height growth of small trees in uneven-aged Picea abies stands in southern Finland

Abstract

The purpose of the study was to analyse height growth, mortality, and ingrowth of individual small-sized trees in uneven-aged spruce-dominated stands. It was based on experimental data from 16 stands for a 15-year observation period including four measurements with a 5-year interval. In the data of this study, the heights of small-sized trees varied from 0.1 to about 9 m. Results showed that the growth of small trees was rather slow, particularly in the smallest size classes. With average growth rates it would take about 60 years for a freshly emerged spruce germinant to achieve 1.3 m in height. The stand density, site quality and selection cuttings affected the growth of small-sized spruces. Average five-year mortality rates for spruce, birch and pine were 17.0%, 40.9% and 33.9%, respectively. Annual ingrowth rates with the threshold height of 1.3 m for the three species were on average 30.4, 2.8 and less than 0.1 trees per hectare, respectively. Even if, a selection cutting of modest intensity (25% of basal area removed on average) seemed to have accelerated the growth of small spruces, it is recommended that more intensive harvestings be applied to enhance the survival and growth of small spruces. It is also concluded that shade intolerant species like birch and pine do not seem to be capable of developing into viable undergrowth in spruce selection stands with their current levels of stand density.

Post-harvest height growth of Norway spruce seedlings in northern Finland peatland forest canopy gaps and comparison to partial and complete canopy removals and plantations

“…Based on simulations with the model constructed in this study, it would take 11-12 years for a 10 cm-tall spruce seedling to reach a height of 1.3 m. If an assumption is made that for a spruce seedling it takes three to five years to reach 10 cm (Hökkä et al 2011), breast height can be reached in 20 years or less in the gaps of this study site. That would be significantly quicker when compared to the average of 60 years in an uneven-aged stand in southern Finland mineral soil sites (Eerikäinen et al 2014), or 24-47 years as reported by Lundqvist (1989) from mineral soil sites in Sweden. One possible reason may be that after uneven-aged cutting in the more southerly located mineral soils sites, the retained stand remains rather stocked (Eerikäinen et al 2014) and conditions more shady than after cutting canopy gaps in naturally more open (e.g., Heikurainen 1971;Norokorpi et al 1997) spruce mire stands in northern Finland.…”

“…In this study the average growth was two to three times better than in uneven-aged harvest stands observed in southern Finland by Eerikäinen et al (2014) or in Sweden (Lundqvist 1989). Based on simulations with the model constructed in this study, it would take 11-12 years for a 10 cm-tall spruce seedling to reach a height of 1.3 m. If an assumption is made that for a spruce seedling it takes three to five years to reach 10 cm (Hökkä et al 2011), breast height can be reached in 20 years or less in the gaps of this study site.…”

“…Eerikäinen et al's (2014) results on spruce height growth after uneven-aged harvest in mineral soil experimental sites in southern Finland also indicated very slow rates of growth. During a 15-year period after cutting for a medium growth forest site, the annual height growth varied from 1 to 4 cm (Table 3).…”

“…Eerikäinen et al (2014) also used growth model analysis as the method to investigate factors affecting the height growth of spruce seedlings. Annual shoot length was used as the response variable.…”

“…Eerikäinen et al (2014) investigated the growth rate of seedlings growing in uneven-aged cut stands in southern Finland and concluded that spruce seedling height growth was very slow, only a couple of centimetres annually and strongly related to tree height. They also found that cutting intensity influenced the growth of the seedlings.…”