Comparison of different site preparation techniques: quality of planting spots, seedling growth and pine weevil damage
Comparison of different site preparation techniques: quality of planting spots, seedling growth and pine weevil damage
Kristina Wallertz 0 1 2 3
Niklas Björklund 0 1 2 3
Karin Hjelm 0 1 2 3
Magnus Petersson 0 1 2 3
Lars‑Göran Sundblad 0 1 2 3
Kristina Wallertz 0 1 2 3
0 The Forestry Research Institute of Sweden , Skogforsk, Ekebo 2250, 26890 Svalöv , Sweden
1 Department of Ecology, Swedish University of Agricultural Sciences , Box 7044, 750 07 Uppsala , Sweden
2 Asa Forest Research Station, Swedish University of Agricultural Sciences , Lammhult , Sweden
3 Södra Forest Owner Association , Skogsudden, 351 89 Växjö , Sweden
In northern Europe, there are high risks of severe pine weevil (Hylobius abietis) damage to newly planted conifer seedlings. Site preparation is one of the most important measures for reducing these risks and as several studies have shown the damage is highly dependent on the amount of pure mineral soil around the seedlings. We investigated effects of three site preparation techniques: (1) disc trenching with a conventional Bracke T26, (2) MidiFlex unit and (3) soil inversion with a Karl Oskar unit on characteristics of the planting spots, growth and pine weevil damage and survival rates of untreated and insecticide treated planted Norway spruce (Picea abies) seedlings. All three site preparation techniques reduced pine weevil damage in comparison with no site preparation, and the proportion of spots with pure mineral soil they created was inversely related to the rate of mortality caused by pine weevil. The results indicate that the quality of the planting spots depends on the technique used. In areas where pine weevil is the major threat to seedling survival, the amount of mineral soil in the planting spots is the most important factor in order to protect the seedling from damage. Without site preparation most planting spots consisted of undisturbed humus. Generally, the Karl-Oskar created the most spots with pure mineral soil, but on very stony soils the Bracke T26 created more mineral soil spots than other methods. Site preparation is a valuable tool in order to improve survival in regeneration areas and it is of great importance to make the right choice of technique depending on the particular circumstances on the actual site.
Hylobius abietis; Pine weevil; Planting; Site preparation techniques
Introduction
The management of vegetation competition in forests is an integral part of silvicultural
practices in many parts of the world
(Wagner et al. 2006; Richardson et al. 2006; Newton
2006)
. Mechanical site preparation is therefore used in many countries in order to reduce
competition from other vegetation (Löf et al. 2012; Nilsson and Örlander 1999a, b;
Thiffault and Jobidon 2006
), but also to improve growing other conditions for newly planted
seedlings (Sutton and Bedford 2001; Petersson et al. 2005;
Luoranen and Viiri 2012
). The
improvement is due to interactive effects of many factors that facilitate seedlings’
establishment. These include alterations of the microenvironment that increase nutrient availability
(Munson et al. 1993; Schmidt et al. 1996. Grossnickle 2000)
and beneficial changes in both
soil moisture and temperature
(Folk and Grossnickle 2000)
.
Another, often crucial factor is that mechanical site preparation can affect the frequency
and severity of attacks by pine weevils (Hylobius abietis), the most serious pests of planted
conifer seedlings on forest land in northern Europe
(Leather et al. 1999; Örlander and
Nilsson 1999; Långström and Day 2004)
, The seedlings’ survival is highly dependent on the
degree of suppression of damage caused by the weevils. To reduce damage, large
proportions of conifer seedlings are treated with insecticides, or various coatings or feeding
barriers. However, at most sites there is high feeding pressure from pine weevils, and at least
two measures must be used to protect seedlings sufficiently (Petersson and Örlander 2003).
If no measures are applied to protect newly planted seedlings, up to 80% of them may die
during the first 3 years
(von Sydow 1997)
. Several studies have shown that site preparation
methods can reduce the damage caused by pine weevils
(Lekander and Söderström 1969;
von Sydow 1997; Örlander and Nilsson 1999; Sutton; 1993)
, especially if they result in
planted seedlings being surrounded by pure mineral soil (
Lindström et al. 1986
;
Björklund
et al. 2003
; Petersson and Örlander 2003; Petersson et al. 2005). Pine weevils seem to
avoid areas of mineral soil by increasing their speed and moving straighter. This reduces
the time they remain on the patch resulting in less feeding on those seedlings compared to
seedlings planted in humus
(Kindvall et al. 2000)
.
In practice, planting spots’ quality varies considerably depending on site conditions, site
preparation method and equipment used but the result could also be affected by the skills
and motivation of the operators.
Disc-trenching (...truncated)