In the Nordic countries Finland, Norway and Sweden, the most common regeneration method is planting after clearcutting and, often, mechanical site preparation (MSP). The main focus of this study is to review quantitative effects that have been reported for the five main MSP methods in terms of survival and growth of manually planted coniferous seedlings of Norway spruce ( (L.) Karst.), Scots pine ( L.) and lodgepole pine ( var. Engelm.) in clearcuts in these three countries. Meta analyses are used to compare the effects of MSP methods to control areas where there was no MSP and identify any relationships with temperature sum and number of years after planting. In addition, the area of disturbed soil surface and the emergence of naturally regenerated seedlings are evaluated. The MSP methods considered are patch scarification, disc trenching, mounding, soil inversion and ploughing. Studies performed at sites with predominately mineral soils (with an organic topsoil no thicker than 0.30 m), in boreal, nemo-boreal and nemoral vegetation zones in the three Fenno-Scandinavian countries are included in the review. Data from 26 experimental and five survey studies in total were compiled and evaluated. The results show that survival rates of planted conifers at sites where seedlings are not strongly affected by pine weevil ( L.) are generally 80â90% after MSP, and 15â20 percent units higher than after planting in non-prepared sites. The experimental data indicated that soil inversion and potentially ploughing (few studies) give marginally greater rates than the other methods in this respect. The effects of MSP on survival seem to be independent of the temperature sum. Below 800 degree days, however, the reported survival rates are more variable. MSP generally results in trees 10â25% taller 10â15 years after planting compared to no MSP. The strength of the growth effect appears to be inversely related to the temperature sum. The compiled data may assist in the design, evaluation and comparison of possible regeneration chains, i.e. analyses of the efficiency and cost-effectiveness of multiple combinations of reforestation measures.Picea abiesPinus sylvestrisPinus contortalatifoliaHylobius abietis
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.
Highlights • Analysis of survey data from 292 reforestation areas in northern Sweden show that the probability of pine weevil damage can be predicted with a standard error of 0.12. • Three variables are important in the optimal model: proportion of seedlings in mineral soil, age of clear-cut, and temperature sum. • Temperature sum in the model can be adjusted to reflect future climate scenarios.
Mechanical site preparation is commonly used to increase survival and early growth of newly planted seedlings. Ideally, any early positive effects of site preparation should persist for a long time, but concerns have been raised as to whether intensive site preparation might have a negative effect on the long-term productivity of a stand. The present study was therefore designed to investigate the long-term effects of different site-preparation methods on productivity and determine any possible interactions with tree species and site fertility. In the 1980s, a randomized block experiment was established at sites throughout Sweden. Four site-preparation methods of various intensities were performed on different sites: (i) an untreated control, (ii) disc trenching, (iii) mounding, and (iv) ploughing. As a complementary treatment, slash was either retained or removed from some plots. Depending on soil moisture class, geographical position, and site index, Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.), or lodgepole pine (Pinus contorta Douglas ex Loudon) were planted in pure stands. Growth variables such as height and diameter were measured during the first years after establishment. After about 30 years, these variables were remeasured at the level of individual trees. Overall, an increased production of the planted trees after site preparation was found. Neither intensive site preparation (such as ploughing) nor slash removal had any negative effect on the long-term productivity of these experimental stands.
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