Control of Heterobasidion in Norway Spruce Stands: The Impact of Stump Cover on Efficacy of Urea and Phlebiopsis gigantea and Implications for Forest Management

This study investigated the efficacy of Rotstop®, a native Latvian Phlebiopsis gigantea strain and 35% urea solution in combination with a stump cover treatment to control against natural spore infection by Heterobasidion spp. upon precommercial thinning of Norway spruce in three stands growing on former agricultural lands. The major findings were that (i) infection rates of Heterobasidion spp. on stumps treated with the native P. gigantea strain, Rotstop® or urea are similar when stumps are uncovered, and (ii) stump cover promotes stump colonization by the Latvian P. gigantea strain and Rotstop®, leading to a significantly smaller relative area colonized by Heterobasidion spp., as well greater efficiency against Heterobasidion in comparison with urea. Covering of stumps appears beneficial for controlling Heterobasidion stump colonization and may be valuable to forest owners if used in small-scale operations, but it is impractical in automatized thinnings, where managers should consider using regular Rotstop® without covering the stumps.

Precommercial Thinning Increases Spruce Yields in Boreal Mixedwoods in Alberta, Canada

A few studies in young mixedwood stands demonstrate that precommercial thinning of aspen at early ages can improve the growth of spruce and increase stand resilience to drought. However, information on tree and stand responses to thinning in older mixedwood stands is lacking. To address this need, a study was initiated in 2008 in Alberta, Canada in 14 boreal mixedwood stands (seven each at ages 17 and 22). This study investigated growth responses following thinning of aspen to five densities (0, 1000, 2500, 5000 stems ha−1 and unthinned (control)). Measurements were collected in the year of establishment, and three and eight years later. Mortality of aspen in the unthinned plots was greater than in the thinned plots which were not significantly different amongst each other. Eight years following treatment, aspen diameter was positively influenced by thinning, while there was no effect on aspen height. The density of aspen had no significant effect on the survival of planted spruce. Spruce height and diameter growth increased with both aspen thinning intensity and time since treatment. Differentiation among treatments in spruce diameter growth was evident three years from treatment, while differentiation in height was not significant until eight years following treatment. Yield projections using two growth models (Mixedwood Growth Model (MGM) and Growth and Yield Projection System (GYPSY)) were initialized using data from the year eight re-measurements. Results indicate that heavy precommercial aspen thinning (to ~1000 aspen crop trees ha−1) can result in an increase in conifer merchantable volume without reducing aspen volume at the time of harvest. However, light to moderate thinning (to ~2500 aspen stems ha−1 or higher), is unlikely to result in gains in either deciduous or conifer merchantable harvest volume over those of unthinned stands.

Cost–Benefit Analysis of Measures to Reduce Windstorm Impact in Pure Norway Spruce (Picea abies L. Karst.) Stands in Latvia

Wind is one of the major natural forest disturbances in Europe, and reduces the total economic (including carbon sequestration) value of forests. The aim of this study was to assess the financial benefit of silvicultural measures in young, pure, planted Norway spruce stands by reduction in the impact of wind damage over the rotation period. The analyzed measures are promptly applied precommercial thinning and low-density planting with improved plant material. Spatial information on factors affecting wind damage—wind climate and soil—were gathered and combined with the local growth model and empirical data from tree pulling experiments in Latvia to assess the economic value loss due to wind damage over a rotation period. Timely precommercial thinning and lower-density planting with improved plant material would ensure a positive net present value with an interest rate of 3%, using conservative estimates. The financial benefit is highest in windier (coastal) regions and for the planting, followed by moderate thinning. The results demonstrate that, even without changing the dominant tree species, a considerable reduction in wind-damage risk can be achieved.

Effects on understory biomass and forage 8–10 years after precommercial thinning of Sitka spruce – western hemlock stands in southeast Alaska

In southeast Alaska, United States, multiple-use forest management objectives include both timber production and wildlife habitat. Following stand-replacing disturbances such as clear-cutting, Sitka spruce (Picea sitchensis (Bong.) Carrière) and western hemlock (Tsuga heterophylla (Raf.) Sarg.) naturally regenerate and competitively dominate resources, excluding understory biomass and biodiversity. Thinning may mitigate the effects of canopy closure and permit understory development, but evidence of the effect on understories 8–10 years after thinning is lacking. We report results 4–5 and 8–10 years after thinning experiments on the Tongass National Forest to demonstrate the effects of precommercial thinning (thinned versus control), stand age (15–25, 25–35, and 35–50 years), and weather on understory dynamics and Sitka black-tailed deer (Odocoileus hemionus sitkensis Merriam, 1898) forage availability. Stand density negatively affected understory biomass, whereas temperature and precipitation positively interacted to increase biomass. Thinning had an enduring effect on understories, with biomass at least twice as great in thinned versus unthinned stands through year 10. We identified compositional differences from thinning as stand age class increased. Deer forage responded similarly to biomass, but thinning-induced differences faded with increased winter snowfall scenarios, especially in older stands. This study aids the understanding of stand overstory and understory development following silvicultural treatments in the coastal temperate rain forest of Alaska and suggests management implications and applications for balancing objectives throughout the forest type.

Benefits of juvenile stand management in Finland—impacts on wood production based on scenario analysis

We evaluated the impacts of juvenile stand management on wood production based on a nationwide scenario analysis. Measured plot-level information of the Finnish 11th National Forest Inventory (NFI) from juvenile stands formed the initial data for the analysis. To represent a total of 2.5 million hectares of productive forest land available for wood production, 6900 sample plots were selected. We predicted the development of the sample-plot stands for the next 100 years using the Motti stand simulator. We examined the impacts of juvenile stand management, including early cleaning and precommercial thinning, with three scenarios of different intensities of early-stage management (intensive, no management and business-as-usual). The results showed the benefits of juvenile stand management: earlier harvesting revenues, larger total removals, more valuable wood in the removals, and additional benefits that are associated with the first commercial thinning (i.e. no need for clearing before thinning, a larger stem size of removed trees). The main downside of juvenile stand management was the cost of the early cleaning and precommercial thinning. According to the results, a €560 million increase in costs would result in a €1700 million increase in stumpage earnings in Finnish forests during the next 100-year period. The 34 million m3 increase in the sawlog yield together with 28 million m3 decrease in the pulpwood yield also demonstrated the nationwide potential for increasing valuable sawlog production by intensive management of juvenile stands.