Staffan Jacobson

Impact of whole-tree harvesting and compensatory fertilization on growth of coniferous thinning stands

Abstract A series of 16 field experiments was established to quantify the growth response of first-thinning stands of Pinus sylvestris and Picea abies to whole-tree harvesting (WTH), and to estimate the need for nutrient compensation. The experiments were undertaken in Finland, Norway and Sweden and represent a wide range of climatic and soil conditions. The biomass and nutrient amounts removed were estimated on the basis of felled sample trees. On average, WTH reduced tree volume growth in both pine and spruce stands (5% and 6%, respectively) during the first 10-year period. The growth reduction was counteracted by fertilization (NPK) and the results indicate that the reduction was an effect of reduced N supply. The inclusion of various site descriptive variables in the linear models did not explain variation in growth response to WTH. Since the growth reductions due to WTH after 10 years were still present, the observation period needs to be extended.

Effects on ground vegetation of the application of wood ash to a Swedish Scots pine stand

Summary The impact of different doses and types of wood ash on ground flora was studied over a 5-year period following ash application to a medium-aged Scots pine stand in the central part of Sweden. Generally, there were only minor changes in the vegetation cover as a result of the treatments, and the species composition was unaltered after five years. When treated with hardened and crushed wood ash, the three most common bryophytes reacted rapidly, displaying severe visible damage in the initial phase of the study period. Two years after ash application, the bryophytes had started to recover, and after five years no visible damage could be discerned. At the highest ash dose (9 tons ha−1), however, the cover of bryophytes was significantly reduced, even after five years. No visible damage to the bryophytes was found after treatment with pelleted ash or after N treatment, and no visible damage to lichens was found for any treatment. However, by the end of the study period, the addition of wood ash, including the pelleted ash, had significantly reduced the cover of Cladina lichens. All wood ash treatments tended to lead to a decrease in the cover of dwarf shrubs. Nitrogen addition tended to increase the cover of Vaccinium myrtillus and decrease the cover of Vaccinium vitis-idaea and Calluna vulgaris. The results from this study highlight the need for legal restrictions on the chemical and physical properties of wood ash recycled within forest systems, in order to avoid a negative impact on ground flora. Die Folgen der Ausbringung von Holzasche auf die Bodenvegetation in einem schwedischen Waldkiefernbestand. Die Auswirkungen unterschiedlicher Dosierungen und Typen von Holzasche auf die Bodenflora wurde uber eine 5-Jahres-Periode untersucht, im Anschluss an die Aschen-Ausbringung auf einen mittelalten Waldkiefernbestand in Zentral-Schweden. Generell resultierten nur geringe Veranderungen in der Vegetation als Folge der Behandlungen, und die Artenzusammensetzung hatte sich nach funf Jahren nicht geandert. Nach einer Behandlung mit harter und zerstossener Holzasche reagierten die drei haufigsten Moosarten sehr schnell und zeigten einen gut sichtbaren Schaden in der Anfangsphase der Untersuchungsperiode. Zwei Jahre nach der Aschen-Ausbringung hatten die Moose begonnen, sich zu erholen, und nach funf Jahren konnte kein sichtbarer Schaden mehr entdeckt werden. Bei der hochsten Aschendosis (9 Tonnen pro ha) war jedoch die Moos-Deckung deutlich reduziert, auch nach funf Jahren noch. Nach der Behandlung mit Pellet-Asche oder nach N-Behandlung konnte kein sichtbarer Moos-Schaden festgestellt werden, und auch fur die Flechten gab es bei keiner Behandlung einen sichtbaren Schaden. Am Ende der Untersuchungsperiode hatte die Zugabe von Holzasche, inklusive der Pellet-Asche, jedoch eine signifikante Reduktion in der Deckung von Cladina Flechten zur Folge. Alle Holzasche-Behandlungen tendierten dazu, die Deckung an Zwergbuschen zu verringern, die Stickstoff-Zufuhr tendierte die Deckung von Vaccinium myrtillus zu erhohen und die Deckung von Vaccinium vitis-idaea und Calluna vulgaris zu verringern. Die Ergebnisse dieser Studie zeigen die Notwendigkeit fur gesetzliche Vorgaben zu den chemischen und physikalischen Eigenschaften der im Forst recycelten Holzasche, um negative Einflusse auf die Bodenflora zu verhindern.

Growth response of coniferous stands to whole‐tree harvesting in early thinnings

A series of 15 field experiments was established to quantify the growth response of first‐thinning stands of Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst) to whole‐tree harvesting and to estimate the need for nutrient compensation. The experiments were undertaken in Finland, Norway and Sweden and represent a wide range of site conditions. The site index (H 100) of Scots pine stands varied from 19 to 29 m, and that of Norway spruce stands from 28 to 36 m. Total amounts of biomass and nutrients removed were calculated based on data obtained from felled sample trees. During the first 5‐yr period the growth response to the removal of logging residues varied considerably in both pine and spruce stands. Regression analyses did not reveal any functions that explained the variation in results satisfactorily. In cases where whole‐tree harvesting influenced tree growth negatively, this effect was counteracted by compensatory fertilization. It was concluded that to determine the respons...

Effects of repeated urea doses on soil chemistry and nutrient pools in a Norway spruce stand

Abstract Pools of macro-nutrients in soil and vegetation were studied in an old fertilization experiment with a large previous input of N. Different doses of N, in the form of urea, had been added four times during a 20-year period. In total, between 480 and 2400xa0kg Nxa0ha −1 had been given. The experiment was established in a relatively productive Norway spruce stand and the expectation was that the large N input would cause an accelerated leaching of N, especially nitrate, accompanied by soil acidification and losses of several nutrients. The aim was to test for possible residual effects. Thirteen years after the last N addition, samples from the aboveground part of trees, field layer, S-layer, humus layer and mineral soil (0–10xa0cm) were analyzed for concentrations of most major nutrients. Nutrient pools were calculated. In the humus layer, the concentration of N increased and the C/N-ratio decreased with increasing N dose. The calculated recovery of added N in soil including ground vegetation was complete for the lowest N dose, while it was 25–50% for higher doses. The amount of N retained was unaffected by the N dose. The amount of extractable P in the upper part of the mineral soil was negatively correlated with N dose, as was also the concentration of total P in the S-layer. Neither soil pH, nor concentrations or amounts of Ca, Mg and K were affected by the previous fertilization. The calculated total soil-plant pool was only influenced by N dose in the case of P, which was 20% lower at the highest N dose compared with unfertilized conditions. Despite the large extra N input, the nutritional changes in plants and soil of the actual study site seemed surprisingly small.

Stem-growth response of Pinus sylvestris and Picea abies to nitrogen fertilization as related to needle nitrogen concentration

Abstractu2003Responses of stem-volume growth to N application were evaluated in relation to foliar N concentrations. Data from N-fertilization experiments in 28 Pinus sylvestris stands and 21 Picea abies stands were used. Relative stem-growth responses were negatively related to concentrations of N in current-year needles of unfertilized trees. There appeared to be a threshold value of 15–16 mg (g DM)–1 N in current-year needles, above which N-application is unlikely to stimulate growth. However, relations were non-significant between N concentrations in current-year needles and the absolute stem-growth response [dm3 ha–1 (5 years)–1]. The indicated threshold values are discussed in relation to other variables reflecting the N richness of the environment.-->

Is tree growth in boreal coniferous stands on mineral soils affected by the addition of wood ash

Increasing use of forest fuels for energy production is generating greater quantities of wood ash. In Sweden, it is recommended that this ash should be returned to the forest to counter soil acidification and avoid potential future nutrient deficiencies, but the effects on tree growth require clarification. Thus, 10 field experiments were established in Sweden in 1990–2006 to study the effects of adding wood ash of various origins, doses and combinations of both ash and nitrogen on stem growth in Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies L. Karst.) stands on mineral soil. Observations after 5–15 years show that growth responses were strongest when N was added, either alone or with wood ash. Growth responses to additions of wood ash without N were small and variable and statistically insignificant at all study sites. However, there were indications that adding wood ash may increase stem-wood growth at fertile sites and decrease it at less fertile sites. Hence, at fertile sites, it may compensate for the growth reductions that normally follow whole-tree harvests, at least temporarily, presumably due to its effects on soil N turnover. At less fertile sites, adding N is probably essential to counteract these growth reductions.

Long-term effects of nitrogen fertilization on soil chemistry in three Scots pine stands in Sweden

Adding nitrogen to coniferous forests on mineral soils will increase stem-wood growth in most boreal forests. The addition of nitrogen affects soils and waters as well. This investigation was conducted to evaluate the long-term effects of nitrogen fertilization at different intensities on soil chemistry in nitrogen-limited ecosystems. The study was performed at three experimental sites that were originally established around 1980 in Scots pine (Pinus sylvestris L.) stands. Fertilization regimes with applications ranging from conceivable commercial rates to very intensive rates (3× 150xa0kg N·ha–1 up to 12× 150xa0kg N·ha–1) had been applied. Samples were collected from the FH horizon at all sites and 0–20xa0cm in the mineral soil at two sites and analyzed for pH and major nutrients. The carbon to nitrogen ratio in the FH horizon decreased with increasing total nitrogen application, while the concentrations and contents of nitrogen and exchangeable magnesium and phosphorus increased. The concentration and content...

Effects of Previous High N Addition on Nutrient Conditions in Above-ground Biomass of a Picea abies Stand in Sweden

Deposition of air pollutants, together with intensified harvesting practices, has led to concern about the declining base cation status and the acidifying effects in the soil, with possible implications for silviculture. The aim of this study was to analyse the effects of a previous high N addition on the nutritional status in the above - ground part of a tree stand. We sampled various biomass fractions in a highly productive Norway spruce (Picea abies (L.) Karst.) stand in the province of Värmland, western Sweden. The experimental plots had been fertilized with urea four times at intervals of 5 yrs, the last time being 13 yrs before our study. The total amount of N added was in the range 480 - 2400 kg ha?1. Despite the high N addition and an insignificant growth increase following N input, there were no obvious residual changes of nutrient concentrations in the above - ground parts of trees.

The distribution of logging residues and its impact on seedling establishment and early plant growth in two Norway spruce stands

ABSTRACT In Fennoscandia, logging residues (LR) are increasingly being harvested to provide fuel for renewable energy. However, the removal of LR is thought to lead to decreased growth in the next generation of trees. The effect on tree growth has generally been obtained by comparing the total removal of residues with retained residues spread evenly on the ground. With current clear-cutting practices, residues can be left with different spatial distributions, confounding the effects of residue removal. Field experiments were, therefore, established at two Norway spruce sites, comprising six treatments with varying distributions and volumes of residues. Before planting seedlings, the sites were disc-trenched. At one of the sites, seedling survival was significantly lower when all residues were removed immediately. At both sites, after 10 years there were statistically significant growth losses after removal of residues. There were no differences in plant growth if the residues were concentrated in small heaps and strings, simulating the normal distribution of LR following stem-only harvesting, compared with residues left evenly spread on the ground. To determine the duration of the observed growth effects, these study sites must be monitored more long term.

Clonal variation in root suckering ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.)

ABSTRACT Current information on the root sucker ability of hybrid aspen (Populus tremula L. × P. tremuloides Michx.) is in most cases based on clone mixtures. In this study, we could separate the performance among clones by using two experimental sites with monoclonal plots of the crossing. The natural regeneration was followed for 2 years after harvest of the formerly planted stands, clear-cut at 22 and 25 years of age, respectively. We found that clonal differences were present in the number of root suckers produced per area unit and their biomass production. However, all included clones produced sufficiently many root suckers for a successful regeneration. To receive a more complete evaluation of the root sucker dynamics for future selection on the clonal level, further studies are needed where vitality, self-thinning and effects of thinning measures are coupled to the goal of the aspen forestry.