Petter Nilsen

Main Findings and Future Challenges in Forest Nutritional Research and Management in the Nordic Countries

Previous research has documented that nitrogen fertilization can lead to a significant tree growth increase in large parts of Scandinavia. Nutrient management of Nordic forests is currently under debate, mainly because environmental values are believed to be unnecessarily endangered by these actions. Nutrient management including fertilization, liming, recycling of wood ash or application of alternative nutrient sources can counteract nutrient deficiencies and imbalances, and be used for compensating the nutrients removed through harvesting. For successful implementation of nutritional management measures, several questions should still be studied. These questions mainly concern diagnosis of the need for applications, nutritional sustainability and treatment effects on the forest ecosystem and the surrounding environment.

Nitrogen and drought effects on ectomycorrhizae of Norway spruce [Picea abies L.(Karst.)]

Effects of N addition and drought on ectomycorrhizae of Norway spruce trees were investigated in an outdoor pot lysimeter study. Three levels of N were applied as ammonium nitrate in irrigation water for five years; ambient rainwater (N0) and 5 (N5) and 15 (N15) times this N concentration. Mean annual N addition during the five years corresponded to 5, 27 and 82 kg·ha-1·y-1 for the N0, N5 and N15 treatments, respectively. During the third and fifth growth seasons two levels (lengths) of drought were artificially induced in addition to a watered control. Soil cores taken from each pot lysimeter were analyzed for mycorrhizal colonization and ectomycorrhizae were categorized according to macroscopic morphology. Drought decreased mycorrhizal colonization significantly. There was a significant interaction of drought and N effects on reduction of the mycorrhizal colonization. Although all of the mycorrhiza types were influenced by drought, only Cenococcum geophilum showed a significant change. N treatment alone did not show any significant effect either on mycorrhizal colonization or mycorrhizal types.

Fertilization Experiments on Forest Mineral Soils: A Review of the Norwegian Results

The paper gives a brief overview of the background, history and main results of forest fertilization experiments on mineral soils in Norway. Positive results of initial phosphorus (P) fertilization on survival and growth of Norway and Sitka spruce have only been achieved in the coastal districts of western Norway. Other elements have seldom given any significant effect. In young and old stands of Norway spruce and Scots pine nitrogen (N) fertilization with 150 kg N ha -1 usually gave increment increases in the range of 1-2 m 3 ha -1 yr -1 , for a period of 6-8 yrs after application. Given individually, no other element has proved stimulating to stem growth in a similar way. In young Norway spruce stands P has often given additional growth response when given together with N. Liming has been shown to have no or negative effects on tree growth. Fertilization experiments have changed from being management orientated towards addressing the problems of possible nutrient imbalances.

Effect of nitrogen on drought strain and nutrient uptake in Norway spruce Picea abies (L.) Karst.) trees

A field lysimeter study was established with the aim of investigating the effect of nitrogen availability upon drought strain in Norway spruce trees. Forest soil (Typic Udipsamment) was filled in lysimeters 1 m in diameter and 1 m deep. Small trees of Norway spruce from five different clones were planted in the lysimeters. Roofs under the canopy of the trees ensured full control of water and nutrient input. Three levels of nitrogen were given to the trees during five years; ambient rainwater, and five and fifteen times this N concentration, respectively. Additional N was given as NH4NO3 in irrigation water. Mean annual N-addition during the five years corresponded to 5, 27 and 82 kg per ha and year for the three treatments, respectively. During the third and fifth growth season drought was artificially induced. In addition to a watered control, two levels of drought were applied, representing water deprivation for 2 and 3 months, respectively, in 1990 and 3 and 4 months, respectively in 1992. A higher water consumption in the nitrogen fertilized trees during the droughts resulted in a significantly lower pre-dawn shoot water potential compared to the trees receiving ambient rain N. The interaction between drought and nitrogen fertilization was clear also for photosynthesis and transpiration. A decrease in height- and diameter increment caused by drought was most pronounced in the 82 kg N ha−1 yr−1 treatment. A water strain integral showed a strong positive correlation to the needle biomass of the trees. Foliar concentrations of several nutrients decreased significantly with increasing drought strain in the trees. Concentration of potassium and boron were especially low and visual symptoms of deficiency occurred.

Production of Picea abies in South-east Norway in Response to Climate Change: A Case Study Using Process-based Model Simulation with Field Validation

A process-based model was used to simulate biomass production of Norway spruce under both current climate and climate change scenarios. The model was parameterized for Nordmoen in south-east Norway using real climate data for the period 1987-1989. The model was applied to predict the biomass production responses to three climate change scenarios. The results showed that net primary production (NPP) increased by 7% under an elevated annual mean air temperature of 4°C from the current 10.1 t dry mass ha -1 yr -1 . A doubled current ambient CO 2 concentration significantly increased NPP by 36%. The scenario of both elevated temperature and elevated CO 2 concentration led to an increase in the NPP of 49%, higher than the sum of the two effects acting singly. The results also showed that forest production responses to climate change depend on the conditions of climate used for reference.

Nitrogen cycling in Pinus sylvestris stands exposed to different nitrogen inputs

The objective of this study was to quantify the effects of high nitrogen (N) inputs on N cycling in a 35–45-yr-old Scots pine (Pinus sylvestris L.) forest. Nitrogen was added annually (single doses) as NH4NO3 in doses of 0 (N0), 30 (N1) and 90 (N2) kg N ha−1 yr−1. The only N input to the N0 plots was atmospheric deposition of 10 kg N ha−1 yr−1. The N cycle in these plots was tight, with almost complete retention of the incoming N. In the N1 plots the N retention was 83% after 9 yrs of N addition. The trees were the major sink, but the soil also contributed to the N retention. In the N2 plots the N retention was 63%, being mainly accounted for by accumulation in the soil. The leaching of N from the N2 stands was as high as 35 kg N ha−1 yr−1. The N2 system was N saturated.

Nutrient balance in Scots pine (Pinus sylvestris L.) forest. 5. Tree growth in a field plot experiment

A field plot experiment on fertilization with N, Mg and P in Scots pine forest was established. The experiment had a factorial design with three levels of N (0, 30 and 90 kg ha−1), two levels of Mg (0 and 1.5 kg ha−1) and two levels of P (0 and 5.3 kg ha−1). The application was done annually. There was a significant growth increase for the two N treatments. During a period of 5-years the mean increase in volume increment was 2.3 and 4.5 m3 ha−1 for the 30 N and 90 N kg ha−1 yr−1 treatments, respectively. This represents a percentage increase in volume increment of 53 and 102% compared to the untreated control plots. No significant growth effect of P and Mg application was detected, either alone or in combination with N. The needle nutrient concentrations have been followed along with the annual measurements. An increase in N-concentration was detected after the first growing season in the N treated trees. After five years the Mg concentrations in the needles are lower in these treatments. The one year old needles have concentrations as low as 0.05% Mg. No visible deficiency symptoms have been observed. The field experiment effects demonstrates that N is still the most limiting nutrient under these conditions and that there is a relative large potential for N accumulation in these forest types without negative effects.

Effect of nitrogen on drought resistance of Norway spruce and scots pine

Abstract Six fertilization experiments in mature spruce and pine stands were analyzed for growth response during two successive extremely dry summers, to evaluate the hypothesis that nitrogen deposition increases canopy growth and water demand, leaving the trees less drought resistant. Nitrogen had been applied at rates varying from a single application of 150 kg ha −1 , up to repeated applications of 600 kg ha −1 . The last application was 2–5 years before the drought. In two experiments, growth showed a slight depression during one of the two dry years, compared with what would be expected as normal. The growth depression was rather small and absolute growth was far greater than that of the control tress. In the other four experiments, no signs of deviation from normal growth were detected. The study indicates that the present level of nitrogen deposition in southern Norway has not significantly reduced the drought resistance of spruce and pine forests.

Counteractions Against Acidification in Forests Ecosystems. Effects on stream water quality after dolomite application to forest soil in Gjerstad, Norway

The deposition of strong acids is one of many threats to forest ecosystems and viable forestry. Several counteractions against acidification have been launched, e.g. changes in forestry management and the introduction of chemicals. The inter-institutional programme “Counteractions Against Acidification in Forest Ecosystems” was established in 1993 to evaluate existing knowledge and run experimental and fullscale field experiments. A total of 240 metric tons of coarse dolomite powder was spread by helicopter in September 1994 on 84 ha forest catchment dominated by pine (Pinus sylvestris) and Norway spruce (Picea abies). Potential desirable and undesirable effects after this carbonate application may be less pronounced than recorded at other sites due to the relatively moderate dose (3 tons ha−1). Pre-liming stream water quality (mean values for May 1993-September 1994) was as follows: pH 4.8; Ca 1.13 mg L−1; reactive Al (RAl) 248 μg L−1; inorganic monomeric Al (Al) 72 μg L−1. The reference station was slightly higher in Ca and slightly lower in both RAl and Al. Dolomite application resulted in a significant increase in pH to 5.7 as mean value for the post-liming period (September 1994-April 1995). Both Ca and Mg increased significantly after liming, and both RAl and Al, declined significantly. The rapid detoxification of stream-water may be explained by dissolution of dolomite particles in both streams and catchment, a resulting pH increase and change in Al species composition. Retention of Al in the catchment probably explains the reduction in RAl. No increase in NO3, total N, total P or TOC was recorded the first seven months.