Gunnar Thelin

The production of ectomycorrhizal mycelium in forests: Relation between forest nutrient status and local mineral sources

Due to acid rain and nitrogen deposition, there is growing concern that other mineral nutrients, primarily potassium and phosphorus, might limit forest production in boreal forests. Ectomycorrhizal (EcM) fungi are important for the acquisition of potassium and phosphorus by trees. In a field investigation, the effects of poor potassium and phosphorus status of forest trees on the production of EcM mycelium were examined. The production of EcM mycelium was estimated in mesh bags containing sand, which were buried in the soil of forests of different potassium and phosphorus status. Mesh bags with 2% biotite or 1% apatite in sand were also buried to estimate the effect of local sources of nutrients on the production of EcM mycelium. No clear relation could be found between the production of EcM mycelium and nutrient status of the trees. Apatite stimulated the mycelial production, while biotite had no significant effect. EcM root production at the mesh bag surfaces was stimulated by apatite amendment in a forest with poor phosphorus status. The contribution of EcM fungi to apatite weathering was estimated by using rare earth elements (REE) as marker elements. The concentration of REE was 10 times higher in EcM roots, which had grown in contact with the outer surface of apatite-amended mesh bags than in EcM roots grown in contact with the biotite amended or sand-filled mesh bags. In a laboratory study, it was confirmed that REE accumulated in the roots with very low amounts <1 translocated to the shoots. The short-term effect of EcM mycelium on the elemental composition of biotite and apatite was investigated and compared with biotite- and apatite-amended mesh bags buried in trenched soil plots, which were free from EcM fungi. The mesh bags subjected to EcM fungi showed no difference in chemical composition after 17 months in the field. This study suggests that trees respond to phosphorus limitation by increased exploitation of phosphorus-containing minerals by ectomycorrhiza. However, the potential to ameliorate potassium limitation in a similar way appears to be low.

Acidification-induced chemical changes in coniferous forest soils in southern Sweden 1988–1999

Thirty-two Norway spruce [Picea abies (L.) Karst.] and Scots pine (Pinus sylvestris L.) stands in southern Sweden were studied for a period of 12 years to evaluate acidification-induced chemical changes in the soil. Soil, at 20-30 cm depth in the mineral layer, was sampled three times during this period (1988, 1993 and 1999). The results show that pH(BaCl2) in mineral soil decreased by, on average, 0.17 units between 1988 and 1999, accompanied by an increase in aluminium (Al) concentration and a decrease in base saturation in the soil. In 1999, the base saturation was below 5% in 58% of the 32 sites compared with 16% in 1988 and 7% in 1993. Concentrations of calcium (Ca), potassium (K) and magnesium (Mg) are low and decreasing. Based on C/N ratios in humus, 45% of the sites may be subjected to leaching of considerable amounts of nitrate. The results show that the acidification of coniferous forest soils in southern Sweden is continuing, and that the negative effects on the nutrient status in soil are extensive. The results are compared with reference values for productive, long-term sustainably managed boreal coniferous or mixed forest soils and implications for long-term sustainability are discussed.

Trends in needle and soil chemistry of Norway spruce and Scots pine stands in South Sweden 1985-1994

The nutrient status of the trees and soil in 42 stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in Scania, South Sweden was followed from 1985 to 1994. Samples from needles taken in winter 1985, 1987, 1990, and 1994, and soils in 1988 and 1993 were analyzed. Concentrations, as well as ratios to N, of K and Cu in needles of both species decreased by approximately 40% from 1985 to 1994. Soil analyses indicate ongoing soil acidification and leaching of mineral nutrients from the soil profile. Together with deposition data and corroboration from modeled scenarios, these data support the recent contention that one consequence of enhanced deposition of N and S will be the development of nutrient imbalances in trees growing in southern Sweden.

The nutrient status of Norway spruce in pure and in mixed-species stands

Atmospheric deposition of N and S appears to have caused nutrient imbalance in Norway spruce stands in southern Sweden. This calls for a change of forest management to procedures that promote nutrient balance. Studies have shown lower soil acidity in Norway spruce/deciduous mixed stands than in spruce monocultures, but the tree nutrient status in such mixtures has not been much investigated so far. The nutrient status of Norway spruce foliage and top mineral soil chemistry in monocultures and in stands mixed with beech, birch, or oak was investigated through paired comparisons on 30 sites in southern Sweden (27 sites) and eastern Denmark (three sites). In total, 45 mixed stands and 34 pure stands were included in the study. Spruce needles from mixed stands had higher concentrations and ratios to N of K, P, and Zn than needles from pure spruce stands. Among the mixed stands, the K status appeared to be positively correlated with the percentage of deciduous tree basal area. Soil samples from mixed stands had a higher Mg concentration, base saturation, and BC/Al ratio than soil samples from pure stands. The spruce needle nutrient status was comparable in pure stands on fertile sites and in mixed stands on poor sites. We did not detect any differences in spruce tree growth between pure and mixed stands. This paper discusses possible reasons for a positive effect on the tree nutrient status in mixed-species stands and the possibility of using mixed-species stands as a forest management procedure to avoid nutrient imbalance

Sustainability in spruce and mixed-species stands

It is important to find and develop forest management strategies that do not result in the depletion of soil nutrient pools and at the same time are financially competitive in relatively short-term, 1–2 rotations. Mixed-species stands, which combine the elements of fast growing, highly productive softwood and more slowly growing, high quality hardwood, appear to be an interesting alternative in this respect, one worthy of further investigation. Among the mixtures of trees tried out in southern Swedish forestry thus far the Norway spruce/oak-system developed by Erik St”l and his heirs at their estate in Jamjo, Southeastern Sweden, appears promising. According to the owners, the mixed-species stands perform well financially. The management system is well defined and aims at the production of veneer-quality oak wood with Norway spruce as an economic buffer early in the rotations (Staal 1986). We decided to investigate both the biogeochemical and the economic sustainability of the mixed-species stands there as well as of the adjacent Norway spruce monocultures. Matters of biodiversity are as yet to be investigated. It is reasonable, however, to expect there to be better possibilities for maintaining a high level of biodiversity in mixed spruce/oak forest stands than in Norway spruce monocultures.

Functional Biodiversity Aspects on the Nutrient Sustainability in Forests–: Importance of Root Distribution

Abstract Nutrient availability is of major importance for plant productivity. When estimating long-term sustainability from a nutrient perspective it is therefore interesting to focus on long-term changes in the soil nutrient pools when comparing different forest types. Here, we have highlighted some factors of importance for long term nutrient sustainability (e.g., several forest rotations) and pointed out some important features that differ between forest tree species and also between monocultures and mixed species stands. Using computer models like PROFILE reveals tree rooting depth to be a crucial factor when assessing long-term nutrient sustainability. Literature studies show that soil type and other soil conditions have a strong effect on root distribution. However, Norway spruce is generally a very shallow rooted species, with approximately 80% of it fine roots in the top 20–25 cm, whereas for pendiculate oak, generally 80% of the roots are found down to 60 cm soil depth. Rooting depth of Scots pine and beech seem to be intermediate with 80% of the roots down to approximately 25–30 cm and 30–35 cm, respectively. Importance of mycorrhiza for nutrient uptake in a sustainability perspective is discussed in the paper.

Assessment of sustainability in the Asa Forest Park

The main objectives of the geochemical investigation in Asa Forest Research Park (referred to henceforth simply as Asa) were as follows: 1. to calculate the release of Ca, Mg, K, and P from mineral weathering using PROFILE, a biogeochemical soil model, 2. to determine the geographical distribution of the results of weathering rate calculations carried out both at the site level and on a regional scale and 3. to propose a mass balance method for calculating the optimal sustainable biomass production of a forested area in southern Sweden

Application of natural, social, and economical sustainability limitations to forest management, based on Swedish experiences

Abstract We suggest a method of analyzing the sustainability conditions for forestry from three major realms: environmental, social, and economic. The tools and methods were tested at sites in Sweden. Assessments were made for the long-term sustainability concerning the impact of present management practices on the balances of nutrients in monocultures and mixed-species stands. In the economic assessments, both traditional terms but also costs and revenues from adaptation to defined biodiversity criteria and public service demands were accounted for. An alternative to traditional discounting was used for transferring monetary value over time, by introducing spruce pulp equivalent units. Several scenarios with unsustainable conditions could be identified as well as appropriate management measures that can be taken to correct the issue. Results showed that the changes in management methods needed are possible and feasible. No significant difference in the net profit from the Norway spruce monocultures and the deciduous-conifer mixed stands were found. An increased use of deep rooting tree species has the potential to increase the total sustainable harvest volume.

Increasing the Sensitivity of the 15N Root Bioassay Technique: Suggested Procedures

The diagnosis of tree nutrient demand for nitrogen (N), phosphorus (P), and potassium (K) is possible using a root bioassay with excised roots, to measure the rate of uptake of the corresponding isotope. In this study, Norway spruce (Picea abies) roots were used to test the uptake response in roots of different diameter. The 15N bioassay has been developed to test for nitrogen demand by plants, where high 15N uptake demonstrates nitrogen limitation. Sometimes sample variability may mask potential treatment differences, but we have shown that when the fine root fraction of <1 mm diameter is selected rather than the whole root, the sensitivity can be significantly increased. Roots of different diameters revealed a 2–50 fold difference in the response to the N bioassay. If samples are restricted to the fine roots, the method is also more comparable to the bioassays for P and K.

Principles of sustainable forest management

The Royal Forester A. D. Israel Strom made the statement cited above in his 1822 book ”Forslag till en Forbattrad Skogshushallning i Sverige” (A Proposal for Improved Forest Husbandry in Sweden), which was the main textbook on the subject in Sweden for almost a century. He was uncritically in favour of systematic clear-felling and the development of single aged stands. Israel Strom and his followers taught and defended clear-cutting in an era in which unregulated forest use was common. They rejected the method of selective use and of tree and branch harvesting practiced in Germany and in France. During the period since 1800 a number of different periods in south Swedish forestry can be identified, before 1820 natural householding was practiced, where forest were not industrially used in any significant degree, except in the mining areas in Bergslagen. During the period of 1820–1890, the influence of the Royal forester Israel af Strom was felt, leading to ordered clear-cutting systems, and the development of forest yield tables, production planning and growth promotion systems. In the period 1890–1910 much open land was replanted, due to a perceived lack of forests. During 1905 the first Swedish forest management law was enacted, stipulating the requirements placed on forest regeneration (Skogen-Sveriges Nationalatlas 1990).