Hannu Ilvesniemi

Increasing the proportion of broadleaved species in conifer-dominated forests can enhance forest multifunctionality and resilience in Fennoscandia, where forest management has long been dominated by conifer monocultures. We combined empirical field data with contemporary statistical methods to study the effects of tree species identity and species admixing on soil carbon (C) stocks, and key soil properties in mixed stands and in single-species birch (Betula spp.), pine (Pinus sylvestris), and spruce (Picea abies) stands. Our results show that soil C stocks in the organic horizon were lower in birch monocultures than in spruce monocultures. One of the datasets suggested increased soil C stocks under birch-spruce mixtures in middle-fertile sites, but the other two datasets did not show significant differences in C stocks between mixed vs. conifer stands. Generally, mixed stands had higher N content, pH and exchangeable Mg and K concentrations in the organic horizon than conifer monocultures. Birch monocultures were characterized by a greater abundance of fine roots in deeper soil layers relative to mixed stands and conifer monocultures. Furthermore, C mineralisation rates in the organic horizon were higher in birch monocultures compared with pine monocultures, indicating enhanced microbial activity and accelerated organic matter turnover. Our results point to positive effects of birch admixture on several soil properties relevant to soil fertility and functioning, highlighting important implications for the management of mixed-species forests in Fennoscandia.

Successful afforestation in arid and semi-arid environments depends on seedling survival during establishment, yet the relative effects of irrigation method, soil amendment, and species identity remain poorly quantified, particularly when irrigation methods deliver equivalent water volumes. We established a factorial field experiment in semi-arid Morocco and monitored survival and growth over four years to evaluate the effects of irrigation regime (subsurface drip, tank, rainfed), soil amendment (biochar, peat moss, control), and species identity on early establishment of seven native and exotic tree species.Water availability was the dominant driver of establishment success. Relative to drip irrigation, tank irrigation increased mortality risk 2.7-fold despite comparable water volumes, while rainfed conditions increased risk 12.4-fold. Most mortality occurred during the first post-planting dry season. Fast-growing species (Paulownia, Moringa) exhibited very high mortality under water limitation, whereas native species (Pistacia, Pinus, Vachellia) maintained low mortality risk despite slower growth. Differences between tank and drip irrigation diminished over time for native species, suggesting simpler irrigation may suffice for drought-adapted taxa.Soil amendment effects were conditional on water availability. Under rainfed conditions, biochar and peat moss reduced mortality risk by 51% and 39%, respectively, but had negligible effects under irrigation. Growth responses paralleled survival patterns, with irrigation exerting a stronger influence than soil amendments.These single-site results demonstrate that early afforestation success is governed primarily by water delivery consistency, with species identity modulating responses and soil amendments playing a secondary, context-dependent role.

Weathering rates of Ca and Mg related to granitic and gabbro mineralogy in boreal forest soils and the effect of mechanical soil disturbance on weathering release Lindroos A.-J., Ilvesniemi H. (2023). Weathering rates of Ca and Mg related to granitic and gabbro mineralogy in boreal forest soils and the effect of mechanical soil disturbance on weathering release.

Soil hydraulic properties are central for soil quality and affect forest productivity and the impacts of climate change on forests. The water retention characteristics (WRC) of mineral forest soils in Finland are not well known, and practical tools to predict them for hydrological, biogeochemical and forest models are lacking. We statistically analyzed mineral forest soils WRC from over 130 sites in Finland, focusing on the humus layer and main root zone (0–19 cm depth). We showed that mineral forest soils can be grouped into five WRC classes that are well predictable from soil bulk density, organic matter content and clay fraction. However, the majority of the forest soils are hydrologically rather similar. We found that neither topsoil maps nor any combination of open geospatial data were able to predict WRC. Thus, in the absence of site-specific soil data, parameterizing WRC as a function of forest site fertility type was proposed. We demonstrated the approach in soil moisture modeling at a small forest headwater catchment and showed that the soil moisture response to weather conditions is jointly affected by WRC, stand attributes and topography. We showed that drought risks are highest for dense mature forests at nutrient-poor, coarse-textured sites and lower for young stands on peatlands and lowland herb-rich sites with groundwater influence. The results improve hydrological predictions for Finnish forests, and the open dataset can contribute to the larger synthesis and development of boreal forest soil pedo-transfer functions.

The aim of the study was to quantify total extractive contents and lipophilic compounds, stilbenes, and lignans in Scots pine stem wood, stem bark, branch biomass, and sawmill residues in four climatic regions of Finland to evaluate the most optimal sources of extractives for bio-based chemical biorefining and bioenergy products. Data were derived from 78 chip samples from the before-mentioned raw materials, the samples being pooled by tree height position from the sample trees of 42 experimental forest stands, and sawdust lots from 10 log stands. Accelerated solvent extraction (ASE) was employed to determine total extractive contents, followed by gas chromatography with flame ionization detection (GC–FID) to quantify extractive groups and gas chromatography-mass spectrometry (GC–MS) to analyse individual extractive compounds. Resin acids and triglycerides followed by fatty acids were the dominant extractive groups. Resin acids were most abundant in stem wood from final fellings and in sawdust, fatty acids in bark and branch biomass, and triglycerides also in stem wood from thinnings and the top parts of trees. Of the minor extractive groups, stilbenes were the most abundant in stem wood from final fellings and in sawdust, and steryl esters, sterols, and lignans in bark and branch biomass, the two last groups almost missing from other biomass components. Regional differences in the contents of extractive groups were generally small, 1.0−1.5 percentage points at the maximum, but factor analysis distinguished northern and southern regions into their own groups. Bark was the most potential source of fatty acids and sterols in southern Finland, and triglycerides and steryl esters in northern Finland. In stem wood, steryl esters, triglycerides, and lignans decreased and stilbenes increased from north to south. Certain fatty acids and resin acids were more frequent in the north. The results highlighted the importance of focused procurement and efficient sorting of raw materials, purity, unique properties, and feasible isolation techniques for competitive ability as well as large raw material volumes or well-defined value-added products.

This study aimed to identify and quantify phenolic and resin acid extractive compounds in Scots pine stemwood and sawmill residues in four climatic regions of Finland to evaluate their most optimal sources for bio-based chemical biorefining and bioenergy products. The sample consisted of 140 trees from 28 stands, and sawdust lots from 11 log stands. NMR for the overall extractive analysis and HPLC for the quantitative estimation of phenolic and resin acid compounds were employed. Correlation analysis, multivariate factor analysis, principle component analysis and multiple linear regression modelling were applied for statistical analysis. HPLC identified 12 extractive compounds and NMR five more resin acids. Pinosylvin (PS), pinosylvin monomethyl ether (PSMME), and partly neolignans/lignans occurred in the largest concentrations. Wood type caused the most variation, heartwood having larger concentrations than sapwood (sawdust between them). Regional differences in the concentrations were smaller, but factor analysis distinguished the northern and the southern regions into their own groups. The results indicated higher concentrations of PS, PSMME, and vanillic acid in southern regions and those of, e.g., PSMME glycoside, lignan 2, and neolignan 1 in northern regions. The rather low concentrations of extractives in stemwood and sawdust imply value-added products, efficient sorting and/or large raw material volumes.