Pasi Rautio

Cronartium pini , Scots pine blister rust, is a rust fungus that has caused severe damage in both old and young Scots pine ( P. sylvestris ) forest stands in northern Fennoscandia. To understand the many drivers of these outbreaks we examined putative factors and their explanatory power of C.  pini incidence based on data collected in Lapland, northern Finland. Diseased stands were selected from the 10th Finnish National Forest Inventory (NFI) and control plots were randomly selected from the 11th NFI. A damage assessment was conducted in 2014, 4 years later in separate 10–15 sample plots within each stand. Stand and tree characteristics, including incidence of C. pini , were recorded. Site type (fertility) and age of trees significantly explained the incidence of C. pini in sample plots. Incidence of C. pini infection increased significantly in fertile sites, while the risk was non‐significant in more arid sites. Risk of infection by C. pini was significantly reduced when the proportion of deciduous trees increased. There was an increased infection risk (up to over 50%) proportional to how well the trees grew for the last 5 years if Melampyrum spp. were present. Our results support previous observations that fertile sites are more susceptible to infection by C. pini . For the first time, we also demonstrate that an increase in the number of deciduous trees reduces the risk of C. pini infections. These results offer tools to improve forest management practices in reducing the risk of damage caused by C. pini in northern pine forests.

Dry and unproductive Scots pine forests in the northern boreal forest zone provide conditions where ground-dwelling lichens can thrive. These lichens are a crucial winter forage for reindeer. Reindeer reduce lichen biomass both by consumption and trampling, leading to cascading effects on microclimate, litter inputs, and soil carbon dynamics. To investigate long-term impacts of reindeer exclusion, we assessed the plant biomass, soil nutrients, and soil organic carbon (SOC) quantity and quality in three dry pine forest sites in northern Finland, where reindeer have been excluded for over 50 years. Within exclosures, lichen biomass was 4.5 times higher and dwarf shrub biomass nearly doubled compared to grazed controls. These vegetation changes were associated with a 33% higher soil moisture and 0.8 °C lower summer soil temperatures at 10 cm depth beneath the thicker lichen mats. The organic layer SOC stock was 28% higher in exclosures. Spectroscopic analysis using ¹³ C NMR spectroscopy revealed 9.5% higher O-alkyl carbon (carbohydrates) content and lower methoxy (−5.1%), alkyl (−6.9%), and carbonyl (−8.7%) content, reflecting a younger, more labile carbon pool in the exclosures. Despite these changes, soil nutrient concentrations and C:N ratios remained unchanged between treatments, suggesting that altered SOC storage and composition result primarily from increased litter inputs and microclimatic changes. We conclude that in lichen-rich boreal forests, long-term reindeer exclusion enhances SOC stocks and promotes a shift toward more decomposable soil organic matter, with potential implications for carbon stability under changing grazing regimes.

Key message: A large European forest monitoring dataset reveals a pattern of reduced foliar nitrogen (N) and phosphorus (P) concentrations following drought conditions in spruce and pine, and, in the case of P, beech and oak, often exhibiting N:P imbalances. Gradual nutritional imbalance and nutrient deficiency during droughts raise concern for tree vitality and forest carbon sequestration under climate change. Context: Nitrogen (N) and phosphorus (P) are essential nutrients for tree metabolism, forest growth, and carbon sequestration, yet the drivers of their availability to trees are often complex to untangle. Aims and methods: In this study, we investigated environmental controls of foliar N, P, and N:P based on > 4100 N and P measurements in foliage samples of main tree species (beech, oak, spruce, and pine) across 279 European monitoring sites by applying mixed regression models. Results: We found overall nutritional declines over the past three decades that ranged from − 1.8% to − 2.7% and from − 3.5% to − 4.2% per 10 years for foliar N and P concentrations respectively. At around two-thirds of monitoring sites, where foliar N:P significantly increased over the examined time span, these increases were dominated by declines in foliar P. Foliar sampling years with summer droughts (standardized precipitation evapotranspiration index < − 1.2) were associated with lower standardized foliar P concentrations in all tree species compared to average years. Conclusion: We concluded that variations in drought conditions drive foliar N and P on a short-term, mostly annual basis, while throughfall deposition of N impacted foliar N over larger time spans of several decades depending on tree species.

Summary: Ectomycorrhizal fungi (EMF) produce mycelia with variable extension and complexity, which can be classified according to soil ‘exploration types’ (ETs). ETs have received attention as one of the few mycorrhizal trait frameworks, but without an empirical classification of ET functional diversity and environmental preferences, understanding and interpreting EMF biogeographic patterns has been difficult. We conducted a synthesis combining: comparative EMF genomics to describe functional divergence in decomposition and nutrient cycling genes across ETs; and EMF trait distribution modeling across continental Europe, pairing soil and root EMF surveys to establish biogeographic ET niche profiles. We demonstrate a signature of ETs encoded in EMF genomes, which is independent from phylogeny and linked to biomass production strategies. EMF ET relative abundances were separated by soil, root, and dominant tree leaf type habitats and exhibited unique correlations with forest biotic (e.g. plant productivity and plant pathogen densities) and abiotic (e.g. nitrogen deposition and soil pH) conditions. These findings support a theory that EMF niche partitioning can be partially explained by extraradical mycelial traits, with underlying variation in ET biogeography likely arising from distinct decomposition and nutrient cycling potentials. We also identify important limitations to this trait framework and provide a guided outlook for future research.

Suojametsäalueella metsää tulee valtioneuvoston säädösten mukaan hoitaa ja käyttää erityistä varovaisuutta noudattaen ja siten, ettei toimenpiteillä aiheuteta metsänrajan alenemista. Tässä artikkelissa esitetään tiivistelmä aiempien suojametsäaluetta koskevien selvitysten tuloksista, tarkastellaan metsätaloustoimintaa suojametsäalueilla ja Pohjois-Suomen korkeilla alueilla sekä Metsäkeskuksen aineistojen että valtakunnan metsien inventoinnin (VMI) aineistojen perusteella, alueella tehtyä metsänuudistamis- ja metsätuhotutkimusta sekä ilmastotrendejä ja niiden vaikutuksia metsän uudistumiseen suojametsäalueilla. Suojametsäalueen ja Pohjois-Suomen korkeiden alueiden metsän uudistumistulokset ovat Suomen metsäkeskuksen vuosien 2015–2020 tarkastusaineiston perusteella hyviä; virheelliseksi luokiteltuja kohteita on näissä luokissa vain 7 % suojametsäalueella ja 12 % Pohjois-Suomen korkeilla alueilla. VMI-tulosten valossa suoja­metsäalueen metsät ovat taimettuneet paremmin kuin vuosikymmen aikaisemmin: 2020-luvun taitteen VMI13-aineistossa vain noin 12 % tuoreista uudistusaloista alitti taimikoiden kasvatettavan puuston vähimmäisrajan 1200 r/ha, kun VMI11-aineistossa vastaava luku oli yli kolminkertainen. Myös pituuskehityksen ja metsänhoidollisen laadun kohdalla suojametsäalueen metsiköt ovat samalla tai hieman paremmalla tasolla kuin aiemmin. Suojametsäalueen havupuutaimikoissa ei ole 2010-luvulla havaittu samankaltaisia luonnontuhoja kuin tunturimittarin tunturikoivikoissa 1960-luvulla aiheuttamat laajat metsäkuolemat. Myöskään ilmasto-oloissa ei ole havaittavissa äärevyyden lisääntymistä. Metsänuudistamistutkimusten tulosten perusteella maanmuokkauksen tarpeellisuutta on edelleen tarpeen korostaa suojametsäalueella. Myös maanmuokkauksen ja hyvien siemenvuosien välinen yhteys on tärkeää riittävän taimiaineksen saavuttamiseksi. Toisaalta metsänhoitosuositusten mukaiseen taimikon tavoitetiheyteen esimerkiksi kuivahkojen kankaiden kohdalla päästään jo sillä, että harvennetaan puusto harvaksi tai tehdään maankäsittely. Kokonaisuutena metsien uudistuminen suojametsäalueella on 2010-luvulla onnistunut pääasiassa hyvin. Keinollisten ja luontaisten uudistamismenetelmien yhdistelmän käyttö on edelleenkin perusteltua suojametsäalueella ja Pohjois-Suomen korkeilla alueilla, sillä olosuhteet alueella ovat edelleenkin äärevät ja uudistumistuloksiin liittyy aina epävarmuutta. Mitään erityisiä uhkatekijöitä ei tällä hetkellä ole näköpiirissä, mutta seuranta on jatkossakin tarpeen etenkin tautien ja tuholaisten varalta.

In northern Finland, continuous cover forestry (CCF), has been introduced to better reconcile multiple land uses, including commercial forestry and reindeer husbandry. We studied how small gap cutting, a CCF method, can facilitate the colonization of pendulous lichens (Alectoria sp., Bryoria sp., and Usnea sp.), a bottle-neck resource for reindeer (Rangifer tarandus tarandus), into harvested areas. To assess the potential for balancing between forestry and reindeer husbandry, we investigated the colonization success of pendulous lichen on seedlings within the gaps created ten years before onset of our study in a pine-dominated boreal forest in central Finnish Lapland. The study included three gap sizes (diameters 20, 40, and 80 m) in xeric and sub-xeric sites, arranged in six randomized blocks, with 18 replicates per each gap size. Additionally, we examined the influence of gaps on the abundance of pendulous lichens in mature trees in the surrounding forest. Our results indicate that pendulous lichens colonized the smallest gaps (d = 20 m) efficiently, while colonization success declined as gap size increased. Colonization was strongly associated with seedling density, as a higher number of seedlings within gaps increased the probability of lichen colonized seedlings. The highest colonization rates occurred near gap edges, with lower colonization in the center. Furthermore, seedling height positively influenced colonization, and the presence of pendulous lichens on adjacent mature trees enhanced seedling colonization within gaps. However, we also observed that gap edges significantly reduced the amount of pendulous lichens on mature trees.

The aim of this study was to experimentally test the most favourable seeding times for Scots pine (Pinus sylvestris L.), and to compare Scots pine and lodgepole pine (Pinus contorta Douglas ex Loudon) in respect to suitable seeding times and site factors. The experimental area was located in Sodankylä, Central Finnish Lapland. Generalized linear mixed effects models with binomial distribution assumption were applied to model the presence or absence of a seedling at a seeding point. The study shows that in addition to spring and early summer, direct seeding of Scots pine can also be carried out during late autumn or even early winter (October and November) in northern Fennoscandia. On the contrary, seeding in late summer and early autumn (August and September) is much less successful and cannot be recommended as such, but can be used if the amount of seeding material is increased to compensate the loss. There is more flexibility for lodgepole pine for which the proper seeding period seems to be from spring through to late autumn. Whether lodgepole pine seeds were stratified or not had no statistically significant effect on regeneration success. Our results clearly indicate that lodgepole pine is less susceptible to unfavourable site and soil factors than Scots pine. Our results give support to extend the period of direct seeding from the present early summer to another period in late autumn and even early winter.

In the context of continuous cover forestry (CCF), natural regeneration is the preferred form of regeneration, but it is a long-lasting and complex process. Shelter density has a large effect on the regeneration process and results. The selection system, particularly suited for shade-tolerant species like Norway spruce, relies on continuous regeneration and ingrowth into larger size classes. Regeneration and ingrowth rates vary significantly among stands, influenced by site and historical factors, with no clear relationship to current stand conditions. In the group system, edge trees influence regeneration by providing seeds, checking weed growth, and exerting competition. Regeneration in gaps is generally satisfactory for both Norway spruce and Scots pine. However, seedlings usually grow slower, especially close to the gap edges. The shelterwood system promotes regeneration through a successive, uniform opening of the canopy. Shelter trees provide seeds, and reduce seedling damage and competition from ground vegetation. On the other hand, the remaining overstorey shelter trees reduce seedling growth. Conversion to the selection system initiates regeneration in young stands, aiming for slow and steady regeneration. Given the rapid growth and crown closure in young stands, frequent manipulation of shelter density is essential during conversion, for example by opening small gaps.