Tormikahjustuste käigus tekkinud mikroalade dünaamika ja häiringujärgne puurinde uuenemine hemiboreaalses segametsas

Windstorm, among the main natural disturbance agents in central and northern Europe, is found to have controversial effects on the direction of forest succession. Storm severity explains part of the contradiction, but the composition and distribution of biotic and abiotic storm legacies may also play a role. Storm-related microsites consist of the pit and mound complexes caused by uplifted root-plates, and of coarse woody debris (CWD). This thesis discusses availability and relevant conditions of microsites for tree regeneration development in storm-damaged areas at different successional stages. Furthermore, post-disturbance regeneration performance is evaluated based on a series of field inventories in two mature spruce-broadleaf mixed forests on humid, eutrophic soils in Estonia. Two major storms hit the areas in 2001 and 2002 respectively. Regeneration was investigated in patches with different disturbance severities. The focal species were Norway spruce (Picea abies (L.) Karst.), silver and downy birch (Betula pendula Roth. and B. pubescens Ehrh.), black alder (Alnus glutinosa (L.) J. Gaertn.) and European rowan (Sorbus aucuparia L.). Heterogeneity in microsite conditions is the result of variation in elevation, vegetation cover, surfacing bare mineral soil, litter and nutrients accumulation or runoff and substrate stability and penetrability. With time since disturbance, light incidence generally decreases while CWD gets more suitable as a germination substrate, which implies that timing of establishment and optimal growth conditions do not always match. Throughout inventories in the two storm areas in Estonia, pits in heavily damaged areas were dominated by birch, pits in moderately damaged areas by black alder and the mounds in heavily and moderately damaged areas by rowan and Norway spruce, respectively. Regeneration species composition turned out most diverse in moderately damaged areas. Harvested sites were significantly most densely populated, with birch as the dominant species, whereas control areas hosted least regeneration. Differences in regeneration density between heavily and moderately damaged areas were not significant. Disturbance severity exerted significant effect on height and height growth of shade-intolerant species throughout the inventories. Past performance, in its turn, was negatively linked to mortality probability. In contrast, more shade-tolerant species only showed impact of past competition on mortality at later stages since disturbance. Factors affecting regeneration mortality probability varied considerably among regeneration species, microsites and inventory moments since disturbance. Soil moisture explains occurrence and good performance of black alder in pits. The roles of CWD can range from sun-blocking in the first years after germination, to protection from ungulate browsing in later stages. Pre-disturbance management affects future species composition and stand structure. Salvage logging of wind disturbed areas increases the share of shade-intolerant species. Local post-disturbance retention of CWD and targeted pre-commercial thinning are tools to promote certain groups of tree species. The presence of storm-induced microsites is expected to increase long-term tree species diversity on the stand level, due to the species’ preferences. However, future research is necessary to judge whether the observed trends are persistent.Uurimistulemused tugevate tormide, mis on üheks olulisemaks häiringufaktoriks Põhja-Euroopa metsades, mõjust metsade suktsessioonilisele dünaamikale on küllaltki vastuolulised. Oluline tegur, mis aitab selgitada erinevaid arengustsenaariume on tormi tugevus, samas mängivad suurt rolli tormi käigus tekkinud biootilised ja abiootilised häiringuelemendid, mida nimetatakse mikroaladeks. Mikroalad moodustuvad juureaukudest ja -mätastest, mis tekkivad tormi poolt ümberpaisatud puude juurestike üleskerkimisega pinnasest ning suurte puude lamapuidust. Käesolevas uurimuses käsitletakse tormi poolt mõjutatud metsa mikroalade olemit ja tingimusi looduslikul uuenemisel häiringujärgse arengu eri etappides. Metsa uuenemise jälgimisel on kasutatud kordusmõõtmisi püsiproovialadel kahes erinevas Eesti piirkonnas küpsetes kuuse-lehtpuu segapuistutes. Häiringute näol on tegemist on 2001. ja 2002. aasta tugevate suvetormidega. Uuendust uuriti erineva kahjustusastmega metsaosades. Töö keskendus järgmiste puuliikide uuendusele: harilik kuusk (Picea abies (L.) Karst.), aru- ja sookask (Betula pendula Roth. and B. pubescens Ehrh.), sanglepp (Alnus glutinosa (L.) J. Gaertn.) ja harilik pihlakas (Sorbus aucuparia L.). Varieeruvus uuenduskohtade kõrguses maapinnast, taimkatte olemasolus, mulla mineraalse osa paljastumises ja surnud orgaanilise aine ja toitainete akumuleerumine või minemauhtumine ning idanemise ja kasvusubstraadi stabiilsus ja kättesaadavus taimejuurtele loovad mikroalade väga heterogeense mustri. Tavaliselt valgustatus häiringu järgselt tekkiva uuenduse all väheneb, samas muutub lagunev puit taimedele soodsamaks idanemis- ja kasvupinnaseks. Kasvu mõjutavate erinevate tegurite optimumid ei lange sageli kokku. Kahel tormikahjustatud alal läbi viidud kordusmõõtmised näitavad, et enamlevinud uuenduspuuliigid tugeva kahjustusastmega alade juureaukudes on aru- ja sookask , keskmise kahjustusastmega alade juureaukudes sanglepp ning juuremätastel vastavalt tugeva ja keskmise kahjustusastme korral harilik kuusk ja harilik pihlakas. Kõige liigirikkam oli uuendus keskmise kahjustusastmega aladel. Häiringujärgselt koristatud aladel oli uuendus kõige arvukam ja domineerisid aru- ja sookask. Kõige vähem oli uuendust kontrollaladel . Uuenduse arvukus keskmise ja tugeva kahjustusastmega aladel ei olnud usaldatavalt erinev. Kahjustusastme tugevus avaldas suurt positiivset mõju valgusnõudlike liikide kõrguskasvule ja kõrgusele, puutaimede kõrguskasv oli negatiivses korrelatsioonis suremise tõenäosusega. Varjutaluvatel liikidel hakkas konkurents suremust mõjutama alles koosluse arengu hilisemas faasis. Uuenduse suremust mõjutavad tegurid varieerusid suuresti sõltudes uuenduse liigist, mikroala omadustest ja vaatluse ajast. Sanglepa uuenemine ja hea kasv juureaukudes on põhjustatud paremate niiskustingimuste poolt. Lamapuidu mõju võib olla erinev, vahetult pärast häiringut vähendab suur kogus langenud puid uuenevate taimede valgustatust ning hilisemalt kaitseb see puutaimi metsloomade eest. See, milliselt majandati metsa häiringueelsel perioodil mõjutab häiringujärgse koosluse arengut. Häiringujärgsete alade koristamine (sanitaarraie) suurendab valgusnõudlike liikide osakaalu. Lamapuidu jätmine häiringualale ja harvendusraied häiringueelses metsas soosivad liikide uuendust vastavalt nende kohastumuslikele omadustele. Uuenevatel puuliikidel on erinev nõudlus mikroalade poolt loodavate tingimuste osas, seetõttu suurendab mikroalade olemasolu puurinde liigirikkust pikemas arenguperspektiivis. Edasiste uuringutega on vaja selgitada, kuivõrd püsivad ja millise suunaga on käesolevaks ajaks kirjeldatud arengutrendid

Forest Multifunctionality

To meet all demands and challenges that we, as a society, exert on our forests, knowledge-based cross-sectorial interdisciplinary research is needed to move forward. Areas are becoming scarce; stakeholders are in conflict, but, multiple use approaches point at integration and synergy opportunities. Accordingly, there is an increasing need for science-based policy support for EU decision-making concerning multiple uses of forests. In the end, future-proofing Europe’s forest is an aspiration we all share

Imprints of management history on hemiboreal forest ecosystems in the Baltic States

In the Baltic States region, anthropogenic disturbances at different temporal and spatial scales mostly determine dynamics and development phases of forest ecosystems. We reviewed the state and condition of hemiboreal forests of the Baltic States region and analyzed species composition of recently established and permanent forest (PF). Agricultural deforestation and spontaneous or artificial conversion back to forest is a scenario leading to ecosystems designated as recent forest (RF, age up to two hundred years). Permanent forest (PF) was defined as areas with no records of agricultural activity during the last 200 yr, including mostly forests managed by traditional even-aged (clear-cut) silviculture and salvage after natural disturbances. We hypothesized that RF would have distinctive composition, with higher dominance by hardwoods (e.g., aspen and birch), compared to PF. Ordination revealed divergence in the RF stands; about half had the hypothesized composition distinct from PF, with a tight cluster of stands in the part of the ordination space with high hardwood dominance, while the remaining RF stands were scattered throughout the ordination space occupied by PF with highly variable species composition. Planting of conifers, variability in site quality, and variability in spatial proximity to PF with relatively natural ecosystem legacies likely explained the variable compositions of this latter group of RF. We positioned the observations of RF in a classic quantification of site type conditions (based on Estonian forest vegetation survey previously carried out by LA mu hmus), which indicated that RF was more likely to occur on areas of higher soil fertility (in ordination space). Climatic and anthropogenic changes to RF create complex dynamic trends that are difficult to project into the future. Further research in tracing land use changes (using pollen analysis and documented evidence) should be utilized to refine the conceptual framework of ecosystem legacy and memory. Occurrence and frequency of deforestation and its characteristics as a novel disturbance regime are of particular interest.Peer reviewe

Globally consistent climate sensitivity of natural disturbances across boreal and temperate forest ecosystems

Disturbance regimes are changing in forests across the world in response to global climate change. Despite the profound impacts of disturbances on ecosystem services and biodiversity, assessments of disturbances at the global scale remain scarce. Here, we analyzed natural disturbances in boreal and temperate forest ecosystems for the period 2001-2014, aiming to 1) quantify their within- and between-biome variation and 2) compare the climate sensitivity of disturbances across biomes. We studied 103 unmanaged forest landscapes with a total land area of 28.2 x 10(6) ha, distributed across five continents. A consistent and comprehensive quantification of disturbances was derived by combining satellite-based disturbance maps with local expert knowledge of disturbance agents. We used Gaussian finite mixture models to identify clusters of landscapes with similar disturbance activity as indicated by the percent forest area disturbed as well as the size, edge density and perimeter-area-ratio of disturbed patches. The climate sensitivity of disturbances was analyzed using Bayesian generalized linear mixed effect models and a globally consistent climate dataset. Within-biome variation in natural disturbances was high in both boreal and temperate biomes, and disturbance patterns did not vary systematically with latitude or biome. The emergent clusters of disturbance activity in the boreal zone were similar to those in the temperate zone, but boreal landscapes were more likely to experience high disturbance activity than their temperate counterparts. Across both biomes high disturbance activity was particularly associated with wildfire, and was consistently linked to years with warmer and drier than average conditions. Natural disturbances are a key driver of variability in boreal and temperate forest ecosystems, with high similarity in the disturbance patterns between both biomes. The universally high climate sensitivity of disturbances across boreal and temperate ecosystems indicates that future climate change could substantially increase disturbance activity.Peer reviewe

Are Secondary Forests Ready for Climate Change? It Depends on Magnitude of Climate Change, Landscape Diversity and Ecosystem Legacies

In this review and synthesis paper, we review the resilience of secondary forests to climate change through the lenses of ecosystem legacies and landscape diversity. Ecosystem legacy of secondary forests was categorized as continuous forest, non-continuous forest, reassembled after conversion to other land uses, and novel reassembled forests of non-native species. Landscape diversity, including landforms that create varied local climatic and soil conditions, can buffer changing climate to some extent by allowing species from warmer climates to exist on warm microsites, while also providing refugial locations for species that grow in cool climates. We present five frames that allow forest managers to visualize a trajectory of change in the context of projected regional climate change, which are: Frame 1 (persistence), keep the same dominant tree species with little change; Frame 2 (moderate change), keep the same tree species with large changes in relative abundance; Frame 3 (forest biome change), major turnover in dominant tree species to a different forest biome; Frame 4 (forest loss), change from a forest to a non-forest biome; and Frame 5 (planted novel ecosystem), establish a novel ecosystem to maintain forest. These frames interact with ecosystem legacies and landscape diversity to determine levels of ecosystem resilience in a changing climate. Although forest readiness to adapt to Frame 1 and 2 scenarios, which would occur with reduced greenhouse gas emissions, is high, a business as usual climate change scenario would likely overwhelm the capacity of ecosystem legacies to buffer forest response, so that many forests would change to warmer forest biomes or non-forested biomes. Furthermore, the interactions among frames, legacies, and landscape diversity influence the transient dynamics of forest change; only Frame 1 leads to stable endpoints, while the other frames would have transient dynamics of change for the remainder of the 21st century

Future trends in forest management

The Northern European forest sector is a key contributor to the EU Green Deal and the forest-based bioeconomy. The sector is a key actor both today and in the future for promoting sustainable, multi-functional forests and regional forest ecosystem resilience to climate change. However, there are a number of conflicting forest management goals that must be identified and discussed

Hemiboreal forest: natural disturbances and the importance of ecosystem legacies to management

The condition of forest ecosystems depends on the temporal and spatial pattern of management interventions and natural disturbances. Remnants of previous conditions persisting after disturbances, or ecosystem legacies, collectively comprise ecosystem memory. Ecosystem memory in turn contributes to resilience and possibilities of ecosystem reorganization following further disturbance. Understanding the role of disturbance and legacies is a prerequisite for maintaining resilience in the face of global change. Several legacy concepts discussed in the peer-reviewed literature, including disturbance, biological, soil, land-use, and silvicultural legacies, overlap in complex ways. Here, we review these established legacy concepts and propose that the new terms “material legacy” (individuals or matter, e.g., survivors, coarse woody debris, nutrients left after disturbance) and “information legacy” (adaptations to historical disturbance regimes) cut across these previous concepts and lead to a new classification of legacies. This includes six categories: material legacies with above- and belowground, and biotic and abiotic categories, and information legacies with above- and belowground categories. These six legacies are influenced by differential patterns of editing and conditioning by “legacy syndromes” that result from natural or human-manipulated disturbance regimes that can be arranged along a gradient of naturalness. This scheme is applied to a case study of hemiboreal forests in the Baltic States of Estonia, Latvia, and Lithuania, where natural disturbance, traditional clearcut silviculture, and afforestation of abandoned agricultural lands constitute the three main legacy syndromes. These legacy syndromes in turn influence forest response to management actions and constrain resilience, leading to a mosaic of natural, manipulated, and artificial (novel) ecosystems across the landscapeVytauto Didžiojo universitetasŽemės ūkio akademij

Imprints of management history on hemiboreal forest ecosystems in the Baltic States

Article e02503In the Baltic States region, anthropogenic disturbances at different temporal and spatial scales mostly determine dynamics and development phases of forest ecosystems. We reviewed the state and condition of hemiboreal forests of the Baltic States region and analyzed species composition of recently established and permanent forest (PF). Agricultural deforestation and spontaneous or artificial conversion back to forest is a scenario leading to ecosystems designated as recent forest (RF, age up to two hundred years). Permanent forest (PF) was defined as areas with no records of agricultural activity during the last 200 yr, including mostly forests managed by traditional even-aged (clear-cut) silviculture and salvage after natural disturbances. We hypothesized that RF would have distinctive composition, with higher dominance by hardwoods (e.g., aspen and birch), compared to PF. Ordination revealed divergence in the RF stands; about half had the hypothesized composition distinct from PF, with a tight cluster of stands in the part of the ordination space with high hardwood dominance, while the remaining RF stands were scattered throughout the ordination space occupied by PF with highly variable species composition. Planting of conifers, variability in site quality, and variability in spatial proximity to PF with relatively natural ecosystem legacies likely explained the variable compositions of this latter group of RF. We positioned the observations of RF in a classic quantification of site type conditions (based on Estonian forest vegetation survey-previously carried out by Lohmus), which indicated that RF was more likely to occur on areas of higher soil fertility (in ordination space). Climatic and anthropogenic changes to RF create complex dynamic trends that are difficult to project into the future. Further research in tracing land use changes (using pollen analysis and documented evidence) shouldVytauto Didžiojo universitetasŽemės ūkio akademij