Puuliikide mõju seente liigirikkusele ja liigilisele koosseisule

Väitekirja elektrooniline versioon ei sisalda publikatsiooneErinevad seenerühmad on looduses olulised orgaanilise aine lagundajad, haigustekitajad või juursümbiondid, kes aitavad puudel omastada mineraalaineid. Puud mõjutavad oma ümbrust läbi varise ja juureeritiste. Puuliikide kooskasvamine loob segametsades erinevad elupaigalaigud, mis suurendab muude organismide elurikkust metsades, kus kasvab rohkem puuliike. Elurikkus suurendab ökosüsteemide tootlikkust ja stabiilsust muutuvate keskkonnatingimuste vastu. Enda doktoritöös käsitlen seente elurikkuse seost puude varise ja peremeestaimede liigirikkusega ning teiste puuliikide naabruse mõjuga. Leidsin, et mida rohkem sisaldab lagunev lehevaris erinevate puuliikide lehti, seda suurem on selles seente liigirikkus. Samas juurte liigirikkuse mõju seente mitmekesisusele on nõrk. Lehevarise koosseis määrab ka lagundajate ja taimepatogeenide liigilise koosseisu. Kuuse ektomükoriisaseente liigiline koosseis erineb kase–kuuse segametsa ning kuuse monokultuuri vahel. Kase naabrus mõjutab mulla keemilisi omadusi ja seeläbi ektomükoriissete seente kooslusi. Ektomükoriisaseente liigirikkus on globaalsel skaalal seotud peremeestaimede liigirikkusega, kuid regionaalsel tasemel on seosed mulla omaduste ja konkreetsete puuliikidega tähtsamad. Oma tööst järeldan, et metsa liigirikkus tõepoolest suurendab seente elurikkust, mõju tugevus sõltub aga konkreetsetest puuliikidest ning mulla ja muu taimkatte omadustest.Fungi play key roles in forest ecosystems. Various groups of fungi drive organic matter decomposition and soil nutrient cycling, act as tree root symbionts or cause diseases. Trees are influential components of forest habitats that modify their surroundings via shedding litter and root exudates, but little is known about the functional importance of tree species diversity on soil organisms and soil biological processes. Mixtures of tree species can create fine-scale environmental heterogeneity that supports higher biodiversity in forest stands. Biodiversity enhances productivity and stability, buffering ecosystems against changing environmental conditions. In this thesis, I examined fungal diversity in relation to plant litter, host plant diversity and tree neighbourhood effects. Leaf litter mixtures with higher plant species richness harboured higher fungal diversity, indicating that heterogeneity of resources in litter mixtures provides more habitats and allows a larger number of fungal species to co-exist. Conversely, the root litter richness effect on fungal diversity was weak. Furthermore, leaf litter composition had a strong effect on composition of saprotrophic and plant pathogenic fungi. Richness of ectomycorrhizal fungi was positively related to host plant richness at global scale. At regional scale, fungal richness correlated with plant richness, but this effect was related to improved soil conditions in mixed forests. Communities of ectomycorrhizal fungi on spruce roots differed in spruce monocultures and mixed stands of birch and spruce, which points to the influence of birch on soil quality. To conclude, tree species richness and fungal diversity are usually positively correlated, but the direct impact of plant richness depends on the context, including the influence of particular plant species and analysis of other factors.https://www.ester.ee/record=b538405

Post-harvest establishment influences ANPP, soil C and DOC export in complex mountainous terrain

The link between aboveground net primary productivity (ANPP) and resource gradients generated by complex terrain (solar radiation, nutrients, and moisture) has been established in the literature. Belowground ecosystem stocks and functions, such as soil organic carbon (SOC), dissolved organic carbon (DOC), and belowground productivity have also been related to the same topography and resource distributions, and therefore it is expected that they share spatial and temporal patterns with ANPP. However, stand structure on complex terrain is a function of multiple trajectories of forest development that interact with existing resource gradients, creating feedbacks that complicate the relationships between resource availability and ANPP. On a 96 ha forested watershed in the H.J. Andrews Experimental Forest in the Western Cascades range of Oregon, spatiotemporal heterogeneity in the secondary succession of a replanted Pseudotsuga menziesii stand following harvest results from the interaction of stand composition and abiotic drivers and may create unique "hot spots" and "hot moments" that complicate gradient relationships. In this dissertation, I tested the hypotheses that (chapter 3) multiple successional trajectories exist and can be predicted from a general linear model using specific topographic, historical, and biological parameters and that an estimated "maximum ANPP" may better represent stand characteristics than ANPP measured at a particular moment in time. I also test that (chapter 4) the distribution of light fraction carbon (LFC; C with a density of less than 1.85 g/cm³) is spatially variable, elevated on hardwood-initiated sites (hardwood biomass > 50% of biomass), and positively correlated with litter fall and ANPP. Chapter 4 also tests that heavy fraction carbon (HFC; C with a density of greater than 1.85 g/cm³) is a function of both soil mineralogy, stand composition, and ANPP, such that edges observed spatially in site mineralogy (changes in soil type) are reflected in sharp changes in the composition of the forest community and the magnitude of HFC stores. Finally, I hypothesized (chapter 5) that in complex terrain, dissolved organic carbon (DOC) export can be predicted from landform characteristics, relates to ANPP, and may be measured by several methods which are well-correlated with one another. In chapter 6, I discuss how litter fall measurements can be extrapolated to a watershed extent, and use litter fall as an example of the error that can occur in scaling up measurements taken at a small scale, within a heterogeneous stand on complex terrain, to a landscape scale extent

Hidden Mechanisms of Climate Impacts in Western Forests: Integrating Theory and Observation for Climate Adaptation

Fire, insects, and disease are necessary components of forest ecosystems. Yet, climate change is intensifying these tree stressors and creating new interactions that threaten forest survival. This dissertation combined field observations with statistical predictions of changing disturbances in western forests to identify 1) how conventional models may underestimate future forest loss, and 2) how positive relationships between trees may be exploited by managers to prevent forest loss. In Chapter II, I tested whether increasingly extreme weather with climate change increases Pacific yew extinction risk. I found that conventional modeling methods underestimated local extinction risk because trees were adapted to a range in average conditions, but had limited tolerance of extreme drought. In Chapter III, I predicted whether future climate change will alter the strength of competition between species (heterospecifics) versus within species (conspecifics). I found that heterospecific competition is more sensitive to drought than conspecific competition, leading to higher tree mortality during drought than is currently expected. In Chapter IV, I looked at sugar pine tree rings to measure how pines respond to three centuries of fire exclusion, drought, fire, and a bark beetle outbreak. I found that fire suppression led to higher competitive stress, which decreased pines’ resilience to fire, and consequently, decreased pines’ survival during a subsequent bark beetle outbreak. Woody species diversity, however, was able to increase pine survival following fire and bark beetles by allowing higher pine growth and defenses. In Chapter V, I tested whether beneficial relationships between trees and mutualistic fungi could help trees survive across regional differences in climate, environmental conditions, and disturbances. I found that woody species diversity increased large-diameter tree resistance to insects and disease, but only if those species shared a mycorrhizal network. Large trees comprising 17 common western species across three canonical forest types showed this pattern –– despite residing in different topographic positions and climatological contexts. I identified how biodiversity can increase forest resistance and resilience to disturbances, but also found climate change to be weakening the processes responsible for maintaining biodiversity. Managers must take a more active approach to cultivating and preserving forest tree biodiversity to ensure forests are able to continue provisioning essential services, such as carbon storage, in the future. These four long-term studies of spatially explicit, cause-specific tree mortality provided useful insights into tree survival and forest change that will improve vegetation model accuracy and inform management of mature forests in western North America

Quantifying Ecosystem Trajectories: Tree Growth Response to Biophysical Gradients and Disturbance

Disturbance and climate are important drivers of tree physiological functioning, community assemblages and trends in recruitment and species presence across time and space. Fire exclusion-driven changes to the disturbance regime of frequent fire-adapted forests of the southern Rocky Mountains, North America, followed by modern megafires has strongly influenced stand structure and led to density increases in many forest types. Recent decadal drought has led to widespread mortality of some tree species, exacerbated fire extent and effects, and contributed to insect outbreaks. With climate change ongoing, hotter and drier conditions and droughts are expected, leading to increased risk of widespread tree mortality and vegetation type change. Forest ecosystem changes result from compounding effects on individual tree establishment, growth, and survival, which leads to changes in stand structure and composition, and drives patterns appreciable at the broadest scale. Here I focus on tree-environment interactions in the context of disturbance and climate across three scales, from tree-stand, to stand-watershed, to forest-ecosystem. By working across scales we can observe how fine-scale tree responses to interact with the environment to create broad patterns. At the tree scale, I considered the influence of increased forest density on tradeoffs of water and nutrient limitation affecting growth and physiological functioning in old-growth ponderosa pine (Pinus ponderosa Douglas ex C. Lawson) (Appendix A). I identified a novel interaction in which lower leaf nitrogen in dense stands was associated with lower tree-ring growth yet higher carbon isotope discrimination, rather than the expected negative relationship between discrimination and density-driven water stress. Reduced leaf nitrogen likely limited photosynthetic capacity, resulting in discrimination values more decoupled from water stress than is expected in the Southern Rockies. At the stand level to watershed scale, I investigated climate-growth relationships and species distributions across a biophysical gradient in southwestern mixed-conifer forest (Appendix B). I used model selection to find how climate drivers of tree-ring growth varied by species, elevation, and aspect, and found differences were in accordance with relative species drought tolerance. I combined this with stand-level regeneration patterns to predict shifts in species dominance across the watershed. In the absence of fire, I found increased regeneration in pinyon pine (Pinus edulis Engelm.) at low elevations and white fir (Abies concolor (Gord. & Glend.) Lindl. ex Hildebr.) at high elevations, while regeneration of ponderosa pine and Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) decreased everywhere across the study area. At the ecosystem scale I used Forest Inventory and Analysis (FIA) data to derive the novel Community Mean Tolerance Index, based on relating species shade and drought tolerance to ecosystem changes and applied it to investigate demographic trends within and across forest types (Appendix C). With the index I mapped responses within and across forest ecosystems in the southern Rocky Mountains, and found areas at risk for vegetation type conversion to oak woodland following severe fire. Substantial shifts in mean drought and shade tolerance in tree regeneration was found in forest types that had exceeded their historic fire interval. Across forest types, drought tolerance in seedling groups increased at lower elevation sites, while shade tolerance increased at higher elevation sites. The difference in drought tolerance across demographic groups was significantly associated with PRISM-derived recent temperature and precipitation means, indicating the potential for climate-driven community shifts. Investigating the effects of disturbance and climate on trees, watersheds, and ecosystems allows for a holistic view across scales of the current state of southwestern forests, and the potential for future changes

Mullahingamist ja selle komponente mõjutavad tegurid arukase ja hariliku kuuse puistutes

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Mulla CO2 voog ehk mullahingamine moodustab suure osa kogu metsaökosüsteemi hingamisest ja põhjapoolkera kõrgemate laiuskraadide metsad omavad olulist rolli globaalses süsinikuringes, mistõttu on selle voo kvantitatiivne hindamine väga aktuaalne teema. Käesolevas doktoritöös käsitleti kolme uudset aspekti. Esiteks suurenenud suhtelise õhuniiskuse mõju mullahingamisele, mis on oluline teave kõrgematel laiuskraadidel prognoositud kliimamuutuste valguses. Teiseks saadi Eesti jaoks uudsed tulemused mullahingamise jaotumisest autotroofseks ja heterotroofseks komponendiks arukase ja hariliku kuuse puistutes. Kolmandaks analüüsiti Eestis esmakordselt kändude juurimise mõju mulla CO2 voogudele. Doktoritöö laiemaks eesmärgiks oli analüüsida erinevate abiootiliste (suurenenud suhteline õhuniiskus, mullatemperatuur ja mullaniiskus) ja biootiliste (puuliik, puistu vanus ja arengustaadium, peenjuurte biomass ja käive, maapealne varise voog mulda, mulla mikroobne biomass ja selle aktiivsus) tegurite ning metsamajandamise (lageraiejärgne kändude juurimine) mõju mullahingamisele ja selle autotroofsele ja heterotroofsele komponendile erineva vanusega arukaasikutes ja hariliku kuuse puistutes. Töö tulemusena selgus, et mullatemperatuur on peamine keskkonnategur mullahingamise sesoonse dünaamika kirjeldamiseks ja mullaniiskusel on nõrk mõju. Suurendatud suhteline õhuniiskus vähendas mullahingamist, kuigi alustaimestiku juurte biomass, produktsioon ja mikroobikoosluste aktiivsus kasvas. Puistu vanus mõjutas mulla CO2 vooge nii arukase kui hariliku kuusiku vanusereas, mis seostus pigem muutustega biootilistes tegurites (peenjuurte dünaamika) kui muutustega mullatemperatuuris ja mullaniiskuses. Mullahingamise komponentide temperatuuritundlikkus oli vastupidine lehtpuu- ja okaspuupuistutes. Esmased tulemused näitasid, et viljaka kasvukohatüübi korral lageraiejärgne kuusekändude juurimine mulla¬hingamist oluliselt ei mõjuta. Antud töö näitab, et metsaökosüsteemi mullahingamine on väga keeruline protsess ning erinevaid looduslikke ja inimtekkelisi tegureid, mis seda protsessi mõjutavad, tuleb metsa süsinikuringe prognoosimisel arvesse võtta – eriti kliimamuutuste kontekstis.Soil CO2 efflux i.e. soil respiration can form a remarkable part of total forest ecosystem respiration and as northern forests at higher latitudes play an important role in global carbon cycle it is highly actual to quantify their soil CO2 effluxes. There are three novel aspects in this thesis. First, in the light of global climate change, the knowledge about the effect of elevated air humidity on soil CO2 effluxes will help to predict and understand the con¬sequences of a changing pattern of humidity on the forest carbon cycle. Second, the first results are obtained about soil respiration partitioning into the heterotrophic and autotrophic components in Estonian silver birch and Norway spruce forests. Third, for the first time in Estonia the effect of stump harvesting on soil respiration is analysed. The general aim of the thesis was to ascertain the effect of several factors: abiotic (elevated air humidity, soil temperature and moisture); biotic (stand age and development stage, fine root biomass and turnover, above-ground litter input, soil microbial biomass and activity) and forest management (stump harvesting) on total soil respiration and its autotrophic and heterotrophic components in silver birch and Norway spruce stands of different ages. The findings showed that soil temperature was the main climatic factor explaining the seasonal variation of soil respiration and soil moisture had a weak effect. Increased air humidity reduced soil respiration, however, it increased the fine root biomass and production of the understorey and the basal respiration of microbes. Stand age affected soil CO2 effluxes in both silver birch and Norway spruce stands, which were mostly explained by changes in biotic factors such as fine root dynamics than by changes in soil temperature and moisture. The temperature sensitivity of soil respiration components showed opposite response for deciduous and for coniferous tree species. First results of Estonian case study imply that stump harvesting does not affect the soil respiration on fertile sites. This thesis demonstrates the complexity of below-ground respiration processes and the importance to consider the effect of several natural and anthropogenic factors into the predictions of the carbon cycle of forest ecosystem in changing climate

Stable Isotopes in Tree Rings

This Open Access volume highlights how tree ring stable isotopes have been used to address a range of environmental issues from paleoclimatology to forest management, and anthropogenic impacts on forest growth. It will further evaluate weaknesses and strengths of isotope applications in tree rings. In contrast to older tree ring studies, which predominantly applied a pure statistical approach this book will focus on physiological mechanisms that influence isotopic signals and reflect environmental impacts. Focusing on connections between physiological responses and drivers of isotope variation will also clarify why environmental impacts are not linearly reflected in isotope ratios and tree ring widths. This volume will be of interest to any researcher and educator who uses tree rings (and other organic matter proxies) to reconstruct paleoclimate as well as to understand contemporary functional processes and anthropogenic influences on native ecosystems. The use of stable isotopes in biogeochemical studies has expanded greatly in recent years, making this volume a valuable resource to a growing and vibrant community of researchers

Webs of influence: Investigating the effects of the forest mycorrhizosphere on soil carbon storage in a changing world

Anthropogenic climate change is broadly accepted to be the biggest threat to ecosystems in the 21st century, with the most rapid change occurring in Arctic regions. It is necessary to understand the consequences of on-going warming, such as changing vegetation and northward advance of Arctic treelines, as well as examining the robustness of proposed mitigation strategies, such as intensified tree planting. Using field based approaches in soil carbon rich sub-Arctic and high latitude boreal regions, I found that Betula pubescens roots and associated mycorrhizal fungi extend 3-4.5 m away from trees, thereby covering open forest gaps, possibly creating a ‘wood-wide-web’. However, I found no evidence of common mycelial networks between trees or the understorey in these forests. My findings indicate consistent high production of roots and mycorrhizas throughout the forest floor, coupled with declining soil organic carbon (SOC) stocks with increasing distance from trees. In the Scottish uplands, with comparable tree and understorey species, I found that planting B. pubescens onto heather moorland leads to a 58 and 50% loss of SOC stocks 12 and 39 years after planting, resulting in no net gain in ecosystem C. Long term tree planting experiments provide empirical evidence for the consequences of tree planting schemes as a climate change mitigation strategy and the potential effects of warming-driven encroachment of Arctic treeline forests onto globally important ericaceous soil carbon stores. Combined, my results show how B. pubescens mycorrhizospheres - their roots and associated mycorrhizas - effectively explore throughout the forest floor and shape the spatial dynamics and depletion of soil carbon stocks in Arctic and boreal regions most vulnerable to climate change. Furthermore, this work suggests that, although urgent action on climate change is needed, awareness of the ecological context is crucial if planting trees is to be a robust strategy for climate change mitigation

Causes and Consequences of Species Diversity in Forest Ecosystems

What are the causes and consequences of species diversity in forested ecosystems, and how is this species diversity being affected by rapid environmental and climatic change, movement of invertebrate and vertebrate herbivores into new biogeographic regions, and expanding human populations and associated shifts in land-use patterns? In this book, we explore these questions for assemblages of forest trees, shrubs, and understory herbs at spatial scales ranging from small plots to large forest dynamics plots, at temporal scales ranging from seasons to centuries, in both temperate and tropical regions, and across rural-to-urban gradients in land use

ESTIMATION AND MODELING OF FOREST ATTRIBUTES ACROSS LARGE SPATIAL SCALES USING BIOMEBGC, HIGH-RESOLUTION IMAGERY, LIDAR DATA, AND INVENTORY DATA

The accurate estimation of forest attributes at many different spatial scales is a critical problem. Forest landowners may be interested in estimating timber volume, forest biomass, and forest structure to determine their forest\u27s condition and value. Counties and states may be interested to learn about their forests to develop sustainable management plans and policies related to forests, wildlife, and climate change. Countries and consortiums of countries need information about their forests to set global and national targets to deal with issues of climate change and deforestation as well as to set national targets and understand the state of their forest at a given point in time. This dissertation approaches these questions from two perspectives. The first perspective uses the process model Biome-BGC paired with inventory and remote sensing data to make inferences about a current forest state given known climate and site variables. Using a model of this type, future climate data can be used to make predictions about future forest states as well. An example of this work applied to a forest in northern California is presented. The second perspective of estimating forest attributes uses high resolution aerial imagery paired with light detection and ranging (LiDAR) remote sensing data to develop statistical estimates of forest structure. Two approaches within this perspective are presented: a pixel based approach and an object based approach. Both approaches can serve as the platform on which models (either empirical growth and yield models or process models) can be run to generate inferences about future forest state and current forest biogeochemical cycling