Metsade majandamise mõju hindamine süsiniku kontekstis: turbulentse kovariatsiooni meetod

A Thesis for applying for the degree of Doctor of Philosophy in Forestry.Boreal forest, being a widely distributed vegetation type as well being a substantial part of the global carbon (C) cycle, must be addressed to understand the consequences of climate change. Forest ecosystems are part of the biosphere as a whole and have a role in maintaining global equilibrium. Also, forest ecosystems have the ability to regulate Earth´s climate and energy fluxes. The forests, including boreal and hemiboreal forests, can absorb CO2 from the atmosphere and store carbon in biomass. This kind of ecosystem study is conducted by the widely used eddy covariance (EC) method. It is the most adequate way to measure net ecosystem exchange (NEE) between ground and atmosphere. EC is a direct micrometeorological measurement method for identifying C-fluxes in forest ecosystems. Clear-cutting changes the forest ecosystem C-balance. It is assumed that immediately after a clearcut, a huge amount of C is released, which make a forest stand act as a C-source. The time necessary for forest ecosystem recovery after clear-cutting also depends on the choice of regeneration method. Natural regeneration usually takes more time than artificial regeneration by planting or sowing and the proper regeneration method may shorten the recovery period. In Estonia, clear-cutting is the common forest management practice followed by planting to establish the new forest generation. Planting may speed up revegetation that increases C sequestration. Thus, proper forest management practices provide important strategies to mitigate global climate change. After clear-cutting, a 5-year-old mixed stand acted as C-neutral forest ecosystem during the measurement period (May to August). In the 6- and 8-year-old study stands, the ecosystem showed already C-sink status during the measurement period (June to September). Literature review showed that after clear-cutting, recovery to C-sink status could take 10 years and in some cases even 20 years. Forest recovery after wildfire may take up to 50 years and most likely even more. Measurements after insect outbreaks and windstorm disturbance detected recovery after 3 to 6 years; however there were few such studies and more research is needed for further comparisons.Boreaalsed metsad katavad maakeral kõige suurema maa-ala, olles seega ka suur osa globaalsest süsinikuringest. Sellele tuginedes kannavad boreaalsed metsad ka suuremat rolli kliimamuutustes. Metsade ökosüsteemid on osa biosfäärist ja globaalses mõttes olulised, säilitades märkimisväärset osa elusloodusest. Samuti on metsadel täita tähtis roll: võime reguleerida maakera kliimat ja energiavooge. Nii boreaalsed kui ka hemiboreaalsed metsad on võimelised atmosfäärist süsinikku siduma ja säilitama seda biomassis. Metsaökosüsteemi uurimiseks on võimalik kasutada täpset ja usaldusväärset turbulentse kovariatsiooni meetodit. Selle meetodi abil saab mõõta ökosüsteemi neto süsinikuvahetust (Net Ecosystem Exchange, NEE) maapinna ja atmosfääri vahel. See on otsene meetod ökosüsteemi energiavoogude tuvastamiseks. Pärast lageraiet metsaökosüsteemi süsinikubilanss muutub. On eeldatud, et kohe pärast sellist häiringut paisatakse suur kogus süsinikku õhku ja ökosüsteem muutub süsinikku eralduvaks. Metsaökosüsteemi taastumiseks kuluv aeg sõltub metsa valitud metsa uuendamise viisist. Taastumine loodusliku uuenemise korral võtab tavaliselt rohkem aega kui uuendamine istutamise ja külvi teel. Eestis enim kasutatud metsauuendamise võte on lageraie, millele järgneb uue metsapõlvkonna istutamine. Istutamise kaudu saab kiirendada metsaala uuendamist, mis omakorda võib suurendada süsinikusidumise potentsiaali. Oskuslikult metsi majandades on võimalik kliimamuutusi leevendada ja temperatuuritõusu pidurdada. Uuritud viieaastane noor puistu oli mõõtmisperioodi vältel süsinikuneutraalne. Kuue- ja kaheksa-aastased metsaökosüsteemid näitasid mõõtmisperioodil süsinikusiduja rolli. Ülevaateartiklis käsitletud erinevate kirjandusallikate fookus oli suunatud metsaökosüsteemi süsinikubilansi taastumisele ja selleks kuluvale ajale erinevate häiringute järgselt. Kokkuvõttes võib selleks aega kuluda kuni kümme aastat pärast lageraiet, mõnel juhul aga kuni 20 aastat. Pärast põlengut kulub metsaalal taastumiseks märksa kauem aega, vähemalt 50 aastat. Putukarüüstete ja tormide korral näitavad mõõtmistulemused kolme kuni kuue aasta pikkust taastumisaega, kuid väheste teadusuuringute tõttu pole võimalik põhjapanevaid järeldusi teha.Publication of this dissertation is supported by the Estonian University of Life Sciences

Carbon dynamics and h2o flux in forest ecosystem – eddy covariance method

Eestis ja paljudes teistes riikides on väga aktuaalseks teemaks kliima soojenemine ja välisõhu muutused, seepärast on vajalik uurida süsinikdioksiidi kontsentratsiooni tõusuga seonduvaid mõjutusi ning hetkelist olukorda CO2 ja H2O trendides. Töö eesmärgiks on võrrelda raieala süsiniku ja H2O voogusid ööpäevaringselt. Raieala keskele on paigaldati mõõtepunkt, kus oli installeeritud mõõteseadmed. Mõõtepunktist saadud 2014 ja 2015 aasta andmeid on kasutatud CO2 voogude võrdlemiseks ja seose leidmiseks H2O vooga. Peamiseks võrdlusperioodiks on mai lõpp ja juuni algus 2014 ja 2015 aastatel. Analüüsiti erinevate aastate vooge. Selgus, et suurt rolli on mänginud tulemuste erinevuses temperatuur ja pilvisus. 2014. aastal oli temperatuurid soojemad ja ilmad päikesepaistelisemad, millest tulenevalt ka toimus fotosüntees intensiivsemalt. Töös arvestati ka hingamise mõjusid. Oluline oleks mõõtmisi jätkata, et anda terviklikum ülevaade raieala atmosfäärigaaside voogudest. Pikema perioodi andmetega analüüs võimaldaks teha täpsemaid CO2 neelamise ja eraldumise kohta.In Estonia and many other countries it is very important topic to monitor global warming and changes in the ambient air. Particularly it is necessary to examine the carbon dioxide concentration increases and its effect on the current situation. The work is about to compare cutting area carbon and H2O flows during 24 hours (detecting time trends). Equipment is installed on the middle of the cutting area. Data obtained in 2014 and 2015, has been used to compare CO2 and H2O flows. The main reference period is the end of May and beginning of the June on both years. It was concluded that the difference has been in flux in different years. Major role in the differences can be the temperature difference and the cloudy weather. Year 2014 temperatures were higher and weather was more sunny, which is reflected by photosynthesis intensity. We also have to consider influence of respiration. It would be important to continue the measurements in order to provide more comprehensive overview of the cutting area flows and to make better conclusions. Release of CO2 and absorption of CO2 will give us main components to build the model of carbon budget

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

Fine root biomass and production in chronosequence of grey alder stands

Käesoleva töö peamiseks eesmärgiks oli uurida ja hinnata hall-lepikute (Alnus incana (L.) Moench) maa-aluse osa peenjuurte (d<2mm) biomassi ja peenjuurte produktsiooni viiel erineval katsealal, nelja erineva vanusega puistus (7 a, 17 a, 22 a, 32 a). Kõik uurimisalused hall-lepikud kasvavad naadi kasvukohatüübis. Puistute maa-aluse osa hindamiseks kasutati kahte erinevat meetodit: peenjuurte biomassi hindamiseks mullamonoliitide meetodit, peenjuurte produktsiooni hindamiseks juurevõrgu meetodit. Hall-lepikute peenjuurte biomass 22-aastasel Võõpste katsealal oli 2,3 t ha-1 . Vanemates 32-aastastes Agali ja Kõlleste vana puistutes olid peenjuurte biomassid vastavalt 1,7 t ha-1 ja 2,6 t ha-1 . Kõige nooremates hall-lepikutes Kõlleste noor ja Ilmatsalu katsealadel jagunesid peenjuurte biomassid suhteliselt võrdselt vastavalt Kõlleste noores 1,1 t ha-1 ja Ilmatsalus 1,2 t ha-1 . Kõlleste noore peenjuurte produktsioon oli 1,5 t ha-1 a -1 , Ilmatsalus 1,8 t ha-1 a -1 ning Võõpstes 1,4 t ha-1 a -1 . Peenjuurte produktsioon Agali proovialal oli 0,8 t ha-1 a -1 , samavanuselises Kõlleste vana peenjuurte produktsioon oli 1,7 t ha-1 a -1 . Peenjuurte produktsioon puu kohta on Kõlleste noor katsealal 0,1 grammi. Ilmatsalu katseala puistu peenjuurte produktsioon sarnaneb Võõpste katselalaga, kus mõlemad puistud on tootnud ca 0,5 grammi puu kohta. Agali katsealal jääb peenjuurte produktsioon 0,6 grammi puu kohta. Suurim peenjuurte produktsioon on Kõlleste vana katsealal (0,7 g).The present study was carried out in five different grey alder (Alnus incana (L.) Moench) stands in very productive Aegopodium site type in South-Estonia. The fine root (d<2mm) biomass and production of a 7-, 17-, 22 and 32-year-old grey alder stands were estimated. The fine root biomass and production were estimated with two methods: soil coring method was used to estimate biomass of the fine roots and ingorwth core method for estimating production of the fine roots. Fine root biomass in 22-year-old Võõpste stand were estimated 2.3 t ha-1 . In older stands, 32-year-old Agali and Kõlleste vana the fine root biomass is 1.7 t ha-1 and 2.6 t ha-1 . The fine root biomass is 1.1 t ha-1 and 1.2 t ha-1 , respectively in 7-year-old Kõlleste noor and 17-year-old Ilmatsalu grey alder stand. Fine root production in studied grey alder stands is in the range of 0.8-1.8 t ha-1 y -1 , being the highest in Ilmatsalu and the lowest in Agali stand. Fine root production per tree in Kõlleste noor is 0.1 g. In Ilmatsalu stand fine root production is similar to Võõpste stand, both stands produce ca 0.5 g per tree per year. Fine root production in Agali stand is 0.6 g per tree per year. In Kõlleste vana stand fine root production per tree is the highest (0.7 g)

Patterns of Carbon Sequestration in a Young Forest Ecosystem after Clear-Cutting

A large area of Estonian hemiboreal forest is recovering from clear-cut harvesting and changing carbon (C) balance of the stands. However, there is a lack of information about C- source/sink relationships during recovery of such stands. The eddy covariance technique was used to estimate C-status through net ecosystem exchange (NEE) of CO2 in two stands of different development stages located in southeast Estonia in 2014. Measured summertime (June–September) mean CO2 concentration was 337.75 ppm with mean NEE −1.72 µmol m−2 s−1. June NEE was −4.60 µmol m−2 s−1; July, August, and September NEE was −1.17, −0.77, and −0.25 µmol m−2 s−1, respectively. The two stands had similar patterns of CO2 exchange; measurement period temperature drove NEE. Our results show that after clear-cutting a 6-year-old forest ecosystem was a light C-sink and 8-year-old young stand demonstrated a stronger C-sink status during the measurement period.publishedVersio

Patterns of Carbon Sequestration in a Young Forest Ecosystem after Clear-Cutting

A large area of Estonian hemiboreal forest is recovering from clear-cut harvesting and changing carbon (C) balance of the stands. However, there is a lack of information about C- source/sink relationships during recovery of such stands. The eddy covariance technique was used to estimate C-status through net ecosystem exchange (NEE) of CO2 in two stands of different development stages located in southeast Estonia in 2014. Measured summertime (June–September) mean CO2 concentration was 337.75 ppm with mean NEE −1.72 µmol m−2 s−1. June NEE was −4.60 µmol m−2 s−1; July, August, and September NEE was −1.17, −0.77, and −0.25 µmol m−2 s−1, respectively. The two stands had similar patterns of CO2 exchange; measurement period temperature drove NEE. Our results show that after clear-cutting a 6-year-old forest ecosystem was a light C-sink and 8-year-old young stand demonstrated a stronger C-sink status during the measurement period

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