Sirvi Autor "Krasnova, Alisa" järgi

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Greenhouse gas fluxes in hemiboreal forest ecosystems
(2022-04-28) Krasnova, Alisa; Soosaar, Kaido, juhendaja; Mander, Ülo, juhendaja; Noe, Steffen M., juhendaja; Tartu Ülikool. Loodus- ja täppisteaduste valdkond
Metsad on olulised kasvuhoonegaaside (KHG) voogude reguleerijad. Käesolevas doktoritöös keskenduti hemiboreaalsetele metsadele, mis paiknevad boreaalse (põhjala) ning parasvöötme vahevööndis, sh Eestis. Töö eesmärgiks oli analüüsida KHG emissioonide ning neid reguleerivate keskkonnatingimuste dünaamikat hemiboreaalstes metsades. Töös pööratakse tähelepanu uuritud metsade süsihappegaasi (CO2) kui peamise KHG sidumisele, Euroopa 2018.a. kuumalaine mõjule CO2 sidumisel, samuti metaani (CH4) ja naerugaasi (N2O) kui tähtsuselt järgmiste kasvuhoonegaaside rollile üldises kliimamuutuses. Uuritud segamets (kuusk/kask), põlismännik ning veekoguäärne hall-lepik osutusid aastase bilansi alusel selgelt CO2 sidujateks, seejuures oli põlismännikus C02 sidumine mõnevõrra nõrgem. CH4 ja N2O emissioonid hall-lepikus olid periooditi märkmisväärsed, kuid üldises kliima mõjutamise kontekstis oli nende osakaal väike. Mitmed CH4 ja N2O emissiooniga seotud protsessid vajavad aga täiendavat selgitamist. Kaks uuritud lageraielanki ning lageraietega segamets (mänd/kuusk/kask) olid CO2 emiteerijad, seega kliima soojendajad. Peamisteks teguriteks CO2 lendumisel olid mullatemperatuur ja –niiskus. 2018.a. kuumalaine mõju erinevates metsades oli erinev. Suurimat mõju täheldati raielankidel ning lageraietega segametsas, kus CO2 lendumine oluliselt tõusis. Kuival liivasel mullal kasvavas sügava põhjaveega põlismännikus põua mõju CO2 sidumisele puudus, kusjuures veekoguäärses hall-lepikus CO2 sidumine põuaperioodil isegi veidi tõusis. Raielangid olid põua suhtes kõige tundlikumad, neis põua tõttu CO2 emiteerumine suurenes. Seda asjaolu on vaja arvestada lageraiete planeerimisel, vähendamaks metsaga kaetud alade muutumist kliima soojendajaks, eeskätt ekstreemsete ilmastikutingimuste ajal. Järgnevatel aastakümnetel on prognoositud globaalses ulatuses ekstreemsete ilmastikutingimuste ning nendega kaasnevate häiringute sagenemist. See ohustab üha enam maismaaökososteemide KHG bilanssi ning kiirendab kliima soojenemist. Selle leevendamiseks on väga oluline selgitada võimalikke mõjusid erinevates metsades, sh hemiboreaalses vööndis.
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Long-term carbon sequestration and heatwave resilience in an old hemiboreal upland coniferous forest
(Agricultural and Forest Meteorology, 2025) Rogozin, Svyatoslav; Krasnova, Alisa; Mander, Ülo; Uri, Veiko; Soosaar, Kaido
Boreal forests play an important role in the global carbon cycle due to their extensive area and ability to sequester a considerable amount of atmospheric carbon dioxide (CO2). They are generally stable ecosystems that function as carbon sinks. However, their sink capacity is vulnerable to the impact of extreme weather conditions. In this study, we aim to investigate the multi-year and seasonal carbon dynamics of an old upland coniferous forest in the hemiboreal zone, identify the main environmental drivers influencing annual NEP, and explore the potential legacy effects of the 2018 heatwave. Over an eight-year period (2016–2023), the forest shifted from a carbon sink (mean net ecosystem productivity (NEP) of 238 ± 52 g C m−2 year−1) to a carbon-neutral state in 2020 (NEP = -2 ± 5 g C m−2 year−1) and back to a net carbon sink (NEP = 136 ± 50 g C m−2 year−1). The average NEP over the eight-year period was 170 ± 42 g C m−2 year−1. Our research showed no significant year-to-year changes in GEP during the study period, while the changes in Reco were substantial. Our results confirm that air temperature has the greatest influence on annual NEP. The warmest autumn over the past 19 years, recorded in 2020, and an atypical June together resulted in a noticeable increase in ecosystem respiration, which shifted annual NEP towards negative net values, while no significant impact on GEP was found. Additionally, our study found that the old upland hemiboreal forest showed no legacy effect in the years following the 2018 heatwave, demonstrating its resilience to extreme temperature events. Our results underscore the importance of continuous monitoring carbon dynamics variability to determine the ecosystem's resilience to seasonal temperature fluctuations and to inform management strategies for forests preservation.
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Long-term carbon sequestration and heatwave resilience in an old hemiboreal upland coniferous forest
(2026) Rogozin, Svyatoslav; Krasnova, Alisa; Mander, Ülo; Uri, Veiko; Soosaar, Kaido
Boreal forests play an important role in the global carbon cycle due to their extensive area and ability to sequester a considerable amount of atmospheric carbon dioxide (CO2). They are generally stable ecosystems that function as carbon sinks. However, their sink capacity is vulnerable to the impact of extreme weather conditions. In this study, we aim to investigate the multi-year and seasonal carbon dynamics of an old upland coniferous forest in the hemiboreal zone, identify the main environmental drivers influencing annual NEP, and explore the potential legacy effects of the 2018 heatwave. Over an eight-year period (2016–2023), the forest shifted from a carbon sink (mean net ecosystem productivity (NEP) of 238 ± 52 g C m−2 year−1) to a carbon-neutral state in 2020 (NEP = -2 ± 5 g C m−2 year−1) and back to a net carbon sink (NEP = 136 ± 50 g C m−2 year−1). The average NEP over the eight-year period was 170 ± 42 g C m−2 year−1. Our research showed no significant year-to-year changes in GEP during the study period, while the changes in Reco were substantial. Our results confirm that air temperature has the greatest influence on annual NEP. The warmest autumn over the past 19 years, recorded in 2020, and an atypical June together resulted in a noticeable increase in ecosystem respiration, which shifted annual NEP towards negative net values, while no significant impact on GEP was found. Additionally, our study found that the old upland hemiboreal forest showed no legacy effect in the years following the 2018 heatwave, demonstrating its resilience to extreme temperature events. Our results underscore the importance of continuous monitoring carbon dynamics variability to determine the ecosystem's resilience to seasonal temperature fluctuations and to inform management strategies for forests preservation.
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Mature riparian alder forest acts as a strong and consistent carbon sink
(2025) Krasnova, Alisa; Soosaar, Kaido; Rogozin, Svyatoslav; Krasnov, Dmitrii; Mander, Ülo
Alder forests are widely spread across Northern Hemisphere, frequently occupying riparian buffer zones and playing a key role in enhancing soil fertility through symbiosis with nitrogen-fixing bacteria. Despite their ecological significance, studies on carbon (C) and water (H2O) exchange in alder forests remain scarce, particularly in the context of hydroclimatic variability and extreme weather events. In this study, we used eddy-covariance flux measurements from three contrasting years to assess the C balance and H2O exchange of a mature riparian grey alder forest in the hemiboreal zone in Estonia. The site was a strong and consistent carbon sink with annual net ecosystem exchange (NEE) ranging from -496 to -663 g C m⁻² y⁻¹, gross primary production (GPP) from -1258 to -1420 g C m⁻² y⁻¹ and ecosystem respiration (ER) from 595 to 923 g C m⁻² y⁻¹. Evapotranspiration (ET) varied from 194 to 342 kg H2O m⁻² y⁻¹ and ecosystem water use efficiency (EWUE) was 4.2 – 6.5 g C kg H2O-1. The drought and heatwave year (2018) featured the highest net carbon uptake, driven by an increase in GPP during spring and a reduction in ER during late summer and autumn. A minor impact of drought on GPP combined with a 35 % reduction in ET in 2018 lead to peak values of EWUE in response to H2O limitation. In 2019, we found no evidence of a short-term drought legacy effect, as carbon exchange components recovered to the 2017 levels and ET was the highest out of years. Given that this forest is beyond the typical harvestable age, its strong and consistent carbon sequestration, combined with high short-term resilience, provides valuable insights for sustainable forest management. These findings highlight the potential of riparian grey alder forests to maintain productivity under hydroclimatic variability, reinforcing their role in regional carbon cycling as a part of natural climate mitigation solutions.
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Mature riparian alder forest acts as a strong and consistent carbon sink
(2025) Krasnova, Alisa; Soosaar, Kaido; Rogozin, Svyatoslav; Krasnov, Dmitrii; Mander, Ülo
Alder forests are widespread across the Northern Hemisphere, often occupying riparian zones and enhancing soil fertility through symbiosis with nitrogen-fixing bacteria. Despite their ecological importance, the ecosystem-level carbon and water exchange of alder forests remains poorly studied, particularly under contrasting hydroclimatic conditions. We studied ecosystem carbon and water fluxes over three contrasting years (“wet”, “drought”, “recovery”) in a mature riparian grey alder forest in Estonia. The forest was a strong and consistent net carbon sink with annual net ecosystem exchange (NEE) ranging from −496 to −663 g C m−2 yr−1, gross primary production (GPP) from −1258 to −1420 g C m−2 yr−1, ecosystem respiration (ER) from 595 to 923 g C m−2 yr−1 and evapotranspiration (ET) varied from 194 to 342 kg H2O m−2 yr−1. Moderate soil water saturation (40 %–50 %) enhanced all ecosystem fluxes. In contrast, progressive drought reduced ER, ET, and to a much lesser extent GPP, with elevated EWUE and suppressed canopy conductance indicating strong stomatal regulation to limit water loss while maintaining carbon sequestration. While soil saturation affected canopy conductance, its effect was outweighed by vapour pressure deficit during the drought year, even after soil water availability recovered. We observed a full recovery in the following year, which was supported by favourable temperature and precipitation, although partially suppressed canopy conductance suggested some vulnerability to possible consecutive droughts in the future. Overall, the forest demonstrated drought resilience and high net carbon uptake across contrasting years, underscoring the capacity of riparian alder stands to sustain carbon sequestration under variable hydroclimatic conditions.