Photosynthesis of ground vegetation in boreal Scots pine forests

Research on carbon uptake in boreal forests has mainly focused on mature trees, even though ground vegetation species are effective assimilators and can substantially contribute to the CO2 uptake of forests. Here, I examine the photosynthesis of the most common species of ground vegetation in a series of differently aged Scots pine stands, and at two clear-cut sites with substantial differences in fertility. In general, the biomass of evergreen species was highest at poor sites and below canopies, whereas grasses and herbs predominated at fertile sites and open areas. Unlike mosses, the measured vascular species showed clear annual cycles in their photosynthetic activity, which increased earlier and decreased later in evergreen vascular species than in deciduous species. However, intraspecific variation and self-shading create differences in the overall level of photosynthesis. Light, temperature history, soil moisture and recent possible frosts could explain the changes in photosynthesis of low shrubs and partially also some changes in deciduous species. Light and the occurrence of rain events explained most of the variation in the photosynthesis of mosses. The photosynthetic production of ground vegetation was first upscaled, using species-specific and mass-based photosynthetic activities and average biomass of the site, and then integrated over the growing season, using changes in environmental factors. Leaf mass-based photosynthesis was highest in deciduous species, resulting in notably higher photosynthetic production at fertile sites than at poor clear-cut sites. The photosynthetic production decreased with stand age, because flora changed towards evergreen species, and light levels diminished below the canopy. In addition, the leaf mass-based photosynthetic activity of some low shrubs declined with the age of the surrounding trees. Different measuring methods led to different momentary rate of photosynthesis. Therefore, the choice of measuring method needs special attention.Boreaalisten metsien hiilensidontatutkimus on keskittynyt pääasiassa puihin, vaikka monet pintakasvilajit yhteyttävät tehokkaasti ja voivat siten vaikuttaa merkittävästi metsikön hiilensidontaan. Tässä työssä tarkastelen yleisimpien pintakasvilajien yhteytystä viidessä eri-ikäisessä metsässä sekä kahdella ravinteeltaan toisistaan hyvin poikkeavalla hakkuuaukolla. Ainavihantojen kasvien biomassa oli runsain karulla hakkuuaukolla ja metsikön alla, kun taas heinät ja ruohot vallitsivat ravinteikkailla ja avoimilla alueilla. Putkilokasvien yhteytysnopeudella oli selkeä vuosirytmi, joka aikavihannilla varvuilla alkoi aiemmin ja päättyi myöhemmin kuin kesävihannilla kasveilla. Lajinsisäinen vaihtelu ja itsevarjostus aiheuttivat kuitenkin tasovaihtelua yhteytysnopeuteen. Valo, lämpötilahistoria, maan kosteus ja viimeaikaiset hallat selittivät varpujen kuten myös osin muiden kasvilajien yhteytysnopeuden muutoksia. Sammaleilla ei sen sijaan ollut havaittavissa selkeää vuosirytmiä, vaan valo sekä sateisuus selittivät suurimman osan sammalten yhteytysnopeuden muutoksista. Saavutetut laji- ja lehtimassakohtaiset yhteytysnopeudet muutettiin maapinta-alakohtaiseksi hiilensidonnaksi käyttäen inventoitua lajien keskimääräistä lehtimassaa. Koko kasvukauden hiilensidonta integroitiin ympäristötekijöiden muutosten avulla. Lehtimassaan perustuva yhteyttäminen oli nopeinta kesävihannilla lajeilla, mikä johti huomattavasti korkeampaa yhteytystuotokseen viljavalla hakkuuaukolla kuin karulla. Yhteytystuotos laski metsikön iän kasvaessa, sillä lajikoostumus muuttui kohti ainavihantia lajeja ja valon intensiteetti laski latvuksen kasvaessa. Lisäksi varpujen lehtimassakohtainen yhteytysnopeus hidastui ympäröivien puiden iän myötä. Eri mittausmenetelmät johtivat erilaisiin tuloksiin, joten mittausmenetelmän valintaan on pantava erityistä huomiota

Tutkija tarkkailijana ilmastokokouksessa

Maailman johtajat kokoontuivat Kööpenhaminaan 7.–18. joulukuuta 2009 tavoitteinaan uuden, maailmanlaajuisen ilmastosopimuksen laatiminen ja päästövähennyksistä sopiminen. Vuonna 1992 sovittu Kioton pöytäkirjan voimassaoloaika umpeutuu vuoden kuluttua, eivätkä sen velvoitteet ole riittävät ilmastonmuutoksen estämiseksi. Huippuyksikkömme sai kuusi kutsua osallistua kokoukseen tarkkailijoiksi

Simulating urban soil carbon decomposition using local weather input from a surface model

Non peer reviewe

Towards quantitative ecology : Newton’s principia revisited

Peer reviewe

Carbon sequestration potential of street tree plantings in Helsinki

Cities have become increasingly interested in reducing their greenhouse gas emissions and increasing carbon sequestration and storage in urban vegetation and soil as part of their climate mitigation actions. However, most of our knowledge of the biogenic carbon cycle is based on data and models from forested ecosystems, despite urban nature and microclimates differing greatly from those in natural or forested ecosystems. There is a need for modelling tools that can correctly consider temporal variations in the urban carbon cycle and take specific urban conditions into account. The main aims of our study were to (1) examine the carbon sequestration potential of two commonly used street tree species (Tilia x vulgaris and Alnus glutinosa) growing in three different growing media by taking into account the complexity of urban conditions and (2) evaluate the urban land surface model SUEWS (Surface Urban Energy and Water Balance Scheme) and the soil carbon model Yassol5 in simulating the carbon sequestration of these street tree plantings at temporal scales (diurnal, monthly, and annual). SUEWS provides data on the urban microclimate and on street tree photosynthesis and respiration, whereas soil carbon storage is estimated with Yasso. These models were used to study the urban carbon cycle throughout the expected lifespan of street trees (2002-2031). Within this period, model performances were evaluated against transpiration estimated from sap flow, soil carbon content, and soil moisture measurements from two street tree sites located in Helsinki, Finland. The models were able to capture the variability in the urban carbon cycle and transpiration due to changes in environmental conditions, soil type, and tree species. Carbon sequestration potential was estimated for an average street tree and for the average of the diverse soils present in the study area. Over the study period, soil respiration dominated carbon exchange over carbon sequestration due to the high initial carbon loss from the soil after street construction. However, the street tree plantings turned into a modest sink of carbon from the atmosphere on an annual scale, as tree and soil respiration approximately balanced the photosynthesis. The compensation point when street tree plantings turned from an annual source into a sink was reached more rapidly - after 12 years - by Alnus trees, while this point was reached by Tilia trees after 14 years. However, these moments naturally vary from site to site depending on the growing media, planting density, tree species, and climate. Overall, the results indicate the importance of soil in urban carbon sequestration estimations.Peer reviewe

Seasonal dynamics of autotrophic respiration in boreal forest soil estimated by continuous chamber measurements

Peer reviewe

Mobile ground-based measurements of aerosol and trace gases during a prescribed burning experiment in boreal forest in Finland

Peer reviewe