Alustaimestik ja seda mõjutavad tegurid endistel põllumajandusmaadel kasvavates noortes lehtpuuistandikes

The establishment of forest plantations (including short-rotation forest plantations) is seen as one way to reemploy abandoned agricultural sites. The main goal of commercial forest plantations is the production of timber and woody biomass, however, the implications for biodiversity (including floristic diversity) can not be neglected. Due to the agricultural legacy the understorey of forests established on former agricultural land differs from the understorey of forests that were never cleared and these differences may persist for long periods. Since 1999 more than 700 ha of plantations with semi-exotic hybrid aspen (Populus × wettsteinii Hämet-Ahti) have been established on former agricultural land in Estonia that can be managed with 20- to 30-year rotations. Experience from other countries has indicated that environmental problems may occur in the plantations of exotic tree species. Among the native deciduous tree species silver birch (Betula pendula Roth) is considered to be a suitable tree species for the establishment of plantations in Estonia. However, abandoned agricultural sites become afforested also in the process of secondary succession with Betula spp among first arrivers. Studies conducted in former mining areas that have compared unassisted natural succession and the establishment of plantations have pointed out that naturally regenerated stands may support higher understorey species richness and diversity than plantations. Given the above mentioned, the following aims were set to the thesis: 1) to determine which site- and stand-related factors have affected understorey vegetation characteristics in young commercial forest plantations on abandoned agricultural land; 2) to study if plantations of semi-exotic hybrid aspen offer similar habitat for the understorey as plantations of native tree species silver birch; 3) to characterize the formation of the bryophyte layer; 4) to characterize the formation of forest understorey; 5) to compare understorey vegetation characteristics between naturally regenerated birch stands and silver birch plantations. Data on understorey, overstorey and site factors were collected from 73 experimental plots established in 24 hybrid aspen and 11 silver birch plantations and in 11 naturally regenerated birch stands. Two monitorings were carried out in plantations: the first monitoring in 7 to 9-year-old plantations and the second monitoring in 13 to 14-year-old plantations. Based on the results of the thesis, the observable trends in the understorey vegetation of young plantations were mostly driven by the former agricultural land use, site preparation method, and soil properties. With increasing stand age the influence of pre-establishment disturbances becomes less pronounced and the impact of overstorey-related factors increases. The majority of the vascular plant and bryophyte understorey vegetation characteristics were similar in young hybrid aspen and silver birch plantations and it may be concluded that semi-exotic hybrid aspen provides similar habitat for understorey as native silver birch. The proportion of forest species was low in the vascular plant understorey of plantations at the time of both monitorings. Although the number and cover of forest species slowly increased between the two monitorings, clear domininance of grassland species continued. The cover of the bryophyte layer was low in young plantations. Typical bryophytes were light-demanding perennials. The silvicultural management of plantations in the future should include measures that provide habitats for epixylic and epiphytic bryophyte species. The comparison of naturally regenerated stands and plantations showed that the species richness and diversity of bryophytes were higher in naturally regenerated birch stands, but the species richness and diversity of vascular plants did not differ between the two stand types. However, significantly higher numbers of forest species (both vascular plant and bryophyte) indicated that the formation of forest understorey had progressed further in naturally regenerated stands. This can be explained by the longer undisturbed succession and colonization period of naturally regenerated stands. Both natural and artificial regeneration can be recommended as possible alternatives for the establishment of new forests on former agricultural land.Intensiivmeetodil, sh lühikese raieringiga majandatavate puuistandike rajamine on alternatiivseks kasutusvõimaluseks endistele põllumajandusmaadele. Tootmisele suunatud istandikes ehk puupõldudel ei ole peamiseks eesmärgiks metsökosüsteemi kujundamine, vaid soovitakse saavutada maksimaalne puidu või mõne teise puudega seotud toorme produktsioon. Puupõldude pindala pidev kasv maailmas tõstatab aga küsimuse, milline on nende mõju looduslikule, sh floristilisele mitmekesisusele. Kirjanduse andmetel võib endistele põllumajandusmaadele rajatud metsade, sh istandike alustaimestik jääda pikaks ajaks erinevaks põliste metsade alustaimestikust, mis seostub põllumajandusliku maakasutuse mõjudega. Alates 1999. aastast on Eestis endistele põllumajandusmaadele rajatud u 700 ha puuistandikke poolvõõrliigi hübriidhaavaga (Populus × wettsteinii Hämet-Ahti), mida plaanitakse majandada lühikese 20–30-aastase raieringiga. Mujal maailmas on võõrpuuliikidega rajatud istandikes täheldatud mõnikord keskkonnakaitselisi probleeme. Kohalikest lehtpuudest soovitatakse Eestis endiste põllumajandusmaade metsastamiseks eelkõige arukaske (Betula pendula Roth), ent kaasikud võivad endistele põllumajanduskõlvikutele tekkida ka looduslikult. Endiste karjäärialade metsastamisel on istandike ja looduslikult tekkinud puistute võrdlusel täheldatud, et looduslikult tekkinud puistute alustaimestik võib olla liigirikkam ja mitmekesisem kui istandikes. Lähtuvalt eespool toodust seati doktoritööle järgnevad eesmärgid: 1) analüüsida, millised kasvukoha ja puistu tunnused mõjutavad alustaimestiku karakteristikuid endistel põllumajandusmaadel kasvavates noortes istandikes; 2) hinnata, kas poolvõõrliigi hübriidhaava istandikud pakuvad alustaimestiku liikidele sarnaseid kasvutingimusi kodumaise puuliigi arukase istandikega; 3) iseloomustada samblarinde kujunemist ja sammalde liigilist koosseisu; 4) iseloomustada metsa alustaimestiku kujunemist; 5) võrrelda alustaimestiku karakteristikuid arukaseistandikes ja looduslikult tekkinud kaasikutes. Alustaimestikku, puurinnet ja kasvukohta iseloomustav andmestik koguti seitsmekümne kolmelt püsiproovitükilt, mis paiknesid 11 arukase- ja 24 hübriidhaavaistandikus ning 11 looduslikult tekkinud kaasikus. Istandike kohta on doktoritöös esitatud alustaimestiku esimese kirjelduse (vanuses 7 kuni 9 aastat) ja korduskirjelduse (vanuses 13 kuni 14 aastat) andmed. Doktoritöös leiti, et noore istandiku alustaimestiku karakteristikuid mõjutasid esialgu eelnev põllumajanduslik maakasutus, istandiku rajamisel rakendatud maapinna ettevalmistusviis ja mullastiku tingimused. Istandike vanuse kasvades muutub istandiku rajamisele eelnenud häiringute mõjust olulisemaks puurindega seotud tegurite mõju rohu- ja samblarindele. Hübriidhaava- ja arukaseistandike alustaimestiku (soontaimede ja sammalde) karakteristikud olid suures osas sarnased, mis lubab väita, et hübriidhaavikute rajamisega Eestis ei kaasne alustaimestikus ebasobivaid arenguid, nt võõrliikide levikut. Metsaliikide osakaal istandike alustaimestikus oli väike nii esimese kirjelduse kui ka korduskirjelduse ajal. Hoolimata sellest, et metsaliikide arv ja katvus kasvasid vähehaaval, domineerisid ka 13–14-aastaste istandike alustaimestikus jätkuvalt rohumaaliigid. Ka samblarinde katvus noortes istandikes oli väike. Tüüpilised noortes istandikes kasvavad liigid olid valgusnõudlikud mitmeaastased samblad. Istandike edasisel majandamisel oleks soovitatav rakendada abinõusid, mis pakuvad lisakasvukohti epiksüülsetele ja epifüütsetele samblaliikidele. Hüpotees, et endistele põllumajandusmaadele looduslikult tekkinud puistud toetavad suuremat alustaimestiku liigirikkust, leidis kinnitust üksnes maapinnal kasvanud sammalde arvu ja mitmekesisusindeksi osas. Lisaks kasvas looduslike kaasikute alustaimestikus rohkem metsaliike (nii soon- kui sammaltaimi), mida võib seletada pikema rahuliku suktsessiooni ja kolonisatsiooni ajaga.Publication of this dissertation is supported by the Estonian University of Life Sciences and by the Doctoral School of Earth Sciences and Ecology created under the auspices of European Social Fund

Effect of environmental factors on the composition of terrestrial bryophyte and lichen species in Scots pine forests on fixed sand dunes

Aim of the study: To investigate terrestrial bryophyte and lichen species richness and environmental factors affecting the composition of species.Area of the study: Four Boreal zone fixed dunes were selected in the coastal area of the Baltic Sea in southwest Estonia.Material and methods: Non-metric multidimensional scaling was performed to analyse distribution patterns and environmental factors like canopy cover, photosynthetically active radiation, soil organic horizon thickness and decomposition rates, soil volumetric water content, soil pH and electrical conductivity and soil nutrients correlated with bryophyte and lichen species composition.Main results: Thirty bryophytes and 22 lichens were found on 232 sample plots, the most frequent species were Pleurozium schreberi (Willd. ex Brid.) Mitt., Hylocomium splendens (Hedw.) Schimp., Dicranum polysetum Sw. ex anon., Cladonia arbuscula (Wallr.) Flot. and Cladonia furcata (Huds.) Schrad. The lichen species richness was highest on the slopes of the dunes and decreased towards the bottoms and tops; bryophyte species richness was higher on the bottoms and decreased towards the tops of the dunes.Research highlights: The composition of bryophytes and lichens is significantly influenced by the aspect and the location on the dune, light conditions, soil pH, soil salinity (measured as electrical conductivity) and volumetric water content, thickness of moderately decomposed organic horizon and vascular plant species cover.KeywordsInland dunes; terrestrial bryophyte and lichen communities; environmental factors; topography

KIK projekt nr. 12076

Eesti riik on seadnud eesmärgiks biomajanduse jätkusuutliku edendamise, kus prioriteetseteks eesmärkideks on muuhulgas maaressursi efektiivsem kasutamine ja taastuvenergia osakaalu tõstmine. Lisaks biomajanduse eesmärkidele on Eesti sõlminud mitmeid rahvusvahelisi kokkuleppeid nagu Pariisi kliimalepe (2015) ja Kyoto protokoll (1997) kliimamuutuste leevendamiseks. Metsasektoril on oluline roll eelmainitud eesmärkide saavutamiseks, mistõttu võib eeldada suurt raiesurvet metsadele. Juba praegu on Põhja-Euroopa riigid, sealhulgas Eesti, kasutamas energiaks märkimisväärsel hulgal puiduenergiat (Rytter et al. 2016). Seetõttu, leevendamaks üha suurenevat puiduvajadust, on vajalik välja töötada alternatiivsed puidutootmise süsteemid, võttes kasutusse seni tootmisest väljas olevad põllumaad. Hiljutised hinnangud näitavad, et ca 300 000 ha endist põllumaad on aktiivsest kasutusest väljas, kuna taoliste kõlvikute väiksus (keskmiselt ca 1,5 ha) ning raske ligipääsetavus ei võimalda nendel maadel intensiivse põllumajandusega tegeleda (Vohu 2014). Üheks uudseks metsakasvatuslikuks meetodiks Põhja-Euroopas on lühikese raieringiga metsaistandike kasvatamine kasutusest välja jäänud põllumaadel (Tullus et al. 2013). Lühikese raieringiga metsanduse eesmärk on maaressursi maksimaalselt efektiivne ära kasutamine, optimeerides raieringi vastavalt puistu mahuküpsuse saabumisele. Üheks potentsiaalseks puuliigiks lühikese raieringiga metsanduse praktiseerimisel nii Läänemere regioonis tervikuna kui ka Eestis on osutunud hübriidhaab (Tullus et al. 2012; Karacic et al. 2003). Viimased hinnangud näitavad, et Läänemere riikides on hübriidhaavikute pindala kasvanud ca 12 000 hektarile (Lutter 2017). Viimase aja uued hübriidhaavikud Eestis on kasvatanud istandike pindala ca 1000 hektarini ning eeldatavasti on lähiaastatel oodata jätkuvat pindala suurenemist. Hübriidhaavikute kasvatamise peamine eesmärk on tooraine kasvatamine tselluloosi- ja energiapuidu tööstustele, sealhulgas on võimalik tüve alaosast saada väärtuslikumat saepalki (Tullus et al. 2012). Kiirekasvulistest hübriidhaavikutest saadav biomass omab potentsiaali asendamaks puitu, mis raiutakse vanadest kõrge loodusväärtusega haavikutest metsamaal. Esimesed hübriidhaavikud rajati Eestisse 1990-ndate lõpus ja 2000-ndate alguses, mistõttu on istandikud läbinud rohkem kui poole eeldatavast raieringi pikkusest (25–30 aastat). Senised teadusuuringud esimese põlvkonna hübriidhaavikute sobivusest Eesti kliima- ja mullatingimustesse katavad raieringi esimest poolt (Tullus 2013; Lutter 2017). Senised tulemused näitavad, et hübriidhaab on ligikaudu kaks korda produktiivsem kui harilik haab 4 metsamaal sarnastel kasvukohatüüpidel (Lutter et al. 2017). Sealjuures ei ole hübriidhaavikute kiire kasv vähendanud mulla toitainete sisaldusi ja süsinikuvarusid (Lutter et al. 2016ab). Intensiivse biomassi produtseerimise tõttu näitavad hübriidhaavikud suurt potentsiaali kliimamuutuste leevendamisel intensiivse CO2 sidumise kaudu maapealsesse biomassi (Lutter et al. 2016b). Elurikkuse uuringud hübriidhaavikutes on näidanud, et puistute vanuse kasvades suureneb metsaliikide osakaal soontaimede hulgas ning suureneb sammalde arvukus (Tullus 2013; Tullus et al. 2015). Sammalde ja samblike uurimused näitavad, et raieringi keskel olevad hübriidhaavikud pakuvad noorest vanusest hoolimata elupaiku suurele hulgale liikidele (Randlane et al. 2017), seejuures ka uutele samblikuliikidele Eestis (Oja et al. 2016) Sarnaselt harilikule haavale uueneb hübriidhaab peale lageraiet vegetatiivselt juure- ja kännuvõsust (Tullus et al. 2012). Suur võsude arv ning sobiva majandamismudeli valimine teise põlvkonna hübriidhaaviku kasvatamisel on suur metsakasvatuslik väljakutse, kuna senised teadmised hübriidhaavikute vegetatiivse teise põlvkonna erinevate majandamismudelite kohta ei ole rahuldavad nii produktsiooni, keskkonnamõjude, elurikkuse kui ka ökonoomika koha pealt. Vajalik on välja töötada paindlikud majandamismudelid, mis arvestavad puiduturu situatsiooni ja nõudlust (paberipuit, energiapuit), samal ajal arvesse võttes ka võimalikke keskkonnamõjusid nii mulla viljakusele kui ka elurikkusele. Senine Põhjamaade kogemus hübriidhaava teise vegetatiivse põlvkonna majandamise kohta on samuti puudulik. Rohkem teadmisi on viimasel ajal avaldatud hübriidhaava teise põlvkonna produktsiooni ja kloonide vahelise konkurentsi kohta Rootsi ja Soome tingimustes (Rytter 2006; McCarthy and Rytter 2016; Rytter and Rytter 2017; Hytönen 2018), kuid laiemad keskkonna mõjude analüüsid on siiani lünklikud

Effect of environmental factors on the composition of terrestrial bryophyte and lichen species in Scots pine forests on fixed sand dunes

Aim of the study: To investigate terrestrial bryophyte and lichen species richness and environmental factors affecting the composition of species.Area of the study: Four Boreal zone fixed dunes were selected in the coastal area of the Baltic Sea in southwest Estonia.Material and methods: Non-metric multidimensional scaling was performed to analyse distribution patterns and environmental factors like canopy cover, photosynthetically active radiation, soil organic horizon thickness and decomposition rates, soil volumetric water content, soil pH and electrical conductivity and soil nutrients correlated with bryophyte and lichen species composition.Main results: Thirty bryophytes and 22 lichens were found on 232 sample plots, the most frequent species were Pleurozium schreberi (Willd. ex Brid.) Mitt., Hylocomium splendens (Hedw.) Schimp., Dicranum polysetum Sw. ex anon., Cladonia arbuscula (Wallr.) Flot. and Cladonia furcata (Huds.) Schrad. The lichen species richness was highest on the slopes of the dunes and decreased towards the bottoms and tops; bryophyte species richness was higher on the bottoms and decreased towards the tops of the dunes.Research highlights: The composition of bryophytes and lichens is significantly influenced by the aspect and the location on the dune, light conditions, soil pH, soil salinity (measured as electrical conductivity) and volumetric water content, thickness of moderately decomposed organic horizon and vascular plant species cover.KeywordsInland dunes; terrestrial bryophyte and lichen communities; environmental factors; topography

Diversity of lichens and bryophytes in hybrid aspen plantations in Estonia depends on landscape structure

Importance of single-species forest plantations in sustaining biodiversity could be bigger than expected. We described the diversity of lichens and bryophytes in 15 midterm (16â 17-year-old) hybrid aspen (Populus tremula Ă P. tremuloides) plantations in Estonia. Species richness and composition data were linked with environmental and landscape-scale variables. Altogether, 44 lichen and 37 bryophyte species were recorded from plantations; richnesses of bryophytes and lichens were positively correlated. Lichen species composition was significantly affected by landscape-scale parameters (distance to the nearest present forest, distance to the nearest forest continuously occurring in the same place since 1930s, and forest area in the study plot vicinity in 1930s). Bryophyte species composition was affected mainly by light conditions and forest area in 1930s. Among lichens, functional group of sexual crustose species dominated in midterm plantations; appearance of asexual lichens of different growth forms is expected during next years. Our results indicate importance of long-term availability of good-quality forests as sources of propagules. Short-rotation hybrid aspen plantations can provide temporary habitats for forest species and thus in part contribute to preserving landscape-scale biodiversity, if they are close to possible colonisation sources. Green-tree retension in plantations will probably raise the biodiversity value of those short-term communities.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

The Effect of Stand Age on Biodiversity in a 130-Year Chronosequence of Populus tremula Stands

The effect of stand age on biodiversity in the stands of Populus tremula, a keystone tree species in boreal forests, has been insufficiently studied, although this knowledge is crucial for maintaining biodiversity in managed forests. We studied the assemblages of vascular plants, bryophytes and lichens from a chronosequence of aspen stands (n = 20) with an age from 8 to 131 years, aiming to identify the main patterns in species richness and composition. Altogether, 72 vascular plant species were found in the field layer and 17 species in the shrub layer. The total numbers of bryophyte and lichen species were 92 and 104, respectively. Overall, 2 vascular plant, 12 bryophyte and 9 lichen species were the taxa with a high conservation value. Sixteen lichens were regarded as management-sensitive or focal species based on earlier studies, and 10 vascular plant species were hemeraphobic (severely disturbed by human activities). The effect of stand age on average species richness estimates depended on the studied species groups. Stand age had a negative effect on the average number of vascular plants, field layer species, apophytic vascular plants and epixylic lichens and a positive effect on the number of lichens, the number of epiphytic bryophytes and lichens and on bryophytes and lichens with a high conservation value. The compositional patterns of vascular plants, bryophytes and lichens strongly correlated with stand age. In addition, stand characteristics, soil properties and light conditions influenced the assemblages, although the direct effects were variable for different groups. The largest differences could be observed in vascular plant, bryophyte and lichen communities between young and old stands; for lichens, also mature and old stands differed significantly. Our results indicate that more than 60 years are required for the recovery of some species groups after clear-cutting. At the same time, other species groups were either not negatively affected by clear-cutting or showed a higher richness in younger stands. Therefore, we conclude that the management of aspen stands should involve the combination of different management regimes on the landscape scale (variation from short to long rotations in different stands, maintaining retention trees and ceasing of clear-cutting in some stands). Our results also show that as second-storey Tilia cordata played an important role in maintaining biodiversity in the studied stands, this tree species needs to be preserved in forests where lime trees naturally grow as co-dominants

Seventy-year history of management using low-intensity harvesting methods: weak impact on biodiversity of hemiboreal Scots pine forests

Less intensive harvesting methods (e.g., selection cutting, shelterwood cuttings) are recommended as alternatives to clearcutting for maintaining mature forest biodiversity in the process of forest regeneration. However, the long-term impact of low-intensity harvesting methods has rarely been studied. Our aim was to clarify the long-term effects of repeated selective cutting, thinning, and shelterwood cutting on the richness, abundance, and species composition of vascular plants, bryophytes, and lichens in Scots pine forests (Pinus sylvestris L.). Data were collected from 25 mature stands located in dry Podzols in southwestern Estonia with a known management history for the last 70 years. Altogether, 35 vascular plant, 41 bryophyte, and 78 lichen species were recorded, including five species with conservational value. Generally, the management history was not related to species richness, except a negative correlation with the species number of epiphytic lichens on conifer trees. In addition, the abundance of two lichen species from the genus Chaenotheca was lower in more frequently managed stands. Species richness and composition were most strongly affected by soil pH and light conditions. We conclude that long-term, low-intensity harvesting of Scots pine forests on nutrient-poor Podzols maintains suitable habitats for vascular plants, bryophytes, and lichens, confirming its suitability for sustainable forest regeneration.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Climate Change at Northern Latitudes: Rising Atmospheric Humidity Decreases Transpiration, N-Uptake and Growth Rate of Hybrid Aspen

<div><p>At northern latitudes a rise in atmospheric humidity and precipitation is predicted as a consequence of global climate change. We studied several growth and functional traits of hybrid aspen (<em>Populus tremula</em> L.×<em>P. tremuloides</em> Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008–2010) in Estonia, which represents northern temperate climate (boreo-nemoral zone). Data were collected from three humidified (H) and three control (C) plots, and analysed using nested linear models. Elevated air humidity significantly reduced height, stem diameter and stem volume increments and transpiration of the trees whereas these effects remained highly significant also after considering the side effects from soil-related confounders within the 2.7 ha study area. Tree leaves were smaller, lighter and had lower leaf mass per area (LMA) in H plots. The magnitude and significance of the humidity treatment effect – inhibition of above-ground growth rate – was more pronounced in larger trees. The lower growth rate in the humidified plots can be partly explained by a decrease in transpiration-driven mass flow of NO₃⁻ in soil, resulting in a significant reduction in the measured uptake of N to foliage in the H plots. The results suggest that the potential growth improvement of fast-growing trees like aspens, due to increasing temperature and atmospheric CO₂ concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.</p> </div