Hariliku kuuse eeluuenduse kasv lageraie järgselt

Looduslähedase metsamajanduse üheks oluliseks aspektiks on loodusliku uuenduse kasutamine metsade uuendamisel. Loodusliku uuenduse olemasolu tagab antud piirkonnale omase elupaigalise ja liigilise mitmekesisuse ning metsade genofondi säilimise. Loodusliku uuenduse säilitamine metsakasvatuslike (metsamajanduslike) tööde käigus on oluline aspekt uuendusraiete planeerimisel. Sellise struktuuriga metsad on ka haigustele vähem vastuvõtlikud ja tormikindlamad. Metsanduse praktikas on raietööde käigus soovitatav säilitada olemasolevat elujõulist eeluuendust (järelkasvu). Samas tekib küsimus, kuidas harvendada tihedaid eeluuenduse gruppe ja millised on peamised eeluuenduse puude visuaalselt määratavad tunnused, mille põhjal me võiksime otsuseid teha(tuleviku puude valimisel)? Käesolev uurimistöö on keskendunud metsade loodusliku uuenemise aspektidele ja looduslikku eeluuendust mõjutavate faktorite (tunnuste) analüüsile. Töö peamine eesmärk oli uurida vana metsa varjus kasvava hariliku kuuse eeluuenduse kasvu pärast nende vabastamist lageraie aladel. Töö koosneb kirjanduse ülevaate artiklist (I) ja kolmest originaaluuringust(II-IV). Metsa uuendamiseks peale lageraiet (uuendusraiet) on olemas mitmeid võimalusi. Esimene võimalus on raiesmik täielikult kultiveerida, st. istutada puittaimi või külvata seemet kogu raiesmiku pindalale. Teine võimalus on jätta metsastatav ala looduslikule uuenemisele. Kasutada võib ka kahe eelnimetatud meetodi kombinatsiooni. Puuliigid on erineva varju ja valguse kohastumisega. Võrreldes valgusnõudlike puuliikidega suudavad varjutaluvad puuliigid piiratud valguse tingimustes pikemat aega kasvada ja ellu jääda. Enne vana metsa lageraiet või turberaie viimast järku moodustunud noort metsapõlvkonda nimetatakse eeluuenduseks. Harilik kuusk (Picea abies (L.) Karst.) on varjutaluv puuliik, mis suudab anda piisaval hulgal elujõulist eeluuendust. Samas ei ole lihtne leida tunnuseid, mis kirjeldaksid piisava täpsusega eeluuenduse puude arengut lageraie järgselt. Eeluuenduse efektiivseks kasutamiseks on vaja teadmisi faktoritest, mis on olulised uuenduse kasvama minekule ja edasisele arengule. Puistu teket tagava uuenemise korral on nimetatud võte ka majanduslikult õigustatud. Eeluuenduse edasine areng pärast raiet ja häiringut sõltub mitmetest keskkonnateguritest. Seemnete idanemiseks sobivaid substraadi näitajaid on uurinud paljud autorid. Samuti mõjutab uuenemist (eeluuenduse tekkimist) valgussituatsioon ja häilu olemasolu. Mullapinna niiskustingimusele on tähelepanu juhtinud mitmed autorid. Konkurentsi mõju on vaadeldud mitmetes uurimustes. Puu võra, võrse ja okka tunnused (morfoloogia) võivad peegeldada eeluuenudse puude suhtelist kasvu, kohanemist erinevate valgustingimustega ja nende arengut vabastamisjärgselt. Järjestikuste aastate okkamass ja võrse pikkus kirjeldavad eeluuenduse kasvureaktisooni dünaamikat (I, III). Hariliku kuuse eeluuenduse uute võrsete vabastusjärgne kohanemine toimus 4-5 aasta jooksul pärast lageraiet (III). Kuna võrse tunnused on võimelised peegeldama valgustingimuste varieerumist varjus, mida eeluuenduse puud kogevad, on mudelitel mis prognoosivad puude kohanemist vabastamisjärgselt erinevate võrse tunnuste (näitajate), puu suuruse ja konkurentsi põhjal palju suurem täpsus (prognoosivõime) kui neil mis ennustavad ainult puu suuruse põhjal (I). Kõige parema kasvureaktsiooniga puid on võimalik ära tunda eelmise aasta kasvu (külgvõrse ja ladvavõrse pikkus) puu suuruse ning võrse ja okaste tunnuste (okaste arv ja mass võrse pikkusühiku kohta) järgi (I, IV). Loodusliku eeluuenduse puid on võimalik kasutada metsa uuendamisel, kuid vajalik on konkurentsi reguleerimine, eriti kiirekasvulise lehtpuu hulga vähendamine (IV). Praktiline soovitus oleks valgustusraie käigus harvendada tihedaid eeluuenduse gruppe ja vähendada teiste eeluuenduse kuuskede ja lehtpuude poolt avaldatavat konkurentsi (IV). Praktilise soovitusena võiks kasutada valikraiet, keskendudes üksikpuudele ja puude gruppidele või turberaiet (nt. aegjärkne raie). Aladel, kus kasutatakse erinevaid uuendusraieviise (lageraie, turberaie), tuleb raietööde käigus säilitada elujõulisi ja hästi kasvavaid hariliku kuuse eeluuenduse puid.The studies in this thesis were financially supported by Estonian Science Foundation Grants 4127 and 4980. Estonian Research Council, Target Financing Projects SF0432486s03 and SF0170014s08

Preface to the special issue : The impact of ungulates and other mammalian herbivores on forest ecosystems

Peer reviewe

Higher Winter-Spring Temperature and Winter-Spring/Summer Moisture Availability Increase Scots Pine Growth on Coastal Dune Microsites Around the South Baltic Sea

Coastal sand dunes near the Baltic Sea are a dynamic environment marking the boundary between land and sea and oftentimes covered by Scots pine (Pinus sylvestris L.) forests. Complex climate-environmental interactions characterize these ecosystems and largely determine the productivity and state of these coastal forests. In the face of future climate change, understanding interactions between coastal tree growth and climate variability is important to promote sustainable coastal forests. In this study, we assessed the effect of microsite conditions on tree growth and the temporal and spatial variability of the relationship between climate and Scots pine growth at nine coastal sand dune sites located around the south Baltic Sea. At each site, we studied the growth of Scots pine growing at microsites located at the ridge and bottom of a dune and built a network of 18 ring-width and 18 latewood blue intensity chronologies. Across this network, we found that microsite has a minor influence on ring-width variability, basal area increment, latewood blue intensity, and climate sensitivity. However, at the local scale, microsite effects turned out to be important for growth and climate sensitivity at some sites. Correlation analysis indicated that the strength and direction of climate-growth responses for the ring-width and blue intensity chronologies were similar for climate variables over the 1903–2016 period. A strong and positive relationship between ring-width and latewood blue intensity chronologies with winter-spring temperature was detected at local and regional scales. We identified a relatively strong, positive influence of winter-spring/summer moisture availability on both tree-ring proxies. When climate-growth responses between two intervals (1903–1959, 1960–2016) were compared, the strength of growth responses to temperature and moisture availability for both proxies varied. More specifically, for the ring-width network, we identified decreasing temperature-growth responses, which is in contrast to the latewood blue intensity network, where we documented decreasing and increasing temperature-growth relationships in the north and south respectively. We conclude that coastal Scots pine forests are primarily limited by winter-spring temperature and winterspring/summer drought despite differing microsite conditions.We detected some spatial and temporal variability in climate-growth relationships that warrant further investigation

Impact of post-fire management on soil respiration, carbon and nitrogen content in a managed hemiboreal forest

Boreal forests are an important carbon (C) sink and fire is the main natural disturbance, directly affecting the C-cycle via emissions from combustion of biomass and organic matter and indirectly through long-term changes in C-dynamics including soil respiration. Carbon dioxide (CO2) emission from soil (soil respiration) is one of the largest fluxes in the global C-cycle. Recovery of vegetation, organic matter and soil respiration may be influenced by the intensity of post-fire management such as salvage logging. To study the impact of forest fire, fire and salvage, and recovery time on soil respiration and soil C and N content, we sampled two permanent research areas in north-western Estonia that were damaged by fire: Vihterpalu (59 degrees 13' N 23 degrees 49' E) in 1992 and Nova (59 degrees 10' N 23 degrees 45' E) in 2008. Three types of sample plots were established: 1) unburned control with no harvesting (CO); 2) burned and uncleared (BU); and 3) burned and cleared (BC). Measurements were made in 2013, 21 years after wildfire in Vihterpalu and 5 years after wildfire in NOva. Soil respiration ranged from 0.00 to 1.38 g CO2 m(-2) h(-1). Soil respiration in the burned and cleared areas (BC) was not reduced compared to burned and uncleared (BU) areas but the average soil respiration in unburned control areas was more than twice the value in burned areas (average soil respiration in CO areas was 0.34 CO2 m(-2) h(-1), versus 0.16 CO2 m(-2) h(-1), the average soil respiration of BC and BU combined). Recovery over 20 years was mixed; respiration was insignificantly lower on younger than older burned sites (when BC and BU values were combined, the average values were 0.15 vs. 0.17 g CO2 m(-2) h(-1), respectively); soil-C was greater in the older burned plots than the younger (when BC and BU values were combined, the average values were 9.71 vs. 5.99 kg m(-2), respectively); but root biomass in older and recently burned areas was essentially the same (average 2.23 and 2.11 kg m(-2), respectively); soil-N was highest on burned areas 20 years after fire. Twenty years post-fire may be insufficient time for carbon dynamics to fully recover on these low productivity sandy sites.Peer reviewe

Long-term effects of forest fires on soil greenhouse gas emissions and extracellular enzyme activities in a hemiboreal forest

Fire is the most important natural disturbance in boreal forests, and it has a major role regulating the carbon (C) budget of these systems. With the expected increase in fire frequency, the greenhouse gas (GHG) budget of boreal forest soils may change. In order to understand the long-term nature of the soil–atmosphere GHG exchange after fire, we established a fire chronosequence representing successional stages at 8, 19, 34, 65, 76 and 179years following stand-replacing fires in hemiboreal Scots pine forests in Estonia. Changes in extracellular activity, litter decomposition, vegetation biomass, and soil physicochemical properties were assessed in relation to carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) emissions. Soil temperature was highest 8years after fire, whereas soil moisture varied through the fire chronosequences without a consistent pattern. Litter decomposition and CO2 efflux were still lower 8years after fire compared with pre-fire levels (179years after fire). Both returned to pre-fire levels before vegetation re-established, and CO2 efflux was only strongly responsive to temperature from 19years after fire onward. Recovery of CO2 efflux in the long term was associated with a moderate effect of fire on enzyme activity, the input of above- and below-ground litter carbon, and the re-establishment of vegetation. Soil acted as a CH4 sink and N2O source similarly in all successional stages. Compared with soil moisture and time after fire, soil temperature was the most important predictor for both GHGs. The re-establishment of overstorey and vegetation cover (mosses and lichens) might have caused an increase in CH4 and N2O effluxes in the studied areas, respectively.Peer reviewe

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

Mixing effects on Scots pine (Pinus sylvestris L.) and Norway spruce (Picea abies (L.) Karst.) productivity along a climatic gradient across Europe

Mixed-species stands have been found to be more productive than would be expected from the performance of their component species in monocultures due to facilitation and complementarity between species, although these interactions depend on the combination of species present. Our study focuses on monospecific and mixed species stands of Scots pine and Norway spruce using 20 triplets established in nine countries along a climatic gradient across Europe. Differences in mean tree and stand characteristics, productivity and stand structure were assessed. Basal area increment in mixed stands was 8% higher than expected while volume increment was only 2% greater. Scots pine trees growing in mixed-species stands showed 11% larger quadratic mean diameter, 7% larger dominant diameter, 17% higher basal area and 25% higher stand volume than trees growing in mono specific stands. Norway spruce showed only a non-significant tendency to lower mean values of diameters, heights, basal area, as well standing volume in mixtures than monocultures. Stand structure indices differed between mixed stands and monocultures of Scots pine showing a greater stratification in mixed-species stands. Furthermore, the studied morphological traits showed little variability for trees growing in monospecific stands, except for diameter at breast height, crown length and crown length ratio. For trees growing in mixed stands, all the morphological traits of the trees were identified as different. Some of these morphological traits were associated with relative productivity. Nevertheless, relative productivity in mixed-species stands was not related to site conditions

How Time since Forest Fire Affects Stand Structure, Soil Physical-Chemical Properties and Soil CO2 Efflux in Hemiboreal Scots Pine Forest Fire Chronosequence?

We compared the changes in aboveground biomass and initial recovery of C pools and CO2 efflux following fire disturbances in Scots pine (Pinus sylvesteris L.) stands with different time since stand-replacing fire. The study areas are located in hemiboreal vegetation zone, in north-western Estonia, in Vihterpalu. Six areas where the last fire occurred in the year 1837, 1940, 1951, 1982, 1997, and 2008 were chosen for the study. Our results show that forest fire has a substantial effect on the C content in the top soil layer, but not in the mineral soil layers. Soil respiration showed a chronological response to the time since the forest fire and the values were lowest in the area where the fire was in the year 2008. The respiration values also followed seasonal pattern being highest in August and lowest in May and November. The CO2 effluxes were lowest on the newly burned area through the entire growing season. There was also a positive correlation between soil temperature and soil respiration values in our study areas.Peer reviewe

Timing and duration of drought modulate tree growth response in pure and mixed stands of Scots pine and Norway spruce

Climate change is increasing the severity and frequency of droughts around the globe, leading to tree mortality that reduces production and provision of other ecosystem services. Recent studies show that growth of mixed stands may be more resilient to drought than pure stands. The two most economically important and widely distributed tree species in Europe are Norway spruce (Picea abies (L.) Karst) and Scots pine (Pinus sylvestris L.), but little is known about their susceptibility to drought when coexist. This paper analyses the resilience (resistance, recovery rate and recovery time) at individual-tree level using a network of tree-ring collections from 22 sites along a climatic gradient from central Europe to Scandinavia. We aimed to identify differences in growth following drought between the two species and between mixed and pure stands, and how environmental variables (climate, topography and site location) and tree characteristics influence them. We found that both the timing and duration of drought drive the different responses between species and compositions. Norway spruce showed higher vulnerability to summer drought, with both lower resistance and a longer recovery time than Scots pine. Mixtures provided higher drought resistance for both species compared to pure stands, but the benefit decreases with the duration of the drought. Especially climate sensitive and old trees in climatically marginal sites were more affected by drought stress. Synthesis. Promoting Scots pine and mixed forests is a promising strategy for adapting European forests to climate change. However, if future droughts become longer, the advantage of mixed stands could disappear which would be especially negative for Norway spruce