Häiringurežiimi mõju boreaalse metsaökosüsteemi süsinikuvoogudele

Fire is the most prevalent form of stand-replacing natural disturbance in boreal forests. However, corresponding with increasing global resource demand, harvesting now affects millions of ha of boreal forest each year, yet our understanding of harvesting impacts on boreal carbon (C) dynamics relative to fire remains debated. Although lot of work has been done to quantify and model boreal forest C dynamics, several knowledge caps remain. For example, pools like dead roots, medium and fine roots and stumps are rarely studied. Also, there are only few studies reporting total ecosystem C and there is no clear understanding of the primary processes. This thesis looks how anthropogenic and natural disturbances (clearcutting and wildfire) influence forest ecosystem C balance. Thesis consists of four articles. First is a literature review of boreal forest C dynamics. Second is a study about the aboveground biomass C dynamics. Third paper reports dead wood densities in the area so that collected dead wood volume data could be converted to dead wood mass estimates. Fourth paper combines all relevant C pools and looks at the total ecosystem C dynamics in young boreal forests. Result is a direct comparison of C stocks following clear-cut harvesting and fire over a 27-year chronosequence in the boreal forest of central Canada. While many past studies have lacked complete measurement of all C pools, this thesis provides full coverage of all C pools, including live biomass, deadwood, forest floor and mineral soil. Results indicate that there is no significant difference in overall ecosystem C stocks during early stand development, but that the relative contribution of C pools to total forest ecosystem C varies between disturbance types. Live biomass C was significantly higher following harvesting compared with post-fire stands, because of residual live trees and advanced regeneration left intact during harvest. On the contrary, most live biomass was killed following intense crown fire and therefore post-fire stands contained higher stocks of deadwood C. Snag and stump C mass peaked immediately following fire, but dramatically decreased 8 years after fire as dead trees began to fall over, contributing to the downed dead wood C pool. Contrary, snag and stump C mass increased after logging. Although the thesis did not show the initial decrease in forest floor C mass commonly acknowledged directly after stand-replacing disturbance, forest floor C stock steadily increased over time. C amount in mineral soil did not change after harvest but increased after fire. Therefore, current management practices (i.e. harvesting and planting or seeding) in boreal mixedwood forests of central Canada have no negative impact on total ecosystem carbon. Considering also the life cycle of products made from this wood and the displacement effect (i.e. use of wood instead of concrete or steel that have higher C footprint), shows that harvesting results an increased C uptake from the atmosphere, therefore moderating climate change. For better comparison of disturbance effects it is necessary also to compare C dynamics in older forest.Boreaalne mets sisaldab hulgaliselt süsinikku ja mängib seetõttu globaalses süsinikuringluses olulist rolli. Muutused boreaalse metsa süsinikuringes avaldavad mõju ka globaalsele kliimale. Ajalooliselt on olnud tuli Põhja-Ameerika boreaalse metsa ökosüsteemi protsesside peamine mõjutaja. Üha suurenenud vajadus metsa bioproduktsiooni kasutamiseks on muutnud metsaraied olulise tähtsusega häiringuteguriks. Kuigi palju tööd on tehtud boreaalse metsa süsinikuvoogude kvantifitseerimisega ja modelleerimisega, on teadmistes mitmeid olulisi lünki (näiteks: surnud juurte mass, peen- (<2 mm) ja keskmiste (2–10 mm) juurte mass, kännud). Samuti on vähe koostatud kogu metsaökosüsteemi süsinikuringet käsitlevaid üldistusi ning puudub täpne ülevaade peamistest protsessidest. Käesolevas töös on uuritud, kuidas inimtekkelised ja looduslikud häiringud (lageraie ja tulekahju) mõjutavad metsaökosüsteemi süsinikutagavara. Töö koosneb neljast artiklist. Esimeses on esitatud kirjandusülevaade boreaalse metsa süsiniku dünaamikast. Teine keskendub elustaimestiku süsiniku dünaamikale. Kolmas töö kirjeldab lagupuidu tihedust, mis on vajalik lagupuidu mahus massi arvutamiseks. Neljas töö, mis on doktoritöö põhitulemus, kirjeldab kogu metsaökosüsteemis oleva süsiniku dünaamikat noores boreaalses metsas. Süsinik on metsaökosüsteemis jaotunud nelja põhilise struktuurikomponendi vahel: elus biomass, surnud biomass, mulla orgaaniline osa ja mineraalse mulla orgaaniline süsinik. Pärast häiringut muutuvad loetletud komponendid erinevalt, mõjutades üksteist metsa kasvades ning süsiniku paigutumisel ühest reservuaarist teise. Süsiniku kogust hinnati kvantitatiivselt aegrea meetodil (1, 8 ja 27 aastat pärast häiringut). Koostatud üldine andmebaas annab detailse ülevaate häiringujärgse boreaalse metsa süsinikudünaamikast. Kogu metsaökosüsteemi süsinikutagavara (KMS) muutub pärast häiringuid oluliselt, kuid süsinikutagavara pärast metsatulekahju ja lageraiet ei erine. Kogutud andmed on sarnased teiste boreaalse metsa uuringuandmetega. Pärast raiet langeb KMS 146.5 tonnilt hektaril 127.7 tonnini ja tõuseb seejärel 185.1 tonnini hektari kohta. Pärast metsapõlengut langeb KMS 133.7 tonnilt hektaril 127.4 tonnini ja tõuseb seejärel 163.6 tonnini hektari kohta. Elus biomass, orgaaniline mulla horisont ja mineraalse mulla süsinikukogused muutusid pärast häiringuid erinevalt, surnud puidu muutumine oli pärast tulekahju ja raiet sarnane. Keskmiselt moodustas mineraalse mulla süsinik 38% süsiniku kogutagavarast, järgnesid surnud puit (29%), mulla orgaaniline horisont (20%) ja elus biomass (13%). Võttes arvesse, et nähtav on kõigest pealmine osa orgaanilisest mullast, selgitati, et noortes puistutes on kogu süsinikutagavarast (maapealsed reservuaarid) pärast lageraiet nähtav vaid 20% ja pärast põlengut 33%. Tänased metsade majandamise võtted (lageraie ja istutus) Põhja-Ameerika keskosa boreaalses metsas KMS-i negatiivselt ei mõjuta. Arvestades puittoodete kogu elutsükli ja tooraine asenduse mõju (puidu kasutus betooni ja metalli asemel, mis omavad oluliselt suuremat süsiniku jalajälge), leiti, et lageraie põhjustab atmosfäärist suurema süsiniku netosidumise kui looduslik häiring. Uurimuse tulemused näitavad, et süsinikubilansi täpseks kirjeldamiseks on vaja arvesse võtta kõik süsinikukogused vastavalt selle paiknemisele metsaökosüsteemi eri osades

Saproxylic beetles in artificially created high stumps of spruce and birch three years after cutting

According to the FSC and PEFC certification standards in Sweden, high stumps should be created during thinning and regeneration felling to reduce the negative effect of intensive forestmanagement on biodiversity, especially for the ca. 1000 species of wood dependent (saproxylic) beetles. To study the importance of high stumps for saproxylic beetles the fauna of 120 three-year old mechanically created high stumps of Norway spruce and Silver birch were sampled in the provinces of Halland, Kronoberg and Kalmar in Southern Sweden. Using bark peeling and sieving, 4179 individuals of saproxylic beetles were found, belonging to 66 species. Nine of the species were on the Swedish red-list. Of all caught beetle species the most common were Crypturgus pusillus, Phloeocharis subtilissima and Crypturgus hispidulus. The number of species was significantly different between spruce and birch high stumps, on average spruce stumps hosted 4.6 saproxylic species and birch stumps 5.5. Also the beetle assemblage on spruce and birch were different, implying that high stumps of both deciduous and coniferous species should be left, if possible. Other ecological variables like presumed diversity 'rich-poor' landscapes, geographical location and stump diameter (within the range of 20-58 cm and 21-40 cm for spruce and birch stumps, respectively) did not affect the species richness on stumps. Nevertheless, the 66 found species show the biological value of making high stumps. Furthermore, the occurrence of nine red-listed species indicates that high stumps are not only important for trivial species but contribute also to protection of threatened beetles. I conclude that mechanically created high stumps are important and valuable habitat supplement for saproxylic fauna

Carbon dynamics of boreal mixedwoods in central Canada

Large amount of carbon (C) stored in boreal forest ecosystems plays an important role in the global carbon cycle. Forest ecosystem C is stored in four major pools: live vegetation (above-and below ground), dead woody material (snags, down woody debris, and stumps), organic soil horizons (forest floor), and mineral soil. Carbon cycling among these pools is mainly determined by disturbance. A large portion of previously fire-driven ecosystems in boreal North American forest are now managed

Protected area designation and management in a world of climate change: A review of recommendations

Climate change is challenging conservation strategies for protected areas. To summarise current guidance, we systematically compiled recommendations from reviews of scientific literature (74 reviews fitting inclusion criteria) about how to adapt conservation strategies in the face of climate change. We focussed on strategies for designation and management of protected areas in terrestrial landscapes, in boreal and temperate regions. Most recommendations belonged to one of five dominating categories: (i) Ensure sufficient connectivity; (ii) Protect climate refugia; (iii) Protect a few large rather than many small areas; (iv) Protect areas predicted to become important for biodiversity in the future; and (v) Complement permanently protected areas with temporary protection. The uncertainties and risks caused by climate change imply that additional conservation efforts are necessary to reach conservation goals. To protect biodiversity in the future, traditional biodiversity conservation strategies should be combined with strategies purposely developed in response to a warming climate

What is the impact of continuous cover forestry compared to clearcut forestry on stand-level biodiversity in boreal and temperate forests? A systematic review protocol

BackgroundThe ecosystem services provided by forests are essential for societal well-being. Production forests are increasingly expected to provide a range of ecosystem services in addition to wood biomass, as well as the biodiversity upon which many of these services depend. Production forests can be managed using different methods that affect the habitat provided and the biodiversity supported. Clearcutting (CC) is a widely used forest management system that has been criticised due to its negative effects on biodiversity. Alternative less intensive forest management systems have been developed with the hope of producing comparable levels of biomass with fewer negative impacts on forest biodiversity. One of these alternatives is continuous cover forestry (CCF); a management system that always maintains tree cover in an uneven-aged production forest stand. Many studies have been conducted which contrast the effects of CCF and CC on biodiversity with varying results. The aim of the review is to explore how CCF system compares to CC in terms of outcomes for terrestrial forest biodiversity.MethodsDue to the diverse vocabulary used to describe CCF, a systematic search for terms was carried out and a comprehensive search string will be used to maximise the likelihood of finding all relevant papers. We will gather, summarise and synthesise primary field studies, both peer-reviewed and grey literature, from temperate and boreal forest comparing biodiversity in CCF and CC stands. Species richness and abundance of plants, animals and fungi will be used to conduct a meta-analysis. Other biodiversity indicators and indices will be used for a narrative synthesis. As the effects of forest management depend on local conditions, we place a special emphasis on exploring the influence of various effect modifiers

Decadal‐Scale Recovery of Carbon Stocks After Wildfires Throughout the Boreal Forests

Boreal forests store 30% of the world's terrestrial carbon (C). Consequently, climate change mediated alterations in the boreal forest fire regime can have a significant impact on the global C budget. Here we synthesize the effects of forest fires on the stocks and recovery rates of C in boreal forests using 368 plots from 16 long-term (>= 100 year) fire chronosequences distributed throughout the boreal zone. Forest fires led to a decrease in total C stocks (excluding mineral soil) by an average of 60% (range from 80%), which was primarily a result of C stock declines in the living trees and soil organic layer. Total C stocks increased with time since fire largely following a sigmoidal shape Gompertz function, with an average asymptote of 8.1 kg C m(-2). Total C stocks accumulated at a rate of 2-60 g m(-2) yr(-1)during the first 100 years. Potential evapotranspiration (PET) was identified as a significant driver of C stocks and their post-fire recovery, likely because it integrates temperature, radiation, and the length of the growing season. If the fire return interval shortens toPeer reviewe