Perturbations in the carbon budget of the tropics

The carbon budget of the tropics has been perturbed as a result of human influences. Here, we attempt to construct a ‘bottom-up’ analysis of the biological components of the budget as they are affected by human activities. There are major uncertainties in the extent and carbon content of different vegetation types, the rates of land-use change and forest degradation, but recent developments in satellite remote sensing have gone far towards reducing these uncertainties. Stocks of carbon as biomass in tropical forests and woodlands add up to 271 ± 16 Pg with an even greater quantity of carbon as soil organic matter. Carbon loss from deforestation, degradation, harvesting and peat fires is estimated as 2.01 ± 1.1 Pg annum(−1); while carbon gain from forest and woodland growth is 1.85 ± 0.09 Pg annum(−1). We conclude that tropical lands are on average a small carbon source to the atmosphere, a result that is consistent with the ‘top-down’ result from measurements in the atmosphere. If they were to be conserved, they would be a substantial carbon sink. Release of carbon as carbon dioxide from fossil fuel burning in the tropics is 0.74 Pg annum(−1) or 0.57 MgC person(−1) annum(−1), much lower than the corresponding figures from developed regions of the world

Forests and Carbon: A Synthesis of Science, Management, and Policy for Carbon Sequestration in Forests

The goal of this volume is to provide guidance for land managers and policymakers seeking to understand the complex science and policy of forest carbon as it relates to tangible problems of forest management and the more abstract problems of addressing drivers of deforestation and negotiating policy frameworks for reducing CO2 emissions from forests. It is the culmination of three graduate seminars at the Yale School of Forestry & Environmental Studies focused on carbon sequestration in forest ecosystems and their role in addressing climate change

The Fire in the Mediterranean Region: A Case Study of Forest Fires in Portugal

Forest fires are a common disturbance in many forest systems in the world and in particular in the Mediterranean region. Their origins can be either natural or anthropogenic. The effects in regard to the time trends, vegetation, and soil will be reflected in the species distribution, forest composition, and soil potential productivity. In general, it can be said that the larger the fire and the shorter the time between two consecutive occurrences, the higher the probability to originate shifts in vegetation and soil degradation. In the Mediterranean region, the number of fire ignitions does not reflect the burnt area due to the occurrence of very large fires. The latter occur in a very small proportion of the number of ignitions, but result in very large burnt areas. Also there seems to be an increasing trend toward larger fires in the Mediterranean region due mainly to climatic and land use changes. This case study highlights the importance of vegetation regrowth a short time after the fire to maintain both forest systems and soil conservation

Mullahingamist ja selle komponente mõjutavad tegurid arukase ja hariliku kuuse puistutes

Väitekirja elektrooniline versioon ei sisalda publikatsioone.Mulla CO2 voog ehk mullahingamine moodustab suure osa kogu metsaökosüsteemi hingamisest ja põhjapoolkera kõrgemate laiuskraadide metsad omavad olulist rolli globaalses süsinikuringes, mistõttu on selle voo kvantitatiivne hindamine väga aktuaalne teema. Käesolevas doktoritöös käsitleti kolme uudset aspekti. Esiteks suurenenud suhtelise õhuniiskuse mõju mullahingamisele, mis on oluline teave kõrgematel laiuskraadidel prognoositud kliimamuutuste valguses. Teiseks saadi Eesti jaoks uudsed tulemused mullahingamise jaotumisest autotroofseks ja heterotroofseks komponendiks arukase ja hariliku kuuse puistutes. Kolmandaks analüüsiti Eestis esmakordselt kändude juurimise mõju mulla CO2 voogudele. Doktoritöö laiemaks eesmärgiks oli analüüsida erinevate abiootiliste (suurenenud suhteline õhuniiskus, mullatemperatuur ja mullaniiskus) ja biootiliste (puuliik, puistu vanus ja arengustaadium, peenjuurte biomass ja käive, maapealne varise voog mulda, mulla mikroobne biomass ja selle aktiivsus) tegurite ning metsamajandamise (lageraiejärgne kändude juurimine) mõju mullahingamisele ja selle autotroofsele ja heterotroofsele komponendile erineva vanusega arukaasikutes ja hariliku kuuse puistutes. Töö tulemusena selgus, et mullatemperatuur on peamine keskkonnategur mullahingamise sesoonse dünaamika kirjeldamiseks ja mullaniiskusel on nõrk mõju. Suurendatud suhteline õhuniiskus vähendas mullahingamist, kuigi alustaimestiku juurte biomass, produktsioon ja mikroobikoosluste aktiivsus kasvas. Puistu vanus mõjutas mulla CO2 vooge nii arukase kui hariliku kuusiku vanusereas, mis seostus pigem muutustega biootilistes tegurites (peenjuurte dünaamika) kui muutustega mullatemperatuuris ja mullaniiskuses. Mullahingamise komponentide temperatuuritundlikkus oli vastupidine lehtpuu- ja okaspuupuistutes. Esmased tulemused näitasid, et viljaka kasvukohatüübi korral lageraiejärgne kuusekändude juurimine mulla¬hingamist oluliselt ei mõjuta. Antud töö näitab, et metsaökosüsteemi mullahingamine on väga keeruline protsess ning erinevaid looduslikke ja inimtekkelisi tegureid, mis seda protsessi mõjutavad, tuleb metsa süsinikuringe prognoosimisel arvesse võtta – eriti kliimamuutuste kontekstis.Soil CO2 efflux i.e. soil respiration can form a remarkable part of total forest ecosystem respiration and as northern forests at higher latitudes play an important role in global carbon cycle it is highly actual to quantify their soil CO2 effluxes. There are three novel aspects in this thesis. First, in the light of global climate change, the knowledge about the effect of elevated air humidity on soil CO2 effluxes will help to predict and understand the con¬sequences of a changing pattern of humidity on the forest carbon cycle. Second, the first results are obtained about soil respiration partitioning into the heterotrophic and autotrophic components in Estonian silver birch and Norway spruce forests. Third, for the first time in Estonia the effect of stump harvesting on soil respiration is analysed. The general aim of the thesis was to ascertain the effect of several factors: abiotic (elevated air humidity, soil temperature and moisture); biotic (stand age and development stage, fine root biomass and turnover, above-ground litter input, soil microbial biomass and activity) and forest management (stump harvesting) on total soil respiration and its autotrophic and heterotrophic components in silver birch and Norway spruce stands of different ages. The findings showed that soil temperature was the main climatic factor explaining the seasonal variation of soil respiration and soil moisture had a weak effect. Increased air humidity reduced soil respiration, however, it increased the fine root biomass and production of the understorey and the basal respiration of microbes. Stand age affected soil CO2 effluxes in both silver birch and Norway spruce stands, which were mostly explained by changes in biotic factors such as fine root dynamics than by changes in soil temperature and moisture. The temperature sensitivity of soil respiration components showed opposite response for deciduous and for coniferous tree species. First results of Estonian case study imply that stump harvesting does not affect the soil respiration on fertile sites. This thesis demonstrates the complexity of below-ground respiration processes and the importance to consider the effect of several natural and anthropogenic factors into the predictions of the carbon cycle of forest ecosystem in changing climate

Carbon sink and CarbonSink+ : from observations to global potential

Carbon balance of forests is defined by three main processes; photosynthesis, autotrophic respiration, and heterotrophic respiration. Climate impact of forests include also non-carbon effects like albedo, biogenic aerosols, effect on clouds, evaporation and surface roughness. A well-thought measurement setup as well as standardised procedures are essential for a meaningful and robust monitoring and the comparability of the observations at the same site and in inter-site comparisons. Depending on the mitigation project objectives and scale different combination of methodologies could be used including forest carbon inventories, chamber measurements, tower-based eddy covariance flux measurements, large-scale atmospheric greenhouse gas measurements, aircraft and satellite remote sensing. In addition to GHGs, forests have other important climate effects. They change surface albedo (warming effect), are source of volatile organic compounds (VOC), have effect on aerosol particle formation and growth, increases amount of cloud condensation nuclei (CCN), and has effect on cloud formation as well as on the precipitation. Moreover, any modification of the carbon cycle by removing or increasing CO2-binding vegetation has impact on the complex climate - carbon cycle feedback. We define these additional cooling effects as CarbonSink+. Accounting all these effects, this CarbonSink+ may increase the climate cooling impact of forests compared with pure carbon sink effect. Land use based mitigation plays an important role in current Nationally Determined Contributions of Paris Agreement. Scientific findings indicate that through different actions land sector could provide up to 1/3 of the needed total mitigation through year 2030. However, permanence of ecosystem based carbon storages is still a challenge and trade-offs between different land use form exist and should be properly acknowledged in the mitigation projects. We define in this report a cost effective, i.e. as simple as possible but good enough, measurement setup to verify both ordinary carbon sink and CarbonSink+ -effect. The methodology is planned for commercial applications, rather than for scientific purposes. The estimated prices of the instrumentation are based on present-day situation. In the conclusions of the report, we also describe first level principles and challenges which could help to formulate protocols for larger framework needed for the global commercial carbon marketNon peer reviewe

Satellite-based estimation of soil organic carbon in Portuguese grasslands

Soil organic carbon (SOC) sequestration is one of the main ecosystem services provided by well-managed grasslands. In the Mediterranean region, sown biodiverse pastures (SBP) rich in legumes are a nature-based, innovative, and economically competitive livestock production system. As a co-benefit of increased yield, they also contribute to carbon sequestration through SOC accumulation. However, SOC monitoring in SBP require time-consuming and costly field work. Methods: In this study, we propose an expedited and cost-effective indirect method to estimate SOC content. In this study, we developed models for estimating SOC concentration by combining remote sensing (RS) and machine learning (ML) approaches. We used field-measured data collected from nine different farms during four production years (between 2017 and 2021). We utilized RS data from both Sentinel-1 and Sentinel-2, including reflectance bands and vegetation indices. We also used other covariates such as climatic, soil, and terrain variables, for a total of 49 inputs. To reduce multicollinearity problems between the different variables, we performed feature selection using the sequential feature selection approach. We then estimated SOC content using both the complete dataset and the selected features. Multiple ML methods were tested and compared, including multiple linear regression (MLR), random forests (RF), extreme gradient boosting (XGB), and artificial neural networks (ANN). We used a random cross-validation approach (with 10 folds). To find the hyperparameters that led to the best performance, we used a Bayesian optimization approach. Results: Results showed that the XGB method led to higher estimation accuracy than the other methods, and the estimation performance was not significantly influenced by the feature selection approach. For XGB, the average root mean square error (RMSE), measured on the test set among all folds, was 2.78 g kg−1 (r2 equal to 0.68) without feature selection, and 2.77 g kg−1 (r2 equal to 0.68) with feature selection (average SOC content is 13 g kg−1). The models were applied to obtain SOC content maps for all farms. Discussion: This work demonstrated that combining RS and ML can help obtain quick estimations of SOC content to assist with SBP managementinfo:eu-repo/semantics/publishedVersio