Carbon stocks, greenhouse gas emissions and water balance of Sudanese savannah woodlands in relation to climate change

Understanding the carbon (C) sequestration potential of drylands requires knowledge of the stocks of C in soils and biomass and on the factors affecting them. The overall aim of the study was to determine and evaluate the variation in the C stocks and water balance of Acacia savannah woodlands across the dryland (arid and semi-arid) region (10-16 ºN; 21-36 °E) of the former Sudan (now mainly in the Republic of the Sudan) and how they are related to climatic factors and may be affected by climate change. The role played by small but numerous brick making industries on woodland deforestation in the region and greenhouse gas production was also investigated. The study region is often referred to as the gum belt because it is the world s major source of gum Arabic, which is harvested from Acacia trees. The soils in the centre and west of the region are mainly Arenosols (sandy soils) and those in the eastern part are mainly Vertisols (clay soils). The soils are C poor and often in a degraded state. This dissertation consists of a summary section and four articles (Study I, II, III and IV). Study I focuses on fuelwood consumption by the brick making industries (BMIs) and associated deforestation and greenhouse gas (GHG) emissions. In Study II the C densities (g C m-2) of the woodland tree biomass and soil (1 m) for 39 map sheets covering the study region were determined from national forest inventory data and global soil databases and the dependence on mean annual precipitation (MAP) and mean annual temperature (MAT) determined. The water balance of savannah woodlands for the same 39 map sheets was modelled in Study III and the variation in water balance components across the region evaluated. The potential impacts of climate change on woodland biomass C density and water-use (actual evapotranspiration, AET) was analysed for eight of the map sheets in Study IV. Sudanese BMIs consume a considerable amount of fuelwood that mainly comes from unsustainably managed woodland and contributes to deforestation and GHG emissions (Study I). While GHG emissions from BMIs only account for a small part of Sudan s total GHG emissions, the associated deforestation and land degradation is of concern. Implementation of better regulation, use of biomass fuel from sustainable sources and technological improvement in BMIs kilns will reduce deforestation and GHG emissions. Savannah woodland C densities, both biomass and soil, were low and clearly below potential C sequestration capacity (Study II). The loss of trees across the region was indicated by very low biomass C density values in comparison to modelled NPP (net primary production) values. The estimated SOC densities although low, were higher than reported in some recent soil C studies from the region. This was attributed to the use of old data in the global soil database and indicates the degree of land degradation and loss of SOC that has taken place over the last few decades. However, in spite of woodland and soil degradation, biomass C and SOC densities remained positively and significantly correlated with each other and both were significantly correlated to MAP. The results highlighted the need for improved land-use management and stewardship, which should involve increasing the cover of trees, and the need for up-to-date regional and integrated soils and forest (woodland) inventories to be made. Water-use (AET) of savannah woodlands is strongly limited by rainfall. Rainfall exceeded AET only during some of the wet season months resulting in a small increase in soil moisture storage and production of surface runoff for some areas (Study III). Drainage (to groundwater) was negligible. Since AET was strongly limited by MAP, AET for both Arenosol and Vertisol soil types increased southwards across the study region. Runoff also increased southwards across the study region for both soil types but were highest in south western and eastern areas. The restoration of woodlands may be expected to improve the soil-water conditions. Compared to baseline (1961-1990) climate values, General Circulation Model (GCM) based results for 2080s indicated that MAT would increase across the study region but that MAP would either increase or decrease depending on climate change scenario (Study IV). Biomass C densities will be significantly affected by climate change. However, the impact varies with climate change scenario, with either increases or decreases in biomass C density being indicated for the same area. In general, water-use on Arenosols will increase while that on Vertisols will decrease. The largest relative changes in AET were associated with the areas receiving the lowest rainfall. Thus, even if MAP increases, the increase will have little impact on biomass levels in the driest areas of the region.Työssä tarkasteltiin tropiikin kuivien alueiden hiilensidontakykyä ja siihen vaikuttavia tekijöitä. Tarkastelussa keskityttiin Sudanin savannialueen (10-16 ºN; 21-36 °E) hiilivarastojen ja vesitaseen vaihteluihin ja siihen kuinka ne riippuvat alueen ilmastollisista tekijöistä ja ennustetusta ilmastonmuutoksesta. Työssä selvitettiin myös, kuinka laajalti harjoitettu pienen mittakaavan tiilenpoltto vaikuttaa kuivuusalueen puustonkatoon ja hiilipäästöihin. Alue tunnetaan yleisesti esiintyvistä akaasiapuista ja niistä saatavasta arabikumista, jonka pääasiallinen lähde kyseinen Afrikan ilmastovyöhyke (gum belt) on maailmassa. Työ koostuu neljästä osatutkimuksesta ja niiden yhteenvedosta. Ensimmäisessä osajulkaisussa selvitettiin tiiliteollisuuden polttopuun käyttöä ja siihen liittyvää puustonkatoa ja kasvihuonekaasujen (KHK) päästöjä. Toisessa osajulkaisussa arvioitiin julkaistujen valtakunnan metsien inventointitietojen ja maailman maaperätietokannan perusteella savannialueiden puuston ja pintamaan (1 m syvyyteen asti) hiilimääriä ja niiden korreloitumista vuotuisen keskimääräisen sadannan ja lämpötilan kanssa. Kolmannessa osajulkaisussa mallinnettiin alueen vesitaseen ja sen eri tekijöiden vaihtelua ja neljännessä osatyössä analysoitiin eri ilmastonmuutosskenaarioiden vaikutusta kasvillisuuteen sitoutuvaan hiilimäärään ja kasvillisuuden veden käyttöön. Osatyöt II ja III tehtiin 39 karttapohjalle, jotka kattoivat koko alueen, mutta osatyössä IV käytettiin vain kahdeksan karttapohjan osajoukkoa. Pääosa Sudanin tiilitehtaiden polttopuusta poimitaan hoitamattomista luonnonpuustoista. Vaikka tiiliteollisuuden hiilipäästöt ovat pieniä suhteessa koko maan hiilipäästöihin, kestämätön puunkäyttö aiheuttaa puustonkatoa ja maaperän köyhtymistä. Nykyhetkellä savannialueen hiilimäärät ovat paljon potentiaalista kapasiteettia alhaisempia. Maailman maaperätietokannan suhteellisen vanhojen tietojen perusteella lasketut maan hiilimäärät osoittautuivat suuremmiksi kuin mitä alueella hiljattain tehdyt tutkimukset antoivat. Tämä osoittaa maan köyhtymistä ja orgaanisen hiilen määrän vähenemistä maaperästä. Kuitenkin sekä puuston että maaperän hiilimäärät korreloivat merkitsevästi sekä keskenään, että keskimääräisen sadannan kanssa. Alueen kasvillisuuden vedenkäyttöä rajoittaa sadannan vähyys. Vain joinakin sadekauden kuukausina vettä kertyi maan vesivarastoihin ja siirtyi pintavaluntana vesistöihin, lisääntyen kuitenkin etelää kohti mentäessä yhdessä sadannan kanssa. Ilmastomallien perusteella vuotuinen keskilämpötila nousee koko alueella referenssitasoon (1961-1990) verrattuna, mutta keskimääräinen sadanta joko nousee tai laskee riippuen käytetystä skenaarioarviosta. Tällä tulee olemaan selkeä joko lisäävä tai vähentävä vaikutus ekosysteemeihin sitoutuneeseen hiileen. Suurimmat vaikutukset on odotettavissa jo nykyään kuivimmilla alueilla. Tutkimus osoitti selvästi, että alueen ekosysteemeihin sitoutunut hiili on vähentynyt ja sillä on negatiivinen vaikutus maaperän vesitaseeseen. Ilmastonmuutoksen myötä kyseiset ongelmat saattavat edelleen kärjistyä. Polttopuun käyttöä järkeistämällä ja kestävällä puustonhoidolla voidaan kyseistä ongelmaa pienentää ja varautua ilmastonmuutoksen vaikutuksiin

Reconstructing Geometric Structures from Combinatorial and Metric Information

In this dissertation, we address three reconstruction problems. First, we address the problem of reconstructing a Delaunay triangulation from a maximal planar graph. A maximal planar graph G is Delaunay realizable if there exists a realization of G as a Delaunay triangulation on the plane. Several classes of graphs with particular graph-theoretic properties are known to be Delaunay realizable. One such class of graphs is outerplanar graph. In this dissertation, we present a new proof that an outerplanar graph is Delaunay realizable. Given a convex polyhedron P and a point s on the surface (the source), the ridge tree or cut locus is a collection of points with multiple shortest paths from s on the surface of P. If we compute the shortest paths from s to all polyhedral vertices of P and cut the surface along these paths, we obtain a planar polygon called the shortest path star (sp-star) unfolding. It is known that for any convex polyhedron and a source point, the ridge tree is contained in the sp-star unfolding polygon [8]. Given a combinatorial structure of a ridge tree, we show how to construct the ridge tree and the sp-star unfolding in which it lies. In this process, we address several problems concerning the existence of sp-star unfoldings on specified source point sets. Finally, we introduce and study a new variant of the sp-star unfolding called (geodesic) star unfolding. In this unfolding, we cut the surface of the convex polyhedron along a set of non-crossing geodesics (not-necessarily the shortest). We study its properties and address its realization problem. Finally, we consider the following problem: given a geodesic star unfolding of some convex polyhedron and a source point, how can we derive the sp-star unfolding of the same polyhedron and the source point? We introduce a new algorithmic operation and perform experiments using that operation on a large number of geodesic star unfolding polygons. Experimental data provides strong evidence that the successive applications of this operation on geodesic star unfoldings will lead us to the sp-star unfolding

Challenges and Adaptation Strategies of Students with Disabilities in Higher Education in Bangladesh

Education is a fundamental human right to which every human should have access. However, in Bangladesh, people with disabilities continue to be denied access to education in a variety of ways; even with the widespread expansion of higher education, they have limited access to it. Also, those who have crossed various barriers and got admission to different higher education institutions face various challenges, including infrastructural barriers and other academic and administrative problems that affect their chances of growing up as average students. Considering this aspect, this article is intended to determine the challenges faced by students with disabilities and their adaptation strategies in higher education in Bangladesh. It applied a mixed-method approach in which quantitative and qualitative data were collected from four leading public universities in Bangladesh. The results indicate that students with disabilities still face a variety of challenges on their campuses. However, to overcome these challenges, they apply adaptive strategies such as using assistive devices, bilingual books, and the help of friends, which are not favorable enough for them to cope with the situation and continue their studies