| 1. |
- Wachiye, Sheila, et al.
(författare)
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Effects of livestock and wildlife grazing intensity on soil carbon dioxide flux in the savanna grassland of Kenya
- 2022
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Ingår i: Agriculture, Ecosystems and Environment. - : Elsevier BV. - 0167-8809. ; 325
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Tidskriftsartikel (refereegranskat)abstract
- Although grazing is the primary land use in the savanna lowland of southern Kenya, the effects of grazing on soil carbon dioxide flux (RS) remain unclear. A 12-month study was conducted from January to December 2020 on the effects of six grazing intensities sites (overgrazed (OG), heavily grazed (HG), moderately grazed (MG), moderately to lightly grazed (M-LG), lightly grazed (LG) and no grazing (NG)) on RS on. A camera trap was used to monitor the total number of animals at each site, indicating the grazing intensity. Weekly measurements of RS were taken using static greenhouse gas chambers along with simultaneous measurements of soil temperature (TS) and volumetric soil water content (WS) (depth of 5 cm). Mean RS at HG, MG, M-LG and LG sites was approximately 15–25% higher than at NG and OG sites (p < 0.001). Mean WS increased with decrease in grazing especially in the dry season, while TS increased with increase in grazing. We observed bimodal temporal variation in RS and WS due to two wet seasons in the year. Thus, variation in RS across the study period followed the changes in WS rather than those in TS. Mean values of RS in the wet seasons were significantly higher (> 45%) than those in the dry seasons, and WS accounted for 71% of the temporal variability in RS (p < 0.05). In addition, the enhanced vegetation index (EVI, interpreted as a proxy for vegetation cover) explained 60% of the variance of RS, and WS and EVI together explained 75%. EVI showed a negative relationship (p < 0.05) with animal intensity, indicating that more grazing reduced vegetation cover and, consequently, soil organic carbon and biomass. Soil bulk density was lower at less grazed sites. While RS variability was unaffected by total nitrogen content, pH, and texture, correspondence analysis demonstrated that the main factors influencing RS dynamics across the year under different grazing intensities were WS and vegetation cover. Our results contribute to closing the existing knowledge gap regarding the effects of grazing intensity on RS in East Africa savannas. Therefore, this information is of great importance in understanding carbon cycling in savanna grassland, as well as the identification of the potential consequences of increasing land pressure caused by rising livestock numbers, and will assist in the development of climate-smart livestock management in East Africa.
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| 2. |
- Wachiye, Sheila, et al.
(författare)
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Soil greenhouse gas emissions from a sisal chronosequence in Kenya
- 2021
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Ingår i: Agricultural and Forest Meteorology. - : Elsevier BV. - 1873-2240 .- 0168-1923. ; 307
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Tidskriftsartikel (refereegranskat)abstract
- Sisal (Agave sisalana) is a climate-resilient crop grown on large-scale farms in semi-arid areas. However, no studies have investigated soil greenhouse gas (GHGs: CO2, N2O and CH4) fluxes from these plantations and how they relate to other land cover types. We examined GHG fluxes (Fs) in a sisal chronosequence at Teita Sisal Estatein southern Kenya. The effects of stand age on Fs were examined using static GHG chambers and gas chromatography for a period of one year in seven stands: young stands aged 1–3 years, mature stands aged 7–8 years, and old stands aged 13–14 years. Adjacent bushland served as a control site representing the surrounding land use type. Mean CO₂ fluxes were highest in the oldest stand (56 ± 3 mg C m-2 h-1) and lowest in the 8-year old stand (38 ± 3 mg C m-2 h-1), which we attribute to difference in root respiration between the stand. All stands had 13–28% higher CO₂ fluxes than bushland (32 ± 3 mg C m-2 h-1). CO2 fluxes in the wet season were about 70% higher than dry season across all sites. They were influenced by soil water content (WS) and vegetation phenology. Mean N2O fluxes were very low (<5 μg N m-2 h-1) in all sites due to low soil nitrogen (N) content. About 89% of CH4 fluxes were below the detection limit (LOD ± 0.02 mg C m-2 h-1). Our results imply that sisalplantations have higher soil CO2 emissions than the surrounding land use type, and the seasonal emissions were largely driven by WS and the vegetation status. Methane and nitrous oxide are of minor importance. Thus, soil GHG fluxes from sisal plantations are a minor contributor to agricultural GHG emissions in Kenya.
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| 3. |
- Cuni-Sanchez, Aida, et al.
(författare)
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High aboveground carbon stock of African tropical montane forests
- 2021
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 596:7873, s. 536-542
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Tidskriftsartikel (refereegranskat)abstract
- Tropical forests store 40–50per cent of terrestrial vegetation carbon. However, spatial variations in aboveground live tree biomass carbon (AGC) stocks remain poorly understood, in particular in tropical montane forests. Owing to climatic and soil changes with increasing elevation, AGC stocks are lower in tropical montane forests compared with lowland forests. Here we assemble and analyse a dataset of structurally intact old-growth forests (AfriMont) spanning 44 montane sites in 12 African countries. We find that montane sites in the AfriMont plot network have a mean AGC stock of 149.4megagrams of carbon per hectare (95% confidence interval 137.1–164.2), which is comparable to lowland forests in the African Tropical Rainforest Observation Network4 and about 70per cent and 32per cent higher than averages from plot networks in montane and lowland forests in the Neotropics, respectively. Notably, our results are two-thirds higher than the Intergovernmental Panel on Climate Change default values for these forests in Africa8. We find that the low stem density and high abundance of large trees of African lowland forests is mirrored in the montane forests sampled. This carbon store is endangered: we estimate that 0.8 million hectares of old-growth African montane forest have been lost since 2000. We provide country-specific montane forest AGC stock estimates modelled from our plot network to helpto guide forest conservation and reforestation interventions. Our findings highlight the need for conserving these biodiverse and carbon-rich ecosystems.
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| 4. |
- Heiskanen, Janne, et al.
(författare)
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Aerial photo interpretation for change detection of treeline ecotones in the Swedish mountains
- 2008
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- It is expected that the ongoing climate change will have a strong influence on the Earth’s vegetation and cause the advancement of treelines towards the poles and up to higher elevations. In the Swedish mountains, changes in the positions of alpine treelines have already been reported, and major changes due to changing climate are predicted for the near future. Remote sensing techniques have considerable potential to improve the monitoring of spatially complex treeline ecotones, which are likely to show site dependent responses to changing climate. Aerial photos provide the longest temporal record of remote sensing data for studying the historical treeline changes. High spatial resolution and the possibility of interpreting photos in three-dimensions are the main strengths of aerial photos. The National Inventory of Landscapes in Sweden (NILS) is a nationwide environmental monitoring program, which provides sampling infrastructure for monitoring treelines over the Swedish mountains using high spatial resolution remote sensing data.
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| 5. |
- Heiskanen, Jouni, et al.
(författare)
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The Integrated Carbon Observation System in Europe
- 2022
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Ingår i: Bulletin of the American Meteorological Society. - 0003-0007. ; 103:3, s. 855-872
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Tidskriftsartikel (refereegranskat)abstract
- Since 1750, land-use change and fossil fuel combustion has led to a 46% increase in the atmospheric carbon dioxide (CO2) concentrations, causing global warming with substantial societal consequences. The Paris Agreement aims to limit global temperature increases to well below 2C above preindustrial levels. Increasing levels of CO2 and other greenhouse gases (GHGs), such as methane (CH4) and nitrous oxide (N2O), in the atmosphere are the primary cause of climate change. Approximately half of the carbon emissions to the atmosphere are sequestered by ocean and land sinks, leading to ocean acidification but also slowing the rate of global warming. However, there are significant uncertainties in the future global warming scenarios due to uncertainties in the size, nature, and stability of these sinks. Quantifying and monitoring the size and timing of natural sinks and the impact of climate change on ecosystems are important information to guide policy-makers' decisions and strategies on reductions in emissions. Continuous, long-term observations are required to quantify GHG emissions, sinks, and their impacts on Earth systems. The Integrated Carbon Observation System (ICOS) was designed as the European in situ observation and information system to support science and society in their efforts to mitigate climate change. It provides standardized and open data currently from over 140 measurement stations across 12 European countries. The stations observe GHG concentrations in the atmosphere and carbon and GHG fluxes between the atmosphere, land surface, and the oceans. This article describes how ICOS fulfills its mission to harmonize these observations, ensure the related long-term financial commitments, provide easy access to well-documented and reproducible high-quality data and related protocols and tools for scientific studies, and deliver information and GHG-related products to stakeholders in society and policy.
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| 6. |
- Papale, Dario, et al.
(författare)
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Standards and Open Access are the ICOS Pillars Reply to "Comments on 'The Integrated Carbon Observation System in Europe'"
- 2023
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Ingår i: Bulletin of the American Meteorological Society. - 0003-0007. ; 104:12, s. 953-955
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Tidskriftsartikel (refereegranskat)abstract
- In his comment (Kowalski 2023) on our recent publication (Heiskanen et al. 2022) where we present the Integrated Carbon Observation System (ICOS) research infrastructure, Andrew Kowalski introduces three important and, in our opinion, different potential issues in the definition, collection, and availability of field measurements made by the ICOS network, and he proposes possible solutions to these issues.
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| 7. |
- Rautiainen, Miina, et al.
(författare)
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Ecological applications of physically based remote sensing methods
- 2010
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Ingår i: Scandinavian Journal of Forest Research. - : Informa UK Limited. - 0282-7581 .- 1651-1891. ; 25:4, s. 325-339
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Forskningsöversikt (refereegranskat)abstract
- Global monitoring of vegetation using optical remote sensing has undergone rapid technological and methodological development during the past decade. Physically based methods generally apply reflectance models for interpreting remotely sensed data sets. These methods have become increasingly important in the assessment of terrestrial variables from satellite-borne and airborne images. Products based on satellite images currently include various ecological variables that are needed for monitoring changes in forest cover, structure and functioning, including biophysical variables such as the amount of photosynthesizing leaf area. This paper reviews variables and global products estimated from optical satellite sensors describing, for example, the amount and functioning of green biomass and forest carbon exchange. Continuous validation work as new vegetation products are released continues to be important. More emphasis is needed on the collection of field data equivalent to satellite retrievals, data harmonization and continuous measurements of seasonal forest dynamics.
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