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During the past century, the biomass of woody species has increased in many grassland and savanna ecosystems. As many of these species fix nitrogen symbiotically, they may alter not only soil nitrogen (N) conditions but also those of phosphorus (P). We studied the N-fixing shrub Dichrostachys cinerea in a mesic savanna in Zambia, quantifying its ef...
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... we present a study of the effects of woody encroachment on soil nutrient availabilities and carbon sequestration, as well as potential feedbacks upon encroaching shrubs. The work was conducted in a mesic savanna habitat in Zambia that was encroached to varying degrees by the leguminous thorny shrub Dichrostachys cine- rea (Fig. 1). This species is widely distributed in subtropical and tropical Africa and can be found in Arabia, tropical Asia, America, and Australia (PROTEA 2014). It is an important woody encroacher in many African savannas (Lock 1993;Roques et al. 2001;Moleele et al. 2002;Tobler et al. 2003;Hagenah et al. 2009;Eldridge et al. 2011). In the Kafue ...
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Citations
... Increased SOC in woody communities can also be explained by direct acquisition of organic nitrogen by symbiotic fungi, which may bypass the decomposition of carbon compounds and allow nutrient uptake in the absence of soil carbon mineralization (Averill at al., 2014;Orwin et al., 2011). Our results align with Häger & Avalos, (2017) and Blaser et al. (2014) who showed woody communities with high wood density to be related to high SOC. Together, these results highlight the significant influence of abiotic components and substrate inputs in shaping SOC across elevational gradients. ...
1. Plant functional traits play an important role in shaping plant ecological responses to environmental conditions and influencing ecosystem functioning. However, how whole-plant functional strategies manifest at the community level to influence aboveground and belowground carbon storage across environmental gradients remains poorly understood.
2. We measured aboveground and belowground carbon stocks and the variation in whole-plant (above- and belowground) functional strategies at the community level in twelve ecosystem types across a broad savanna-forest-alpine elevational gradient of climate and land use on Mt. Kilimanjaro, Tanzania. Using Structural Equation Models, we disentangled the direct and land use mediated influences of climate on carbon storage from indirect influences mediated by variation in plant functional strategies.
3. We found strong coordination between above- and belowground functional traits at the whole community level, which corresponded with functional strategies related to two major trade-offs: a slow -conservation to fast -resource acquisition axis represented by a spectrum from high leaf dry matter content to high fine root nitrogen concentration; and a size-related woody to grassy community axis represented by a spectrum spanning high canopy height to high specific root length. The slow-fast and woody-grassy strategy axes were primarily driven by precipitation and land-use intensity, respectively.
4. Both functional strategies mediated the effects of climate on carbon storage. The slow-fast strategy axis was strongly and positively associated with aboveground carbon stocks. Meanwhile, the woody-grassy strategy axis was negatively associated with both aboveground carbon stocks and soil organic carbon stocks.
5. Synthesis . We demonstrated that major plant functional strategies manifest at the community level along elevational gradients. These strategies also explain variation in carbon storage, although aboveground storage is mostly driven by trait effects, and belowground storage by direct effects of climate. Together, these results underscore the importance of incorporating functional community data into future analysis of climate change impacts on carbon storage, which would enhance our ability to predict potential shifts in ecosystem functioning.
... Yimer et al. 2006;Montané et al. 2010;Drewnik et al. 2016;Fan et al. 2022). The results obtained in this study indicate that the aboveground parts of V. myrtillus L. and tall-grass vegetation differ significantly in the content of TC and TN as well as in chemical composition (Tables 2 and 4), and this finding is in agreement with the results obtained by other authors (Montané et al. 2010;Blaser et al. 2014). However, the belowground parts of the two studied types of vegetation exhibit a similar content of TC and TN ( Table 2). ...
... These findings are generally in agreement with results reported in other studies (e.g. Blaser et al. 2014;Li et al. 2019;Liu et al. 2021;Yu et al. 2022). This underscores the significance of Kalbitz et al. 2000a, b;McDowell 2003;De Feudis et al. 2017). ...
... V. myrtillus L. may produce litter with higher concentration of aliphatic compounds and carboxylic groups compared to tall-grass vegetation, which can be attributed to differences in the composition and quality of plant residues, such as leaves, twigs, and other organic materials, that contribute to the litter inputs in the O horizons. The chemical composition of these plant residues can vary depending on the plant species, tissue types, and stage of decomposition (Montane et al. 2010;Blaser et al. 2014). The decomposition processes occurring in the O horizons can also influence the abundance and distribution of these organic compounds. ...
Aims
This study aimed to define how vegetation affects the content and chemistry of soil organic matter (SOM) in topsoil (O and A) horizons under blueberry shrubs (Vaccinietum myrtilli) and tall-grass vegetation in the subalpine zone of the Bieszczady Mountains (Eastern Carpathians, SE Poland).
Methods
Topsoil samples (O and A horizons) were collected from ten sites covered with Vaccinium myrtillus L. and at ten sites covered with tall-grass vegetation. Above- and belowground parts of vegetation from each vegetation type were sampled. Total carbon (TC) and nitrogen (TN) content in soil and vegetation samples were determined using an elemental analyzer. SOM chemical properties were determined via Fourier-transform infrared spectroscopy and UV-Vis spectrophotometry. The mineral composition of the A horizons was determined via X-ray diffractometry (XRD).
Results
V. myrtillus L. showed significantly higher TC content and C/N ratio in its aboveground parts compared to tall-grass vegetation, though TN content was significantly lower. FTIR-ATR spectra showed more intense absorption bands for V. myrtillus L. The soil mineral composition was similar across vegetation types. Soils under blueberry shrubs showed significantly higher mean content of organic carbon and TN in the O horizon compared to tall-grass vegetation, with no significant differences in the A horizon.
Conclusions
Topsoil horizons under blueberry shrubs show higher soil organic carbon (SOC) content and C/N ratios than those under tall-grasses. Our results suggest that shrubification may affect carbon concentration in the soil; however, the lack of bulk density measurements prevents the quantification of SOM content and overall carbon sequestration, necessitating further studies.
... According to Rumpel and Kögel-Knabner (2011), SOC concentration is expected to be higher in deeper soils of woody vegetated landscapes due to higher root litter and decomposition. However, most studies that have investigated SOC in deeper soils of woody encroached grasslands have typically utilized traditional methods that rely on eld-based observation that are expensive, labour demanding and protract (Blaser et al., 2014;Mureva et al., 2018). Over the last few decades, advancements in satellite technology and data storage have tremendously revolutionized SOC stocks modelling. ...
Woody plants encroachment into grasslands has considerable hydrological and biogeochemical consequences to grassland soils that include altering the Soil Organic Carbon (SOC) pool. Consequently, continuous SOC stock assessment and evaluation at deeper soil depths of woody encroached grasslands is essential for informed management and monitoring of the phenomenon. Due to high litter biomass and deep root structures, woody encroached landscapes have been suggested to alter the accumulation of SOC at deeper soil layers, however, the level at which woody encroachment sequestrate SOC within localized protected grasslands is still poorly understood. Remote sensing methods and techniques have recently been popular in SOC analysis due to better spatial and spectral data properties as well as the availability of affordable and eco-friendly data. In this regard, the study sought to quantify the accumulation of SOC at various depths (30 cm, 60 cm, and 100 cm) in a woody-encroached grassland by integrating Sentinel-1 (S1), Sentinel-2 (S2), PlanetScope (PS) satellite imagery, and topographic variables. SOC was quantified from 360 field-collected soil samples using the loss-On-Ignition (LOI) method and spatial distribution of SOC across the Bisley Nature Reserve modelled through employing the Random Forest (RF) algorithm. The study’s results demonstrate that the integration of topographic variables, Synthetic Aperture Radar (SAR), and PlanetScope data effectively modelled SOC stocks at all investigated soil depths, with high R² values of 0.79 and RMSE of 0.254 t/ha. Interestingly, SOC was established to be high at 30 cm compared to 60 cm and 100 cm depths. The horizontal reception (VH), Slope, Topographic Weightiness Index (TWI), Band 11 and vertical reception (VV) were optimal predictors of SOC in woody encroached landscapes. These results highlight the significance of integrating RF model with spectral data and topographic variables for accurate SOC modelling in woody encroached ecosystems. The findings of this study are pivotal for developing a cost-effective and labour-efficient assessment and monitoring system for the appropriate management of SOC in woody encroached habitats
... The low amounts of soil C could be attributed to grazing and burning as these are major controls of carbon input quantity and quality in grasslands [82]. The soil carbon may initially increase with woody plant density, but then declines when woody plant density becomes high, which also inhibits understory grass growth [76,83]. This suggests that most soil C is derived from herbaceous plants such as grasses, which declines in abundance with increased density of woody plants. ...
Increasing densities of woody plants, known as woody plant encroachment, is a phenomenon affecting savannas and grasslands in many parts of the world. Yet, these ecosystems sustain a significant proportion of the human population through the provision of ecosystem services, such as forage for livestock and wildlife production. While low to medium altitude rangelands are encroached by many species of woody plants, high altitude rangelands in southern Africa show increasing densities of Leucosidea sericea, a woody shrub or small to medium-sized tree. Influences of this species on rangeland dynamics are unknown. This study aimed to determine the influence of L. sericea on rangeland functioning in the Vuvu communal area in the Eastern Cape, South Africa. Effects of L. sericea on plant species diversity and composition, rangeland condition and grazing capacity were measured in sites of variable densities of the species in topographical locations designated as plains, upland and stream sites, using a point-to-tuft method along 50-m long transects. Soil samples were collected to a depth of 5 cm from plains, streams, and upland sites, and analysed for organic carbon, nitrogen, phosphorus, magnesium, calcium, and pH. Plant species richness and abundance were similar among topographical locations, which was reflected by the similar Shannon-Weiner (H′) diversity indices among sites. Topographical locations differed significantly in species composition. The plains sites had a higher grazing capacity than stream sites, which had a grazing capacity similar to that of upland sites. Values of soil physicochemical properties were similar among the sites. Overall, soils were acidic (range in pH: 4.4–4.6) and had low amounts of organic carbon and total nitrogen. These findings suggest that L. sericea is not the primary cause of rangeland degradation as all sites were in poor condition as shown by the low grazing capacity, poor rangeland condition and depauperate species richness and diversity. Therefore, rangeland management should shift towards restoration strategies aimed to revitalise the rangeland.
... One intriguing observation is that nutrient availability is typically not a limiting factor for the enhanced productivity of woody plants in grasslands. Some woody plant species, such as honey mesquite, possess the capacity to acquire nitrogen through symbiotic fixation and are able to obtain nitrogen and phosphorus from deeper soil layers, which are inaccessible to grass (Blaser et al., 2014). This active cycling of nitrogen and phosphorus in encroached grasslands can contribute to enlarging the nutrient pool in soil (Zhou et al., 2018). ...
Woody Plant Encroachment (WPE) is a key driver of grassland collapse in the Southern Great Plain (SGP), resulting in a series of adverse ecological and socioeconomic consequences. Climate change will interact with ongoing WPE as it will likely shift the potential ranges of WPE species. In this study, we employed an ensemble approach integrating results from multiple Species Distribution Models to project future distribution ranges of four major WPE species (Ashe juniper, honey mesquite, post oak, and eastern redcedar) in the SGP across the 21st century. The findings highlighted a noteworthy trend: under future climate conditions, the distribution ranges for these WPE species were projected to shift northward and eastward. Of particular concern is honey mesquite with significant expansion in distribution range, potentially covering up to two‐thirds of the SGP's non‐agricultural area by the end of the 21st century. Conversely, the other three WPE species were expected to experience a contraction in their distribution ranges. Ashe juniper may experience a decline in its current habitats in central Texas but gain new habitats in northern Texas, Oklahoma, and Kansas. The suitable ranges of post oak and eastern redcedar were projected to shrink eastward, primarily being restricted to eastern portions of Oklahoma and Texas under the RCP4.5 and a smaller area in eastern Oklahoma under the RCP8.5. The projected shift in WPE ranges provides a scientific basis for governments to optimize the allocation of management resources and implement timely practices to control the spread of woody plants during the early encroachment stage. Our study methodology is applicable to other regions and continents with WPE issues, including Africa, South America, and Australia.
... Ecological studies often rely on chronosequences (i.e., space for time substitutions) to investigate succession of plant communities, diversity, primary production, soil nutrients, soil microbial activity, and fungal communities over long timeframes (Springsteen et al. 2010;Hollingsworth et al. 2010;Blaser et al. 2014;Cava et al. 2018;Yang et al. 2019;Li et al. 2020). Chronosequences enable long-term studies in a more compressed time scale. ...
Drivers of shrub primary production and associated landscape impacts of encroachment are well known in drylands but have not been thoroughly studied in mesic and coastal habitats. The native, nitrogen-fixing shrub, Morella cerifera, has expanded into coastal grassland along the US Atlantic coast due to warming temperatures, but impacts on ecosystem function are not well known. Annual net primary production (ANPP) of Morella cerifera and key environmental drivers were measured long-term (1990 – 2007) across a chronosequence of shrub age on a mid-Atlantic barrier island. Soil and groundwater nutrients were compared with un-encroached grassland soil to evaluate impacts of vegetation on nutrient dynamics. Shrub ANPP declined with age at the same rate among all thickets, but there was variability from year to year. When climate variables were included in models, shrub age, precipitation, and freshwater table depth were consistent predictors of ANPP. Water table depth decreased over time, reducing ANPP. This may be due to rising sea-level, as well as to feedbacks with shrub age and evapotranspiration. Soil N and C increased with shrub age and were higher than adjacent grassland sites; however, there was a significant loss of N and C to groundwater. Our results demonstrate that drivers influencing the encroachment of shrubs in this coastal system (i.e., warming temperature) are not as important in predicting shrub primary production. Rather, interactions between shrub age and hydrological properties impact ANPP, contributing to coastal carbon storage.
... Different letters represent significant differences between vegetation types (p < 0.05) within specific geological formations. al., 2017; Barger et al., 2011;Blaser et al., 2014;Eldridge et al., 2011;Zhou et al., 2017Zhou et al., , 2018bZhou et al., , 2021. ...
Woody-plant encroachment into grasslands and savannas has been globally widespread during the past century, likely driven by interactions between grazing, fire suppression, rising atmospheric CO2, and climate change. In the southernmost US Great Plains, Ashe juniper and live oak have increased in abundance. To evaluate potential interactions between this vegetation change and the underlying soil parent material on ecosystem biogeochemistry, we quantified soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), and δ13C of SOC in soils obtained from trenches passing through grassland, juniper, and oak patches on soils lying atop the respective Edwards and Buda limestone formations in central Texas. Soils on the Edwards formation are more shallow and have more rock outcropping than those on Buda. The δ13C values of SOC under grasslands was -19 ‰, whereas those under woody patches were -21 ‰ to -24 ‰, indicating that wooded areas were relatively recent components of the landscape. Compared with grasslands, areas now dominated by juniper or oak had elevated SOC, TN, and TP storage in soils lying atop Edwards limestone. In Buda soils, only oak patches had increased SOC, TN, and TP storage compared with grasslands. Woody encroachment effects on soil nutrients were higher in soils on the Edwards formation, perhaps because root and litter inputs were more concentrated in the relatively shallow layer of soil atop the Edwards bedrock. Our findings suggest that geological factors should be considered when predicting nutrient store responses in savannas following vegetation change. Given that woody encroachment is occurring globally, our results have important implications for the management and conservation of these ecosystems. The potential interactive effects between vegetation change and soil parent material on C, N, and P storage warrant attention in future studies aimed at understanding and modeling the global consequences of woody encroachment.
... Woody encroachment often alters above-and belowground primary productivity as well as soil C, N, and P storage and cycling rates (Barger et al., 2011;Blaser et al., 2014;Boutton et al., 2009;Jackson et al., 2002;Jackson et al., 2000;Li et al., 2016;O'Donnell and Caylor, 2012;Saintilan and Rogers, 2015;Zhou et al., 2018). As both increases and decreases in soil organic C and total N have been observed in response to woody encroachment (Barger et al., 2011;Eldridge et al., 2011;Jackson et al., 2002;Eldridge et al., 2016;Li et al., 2016;Mureva et al., 2018;Zhou et al., 2023), this widespread land cover change represents an uncertainty in regional and global C cycling models (Asner et al., 2004;Barger et al., 2011;Goodale and Davidson, 2002;Pacala et al., 2001) that needs to be better constrained to improve the accuracy of future carbon budget projections and climate models. ...
Semi-arid grasslands and savannas in the southern Great Plains USA are extensively used for livestock grazing. Over the past century, Juniperus (juniper) and Quercus (oak) species abundance have increased due to intensive grazing and reduced fire frequency. We investigated the interactions between livestock grazing history (none, moderate, heavy) and vegetation cover (grassland, juniper, oak) using a ∼ 70-year grazing experiment in west-central Texas. We explored effects on soil organic carbon (SOC), total nitrogen (TN), total phosphorus (TP), microbial community composition, and function. SOC and TN were 50–150 % higher under juniper and oak compared to grasslands, and 10–30 % lower in grazed vs. ungrazed areas. Vegetation × grazing interaction showed greater SOC and TN loss under oak than juniper or grasslands. Ungrazed controls had higher soil TP than grazed areas, with oak and juniper soils having more TP than grasslands. Bacterial and fungal communities differed between grassland and woody vegetation. Grazing affected only bacterial communities. SOC, TN, TP accounted for differences in community structure. Abundances of genes related to methane, nitrogen, sulfur metabolisms, and dominant fungal trophic modes were linked to soil C, N, P ratios. These findings highlight how long-term livestock grazing and woody plant encroachment influence soil C, N, P cycles, altering soil microbial community structure and function. This study provides insights for savanna ecosystem management and integrating land cover effects into biogeochemical models for global change scenarios.
... WPE can be a significant pathway for increased ecosystem C sequestration (Bastin et al., 2019;Blaser et al., 2014;Cook-Patton et al., 2021;Geesing et al., 2000;Griscom et al., 2017;Hibbard et al., 2001;Hudak et al., 2003); however, these effects depend on climatic conditions and plant rooting profiles (Jackson et al., 2002). ...
Woody plant encroachment (WPE) is a global trend that occurs in many biomes, including savannas, and accelerates with fire suppression. Since WPE can result in increased storage of soil organic carbon (SOC), fire management, which may include fire suppression, can improve ecosystem carbon (C) sequestration in savannas.
At our study site in Kruger National Park, South Africa, we used a long‐term (~70 year) fire experiment to study the drivers and consequences of changes in woody cover (trees and shrubs) on SOC sequestration. We surveyed four fire manipulation treatments, replicated at eight locations within the park: annual high‐intensity burns, triennial high (dry season) and low‐intensity (wet season) burns, and fire exclusion, to capture the range of fire management scenarios under consideration. The changes in woody cover were calculated over a period similar to the experiment's duration (~80 years) using aerial photographs (1944–2018). Soils were analysed to 30 cm depth for SOC and δ¹³C, under and away from the tree canopy to isolate local‐ and landscape‐level effects of WPE on SOC.
The largest increases in woody cover occurred with fire exclusion. We found that plots with higher increases in woody cover also had higher SOC. However, trees were not the only contributor to SOC gains, sustained high inputs of C4‐derived C (grasses), even under canopies in fire suppression plots, contributed significantly to SOC. We observed little difference in SOC sequestration between cooler triennial (wet season) burns and fire suppression.
Synthesis. Grass input to soil organic carbon (SOC) remained high across the full range of woody cover created by varying burning regimes. The total SOC stocks stored from tree input only matched grass‐derived SOC stocks after almost 70 years of fire exclusion. Our results point to C4 grasses as a resilient contributor to SOC under altered fire regimes and further challenge the assumption that increasing tree cover, either through afforestation schemes or fire suppression, will result in large gains in C sequestration in savanna soils, even after 70 years.
... Woody plant encroachment into savanna ecosystems is a geographically widespread phenomenon that appears to be driven by fire suppression, livestock grazing, climate change, and rising atmospheric CO 2 concentration (Archer et al., 2017;Boutton et al., 1998;Buitenwerf et al., 2012;Sankaran et al., 2005;Stevens et al., 2017). Woody encroachment generally increases soil organic C, nitrogen (N), and P storage in soils in arid/semi-arid regions (Blaser et al., 2014;Eldridge et al., 2011;Krull et al., 2005;Sitters et al., 2013), which likely increase the source of colloidal OC and P (Krause et al., 2020;Zhang et al., 2021). Furthermore, other soil properties may be altered following woody encroachment, such as porosity (Yu et al., 2018) and hydrologic characteristics (Holdo et al., 2020). ...