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Forests and grasslands often occur side by side in the landscape, forming a complex mosaic system with contrasting environmental conditions, maintained by different fire-vegetation stabilising feedbacks. Woody species that occur along this sharp gradient must adopt viable ecological strategies to deal with the contrasting environments of these ecosystems. For this, plants are challenged to efficiently coordinate the functioning of ecological strategy dimensions above- and below-ground. We tested hypotheses related to structural changes in vegetation and associated shifts in community-level trait patterns and ecological strategies during woody plant encroachment. We surveyed 60 permanent plots in forest-grassland mosaics at two different times (2012-2022) to obtain data on changes in vegetation structure, species composition, abundance and ecological strategies after 10 years without disturbance, capturing a gradient from open and woody plant-encroached grasslands to closed forests. An integrated functional approach was used to assess the different dimensions of plant trait variation, including 10 above- and below-ground traits, representing whole-plant, leaf, stem and root strategies. Woody plant encroachment led to a substantial increase in woody plant density in former grasslands, transforming their structure to resemble that of young forests. Interestingly, we found clear trade-offs between above- and below-ground traits among woody species. On the one hand, the species occurring in grassland had conservative leaves, a strategy for protection against high solar incidence, physical damage and drought, and had roots with a 'do-it-yourself' strategy, which ensures efficiency in the acquisition of nutrients and water in nutrient-limited soils, and had thick bark related to fire resistance. On the other hand, forest species were usually taller and had acquisitive leaves, indicating highly competitive ability in light-limited forests, whereas their roots had an 'outsourcing' strategy of resource uptake to mycorrhizal fungi in the nutrient-rich soils of forests. Synthesis: We advanced the current understanding of woody plant encroachment in grasslands by showing the underlying trait-based trade-offs that enable woody species to occur along the transition between forest and grassland through space and time. Importantly, we have shown how below-ground traits are important in explaining the species strategies, with a negative covariance between above- and below-ground. Our integrative trait-based approach will be helpful in better understanding and managing forest-grassland mosaics in southern Brazil and analogous patchy ecosystems around the world. Florestas e campos frequentemente ocorrem lado a lado na paisagem, formando um sistema mosaico complexo com condiçõ es ambientais contrastantes, mantido por diferentes feedbacks estabilizadores entre fogo e vegetaçã o. Espé cies lenhosas que ocorrem ao longo desse acentuado gradiente devem adotar estraté gias ecoló gicas viá veis para lidar com os ambientes contrastantes desses ecossistemas. Para isso, as plantas precisam coordenar eficientemente o seu funcionamento acima e abaixo do solo. No presente artigo nó s avaliamos mudanç as estruturais na vegetaçã o associadas com mudanç as funcionais na escala de comunidades e nas estraté gias ecoló gicas das espé cies durante o processo de adensamento de espé cies lenhosas. Para isso, realizamos a amostragem de 60 parcelas permanentes localizadas nos mosaicos campo-floresta, em dois perí odos de tempo (2012 e 2022). O objetivo foi de obter dados sobre mudanç as na estrutura da vegetaçã o, composiçã o de espé cies, abundâ ncia e estraté gias ecoló gicas apó s 10 anos sem distú rbios, capturando um gradiente que vai de campos abertos, campo adensado por plantas lenhosas até florestas fechadas. Utilizamos uma abordagem funcional integrada para aavaliar as diferentes dimensõ es funcionais das plantas, incluindo 10 atributos funcionais acima e abaixo do solo (incluindo atributos de folha, caule e raiz). O adensamento de espé cies lenhosas resultou em um aumento substancial na densidade de plantas lenhosas em á reas anteriormente ocupadas por campos, transformando sua estrutura que atualmente se assemelha à de florestas jovens. Curiosamente, identificamos claros trade-offs entre atributos funcionais acima e abaixo do solo em espé cies lenhosas. Por um lado, as espé cies ocorrendo em campos apresentaram folhas conservativas, uma estraté gia para proteçã o contra alta incidê ncia solar, danos fí sicos e seca, alé m de raí zes com uma estraté gia 'faç a você mesmo', garantindo eficiê ncia na aquisiçã o de nutrientes e á gua em solos pobres, e casca espessa relacionada à resistê ncia ao fogo. Por outro lado, espé cies de floresta foram geralmente mais altas e apresentaram folhas aquisitivas, indicando alta competitividade onde existe limitaçã o de luz, enquanto suas raí zes exibiram uma estraté gia de aquisiçã o de recursos mediada por fungos micorrí zicos, no ambiente onde os solos sã o mais ricos. Sí ntese. Avanç amos no entendimento atual sobre o adensamento de espé cies lenhosas sobre os campos ao demonstrar os trade-offs funcionais que permitem a ocorrê ncia de espé cies lenhosas ao longo da transiçã o entre floresta e campo no espaç o e no tempo. Mostramos, especialmente, como atributos funcionais abaixo do solo sã o importantes para explicar as estraté gias das espé cies, com uma covariâ ncia negativa entre atributos funcionais acima e abaixo do solo. Nossa abordagem integrativa baseada em atributos foi ú til para um melhor entendimento e manejo de mosaicos floresta-campo no sul do Brasil e em ecossistemas aná logos ao redor do mundo.

期刊论文 2025-05-01 DOI: 10.1111/1365-2745.70003 ISSN: 0022-0477

Uncertainties in carbon storage estimates for disturbance-prone dryland ecosystems hinder accurate assessments of their contribution to the global carbon budget. This study examines the effects of land-use change on carbon storage in an African savanna landscape, focusing on two major land-use change pathways: agricultural intensification and wildlife conservation, both of which alter disturbance regimes. By adapting tree inventory and soil sampling methods for dryland conditions, we quantified aboveground and belowground carbon in woody vegetation (AGC and BGC) and soil organic carbon (SOC) across these pathways in two vegetation types (scrub savanna and woodland savanna). We used Generalized Additive Mixed Models to assess the effects of multiple environmental drivers on AGC and whole-ecosystem carbon storage (C-total). Our findings revealed a pronounced variation in the vulnerability of carbon reservoirs to disturbance, depending on land-use change pathway and vegetation type. In scrub savanna vegetation, shrub AGC emerged as the most vulnerable carbon reservoir, declining on average by 56% along the conservation pathway and 90% along the intensification pathway compared to low-disturbance sites. In woodland savanna, tree AGC was most affected, decreasing on average by 95% along the intensification pathway. Unexpectedly, SOC stocks were often higher at greater disturbance levels, particularly under agricultural intensification, likely due to the preferential conversion of naturally carbon-richer soils for agriculture and the redistribution of AGC to SOC through megaherbivore browsing. Strong unimodal relationships between disturbance agents, such as megaherbivore browsing and woodcutting, and both AGC and C-total suggest that intermediate disturbance levels can enhance ecosystem-level carbon storage in disturbance-prone dryland ecosystems. These findings underline the importance of locally tailored management strategies-such as in carbon certification schemes-that reconcile disturbance regimes in drylands with carbon sequestration goals. Moreover, potential trade-offs between land-use objectives and carbon storage goals must be considered.

期刊论文 2025-04-01 DOI: 10.1111/gcb.70163 ISSN: 1354-1013

Transboundary wildlife species like the African savannah elephant (Loxodonta africana) requires a comprehensive regional approach to monitoring and effective conservation. This requires a thorough understanding of their ecology, ranging behaviour and the distribution of suitable habitats. In diverse landscapes, the management and conservation of the African savannah elephant are critical, particularly in dry protected areas where water and food resources are limited. The use of innovative Geographic Information Science (GIS) and remote sensing tools is revolutionising the understanding of the ranging behaviour and habitat dynamics of the African savannah elephant. When adopting GIS and remote sensing tools, park managers and conservationists must remember that: (i) the African savannah elephant has a determinate movement pattern and clusters around dominant vegetation types, (ii) the soil-adjusted vegetation index (SAVI) performs better relative to other indices in modelling the distribution of the African savannah elephant in arid areas, (iii) cellular automata-artificial neural network (CA-ANN) is a robust technique in modelling future landscapes, (iv) landscapes or environments near water points are significantly utilised by the African savannah elephant and vegetation performance is usually better far from the piosphere, (v) significant difference in the size of the home ranges and habitat selection by the African savannah elephant is mostly influenced by vegetation type and seasonal variations of resources, (vi) hyperslender stems in forest gaps confirms minimal damage in African savannah elephant dominated landscapes (satellite data confirms evidence of high tree regeneration) and (vii) the dynamic Brownian Bridge Movement Model (dBBMM) is a smart technique for home range and utilisation distribution construction in different protected zones.

期刊论文 2024-12-01 DOI: 10.1111/aje.70000 ISSN: 0141-6707

In landscapes with high elephant density, trees often exhibit more open canopies with fewer branches and foliage due to browsing pressure. This can result in altered tree morphology, with trees exhibiting stunted growth, multiple stems or unusual branching patterns in response to repeated damage from browsing. The objectives of this research were to (i) model the vegetation structure allometries, (ii) assess the impact of African savannah elephant (Loxodonta africana) herbivory on the vegetation structure and (iii) assess tree cover change and vegetation performance over time in Mana Pools National Park in Zimbabwe. We established 26 plots of 30 x 30 m size. Selection of sampling plots was done following several steps. First, a fish net grid with 30 x 30 m polygons was created and projected on the polygon of Mana Pools National Park. The polygons for exclusion zones were then clipped from the fish net grid using the clip tool in ArcGIS Pro 3.0. Then, selection of sampling plots was done initially by stratified random sampling using the Sampling Design Tool add in for ArcGIS Pro 3.0. Landsat images for the years 2003, 2013 and 2023 were used to assess land use land cover (LULC) time series and to calculate Normalised Difference Vegetation Index (NDVI) and Soil Adjusted Vegetation Index (SAVI) for the period. A generalised linear model (GLM) was used to analyse tree allometries. Further statistical investigations were performed using Bayesian piecewise regression (BPR) and Bayesian regression modelling (BRM). Basal area, number of stems, height, long canopy, diameter and basal circumference were all significantly different (p < 0.05) across all sampled plots. The change in growing conditions occurring as a tree grows beyond the reach of the African savannah elephant browsing indicates a natural system breakpoint. The best-fitting models were a simple linear model and a two breakpoint model for the plant population exposed to elephant herbivory. LULC, NDVI and SAVI confirm evidence of high tree regeneration over 2 decades. Understanding the dynamics in vegetation and LULC changes is critical for effective conservation and management of the habitats for African savannah elephants, as well as for maintaining the health and resilience of forest ecosystems.

期刊论文 2024-12-01 DOI: 10.1111/aje.13336 ISSN: 0141-6707

Termite mounds are keystone structures in African savannas, affecting multiple ecosystem processes. Despite the large size of termite mounds having the potential to modify conditions around them, patterns of mound-induced ecosystem effects have been assumed to be isotropic, with little attention given to how effects might vary around mounds. We measured soil nitrogen content, grass species composition, and mammalian grazing on and off termite mounds in the four cardinal directions, and across wet and dry seasons at three savanna sites varying in mean annual rainfall in South Africa's Kruger National Park. Evidence of directional effects (anisotropy) on ecosystem properties around termite mounds varied with site. Grass species composition differed between north- and south-facing slopes at the two drier sites where mounds were taller. However, differences in grazing extent and soil nitrogen content around mounds were only present at the intermediate rainfall site where mammalian herbivore biomass was highest, and mounds were of medium height. Our results suggest that termite mound effects display significant variation with direction, but that the emergence of directional effects is context dependent. Our results further suggest that such context-dependent directional effects can lead to positive feedback loops between termites, abiotic conditions, and mammalian herbivores.

期刊论文 2024-09-01 DOI: 10.1002/ecs2.4978 ISSN: 2150-8925

Biomass burning is a huge source of atmospheric aerosols and is poorly understood leading to large uncertainties in estimates of radiative forcing of climate. Aerosols have both a direct effect on climate by reflecting and absorbing solar radiation and an indirect effect by acting as cloud condensation nuclei (CCN) and ice nuclei (IN). Biomass burning aerosols are produced from burning of vegetation with the vast majority occurring in the tropics. This research presents data collected during the aircraft campaign of the South American Biomass Burning Analysis (SAMBBA) project during September and October 2012. A smouldering rainforest fire and a flaming savannah-like fire were selected for in-depth case studies of the atmospheric plume constituents and provide a comparison between the two fire types. The physiochemical characterization of the two plumes are identified, with preliminary results showing a significant difference in the black carbon concentration of the two plumes; 6 mu g m(-3) for the smouldering rainforest fire and 50 mu g m(-3) for the flaming savannah-like fire. However, organic matter concentrations were similar, peaking at 5mg m(-3). Analysis of the gas phase data and calculations of emission ratios (ER) and modified combustion efficiencies (MCE) will be presented together with an analysis of black carbon mixing state using data from a single particle soot photometer and organic aerosol composition.

期刊论文 2013-01-01 DOI: 10.1063/1.4803342 ISSN: 0094-243X
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