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Shrublands
Introduces some animals and plants that live in areas too dry for forests but too wet to be deserts.
Book
Increased aridity drives post-fire recovery of Mediterranean forests towards open shrublands
Recent observations suggest that repeated fires could drive Mediterranean forests to shrublands, hosting flammable vegetation that regrows quickly after fire. This feedback supposedly favours shrubland persistence and may be strengthened in the future by predicted increased aridity. An assessment was made of how fires and aridity in combination modulated the dynamics of Mediterranean ecosystems and whether the feedback could be strong enough to maintain shrubland as an alternative stable state to forest. A model was developed for vegetation dynamics, including stochastic fires and different plant fire‐responses. Parameters were calibrated using observational data from a period up to 100 yr ago, from 77 sites with and without fires in Southeast Spain and Southern France. The forest state was resilient to the separate impact of fires and increased aridity. However, water stress could convert forests into open shrublands by hampering post‐fire recovery, with a possible tipping point at intermediate aridity. Projected increases in aridity may reduce the resilience of Mediterranean forests against fires and drive post‐fire ecosystem dynamics toward open shrubland. The main effect of increased aridity is the limitation of post‐fire recovery. Including plant fire‐responses is thus fundamental when modelling the fate of Mediterranean‐type vegetation under climate‐change scenarios.
Journal Article
Carbon pools in China’s terrestrial ecosystems
China’s terrestrial ecosystems have functioned as important carbon sinks. However, previous estimates of carbon budgets have included large uncertainties owing to the limitations of sample size, multiple data sources, and inconsistent methodologies. In this study, we conducted an intensive field campaign involving 14,371 field plots to investigate all sectors of carbon stocks in China’s forests, shrublands, grasslands, and croplands to better estimate the regional and national carbon pools and to explore the biogeographical patterns and potential drivers of these pools. The total carbon pool in these four ecosystems was 79.24 ± 2.42 Pg C, of which 82.9% was stored in soil (to a depth of 1 m), 16.5% in biomass, and 0.60% in litter. Forests, shrublands, grasslands, and croplands contained 30.83 ± 1.57 Pg C, 6.69 ± 0.32 Pg C, 25.40 ± 1.49 Pg C, and 16.32 ± 0.41 Pg C, respectively. When all terrestrial ecosystems are taken into account, the country’s total carbon pool is 89.27 ± 1.05 Pg C. The carbon density of the forests, shrublands, and grasslands exhibited a strong correlation with climate: it decreased with increasing temperature but increased with increasing precipitation. Our analysis also suggests a significant sequestration potential of 1.9–3.4 Pg C in forest biomass in the next 10–20 years assuming no removals, mainly because of forest growth. Our results update the estimates of carbon pools in China’s terrestrial ecosystems based on direct field measurements, and these estimates are essential to the validation and parameterization of carbon models in China and globally.
Journal Article
Rockrose Land Management: Contribution of Periodic Harvesting to Increase Value and to Control ICistus ladanifer/I L. Shrublands
Cistus ladanifer L. (Cistaceae) occupies extensive areas as a dominant species (shrublands) or is associated to other major forest typologies in the Iberian Peninsula. Cistus ladanifer shrublands are mostly present in oligotrophic lands with little valorisation and management and as they develop over the years (up to 20-years-old) they promote the ignition and perpetuation of fire. To contribute to the proper management and valorisation of such systems, a 5-year-old dense shrubland was evaluated for its labdanum resin, seeds, and biomass productivity using different non-destructive harvest periodicities (annual and biennial) and seasons (early, mid-, and late summer), in a two-year case-study. Annual harvest modality maximized labdanum resin productivity (reaching 230 ± 50 kg∙ha[sup.−1]∙2 years[sup.−1] at late summer) and photosynthetic biomass productivity. In contrast, a biennial harvest yielded significant amounts of more diversified products. It maximized seeds productivity (reaching 75 ± 41 kg∙ha[sup.−1]∙2 years[sup.−1] independently of the summer season) and lignified biomass. However, it also reached a labdanum resin productivity of 134 ± 20 kg∙ha[sup.−1]∙2 yearrs[sup.−1] at late summer and a photosynthetic biomass productivity around two times lower than the annual harvest. In this study, we propose two modalities of periodic harvest to be considered as proper long cycle management practices of rockrose lands. It intends to minimize fire risks, break the vegetation auto-succession mechanism, and increase profit from non-productive lands based on three direct outputs with a myriad of applications and valorisation pathways.
Journal Article
Traits of neighbouring plants and space limitation determine intraspecific trait variability in semi-arid shrublands
Understanding how intraspecific trait variability (ITV) responds to both abiotic and biotic constraints is crucial to predict how individuals are assembled in plant communities, and how they will be impacted by ongoing global environmental change. Three key functional traits [plant height, leaf area (LA) and specific leaf area (SLA)] were assessed to quantify the range of ITV of four dominant plant species along a rainfall gradient in semi-arid Mediterranean shrublands. Variance partitioning and confirmatory multilevel path analyses were used to assess the direct and indirect effects of rainfall, space limitation (crowding) and neighbouring plant traits on ITV. The direct effect of the local neighbourhood on the trait values of subordinate individuals was as strong as the effect of rainfall. The indirect effect of rainfall, however, mediated by the effect of the local neighbourhood on the trait values of subordinate individuals, was weak. Rainfall decreased the height and SLA of subordinate individuals, but increased their LA. Neighbouring plant traits were just as strong predictors as crowding in explaining changes in ITV.Synthesis. Our study provides a framework to disentangle the direct effects of abiotic factors and their indirect effects on ITV mediated by the local neighbourhood. Our results highlight that abiotic and biotic constraints are both substantial sources of trait variations at the individual level, and can blur processes underlying changes in ITV. Considering and disentangling combined sources with an individual perspective would help to refine our predictions for community assembly and functional ecology.
Journal Article
Changes in vegetation structure and fuel characteristics along post-fire succession promote alternative stable states and positive fire–vegetation feedbacks
Aims: Structural and compositional changes along post-fire succession modify plant community proneness to burn (flammability). The dominant regeneration strategies and life forms, and their interactions along post-fire succession, modulate these changes by affecting density, amount and connectivity of fuels. Depending on how flammability evolves during post-fire succession it may feed back negatively, neutrally or positively into fire probability and behaviour. Negative fire-vegetation feedbacks arise when communities increase flammability as stands age, while positive feedbacks occur where early stages have higher flammability than later stages. We characterized changes in vegetation structure and fuel characteristics with time since fire in sites where either resprouters maintained dominance (shrublands), or where colonizer trees reached the sites and dominate later post-fire stages (forests). Location: Northwestern Patagonia, Argentina. Methods: We measured vegetation structure and characterized fine fuels with the intercept pole method in stands of different post-fire age in 18 shrublands (range 1–115 years) and 18 forests (range 7–216 years). Results: In shrublands fuel amount quickly recovered after fire to a relatively constant value and fine fuel density remained high. Conversely, in forests, fuel amount rapidly increased during early post-fire stages (when resprouting shrubs dominate the community), peaked at c. 30–50 years (related to the co-existence of resprouters and young trees) and decreased to a relatively constant value (when tall trees dominate the community and suppress resprouters). Moreover, forest fuel density decreased with time. These changes in fuel characteristics were largely linked to changes in vegetation structure, which in turn were modulated by the dominant regeneration strategies and life forms. Conclusions: Our results provide evidence of a positive fire–vegetation feedback for the community dominated by colonizer trees, while the community dominated by resprouter shrubs showed a neutral feedback. Given the co-existence of flammable shrublands bordering fire-sensitive forests and their low tree regeneration rates, we argue that forest communities are especially sensitive to changes in fire frequency and severity driven by global change. Anthropogenic or climate-driven changes in ignitions are threatening these landscapes, which may undergo potentially rapid transformations, as seen in other temperate ecosystems.
Journal Article
Differential effects of N addition on the stoichiometry of microbes and extracellular enzymes in the rhizosphere and bulk soils of an alpine shrubland
Background and aims
While large differences in microbial biomass and extracellular enzyme activities (EEAs) between rhizosphere and bulk soils have been demonstrated, the potentially different response of microbes and their EEAs in rhizosphere and bulk soils to nitrogen (N) deposition is still not elucidated.
Methods
We analyzed the microbial biomass and EEAs in the rhizosphere and bulk soils of
Sibiraea angustata
in an alpine shrubland on the eastern Qinghai-Tibet Plateau after chronic N application. We also analyzed the stoichiometric linkages between plants, microbes, enzymes and soils to clarify the coupled responses of aboveground plants and belowground ecological processes.
Results
Microbial nutrient concentrations and activities of EAAs responded differently to N addition in the rhizosphere and bulk soils. In the rhizosphere, N addition caused a significant increase in microbial biomass carbon (C), N and phosphorus (P) concentrations and greater P-degrading enzyme activity (relative to the activities of C- and N-degrading enzymes), which induced a significant reduction in enzyme C:P and N:P ratios. The rhizosphere enzyme N:P ratio was negatively correlated with the N:P ratios of plant, soil and microbe, implying that increased plant and microbial P uptake under N addition may gradually aggravate rhizosphere P limitation. However, for the bulk soil, N addition did not affect microbial biomass but significantly enhanced C-degrading enzyme activity and decreased the enzyme C:N ratio. Meanwhile, the bulk-soil enzyme C:N ratio was negatively correlated with the soil C:N ratio but independent of the plant C:N ratio, implying that N addition may enhance bulk-soil microbial C limitation.
Conclusions
Our study suggests that elevated N deposition may induce differential microbial nutrient limitation between the rhizosphere and bulk soils due to the plant-microbe-soil interactions in the rhizosphere. This study highlights the importance of incorporating rhizosphere microbial processes into biogeochemical models describing environmental changes.
Journal Article
Plant diversity enhances productivity and soil carbon storage
Despite evidence from experimental grasslands that plant diversity increases biomass production and soil organic carbon (SOC) storage, it remains unclear whether this is true in natural ecosystems, especially under climatic variations and human disturbances. Based on field observations from 6,098 forest, shrubland, and grassland sites across China and predictions from an integrative model combining multiple theories, we systematically examined the direct effects of climate, soils, and human impacts on SOC storage versus the indirect effects mediated by species richness (SR), aboveground net primary productivity (ANPP), and belowground biomass (BB). We found that favorable climates (high temperature and precipitation) had a consistent negative effect on SOC storage in forests and shrublands, but not in grasslands. Climate favorability, particularly high precipitation, was associated with both higher SR and higher BB, which had consistent positive effects on SOC storage, thus offsetting the direct negative effect of favorable climate on SOC. The indirect effects of climate on SOC storage depended on the relationships of SR with ANPP and BB, which were consistently positive in all biome types. In addition, human disturbance and soil pH had both direct and indirect effects on SOC storage, with the indirect effects mediated by changes in SR, ANPP, and BB. High soil pH had a consistently negative effect on SOC storage. Our findings have important implications for improving global carbon cycling models and ecosystem management: Maintaining high levels of diversity can enhance soil carbon sequestration and help sustain the benefits of plant diversity and productivity.
Journal Article
Global 10 m Land Use Land Cover Datasets: A Comparison of Dynamic World, World Cover and Esri Land Cover
The European Space Agency’s Sentinel satellites have laid the foundation for global land use land cover (LULC) mapping with unprecedented detail at 10 m resolution. We present a cross-comparison and accuracy assessment of Google’s Dynamic World (DW), ESA’s World Cover (WC) and Esri’s Land Cover (Esri) products for the first time in order to inform the adoption and application of these maps going forward. For the year 2020, the three global LULC maps show strong spatial correspondence (i.e., near-equal area estimates) for water, built area, trees and crop LULC classes. However, relative to one another, WC is biased towards over-estimating grass cover, Esri towards shrub and scrub cover and DW towards snow and ice. Using global ground truth data with a minimum mapping unit of 250 m2, we found that Esri had the highest overall accuracy (75%) compared to DW (72%) and WC (65%). Across all global maps, water was the most accurately mapped class (92%), followed by built area (83%), tree cover (81%) and crops (78%), particularly in biomes characterized by temperate and boreal forests. The classes with the lowest accuracies, particularly in the tundra biome, included shrub and scrub (47%), grass (34%), bare ground (57%) and flooded vegetation (53%). When using European ground truth data from LUCAS (Land Use/Cover Area Frame Survey) with a minimum mapping unit of <100 m2, we found that WC had the highest accuracy (71%) compared to DW (66%) and Esri (63%), highlighting the ability of WC to resolve landscape elements with more detail compared to DW and Esri. Although not analyzed in our study, we discuss the relative advantages of DW due to its frequent and near real-time data delivery of both categorical predictions and class probability scores. We recommend that the use of global LULC products should involve critical evaluation of their suitability with respect to the application purpose, such as aggregate changes in ecosystem accounting versus site-specific change detection in monitoring, considering trade-offs between thematic resolution, global versus. local accuracy, class-specific biases and whether change analysis is necessary. We also emphasize the importance of not estimating areas from pixel-counting alone but adopting best practices in design-based inference and area estimation that quantify uncertainty for a given study area.
Journal Article
Wildfire severity and vegetation recovery drive post‐fire evapotranspiration in a southwestern pine‐oak forest, Arizona, USA
Post‐fire stand water balance is a critical factor influencing tree regeneration and survival, which are often modulated by fire severity. We examined influences of the post‐fire vegetation matrix and fire severity on diurnal, seasonal, and multi‐year variation in evapotranspiration (ET) by analyzing the relationship between post‐fire vegetation and ECOsystem Spaceborne Thermal Radiometer Experiment on the International Space Station (ECOSTRESS) ET data using multivariate and linear mixed effects modeling. Unlike many high‐severity fire sites where ET drops after burning, post‐fire ET was high at shrubland sites that burned at high fire severity in southern Arizona, USA. In this study, post‐fire ET was driven by plant species composition and tree canopy cover. ET was significantly higher in the morning and midday in densely vegetated post‐fire shrublands than pine‐dominated forests that remained 5–7 years after wildfire. Our results demonstrate that plant functional traits such as resprouting and desiccation tolerance drive post‐fire ET patterns, and they are likely to continue to play critical roles in shaping post‐fire plant communities and forest water cycling under future environmental change. Wildfire‐driven transitions from forests to shrublands are an increasingly prevalent landscape feature, as fires across western North America continue to grow in size and severity under climate change. Post‐fire stand water balance is a critical factor influencing tree regeneration and survival success, which are often modulated by fire severity. We examined influences of the post‐fire vegetation matrix and fire severity on diurnal, seasonal, and multi‐year variation in evapotranspiration (ET) ECOSTRESS remotely sensed data via multivariate and linear mixed effects modeling. Unlike many high‐severity fire sites where ET drops after burning, post‐fire ET was high at type‐converted shrubland sites in southern Arizona, USA. Five‐ to seven‐year‐old post‐fire shrublands had higher ET in the morning and at midday than pine‐dominated forests that remained intact after the wildfire. This study highlights the importance of post‐fire plant species composition as a control on stand water status and cycling.
Journal Article