Rapid response of habitat structure and above-ground carbon storage to altered fire regimes in tropical savanna

Fire regimes across the globe have been altered through changes in land use, land management, and climate conditions. Understanding how these modified fire regimes impact vegetation structure and dynamics is essential for informed biodiversity conservation and carbon management in savanna ecosystems. We used a fire experiment at the Territory Wildlife Park (TWP), northern Australia, to investigate the consequences of altered fire regimes for vertical habitat structure and above-ground carbon storage. We mapped vegetation three-dimensional (3-D) structure in high spatial resolution with airborne lidar across 18 replicated 1&thinsp;ha plots of varying fire frequency and season treatments. We used lidar-derived canopy height and cover metrics to extrapolate field-based measures of woody biomass to the full extent of the experimental site (R2=0.82, RMSE&thinsp;=&thinsp;7.35&thinsp;t&thinsp;C&thinsp;ha−1) and analysed differences in above-ground carbon storage and canopy structure among treatments. Woody canopy cover and biomass were highest in the absence of fire (76&thinsp;% and 39.8&thinsp;t&thinsp;C&thinsp;ha−1) and lowest in plots burnt late in the dry season on a biennial basis (42&thinsp;% and 18.2&thinsp;t&thinsp;C&thinsp;ha−1). Woody canopy vertical profiles differed among all six fire treatments, with the greatest divergence in height classes &lt;5&thinsp;m. The magnitude of fire effects on vegetation structure varied along the environmental gradient underpinning the experiment, with less reduction in biomass in plots with deeper soils. Our results highlight the large extent to which fire management can shape woody structural patterns in savanna landscapes, even over time frames as short as a decade. The structural profile changes shown here, and the quantification of carbon reduction under late dry season burning, have important implications for habitat conservation, carbon sequestration, and emission reduction initiatives in the region.</p

Towards understanding belowground resources acquisition: Applying data driven methods for deriving root water uptake profiles in grasslands of different diversity

Although root water uptake is an important component in the plant-soil-water relation for single plants and on ecosystem scale, studies investigating the effect of co-existing plant species on community water use have been conducted without estimating root water uptake profiles. However, knowledge of root water uptake is essential for understanding of intra- and interspecific interactions of plants. For those reasons, minimal-invasive and easy to use methods for estimating root water uptake are inevitable. Within this dissertation, an attempt has been made to identify a simple but sufficient accurate method for estimating evapotranspiration and root water uptake profiles from soil water content measurements without a priori information on root distribution parameters. Subsequently, this method was applied to investigate the effect of co-existing plant species on community root water uptake. First, four different complex water balance methods were evaluated regarding their applicability on the ecohydrological issue. Therefore, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. In the second part, an additional accuracy assessment considering magnitudes of evapotranspiration, soil texture variability, and sensor uncertainty was carried out on 12 weighable lysimeters. Third, we investigated the effect of co-existing plant species on the community root water uptake. Analysis of estimated root water uptake profiles were combined with measurements of leaf water potentials and stomatal conductance, which constitutes the novelty of this thesis. The results indicate that the investigated communities with higher species richness are able to adjust their root water uptake strategy in a way that the water use of the entire community is optimized

Using measured soil water contents to estimate evapotranspiration and root water uptake profiles – a comparative study

Understanding the role of plants in soil water relations, and thus ecosystem functioning, requires information about root water uptake. We evaluated four different complex water balance methods to estimate sink term patterns and evapotranspiration directly from soil moisture measurements. We tested four methods. The first two take the difference between two measurement intervals as evapotranspiration, thus neglecting vertical flow. The third uses regression on the soil water content time series and differences between day and night to account for vertical flow. The fourth accounts for vertical flow using a numerical model and iteratively solves for the sink term. None of these methods requires any a priori information of root distribution parameters or evapotranspiration, which is an advantage compared to common root water uptake models. To test the methods, a synthetic experiment with numerical simulations for a grassland ecosystem was conducted. Additionally, the time series were perturbed to simulate common sensor errors, like those due to measurement precision and inaccurate sensor calibration. We tested each method for a range of measurement frequencies and applied performance criteria to evaluate the suitability of each method. In general, we show that methods accounting for vertical flow predict evapotranspiration and the sink term distribution more accurately than the simpler approaches. Under consideration of possible measurement uncertainties, the method based on regression and differentiating between day and night cycles leads to the best and most robust estimation of sink term patterns. It is thus an alternative to more complex inverse numerical methods. This study demonstrates that highly resolved (temporally and spatially) soil water content measurements may be used to estimate the sink term profiles when the appropriate approach is used

Variability in fire-induced change to vegetation physiognomy and biomass in semi-arid savanna

Fire plays an intrinsic role in shaping the biophysical attributes of savanna ecosystems. Savanna fires limit vegetation biomass below their climatically determined potential, but the magnitude of this effect and how it varies across heterogeneous landscapes are poorly understood. In this study, we explore woody tree structure and canopy characteristics across a fire manipulation experiment that has been maintained for 63 yr in South Africa's Kruger National Park. Our study design assessed three late dry‐season fire regimes (biennial, triennial, and unburnt) across a precipitation gradient (737–496 mm/yr) spanning four different landscapes with a mixture of sandy and clay soils. We used terrestrial laser scanning (TLS) to quantify tree height, canopy cover, and aboveground carbon storage across the experimental treatments. Vegetation physiognomy was influenced by the interaction between landscape and fire frequency. In the absence of fire, woody height, cover, and biomass increased with increasing rainfall. The presence of fire acted to reduce structure and biomass as expected, but the magnitude of this effect increased with increasing rainfall. We found minimal difference between the effects of biennial or triennial burning—except at the wettest site where the triennial fire plots had half the biomass of those burnt biennially. The rainfall dependent fire–vegetation relationships shown here provide empirical quantification of top‐down constraint by fire and highlight the challenges of predicting responses to disturbances in these inherently heterogeneous ecosystems. Robust quantification of 3D structure and dynamics through TLS will be useful for constraining carbon stock models and predicting trajectories of change under future climate and land‐use conditions

Rapid response of habitat structure and above-ground carbon storage to altered fire regimes in tropical savanna

Fire regimes across the globe have been altered through changes in land use, land management, and climate conditions. Understanding how these modified fire regimes impact vegetation structure and dynamics is essential for informed biodiversity conservation and carbon management in savanna ecosystems. We used a fire experiment at the Territory Wildlife Park (TWP), northern Australia, to investigate the consequences of altered fire regimes for vertical habitat structure and above-ground carbon storage. We mapped vegetation three-dimensional (3-D) structure in high spatial resolution with airborne lidar across 18 replicated 1 ha plots of varying fire frequency and season treatments. We used lidar-derived canopy height and cover metrics to extrapolate field-based measures of woody biomass to the full extent of the experimental site (R2 D 0:82, RMSED7.35 tC ha) and analysed differences in above-ground carbon storage and canopy structure among treatments. Woody canopy cover and biomass were highest in the absence of fire (76% and 39.8 tC ha) and lowest in plots burnt late in the dry season on a biennial basis (42% and 18.2 t Cha). Woody canopy vertical profiles differed among all six fire treatments, with the greatest divergence in height classes < 5 m. The magnitude of fire effects on vegetation structure varied along the environmental gradient underpinning the experiment, with less reduction in biomass in plots with deeper soils. Our results highlight the large extent to which fire management can shape woody structural patterns in savanna landscapes, even over time frames as short as a decade. The structural profile changes shown here, and the quantification of carbon reduction under late dry season burning, have important implications for habitat conservation, carbon sequestration, and emission reduction initiatives in the region

Positive association between forest management, environmental change, and forest bird abundance

Abstract Background The global decrease in wildlife populations, especially birds, is mainly due to land use change and increasing intensity of land use (Parmesan and Yohe 2003). However, impacts of management tools to mitigate biodiversity loss at regional and global scales are less apparent in forest regions that have a constant forest area, and which did not suffer from habitat degradation, and where forests are sustainably managed, such as in Central Europe or the northeastern USA. A biodiversity assessment for Germany suggested, for example, that bird populations were constant (Bundesamt für Naturschutz 2015). Results This study shows that changes in the environment and in forest management over the past 45 years have had a significant, positive effect on the abundance of non-migratory forest bird species in Central Europe. Economy (timber prices and GDP), forest management (timber harvest and mixed forest area), and environmental factors (atmospheric CO2 concentration and nitrogen deposition) were investigated together with changes in abundances of migratory and non-migratory forest birds using partial least squares path modeling. Climate change, resulting in longer seasons and milder winters, and forest management, promoting tree diversity, were significantly positively related to the abundance of non-migratory forest birds and explained 92% of the variation in their abundance in Europe. Regionally-migrating forest birds had stable populations with large variation, while birds migrating across continents declined in recent decades, suggesting significant, contrasting changes in bird populations in Europe. In northeastern North America we also found evidence that non-migratory forests have experienced long-term increases in abundance, and this increase was related to management. The increase of populations of non-migratory forest birds in Europe and North America is associated with an increase in structural diversity and disturbances at the landscape level. Conclusions Our results suggest that reports about bird decline in forests should separate between migratory and non-migratory bird species. Efforts to mitigate the general decline in bird abundance should focus on land-use systems other than forests and support sustainable forest management independent of economic conditions

Plant functional diversity increases grassland productivity‐related water vapor fluxes: an Ecotron and modeling approach

The impact of species richness and functional diversity of plants on ecosystem water vapor fluxes has been little investigated. To address this knowledge gap, we combined a lysimeter setup in a controlled environment facility (Ecotron) with large ecosystem samples/ monoliths originating from a long-term biodiversity experiment (“The Jena Experiment”) and a modelling approach. We aimed at (1) quantifying the impact of plant species richness (4 vs. 16 species) on day- and night-time ecosystem water vapor fluxes, (2) partitioning ecosystem evapotranspiration into evaporation and plant transpiration using the Shuttleworth and Accepted Article This article is protected by copyright. All rights reserved. Wallace (SW) energy partitioning model, and (3) identifying the most parsimonious predictors of water vapor fluxes using plant functional trait-based metrics such as functional diversity and community weighted means. Day-time measured and modeled evapotranspiration were significantly higher in the higher diversity treatment suggesting increased water acquisition. The SW model suggests that at low plant species richness, a higher proportion of the available energy was diverted to evaporation (a non-productive flux), while at higher species richness the proportion of ecosystem transpiration (a productivity-related water flux) increased. While it is well established that LAI controls ecosystem transpiration, here we also identified that the diversity of leaf nitrogen concentration among species in a community is a consistent predictor of ecosystem water vapor fluxes during day-time. The results provide evidence that, at the peak of the growing season, higher LAI and lower percentage of bare ground at high plant diversity diverts more of the available water to transpiration – a flux closely coupled with photosynthesis and productivity. Higher rates of transpiration presumably contribute to the positive effect of diversity on productivity

Dynamic niche partitioning in root water uptake facilitates efficient water use in more diverse grassland plant communities

1.Efficient extraction of soil water is essential for the productivity of plant communities. However, research on the complementary use of resources in mixed plant communities, and especially the impact of plant species richness on root water uptake, is limited. So far, these investigations have been hindered by a lack of methods allowing for the estimation of root water uptake profiles. 2.The overarching aim of our study was to determine whether diverse grassland plant communities in general exploit soil water more deeply and whether this shift occurs all the time or only during times of enhanced water demand. 3.Root water uptake was derived by analyzing the diurnal decrease of soil water content separately at each measurement depth, thus yielding root water uptake profiles for 12 experimental grasslands communities with two different levels of species richness (4 and 16 sown species). Additional measurements of leaf water potential, stomatal conductance, and root traits were used to identify differences in water relations between plant functional groups. 4.Although the vertical root distribution did not differ between diversity levels, root water uptake shifted towards deeper layers (30 cm and 60 cm) in more diverse plots during periods of high vapor pressure deficit. Our results indicate that the more diverse communities were able to adjust their root water uptake, resulting in increased water uptake per root area compared to less diverse communities (52% at 20 cm, 118% at 30 cm, and 570% at 60 cm depth) and a more even distribution of water uptake over depth. Tall herbs, which had lower leaf water potential and higher stomatal conductance in more diverse mixtures, contributed disproportionately to dynamic niche partitioning in root water uptake. 5.This study underpins the role of diversity in stabilizing ecosystem function and mitigating drought stress effects during future climate change scenarios. Furthermore, the results provide evidence that root water uptake is not solely controlled by root length density distribution in communities with high plant diversity but also by spatial shifts in water acquisition