Vegetation Layer Research Articles

Performance of a gross pollutant trap-biofilter and sand filter treatment train for the removal of organic micropollutants from highway stormwater (field study)

This field study assessed the occurrence, event mean concentrations (EMCs), and removal of selected organic micro-pollutants (OMPs), namely, polycyclic aromatic hydrocarbons (PAHs), petroleum hydrocarbons (PHCs), nonylphenol (NP), 4-t-octylphenol (OP), and bisphenol A (BPA), in a gross pollutant trap (GPT)-biofilter/sand filter stormwater treatment train in Sundsvall, Sweden. The effects of design features of each treatment unit, including pre-sedimentation (GPT), sand filter medium, vegetation, and chalk amendment, were investigated by comparing the units' removal performances. Overall, the treatment train removed most OMPs from highway runoff effectively. The results showed that although the sand filter provided moderate (<50 % for phenolic substances) to high (50–80 % for PAHs and PHCs) removal of OMPs, adding a vegetated soil layer on top of the sand filter considerably improved the removal performance (by at least 30 %), especially for BPA, OP, and suspended solids. Moreover, GTP did not contribute to the treatment significantly. Uncertainties in the removal efficiencies of PAHs and PHCs by the filter cells increased substantially when the ratio of the influent concentration to the limit of quantification decreased. Thus, accounting for such uncertainties due to the low OMP concentrations should be considered when evaluating the removal performance of biofilters.

Tropical forests are mainly unstratified especially in Amazonia and regions with lower fertility or higher temperatures

The stratified nature of tropical forest structure had been noted by early explorers, but until recent use of satellite-based LiDAR (GEDI, or Global Ecosystems Dynamics Investigation LiDAR), it was not possible to quantify stratification across all tropical forests. Understanding stratification is important because by some estimates, a majority of the world’s species inhabit tropical forest canopies. Stratification can modify vertical microenvironment, and thus can affect a species’ susceptibility to anthropogenic climate change. Here we find that, based on analyzing each GEDI 25 m diameter footprint in tropical forests (after screening for human impact), most footprints (60%–90%) do not have multiple layers of vegetation. The most common forest structure has a minimum plant area index (PAI) at ∼40 m followed by an increase in PAI until ∼15 m followed by a decline in PAI to the ground layer (described hereafter as a one peak footprint). There are large geographic patterns to forest structure within the Amazon basin (ranging between 60% and 90% one peak) and between the Amazon (79 ± 9% sd) and SE Asia or Africa (72 ± 14% v 73 ± 11%). The number of canopy layers is significantly correlated with tree height (r 2 = 0.12) and forest biomass (r 2 = 0.14). Environmental variables such as maximum temperature (T max) (r 2 = 0.05), vapor pressure deficit (VPD) (r 2 = 0.03) and soil fertility proxies (e.g. total cation exchange capacity −r 2 = 0.01) were also statistically significant but less strongly correlated given the complex and heterogeneous local structural to regional climatic interactions. Certain boundaries, like the Pebas Formation and Ecoregions, clearly delineate continental scale structural changes. More broadly, deviation from more ideal conditions (e.g. lower fertility or higher temperatures) leads to shorter, less stratified forests with lower biomass.

Research and Application of the Calculation Method of River Roughness Coefficient with Vegetation

The roughness coefficient is a comprehensive parameter reflecting river resistance, which is widely used in the planning and design of river regulation and flood control projects. In recent years, as the upstream water conservancy and hydro-power projects have been put into operation, the frequency of low flow in the middle and lower reaches has increased, and the frequency of flood flow has decreased. All kinds of vegetation in the river floodplain grow luxuriantly, which causes a change in the river resistance and roughness coefficient. The present study was carried out with theoretical analysis and laboratory tests. A formula for the roughness coefficient calculation was derived based on the momentum equilibrium equation and momentum exchange between the vegetation layer and upper layer. The relationship between the depth-averaged velocity within the vegetation layer and depth-averaged velocity of the whole flow was analyzed. The reliability of the formula was verified by a large amount of previous experimental data. Based on the derived formula, the variation law of the roughness coefficient with vegetation density, vegetation height, and water depth were obtained. For the emerged vegetation flow, the Manning coefficient tended to increase with the increase in the vegetation density and water depth. For the submerged vegetation flow, the Manning coefficient showed a trend of decreasing with the increase in the water depth and increased with the increase in the vegetation height. Finally, the derived formula was applied in the Yueyang reach of the Yangtze River and the Duliujian River. The study can be applied in the fields of water level-flow discharge relationship analysis and the water surface line calculation of vegetated rivers.

Chlorine Distribution in Soil and Vegetation in Boreal Habitats along a Moisture Gradient from Upland Forest to Lake Margin Wetlands.

The assumed dominance of chloride (Cl-) in terrestrial ecosystems is challenged by observations of extensive formation of organically bound Cl (Clorg), resulting in large soil Cl storage and internal cycling. Yet, little is known about the spatial distribution of Cl in ecosystems. We quantified patterns of Cl distribution in different habitats along a boreal hillslope moisture gradient ranging from relatively dry upland coniferous forests to wet discharge areas dominated by alder. We confirmed that dry habitats are important for Cl storage but found that Cl pools tended to be larger in moist and wet habitats. The storage of Clorg was less important in wet habitats, suggesting a shift in the balance between soil chlorination and dechlorination rates. Cl concentrations in the herb layer vegetation were high in wet and moist sites attributed to a shift in plant species composition, indicating plant community-dependent ecosystem Cl cycling. Mass-balance calculations showed that internal Cl cycling increased overall ecosystem Cl residence times at all sites and that plant uptake rates of Cl- were particularly high at wet sites. Our results indicate that habitat characteristics including plant communities and hydrology are key for understanding Cl cycling in the environment.

Relationship between Lidar-Derived Canopy Densities and the Scattering Phase Center of High-Resolution TanDEM-X Data

The estimation of forestry parameters is essential to understanding the three-dimensional structure of forests. In this respect, the potential of X-band synthetic aperture radar (SAR) has been recognized for years. Many studies have been conducted on deriving tree heights with SAR data, but few have paid attention to the effects of the canopy structure. Canopy density plays an important role since it provides information about the vertical distribution of dominant scatterers in the forest. In this study, the position of the scattering phase center (SPC) of interferometric X-band SAR data is investigated with regard to the densest vegetation layer in a deciduous and coniferous forest in Germany by applying a canopy density index from high-resolution airborne laser scanning data. Two different methods defining the densest layer are introduced and compared with the position of the TanDEM-X SPC. The results indicate that the position of the SPC often coincides with the densest layer, with mean differences ranging from −1.6 m to +0.7 m in the deciduous forest and +1.9 m in the coniferous forest. Regarding relative tree heights, the SAR signal on average penetrates up to 15% (3.4 m) of the average tree height in the coniferous forest. In the deciduous forest, the difference increases to 18% (6.2 m) during summer and 24% (8.2 m) during winter. These findings highlight the importance of considering not only tree height but also canopy density when delineating SAR-based forest heights. The vertical structure of the canopy influences the position of the SPC, and incorporating canopy density can improve the accuracy of SAR-derived forest height estimations.

Upland forest community composition and structure by ecoregion in 73 Florida state parks – Insights for ongoing management

Plot based forest/vegetation data is used to establish current conditions and inform natural resources management decisions. The Florida Department of Environmental Protection – Division of Recreation and Parks (DRP) manages 175 state parks. As part of its mission, DRP strives to restore landscapes and natural communities by reintroducing dynamic natural processes such as fire. DRP also uses other methods of active management to achieve desired future conditions (DFCs) in multiple communities including those characterized by longleaf pine (Pinus palustris Mill.) and native groundcover (GC) species. To meet the challenge of managing natural resources across the State, DRP initiated an objective and repeatable forest/vegetation inventory system. The primary objective of this paper was to analyze and summarize the resultant data and compare current community type (ComType) vegetation conditions. Current conditions were quantified using nested plots distributed within sample areas across 73 state parks and 15 ecoregions via the line-plot method. Over 37,000 plots were inventoried; 36% were in pine flatwoods. Ten actively managed and dominant ComTypes were central to this paper and when aggregated by ecoregion, 76 ComType by ecoregion (CTER) groups were examined. Descriptive statistics for various measurements, e.g., diameter at breast height, height, and density, were calculated for overstory, midstory and understory (vegetation layer) separately per CTER. Mean importance value index (IVI) was calculated by species or species-group per vegetation layer and CTER. Community classification was conducted via hierarchical clustering of CTERs per vegetation layer using mean IVI scores. Across CTERs, pine overstory and midstory abundance/stocking levels were generally low, non-pine overstory and midstory stocking levels were high, pine regeneration was sparse, and GC was dominated by leaf litter, pine straw, and non-pine woody seedlings. Results strongly suggest that some ComTypes were similar within certain ecoregions. Various pine species are considered dominant or one of the prominent overstory species for eight of the ten ComTypes. The ability to manage upland pine ComTypes using natural regeneration systems will become increasingly challenging in the near- to medium-term given relatively low overstory pine stocking for most CTERs, and the virtual lack of young pines within midstory and understory layers. Further investigations could help identify potential causal agents concerning low young pine stocking levels, e.g., timing and frequency of prescribed fires, frequency of logging, and/or increased competition from high densities of midstory non-pines and appropriate natural regeneration systems, e.g., seed tree, shelterwood, or group selection, or underplanting longleaf pine, that would accelerate understory pine recruitment.

Unit-scale- and catchment-scale-based sensitivity analysis of bioretention cell for urban stormwater system management

Abstract An improved understanding of bioretention cell (BC) design configuration at both the unit scale and catchment scale is necessary for critical insight into dynamical behaviors of design parameters, which resultantly guides and improves the effectiveness and efficiency of a BC. A comprehensive sensitivity analysis (SA) of BC design parameters was conducted in this study by using the Stormwater Management Model (SWMM) which is globally used for BC's modeling. The preliminary screening of various design parameters is conducted by the one-factor-at-a-time (OAT) SA method and the key influential parameters (i.e., conductivity, berm height, vegetation volume, suction head, porosity, wilting point, and soil thickness) are selected for further SA. To this end, 1,000 random uniformly distributed samples of each sensitive design parameter are simulated by a Python wrapper of SWMM (PySWMM) under different design storms at the unit scale and catchment scale, respectively. Unit-scale SA results found unique characteristics of each design parameter under different storm scenarios, and their behaviors toward different model responses dynamically change within their factor spaces. Catchment-scale SA results conclude vegetation and soil layers design parameters have significant impacts on controlling stormwater at the catchment scale, and optimal selection of design parameters of vegetation (type, density, and height) and soil (type, layer thickness, and void ratio) is necessary for significantly improving the effectiveness of the BC at the catchment scale.

Prospects for creating surfaces with vegetation on buildings in Poland

According to the World Green Building Council, energy demand in buildings will increase double, by 2050. Worldwide, construction and the built environment contribute about 39% of global carbon dioxide (28% from operational emissions, from energy needed to heat, cool and power them, and the remaining 11% from materials and construction) and 50% of the world’s resource consumption. Thus, maximising energy efficiency and improving the environment are the main directions of construction development. Both tasks can be solved using green structures that connect living plants with building structures (green roofs, living facades and living interior walls). The data from the main organisations in the branch has been analysed: United Nations, The World Green Building Council, European Parlament and Council, and also Global Alliance for Buildings and Construction. They state the need for green and blue infrastructure, and sustainable urbanisation, incl. decarbonising of buildings and mitigation of urban heat islands. Greening of buildings is a measure to achieve the requirements. In addition, it improves health and well-being or increases biodiversity. Poland has the corresponding norms to stimulate the greening of buildings. The term “biologically active area” is defined as the area with an area arranged in a way that ensures natural vegetation of plants and rainwater retention; such an area also covers 50% of the surface of terraces and flat roofs with a vegetation layer with vegetation and other surfaces (e.g. green facade), providing natural vegetation of plants, with an area of not less than 10 m2, surface water in this area. Special tax policies give privileges to those who green their building(s). These measures have a good result in spreading green structures, which is proved by the objects represented in the article.

Satellite observed response of fire dynamics to vegetation water content and weather conditions in Southeast Asia

Fires greatly affect terrestrial ecosystems, climate, human health, and economy. Under the threat of global warming, assessing fire occurrence frequency and fire danger is critical to mitigate fire’s negative impacts. The state-of-the-art satellite microwave observation provides the unique opportunity to monitor vegetation water content (VWC) for multiple vegetation strata, yet still lacks associated investigation in fire dynamics. Here, we applied the multiple microwave Emissivity Difference Vegetation Indexes (EDVIs) as VWC proxies of different vegetation strata to explore their influence on fire occurrence frequency (given by the number of fires, NOF) and the cumulative fire radiant energy (FRE) in mainland Southeast Asia during 2015–2019; and compared to that with the commonly used fire weather indices from the Canadian Forest Fire Weather Index system. Then, we identified the optimal regression models to depict the relationship of fires with EDVIs and fire weather indices, respectively; and incorporated both kinds of indices in models to retrospectively predict NOF and FRE. Results show that: (1) the monthly mean NOF and FRE nonlinearly decrease with EDVI in mainland Southeast Asia, and 40–60% of the variances are explained by EDVI, which further improve to 60–70% by incorporating EDVIs of two different vegetation layers. (2) In comparison, NOF and FRE nonlinearly increase with fire weather indices, and connections are stronger than that with EDVI; nevertheless, combing fire weather indices with EDVI, especially with EDVIs of two vegetation layers provides almost the highest explanation for fires. (3) The log-linear and/or log-quadratic models are identified to outperform the other models in depicting the fire-EDVI and fire-fire weather indices relationships; and incorporating EDVI and fire weather indices in models generally improves the prediction accuracy. These findings reveal the differentiated VWC effects on NOF and FRE among vegetation strata and quantify the strong nonlinear response of fires to VWC and weather conditions in mainland Southeast Asia, which could provide new insight for fire prediction and fire danger assessments with the utility of microwave observations.

Soil biological quality as affected by vegetation types in shrublands of a semi-arid montane environment

Mountain shrublands in semi-arid zones have a relevant effect in protecting water and soil, and conserving biodiversity. Nutrient availability in vegetation layers of semi-arid shrublands, may increase biomass production and litter accumulation rates that may affect the soil nutrient cycle through the positive feedback. However, the effect of semi-arid mountainous shrublands on litter quality and soil properties is poorly studied. To fill these gaps, we studied different vegetation types (i.e., Ulmus carpinifolia Gled., Berberis integerrima Bunge, Malus orientalis Ugl., Pistacia atlantica Desf., Amygdalus lycioides Spach., Rhus coriaria L., Cotoneaster kotschyi Klotz. and Juniperus excelsa M. Bieb.), to assess litter quality, soil properties, and C and N mineralization in Iran. Totally, 240 litter or organic horizon and topsoil (0–10 cm depth) samples were taken under the studied vegetation types. Based on analysis of variance and Tukey test, soil fauna (earthworms, acarina, collembola, nematode, protozoa), microflora (bacteria and fungi), microbial (basal and substrate-induced respirations, microbial biomass) and enzyme (urease, acid phosphatase, arylsulfatase and invertase) properties, as well as C and N mineralization were highest under deciduous species, especially U. carpinifolia vegetation type. Conversely, J. excelsa, as an evergreen species, decreased soil quality bio-indicators by decreasing litter quality and soil fertility in the high mountain vulnerable semi-arid sites. Based of heat plots of principal component analysis, soil biological and biochemical properties, especially enzyme indicators, created hot spots of soil quality under the studied vegetation types. As a conclusion, deciduous species are the hotspot's bioindicator in the mountainous ecosystems, indicating their potential role in enriching soil nutrient cycles.

Vertical temperature and air humidity gradients in beech and oak forests, and the forest interior climate created by beech

Forests dominated by European beech are characterized by a humid and relatively cool forest interior climate with low light intensities on the forest floor, which harbors an adapted herb layer vegetation. With the aim to quantify the air temperature and humidity (RH) conditions in the beech forest interior in direct comparison to the conditions in thermophilic oak forests at the drought-induced range limit of beech, we conducted air temperature and RH measurements in mid-summer at three height levels (7 m, 2 m, and 0.5 m above ground) in 12 forest stands in the natural beech-oak ecotone in Western Romania. On cloudless mid-summer days, the shade canopy layer of the oak forests (7 m) was at noon usually up to 3 °C warmer than the beech shade canopy; the daily maxima differed even by up to 6 °C (extremes: 32.1 °C and 27.5 °C in the beech and oak shade canopies, respectively). RH reached by about 4 percentage points lower values in the shade canopy of the oak forests than in the beech forests; the RH minima differed by up to 9 percentage points (28.2 vs. 37.4%). Vapor pressure deficit (VPD) was between noon and midnight by 2–6 hPa higher in the oak than in the beech shade canopy; even more differed the VPD maxima (38.7 vs. 22.6 hPa). We conclude that closed beech forest canopies have a considerable microclimatic buffering capacity that can reduce the severity of climate warming impacts on the vitality of the herb layer and the beech shade crown.

POTENTIAL OF MOBILE MAPPING TO CREATE DIGITAL TWINS OF FORESTS

Abstract. Forests are irreplaceable and are being studied extensively. Better forest inventory and understanding necessitate effective mapping, modeling, and automatic analysis. As a result, considerable research effort is being devoted to digitizing forest environments. Recently, digital twins have come to the attention of the geospatial community as a virtual representation of the Earth’s surface linked to its corresponding physical asset. This concept is applicable to forests and has been studied in the literature. This requires initial input data obtained through reality capture. Among mapping techniques, laser scanning has emerged as a state-of-the-art technology for vegetation modeling. In this paper, we look into the potential of mobile laser scanning for forest digital twinning. While most studies concentrate on single tree detection, modeling, and estimation of dendrometric parameters, we also include lower vegetation in our investigations. To accomplish this, we first detect single trees and then investigate different vegetation densities and levels using geometric metrics. We also demonstrate how to model the underlying layers of vegetation in a digital twin. We perform the tests on data from mobile laser scanning (MLS) and compare the results to those from airborne laser scanning (ALS).We show that single tree detection based on crown separation using MLS data works similarly to or slightly better than ALS data. Furthermore, we demonstrate that MLS data allows for more detailed analysis of understory vegetation taking into account different height levels and a multi-level representation, whereas ALS data only allows for rough analysis of the lower parts of forest vegetation.

A multiple-fluids-mechanics-based model of velocity profiles in currents with submerged vegetation

Submerged aquatic vegetation can provide a habitat and food for marine and river organisms, and it has the ecological effect of purifying water by absorbing harmful substances. Therefore, it plays an important role in the maintenance, restoration, and improvement of marine and river ecosystems. Hydrodynamic problems caused by submerged vegetation have been a matter of wide concern. According to the distribution of submerged vegetation, the flow can be divided into three layers in the vertical direction: uniform, mixing, and logarithmic layers. This paper proposes an analytical model for the vertical distribution of longitudinal velocity in open-channel flows with submerged vegetation. A concept of velocity superimposition is applied in mixing and logarithmic layers. The velocity inside the vegetated layer can be solved by the balance between the drag force and bed gradient. The velocity difference between the vegetated layer and the free surface layer results in the formation of a mixing layer near the top of the vegetation. Flow at the junction between the vegetation and free surface layers is mainly controlled by the vortices in the mixing layer. The velocity in the mixing layer is commonly described by a hyperbolic tangent formula. The logarithmic distribution formula is applied to the free surface layer, where the velocity without effect arising from vortices is similar to the open-channel flow. The concept of the wake function is introduced to modify the distribution of velocity in the free surface layer. The longitudinal velocities from the theoretical model are compared to the measured velocities in the literature. The theoretical velocities agree well with the measured values in the flows with submerged vegetation, proving that the theoretical model proposed here can successfully predict the vertical distribution of velocity and has extensive adaptability.

Plant water use related to leaf traits and CSR strategies of 10 common European green roof species

The vegetation layer contributes to multiple functions of green roofs including their hydrological function as plants remove water from substrates between rainfall events through evapotranspiration, restoring the green roofs storage capacity for rainfall retention. While individual traits have been related to water use strategies of green roof plants, these traits are inconsistent, suggesting the importance of trait combinations which may be reflected in CSR (competitor, stress tolerator, ruderal) strategies. Therefore, relating plant water use to leaf traits and CSR strategies could help facilitate green roof plant selection into new geographical regions where green roof technology is developing. For example, in high latitude northern European regions with long daylight during the growing season. Growth (shoot biomass, relative growth rate and leaf area), leaf traits (leaf dry matter content, specific leaf area and succulence) and CSR strategies were determined of 10 common European green roof plants and related to their water use under well-watered (WW) and water-deficit (WD) conditions. All three succulent species included in the experiment showed mostly stress tolerant traits and their water loss was less than the bare unplanted substrate, likely due to mulching of the substrate surface. Plants with greater water use under WW conditions had more ruderal and competitive strategies, and greater leaf area and shoot biomass, than species with lower WW water use. However, the four species with the highest water use under WW conditions were able to downregulate their water use under WD, indicating that they could both retain rainfall and survive periods of water limitations. This study indicates that, for optimal stormwater retention, green roof plant selection in high latitude regions like northern Europe, should focus on selecting non-succulent plants with predominantly competitive or ruderal strategies to make the most of the long daylight during the short growing season.

3D numerical investigation of flow behavior in an open channel with uniform and layered vegetation patches under varying submergence conditions

Staggered vegetation patches (central and outer) in an open channel have a significant effect on flow structure and river geomorphology. Although investigation on vegetation patches has been done in the past, however none of the past studies was carried out for varying submergence conditions from outer to central patches or for layered staggered patches with varying submergence. This knowledge gap has been attempted to bridge in this study. In this research work, a numerical technique has been used to analyze the flow behavior in a riverine flow by modeling central and outer vegetation patches as rigid elements in a rectangular channel. The influence of various vegetation patch configurations and submergence conditions were studied on flow characteristics. Computational fluid dynamics (CFD) package FLUENT was used for simulation purposes. Results showed that the flow in the central region of the channel was highly non-uniform, having a longitudinal distribution of velocities with alternating peaks and troughs throughout the central portion of the channel. However, in the outer regions, the velocity pattern acquired sawtooth distribution inside the patch regions (PR) but stabilized in the free regions (FR). Outer FR has 9% less velocities as compared to central FR. Moreover, the inflection point in velocity profiles and the bulge in contour plots was observed which triggered the shear layer at the top of submerged vegetation and at the interface of outer FR and central PR or vice versa. A complex pattern of secondary flow was also observed due to the turbulence anisotropy in the channel and its magnitude ranged from 0.1 to 3.7% of average velocity U. The results also showed that the state of submergence has a notable effect on the flow blockage and percentage of discharge passing through various regions.

Influence of vegetation and additional surface layers on the water balance of a reclamation cover with elevated water table

Influence of vegetation and additional surface layers on the water balance of a reclamation cover with elevated water table

Solute cloud evolution in channels with suspended vegetation of different configurations

Suspended vegetation's ability to handle solute accumulation in natural waters through their roots has sparked significant interest and research in using them to improve water quality. This research semi-analytically investigates the unsteady solute cloud evolution in channels with suspended vegetation after the point source release on the water surface, by solving the solute transport model with spatially variable flow field coefficients. Results show that regardless of gap ratio (the ratio of the height of the gap region to the water depth) and vegetation density, the solute cloud evolution in the preasymptotic stage (the dimensionless time ⟨Dz*⟩t*/h*2<1, where ⟨Dz*⟩ is the depth-averaged vertical turbulent diffusion coefficient. t* is the time, and h* is water depth.) can be featured by: the cloud centroid shifts upstream; the longitudinal dispersion coefficient increases; the solute cloud is positively skewed; and the solute accumulates in the vegetation layer on the upstream side and the bottom boundary layer on the downstream side. At around ⟨Dz*⟩t*/h*2∼1, the cloud centroid position and the longitudinal dispersion coefficient approach their asymptotic values, and the solute cloud is basically considered to follow the normal distribution longitudinally. In terms of the influences of configurations on the solute cloud during the whole dispersion process, the cloud centroid moves faster and reaches a farther asymptotic location due to a more serious blockage effect for a smaller gap ratio or larger vegetation density. In addition, a small gap ratio enhances the skewness and kurtosis of the cloud, while the vegetation density has little effect on them. Benefiting from the combined action of the violent velocity shear and the strong shear-scale diffusion which dominates the vertical mixing, the smallest gap ratio or highest vegetation density promotes the vertical mixing and yields the largest asymptotic longitudinal dispersion coefficient. Consequently, the vertical concentration distribution is the most uniform and the longitudinal concentration distribution is the flattest in these two cases.

Study on the Turbulent Flow Behavior of Inland Inundating Tsunami Current Through Vertically Layered Vegetation

Study on the Turbulent Flow Behavior of Inland Inundating Tsunami Current Through Vertically Layered Vegetation

SAR and InSAR data linked to soil moisture changes on a temperate raised peatland subjected to a wildfire

Interferometry of Synthetic Aperture Radar (InSAR) can potentially contribute to the cost-effective regional or global monitoring of the degradation and restoration of peatlands. However, there are uncertainties about the links between InSAR results and peatland ecohydrological parameters, especially soil moisture. Here, we analyse the relationships between the temporal evolutions of InSAR coherence, ground displacements, and in-situ soil moisture measurements for a temperate raised bog at Ballynafagh, Co. Kildare, Ireland, in the period 2017-mid-2021. We also investigate the effects of a wildfire in June–July 2019 on those relationships. InSAR-derived ground displacements from Sentinel-1 C-band radar data indicate long-term subsidence of the intact and Active Raised Bog. Superimposed on the long-term displacement trends are annual oscillations that are linked to variations in rainfall and temperature and that are in phase with changes in soil moisture. We show that InSAR coherence is directly related to the change in soil moisture, with large changes causing coherence decrease or loss. The wildfire removed a 10–20 cm thick mossy vegetation layer across 60–70% of the intact bog area. The SAR backscatter intensity in VV polarisation increased after the wildfire, but the InSAR coherence, the InSAR-derived surface displacements and the soil moisture were not noticeably affected. We therefore infer that C-band radar waves attenuate in the active vegetation layer, but penetrate through it into the upper few cm of the underlying peat. The SAR backscatter occurs primarily at this level in the peat, where its coherence is controlled by the soil moisture. These findings underpin application and interpretation of radar for monitoring of peatlands, even if affected by wildfires, which are forecast to increase in both frequency and intensity due to global warming.

A simulation model of functional habitat connectivity demonstrates the importance of species establishment in older forests

Fragmented natural habitats, such as old-growth forests, have been often considered island-like systems. However, whereas the isolation of real islands is mostly a function of their spatial arrangement, the biodiversity of old-growth forest patches is also affected by how well the surrounding suboptimal habitats, such as younger forests, can support the functional connectivity between the old-forest fragments. The latter topic remains largely unclear due to the lack of mechanistic knowledge about the processes behind species’ affinity for old forest. Although in animal ecology, functional connectivity has often been investigated with mechanistic agent-based models, these have rarely been applied for passively dispersing organism groups. We used a pattern-oriented modeling approach by combining a spatially explicit agent-based model and an empirical biodiversity dataset of Estonian old-growth nemoral forest sites, to study how forests of different ages between the old-forest fragments are exploited by different passively or slowly dispersing functional groups. We found that the establishment of ground layer vegetation, epiphytes, ectomycorrhizal and pathogenic fungi is significantly restricted in the younger forests, whereas no clear difference between forest-age classes emerged for survival. Our results thus suggest that establishment, not survival, is the main process behind the species’ affinity for old forest, concurring with studies that have demonstrated the importance of suitable microhabitat availability in older forests. We conclude that young secondary forests do not support the connectivity – and consequently, biodiversity – of many old-forest specific groups.