Shrub Height Research Articles

Plasticity response of desert shrubs to intense drought events at different phenophases under the context of climate change

Global climate change has led to the frequent occurrence of intense drought events in mid-latitude desert ecosystems, coupled with uneven rainfall distribution across phenophases within the year. However, the impact of intense drought events at different phenophases on plant growth and drought resistance strategies still lacks clear conclusions. We selected the typical desert semi-shrubs Artemisia ordosica as our research object, and constructed a rain shelter to simulate intense drought events (without rainfall for 30 consecutive days) during the sprouting, vegetative growth, flowering and fruiting stages. Based on this, we analyzed the differential impacts of intense drought events at different phenophases on the phenotypic characteristics (e.g. shrub height, cover, volume, specific leaf area) and functional traits (ANPP accumulation and allocation) of A. ordosica. The experiment employed a randomized complete block design with three replicates for each treatment. The results indicate that: (1) Under intense drought events at different phenophases, all phenotypic characteristic indicators of A. ordosica significantly decreased. (2) Contrary to the significant negative correlation between twig number and twig size in response to rainfall variations, under intense drought conditions, there is a significant positive correlation between the two, indicating a synergistic effect. (3) The impact of intense drought events at different phenophases on the ANPP (aboveground net primary production) accumulation of A. ordosica varied significantly. The degree of impact is as follows: the flowering and fruiting stage > the sprouting stage > the vegetative growth stage. (4) A. ordosica adapted to intense drought by increasing the proportion of reproductive growth and decreasing the proportion of vegetative growth. Our results reveal the phenotypic and functional trait plasticity response mechanisms of A. ordosica to intense droughts at different phenophases, laying a foundation for predicting the impacts of climate change on desert ecosystems.

Thinning relationships of woody encroachers in a US southwestern shrubland

Woody plant encroachment degrades the economic and environmental potential of drylands by altering processes such as nutrient fluxes, ecohydrology, and ecosystem services. Though past research has investigated the encroachment process, relatively little is known about post-encroachment shrub community ecology. To better quantify dynamics within post-woody encroachment shrub communities, we combined USGS lidar height data and multispectral imagery to estimate shrub density, shrub height, shrub cover, and shrub volume across the Jornada Basin Long Term Ecological Research (JRN-LTER) site in southern New Mexico, USA. Structural estimates were analyzed in search of telltale signs of community competition, specifically, the presence of thinning relationships. Results demonstrated density-dependent thinning relationships in shrub communities of creosote and mesquite, indicating a large role for competition in arid shrub communities even at relatively low shrub densities and cover (∼35% cover). In addition, shrub volume estimates better modeled the expected thinning dynamics of shrub communities than shrub canopy cover measurements. Overall, our results indicate the utility of lidar data in extending two-dimensional descriptions of woody vegetation structure (i.e., woody canopy cover) into the critical third dimension (i.e., woody plant volume), as well as the relative importance of competition and demographic bottlenecks to vegetation structure in drylands.

Carboxylation capacity is the main limitation of carbon assimilation in High Arctic shrubs.

Increases in shrub height, biomass and canopy cover are key whole-plant features of warming-induced vegetation change in tundra. We investigated leaf functional traits underlying photosynthetic capacity of Arctic shrub species, particularly its main limiting processes such as mesophyll conductance. In this nutrient-limited ecosystem, we expect leaf nitrogen concentration to be the main limiting factor for photosynthesis. We measured the net photosynthetic rate at saturated light (Asat) in three Salix species throughout a glacial valley in High-Arctic tundra and used a causal approach to test relationships between leaf stomatal and mesophyll conductances (gsc, gm), carboxylation capacity (Vcmax), nitrogen and phosphorus concentration (Narea, Parea) and leaf mass ratio (LMA). Arctic Salix species showed no difference in Asat compared to a global data set, while being characterized by higher Narea, Parea and LMA. Vcmax, gsc and gm independently increased Asat, with Vcmax as its main limitation. We highlighted a nitrogen-influenced pathway for increasing photosynthesis in the two prostrate mesic habitat species. In contrast, the erect wetland habitat Salix richardsonii mainly increased Asat with increasing gsc. Overall, our study revealed high photosynthetic capacities of Arctic Salix species but contrasting regulatory pathways that may influence shrub ability to respond to environmental changes in High Arctic tundra.

High Arctic Vegetation Communities With a Thick Moss Layer Slow Active Layer Thaw

AbstractSvalbards permafrost is thawing as a direct consequence of climate change. In the Low Arctic, vegetation has been shown to slow down and reduce the active layer thaw, yet it is unknown whether this also applies to High Arctic regions like Svalbard where vegetation is smaller, sparser, and thus likely less able to insulate the soil. Therefore, it remains unknown which components of High Arctic vegetation impact active layer thaw and at which temporal scale this insulation could be effective. Such knowledge is necessary to predict and understand future changes in active layer in a changing Arctic. In this study we used frost tubes placed in study grids located in Svalbard with known vegetation composition, to monitor the progression of active layer thaw and analyze the relationship between vegetation composition, vegetation structure and snow conditions, and active layer thaw early in summer. We found that moss thickness, shrub and forb height, and vascular vegetation cover delayed soil thaw immediately after snow melt. These insulating effects attenuated as thaw progressed, until no effect on thaw depth was present after 8 weeks. High Arctic mosses are expected to decline due to climate change, which could lead to a loss in insulating capacity, potentially accelerating early summer active layer thaw. This may have important repercussions for a wide range of ecosystem functions such as plant phenology and decomposition processes.

A Study on Street Tree Planting Strategy in Pingtan Island Based on Road Wind Environment Simulation

In this paper, the landscape of typical roadway trees and their planting parameters on Pingtan Island are investigated and analyzed in the field. A three-dimensional model of street trees was created using AutoCAD 2020, and Ansys Fluent 2022 was used to simulate the wind condition of trees with various planting parameters under high wind circumstances. The study explores the stress and adaptability of roadway trees in the wind environment under different planting parameters, such as different heights, plant spacing, lower shrub heights, and two-row and three-row planting with different row spacings. The results show that the wind resistance of street trees is connected to the planting parameters and that modifying the appropriate planting parameters can improve the wind stability of road green space. The height of street trees is more suitable between 6.0~9.0 m. The planting spacing should be not less than 1.0 times the crown and not more than 1.75 times the crown. The form of planting has an important effect on wind resistance. Two rows of planting of street trees have a better utility and wind resistance, and a row spacing of 2.0~6.0 m is more appropriate. The height of the lower shrubs should be lower than the height of the first branch, with 0.5~1.0 m being more suitable. Based on the results of the data simulation and analysis, this paper proposes corresponding tree species selections and planting strategies for road green belts on Pingtan Island from the perspective of street tree species, planting parameters, and planting forms to provide references for the upgrading and planning of roadway tree landscapes on Pingtan Island as well as in similar climatic regions.

Nonlinear responses of ericaceous and ectomycorrhizal Arctic shrubs across a long‐term experimental nutrient gradient

AbstractIn the Arctic tundra, warming is anticipated to stimulate nutrient release and potentially alleviate plant nutrient limitations. Typically simulated by fertilization experiments that saturate plant nutrient demand, future increases in soil fertility are thought to favor ectomycorrhizal (EcM) over ericaceous shrubs and have often been identified as a key driver of Arctic shrub expansion. However, the projected increases in fertility will likely vary in their alleviation of nutrient limitations. The resulting responses of shrubs and their mycorrhizae across the gradient of nutrient limitation may be nonlinear and could contradict the current predictions of tundra vegetation shifts. We compared the functional responses of two dominant shrubs, EcM dwarf birch (Betula nana) and ericaceous Labrador tea (Rhododendron tomentosum), across a long‐term nitrogen and phosphorus fertilization gradient experiment in Arctic Alaska. Using linear mixed‐effects modeling, we tested the responses of shrub cover, height, and root enzyme activities to soil fertility. We found that B. nana cover and height linearly increased with soil fertility. In contrast, R. tomentosum cover initially increased, but decreased after surpassing the intermediate levels of increased soil fertility. Its height did not change. Enzyme activity did not respond to soil fertility on EcM‐colonized B. nana roots, but sharply declined on R. tomentosum roots. Overall, the nonlinear responses of shrubs to our fertility gradient demonstrate the importance of experiments grounded in replicated regression design. Our results indicate that under moderate increases in soil fertility, Arctic shrub expansion may not only include deciduous EcM shrubs but also ericaceous shrubs. Regardless of shifts aboveground, changes in root enzyme activity belowground point to some EcM shrub species playing a more influential role in tundra soils; as EcM roots remained steady in their liberation of soil organic nutrients with heightened soil fertility, degradative root enzyme activity on the dominant ericaceous shrub dropped—in some instances with even the slightest increase in fertility.

A comparison and development of methods for estimating shrub volume using drone‐imagery‐derived point clouds

AbstractShrub volume is used to calculate numerous, essential ecological indicators in rangeland ecosystems such as biomass, fuel loading, wildlife habitat, site productivity, and ecosystem structure. Field techniques for biomass estimation, including destructive sampling, ocular estimates, and allometric techniques, use shrub height and canopy widths to estimate volume and translate it to biomass with species‐specific allometric equations. These techniques are time‐consuming and pose challenges, including removal of plant material and training of observers. We compared canopy volume estimates from field‐based measurements with drone‐collected canopy volume estimates for seven dominant shrub species within mountain big sagebrush (Artemisia tridentata subsp. vaseyana) plant communities in southern Idaho, USA. Canopy height and two perpendicular width measurements were taken from 103 shrubs of varying sizes, and volume was estimated using a traditional allometric equation. Overlapping aerial images captured with a DJI Mavic 2 Professional drone were used to create a 3D representation of the study area using structure‐from‐motion photogrammetry. Each shrub was extracted from the point cloud, and volume was estimated using allometric and volumetric methods. The volumetric method, which involved converting point clouds to raster canopy height models with 2.5‐ and 5‐cm grid cells, outperformed the allometric method (R2 > 0.7) and was more reproducible and robust to user‐related variability. Drone‐estimated volume best‐matched field‐estimated volume (R2 > 0.9) for three larger species: A. tridentata subsp. tridentata, A. tridentata subsp. vaseyana, and Purshia tridentata. The volume of smaller shrubs (canopy widths <1 m) was slightly overestimated from drone‐based models. We argue that drone‐based models provide a suitable alternative to field methods, while having the added benefit of being less time‐consuming, with fewer limitations, and more easily scaled to larger study areas than traditional field techniques. Finally, we demonstrate a proof of concept for automating canopy volume estimates using point‐cloud‐based automatic shrub detection algorithms. These findings demonstrate that drone‐collected images can be used to assess shrub canopy volume for at least five upland sagebrush steppe shrub species and support the integration of drone data collection into rangeland vegetation monitoring.

Assessing canopy height measurements from ICESat-2 and GEDI orbiting LiDAR across six different biomes with G-LiHT LiDAR

The height of woody plants is a defining characteristic of forest and shrubland ecosystems because height responds to climate, soil and disturbance history. Orbiting LiDAR instruments, Ice, Cloud and land Elevation Satellite-2 (ICESat-2) and Global Ecosystem Dynamics Investigation LiDAR (GEDI), can provide near-global datasets of plant height at plot-level resolution. We evaluate canopy height measurements from ICESat-2 and GEDI with high resolution airborne LiDAR in six study sites in different biomes from dryland shrub to tall forests, with mean canopy height across sites of 0.5–40 m. ICESat-2 and GEDI provide reliable estimates for the relative height with RMSE and mean absolute error (MAE) of 7.49 and 4.64 m (all measurements ICESat-2) and 6.52 and 4.08 m (all measurements GEDI) for 98th percentile relative heights. Both datasets slightly overestimate the height of short shrubs (1–2 m at 5 m reference height), underestimate that of tall trees (by 6–7 m at 40 m reference height) and are highly biased (>3 m) for reference height <5 m, perhaps because of the difficulty of distinguishing canopy from ground signals. Both ICESat-2 and GEDI height estimates were only weakly sensitive to canopy cover and terrain slope (R 2 < 0.06) and had lower error for night compared to day samples (ICESat-2 RMSE night: 5.57 m, day: 6.82 m; GEDI RMSE night: 5.94 m, day: 7.03 m). For GEDI, the day versus night differences varied with differences in mean sample heights for the day and night samples and had little effect on bias. Accuracy of ICESat-2 and GEDI canopy heights varies among biomes, and the highest MAE was observed in the tallest, densest forest (GEDI: 7.85 m; ICESat-2: 7.84 m (night) and 12.83 m (day)). Improvements in canopy height estimation would come from better discrimination of canopy photons from background noise for ICESat-2 and improvements in the algorithm for decomposing ground and canopy returns for GEDI. Both would benefit from methods to distinguish outlier samples.

Summer habitat selection by Mrs Hume’s Pheasant (Syrmaticus humiae) on Jinzhong Mountain, northwest Guangxi, China: implications for determining effective conservation actions using radio transmitters

Abstract In the present study, summer habitat preference of Mrs Hume’s Pheasant (Syrmaticus humiae) was studied in Jinzhong Mountain Nature Reserve, Guangxi Province. Eight birds were equipped with radio transmitters and habitat characteristics of experiment and control quadrat sites, respectively, were measured. Our results indicated that: 200 m to 400 m distance to habitat edge, less than 200 m distance to water, over 400 m distance to human habitation, over 601 m distance to the road, over 60% tree cover, less than 40% shrub cover, less than 20% herb cover, over 60% leaf litter cover, height of tree over 10.1 m, tree density over 20 individuals per quadrat, shrub height over 2.1 m, shrub density less than 10 individuals per quadrat, height of herb species over 0.5 m, herb density less than 10 Individuals per quadrat, diameter of tree over 30 cm, and abundant food were the habitat characteristics. The elevation, herb density, and height of tree and shrub exhibited no significant differences (), but other factors showed significant differences between quadrat sites and control quadrat plot (). Results of a principal components analysis (PCA) demonstrated that the first five components accounted for 64.282% of the total variance. Food availability in different habitat patches is the vital factor affecting habitat selection by Mrs Hume’s Pheasant; the other factors showed no significant effects on habitat selection by Mrs Hume’s Pheasant in the subtropical forest. This suggests that habitat selection behavior of Mrs Hume’s Pheasant is in fact a trade-off between obtaining food and prey escape, which is an adaptive behavior and a life strategy of this near-threatened bird species.

Vegetation, fuels, and fire-behavior responses to linear fuel-break treatments in and around burned sagebrush steppe: are we breaking the grass-fire cycle?

BackgroundLinear fuel breaks are being implemented to moderate fire behavior and improve wildfire containment in semiarid landscapes such as the sagebrush steppe of North America, where extensive losses in perennial vegetation and ecosystem functioning are resulting from invasion by exotic annual grasses (EAGs) that foster large and recurrent wildfires. However, fuel-break construction can also pose EAG invasion risks, which must be weighed against the intended fire-moderation benefits of the treatments. We investigated how shrub reductions (mowing, cutting), pre-emergent EAG-herbicides, and/or drill seedings of fire-resistant perennial bunchgrasses (PBGs) recently applied to create a large fuel-break system affected native and exotic plant abundances and their associated fuel loading and predicted fire behavior.ResultsIn heavily EAG-invaded areas, herbicides reduced EAG and total herbaceous cover without affecting PBGs for 2–3 years and reduced predicted fire behavior for 1 year (from the Fuel Characteristic Classification System). However, surviving post-herbicide EAG cover was still > 30%, which was sufficient fuel to exceed the conventional 1.2-m-flame length (FL) threshold for attempting wildfire suppression with hand tools. In less invaded shrubland, shrub reduction treatments largely reduced shrub cover and height by ~ half without increasing EAGs, but then redistributed the wood to ground level and increased total herbaceous cover. Herbicides and/or drill seeding after shrub reductions did not affect EAG cover, although drill seedings increased PBG cover and exotic forbs (e.g., Russian thistle). Fire behavior was predicted to be moderated in only one of the many yearly observations of the various shrub-reduction treatment combinations. Over all treatments and years, FLs were predicted to exceed 1.2 m in 13% of simulations under average (11 km h−1) or high (47 km h−1) wind speed conditions and exceed the 3.4-m threshold for uncontrollable fire in 11% of simulations under high-wind speeds only.ConclusionsPredicted fire-moderation benefits over the first 4 years of fuel break implementation were modest and variable, but, generally, increases in EAGs and their associated fire risks were not observed. Nonetheless, ancillary evidence from shrublands would suggest that treatment-induced shifts from shrub to herbaceous fuel dominance are expected to improve conditions for active fire suppression in ways not readily represented in available fire models.

Slope aspect of a mountainous grassland landscape shapes the structure of an encroaching shrub (Euryops floribundus N.E. Br): insights from communal grazing sites located at varying distances from rural homesteads

Mountainous grassland landscapes are severely threatened by the proliferation of shrub encroachment. So far, it remains unclear though how slope aspect coupled with land disturbances linked to the proximity of homesteads to communal grazing sites affects the distribution, density and structure of the encroaching shrubs in these grassland ecosystems. In this study, we investigated the role that slope aspect plays in determining the density and structure of an encroaching shrub species Euryops floribundus N.E. Br in three communal grazing sites located at varying distances from rural homesteads in a semi-arid mountainous grassland in the Eastern Cape Province of South Africa. Three sites were strategically chosen in Cala communal grazing lands in an encroached mountainous grassland landscape that depicted north and south-facing slope aspects. The selected sites were Tsengiwe; a site located in close proximity to homesteads at a distance of less than 100 m, Upper Mnxe situated at an intermediate distance ranging from 200 to 800 m away from homesteads and Manzimdaka, which was located furthest from homesteads at a distance greater than 1600 m. In each site and corresponding slope aspect, the density and structure of the shrub E. floribundus were evaluated on 36 randomly distributed plots, yielding a total of 108 plots across all sites. We found that shrub density was significantly higher (50%) on the north-facing slope compared to the south-facing slope in Tsengiwe, the site located near homesteads. Shrub height was significantly higher (53 and 17%) on the north-facing slope compared to the south-facing slope at Upper Mnxe and Manzimdaka, which were located at intermediate and furthest distances from the homesteads. Notably, shrub height was significantly lower (37%) in the north-facing slope compared to the south-facing slope in Tsengiwe. Following a similar pattern to shrub height, total stem number was significantly higher (20 and 85%) in the north-facing slope compared to the south-facing slope at Upper Mnxe and Tsengiwe, respectively. Shrub crown area was higher (33 and 11%) in the north-facing slope compared to the south-facing slope at Upper Mnxe and Manzimdaka, respectively. A strong positive relationship was established between the height of shrubs and their longest crown diameter, shortest crown diameter and shrub crown area across all sites, suggesting that the investigated shrub species E. floribundus employs its structural characteristics to survive, and thrive and this was more evident in the north-facing slope. The results highlight the importance of considering the proximity of homesteads into account in ecological studies, and puts emphasis on improved understanding of the vegetation patterns shaped by shrub encroachment in mountainous grasslands, which is crucial in the development of effective land management strategies.

Multiple vegetation layers interactively enhance habitat values of endangered Kashmir Musk Deer

The Kashmir musk deer (Moschus cupreus) is a globally endangered species hunted for its musk pod. Despite its endangered status, it remains one of the least studied species of musk deer. In 2019, the genetic discovery of Kashmir musk deer in Mustang district of Nepal – outside of its historically known range in Kashmir, India – opened up new avenues for research on this elusive species. Communication among individuals of musk deer is primarily based on latrine sites, which serve various purposes such as territorial marking and reproductive signaling. Hence, this study aims to investigate the association between microhabitat and latrine sites of Kashmir musk deer in the Mustang, Nepal. A systematic survey was conducted to identify latrine presence and absence sites at an elevational gradient. Data on biophysical parameters, including altitude, slope, aspect, tree height, shrub height, and regeneration height were recorded for both latrine presence and absence plots. Significant differences in tree height and regeneration height, crown cover, and trail width were observed between the presence and absence plots. Latrine presence and absence data fitted with the generalized linear model using logistic function, revealed that the interaction between tree height and regeneration height plays a pivotal role in determining the suitability of a particular site within the habitat for establishing a latrine site. This significant positive interaction indicated that the probability of discovering latrines significantly increases when the areas have taller trees and taller regeneration. This finding affects microclimate factors, such as sunlight exposure, wind speed, soil moisture, and temperature, influencing their role in sustaining scent retention in the latrine sites. Incorporating knowledge about the association between microhabitats and latrine sites can aid in preserving suitable habitats that are critical for establishing communication among individual musk deer. This information can inform various conservation efforts, including captive breeding programs, anti-poaching operations, and reintroduction initiatives.

Адаптивный потенциал видов рода Spiraea L. в условиях Дендрологического сада им. И.М. Стратоновича

This article presents the results of a comprehensive study of decorative flowering shrubs of the genus Spiraea (Spiraea L.). 7 species of Spiraea L. from the collection of the Dendrological Garden of Northern (Arctic) Federal University named after M.V. Lomonosov have been selected for analysis: Spiraea × Bumalda Burv, Spiraea ulmifolia Scop (L.) Maxim, Spiraea chamaedryfolia L., Spiraea salicifolia L., Spiraea nipponica var. tosaensis, Spiraea betulifolia Pall and Spiraea sericea Turcz. It has been established that the shrub height varies from 0.8 m (for Spiraea Bumalda Burv, Spiraea betulifolia and Spiraea nipponica var. tosaensis ) to 2.1 m (for Spiraea ulmifolia Scop (L.) Maxim and Spiraea sericea Turcz.). Spiraea ulmifolia Scop (L.) Maxim has the largest crown span (2.4 × 2.7 m) with a maximum number of 42 stems for a shrub. The compact shape of the shrub has been noted in Spiraea betulifolia Pall and Spiraea Bumalda Burv (1.0 × 1.3 and 1.0 × 1.1 m, respectively). While conducting phenological observations, it has been recorded that the first leaves of Spiraea sericea Turcz, Spiraea salicifolia L., Spiraea ulmifolia Scop (L.) Maxim and Spiraea nipponica var. tosaensis Maxim begin to appear in mid-May. The leaf blades of the remaining introduced species under study unfold with a difference of two weeks from the previously listed ones. It has been established that all the species of Spirea L. under study successfully tolerate the harsh northern climate (winter hardiness score I–II) and have become naturalized, which has been confirmed by the abundance of fruiting and the sowing quality of the seeds. According to archival data, the seeds of all the species of Spiraea L. under study ripen annually. The largest proportion of germinable seeds has been observed in Spiraea betulifolia Pall (92 %). High seed germination energy has been noted in Spiraea sericea Turcz and Spiraea betulifolia Pall. The period of seed germination for all Spiraea has been 15 days, except for Spiraea Bumalda Burv., which has been left on the bed for up to 20 days, however, the germination rate has been only 57 %, and a fifth of the tested seeds have been empty. The high quality of self-reproducing seeds leads to the conclusion that Spiraea sericea Turcz., Spiraea nipponica var. tosaensis, Spiraea betulifolia, Spiraea ulmifolia Scop (L.) Maxim and Spiraea salicifolia L. can be grown from seed stock. All the species under study are characterized by the full extent of adaptability. The decisive factor influencing the degree of adaptability of Spiraea is high winter hardiness of these plants. The adaptive capacity of introduced species determines the boundaries of the secondary distribution area. All the species under study can be recommended for northern city landscaping.

Encroachment drives facilitation at alpine shrublines

Ongoing encroachment is driving recent alpine shrubline dynamics globally, but the role of shrub-shrub interactions in shaping shrublines and their relationships with stem density changes remain poorly understood. Here, the size and age of shrubs from 26 Salix shrubline populations along a 900-km latitudinal gradient (30°–38° N) were measured and mapped across the eastern Tibetan Plateau. Point pattern analyses were used to quantify the spatial distribution patterns of juveniles and adults, and to assess spatial associations between them. Mean intensity of univariate and bivariate spatial patterns was related to biotic and abiotic variables. Bivariate mark correlation functions with a quantitative mark (shrub height, basal stem diameter, crown width) were also employed to investigate the spatial relationships between shrub traits of juveniles and adults. Structural equation models were used to explore the relationships among conspecific interactions, patterns, shrub traits and recruitment dynamics under climate change. Most shrublines showed clustered patterns, suggesting the existence of conspecific facilitation. Clustered patterns of juveniles and conspecific interactions (potentially facilitation) tended to intensify with increasing soil moisture stress. Summer warming before 2010 triggered positive effects on population interactions and spatial patterns via increased shrub recruitment. However, summer warming after 2010 triggered negative effects on interactions through reduced shrub recruitment. Therefore, shrub recruitment shifts under rapid climate change could impact spatial patterns, alter conspecific interactions and modify the direction and degree of shrublines responses to climate. These changes would have profound implications for the stability of alpine woody ecosystems.

Increased understanding of structural complexity in nature: relationship between shrub height and changes in spatial patterns

Increased understanding of structural complexity in nature: relationship between shrub height and changes in spatial patterns

Developing customized fuel models for shrub and bracken communities in Galicia (NW Spain)

Geospatial fire behaviour and fire hazard simulators, fire effects models and smoke emission software commonly use standard fuel models in order to simplify data collection and the inclusion of complex fuel scenarios. These fuel models are often mapped using remotely sensed data. However, given the great complexity of fuelbeds, with properties that vary widely in both time and space, the use of these standard fuel models can greatly limit accurate fuel mapping. This affects fuel hazard assessment, fuel reduction treatment plans, fire management decision-making and evaluation of the environmental impact of wildfire. In this study, we developed unique customized fire behaviour fuel models for shrub and bracken communities, by using k-medoids clustering analysis based on both fuel structural characteristics and potential fire behaviour. We used an original database of 722 destructive sample plots in nine different shrub and bracken communities covering the entire distribution area in Galicia (NW Spain), one of the regions in Europe most affected by forest fires. Measurements of cover, height and fuel fractions loads differentiated by size and vegetative state (live or dead) were used to estimate the potential rate of fire spread with five different models including fireline intensity, heat per unit area and the flame length for each sampling site and considering extreme environmental conditions. The optimal number of clusters was established by combining practical knowledge about the shrubland communities under study and their associated fire behaviour, with maximization of the mean value of the silhouette variable and minimization of the within-cluster sum of squares. The structural characteristics of the medoids derived from the analysis were associated with each of the proposed customized fuel models. Finally, a simple dichotomous classification based only on shrub height was developed to enable construction of spatially explicit fuel model maps based on remotely sensed data. Thus, the methodology applied allows generation of a more realistic representation of fuel distribution in the landscape, based on fuel structure measurements of natural regional ecosystems rather than on the use of standard models. We believe that the proposed methodology is generally applicable to communities composed of other shrub and fern species in different biogeographical regions.

Development and validation of vegetation indicators for the occurrence of saltation that consider the spatial distribution of vegetation

Conventional indicators of vegetation, such as kinds of vegetation and lateral cover, assume spatially homogeneous distribution of vegetation and are insufficient for predicting wind erosion. Conventional indicators for monitoring wind erosion often focus on dust and are not directly related to soil and vegetation, which prevent practitioners from applying monitoring data to rangeland management. We proposed two new indicators—the Height Area Effect (HAE) and Total Height (TH)—as metrics of wind erosion and that consider the spatial distribution of vegetation. The HAE is the sum of windbreak effects calculated from shrub heights, and TH is the sum of the heights of shrubs within the range of calculation. We used field observation data to compare the ability of these new indicators and existing indicators (vegetation cover, shrub height, lateral cover λ, and canopy gap) to explain saltation fluxes. We conducted saltation and meteorological observations in a Nitraria sibirica community on Tsogt-Ovoo, Mongolia. We surveyed the spatial arrangements and heights of shrubs. Indicators calculated in the upwind direction from the observation point over different calculation ranges were analyzed by piecewise regression and logarithmic regression. Models were compared based on coefficients of determination. The HAE and TH had the highest coefficients of determination and the highest robustness against the different calculation ranges. This result was encouraging because HAE was the most detailed indicator of the effect of shrubs on wind erosion. The TH could be measured easily in the field and is expected to be an effective indicator for rangeland management purposes.

Assessing canopy rainfall partitioning by Mediterranean dryland shrubs under extreme rainfall

AbstractIntense rain events have become more frequent in some regions due to climate change, and this trend is particularly concerning in dryland regions where the ecological and geomorphological impacts of rainfall are intimately tied to its intensity. The interception of rainfall by vegetation is a critical process in the water balance of drylands; thus, this study estimated the canopy interception capacity and interception rates as well as stemflow of three typical Mediterranean shrub species (Rosmarinus officinalis, Thymus vulgaris, and Macrochloa tenacissima) of three size classes in Spain under a simulated extreme rainfall rate (~8 mm min−1, historical return period of &gt;100 years). Given that these plants' canopy structures markedly differ from taller woody plants (i.e., trees), a novel method was developed to assess the stemflow fraction. Results showed significant differences in interception amount, rates, and storage capacity among the shrub species, with variations in plant morphology, such as shrub height and canopy diameter, being the key factors determining interception capacity. R. officinalis had the highest interception fraction per unit canopy area, or ‘specific interception,’ (18.4%). In contrast, the lowest specific interception fraction was measured for M. tenacissima (6.5%). Thymus vulgaris was characterized by the highest stemflow yields per unit canopy area (4.85 mm) and fraction (up to 29.6% of rainfall), which was the lowest for M. tenacissima (1.09 mm, ~1%–4%). Strong linear correlations were found between canopy interception and shrub canopy diameter (|r| &gt; −0.51, max = −0.90), when observations were grouped for size class. These linear correlations between shrub morphology and partitioning enabled multiple‐regression linear models to be developed that predicted canopy interception and stemflow with good accuracy (r2 &gt; 0.64, with a maximum of 0.82) from shrub height, canopy diameter, dry biomass, size class, and species. Despite these measurements being conducted under one extreme storm depth and intensity, the results provide: (i) values of rainfall partitioning for important shrub species in Mediterranean dryland environments; and (ii) a simple but reliable model that may be further developed (e.g., embedding variable rainfall values as weather input or incorporating other morphological parameters) and may be integrated into complex hydrological models.

Contribution to the evaluation of the biomass of medicinal and aromatic plants in Mo-rocco: Case of Globularia alypum

Morocco is distinguished by the richness of its flora, including medicinal and aromatic plants (MAPs) which play an important role, particularly in rural populations. Due to pressures often associated with overexploitation, monitoring of MAPs is essential to ensure their sustainability. This study looked to explore the status of Globularia alypum in the Amsittene site of biological and ecological interest (SBEI) in Morocco. A destructive technique was adopted to quantify biomass and productivity of G. alypum at six sites with different ecological characteristics in the Amsisttene SBEI. Linear regression was used to model G. alypum biomass as a function of the normalized difference vegetation index (NDVI). Tree cover had the greatest influence on G. alypum dynamics, showing a significant effect on shrub height, leaf productivity, and total productivity, as did the cutting method, with the highest biomass estimated based on pair matching of similar individuals. NDVI was found to be an adequate indicator of G. alypum biomass, given their high correlation (0.84) with the selected model having an R2 of 0.7. The yield of extracted essential oils ranged from 3.19 to 113.43 L, from which 10 chemical compounds were identified, with ethylvanillin being the most prominent.

Planting a Linear Vegetation Element in Landscape Using a Forestry and Landscaping Method—Can We Tell Which Deliver Greater Success?

Since the end of the 20th century, the Czech Republic has been developing an ecological network. Areas of ligneous greenery are being established throughout the landscape. The projects use different sizes of planting material: forestry seedlings and landscaping seedlings. In the South Moravian Region, in the vicinity of the village of Šardice, a series of measurements was carried out in 2016–2019 to compare the vitality of the greenery elements established by each of the methods. The height of the seedlings and trunk diameter were measured for the young trees while the shrubs were monitored for the seedling height only. Mortality was recorded successively for all the seedlings. The forestry method demonstrated greater growing vigour as indicated by the ratio of the trunk diameter increment to height while the landscaping method had lower mortality. In the forestry plantations, high mortality was found especially in poplars, oaks and hornbeams while in the landscaping plantations the poplars and oaks had the highest mortality. Elm, sycamore and poplar trees had the highest increments in the forestry plantations (but the latter was planted at different size). In the landscaping plantations, poplar trees (planted at a different size) delivered the best results, followed by maple, elm and lime trees. Shrub mortality was similar in both types of plantings. Hazel had a very high mortality while ivy, privet and honeysuckle had low mortality. Shrub height gain was higher in fenced forestry plantations. In unfenced landscaping plantations, damage by game was evident.