Slope Position Research Articles

Spatial Variability of Preferential Flow and Infiltration Redistribution along a Rocky-Mountain Hillslope, Northern China

Rock fragments in soil strongly increase the complexity of hydrological processes. Spatial variability of preferential flow and infiltration characteristics, especially along a rocky-mountain hillslope are poorly understood. In this study, five rainfall–dye tracer experiments were performed in the rocky Taihang Mountains, northern China, to investigate the spatial variability of preferential flow and infiltration redistribution on different hillslope positions. Tracers were used to distinguish macropore flow and actual water flow patterns, and preferential flow indices and spatial non–uniformity of the infiltration redistribution were calculated using image analysis. Results showed increasing trends in the dye coverage, maximum infiltration depth, and steady infiltration rate with increased hillslope position, with a preferential flow fraction of 0.10, 0.11, 0.15, 0.29, and 0.26 for the bottom–, down–, mid–, upper–, and top–slope positions, respectively. With increased hillslope position, the spatial non–uniformity of the infiltration redistribution gradually increased in orthogonal and parallel directions to the stained section, and was supported by the fractal dimensions. Positive (gravel mass ratio, saturated water content, altitude, hydraulic conductivity and roots) and negative (bulk density and clay content) impacts on preferential flow and infiltration redistribution were quantitatively emphasized. The characteristic and mechanism of infiltration process were further identified along a rocky-mountain hillslope.

Variations in stem radii of Larix principis-rupprechtii to environmental factors at two slope locations in the Liupan Mountains, northwest China

Relationships between stem growth and climatic and edaphic factors, notably air temperatures and soil moisture for different slopes, are not completely understood. Stem radial variations were monitored at the bottom and top slope positions in a Larix principis-rupprechtii plantation during the 2017 and 2018 growing seasons. Total precipitation during the growing season in 2017 and 2018 was 566 mm and 728 mm, respectively. Stem contractions typically occurred after mid-morning followed by swelling in the late afternoon in both plots, reflecting the diurnal cycle of water uptake and loss. Trees at the two locations showed the same growth initiation (mid-May) because of the small differences in air and soil temperatures. There were no significant differences in cumulative stem radial growth between the bottom plot (1.57 ± 0.34 mm) and the top plot (1.55 ± 0.26 mm) in 2018. However, in 2017, the main growth period of the bottom plot ceased 17 days earlier than in the top plot, while cumulative seasonal growth of the bottom plot (1.08 ± 0.25 mm) was significantly less than the top plot (1.54 ± 0.43 mm). Maximum daily stem shrinkage was positively correlated with air and soil temperatures, solar radiation, vapor pressure deficits, and negatively correlated with volumetric soil moisture content. The maximum daily shrinkage reflected transpiration rates as affected by environmental factors. Daily radial stem increment was correlated with precipitation and volumetric soil moisture in both years, but with air temperatures only in 2017. The seasonal growth of L. principis-rupprechtii Mayr thus shows interannual dynamics, while precipitation constitutes a key driving factor.

Modelling the site index of Pinus pinaster plantations in Turkey using ecological variables

The determination of site productivity in forest ecosystems plays a crucial role in resource management. This study was carried out to identify relationships between site characteristics and height growth of Corsican maritime pine (Pinus pinaster Ait.) plantations in Turkey. Sixty-nine sample plots > 20 years of age were selected from locations with different inclinations, aspects, elevations, slope positions and site class. Soil samples were taken at various depths. Height and age were measured on a dominant tree after felling in each plot. Physical and chemical properties of the soil were determined. Relationships between site index (SI25) and physiographic factors, climatic attributes as well as soil properties were evaluated using correlation analysis and multiple regression analysis. Site index was significantly related with annual precipitation, mean spring rainfall, rainfall June to September, rainfall of the driest month, length of the dry period, mean maximum temperature, mean temperature of the warmest month, stoniness of the soil, sand, silt, clay, pH, electrical conductivity, and available water capacity. Multiple regression accounted for 57.9% of variations in height growth. The models obtained can be used to determine the site index of potential areas in Turkey for maritime pine. It can be said that the productivity of maritime pine may decline in the future due to global climate change.

Genesis and classification of soils along a toposequence in the teaching and research farm of Taraba State University, Jalingo, Nigeria

Investigations were made to reflect the genesis and classification of soils along a toposequence in the Teaching and Research farm of Taraba State University. The topographic map of the farm was developed in the ArcGIS 10.8 environment and a profile graph plotted out. One profile pit was sunk in each elevation range to represent soils in the summit, shoulder, back slope, foot slope and toe slope positions using the free survey approach. The soils were deep, well drained and generally described as A, B, C soils with extensive B horizons that showed clear illuviation of clay and sesquioxides. The soils were brown (7.5YR 3/4), dark brown (10YR 3/3) and dark yellowish brown (10YR 4/6) in the surface and dominated by sand with bulk density values that exceeded 1.5 Mg/m3. Soil pH values were moderately acid to neutral while organic C and exchangeable bases were low in all but foot slope position where high values of organic carbon were obtained in the surface soils. The content of dithionite and oxalate Fe and Al, and their derivatives indicate intense weathering condition of the soils as well as their combined movement with clay to endopedons. However, moderately high CEC and the likely presence of montmorillonite (via CECE/clay) are indications that the soils had good potentials for agriculture. Among the soil forming processes in the area were mineralization, eluviation-illuviation as well as ferritization. The soils were classified as Typic Rhodustults (Pretic Acrisols), Arenic Haplustults (Chromic Acrisols) and Paleustults (Haplic Acrisols).
 Keywords: pedogenesis, sesquioxides, classification, Basement Complex

Effect of harvest residue management on soil properties of Eucalyptus hybrid and Acacia mangium plantations planted on steep slopes in northern Vietnam

Burning harvest residues during site preparation can compromise the soil-nutrient stock in short-rotation plantations, but this practice remains common in northern Vietnam. This study compared the effect of two contrasting harvest-residue treatments (burning vs retention) on soil total carbon (TC), total nitrogen (TN), extractable P (ext-P), exchangeable K (exch-K) and bulk density (BD) of two adjacent randomised complete-block trials, one of Eucalyptus hybrid (Eucalyptus urophylla × E. pellita) and the other of Acacia mangium planted on steep slopes. Harvest-residue management had no effect on soil properties of either E. hybrid or A. mangium two years after planting. Soil pH in E. hybrid increased and exch-K in A. mangium decreased during the first year; ext-P decreased over time in both species though this was only significant in the residue-retention treatment in A. mangium. Slope significantly influenced pH and TC of E. hybrid and TC and TN of A. mangium. It appeared that slope position and correlative factors such as surface runoff and erosion had led to the observed distribution of some soil properties along the steep slope.

Soil chemical characteristics at three slope positions in the smallholder’s Piper nigrum L. in Lhokseumawe City, Aceh Province

The spatial variation of soil properties is significantly influenced by several factors. Slope position belongs to a component of topography as one soil-forming factor which would be influenced by soil development. The purpose of this study is to understand the pedogenesis of soil chemical characteristics on the diversity of slope positions in the smallholder’s Piper nigrum L. in Lhokseumawe City Aceh Province, start from October to December 2017. The research was conducted using the descriptive survey method and fifteen soil samples from three slope positions, i.e. upper slope position [33%], middle slope position [22%], and lower slope position [6.6%] were collected. The soil samples were analyzed using appropriate methods such as soil pH using pH meter, soil organic carbon using Walkley and Black, total nitrogen using Kjehdahl, available phosphorus using Bray II, and potassium exchangeable using Morgan. This research has studied the correlation between soil chemical properties and the differentiation of soil chemical characteristics at each slope position by the DMRT test method. The result showed that the slope position affected soil chemical properties. The slope position had affected water movement from the upper to the lower slope position and this process caused variation of soil chemical characteristic formation. The value of soil pH, soil organic carbon, total nitrogen, available phosphorus, and potassium exchangeable was higher in the lower slope position than those in the middle and upper slope positions.

Changes in selected soil properties across a chronosequence of exclosures in the central dry lowlands of Ethiopia

In Ethiopia, rehabilitation of the natural resource-base in degraded lands through area exclosures has become a necessary intervention, albeit empirical studies on the impact of these exclosures are limited. This study was conducted to investigate changes in selected soil properties along exclosures’ age and slope positions in Kewet district, central dry lowlands of Ethiopia. Soil samples were collected from three slope positions of three purposively selected exclosures of 5, 15 and 20 years old and one adjacent open grazing land from 0-10 cm soil depth for analysis of pertinent soil properties. The effect of exclosure age on bulk density, contents of sand, clay, organic carbon, total nitrogen, available phosphorus, CEC, and exchangeable Mg+ and K+ was significant (P<0.05). All exclosures had low bulk density (1.14-1.16 g cm-3) as compared to the grazing land. Higher available water content (173 mm m-1) was recorded in the old exclosure. Soil organic carbon ranged from 2.58% (young exclosure) to 3.37% (middle age exclosure). Soil total nitrogen increased from 0.24-0.34%, while available phosphorus increased from 27-34%, from young to the old exclosure respectively. However, the influence of exclosures’ age on other soil properties was not significant. The young exclosure had the highest CEC (57 cmolc kg-1), whereas the grazing land had the highest total nitrogen and exchangeable Ca2+. From this result, it can be concluded that area exclosures, if managed properly, can improve some of the dynamic soil properties of open degraded grazing lands in the dry lowlands of Ethiopia.

A statistical approach to estimates of geomorphological-morphotectonic diversity for evaluating the scientific value of geosites: a case study from the southeastern Lut desert, Iran

Abstract The present study aims to investigate the diversity index (dv-index) of morphotectonic and geomorphological land-forms as one of the scientific value indices for evaluation of the geotouristic potential of the southeastern Lut desert using topographic statistical analysis. Scientific index scoring in most models is based on descriptive assessment by geotourists and experts. Statistical analysis of the dv-index in the present study helps experts to base their scoring on scientific methods. The dv-index is controlled by several items. In the present study, we analyse two of these, including the classification of topographic continuity pattern (TCP) and topographic slope position correlation (TSPC). For this purpose, a network of section lines is used to analyse slope continuity. The TSPC analysis is performed by using two parameters of absolute value and slope position. Results for these two evaluated items indicate a score of 1.46 (out of 2) for the dv-index. Given a rating of 5, the score obtained for the two items is a high one. Therefore, an initial estimate of the dv-index indicates a significant scientific value of the study area.

The Effect of Slope Position and Land Use on Some Soil Physical and Chemical Properties in Koohrang Area of Chaharmahal and Bakhtiari Province

The Effect of Slope Position and Land Use on Some Soil Physical and Chemical Properties in Koohrang Area of Chaharmahal and Bakhtiari Province

A laboratory study to disentangle hydrological, mechanical and structural mechanisms of soil stabilization by plant mucilage between eroding and depositional zones of a slope

AbstractBiological exudates, such as plant mucilage, can greatly stabilize soils, but as the mechanical and hydrological drivers depend much on soil particle size composition, eroding and depositional areas of a slope may respond differently. Soils from an eroded midslope and a depositional footslope in an arable farm were amended with chia (Salvia hispanica) seed mucilage at concentrations of 0 g C kg−1, 0.46 g C kg−1 and 2.3 g C kg−1 mucilage, formed into cores, and then imparted with wetting and drying (WD) cycles. Mucilage increased the stability of these inherently stable soils from 80% to &gt;98% water‐stable macroaggregates at 0 WD cycles regardless of slope position. Aggregate stability was maintained after 5 WD cycles by mucilage, whereas the stability of unamended soil dropped by 66.7% in the footslope and 30.1% in the midslope compared with 0 WD. The underlying physical stability properties were measured by tensile strength and penetration resistance for mechanical properties, water sorptivity and repellency for hydrological properties, and micro‐, meso‐, macro‐ and total porosity for structural properties. Almost every soil physical property measured changed less with WD cycles if mucilage was present. Compared to unamended soil, 2.3 g C kg−1 mucilage amendment decreased water sorptivity from 0.289 mm s−1/2 to 0.122 mm s−1/2 in the midslope and 0.230 mm s−1/2 to 0.182 mm s−1/2 in the footslope after 5 WD cycles. Aggregate stability, total porosity and water sorptivity were correlated. In the midslope, hydrology and penetration resistance were affected the most, which was likely to be driven by mucilage deposition in the macropores of this more coarsely textured soil. In the footslope, the greater impact of mucilage on tensile strength was likely to be driven by buffering of macroporosity formation by WD cycles in this finer‐textured soil.Highlights We explored how slope position interacts with plant mucilage to drive soil physical stability. Changes in soil physical stability by plant mucilage have rarely been considered with slope position. Interactions between mucilage and soil particles caused greater physical stability in the midslope than footslope. Mucilage stabilized soil by easing changes in pore structure, DOC redistribution and water repellency, with particle bonding less important.

Mechanical Characteristics of the Fine Roots of Two Broadleaved Tree Species from the Temperate Caspian Hyrcanian Ecoregion

In view of the important role played by roots against shallow landslides, root tensile force was evaluated for two widespread temperate tree species within the Caspian Hyrcanian Ecoregion, i.e., Fagus orientalis L. and Carpinus betulus L. Fine roots (0.02 to 7.99 mm) were collected from five trees of each species at three different elevations (400, 950, and 1350 m a.s.l.), across three diameter at breast height (DBH) classes (small = 7.5–32.5 cm, medium = 32.6–57.5 cm, and large =57.6–82.5 cm), and at two slope positions relative to the tree stem (up- and down-slope). In the laboratory, maximum tensile force (N) required to break the root was determined for 2016 roots (56 roots per each of two species x three sites x three DBH classes x two slope positions). ANCOVA was used to test the effects of slope position, DBH, and study site on root tensile force. To obtain the power-law regression coefficients, a nonlinear least square method was used. We found that: 1) root tensile force strongly depends on root size, 2) F. orientalis roots are stronger than C. betulus ones in the large DBH class, although they are weaker in the medium and small DBH classes, 3) root mechanical resistance is higher upslope than downslope, 4) roots of the trees with larger DBH were the most resistant roots in tension in compare with roots of the medium or small DBH classes, and 5) the root tensile force for both species is notably different from one site to another site. Overall, our findings provide a fundamental contribution to the quantification of the protective effects of forests in the temperate region.

Mapping depth to the argillic horizon on historically farmed soil currently under forests

The Piedmont region of the southeastern United States experienced a period of accelerated erosion in the 1800s. Clear-cutting of the forests coupled with soil tilling and inadequate erosion control practices led to substantial soil redistribution and loss. This redistribution exposed the subsoil clay (argillic) horizon in many locations and altered hydrologic processes (i.e., infiltration or interflow) across the landscape. Describing the current hydrologic and biogeochemical processes in this landscape requires a spatially explicit mapping of soil re-distribution and the current depth to the argillic horizon. To achieve this mapping, we measured the depth to the argillic horizon in highly eroded (historically farmed) and undisturbed hillslopes (reference areas) by direct measures—soil augur and tile push probe—and by electromagnetic induction (EMI) combined with ancillary data (i.e., terrain features). Direct measures indicated that the depth to the argillic horizon in the historically farmed watersheds ranged from 26 ± 2 to 87 ± 12 cm in ridge-top and toe-slope, respectively, while in the reference hillslopes depths from ridge-top to toe-slope only ranged from 30 ± 3 to 48 ± 12 cm. Using remotely-sensed data, the best predictive models of the depth to the argillic horizon were based on measurements of the site topographic characteristics (percent slope and hillslope position), along with the following EMI data products: the 2 m horizontal coplanar (HCP) EMI measurement and some of its derivatives (i.e., 2 m HCP – 2 m perpendicular, 2 m HCP – 1 m HCP). Our data suggest that in this previously farmed and reforested landscape, geophysical sensing is an efficient means of predicting depth-to-clay when combined with landscape feature characteristics (R2 = 0.69).

Inventory, Distribution and Geometric Characteristics of Landslides in Baoshan City, Yunnan Province, China

Inventorying landslides in mountainous areas is of great importance for prevention of geologic hazards. This study aimed to establish a detailed landslide inventory of Baoshan City, Yunnan Province, China, based on a large set of high-resolution satellite images from Google Earth. The landslides of this region were divided into two groups, i.e., recent landslides and old landslides. The spatial distribution and geometric characteristics of the two kinds of landslides were analyzed, respectively. Results show that 2427 landslides are present in the study area, including 2144 recent landslides and 283 old landslides with a total area of 7.2 km2 and 97.6 km2, respectively. The recent landslides occurred primarily at steep slopes with higher elevation, while old landslides took place at gentle terrains. For the slope position, most landslides, whether old or recent, cluster near ridges. The lower boundary of the recent landslides is far away from the valley, while the accumulation area of the old landslide is closer to the valley. The H/L (height to length) ratios are basically the same for all landslides, ranging from 0.2 to 0.5. Old landslides have larger mobility, as their travel distances are longer than recent landslides at the same height. The results would be helpful for further understanding the development and spatial distribution of the landslides in Southwest China, and also provide essential support for the subsequent landslide susceptibility mapping and geologic hazard assessment in this area.

Effect of land terracing on soil physical properties across slope positions and profile depths in medium and high altitude regions of Rwanda

Although land terracing is promoted as a management practice for effective soil conservation in hilly areas, construction of terraces causes changes in soil properties. This study evaluated the effect of land terracing on some soil physical properties across slope positions and profile depths in medium and high altitudes of eastern and north-eastern Rwanda. Soil samples were collected from top, middle and bottom slopes of four year-old terraced and non-terraced lands. Results showed that soil textures were mainly sandy clay loams. At medium altitude, silt (19.6, 18.6%) and hydraulic conductivity (237.9, 129.8 mm h−1) were significantly ( p < 0.05) higher in terraced than non-terraced land, while clay (29.2, 27.8%) and total available water content (TAWC) (222.2, 201.7 mm m−1) were higher in non-terraced than terraced land. At the high altitude, hydraulic conductivity (194.3, 124.1 mm h−1) was higher in terraced than non-terraced land, while soil bulk density (1.42, 1.35 g cm−3) and TAWC (251.6, 235.3 mm m−1) were higher in non-terraced than terraced land. Terracing increased silt content and hydraulic conductivity, and slightly decreased clay and water retention capacity. These changes are important in soil water and fertility management, and therefore need to be considered when using terraced lands.

A novel GIS-MCDA-based spatial habitat suitability model for Posidonia oceanica in the Mediterranean.

Seagrasses are extremely productive flowering plants that produce oxygen by photosynthesis in the marine environment. They are globally in decline and can become endangered due to human activities and natural hazards. In order to maintain seagrass biodiversity, suitable habitats for this species must be determined and marine protected areas must be established. Recent technology allows acoustic systems to collect accurate high resolution data of the seafloor. Additionally, cost-effective optical satellite images, which provide wide coverage, have been used in various benthic studies. In this study, a habitat suitability model was developed using acoustic and optical data for Posidonia oceanica in Gulluk Bay, Turkey, SE Mediterranean, by applying the geographic information system-multi-criteria decision analysis and remote sensing techniques. Various criteria, namely, depth, sheltered area, slope, sediment yield, and topographic position index, were weighted using the analytic hierarchy process method. The model was able to identify suitable habitats for seagrass with 76% accuracy. The proposed model in the study allows fast, temporal, cost-effective, and sustainable production of seagrass habitat maps.

ROZTOCHIA LANDFORM MORPHOTYPES

The issues of relief morphotype classification have not been solved yet, as there are no clear criteria for their selection. The article proposes to use semantic-oriented morphometric relief analysis for relief classifying. The algorithm of its implementation is as follows: 1) reasonable classificating taxonomic relief units; 2) defining their semantic names; 3) evaluating and selecting the morphometric descriptors of identified morphotypes. The study is based on the results of field landscape observations in the Ukrainian part of The Roztochia, which were accompanied by instrumental morphometric measurements and landscapes panoramic photographing. For morphometric analysis of The Roztochia, the digital relief model (DEM) of SRTM 30 version 2.1 with pixel size (60x60 m) has been used, for its Ukrainian part the authors have built DEM on the basis of synthesized horizontals of topographic maps of scale 1:10000 and 1: 25000, laying of horizontals 1 m and 5 m, pixel size (15x15 m). By means of ArcGis 10.0 software package, the following models have been created: slope gradient, horizontal dismemberment, vertical dismemberment (relative elevation), aspect, elevation levels, thalwegs, watersheds, Landform Classificaton, Slope Position Classificaton, Topographic Position Index. The analysis of these models made it possible to select identification descriptors for selecting meso-relief units, i.e. area (according to R. Dikau (1990)), relative elevation, mean slope, compactness. It has been established that the meso-relief gradation of subcategory “B” in The Roztochia differs slightly in area from the “standard” one after R. Dicau and is in range of 105–108 m2. This proves that the morphometric descriptors of the morphological classification of the relief units need to be determined according to the features of the region separately for plains, heighlands and mountains. The semantic analysis made it possible to give names to the selected units of meso-relief. The main names of relief units, used in Polish and Ukrainian literature have been analyzed, and their English-speaking counterparts have been found. The map of The Ukrainian Roztochia meso-relief has been created. The following meso-relief units are distinguished: high-gradient hill, medium-gradient hill, lawe gradient hill, knoll, ridge, escarpment, longitudinal depression, upper plain, lower plain, basin, valley. Nearly 70% of the region is occupied with hill. Keywords: landform morphotype; mesorelief; Roztochia; semantics.

Influence of Toposequence on Physical and Mineralogical Properties of Soils Developed on Basaltic Parent Material under Sub-humid Terrestrial Ecosystem

Understanding of soil forming factors is crucial to define physical, mineralogical and morphological properties of soils. In addition to that soil formations were highly associated with slope positions which have influence on pedogenetic and weathering process of the soils. Because, topography or relief affects how water and other material are added to and removed from soils. The aim of this study is to enhance our understanding of the role toposequence in controlling chemical weathering, influence on physical and mineralogical properties in soils developed on basaltic parent material under sub-humid terrestrial ecosystem in Black Sea region of Turkey using geochemical and mineralogical data obtained from X-ray diffraction and Scanning Electron Microscope analysis. For this purpose, four representative profiles formed on different topographic positions of transect were investigated and designated according to Soil Survey Staff (2014)/IUSS Working Group WRB (2015) classification systems. The results clearly showed that topography strongly affects soil physical, mineralogical and morphological characteristics either directly or indirectly in the local region even soils formed on the same parent material with the same climatic condition. This case was also explained with chemical weathering indices (Chemical Index of Alteration and Chemical Index of Weathering) in this study.

Variability of Soil Extractable Micronutrients in the Upland and Lowland Topoposition Soils of Gubi Village, Bauchi State, North Eastern Nigeria

The aim of this study was to assess the variability of extractable micronutrients in the varying topoposition soils of Gubi village. Four profile pits were dug at each of the designated topopositions making a total of eight profiles. The profiles were dug at the crest, upper slope, middle slope and valley bottom positions of the two toposequences and were named URFGU1, URFGU2, URFGU3 to URFGU4 and URFGL1. URFGL2, URFGL3 to URFGL4 for upland and lowland respectively. The content and profile distribution of extractable micronutrients copper (Cu), Zinc (Zn), manganese (Mn) and Iron (Fe) were extracted using 0.1 m HCl solution and determined using atomic absorption spectrophotometer (AAS) at appropriate wavelengths (Ca at 247 nm, Zn at 214 nm, Mn at 279 nm and Fe at 248 nm. Data generated was statistically analyzed using analysis of variance in nested experimental design. The significance of difference between treatments was determined using fishers LSD. Means that were significantly different were separated using the Least Significant Difference (LSD). The result reveals that Copper (Cu), iron (Fe) and manganese (Mn) varied significantly due to location. Iron and manganese were significantly higher in the upland soil (47.35 and 47.50 mg/kg respectively) than in the lowland soil (17.67 and 27.38 mg/kg respectively). The lowland soil had significantly higher Cu (1.31 mg/kg) than the upland soil (0.37 mg/kg). Zinc (Zn) did not vary significantly due to location however the lowland soil (0.86 mg/kg) had a higher Zn content than the upland soil (0.26 mg/kg).

Relationships between stand spatial structure characteristics and influencing factors of bamboo and broad-leaved mixed forest

ABSTRACTMoso bamboo is an economically valuable plant in southern China and bamboo and broad-leaved mixed forest is a better management model. The relationships between stand spatial structure characteristics and factors influencing (e.g., salt, soil, and terrain factors) bamboo and broad-leaved forest in the Nature Reserve of Tianbaoyan (Yongan city, Fujian provice), China, were investigated using canonical correspondence analysis (CCA). The results showed that the horizontal distribution of bamboo and broad-leaved forest was mainly randomly distributed, that the states of tree growth were at the doctrine of mean as a whole, and the degree of mixing by species was low. The first CCA axis accounted for slope position, soil organic carbon, crown ratio, bamboo density, broad-leaf tree density, soil water content, and C/N, while the second CCA axis showed variation due to altitude level, average diameter of broad-leaf tree, soil total nitrogen, and soil total phosphorus. In general, both axes reflected the response of forest spatial structure to changes in the water thermal gradient and the relationship between forest complexity and changing soil physio-chemical properties. Furthermore, the variation in stand spatial structure of bamboo and broad-leaved mixed forest explained by stand, soil, and terrain factors reached 100%. When broken down, interacting stand and soil factors together accounted for up to 67.3%, stand factors alone for 20.3%, and soil factors alone for 1.7%, while interactions among all three explained 9.69% of the stand spatial structure; terrain factors alone and their interaction with other factors had negligible explanatory power (0.09–0.21%).

Thresholds in woody and herbaceous component co‐existence inform the restoration of a fire‐dependent community

AbstractQuestionsA paradoxical co‐existence challenges woodland and savanna restoration worldwide: How are shade‐intolerant, flammable herbaceous layers promoted while maintaining the shade‐casting, more fire‐sensitive woody regeneration that sustains overstorey structure? Where restoration success consisted of robust, diverse herbaceous layers and vigorous, well‐stocked Pinus echinata regeneration (hereafter, shortleaf‐bluestem response), we asked: are there targetable conditions of overstorey, understorey, topography, and proximity to mature Pinus echinata that simultaneously maximize desired woody and herbaceous understorey components? Do these conditions and dependent responses differ across canopy disturbance level and fire season?LocationCumberland Plateau, Tennessee, USA (36°04′8.11″ N, 84°50′38.36″ W).MethodsWe measured 12 shortleaf‐bluestem response and 17 explanatory condition variables at 345 plots spanning an experimental restoration gradient (canopy disturbance level and fire season combinations). We ordinated variation and identified response thresholds using a multivariate regression tree. Differences across tree groupings and splits associated response thresholds with specific explanatory conditions.ResultsPockets of substantial Pinus echinata regeneration (&gt;3,000 stems/ha), C4 grass density (&gt;40,000 ramets/ha), and herbaceous diversity (increase from 22 to 205 species) occurred 7–14 years after canopy disturbance and 3–8 fires. Such shortleaf‐bluestem response was maximized at 3 m2/ha residual tree basal area, 11% canopy closure, reduced midstorey density (5,000 small‐sapling stems/ha), and southwesterly aspects within 70 m of mature Pinus echinata. In contrast, shortleaf‐bluestem response was negligible at 11.3 m2/ha basal area and 68% canopy closure. Fire season, snag basal area, slope, and slope position effects were minimal.ConclusionsWe identified specific conditions fostering the co‐existence of desired herbaceous and woody understorey components, addressing a major woodland and savanna restoration challenge and expanding on previous threshold concept applications by simultaneously considering multiple desired responses. Results can direct the restoration of imperiled shortleaf‐bluestem communities east of the Mississippi River, USA, where work has been scarce or ineffective, and similar approaches could inform fire‐dependent woodland and savanna restoration worldwide.