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Soil deepening by trees and the effects of parent material
... According to the Devonian Plant Hypothesis, it is assumed that biomechanical and biochemical weathering through deeply rooted vascular plants drove the initial soil development and climate change, primarily through intense mineral weathering (mainly silicates) and the bounding of large amounts of atmospheric CO 2 followed by climatic cooling in the Late Devonian (Algeo and Scheckler, 1998;Retallack, 2001;Beerling and Berner, 2005;Algeo et al., 2001;Le Hir et al., 2011;Goudie and Viles, 2012). At present this issue in relation to soil and regolith evolution is intensively Geomorphology 300 (2018) 1-12 investigated under the Critical Zone paradigm (Pawlik et al., 2016b;Shouse and Phillips, 2016;Brantley et al., 2017;Hasenmueller et al., 2017). 2. Bioprotection which currently is considered as one of the most important functions of trees. ...
... 3. Soil spatial complexity as a derivative of tree/soil feedbacks. Several studies mention soil's spatial complexities, which are at least partly influenced by the presence of trees through, for example, stemflow and stemwash (Levia and Frost, 2003), and/or biomechanical and biochemical processes associated with their living functions, disturbances, mortality and decomposition (Zinke, 1962;Daněk et al., 2016;Shouse and Phillips, 2016;Stutz et al., 2017). Trees are able to modify the structure of soil and regolith by displacing material with their root growth (Phillips and Marion, 2006;Pawlik, 2013). ...
... Their global influence has been suggested in many recent papers which usually point to rhizospheric processes and mycorrhizal associations with plant roots (Morris et al., 2015). It is argued that trees, through the action of their roots, can change physical and chemical characteristics of regolith and soils and they can have repeating influence on the same portion of substrate and bedrock subsequently leading to soil deepening (Zinke, 1962;Limbrey, 1975, after Wood andJohnson, 1978;Phillips and Marion, 2006;Phillips, 2008;Shouse and Phillips, 2016) (Fig. 11). ...
Following previous findings regarding the influence of vascular plants (mainly trees) on weathering, soil production and hillslope stability, in this study, we attempted to test a hypothesis regarding significant impacts of tree root systems on soil and regolith properties. Different types of impacts from tree root system (direct and indirect) are commonly gathered under the key term of “biomechanical effects”. To add to the discussion of the biomechanical effects of trees, we used a non-invasive geophysical method, electrical resistivity tomography (ERT), to investigate the profiles of four different configurations at three study sites within the Polish section of the Outer Western Carpathians. At each site, one long profile (up to 189 m) of a large section of a hillslope and three short profiles (up to 19.5 m), that is, microsites occupied by trees or their remnants, were made. Short profiles included the tree root zone of a healthy large tree, the tree stump of a decaying tree and the pit-and-mound topography formed after a tree uprooting.
In spite of a very complex picture of the resistivity of regolith and bedrock, the long profiles showed that through the presence and action of roots, trees add to this complexity. Trees change soil and regolith properties directly through root channels and moisture migration and indirectly through the uprooting of trees and the formation of pit-and-mound topography. Within tree stump microsites, the impact of tree root systems, evaluated by a resistivity model, was smaller compared to microsites with living trees or those with pit-and-mound topography but was still visible even several decades after the trees were windbroken or cut down.
The ERT method is highly useful for quick evaluation of the impact of tree root systems on soils and regolith. This method, in contrast to traditional soil analyses, offers a continuous dataset for the entire microsite and at depths not normally reached by standard soil excavations. The non-invasive nature of ERT studies is especially important for protected areas.
... The shallow, laterally oriented root systems (Fig. 7) have several implications. Their concentration in the upper regolith, and lack of a central taproot, limit spruce's ability to deepen the soil beneath them, as is common in tap-root type species (see, e.g., Shouse and Phillips, 2016). This root architecture also contributes to a greater propensity to uproot than other trees common in the region, and contributes to a higher propensity for basal mounding in spruce (Šamonil et al., 2017). ...
... Roots penetrate joints and fractures in underlying rock, facilitating weathering by promoting moisture flux, microbial activity, and formation of organic acids. Roots may also encircle rock fragments, causing them to be "mined" if the tree uproots (Phillips, 2008;Shouse and Phillips, 2016;Pawlik et al., 2016). However, these effects are most pronounced in trees with a tap-root architecture (a large, dominant, deep root descending directly below the trunk), and least pronounced in species (such as Picea abies) with a lateral root architecture. ...
Biogeomorphological and ecological succession following a disturbance or the exposure of new ground often proceeds in stages, from domination by abiotic, geophysical factors through stages characterized by increasing effects of biota, biotic-abiotic feedbacks, and eventual domination by ecological processes. However, some studies in forest settings have found more varied development patterns, including persistence of states dominated by biogeomorphic feedbacks. In this study we investigated this phenomenon In Norway spruce (Picea abies (L.) Karst.) dominated forests on the main ridge of the Šumava Mountains in the Czech Republic along the German and Austrian borders. Throughout most of the Holocene, Picea has strongly influenced microtopography and soil/regolith characteristics so as to inhibit hydrological connectivity and development of surface drainage, and maintain hydromorphic soil conditions. These strongly historically and geographically contingent ecosystem engineering effects create and maintain habitat that favors spruce over other trees. These interactions have maintained a landscape dominated by biogeomorphic feedbacks.
... Soil genesis and horizonation are not reset by soil mixture and may gradually continue without potential soil regression (see Johnson et al., 1990). Although roots may penetrate bedrock under the standing trees during axial growth (Shouse and Phillips, 2016), rock mining accompanying tree uprooting on shallow soils may disturb bedrock even more markedly (Fig. 5). ...
... These stump holes may infill with material that slumps in from the walls of the hole, transported material from upslope, organic matter from stump and root decay and local litterfall, and various combinations of these. Stump infilling has significant impacts on soil spatial variability and hillslope mass fluxes but has been studied in detail in only a few cases (Phillips and Marion, 2006;Shouse and Phillips, 2016;Šamonil et al., 2018a). ...
https://authors.elsevier.com/a/1blC23HcE1cwu3
Outbreaks of bark beetles, for example Ips typographus L. in Eurasia or Dendroctonus ponderosae Hopkins in North America, have serious impacts on forest resources, biodiversity, and ecological dynamics, with economical and social ramifications. Moreover, many models predict increasing frequency and severity of such biotic disturbances due to ongoing climate change, and land use driven changes in forest structure and composition. Bark beetles are recognized as keystone species due to their strong and complex effects on ecosystem dynamics. However, due to the increasingly widely recognized biogeomorphic impacts of trees, bark beetles may have significant indirect biogeomorphic and pedogenetic impacts through their effects at scales ranging from individual trees to forest landscapes. These include: (1) Reduced uprooting, with associated impacts on topography , mass movements, regolith and soil formation, and slope hydrology; (2) Reductions in bioprotection via trapping of downslope sediment movement; (3) Hydrological impacts, including increased total runoff and increased proportion of subsurface flow; (4) Decreased microtopographic irregularity (and associated hydrological and pedological impacts); and (5) Changes in biochemical and biomechanical effects on soils, regolith, and hillslope morphology. Five separator factors (discriminators between different developmental trajectories) were revealed for the case of the central European region. These factors may determine the occurrence and severity of biogeomorphic impacts: First is whether the site is prone to potential uprooting or whether an spruce bark beetle (SBB) outbreak is initiated by a blowdown/uprooting event. Second is whether the site is dominated by mineral soils or Histosols. A third discriminating factor is whether the forest is managed or unmanaged, which determines the pre-attack tree species composition and coarse woody debris and disturbance regimes; and a fourth is the post-outbreak management. Finally, the fifth separator factor relates to slope thresholds that determine the significance of impacts on mass movements and erosion. These findings support the need, and provide guidelines , for research on geomorphic impacts of bark beetle infestations. Though we mainly restrict our consideration to bark beetles in Europe, both our approach and findings are likely to have broader relevance for biogeomorphic impacts of extensive tree mortality.
... 1. hillslope surface disturbances, changes in roughness and heterogeneity mainly due to tree uprooting, tree root mounding, baumstaining, stemwashing, and tree breakage (Hoffman and Anderson, 2013;Pawlik et al., 2013Pawlik et al., , 2017Pawlik et al., , 2019Šamonil et al., 2010a, 2015; 2. exposure of fresh material to mass movements and water and wind erosion after soil is uplifted in the rootwad form (Pawlik, 2013), or due to rock fragment mining (Phillips et al., 2008); 3. driving of biogenic soil creep rates over longer time periods (Pawlik and Šamonil, 2018b;Šamonil et al., 2020); 4. soil production and soil accretion, factors which allow trees to be considered a land forming agent (Sullivan et al., 2016); 5. soil horizon simplification (soil homogenization) or differentiation (soil horizon heterogeneity) mainly due to pedoturbations (e.g., tree uprooting, soil mixing, soil horizon inversion; Schaetzl et al., 1989;Šamonil et al., 2010b, 2015Daněk et al., 2016;Pawlik, 2013;Pawlik et al., 2016aPawlik et al., , 2016bPawlik and Šamonil, 2018a) or biochemical effects of trees (e.g. decomposition of leaves, lying trunks with exposed root systems; Binkley and Giardina, 1998;Spears and Lajtha, 2004); 6. soil deepening (Phillips and Marion, 2006;Shouse and Phillips, 2016;Pawlik and Kasprzak, 2018) and rock cliff retreat (Jackson and Sheldon, 1949); 7. modification of biogeochemical cycles of elements in ecosystems (Lucas et al., 1993;Lucas, 2001;Perakis and Pett-Ridge, 2019;Houlton et al., 2018). ...
... In terms of trees this has been demonstrated by Binkley and Giardina (1998), who suggested that a tree species can modify soils to the disadvantage of other species. This is narrowly connected to the already tested ability of trees to deepen the soil horizon by repetitive occupation of the same site by trees of the same or other species Marion, 2004, 2006;Shouse and Phillips, 2016). Physically, plants, especially trees with deep root systems, stabilize soil such that the effects of water and wind erosion are reduced ( Fig. 7A and 7C). ...
Evolution of terrestrial plants, the first vascular plants, the first trees, and then whole forest ecosystems had far reaching consequences for Earth system dynamics. These innovations are considered important moments in the evolution of the atmosphere, biosphere, and oceans, even if the effects might have lagged by hundreds of thousands or millions of years. These fundamental changes in the Earth's history happened in the Paleozoic: from the Ordovician, the time of the first land plants, to the Carboniferous, dominated by forest ecosystems. The Devonian Plant Hypothesis (DPH) was the first concept to offer a full and logical explanation of the many environmental changes associated with the evolution of trees/forests that took place during this time period. The DPH highlighted the impact of deep-rooted vascular plants, particularly trees on weathering processes, pedogenesis, nutrient transport, CO2 cycling, organic and inorganic carbon deposition, and suggests further possible consequences on the marine realm (oceanic anoxia and extinction during the Late Devonian). Here we attempt to combine the DPH and the related expansion in biodiversity, the Devonian Plant Explosion (DePE), with the Biogeomorphic Ecosystem Engineering (BEE) concept. This idea connects tree growth and activity with initiation and/or alteration of geomorphic processes, and therefore the creation or deterioration of geomorphic landforms. We focus on trees and forest ecosystems, as the assumed dominant driver of plant-initiated change. We find that whereas there is a broad evidence of trees as important biogeomorphic ecosystem engineers, addressing the DPH is difficult due to limited, difficult to interpret, or controversial data. However, we argue the concept of BEE does shed new light on DPH and suggest new data sources that should be able to answer our main question: were Devonian trees Biogeomorphic Ecosystem engineers?
... Finally, the infilling of stump holes and trapping of sediments from upslope are distinctive BGIs within rocky hillslopes (Pawlik, 2013;Phillips, 2015;Shouse and Phillips, 2016) as bedrock stream environments have limited potential to display such impacts. Additionally, within hillslope environments, tree growth may enclose (or partly enclose) rock fragments and prevent the downslope movement of sediments until the death of the tree and wood decomposition (Phillips, 2015). ...
... Other studies related to the idea of biogeomorphic feedbacks and biodiversity include Gurnell and Petts (2006), Gurnell et al. (2007), Bertoldi et al. (2009, etc. Moreover, Shouse and Phillips (2016) showed an instance of increasing diversity of geomorphic forms for a non-fluvial hillslope environment. Here, they discussed how vegetation-induced regolith thickening, driven by mechanisms associated with root penetration in bedrock, can promote landform diversity. ...
The dynamic interactions between fluvial processes and vegetation vary in different environments and are uncertain in bedrock settings. Bedrock streams are much less studied than alluvial in all aspects, and in many respects act in qualitatively different ways. This research seeks to fill this lacuna by studying bedrock streams from a biogeomorphic perspective. It aims to identify the impacts of woody vegetation that may be common to fluvial systems and rocky hillslopes in general, or that may be unique to bedrock channels. A review of the existing literature on biogeomorphology – mostly fluvial and rocky hillslope environments – was carried out, and field examples of biogeomorphic impacts (BGIs) associated with fluvial systems of various bedrock environments were then examined to complement the review. Results indicate that bedrock streams exhibit both shared and highly concentrated BGIs in relation to alluvial streams and rocky hillslopes. Bedrock streams display a bioprotective geomorphic form – root banks (when the root itself forms the stream bank) – which is distinctive, but not exclusive to this setting. On the other hand, shared biogeomorphic impacts with alluvial streams include sediment and wood trapping, and bar and island development and stabilization (i.e. bioconstruction/modification and protection). Shared impacts with rocky hillslopes also include bioprotection, as well as displacement of bedrock due to root and trunk growth, and bedrock mining caused by tree uprooting (i.e. bioweathering and erosion). Two BGI triangles were developed to graphically display these relationships. Finally, this paper concludes that bedrock streams exhibit some BGIs that also occur in either alluvial channels or on rocky hillslopes. Therefore, no BGIs were identified that are absolutely unique to bedrock fluvial environments.
... These locally thicker soils may provide favorable sites for future tree establishment, providing another positive feedback. Local soil deepening under individual tree or stump sites has been demonstrated by Phillips and Marion (2004), Phillips (2008), Shouse and Phillips (2016), and Pawlik and Kasprzak (2017), and the mechanisms described above reviewed by Pawlik, Phillips, and Samonil (2016). ...
... The effects discussed here are also likely to be spatially heterogeneous. The soil conditions created by trees, nutrient-rich microsites associated with decomposing trunks and roots, and local concentration of seeds and root stock make it likely that trees preferentially reoccupy the same locations over multiple generations of forest (Finke, Vanwalleghem, Opolot, Poesen, & Deckers, 2013;Kooch, Hosseini, Scharenbroch, Hojati, & Mohammadi, 2015;Moghimian, Jalali, Kooch, & Rey, 2017;Phillips & Marion, 2004;Sullivan et al., 2016;Van Lear, Kapeluck, & Carroll, 2000), evidence of which was found at sites in and near the Inner Bluegrass study area (Phillips, 2016;Shouse & Phillips, 2016). This phenomenon, in combination with the theoretical model presented here, suggests a highly variable spatial pattern of regolith thickness due to tree effects, where the general thickness is greater than or equal to rooting depth, with more uniform thickness otherwise. ...
Tree roots have biogeomorphic engineering effects on epikarst weathering and soil deepening. This is investigated using a system model describing the interactions among biogeomorphic effects of roots, weathering, and soil-epikarst development. The model shows that the system is dynamically unstable when roots are limited by subsurface accommodation space and water availability, and weathering is moisture limited. Instability indicates relatively rapid, unstable growth of epikarst cavities and soil, driven by positive feedbacks. However, when belowground rooting space and moisture are no longer limiting, and weathering is reaction-limited, the system is dynamically stable, indicating steady state or slow growth of epikarst and soils. Results suggest an important role for biogeomorphic ecosystem engineering (BEE) by tree roots in soil and epikarst development, but that BEE is self-limiting. When moisture storage and supply for both plants and dissolution are adequate and sufficient root space is available, BEE effects become negligible. Supportive data and field observations from the Inner Bluegrass region of Kentucky indicate that BEE effects of trees can produce favorable conditions for tree growth, with these effects becoming negligible as soil thickness increases sufficiently.
... Additionally, we assumed that these differences could be partly modified by regional soil properties, as it was described in case of post-uprooting pedogenesis by Šamonil et al. (2018a). Former studies, such as those by Schaetzl et al. (1989), Pawlik (2013), Shouse and Phillips (2016), suggested that trees may cause soil deepening, armoring, disintegration, displacement, mixing, inversion, up-building and removal. The authors also reported a wide range of non-linear processes in soils, with biota among the main driving factors (e.g., Phillips 1999Phillips , 2017Gabet and Mudd 2010;Hoffman and Anderson 2014;Šamonil et al. 2014, 2015. ...
... Gaiser (1952) reported that new roots were able to penetrate heavy clays by using subsoil cracks and root channels. Other important biomechanical effects of trees are soil deepening (Shouse and Phillips 2016) and infilling of stump rot pits (Phillips and Marion 2006), which were first suggested by W.M. Davis, a famous North American geographer (King and Schumm 1980). We did not observe baumsteins (rock fragments displaced by tree growth), but they were ubiquitous around other trees above our study plot in Turbacz where sandstone predominated. ...
Background and aims
The changing soils is a never-ending process moderated by numerous biotic and abiotic factors. Among these factors, trees may play a critical role in forested landscapes by having a large imprint on soil texture and chemical properties. During their evolution, soils can follow convergent or divergent development pathways, leading to a decrease or an increase in soil spatial complexity. We hypothesized that trees can be a strong local factor intensifying, blocking or modifying pedogenetic processes, leading to local changes in soil complexity (convergence, divergence, or polygenesis). These changes are hypothetically controlled by regionally predominating soil formation processes.
Methods
To test the main hypothesis, we described the pedomorphological features of soils under tree stumps of fir, beech and hemlock in three soil regions: Haplic Cambisols (Turbacz Reserve, Poland), Entic Podzols (Žofínský Prales Reserve, Czech Republic) and Albic Podzols (Upper Peninsula, Michigan, USA). Soil profiles under the stumps, as well as control profiles on sites currently not occupied by trees, were analyzed in the laboratory for 20 physical and chemical properties. In total, we analyzed 116 soil samples. The age of trees and time of tree death were determined using the radiometry (¹⁴C), dendrochronology and repeated tree censuses. To process the data, we used multivariate statistics, namely, redundancy analyses (RDAs) and principal component analyses (PCAs). The statistical significance of variables was tested using Kruskal-Wallis, Dunn, and permutation tests. To reach the main aims of the present study, we examined the dataset at three levels of data complexity: 1) soil regions, 2) microsite (i.e., tree stump versus control site), and 3) soil horizon.
Results
Living tree roots and empty or infilled root channels were the most important pedogenic factors that affected the dimensions of soil horizons and the moisture in the root zone under tree stumps. Microsites explained almost 6% of the soil variability (p < 0.001, F = 13.99), demonstrating that trees significantly impacted soil chemical properties in the root zone in all regions. In the Albic Podzols soil region, we found evidence of “basket” podzolization. Our results suggest the rapid eluviation of organic matter-sesquioxide complexes under the stump, probably leading to local soil divergence in Albic Podzols. However, soil analyses under the stumps in the Haplic Cambisols soil region suggested local polygenetic changes in soils (e.g., hydromorphic processes). The thickness of the A and B horizons increased, and soil chemistry changed under trees in the Entic Podzol soil region compared to the control profiles.
Conclusions
In addition to regional environmental factors that manifest themselves in regional pedogenesis and that have a key role in modifying the influence of trees on the soil, the tree species can specifically modify pedogenic processes under standing trees. Trees may influence rate of pedogenesis (hemlock in Albic Podzol region) or even soil evolutionary pathways (beech in Haplic Cambisol region).
... Example references Increasing spatial variability over time due to effects of individual trees in forest soils Šamonil et al., 2008;2014;Kooch et al., 2015;Daněk et al., 2016;Shouse & Phillips, 2016 Increasing variability over time in coastal dune soils Thompson 1983Thompson , 1992 Increasing variability over time due to plant-soillandform feedbacks in karst soils Crowther, 1987;Bárány-Kevei, 1998;Estrada-Medina et al., 2013 Divergent development and sensititivity to small perturbations in coastal marsh soils Orson and Howes 1992, Nyman et al. 1993, Hackney et al. 1996 Increasing soil richness in chronosequence on sandy lake terraces Barrett & Schaetzl, 1993 Disproportionately large microtopographically induced variations in soil morphology Miller et al., 1994;Price, 1994 Divergent development in a single parent material in tropical soils Dubroeucq & Volkoff, 1998 Divergent ...
... This produces the hypothesis that divergent evolution of soil thickness occurs, with increasingly thicker soils at tree-occupied sites. This has been tested and confirmed in several studies (Phillips, 2008;Shouse and Phillips, 2016). However, this phenomenon may only be applicable where soil thickness is less than coarse rooting depth of trees. ...
This paper reviews recent developments in studies of soil complexity, focusing on the variability of soil types within soil landscapes. Changes in soil complexity are directly related to divergent and convergent pedogenesis and to dynamical stability and chaos. Accordingly, strong links exist between nonlinear dynamical systems theory and studies of soil complexity. Traditional conceptual models of soil formation emphasized convergence of the soil cover in the form of progress toward mature, climax soils. A view of divergence as a frequent occurrence rather than an occasional exception is more recent. Measurement of soil complexity is now firmly linked to field pedology. In addition to strong methodological links to pedometrics and soil geography, standard tools for assessing complexity include chronosequences and other historical approaches, relationships between soil properties and soil forming factors, and pedological indicators. Eight general pathways to changes in soil complexity are identified. Three are based on changes in soil-forming factors. These may increase or decrease complexity depending on whether the factors themselves are converging or diverging and the relative magnitudes of soil and state factor divergence. Three pathways are associated with local disturbances. If these occur less frequently than the relaxation time for soil responses, and if internal pedological dynamics are dynamically stable, then disturbance-induced complexity is reduced over time. Otherwise, divergence and increasing complexity occurs. Two additional pathways are directly related to dynamical stability of intrinsic pedological processes, which may result in decreasing or increasing complexity, either in concert with, or independently of, environmental controls or disturbances.
... The depressions may fill with material slumping or eroding from the surrounding soil, sediment transported downslope, organic litter, or a combination. This stump infilling process has significant impacts on soil spatial variability and hillslope mass fluxes, but has been studied in detail in only a few cases (Phillips and Marion, 2006;Shouse and Phillips, 2016). ...
... 28 deepening by trees and reoccupation of these locally deeper patches after tree mortality (Phillips, 2008;2009a;Shouse and Phillips, 2016). In karst landscapes, weathering-related feedback relationships linked to ecosystem engineering by tree roots are described by Crowther (1987), Susteric et al. (2009), Schwinning (2010, Estrada-Medina et al. (2013), and Nie et al. (2014). ...
The role of trees and forests as a critical component of the biosphere and critical zone, and of the Earth system more generally, is widely appreciated. Less known and acknowledged are the geomorphological functions of tree roots, though their importance has been widely referred to in soil studies, paleopedology and palaeobotany. Tree roots and their impact on weathering processes and soil production were incorporated in the Devonian plant hypothesis and tree root casts served as a key evidence of recognition of past soils in geology, sedimentology and palaeopedology. However, knowledge of biomechanical and biochemical weathering induced by vascular plant roots (mainly trees) has been rarely utilized in geomorphic studies. Biogeomorphic and pedologic studies in recent decades have highlighted the importance of tree uprooting, in which roots play a primary role, in soil development, regolith disturbance and bedrock mining. Other important functions of roots were also recognized, e.g.: soil displacement by growing roots, infilling of stump holes and root cavities, root groove development, direct and indirect effects taking place in the rhizosphere and mycorrhizosphere (mainly biochemical weathering of minerals, support by microbial communities and symbiotic fungi), and changes in porosity, permeability and hydrology of soils in the root zone. However, further studies are urgently needed because many aspects of biochemical and biomechanical weathering are not well understood. This is especially true with respect to taxa-specific impacts. Variations in root architectures, edaphic settings, ecological relationships, and geographic ranges result in substantially different biogeomorphic impacts of different tree species. Additionally, the same species in different environmental settings may have different effects.
... The role of trees and tree roots in soil development was highlighted by Phillips and Marion (2006), and soil profile deepening was studied by Shouse and Phillips (2016). Milani et al. (2023) documented the critical zone deepening after the establishment of exotic pines over grasslands. ...
Trees contribute to bedrock weathering in a variety of ways. However, evaluating their full impact is complicated by a lack of direct observation of unexposed root systems of individual trees, especially when the scale of the analysis goes down to the level of microbiomes. In the present study, we investigated the contribution of tree root systems to bioweathering and soil production at the macro- and microscale. Soil profiles developed under trees on granite bedrock were investigated in two parts of the Sudety Mountains, SW Poland: the Rudawy Janowickie Mountains, and the Stołowe Mountains. Soil profiles were gradually excavated and soil samples collected from pre-defined positions of the root zone: 1) bulk soil, 2) rhizosphere, 3) cracks, 4) topsoil, and 5) control positions. In total, we analyzed 103 samples for soil chemistry and microbiological activity. In addition, we analyzed 19 samples using XRF (X-ray Fluorescence). Four parent rock samples, in the form of thin-sections, were the subject of mineralogical evaluation. Soil analyses included: total organic carbon (C) and nitrogen (N) content, soil pHH2O, soluble iron (Fed), and aluminum (Ald), non-crystalline (amorphous) iron (Feox), and aluminum (Alox). For microbiological analyses, we used a Biolog (EcoPlate) system to determine the functional diversity of soil microorganisms. We evaluated the results on soil chemistry and microbiological activity statistically by principal component analysis (PCA) and redundancy analysis (RDA). Differences between soil sampling positions were assessed using a non-parametric Kruskal-Wallis (K-W) rank sum test and a post-hoc pairwise Dunn test.
Trees developed different root architectures, likely shaped by the depth to bedrock and its pre-existing net of fractures and fissures. Tree roots were able to enter bedrock cracks at one study site (at Pstrążna, Stołowe Mountains). The soil profile was too deep for root system penetration at the second study site (Mt Jańska, Rudawy Janowickie Mountains, RJM). The rhizospheric soil along the roots had significantly different chemical properties compared to non-rhizospheric soil types. At Mt Jańska, soil differed from the crack soil in terms of Alox (pHolm-adj. < 0.0006) and Feox (pHolm-adj. < 0.004), and from the bulk soil (pHolm-adj. < 0.02) and topsoil (pHolm-adj. < 0.007). In addition, at Pstrążna, the soil differed from the control soil in terms of C (pHolm-adj. < 0.009) and soil pHH2O (pHolm-adj. < 0.0008) and from the topsoil in terms of soil pHH2O. The highest metabolic activity was in cracks at Mt Jańska and in control samples from Pstrążna. In general, the spatial distribution of soil microbial activity, and the weathering that results from that portion of the soil biome, is spatially heterogeneous and appears to be partially determined by the interaction of root growth and bedrock fracture patterns.
... Cropping, grazing, and conversion to grassland occurred mainly in the Midwest, along the Mississippi River, at the East Coast and Great Plains, and corresponded with thicker A horizons, whereas reforestation occurred in the east (Fig. 3, Supplementary Fig. 3). Land uses may also affect local-scale variation of soil thickness, such as tree stump or tree overturn in the forest 43,44 , but variation at that scale was not explored here. ...
Understanding spatio-temporal changes in soil thickness and their natural and anthropogenic driving factors are essential for earth system modeling and natural resource conservation. It remains challenging to accurately quantify the spatial pattern of soil thickness, and there is no assessment of its temporal changes at the national scale across eco-climatic zones. Here we compiled a long-term (1950–2018), large-scale (conterminous United States of America) topsoil (A horizon, n = 37,712) and solum (22,409) thickness data to quantify their spatial and temporal variations using generalized additive models and selected chronosequences in land resource regions. Climate was found associated with the spatial distribution of soil thickness, and land use and erosion associated with its temporal variation. The A horizon and solum thickness displayed strong longitudinal patterns, correlated with soil moisture and temperature, respectively. Temporal changes in the thickness varied across land resource regions, affected by topography, land use, and erosion. Severe A horizon loss primarily occurred in Mollisols of the Central Great Plains, Alfisols on steep slopes, and soils under cropping. These findings enhanced our fundamental understanding of soil formation and biogeochemical cycles during the Anthropocene across scales and identified regions for conservation practices to reduce further topsoil loss.
... Trees are also a key component of the critical zone (Brantley et al., 2011;Zaharescu et al., 2020). Living trees result in a soil deepening and weathering front migration (Shouse and Phillips, 2016;Pawlik and Kasprzak, 2018;Phillips et al., 2019). Weathering processes, and especially weathering of sandstones, important in the context of the present study, has its own rich history of research within geomorphology and soil science (Turkington and Paradise, 2005;Warke et al., 2006). ...
Rock weathering drives both landform formation and soil production/evolution. The less studied biological component of weathering and soil production caused by tree root systems is the main focus of the present study. Weathering by trees, which likely has been important in soil formation since the first trees emerged in the middle and late Devonian, is accomplished through both physical and biological means, like acids excreted by plants and exudates from associated bacterial communities. However, these processes are relatively poorly known. We assessed the impact of tree roots and associated microbiota on the potential level of biological weathering. Three research plots were selected in two sandstone regions in Poland. Two plots were in the Stołowe Mountains (Złotno, Batorów), a tableland built of Cretaceous sandstones. The third plot (Żegiestów) was in the Sącz Beskidy Mountains, the Carpathians. Soil samples were taken from tree root zones of Norway spruces from predefined sampling positions. Soils from non-tree control positions were also sampled. Soil samples were a subject of laboratory analyses which included the content of Fe and Al (amorphous and labile forms), carbon (C), nitrogen (N), and soil pH. The microbial functional diversity of soil microorganisms was determined using the Biolog (EcoPlate) system. Rock fragments were collected for mineralogical and a subject of optical microscopy and cathodoluminescence analyses in order to examine their mineralogical composition.
Significant differences (pHolm-corrected < 0.05) between sample locations were found mostly for the Żegiestów plot: Soils at control positions differed from the crack and bulk soil sample positions in terms of C, N, C/N, and pH.
Tree roots were able to develop a great variety of sizes and forms by following the existing net of bedrock discontinuities and hillslope microrelief. They developed along the most accessible surfaces, and caused rockcliff retreat and scree slope formation. These two features can be considered as initial stages of soil production. Trees add to the complexity of the soil system and allow formation of rhizospheric soils, and horizons rich in organic matter which are zones of a high microbial activity. However, as our study shows, rock cracks with roots cannot be considered as zones of microbial weathering. In addition, C content and microbial activity decreases with depth but can stay on a high level along living and dead roots. When entering rock fractures, they change the intensity of biomechanical weathering and soil properties. The highest biological activity of microorganisms was found in the control samples.
Overall, tree roots do change the pattern of soil formation and explain the existing pattern of soil chemical properties, microbial activity, and potentially biological weathering intensity, and the intensity of those processes in correlation with root presence varies in space.
... The growth of trees and the process of tree death are inevitably associated with the movement of soil and changes in its chemical, physical and biological properties. The soil is moved, turned, mixed or blocked as the tree roots penetrate the bedrock through axial growth and intensify weathering and soil evolution (Shouse and Phillips, 2016). The radial growth of roots and stems displaces soil and shifts rock fragments (baumsteining, Phillips and Marion, 2006) and forms root or basal mounds (Hoffman and Anderson, 2013). ...
... Uprooted trees can affect hydrology by decreasing interception of rainfall and transpiration due to the disappearance of tree cover (Langohr, 1993). Furthermore, pits and mounds left by uprooted trees can influence surface hydrological connectivity and infiltration (Phillips et al., 2017;Shouse and Phillips, 2016;van der Meij et al., 2020). Soil animals, such as earthworms also influence infiltration through activities such as burrowing, ingesting, and digesting. ...
Biota are major drivers of geomorphological development. Vegetation and soil fauna act as ecosystem engineers, changing the environment through physical structures and individual activities such as litter layering, tree uprooting, and animal mounding. Furthermore, through varying litter quality triggering different degrees of animal bioturbation, they jointly drive soil and landscape development heterogeneously in space over time. Soil-landscape evolution models succeed in incorporating soil development with landscape evolution. However, the roles of biota and biotic interactions in these models are still underexposed. We cannot fully understand changes in environmental and soil-landscape systems without a proper appreciation of biotic processes. In this contribution, we first review the role of biota in pedological and geomorphological processes. Then we compare the coverage of soil and landscape processes of soil-landscape evolution models and outline the role of biota in current soil-landscape evolution models. Finally, we define five levels of soil-landscape evolution model complexity that allow increased detail in biota-soil-landscape interactions. The results show how vegetation characteristics and animal bioturbation in current models are simplified compared with geomorphological processes, and that the geomorphological impact of litter quality and quantity and interactions between vegetation and animals are not taken into consideration at all. As understanding the complex soil-landscape-biota system is fundamental in exploring the coevolution of ecosystem and landscape, it deserves more efforts to develop a biota-soil-landscape evolution model that does more justice to the manifold impacts of biota.
... In the close vicinity of 118 selected tree individuals, soil depth was evaluated according to Shouse and Phillips (2016). We applied five soil augers within a radius of 1 m around the tree and recorded the depth to the point of refusal. ...
The height growth of the trees depends on sufficient mechanical support given by the stem and an effective hydraulic system. On unstable slopes, tree growth is affected by soil pressure from above and potential soil erosion from below the position of tree. The necessary stabilization is then provided by the production of mechanically stronger wood of reduced hydraulic conductivity. Unfortunately, the interaction between tree growth (both radial and axial) and stabilization in the soil is still insufficiently understood. Therefore, in this study, we aimed to quantify the impact of hillslope dynamics on the degree of tree growth and hydraulic limitation, and the potential effect on tree height growth and growth plasticity. To evaluate this effect, we took four cores from 80 individuals of Quercus robur and Fraxinus excelsior and measured tree-ring widths (TRWs) and vessel lumen areas (VLAs). The tree heights were evaluated using a terrestrial laser scanner, and local soil depth was measured by a soil auger. Our data showed a significant limitation of the tree hydraulic system related with the formation of eccentric tree-rings. The stem eccentricity decreased with increasing stem diameter, but at the same time, the negative effect of stem eccentricity on conduit size increased with the increasing stem diameter. Even though this anatomical adaptation associated with the effect of stem eccentricity differed between the tree species (mainly in the different degree of limitations in conduit size), the trees showed an increase in the proportion of hydraulically inactive wood elements and a lowered effectiveness of their hydraulic system. In addition, we observed a larger negative effect of stem eccentricity on VLA in Quercus. We conclude that the stabilization of a tree in unstable soil is accompanied by an inability to create sufficiently effective hydraulic system, resulting in severe height-growth limitation. This affects the accumulation of aboveground biomass and carbon sequestration.
... Under this scenario, the taproots of falling trees essentially dragged the B horizon into the E and vice versa (Fig. 3c). Similar effects of complete soil profile inversion by tree uprooting which caused dramatic change in podzol morphology were observed in temperate forests (Schaetzl 1986;Shouse and Phillips 2016;Pawlik and Šamonil 2018). ...
Aims
We investigated morphological variations in podzols caused by changes in soil porosity and permeability upon the growth of large tree-roots in a tropical barrier island (Ilha Comprida, Brazil).
Methods
Soil morphology was described in a continuous lateral sequence of podzols on a 35 m-long cliff. A soil thin section was used to characterize organic matter (OM) accumulation and to estimate soil porosity, permeability, and saturated hydraulic conductivity (Ksat). Soil texture and the contents of organic carbon, Al, and Fe were determined for each pedogenic horizon containing large tree-roots. The evolution of podzol morphology was interpreted in the context of age determinations by optically stimulated luminescence and ¹⁴C.
Results
Taproots of cashew trees (Anacardium occidentale) penetrated the cemented Bhm horizon and the massive-clayey 2Cgj horizon. Aligned with the taproot, we found a vertical OM-band with lower porosity, permeability, and Ksat than the adjacent Bh and E horizons. Irregular or broken boundaries between the E and Bh horizons were caused by large tree-roots. While the maximum age of these podzols is 3390 ± 530 years, significant and rapid changes in the Bh-horizon morphology occurred within the lifetime of the cashew trees (~ 50 years).
Conclusions
The interplay between reduction in flow adjacent to large taproots and the enhanced vertical infiltration at depth has resulted into the development of irregular and broken boundaries between the E and Bh horizons. Because tree-roots alter both local soil porosity and water flow paths, they simultaneously cause the formation and degradation of podzol Bh-horizon.
... Some soil redistribution can occur as a consequence of creep or tree throw (Gabet et al., 2003). More importantly, tree throw creates local pits and mounds, which temporarily change hillslope hydrology and act as local hotspots for soil development due to a larger influx of water (Šamonil et al., 2015;Shouse and Phillips, 2016). These seemingly random processes create a high degree of heterogeneity in soil patterns, which shows little to no correlation with relief (Vanwalleghem et al., 2010). ...
Humans have substantially altered soil and landscape patterns and properties due to agricultural use, with severe impacts on biodiversity, carbon sequestration and food security. These impacts are difficult to quantify, because we lack data on long-term changes in soils in natural and agricultural settings and available simulation methods are not suitable for reliably predicting future development of soils under projected changes in climate and land management. To help overcome these challenges, we developed the HydroLorica soil–landscape evolution model that simulates soil development by explicitly modeling the spatial water balance as a driver of soil- and landscape-forming processes. We simulated 14 500 years of soil formation under natural conditions for three scenarios of different rainfall inputs. For each scenario we added a 500-year period of intensive agricultural land use, where we introduced tillage erosion and changed vegetation type.
Our results show substantial differences between natural soil patterns under different rainfall input. With higher rainfall, soil patterns become more heterogeneous due to increased tree throw and water erosion. Agricultural patterns differ substantially from the natural patterns, with higher variation of soil properties over larger distances and larger correlations with terrain position. In the natural system, rainfall is the dominant factor influencing soil variation, while for agricultural soil patterns landform explains most of the variation simulated. The cultivation of soils thus changed the dominant factors and processes influencing soil formation and thereby also increased predictability of soil patterns. Our study highlights the potential of soil–landscape evolution modeling for simulating past and future developments of soil and landscape patterns. Our results confirm that humans have become the dominant soil-forming factor in agricultural landscapes.
... Some soil redistribution can occur as a consequence of creep or tree throw (Gabet et al., 2003). More importantly, tree throw creates local pits and mounds, which temporarily change hillslope hydrology and act as local hotspots for soil development due to a larger influx of water (Šamonil et al., 2015;Shouse and Phillips, 2016). These seemingly random processes create a high degree of heterogeneity in soil patterns, which shows little to no correlation with relief (Vanwalleghem et al., 2010). ...
Soils provide numerous functions to support natural and human life. Soils and their functions develop over long timescales (decennia to millennia) under influence of environmental properties and drivers such as water flow, vegetation type and topography of the landscape. At the same time, these environmental properties develop too, often under influence of soil properties and processes. This interactive co-evolution of soils and the landscape forms a complex system that can aggravate, or diminish, rates and direction of soil-landscape evolution. In the Anthropocene, a proposed geological Epoch where humans are the main forcing actors, soil-landscape evolution changed substantially under influence of anthropogenic processes, such as deforestation and tillage. In current intensively managed agricultural landscapes in undulating settings, rates of anthropogenic erosion far exceed rates of natural soil development, leading to severe soil and land degradation. Sustainable nature-based land management is crucial to counteract this degradation, and to preserve and restore soil functions for the environment and future generations. The aim of my thesis is to identify and quantify how soils and landscape have evolved and possibly co-evolved during the transition from natural land cover to intensive land management in the Anthropocene.
The first part of this thesis (Chapter 2-3) aims at reconstructing the impact and rates of anthropogenic landscape change on complex agricultural fields. As study site I use the landscape laboratory CarboZALF D. CarboZALF D is a kettle-hole catchment of 4 ha with elevation differences up to 8 meters, located in north-eastern Germany. The catchment is characterized by complex small-scale topography, heterogeneities in the hydrological system and a long history of agricultural use. The colluvium in the closed kettle hole catchment provides a complete geo-archive of landscape change. In Chapter 2 we reconstruct the paleosurface of study site Carbo-ZALF-D prior to the anthropogenic erosion. We used an extensive dataset of soil descriptions, which enabled a detailed spatial estimate of erosion and deposition by estimating erosion based on soil profile truncations and deposition based on colluvium thickness. The paleosurface shows a high variation in topographic properties and suggests that natural soils and landscapes contain considerable spatial heterogeneity. In Chapter 3 we reconstruct the rates of deposition in Carbo-ZALF-D using Optically Stimulated Luminescence (OSL) dating. We present a novel methodology to apply OSL dating in colluvial sediments, where the soil chronology gets disturbed by reworking by ploughing after deposition. Our results show a 100-fold increase in deposition rates, starting around 5000 years ago. This increase does not solely represent increased erosion in the catchment, but is also caused by indirect effects of agricultural drainage. The kettle hole shows a complex spatiotemporal pattern of colluvial infilling and landscape evolution, which we were only able to reconstruct using a high OSL sampling density and extensive soil geomorphic research.
The second part of this thesis aims at simulating the evolution of soils and landscapes under varying climatic and anthropogenic forcing. In Chapter 4 we review the role of water as dominant driver in natural soil and landscape evolution and its potential as driver in simulations with soil-landscape evolution models (SLEMs). Water plays a pivotal role in soil and landscape evolution, by transporting and transforming soil material and facilitating vegetation growth. In turn, surface and subsurface flow paths of water are controlled by soil and landscape properties. The co-evolution of soils, topography and the hydrological system is essential for understanding the response of soils and landscapes to changes in climate. However, this co-evolution can currently not be simulated over long timescales with SLEMs due to several conceptual and methodological challenges. We provide partial solutions for these challenges. In Chapter 5 we utilize these partial solutions to develop our SLEM HydroLorica. HydroLorica simulates soil and landscape evolution with various dynamic drivers such as water flow, vegetation type and land use. We included additional essential processes such as tree throw, soil creep and tillage. We use HydroLorica to simulate the evolution of soils and landscape under various rainfall and land-use scenarios for an artificial undulating landscape. The results show that in natural systems, rainfall amount is the dominant factor controlling soil and landscape heterogeneity, while for agricultural systems landform explains most of the variation. The cultivation of natural landscapes increases soil heterogeneity, but also increases correlations between soil and terrain properties. Our results confirm that humans have become the dominant soil forming factor in intensively managed landscapes.
In the third part of this thesis (Chapter 6), I synthesize the findings from the research chapters to meet the objectives of this thesis. I critically evaluate the developed reconstruction methods in Chapters 2 and 3 and compare them with other potential methods. The development of HydroLorica in Chapters 4 and 5, with water flow as explicit driver and with increased process coverage, is a big step forward in soil-landscape evolution modelling. A combination of reconstruction and simulation methods is essential for developing and testing hypotheses of soil-landscape co-evolution. Soil-landscape evolution in natural and intensively managed landscapes have different characteristics due to different driving forces and dominant processes. In natural landscapes, soils develop to patterns where individual soils might be disturbed occasionally, but where the average properties are stable. In intensively managed landscapes, disturbance rates are much higher than in natural settings. As a consequence, slowly developing soil properties degrade, while fast-developing soil properties can form a new equilibrium. The co-evolution of soils and landscapes that occurs in natural settings is often controlled by biotic processes. In agricultural settings, humans control vegetation type and aggravate erosion processes through tillage. As a consequence, co-evolution does not occur in the sense that it does in natural settings, because interactions between landscape components are missing. However, the management of soils and landscapes is often adapted to counteract unintended changes to soils and landscapes under earlier management. In intensively managed landscapes, land management may thus co-evolve with the rest of the landscape.
... Where plant roots encounter bedrock they promote both chemical and biomechanical weathering, and may locally thicken the regolith. In forests where soil or regolith depth is less than tree rooting depth, this may result in increasing local spatial variability in depth to bedrock, as trees may preferentially reoccupy the same patches (Phillips and Marion, 2004;Phillips, 2008;Shouse and Phillips, 2016;Pawlik and Kasprzak, 2018;Pawlik and Samonil, 2018). However, due to continued weathering and gradual overall regolith thickening in some cases, the overall thickness may exceed typical rooting depths, with eventual convergence of thicknesses (Pawlik and Kasprzak, 2018;Pawlik and Samonil, 2018;Phillips, 2018). ...
A distinct boundary between unweathered and weathered rock that moves downward as weathering proceeds—the weathering front—is explicitly or implicitly part of landscape evolution concepts of etchplanation, triple planation, dynamic denudation, and weathering- and supply-limited landscapes. Weathering fronts also figure prominently in many models of soil, hillslope, and landscape evolution, and mass movements. Clear transitions from weathered to unweathered material, increasing alteration from underlying bedrock to the surface, and lateral continuity of weathering fronts are ideal or benchmark conditions. Weathered to unweathered transitions are often gradual, and weathering fronts may be geometrically complex. Some weathering profiles contain pockets of unweathered rock, and highly modified and unmodified parent material at similar depths in close proximity. They also reflect mass fluxes that are more varied than downward-percolating water and slope-parallel surface processes. Fluxes may also be upward, or lateral along lithological boundaries, structural features, and textural or weathering-related boundaries. Fluxes associated with roots, root channels, and faunal burrows may potentially occur in any direction. Just as pedology has broadened its traditional emphasis on top-down processes to incorporate various lateral fluxes, studies of weathering profiles are increasingly recognizing and incorporating multidirectional mass fluxes. Examples from karst systems may also be useful, where concepts of laterally continuous weathering fronts, rock-regolith boundaries, and water tables; and an assumption of dominantly diffuse downward percolation are generally inapplicable. We also question the idea of a single weathering front, and of a two-stage process of weathering rock to regolith, and transforming regolith to soil. In many cases there appears to be three stages involving conversion of bedrock to weathered rock, weathered rock to regolith, and regolith to soil.
... Berndt and Gibbons (1958) have found that the roots of the same tree species growing on different bedrock have different root systems. In addition, due to the fact that black pine roots are a taproot system, it is possible that the root length is too high (Shouse and Phillips, 2016) (Table 2 and 4). Kodrík and Kodrík (2002) have noted that the number of roots with a diameter of 3-10 cm is an important factor for tree static stability and the roots with a diameter of 10 cm are most important for tree stability. ...
... These locally thicker soils may provide favorable sites for future tree establishment, providing another positive feedback. Evidence supporting these interrelationships has been reported from studies in central Kentucky by Martin (2006), Phillips (2016b, 2018b, and Shouse and Phillips (2016). ...
Nine axioms for interpreting landscapes from a geoscience perspective are presented, and illustrated via a case study. The axioms are the self-evident portions of several key theoretical frameworks: multiple causality; the law–place–history triad; individualism; evolution space; selection principles; and place as historically contingent process. Reading of natural landscapes is approached from a perspective of place formation. Six of the axioms relate to processes or phenomena: (1) spatial structuring and differentiation processes occur due to fluxes of mass, energy, and information; (2) some structures and patterns associated with those fluxes are preferentially preserved and enhanced; (3) coalescence occurs as structuring and selection solidify portions of space into zones (places) that are internally defined or linked by mass or energy fluxes or other functional relationships, and/or characterized by distinctive internal similarity of traits; (4) landscapes have unique, individualistic aspects, but development is bounded by an evolution space defined by applicable laws and available energy, matter, and space resources; (5) mutual adjustments occur between process and form (pattern, structure), and among environmental archetypes, historical imprinting, and environmental transformations; and (6) place formation is canalized (constrained) between clock-resetting events. The other three axioms recognize that Earth surface systems are always changing or subject to change; that some place formation processes are reversible; and that all the relevant phenomena may manifest across a range of spatial and temporal scales. The axioms are applied to a study of soil landscape evolution in central Kentucky, USA.
... The studies that have been done have suggested that these processes can significantly affect hillslope processes. According to Bennie (1991), roots penetrating the soil and belowground rock can produce pressures of about 1.45 MPa, and significant combined biomechanical and biochemical influences can contribute to weathering processes and deepening of the soil and regolith (Shouse and Phillips, 2016;Pawlik et al., 2016). However, soil close to the surface is lifted up by radial growth of roots and so-called root mounds are formed (Hoffman and Anderson, 2013). ...
The role of biomechanical effects of trees (BETs) in ecosystem and landscape dynamics is poorly understood. In this study, we aim to (i) describe a widely applicable methodology for quantifying the main BET in soil, and (ii) analyze the actual frequencies, areas and soil volumes associated with these effects in a mountain temperate old-growth forest.
The research took place in the Boubínský Primeval Forest in the Czech Republic; this forest reserve, predominated by Fagus sylvatica L. and Picea abies (L.) Karst., is among the oldest protected areas in Europe. We evaluated the effects of 4000 standing and lying trees in an area of 10.2 ha from the viewpoint of the following features: tree uprooting, root mounding, bioprotection, trunk baumsteins (rock fragments displaced by trunk growth), root baumsteins, stump hole infilling, trunk and root systems displacements, depressions formed after trunk fall, stemwash, and trunkwash.
BETs were recorded in 59% of standing and 51% of lying dead trees (excluding the pervasive soil displacement by thickening trunks and roots and the infilling of decayed stumps). Approximately one tenth of the trees showed simultaneous bioprotective and bioerosion effects. Different tree species and size categories exhibited significantly different biomechanical effects.
A bioprotective function was the most frequent phenomenon observed, while treethrows prevailed from the viewpoint of areas and soil volumes affected. The total area influenced by the BETs was 342 m2ha-1. An additional 774 m2ha-1 were occupied by older treethrow pit-mounds with already decayed uprooted trunks. The total volume of soil associated with the studied phenomena was 322 m3ha-1, and apart from treethrows, volumes of the living and decaying root systems and bioprotective functions predominated. Other processes were not so frequent but still significant for biogeomorphology.
... Šamonil et al., 2009; Bobrowsky and Loiko, 2016), and only a few were focused on BETs other than treethrows (Phillips and Marion, 2006). While a few studies have included considerations of mass displacement by trunk growth, stump infilling, and local regolith thickening (e.g., Phillips and Marion, 2006;Shouse and Phillips, 2016), this is the first to include estimates of total root volume. Although we did not evaluate all the possible biomechanical effects of trees, our study should provide the most complete picture so far of the biomechanical influence of trees on the soil in temperate forests. ...
Tree breakage and uprooting are two possible scenarios of tree death that have differing effects on hillslope processes. In this study we aimed to (i) reveal the long-term structure of the biomechanical effects of trees (BETs) in relation to their radial growth and tree death types in four old-growth temperate forests in four different elevation settings with an altitudinal gradient of 152‐–1105 m a.s.l., (ii) quantify affected areas and soil volumes associated with the studied BETs in reserves, and (iii) derive a general model of the role of BETs in hillslope processes in central European temperate forests.
We analyzed the individual dynamics of circa 55,000 trees in an area of 161 ha within four old-growth forests over 3‐–4 decades. Basal tree censuses established in all sites in the 1970s and repeated tree censuses in the
1990s and 2000s provided detailed information about the radial growth of each tree of DBH ≥ 10 cm as well as about types of tree death. We focused on the quantification of: (i) surviving still-living trees, (ii) new recruits, (iii) standing dead trees, (iv) uprooted trees, and (v) broken trees. Frequencies of phenomena were related to affected areas and volumes of soil using individual statistical models.
The elevation contrasts were a significant factor in the structure of BETs. Differences between sites increased from frequencies of events through affected areas to volumes of soil associated with BETs. An average
2.7 m3 ha‐− 1 year‐− 1 was associated with all BETs of the living and dying trees in lowlands, while there was an average of 7.8 m3 ha‐− 1 year‐− 1 in the highest mountain site. Differences were caused mainly by the effects of dying trees. BETs associated with dead trees were 7‐–8 times larger in the mountains. Effects of dying trees and particularly treethrows represented about 70% of all BETs at both mountain sites, while it was 58% at the highland site and only 32% at the lowland site. Our results show a more significant role of BETs in hillslope processes including slope denudation in the mountains. We would expect a significant decrease of the biogeomorphic effect of trees in managed forests, but with a greater relative effect in mountains.
... In a short--term perspective biogenic transport processes are apparently stochastic, and discrete in space and time (Roering et al., 1999;Gabet and Mudd, 2010). Tree uprooting is often cited as an example, though in at least some cases tree establishment and uprooting is self--reinforcing and non--random (Šamonil et al. 2014; Shouse and Phillips, 2016). However, over longer time scales the continuous activity of such discrete biologically driven hillslope processes are essentially diffusive (Carson and Kirkby, 1972;Preston, 2004). ...
Razula forest preserve in the Carpathian Mountains of the Czech Republic is an unmanaged forest that has not been logged or otherwise anthropically disturbed for at least 83 years, preceded by only infrequent selective logging. We examined this 25 ha area to determine the dominant geomorphological processes on the hillslope. Tree uprooting displaces about 2.9 m³ of soil and regolith per year, representing about 1.5 uprooted trees ha− 1 yr− 1, based on forest inventory records dating back to 1972, and contemporary measurements of displaced soil and pit-mound topography resulting from uprooting. Pits and mounds occupy > 14% of the ground surface. Despite typical slope gradients of 0.05 mm− 1, and up to 0.41, little evidence of mass wasting (e.g., slump or flow scars or deposits, colluvial deposits) was noted in the field, except in association with pit-mound pairs. Small avalanche and ravel features are common on the upslope side of uproot pits. Surface runoff features were rare and poorly connected, but do include stemwash erosion associated with stemflow. No rills or channels were found above the valley bottom area, and only small, localized areas of erosion and forest litter debris indicating overland flow. Where these features occurred, they either disappeared a short distance downslope (indicating infiltration), or indicate flow into tree throw pits. Surface erosion is also inhibited by surface armoring of coarse rock fragments associated with uprooting, as well as by the nearly complete vegetation and litter cover. These results show that the combination of direct and indirect impacts of tree uprooting can dominate slope processes in old-growth, unmanaged forests. The greater observed expression of different hillslope processes in adjacent managed forests (where tree uprooting dynamics are blocked by management activities) suggests that human interventions can change the slope process regime in forest ecosystems.
... Additionally, several soil and regolith studies have shown that highly localized, pedon-scale biogeomorphic impacts may profoundly increase local soil variability, particularly in forests (Crowther, 1987;Estrada-Medina et al., 2013;Shouse and Phillips, 2016). These effects are often persistent and result in divergent pedogenesis, rather than being commensurate with the time scale of the biotic effects. ...
Soil diversity and complexity is influenced by a variety of factors, and much recent research has been focused on interpreting or modeling complexity based on soil-topography relationships, and effects of biogeomorphic processes. We aimed to (i) describe local soil diversity in one of the oldest forest reserves in Europe, (ii) employ existing graph theory concepts in pedocomplexity calculation and extend them by a novel approach based on hypothesis testing and an index measuring graph sequentiality (the extent to which soils have gradual vs. abrupt variations in underlying soil factors), and (iii) reveal the main sources of pedocomplexity, with a particular focus on geomorphic controls.
Interflow, throughflow and subsurface stormflow are interchangeable terms that refer to the lateral subsurface flow above a restricting layer of lower hydraulic conductivity that occurs during and following storm events. Interflow (used here) is a more dominant process in steeper catchments with high infiltration capacity soils overlying a more impermeable soil or geologic layer. Interflow as a runoff process was first recognised in the early 1900s, yet hydrologists still struggle to predict its occurrence, persistence, importance, interaction with other streamflow generation processes, and potential to connect to valleys and streams during and following storms. We review the history of interflow research and address some of the challenges in understanding its role in runoff production. We argue that characterising the controls on interflow initiation and occurrence relies on detailed field observations of subsurface properties, which exist only in limited experimental settings. This data shortcoming contributes to our inability to predict interflow or determine its contribution to streamflow more broadly. There remain many opportunities to advance our understanding of interflow that include both modelling and experimental or observational approaches in hydrology.
In this article, we track the evolution of fluvial biogeomorphology from the middle of the 20th century to the present. We consider the emergence of fluvial biogeomorphology as an interdisciplinary research area that integrates knowledge drawn primarily from fluvial geomorphology and plant ecology, but with inputs from hydrology and landscape ecology. We start by assembling evidence for the emergence of the field of fluvial biogeomorphology with a keyword search of the Web of Science and a detailed analysis of papers published in two scientific journals: a geomorphology journal—Earth Surface Processes and Landforms; a multidisciplinary river science journal—River Research and Applications. Based on this evidence, we identify three distinct time periods in the development of fluvial biogeomorphology: the ‘early years’ before 1990; the transitional decade of the 1990s; and the period of rapid expansion and diversification in themes, methods and investigation scales since 2000. Because the literature is vast, we can only summarize developments in each of these time periods, but we refer to recent in‐depth reviews and conceptual perspectives on relevant topics. Thus, rather than a full and deep review, we present an annotated bibliographic overview of the development of fluvial biogeomorphology, whereby the text describes broad trends but is supported by tables of citations that can deliver greater detail. We end with a brief consideration of likely future developments.
Darwinian natural selection acting on individuals is one of only several types of selection influencing landscape evolution. Ecological filtering and abiotic selection (including the least action principle and preferential flows) apply. The overarching principle is one of efficiency selection, whereby more efficient, stable, and durable forms, structures, patterns, networks, and flux pathways are more likely to occur, grow, and persist than less efficient ones. Particularly important forms are gradient selection, favoring steeper and faster flow paths; resistance selection, whereby more resistant features are preferentially preserved; biogeochemical selection, which favors more rapid elemental cycling; network selection, which makes more efficient flux and interaction networks more likely; and thermodynamic selection, reflecting the advantages of energy use efficiency. Efficiency selection is highly local, however, one of several reasons that landscapes and environmental systems are not always inevitably becoming more efficient overall. A case study illustrating selection principles is given.
Various methods have been used to measure or estimate pedogenic processes that are responsible for the differentiation of a soil profile. In this chapter, the modelling and quantification of these processes will be reviewed and discussed.
The state of an Earth surface system (ESS) is determined by three sets of factors: Laws, place, and history. Laws (L = L1, L2, . . . , Ln) are the n general principles applicable to any such system at any time. Place factors (P = P1, P2, . . . , Pm) are the m relevant characteristics of the local or regional environment. History factors (H = H1 , H2, . . . , Hq) include the previous evolutionary pathway of the ESS, its stage of development, past disturbance, and initial conditions. Geoscience investigation may focus on laws, place, or history, but ultimately all three are necessary to understand and explain ESS. The LPH triad is useful as a pedagogical device, illustrated here via application to explaining the world's longest cave (Mammoth Cave, KY). Beyond providing a useful checklist, the LPH framework provides analytical traction to some difficult research problems. For example, studies of the avulsions of three southeast Texas rivers showed substantial differences in avulsion regimes and resulting alluvial morphology, despite the proximity and superficial similarity of the systems. Avulsions are governed by the same laws in all cases [L(A) = L(B) = L
A high degree of soil variability over short distances and small areas is common, particularly in forest soils. This variability is sometimes, but not always, related to readily apparent variations in the environmental factors that control soil formation. This study examines the potential role of biomechanical effects of trees and of lithological variations within the parent material in explaining soil diversity in the Ouachita Mountains of Arkansas. The diversity of soils on Ouachita sideslopes is high, and the soil series vary primarily with respect to morphological properties such as soil thickness and rock fragment content. Soils vary considerably within small more-or-less homogeneous areas, and richness-area analysis shows that the overall pattern of pedodiversity is dominated by local, intrinsic (within-plot) variability as opposed to between-plot variability. This is consistent with variation controlled mainly by individual trees and local lithological variations. Given the criteria used to distinguish among soil types, biomechanical as opposed to chemical and hydrological effects of trees are indicated. Results also suggest divergent evolution whereby the pedologic effects of trees are large and long-lived relative to the magnitude of the initial effects and lifespan of the plants.
Background and Aims
With limited soil depth in northern Yucatán (<30 cm), roots grow deeper through rock fractures and dissolution karst features (i.e., cavities, including soil-filled ones known as soil pockets). We assessed the importance of limestone bedrock and dissolution karst features on tree root growth.
Methods
Fieldwork was conducted in a limestone quarry where the relative proportions of rock matrix, empty cavities, and soil pockets were calculated by observing recently exposed walls. Physical properties of rocks, topsoil, and soil pockets were analyzed. Root distribution was assessed and roots identified.
Results
Soil pockets represented 9% of the rock matrix. The physical properties of rock layers were different with depth. Available water capacity is higher in soil (0.11 m-3 m-3) than in rock layers (<0.05 m-3 m-3). But potential available water was much higher in subsurface features than top soil.
Conclusions
Dissolution karts features allow roots to grow deep into the bedrock, tapping water stored there. Although the limestone upper layer in northern Yucatan is highly restrictive to root growth, subsurface limestone layers and soil pockets are not restrictive and can hold important amounts of water.
In 1877, G. K. Gilbert reasoned that bedrock erosion is maximized under an intermediate soil thickness and declines as soils become thinner or thicker. Subsequent analyses of this “humped” functional relationship proposed that thin soils are unstable and that perturbations in soil thickness would lead to runaway thinning or thickening of the soil. To explore this issue, we developed a numerical model that simulates the physical weathering of bedrock by root fracture and tree throw. The coupled biogeomorphic model combines data on conifer population dynamics, rootwad volumes, tree throw frequency, and soil creep from the Pacific Northwest (USA). Although not hardwired into the model, a humped relationship emerges between bedrock erosion and soil thickness. The magnitudes of the predicted bedrock erosion rates and their functional dependency on soil thickness are consistent with independent field measurements from a coniferous landscape in the region. Imposed perturbations of soil erosion during model runs demonstrate that where bedrock weathering is episodic and localized, hillslope soils do not exhibit runaway thinning or thickening. The pit-and-mound topography created by tree throw produces an uneven distribution of soil thicknesses across a hillslope; thus, although episodes of increased erosion can lead to temporary soil thinning and even the exposure of bedrock patches, local areas of thick soils remain. These soil patches provide habitat for trees and serve as nucleation points for renewed bedrock erosion and soil production. Model results also suggest that where tree throw is a dominant weathering process, the initial mantling of bedrock is not only a vertical process but also a lateral process: soil mounds created by tree throw flatten over time, spreading soil over bedrock surfaces.
Traditional conceptual models of landscape evolution view topography as an outcome of endogenic forces (uplift) working against exogenic forces of denudation. The energy considerations of these concepts have focused on the conver-sion of the potential energy of landscape relief to kinetic energy. The concept of the biosphere as a planetary membrane for capturing and converting solar energy, coupled with the critical geomorphic role of biota, call for a consideration of biotic contribu-tions to geomorphic work. A review of estimates of global rates of kinetic energy of denudation and uplift, and net primary production (NPP) indicates that the energy density of NPP is, on average, three to seven orders of magnitude greater than the others. If even a tiny fraction of NPP is geologically significant, then the biological subsidy to the energy of landscape evolution must be considered on a par with that of geophysical and geochemical phenomena. A case study in eastern Kentucky shows that even if only 0.1 percent of NPP is geomorphically significant, it still far exceeds the energy inputs from uplift and conversion of potential to kinetic energy by denudation. This is unlikely to be unique, though the relative importance of biological and geophysical processes must obviously vary with climate, tectonic setting, and other factors. Results indicate that, particularly where biological activity is significant, geomorphic work performed by biota may be greater than that associated with endogenic processes and with die kinetic energy of denudation.
The architecture of a tree root system may influence its ability to withstand uprooting by wind loading. To determine how
the root branching pattern may alter the anchorage efficiency of a tree, artificial model root systems with different topologies
and branching angles were built. The root systems were embedded at various depths in wet sand and the pull-out resistance
measured. A model to predict the uprooting resistance from the data collected was designed, allowing predictions of anchorage
strength with regards to architecture. The dominant factors influencing pull-out resistance were the depth and length of roots
in the soil. The most efficient type of branching pattern predicted by the program was one with an increased number of roots
deep in the soil. The optimum branching angle most likely to resist pull-out is a vertical angle of 90° between a lateral
and the main axis. The predicted mechanically optimal radial angle between a lateral branch and its daughter is between 0
and 20°. Values of branching angle are compared with those measured in real woody root systems of European larch and Sitka
spruce.
Interpretations of regolith and soil thickness in the context of landscape evolution are typically based on the notion that thickness is controlled by the interaction of weathering rates and erosion and tuned to topography. On sideslopes of the Ouachita Mountains, Arkansas, however, there is a high degree of local spatial variability that is largely unrelated to topography. This indicates nonequilibrium in the sense that there is no evidence of a balance between rates of weathering and removal, as is postulated in some conceptual models in geomorphology and pedology. Johnson's soil thickness model is applied as an alternative to interpret local variations in regolith thickness. At the study sites, regolith thickness is not generally related to slope, curvature, elevation, or pedogenic development in the solum. This indicates that variability in thickness is related chiefly to processes and controls acting in the lower regolith, below the solum. The primary controls of variability are local lithological variation, variable structural resistance associated with fractures and bedding planes in strongly tilted Paleozoic sedimentary parent material, and point-centered pedological influences of trees. A steady state regolith may be relatively rare. Results of this study suggest that an equilibrium regolith thickness is most likely in uniform lithology with a high degree of lithologic purity, less likely in interbedded sedimentary rocks, and more unlikely still if the latter are titled and fractured. Equilibrium thickness would also be more likely where the effects of bioturbation are more areally uniform (as opposed to the point-centered effects of individual trees) and where the biomantle is above the weathering front.
Plants and animals exploit the soil for food and shelter and, in the process, affect it in many different ways. For example, uprooted trees may break up bedrock, transport soil downslope, increase the heterogeneity of soil respiration rates, and inhibit soil horizonation. In this contribution, we review previously published papers that provide insights into the process of bioturbation. We focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production. Using geometrical relationships and data from others' work, we derive simple sediment flux equations for tree throw and root growth and decay.
The complex interplay of biological, physical, and chemical processes in pedogenesis and hillslope evolution limits our ability to predict and interpret landscape dynamics. Here, we synthesize a suite of observations from the steep, forested Oregon Coast Range to analyze the role of trees in topographic modification and bedrock-to-soil conversion. Using topographic data derived from airborne lidar, we demonstrate that the topographic signature of forest-driven soil and bedrock disturbance is pervasive. For length scales greater than 7.5 m, the land surface is defined by ridge-valley landforms, whereas smaller scales are dominated by pit-mound features generated by the turnover of large coniferous trees. From field surveys, the volume of bedrock incorporated in overturned rootwads increases rapidly with diameter for large conifers, reflecting the highly nonlinear increase in root biomass with tree diameter. Because trees younger than 60 years detach negligible bedrock, short timber harvest intervals may limit the extent to which root systems penetrate bedrock and facilitate bedrock fracturing and biogeochemical weathering. Using ground-penetrating radar, we show that the rootwads of large trees root achieve substantial penetration (1–3 m) into shallow bedrock. The radar transects also reveal that variations in soil thickness have characteristic length scales of 1 to 5 m, consistent with the scale of large rootwads, indicating that both the landscape surface and soil-bedrock interface exhibit a biogenic imprint. In our study area, the residence time of bedrock within dense rooting zones directly below large trees is similar to the time required for trees to occupy the entire forest floor through multiple cycles of forest succession, suggesting that biological modification of shallow bedrock is ubiquitous. Given increases in erosion rate, the ability of roots to initiate soil production may decline as bedrock exhumation through the biotic zone is rapid relative to the time required for successive forests and their associated root systems to fracture bedrock. As a result, in rapidly eroding terrain the coupling between biotic and abiotic weathering processes (such as exfoliation fracturing) may dictate the maximum rate of bedrock-to-soil conversion.
Large portions of the world are characterized by shallow soil underlain by weathered bedrock or cemented soil horizons. The implications of this substrate condition for ecohydrological processes have not been systematically explored, but misrepresentation in models could have profound consequences for climate prediction and global vegetation modelling. An issue of particular uncertainty is the characterization of water storage for these regions. A limited number of case studies have shown that plant water uptake is not restricted to shallow soils but can involve uptake from rock layers below. The mechanisms governing root–rock interactions are only beginning to be investigated. Research is needed to further characterize the dynamics of water recharge and depletion in weathered bedrock, to develop a better understanding of plant adaptations and rooting patterns required for effective use of bedrock-stored water, and to explore consequences for below-ground competition. Copyright © 2010 John Wiley & Sons, Ltd.
The influence of root morphology and soil type on the mechanical behaviour of tree anchorage was investigated through numerical
modelling.We developed a simple computer program to construct three-dimensional virtual root architectural patterns. This
tool was used to build four schematic patterns: heart-, tap-, herringbone- and plate-like root systems. Each of these rooting
types was characterised by specific branching characteristics. However, the total volume (proportional to the wood biomass)
and material properties were kept constant. The finite element method was used to calculate the mechanical response of root/soil
systems when the stem was subjected to bending forces. The overturning resistance of the four schematic root patterns was
determined in four different idealistic soil types. These soils were based on Mohr–Coulomb plasticity models. Results showed
that soil internal friction modified the position of the rotation axis during tilting of the root/soil plate. Rooting depth
was a determinant parameter in sandy-like soils. Overturning resistance was greatest in heart- and tap-root systems whatever
the soil type. However, the heart root system was more resistant on clay-like soil whereas the tap root system was more resistant
on sandy-like soil. Herringbone and plate root systems were twice as less resistant on clay soils and 1.5 times less resistant
on sandy soils when compared to heart and tap-like structures.
A high degree of soil variability over short distances and small areas is common, particularly in forest soils. This variability is sometimes, but not always, related to readily apparent variations in the environmental factors that control soil formation. This study examines the potential role of biomechanical effects of trees and of lithological variations within the parent material in explaining soil diversity in the Ouachita Mountains of Arkansas. The diversity of soils on Ouachita sideslopes is high, and the soil series vary primarily with respect to morphological properties such as soil thickness and rock fragment content. Soils vary considerably within small more-or-less homogeneous areas, and richness–area analysis shows that the overall pattern of pedodiversity is dominated by local, intrinsic (within-plot) variability as opposed to between-plot variability. This is consistent with variation controlled mainly by individual trees and local lithological variations. Given the criteria used to distinguish among soil types, biomechanical as opposed to chemical and hydrological effects of trees are indicated. Results also suggest divergent evolution whereby the pedologic effects of trees are large and long-lived relative to the magnitude of the initial effects and lifespan of the plants.
The role of tree uprooting in soil formation was evaluated using an analysis of scientific articles published from 1940 to 2009. The potential for generalizing these published results across a range of regions, forest and soil types was assessed. We focused on the following topics: ecological conditions within pit–mound microsites; the area of pit–mounds in different landscapes; the age of pit–mounds; rotation period; and the effect of tree uprooting on soil properties, including the absence of pit–mound dynamics in forests that have been managed long-term. These topics were analysed on the spatial scales of the pit–mound, forest stand, and landscape.
This paper aims at reviewing the ecological effects of windthrow and the processes by which the structure and composition of the boreal forest are affected. The windthrow problem has been investigated at different levels: landscape; forest community; and fallen tree ecosystem. All original data are from the natural, protected, uneven-aged boreal spruce forests of the central Russian Plain. Mapping of vegetation was used to detect windthrow processes in primary forest communities. The scales of windthrow gaps in space and time determine the patch structure of the forest ecosystems. The main result of this phenomenon is the occurrence of gap-phase dynamics in forest communities. The development of gaps is very important for the survival of small- and broad-leaved trees in boreal coniferous forests.
Bedrock surfaces in the Ouachita Mountains, Arkansas, exposed by spillway construction and which had not previously been subjected to surface weathering environments, developed 15–20 cm thick soil covers in less than three decades. All open bedrock joints showed evidence of weathering and biological activity. Rock surfaces and fragments also showed evidence of significant weathering alteration. The results suggest a soil production function whereby weathering and increases in thickness are initially rapid. The rapid initial rate (5 to 10 mm year− 1) is facilitated by a weathering-favorable regional climate, local topography favoring moisture and sediment accumulation, and aggressive vegetation colonization. The ages of the trees on the bedrock benches suggests that a short period (< 10 years) of pedogenic site preparation is necessary before trees can become established. Initial chemical weathering within newly-exposed rock fractures in resistant sandstone strata and chemical weathering of weak shale layers, coupled with accumulation of organic and mineral debris in fractures and microtopographic depressions facilitates plant establishment, which accelerates local weathering rates.
The interaction of geomorphic and ecologic landscape components has been largely conceptualized as independent. In one direction, geomorphic processes and landforms shape the distribution of biota. Conversely, in the other direction, biota modify geomorphic processes and landforms. Increasingly, the interactions between geomorphic and ecological components are more circular and developmentally intertwined. In this paper, I integrate these two independent perspectives within the framework of complexity theory. I outline four themes that characterize complex systems in biogeomorphology: multiple causality and the concept of recursivity, the influence of organisms that function as ecosystem engineers, the expression of an ecological topology, and ecological memory. Implicit in all of these themes is the recognition that biogeomorphic systems are open and path dependent. They may exhibit a range of assembly states, from self-reinforcing stability domains to more transient configurations of organisms and environment.
Soil profile thickness of mineral soils reflects the relative amounts of deepening, upbuilding, and removals that have occurred during the evolution of the soil. Deepening is the downward migration of the lower soil boundary into fresh unweathered material. Upbuilding refers mainly to surface sedimentation and subsequent pedogeneticization of allochthonous deposits, but also includes autochthonous organic matter production in mineral soils. Removals include material losses via erosion, mass wasting, pervection and leaching. The relationships of these processes are examined in the context of three pathways of soil evolution progressive, regressive, and static pedogenesis. Using these concepts, soil thickness processes are traced in a hypothetical model of a dynamically evolving surface soil. Three examples of actual landscapes, two from California and one from the Sahara, are given and linked to the hypothetical model to augment a conceptual framework for viewing soil thickness processes as aspects of pedogenesis. -from Author
▪ Abstract Plants and animals exploit the soil for food and shelter and, in the process, affect it in many different ways. For example, uprooted trees may break up bedrock, transport soil downslope, increase the heterogeneity of soil respiration rates, and inhibit soil horizonation. In this contribution, we review previously published papers that provide insights into the process of bioturbation. We focus particularly on studies that allow us to place bioturbation within a quantitative framework that links the form of hillslopes with the processes of sediment transport and soil production. Using geometrical relationships and data from others' work, we derive simple sediment flux equations for tree throw and root growth and decay.
Boles of tall trees with large diameters behave as cantilever beams possessing great strength and the capacity for exerting tremendous leverage at the point of support or fulcrum. When trees are uprooted by wind they may move, both vertically and horizontally, rocks having a volume of as much as 50 cu. ft. and a weight of around 4 1/4 tons. Uprooting of trees contributes to downslope movement of the soil and rock mantle and locally may initiate erosion of the gully type. Some of the effects of soil and rock movement by uprooting trees are similar to those resulting from periglacial frost heaving.
Over a period of 25 seasons, wind throw of trees larger than 25.4 cm dbh at Warren Woods, Michigan, USA, was at the rate of 0.2 trees ha-1 yr-1. Beeches Fagus grandifolia Ehrhart larger than 76 cm dbh were more susceptible than smaller trees. In forests where the subcanopy trees are heavily dominated by sugar maple Acer saccharum Marshall and beech, wind throw appears not to maintain canopy diversity; nearly all the replacement trees for current gaps are these two species. Maintenance of canopy diversity in such mature forests is probably by more extensive and severe perturbation. Three to five thousand years would be required for the total soil surface to be disturbed by wind throw. /// В течение 25 сезонов ветровал деревьев диаметром более 25,4 см составлял в Уоррен Вудз (Мичиган, ЧША) 0,2 дерева/га/год. Ьуки Fagus grandifolia Ehrhart толще 76 мм более чувствительны, чем более томкие деревья. В лесях, где во втором ярусе доминирует клен чахарный Acer saccharum Marshall и бук, ветровал не поддерживае разнообразие древостоя. Почти все промежуткм замещаются деревьями именно этих двух видов. Поддержание разнообразия древостоя в таких зрелых лесах является результатом более сильных пертурбаций. Требуется 3-5 тыс. лет для нарушения всей поверхности почвы ветравалом.
Midstory removal can enhance the development of oak advance reproduction on higher quality sites; however, the long-term response of oak species common to intermediate quality sites is relatively unknown. Within the western edge of the Northern Cumberland Plateau, we investigated the
7-year response of natural and underplanted black oak (Quercus velutina Lamb.), white oak (Quercus alba L.), and natural red maple (Acer rubrum L.) reproduction following midstory removal. After implementing midstory removal on four sites with an adjacent unaltered control, we compared survival,
size, and competitive position of black oak, white oak, and red maple seedlings after seven growing seasons. We found that survival, mean height, and mean groundline diameter of oak and red maple seedlings were generally higher following midstory removal. We also characterized oak competition
by observing density and composition of tree reproduction present after seven growing seasons. In both treatments, red maple and other shade tolerant species were more abundant than oak seedlings. Results indicate that while the midstory removal was successful in improving oak development,
removal of competitor species like red maple may be necessary to ensure future oak recruitment.
A high degree of soil variability over short distances and small areas is common, particularly in forest soils. This variability is sometimes, but not always, related to readily apparent variations in the environmental factors that control soil formation. This study examines the potential role of biomechanical effects of trees and of lithological variations within the parent material in explaining soil diversity in the Ouachita Mountains of Arkansas. The diversity of soils on Ouachita sideslopes is high, and the soil series vary primarily with respect to morphological properties such as soil thickness and rock fragment content. Soils vary considerably within small more-or-less homogeneous areas, and richness–area analysis shows that the overall pattern of pedodiversity is dominated by local, intrinsic (within-plot) variability as opposed to between-plot variability. This is consistent with variation controlled mainly by individual trees and local lithological variations. Given the criteria used to distinguish among soil types, biomechanical as opposed to chemical and hydrological effects of trees are indicated. Results also suggest divergent evolution whereby the pedologic effects of trees are large and long-lived relative to the magnitude of the initial effects and lifespan of the plants.
We studied tree uprooting associated with an EF2 tornado that touched down in portions of the Ouachita Mountains in western Arkansas in 2009. In the severe blowdown areas all trees in the mixed shortleaf pine–hardwood forest were uprooted or broken, with no relationship between tree species or size and whether uprooting or breakage occurred. There was also no significant relationship between tree species and amount of soil displaced, and only a weak relationship between tree size and rootwad size. Uprooting resulted in a mean bioturbation rate of 205 m3 ha− 1 (about 240 t ha− 1). Direct transfer of wind energy via tree uprooting to geomorphic work of soil displacement was about 75 to 190 J m− 2. Given the infrequency of tornadoes, this energy subsidy is minor with respect to the long-term energetics of pedogenesis and landscape evolution. However, it does represent a highly significant pulse of geomorphically-significant energy relative to other mechanical processes. Tornadoes such as that of April, 2009—not atypical for the region—are disturbances causing severe, non-selective impacts within the affected area. At a broader, landscape scale, tornadoes are highly localized disturbances, and occur infrequently within any given landform element or forest stand. Only about a third of the uproots revealed root penetration of bedrock, compared to about 90% in other areas of the Ouachita Mountains. This is attributable to the thicker colluvial soils at the study site, and is consistent with the idea that root–bedrock interaction is more likely in thinner regolith covers.
Established species have been shown to affect soil nutrient availability, but the effects of "native invasive" species on soil nutrient availability are relatively unknown. Oak-dominated forests in the eastern deciduous forest are dynamic in their species composition, with increasing dominance of red maple (Acer rubrum L.) in the midstory and overstory. We hypothesized that higher quality red maple litter within a litter matrix dominated by oaks would accelerate N turnover, increase nutrient availability in the soil, and result in a thinner and less massive O horizon. We examined nutrient availability in soils under three overstory tree species (Quercus prinus L., A. rubrum, and Pinus echinata Mill. or Pinus rigida Mill.), under a shrub (Vaccinium spp.), and in locations without tree stems ("no tree"). Ex tract able nutrients (P, K, Mg, Ca) and total and available N were quantified in the O horizon and upper mineral soil at 0.5 m and 1.0 m from the base of individual trees or from the center of Vaccinium and no-tree locations. Despite low lignin concentration in red maple litter and low lignin/N ratio, the lowest N mineralization rates were found in red maple microsites; the highest N mineralization rates were found under oak. Extractable cations were generally highest under red maple and lowest under pines, and red maple had the highest levels of total N (but not NO3 or NH4) in the upper mineral soil. Shifting species composition towards red maple and away from pines in these forests may alter nutrient cycling by increasing surface soil cation availability, but reducing soil N mineralization.
The relationship between soil modeling and field pedology is recursive. Models should be firmly grounded in field observations. Field data are then used to test, calibrate, and refine models. One often-overlooked relationship between models and field studies is the use of models to generate field-testable hypotheses unrelated to the model itself—propositions derived from model outputs or implications, the testing of which provides pedologic insight independent of the model and its underlying assumptions. This paper provides an example using a model of soil thickness. The case study illustrates a stepwise, recursive relationship between field evidence and models. The relationship between bedrock weathering, soil thickness, and surface erosion used in most numerical models of soil and hillslope evolution was generalized into a qualitative nonlinear dynamical systems model, the interaction matrix of which is dynamically stable. This supports the notion of a steady-state equilibrium soil thickness where weathering is balanced by surface removal. However, empirical data in the Ouachita Mountains, Arkansas, USA, shows nonequilibrium soil thickness. This in turn indicates either recent and/or large disturbances or changes in boundary conditions, or that factors other than weathering and erosion play a significant role in determining thickness. The inconsistency between model results and field evidence led to further field investigations, suggesting that biomechanical effects of trees on soil depth are highly significant. A model devised to explore this notion showed that the interrelationships between individual trees and soil depth are dynamically unstable, leading to generation of a specific field-testable hypothesis, that soil should be systematically thicker under trees than in adjacent sites. This relationship was confirmed by augering to bedrock at 108 pairs of tree stumps and immediately adjacent sites. The recursive relations between soil modeling and field pedology thus led to specific findings regarding the influence of trees on soil thickness and nonequilibrium soil thickness that would not have arisen otherwise. Another key lesson is that field observations contrary to a model may be of greater importance in advancing pedology than those consistent with the model.
The validity of the concept of "single-tree influence circles" was tested in a forest dominated by Tsuga canadensis and Liriodendron tulipifera on steep slopes in the Appalachian Mountains of the eastern USA. Samples of forest floors and the 0-5 cm depth of mineral soil were collected at 135 locations within plots 1.3 ha in total area. Examination of particle-size distribution and pH at 33 of these locations confirmed that parent material to a depth of 100 cm was uniform throughout the study area. Soils were sandy and generally low in nutrients. Levels of pH, Ca, Mg, K, and mineralizable N tended to be higher, and forest floor mass tended to be lower, under the crowns of L. tulipifera compared to T. canadensis. Differnces between tree species were better expressed on areas lacking Rhododendron maximum understories. These results indicate that single-tree influence on soil properties is detectable even in mixed stands on steep slopes, and that the soil landscape may be considered a mosaic of profiles reflecting the occurrence and chemical characteristics of the ground cover vegetation and of individuals of the various tree species present.
Early Government Land Office Survey records of Roscommon and Crawford Counties were used to determine the composition and the disturbance history of the pine forests of N lower Michigan. Abundance of pine (mainly Pinus banksiana, P. resinosa and P. strobus) in this area that was between lobes of the Wisconsin Laurentide ice sheet was correlated with the presence of coarse-textured soils derived from outwash and ice-contact deposits. These soils promoted a vegetation type which was extremely susceptible to fire. Average return time for severe crown fires ranged from 80 yr in the case of the jack pine forest type to 120-240 yr for the mixed pine type to 1200 yr for the hemlock-white pine-northern hardwoods type. Blowdowns had a much longer return time and reached their greatest frequency in the swamp conifer and hemlock-white pine-northern hardwoods types. -from Author
The vascular plants of the Berea College Forest (BCF), the oldest managed forest in Kentucky, are presented as an annotated species list. BCF is comprised of 3,380 ha in Madison, Jackson, and Rockcastle counties of east-central Kentucky. Forests and diverse habitats include western mesophytic forest, mixed mesophytic forest, oak-hickory forest, mixed oak-Virginia pine forest, secondary succession areas, wetland habitats, and many anthropogenic-influenced areas. The known vascular plants consist of 1,017 specific and infraspecific taxa, 513 genera, and 139 families. Classification divisions with species are Equisetophyta (2), Lycopodiophyta (4), Polypodiophyta (33), Pinophyta (13), and Magnoliophyta (965). One hundred ninety-six taxa (19.27%) are naturalized, persisting, adventive, or cultivated exotics. The Asteraceae (141), Poaceae (100), Cyperaceae (64), and Fabaceae (56) are the largest families.
A biomantle is a differentiated zone in the upper part of soils produced largely by bioturbation, but often aided by subsidiary processes. One such process is loss of fine particles and redistribution of coarse ones from evolving biomantles. This is accomplished by rainwash and wind sorting of unprotected surface mounds and by vertical and/or lateral eluviation (lessivage) through-flow processes. Also subsidiary are the various processes by which iron, manganese, and other concretions come to reside in some biomantles. Concretions may form in biomantles directly from metal-bearing solutions, they may enter biomantles from upslope via creep and slope processes, or they may enter biomantles from below as the landscape down-wastes.
Faunalmantles are biomantles produced largely by burrowing animals (faunalturbation), and floralmantles are produced largely by tree uprooting (floralturbation). Faunalmantles and floralmantles may be one-, two-, or multilayered, as differentiated by one or more observable or measurable soil properties. Chief among these properties are particle size and biologically produced soil fabric (biofabric). Complex biomantles result where faunal-mantles and floralmantles are conjoined or coevolve on the same tract or landscape.
Stone zones, stone lines, or coarse-textured layers comprise the lower members of two-layered and multilayered faunal-mantles, and stone pavements comprise the upper members of two-layered and multi-layered floralmantles. Prehistoric and historic artifacts may be components of some floralmantle pavements and of some faunalmantle some lines and stone zones.
(C) Williams & Wilkins 1990. All Rights Reserved.
Forest soils are profoundly influenced by the biomechanical as well as the chemical and biological effects of trees. Studies of biomechanical impacts have focused mainly on uprooting (treethrow), but this study shows that at least two other effects are significant: physical displacement of soil by root growth, and infilling of stump rot pits. Rocky soils in the Ouachita Mountains in Arkansas were studied because they allow for the use of rock fragments as a tracer of displacement. Rock fragments displaced by tree growth (baumsteins) are ubiquitous here, and displacement shows characteristic differences between pines and hardwoods. Hardwoods promote primarily lateral displacement, with a higher probability of displaced rock fragments eventually falling into stump holes. Pine displacement has a significant vertical component associated with basal mounding, and a lower probability of baumstein deposition in stump holes. Obvious stump holes are relatively rare, but the high ratio of stumps and snags to uprooted trees indicates that standing dead trees, which would ultimately result in a stump hole, are quite common. This, plus the presence of numerous duff-filled depressions, suggests that such holes are filled rapidly. The presence of surface-derived rock fragments and thick litter and duff accumulations indicate that at least some of the fill is external, as opposed to soil detachment from the pit walls. The primary influence of stump holes, as reflected by rock fragment distributions, is localized subsurface stone accumulations that do not extend laterally. The total area affected by uprooting is larger than that of stump holes, despite the lower frequency, due to the greater area of disturbance per event. Estimated turnover times (time for 100 percent of the forest floor to be affected) are shortest for soil displacement, intermediate for uprooting, and longest for stump hole effects. Although contemporary rates cannot be confidently extrapolated, the geomorphological efficacy of these processes is reflected by the fact that they are rapid enough to result in complete regolith turnover over time scales comparable to the Holocene. Displacement, stump holes, and uprooting help to maintain a continuously mixed surface biomantle, and may in some cases result in distinctive pedological features, local spatial variations in soil morphology, and divergent evolution of the soil cover.
Rock veneers stabilize hillslope surfaces, occur especially in areas of immature soil, and form through a variety of process sets that includes root throw. Near Westcliffe, Colorado, USA, data were collected from a 20 × 500 m transect on the east slope of the Sangre de Cristo Mountains. Ages of pit/mound complexes with rock fragments exposed at the surface by root throw ranged from recent (freshly toppled tree) to unknown (complete tree decay). Calculations based on dimensions of the pit/mound complexes, estimated time of tree toppling, sizes of exposed rock fragments, and percentage rock covers at pit/mound complexes, as well as within the transect area, indicate that recent rates of root throw have resulted in only partial rock veneering since late Pleistocene deglaciation. Weathering of rock fragments prevents development of an extensive rock veneer and causes a balance, achieved within an estimated 700 years, between the rates of rock-fragment exposure by root throw and clast disintegration by chemical reduction. The estimated rate of rock-fragment reduction accounts for part of the fluvial sediment yields observed for forested subalpine areas of western North America. Copyright © 2005 John Wiley & Sons, Ltd.
Steady-state regolith or soil thickness (SSST), whereby surface removals are approximately balanced by production of new soil by bedrock weathering, is a common assumption in most models of hillslope and landscape evolution. SSST is also a fundamental assumption in the use of cosmogenic radionuclides (CRN) to estimate erosion and weathering rates. The steady-state concept is based on feedbacks between soil thickness and weathering at the base of the regolith, such that (sometimes after an optimal or threshold thickness is achieved), thicker soils lead to lower weathering rates (and vice versa). SSST is thus only applicable to soils formed chiefly from weathering of the underlying bedrock, where sufficient time has elapsed for regolith accumulation, and where effects of processes other than weathering and surface removals on thickness are negligible. Even within this domain, the widespread occurrence of deep weathering profiles, regolith stripping, and inherited regolith features makes SSST problematic as a conceptual model for pedogenesis or weathering profile development. The ratio of soil thickness to total weathering profile thickness is proposed as a simple index of steady state. Steady-state profiles formed on weathered bedrock should exhibit ratios close to unity. Data from the Cumberland Plateau region of eastern Kentucky show that soil/weathering profile ratios in shallow (< 1.5 m) profiles formed on sandstone may reach or approach unity, but are generally < 1. Geotechnical core data show depths to bedrock of 2 to > 20 m, and generally significantly greater than soil thicknesses in the region, suggesting ratios <<1. However, while evidence shows that SSST is likely rare and not a viable conceptual framework for assessing soil and weathering profile development, deviations from SSST may have limited influence on results of CRN-based estimates of erosion and weathering and simulation model results. This is because in the landscape settings where SSST is typically assumed, and over the customary time scales involved, rates of denudation and weathering are very small compared to regolith thickness, such that imbalances do not materially affect results of calculations. Steady-state in development of soil, regolith, or weathering profile development thus represents a convenient fiction facilitating the use of some models and tools. The potential pitfalls arise from the possibility that the utility of SSST as a convenient fiction in some contexts may be mistaken for a realistic representation of the dynamics of pedogenesis and weathering profile evolution.
A field study was conducted to analyze root throw and associated sediment transport in Hawk Creek Watershed, Canadian Rockies. A large crown fire in 2003 allowed the opportunity to study pre-fire and post-fire root throw. Based on field data, a significant relation was found between gradient and root plate volume, as well as individual root plate dimensions. Given that tree diameters increase as trees age and that a relation in the field data was found between tree diameter and root plate volumes, sediment transport due to root throw is expected to change in response to forest disturbance and stand age. Sediment disturbance, which is the amount of sediment upheaved during tree topple and does not take into account transport distance, shows higher values on steeper gradients. Sediment transport was notable for the steepest plots, with pre-fire values of 0·016 cm3 cm–1 a–1 and post-fire values of 0·18 cm3 cm–1 a–1. A tree population dynamics model is then integrated with a root throw transport model calibrated for the Canadian Rockies to examine the temporal dynamics of sediment transport. Fire is incorporated as a disturbance that initiates development of a new forest, with the model cycling through generations of forest. Trees fall according to an exponential rate that is based on time since death, resulting in a time lag between tree mortality and sediment transport. When values of time-since-previous-fire are short, trees are generally <13 cm, and minimal sediment is upheaved during toppling. If trees reach a critical diameter at breast height (dbh) at time of fire, a pulse of sediment occurs in the immediate post-fire years due to falling of killed trees, with tree fall rates decreasing exponentially with time-since-fire. A second pulse of root throw begins at about 50 years after the previous fire, once new recruits reach a critical dbh and with initiation of competition-induced mortality. Copyright © 2009 John Wiley & Sons, Ltd.
Organic acids, such as malate, citrate and oxalate, have been proposed to be involved in many processes operating in the rhizosphere, including nutrient acquisition and metal detoxification, alleviation of anaerobic stress in roots, mineral weathering and pathogen attraction. A full assessment of their role in these processes, however, cannot be determined unless the exact mechanisms of plant organic acid release and the fate of these compounds in the soil are more fully understood. This review therefore includes information on organic acid levels in plants (concentrations, compartmentalisation, spatial aspects, synthesis), plant efflux (passive versus active transport, theoretical versus experimental considerations), soil reactions (soil solution concentrations, sorption) and microbial considerations (mineralization). In summary, the release of organic acids from roots can operate by multiple mechanisms in response to a number of well-defined environmental stresses (e.g., Al, P and Fe stress, anoxia): These responses, however, are highly stress- and plant-species specific. In addition, this review indicates that the sorption of organic acids to the mineral phase and mineralisation by the soil's microbial biomass are critical to determining the effectiveness of organic acids in most rhizosphere processes.
This paper expands the dynamic denudation framework of landscape evolution by providing new process insights and details on how soil and its signature morphological feature, the biomantle, form and function in the environment. We examine soils and their biomantles from disparate parts of the world, from the tropics through midlatitudes and hyperarid through perhumid, a range that exhibits varying environments for, and of, life. We then explicate the process pathways that cause soils to thicken and thin, and to even disappear, then reform. We do this by examining thickness relationships, where soil thickness st and biomantle thickness bt are functions of upbuilding u and deepening d minus removal r processes, hence st/bt=f(u+d−r). Upbuilding has two subsets, u1, which includes all exogenous (allochthonous—outside) mineral and/or organic inputs to the soil system, and u2, which includes all endogenous (autochthonous—in situ) processes and productions, including weathering. Exogenous u1 inputs include eolian and slopewash inputs (sedimentations) of mineral and organic materials, mass wasting accumulations and the like. Endogenous u2 processes and productions include the sum of in situ bioturbations, biosynthetic productions, organic accumulations, biovoid productions, weathering and volume increases caused by their sum. Endogenous upbuildings, which dominantly occur in the biomantle, are basically biodynamic bd processes and productions, hence u2=bd. Therefore, if exogenous upbuildings u1 are minimal or zero, then biomantle thickness bt is expressed by bt=f(u2−r) or bt=f(bd−r).
Individual trees may have significant impacts on soil morphology. If these impacts are non-random such that some microsites are repeatedly preferentially affected by trees, complex local spatial variability of soils would result. A model of self-reinforcing pedologic influences of trees (SRPIT) is proposed to explain patterns of soil variability in the Ouachita Mountains, Arkansas. SRPIT postulates that trees are preferentially established on patches that are nutrient-rich and rock fragment poor relative to adjacent sites. The biomechanical effects of trees on soil, and decomposition of roots then maintain and reinforce the rock fragment and nutrient differences relative to surrounding soils, increasing the likelihood of successful future tree establishment. The links hypothesized in the SRPIT model are dynamically unstable, which would be necessary for the self-reinforcing mechanisms to operate. Soil variability in 16 study plots is dominated by local, within-plot variability, pointing to highly localized biological effects and consistent with the SRPIT model. Within each 0.127 ha plot, 4–11 different series, and 4–9 different rock fragment classes were found. Of the 10 paired pits at each plot, 3–7 pairs had different series in pits typically less than 1 m apart. On average, each of the 16 plots had 6.3 different soil types, 6 different rock fragment classes, and 60% of the sample pairs differing in soil series. Richness–area analysis of soil series, and of rock fragment classes, both indicate that pedodiversity is dominated by within-plot rather than between-plot variability. The vertical variations in the concentration of rock fragments in 40 of 58 soil pits is consistent with redistribution of soil material by tree throw, and there is also evidence of rock fragment displacement by tree growth and deposition in stump holes. Overall, results suggest that soil morphological effects of individual trees are an important source of soil spatial variability in forests, and that such effects are non-random over time. Thus even relatively homogeneous areas may be characterized by tree-rich patches which support repeated generations of trees, and tree-poor patches which more rarely host trees.
Oaks (Quercus spp.) are experiencing recurring regeneration failures associated with pervasive mid- and under-story strata of shade tolerant species in intact, undisturbed forests. Where oak regeneration occurs, inadequate vertical height and depleted root carbohydrate stores impede the ability of regenerating oaks to respond when light does become available. A variety of silvicultural techniques have been developed to increase the penetration of diffuse light, enhancing the light environment on the forest floor, and thereby increasing the likelihood of regenerating oaks to successfully respond to increased light transmittance. We measured shoot and root characteristics, and root soluble non-structural carbohydrate concentrations of white oak (Q. alba L.) advance regeneration exposed to enhanced light intensities associated with a mid-story removal and a clearcut, and compared white oak regeneration vigor to untreated controls.Root diameter and soluble non-structural carbohydrates increased with increasing light availability. Our data suggest that white oak responds to increases in light transmittance by building below-ground biomass and carbohydrates in the root system prior to an above-ground response. Our study shows that white oak regeneration vigor increases with only modest increases in light. In the absence of other pressures, enhancing the light environment to the forest floor should contribute to successful regeneration of this species.
The validity of the concept of "single-tree influence circles' was tested in a forest dominated by Tsuga canadensis and Liriodendron tulipifera on steep slopes in the Appalachian Mountains. Parent material to a depth of 100 cm was uniform throughout the study area. Soils were sandy and generally low in nutrients. Levels of pH, Ca, Mg, K, and mineralizable N tended to be higher, and forest floor mass tended to be lower, under the crowns of L. tulipifera compared to T. canadensis. Differences between tree species were better expressed on areas lacking Rhododendron maximum understories. -from Authors
Rock fragments in the regolith are a persistent property that reflects the combined influences of geologic controls, erosion, deposition, bioturbation, and weathering. The distribution of rock fragments in regoliths of the Ouachita Mountains, Arkansas, shows that sandstone fragments are common in all layers, even if sandstone is absent in parent material. Shale and sandstone fragments are produced at the bedrock weathering front, but the shale weathers rapidly and intact fragments are rare in the solum. Sandstone is weathered from ridgetop outcrops and transported downslope. Some of these fragments are moved downward, by faunalturbation and by transport into pits associated with rotting tree stumps. Upward movement by treethrow is common, resulting in a net concentration of rocks near the surface. However, the highest fragment concentrations are in the lower regolith, indicating active production at the weathering front. The regolith is a dynamic feature, reflecting the influences of vertical and horizontal processes, of active weathering at the bedrock interface, and of surficial sediment movements. The role of trees in redistributing rock fragments suggests that significant regolith mixing occurs over time scales associated with forest vegetation communities, and that forest soils have likely been extensively mixed within Holocene and historic time.
Trees growing in rocks without soil are uncommon. In two arid regions in Baja California, Mexico, field surveys found large numbers of rock-colonizing elephant trees (Pachycormus discolor (Benth.) Coville ex Standl. (Mexican name: copalquin) growing in igneous rocks (granite and basalt) as primary colonizers without the benefit of soil or with a very small amount of soil generated by their own growth. Many adult trees broke large granite boulders and were capable of wedging, growing in, and colonizing rocks and cliffs made of ancient lava flows. This is the first record of a tree species, apart from the previously recorded cacti, capable of primary colonization of rocks and rock rubble in hot deserts.
Soil Survey of Powell and Wolfe Counties
- R A Hayes
Hayes, R.A., 1993. Soil Survey of Powell and Wolfe Counties, Kentucky. U.S.D.A.
Hinrichs, E.N., 1978. Geologic Map of the Noble Quadrangle, Eastern Kentucky. U.S.G.S.
Johnson, D., 1985. Soil thickness processes. Catena 6, 29-40 (Suppl.).
Geologic Map of the Noble Quadrangle
- E N Hinrichs
Hinrichs, E.N., 1978. Geologic Map of the Noble Quadrangle, Eastern Kentucky. U.S.G.S.
The vascular plants of the Berea College Forest in Madison
- R L Thompson
Thompson, R.L., 2008. The vascular plants of the Berea College Forest in Madison, Jackson,
and Rockcastle Counties, Kentucky. Castanea 73 (3), 188-209.
- R M Burns
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Burns, R.M., Honkala, B.H., 1990. Silvics of North America. Vol. 1. Conifers. US Dep. Agric.
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Nature of Weathering, The; An Introduction. Sozosha
- E Yatsu
Yatsu, E., 1988. Nature of Weathering, The; An Introduction. Sozosha.