Spatial patterns of vegetation, soils, and microtopography from terrestrial laser scanning on two semiarid hillslopes of contrasting lithology

Abstract

Shrublands in semiarid regions are heterogeneous landscapes consisting of infertile bare areas separated by nutrient rich vegetated areas known as resource islands. Spatial patterns in these landscapes are structured by feedbacks driven by the transport of water and nutrient resources from the intershrub space to areas below shrubs, and the retention of these resources to locally drive productivity and tight biogeochemical cycles. Most understanding of plant‐soil feedbacks is based predominantly on studies of low topographic gradient landscapes, and it is unclear whether the patterns of association between soils and vegetation, and the autogenic processes that create them, also occur on more steeply sloping terrain. Here we analyze the spatial patterns of soils, vegetation, and microtopography on hillslopes of contrasting lithology (one granite at 16°, one schist at 27°) in the Sonoran desert foothills of the Catalina Mountains. We also describe a method of extracting vegetation density from terrestrial laser scanning point cloud data at 5 cm × 5 cm scales and find that it correlates well with soil organic carbon measurements. Vegetation was associated with microtopographic mounds (relative to the mean slope) extending 0.3 m downslope and 1.8 m (schist) and 0.9 m (granite) upslope on the study hillslopes. Soils below the shrub canopies exhibited 2–3 times more soil organic matter and 2–4 times higher hydraulic conductivity than the interspaces. Soils enriched with organic matter were found to extend at least two canopy radii downslope of woody shrubs, but not upslope. These plumes were clearest in the lower gradient granite site where vegetation mounds created distinct patterns of microtopographic convergence and divergence. At the steeper schist site, microtopography appeared to have a weaker control on topographic flow accumulation. Collectively, our findings suggest that the spatial structure of association between soils and microtopography and vegetation on these slopes exhibit many of the features observed in lower gradient areas. However, microtopography and soils are more asymmetric along the downslope axis of the hillslopes than lower gradient areas and vary with lithology. Alluvial and colluvial processes are likely more important in shaping vegetation and soil dynamics on hillslopes, and these factors need further consideration in scaling results to the landscape level.

Unsupervised Clustering Method for Complexity Reduction of Terrestrial Lidar Data in Marshes

“…The use of TLS is now well established in geology and landscape dynamics [17][18][19][20]. More recently, its potential in fluvial geomorphology [21,22], floodplain mapping [16], soil science [23], and wetland mapping [24][25][26][27] have begun to be explored. However, within the coastal marsh environment, the ability of TLS systems to resolve centimeter-level elevation differences between the vegetation and the bare earth surface is limited [28][29][30].…”

Laser vision: lidar as a transformative tool to advance critical zone science

“…Broadly, lidar technology has been useful in studying geomorphic response to extreme events such as fire and storms (e.g., Pelletier and Orem, 2014;Sankey et al, 2013;Perignon et al, 2013;Staley et al, 2014), human activities (e.g., James et al, 2009), and past climatic and tectonic forcings (e.g., Roering, 2008;Belmont et al, 2011;West et al, 2014). Meter-and sub-meter-scale time-varying processes, often derived from TLS, have been quantified in the response of point bar and bank morphodynamics (Lotsari et al, 2014) and in the formation of micro-topography due to feedbacks with biota (e.g., Roering et al, 2010;Harman et al, 2014). Examples of larger scale change detection applications, typically ALS-derived, include measuring changes in stream channel pathways resulting from Holocene climate change and anthropogenic activities (e.g., Day et al, 2013;Kessler et al, 2012;James et al, 2012;Belmont et al, 2011), rates of change in migrating sand dunes (Pelletier, 2013), the influence of lithology and climate on hillslope form (e.g., Marshall and Roering, 2014;Hurst et al, 2013;Perron et al, 2008;West et al, 2014), and channel head formation (e.g., Pelletier et al, 2013;Pelletier and Perron, 2012;Perron and Hamon, 2012).…”

“…We highlight three studies that can serve as possible road maps to guide future transdisciplinary investigations using lidar data sets (Fig. 2): Harman et al (2014), Pelletier et al (2013), and Perignon et al (2013). These studies used complementary information from lidar to develop fundamental transdisciplinary advances in the theories and understanding of CZ processes and structure.…”

“…These studies used complementary information from lidar to develop fundamental transdisciplinary advances in the theories and understanding of CZ processes and structure. For example, Harman et al (2014) applied TLS to investigate co-evolution of lidarderived micro-topography and vegetation (biovolume) at two 100 m long semi-arid hillslopes. Integrating lidar and limited field measurements, Harman et al (2014) found that both alluvial and colluvial processes were important in shaping vegetation and soil dynamics on hillslopes.…”

“…For example, Harman et al (2014) applied TLS to investigate co-evolution of lidarderived micro-topography and vegetation (biovolume) at two 100 m long semi-arid hillslopes. Integrating lidar and limited field measurements, Harman et al (2014) found that both alluvial and colluvial processes were important in shaping vegetation and soil dynamics on hillslopes. The insights found by Harman et al (2014) relied on the high resolution and precision of lidar information and would not have been possible using coarser traditional survey techniques for topography and vegetation structure.…”