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- Title
The Importance of Accounting for Landscape Position When Investigating Grasslands: A Multidisciplinary Characterisation of a California Coastal Grassland.
- Authors
Rowley, Mike C.; Falco, Nicola; Pegoraro, Elaine; Dafflon, Baptiste; Gerlein‐Safdi, Cynthia; Wu, Yuxin; Castanha, Cristina; Peña, Jasquelin; Nico, Peter S.; Torn, Margaret S.
- Abstract
Grasslands are one of the most common land‐cover types, providing important ecosystem services globally, yet few studies have examined grassland critical‐zone functioning throughout hillslopes. This study characterised a coastal grassland over a small hillslope at Point Reyes National Seashore, California, using multidisciplinary techniques, combining remotely‐sensed, geophysical, plant, and soil measurements. Clustering techniques delineated the study area into four landscape zones, up‐, mid‐, and down‐slope, and a bordering riparian ecotone, which had distinct environmental properties that varied spatially across the site, with depth, and time. Soil moisture increased with depth and down slope towards a bordering riparian zone, and co‐varied with soil CO2 flux rates both spatially and temporally. This highlighted three distinct controls of soil moisture on soil respiration: CO2 fluxes were inhibited by high moisture content in the down‐slope during the wet winter months, and converged across landscape positions in the dry summer months, while also displaying post‐rain pulses. The normalised difference vegetation index (NDVI) ranged from 0.32 (September)–0.80 (April) and correlated positively with soil moisture and aboveground biomass, moving down slope. Yet, NDVI, aboveground biomass, and soil moisture were not correlated to soil organic carbon (SOC) content (0.4%–4.5%), which was highest in the mid‐slope. The SOC content may instead be linked to shifts in dominant grassland species and their rhizosphere properties with landscape position. This multidisciplinary characterisation highlighted significant heterogeneity in grassland properties with landscape position, and demonstrated an approach that could be used to characterise other critical‐zone environments on hillslopes. Plain Language Summary: Globally, grasslands are both common and important landscapes, but less studies have investigated the influence of hillslope processes on these environments and their properties. This study investigated a coastal grassland on a hillslope at Point Reyes National Seashore, California, by combining data sets from different disciplines, covering satellite, field, and laboratory measurements. The site could be grouped into four environmental zones with different properties along the hillslope. Satellite measurements revealed that plants were more active in the wetter, down‐slope throughout the dry summer months. Soil carbon content was not linked directly to soil moisture. Yet, soil carbon dioxide emissions were related to soil moisture, displaying three different behaviors depending on the moisture level. First, soil carbon dioxide emission was lower in the down‐slope during the wet months (negative relationship), but then behaved similarly at all slope locations during the summer and early fall, and increased when it rained (positive relationship). The clustering analysis showed that our site varied significantly over a small distance (<8 m elevation and 150 m distance) and time (1 yr). Beyond the investigation of this specific site, this study highlights an approach for combining data sets to study ecosystems along hillslopes. Key Points: The study used a critical‐zone approach to combine multidisciplinary data sets and characterise a California coastal grasslandHeterogeneity was large over a short distance (<150 m) and time (1 yr) and could be clustered by landscape position into four distinct zonesSoil CO2 fluxes exhibited contrasting responses to soil moisture, which differed with slope and season at the grassland
- Subjects
CALIFORNIA; RIPARIAN areas; GRASSLANDS; GRASSLAND soils; CARBON in soils; CARBON emissions; AUTUMN; SOIL moisture; SOIL respiration
- Publication
Earth's Future, 2024, Vol 12, Issue 6, p1
- ISSN
2328-4277
- Publication type
Article
- DOI
10.1029/2023EF004208