Diminishing Spatial Heterogeneity in Soil Organic Matter across a Prairie Restoration Chronosequence

Abstract

Habitat restoration resulting in changes in plant community composition or species dominance can affect the spatial pattern and variability of soil nutrients. Questions about how these changes in soil spatial heterogeneity develop over time at restoration sites, however, remain unaddressed. In this study, a geostatistical approach was used to quantify changes over time in the spatial heterogeneity of soil organic matter (SOM) across a 26-year chronosequence of tallgrass prairie restoration sites at FermiLab, outside of Chicago, Illinois. We used total soil N and C as an index of the quantity of SOM. We also examined changes in C:N ratio, which can influence the turnover of SOM. Specifically, the spatial structure of total N, total C, and C:N ratio in the top 10 cm of soil was quantified at a macroscale (minimum spacing of 1.5 m) and a microscale (minimum spacing of 0.2 m). The magnitude of spatial heterogeneity (MSH) was characterized as the proportion of total sample variation explained by spatially structured variation. At the macroscale, the MSH for total N decreased with time since restoration (r 2 ¼ 0.99, p < 0.001). The decrease in spatial heterogeneity over time corresponded with a significant increase in the dominance of the C 4 grasses. At the microscale, there was significant spatial structure for total N at the 4-year-old, 16-year-old, and 26-year-old sites, and significant spatial structure for total C at the 16-year-old and 26-year-old sites. These results suggest that an increase in dominance of C 4 grasses across the chronosequence is homogenizing organic matter variability at the field scale while creating fine-scale patterns associated with the spacing of vegetation. Areas of higher soil moisture were associated with higher soil N and C at the two oldest restoration sites and at the native prairie site, potentially suggesting patches of increased belowground productivity in areas of higher soil moisture. This study is one of the first to report significant changes over time in the spatial structure of organic matter in response to successional changes initiated by restoration.

Legacy of Land-Use Evident in Soils of Western Australia’s Wheatbelt

“…However, there is some evidence of homogenisation of Pullen old-field soils -we found consistently more variation in soil properties among remnant soils than among old-fields soils at Pullen. A similar finding is reported for northern hemisphere old-fields (Fraterrigo et al, 2005;Lane and BassiriRad, 2005;Robertson et al, 1988Robertson et al, , 1993. Low resource heterogeneity may favour species that are able to withstand uniformly high levels of competition (Day et al, 2003;Hutchings et al, 2003).…”

Variation in small-scale spatial heterogeneity of soil properties and vegetation with different land use in semiarid grassland ecosystem

“…Development of geostatistics has provided an effective tool in assisting assessment of spatial heterogeneity characteristics in ecological processes because the parameters from the semivariogram model offer an index to quantify the magnitude and scale of spatial heterogeneity in a variate (Gross et al 1995;Lane and BassiriRad 2005). Many studies have been carried out to determine spatial heterogeneous characteristics of a variety of terrestrial ecosystems, especially on soil properties, by using this technique (Schlesinger et al 1996;Augustine and Frank 2001;Hutchings et al 2003).…”

Changes in soil organic carbon and total nitrogen after 28 years grassland afforestation: effects of tree species, slope position, and soil order

“…For instance, woody vegetation can increase soil heterogeneity due to the concentration of organic matter and N beneath relatively small canopies, creating 'islands of fertility ' (Schlesinger et al 1996), whereas grassland vegetation has a dense and homogeneous root system. The latter can homogenize spatial distribution of soil nutrients (Pärtel and Wilson 2002;Lane and BassiriRad 2005). Due to such great spatial differences of OC and TN, understanding differences of soil OC and TN under tree canopy and adjacent grassland (outer tree canopy) may be effective in clarifying the effects of grassland to woodland conversion on soil OC and TN and help explain the current inconsistencies.…”