Understanding soil organic matter change: Modeling root and soil interactions across agricultural landscapes

What are some options for enhancing organic content and carbon storage in soils that have been used in intensive row-crop production? The project looked at bioenergy feedstocks and how they might be employed to improve soil properties

Broadscale variability in tree data of the historical Public Land Survey and its consequences for ecological studies

Historical records provide valuable information on the prior conditions of ecological systems and species distribution, especially in the context of growing environmental change. However, historical records may have associated bias and error because their original purpose may not have been for scientific use. The Public Land Survey (PLS) of the U.S. General Land Office (GLO) conducted from the late 1700s to the early 1900s has been widely used to characterize historical vegetation in the United States prior to major Euro-American settlements. Studies have shown that variability and bias exist in the data. However, these studies have not typically encompassed a region large enough to adequately assess this variability across diverse landscapes, nor attempted to distinguish potential ecological significance from statistical differences. Here we do this by analyzing variability in PLS data across all of northern Wisconsin, USA, a 75 000-km2 landscape. We found ecologically significant differences among survey point types for tree species, size, and the distance to survey points. Both corner and line trees show some level of bias for species and size, but corner trees are likely the best sample. Although statistical tests show significant differences in species composition, tree size, and distance by tree sequence and location, the differences in species composition and tree size are not ecologically significant. The species differences are probably caused by fine-scale variability in the forest communities. The value of the PLS data remains high; choice of spatial extent, methods of analyses, and bias significance need to be evaluated according to variables of interest and project purpose. Read More: http://www.esajournals.org/doi/abs/10.1890/10-0232.

Factors Influencing Soil Aggregation and Particulate Organic Matter Responses to Bioenergy Crops across a Topographic Gradient

Bioenergy crops have the potential to enhance soil carbon (C) pools fromincreased aggregation and the physical protection of organicmatter; however, our understanding of the variation in these processes over heterogeneous landscapes is limited. In particular, little is known about the relative importance of soil properties and root characteristics for the physical protection of particulate organic matter (POM). We studied short-term (3-year) changes in aggregation and POM-C pools under three cropping systems (switchgrass, a triticale/sorghumdouble crop, continuous corn) replicated across five landscape positions along a topographic gradient in Iowa, USA.We isolated POMassociated with three aggregate fractions (N2mm, 0.25–2mm, and 0.053–0.25mm) to determine the relative influence of ten soil and three root properties. Aggregation increased in all cropping systems andwas greatest under switchgrass; however cropping systemeffectswere not consistent among positions. Total soil organic C stocks did not change, but Cwithin both physically protected (iPOM-C) and unprotected (frPOM) C pools increased. Shifts in iPOM-C were concurrently influenced by soil properties and root traits. Soil texture had the strongest influence (65% relative importance), with finer-textured soils showing greater gains in total iPOM-C, while greater root biomass influenced (35% relative importance) accrual of total iPOM-C. Aggregate fractions varied in their iPOM-C response to soil and root variables, however individual pools similarly showed the importance of soil texture and root biomass and annual root productivity (BNPP). Changes in frPOM-C were strongly correlated with BNPP. Our data suggest that macroaggregate formation drives short-term responses of POM, which are influenced by both soil and root system properties. Crops that maximize root biomass and BNPP will lead to the largest increases in protected soil C stocks. However, C storage rates will vary across landscapes according to soil conditions, with texture as the primary influence

Enhancing Agroecosystem performance and Resilience through Increased Diversification of Landscapes and Cropping Systems

Over the past two decades, ecologists have gained a considerable amount of insight concerning the effects of biological diversity on how ecosystems function. Greater productivity, greater carbon sequestration, greater retention of nutrients, and greater ability to resist and recover from various forms of stress, including herbivorous pests, diseases, droughts, and floods, are among the effects of increased biological diversity noted in a recent review by Cardinale et al. (2012). The latter effect, often called resilience, is particularly important in managed social-ecological systems, including agroecosystems (Walker and Salt, 2006). In addition to being better able to withstand and recover from disturbances due to pests, weather, and other biophysical factors, resilient agroecosystems can be less susceptible to fluctuations in production costs and market prices

An Ecoregional Context for Forest Management on National Wildlife Refuges of the Upper Midwest, USA

To facilitate forest planning and management on National Wildlife Refuges, we synthesized multiple data sources to describe land ownership patterns, land cover, landscape pattern, and changes in forest composition for four ecoregions and their associated refuges of the Upper Midwest. We related observed patterns to ecological processes important for forest conservation and restoration, with specific attention to refuge patterns of importance for forest landbirds of conservation priority. The large amount of public land within the ecoregions (31–80%) suggests that opportunities exist for coarse and meso-scale approaches to conserving and restoring ecological processes affecting the refuges, particularly historical fire regimes. Forests dominate both ecoregions and refuges, but refuge forest patches are generally larger and more aggregated than in associated ecoregions. Broadleaf taxa have increased in dominance in the ecoregions and displaced fire-dependent taxa such as pine (Pinus spp.) and other coniferous species; these changes in forest composition have likely also affected refuge forests. Despite compositional changes, larger forest patches on refuges suggests that they may provide better habitat for area-sensitive forest landbirds of mature, compositionally diverse forests than surrounding lands if management continues to promote increased patch size. We reason that although finescale research and monitoring for species of conservation priority is important, broad scale (ecoregional) assessments provide crucial context for effective forest and wildlife management in protected areas