Eric D. Vance

Fire effects on temperate forest soil C and N storage

Temperate forest soils store globally significant amounts of carbon (C) and nitrogen (N). Understanding how soil pools of these two elements change in response to disturbance and management is critical to maintaining ecosystem services such as forest productivity, greenhouse gas mitigation, and water resource protection. Fire is one of the principal disturbances acting on forest soil C and N storage and is also the subject of enormous management efforts. In the present article, we use meta-analysis to quantify fire effects on temperate forest soil C and N storage. Across a combined total of 468 soil C and N response ratios from 57 publications (concentrations and pool sizes), fire had significant overall effects on soil C (-26%) and soil N (-22%). The impacts of fire on forest floors were significantly different from its effects on mineral soils. Fires reduced forest floor C and N storage (pool sizes only) by an average of 59% and 50%, respectively, but the concentrations of these two elements did not change. Prescribed fires caused smaller reductions in forest floor C and N storage (-46% and -35%) than wildfires (-67% and -69%), and the presence of hardwoods also mitigated fire impacts. Burned forest floors recovered their C and N pools in an average of 128 and 103 years, respectively. Among mineral soils, there were no significant changes in C or N storage, but C and N concentrations declined significantly (-11% and -12%, respectively). Mineral soil C and N concentrations were significantly affected by fire type, with no change following prescribed burns, but significant reductions in response to wildfires. Geographic variation in fire effects on mineral soil C and N storage underscores the need for region-specific fire management plans, and the role of fire type in mediating C and N shifts (especially in the forest floor) indicates that averting wildfires through prescribed burning is desirable from a soils perspective.

Agricultural site productivity: principles derived from long-term experiments and their implications for intensively managed forests

Abstract Long-term agricultural field experiments provide relevant information for questions being asked about the sustainability of managed forests, particularly as management regimes become more intensive. In this paper, concepts and criteria related to sustainable site productivity are reviewed and findings from a range of long-term agricultural field experiments are evaluated. Based on this evaluation, the following site productivity principles are identified: (1) soil organic matter is the link between most management systems and sustainable site productivity; (2) nutrient deficiencies can be corrected; (3) soil texture is a key variable affecting soil organic matter and site productivity; (4) return of crop residues enhances soil organic matter and site productivity; and (5) productive cropping systems have environmental benefits. While technological advances have proven to be highly successful for enhancing long-term crop yields, they also have the potential to mask underlying declines in site productivity. This hypothesis needs to be rigorously tested. Agricultural field experiments show that crop productivity can be sustained for long time periods when appropriate management approaches are applied. Management requirements to achieve sustainability differ, however, depending on site-specific edaphic and climatic characteristics and the needs of the crop. Site productivity principles derived from agricultural field studies are also highly relevant to sustaining site productivity of managed forests. Several characteristics of managed forests should be considered when extrapolating conclusions from agricultural experiments. These include harvest removals of biomass and nutrients, residue type and distribution, management and system characteristics, and soil types used. Many characteristics associated with even intensively managed forests are sought as goals of conservation cropping systems and should contribute toward sustaining long-term site productivity.

Achieving conservation goals in managed forests of the Southeastern Coastal Plain.

Managed forests are a primary land use within the Coastal Plain of the southern United States. These forests are generally managed under standards, guidelines, or regulations to conserve ecosystem functions and services. Economic value of commercial forests provides incentives for landowners to maintain forests rather than convert them to other uses that have substantially reduced environmental benefits. In this review, we describe the historical context of commercial forest management in the southern United States Coastal Plain, describe how working forests are managed today, and examine relationships between commercial forest management and maintenance of functional aquatic and wetland systems and conservation of biological diversity. Significant challenges for the region include increasing human population and urbanization and concomitant changes in forest area and structure, invasive species, and increased interest in forest biomass as an energy feedstock. Research needs include better information about management of rare species and communities and quantification of relationships between ecosystem attributes and forest management, including biomass production and harvest. Incentives and better information may help commercial forest managers in the Coastal Plain more efficiently contribute to landscape-scale conservation goals.

Challenges in Modeling the Fate of Nitrogen Applied to Forests: Development of a Comprehensive Forest Nutrient Cycle and Export Modeling Package; Cordesville, South Carolina, 6–7 March 2008

Nitrogen (N) fertilizer is commonly applied to increase productivity of forest plantations, and the extent and intensity of forest fertilizer use could increase in the future as a way of enhancing forest productivity to meet demands for both traditional products and emerging markets for energy and biomaterials. While much of the applied N remains in the soilplant system, there are concerns about leaching losses and effects on surface water quality. However, understanding the fate of fertilizer N and its potential environmental impacts is particularly complex due to a wide range of abiotic and biotic factors affecting its forms and movement. There have been many N cycling studies in pine plantations, but relatively few have comprehensively addressed links between terrestrial processes and the ultimate fate of fertilizer N. While a variety of hydrologic and nutrient cycling models have been applied to simulate N fate and transport at different spatial and temporal scales in agricultural and forested ecosystems, available field studies are generally inadequate to validate those model predictions. Experiments are needed to validate model predictions on the transport and fate of N through the soil and water network. Once validated, models can be used in the development of general fertilizer guidelines for resource managers and can help document how fertilizer can be safely and effectively used at stand and landscape scales.