James A. Burger

A Review of Chemical and Physical Properties as Indicators of Forest Soil Quality: Challenges and Opportunities

Foresters have always relied on a knowledge of chemical and physical properties of soils to assess capacity of sites to support productive forests. Recently, the need for assessing soil properties has expanded because of growing public interest in determining consequences of management practices on the quality of soil relative to sustainability of forest ecosystem functions in addition to plant productivity. The concept of soil quality includes assessment of soil properties and processes as they relate to ability of soil to function effectively as a component of a healthy ecosystem. Specific functions and subsequent values provided by forest ecosystems are variable and rely on numerous soil physical, chemical, and biological properties and processes, which can differ across spatial and temporal scales. Choice of a standard set of specific properties as indicators of soil quality can be complex and will vary among forest systems and management objectives. Indices of forest soil quality which incorporate soil chemical, physical, and biological properties will be most readily adopted if they are sensitive to management-induced changes, easily measured, relevant across sites or over time, inexpensive, closely linked to measurement of desired values, and adaptable for specific ecosystems. This paper traces development of the concept of soil quality, explores use of soil chemical and physical properties as determinants of forest soil quality, and presents challenges and opportunities for forest soil scientists to play a relevant role in assessment and advancement of sustainable forest management by developing the concept of soil quality as an indicator of sustainability.

Estimating root respiration, microbial respiration in the rhizosphere, and root-free soil respiration in forest soils

Abstract We hypothesized that respiration measurements made using both the basal and excised-root respiration methods would allow us to quantify three important components of soil respiration: root respiration ( R root ), microbial respiration in the rhizosphere ( R rhizo ), and root-free soil respiration ( R rfs ). Root respiration determined by the basal method was approximately one-third greater than root respiration determined by the excised-root method (52 versus 32% of total soil respiration, respectively). Results from a decomposition model constructed for the root C fractions (easily decomposable, slowly decomposable, and recalcitrant) showed that the easily and slowly decomposable C fractions disappeared approximately 3 months after the basal respiration measurements began. Since these C fractions contained the majority of the C source for rhizosphere microorganisms (i.e., rhizodeposition), microbial respiration in the rhizosphere must have been severely reduced, indicating that respiration measured after 3 months must be dominated by microorganisms in the root-free soil ( R rfs ); this indicated that the basal method actually measured root-free soil respiration. This allowed us to fractionate the components of soil respiration based on the relationship: total soil respiration ( R total )= R root + R rhizo + R rfs ; subtracting R root(excised-root method) and R rfs(basal method) from R total gave us an estimate of microbial respiration in the rhizosphere; and the contribution of these three components to R total : R root =32%, R rhizo =20%, and R rfs =48%. These results are important because they suggest a way that soil respiration can be separated into at least three functionally different components, and they show that microbial respiration in the rhizosphere is a significant sink for photosynthetically-fixed C in forests.

Restoring Forests and Associated Ecosystem Services on Appalachian Coal Surface Mines

Surface coal mining in Appalachia has caused extensive replacement of forest with non-forested land cover, much of which is unmanaged and unproductive. Although forested ecosystems are valued by society for both marketable products and ecosystem services, forests have not been restored on most Appalachian mined lands because traditional reclamation practices, encouraged by regulatory policies, created conditions poorly suited for reforestation. Reclamation scientists have studied productive forests growing on older mine sites, established forest vegetation experimentally on recent mines, and identified mine reclamation practices that encourage forest vegetation re-establishment. Based on these findings, they developed a Forestry Reclamation Approach (FRA) that can be employed by coal mining firms to restore forest vegetation. Scientists and mine regulators, working collaboratively, have communicated the FRA to the coal industry and to regulatory enforcement personnel. Today, the FRA is used routinely by many coal mining firms, and thousands of mined hectares have been reclaimed to restore productive mine soils and planted with native forest trees. Reclamation of coal mines using the FRA is expected to restore these lands’ capabilities to provide forest-based ecosystem services, such as wood production, atmospheric carbon sequestration, wildlife habitat, watershed protection, and water quality protection to a greater extent than conventional reclamation practices.

Using soil quality indicators to assess forest stand management

A general goal of the forestry sector in many countries is developing and applying best management practices that will result in sustainable forestry. Maintaining soil productivity is a criterion in most sustainability initiatives. The purpose of this paper is to outline the steps and rationale of a monitoring approach, using soil-based indicators as an example, to assess stand-level sustainability of intensively managed forests. The monitoring process, described here, includes steps that establish the proper inference space, identify soil functions, attributes, and indicators, combine indicator responses in a soil quality model, establish baseline conditions for comparing soil change, validate relationships between indicators and soil productivity, and implement a sampling scheme to measure indicators, analyze trends, and interpret change for adapting Sustainable Forestry Practises (SFPs) to maximize their effectiveness. This monitoring process is proposed as a method for SFP research and development that will lead to sustainable forest management at the unit level.

Impact of harvesting and atmospheric pollution on nutrient depletion of eastern US hardwood forests

The eastern hardwood forests of the US may be threatened by the changing atmospheric chemistry and by changes in harvesting levels. Many studies have documented accelerated base cation losses with intensive forest harvesting. Acidic deposition can also alter nutrient cycling in these forests. The combination of increased harvesting, shorter rotations, and more intensive harvesting, along with the potential for N and S saturation due to changing atmospheric chemistry in the eastern US, raises concerns about the long-term productivity of these commercially important eastern hardwood forests. We review the literature describing the effects of intensive harvesting and acidic atmospheric deposition on budgets of base nutrients which presents evidence that the ambient levels of N and S deposition are leading to N and S saturation and elevated base leaching from the soil in some eastern forests, and we discuss potential concerns for long-term productivity. We also discuss criteria and indicators for monitoring sustainability of the soils of these forests.

Soil quality assessment in domesticated forests – a southern pine example

Maintenance and enhancement of soil productivity is central to the long-term success of intensive forest management. A simple technique is required for monitoring the effects of different management practices on soils as an aid in developing codes of practice that foster maintenance and enhancement of soil productivity. The objective of our work was to determine if management impacts on soil productivity could be assessed using the soil-quality concepts developed in agriculture. A soil-quality index (SQI) model, that measures the effects of management practices on five key growth-determining attributes of forest soils, namely (1) promote root growth, (2) store, supply and cycle nutrients, (3) accept, hold, and supply water, (4) promote gas exchange, and (5) promote biological activity, was developed and tested as part of a controlled study in intensively-managed pine plantations on the Lower Coastal Plain of South Carolina. Three 20-ha, 20-year-old loblolly pine plantations were harvested under wet and dry conditions to create a broad gradient in soil disturbance. Within each harvested plantation, a subset of 3-ha plots were site prepared by either bedding or mole-plowing plus bedding, then all sites were established as third-rotation pine plantations. Field data were collected spatially for soil bulk density, net N mineralization, water table depth, soil aeration, and soil moisture. Literature-based sufficiency values were determined for each property and substituted into the SQI model as surrogate indicators for the five key attributes, thus obtaining spatial SQI predictions within each harvesting and site preparation treatment. Our study results demonstrate how SQI monitoring could be used to identify the effects of management practices on soil productivity, which should aid in developing codes of practice as a component of achieving long-term sustainability in domesticated forests.

Effects of site preparation on nitrogen dynamics in the southern Piedmont

Abstract The impact of three mechanical site preparation treatments, chop-burn, shear-disc, and shear-pile-disc, on nitrogen dynamics was examined on gauged watersheds in the Piedmont of Virginia. Samples from soil solution and streamwater and a series of soil incubations, both laboratory and in situ, were used to monitor changes in the treatment areas following site preparation. Available nitrogen reserves were lowest in the shear-pile-disc watershed where the logging slash had been piled into windrows. Larger nitrogen reserves were found in the shear-disc and the chop-burn watersheds. Nitrogen mineralization was greater in the site prepared areas than in the uncut stand and mineralization generally increased as site preparation intensity increased. Between 58 and 95 kg/ha of nitrogen were mineralized in the site prepared areas during the first year following treatment compared to only 38 kg/ha during the same period in the uncut stand. Streamwater nitrogen export increased following site preparation with the largest losses of nitrogen occurring in the shear-pile-disc watershed.

Forest restoration potentials of coal-mined lands in the Eastern United States.

The Appalachian region in the eastern United Sates is home to the Earths most extensive temperate deciduous forests, but coal mining has caused forest loss and fragmentation. More than 6000 km in Appalachia have been mined for coal since 1980 under the Surface Mining Control and Reclamation Act (SMCRA). We assessed Appalachian areas mined under SMCRA for forest restoration potentials. Our objectives were to characterize soils and vegetation, to compare soil properties with those of pre-SMCRA mined lands that were reforested successfully, and to determine the effects of site age on measured properties. Soils were sampled and dominant vegetation characterized at up to 10 points on each of 25 post-SMCRA mines. Herbaceous species were dominant on 56%, native trees on 24%, and invasive exotics on 16% of assessed areas. Mean values for soil pH (5.8), electrical conductivity (0.07 dS m(-1)), base saturation (89%), and coarse fragment content (50% by mass) were not significantly different from measured levels on the pre-SMCRA forested sites, but silt+clay soil fraction (61%) was higher, bicarbonate-extractable P (4 mg kg(-1)) was lower, and bulk density (1.20 g cm(-1)) was more variable and often unfavorable. Pedogenic N and bicarbonate-extractable P in surface soils increased with site age and with the presence of weathered rocks among coarse fragments. Our results indicate a potential for many of these soils to support productive forest vegetation if replanted and if cultural practices, including temporary control of existing vegetation, soil density mitigation, and fertilization, are applied to mitigate limitations and aid forest tree reestablishment and growth.

Influence of herbaceous ground cover on forest restoration of eastern US coal surface mines

Competitive effects of dense herbaceous vegetation (ground cover) can inhibit forest restoration on mine sites. Here we review the evidence of ground cover interactions with planted tree seedlings on coal surface mines of the eastern US, discuss recent research into these interactions, and draw conclusions concerning ground cover management when restoring forests on reclaimed coal mines. Reclaimed mine sites have a high potential to support productive forests, however forest establishment is inhibited by reclamation practices that included soil compaction, and the seeding of competitive ground covers. In the first few years after tree planting, a dense ground cover of grass and legume species commonly seeded on mine sites often affect growth and survival negatively. Herbaceous vegetation providing less extensive and competitive ground coverage may either facilitate or inhibit tree establishment, depending on site conditions. The use of quality planting stock promotes the competitive ability of seedlings by improving nutrient status and the ability to capture available resources. Herbaceous species have contrasting functional characteristics, and thus compete differently with trees for available resources. Negative interactions with trees are more frequently reported for non-native cool-season grasses than for native warm-season grasses, while the effects of legumes change over time. Further research is needed to fully understand the mechanisms of tree/ground cover interactions. The development of seeding mixes that can control erosion, facilitate survival and growth of planted trees, and allow establishment by unplanted native species would aid forest restoration on eastern US, coal mines.

Establishing trees in an Appalachian silvopasture: response to shelters, grass control, mulch, and fertilization

In order to successfully introduce trees into existing pastures, it is important to determine and recommend a whole range of tree establishment practices. In the spring of 1995, approximately 350 bare-root seedlings each of black walnut (Juglans nigra L.) and honeylocust (Gleditsia triacanthos L.) were planted in six randomized paddocks within a silvopastoral study area at the Agroforestry Research and Demonstration Site in Blacksburg, Virginia. Three seedling establishment studies were tested, including (1) a tree protection study, (2) a water retention study, and (3) a fertilization study. Seedlings were planted using two different tree shelters (60 cm-tall poultry wire cage and 1.2 m-tall plastic Tubex), two water retention treatments (mulch and herbicide spray), and one fertilizer treatment. All treatments were compared to untreated controls. Tree survival, damage, and stem volume were compared for each species. Tree survival was comparable among all studies over three growing seasons. Tree establishment using poultry wire and Tubex shelters resulted in significant reduction of deer damage and significant increase in stem volume from 1996 to 1998. Tubex shelters had a pronounced positive impact on tree height and also on stem form; height of both black walnut and honeylocust was twice the height of control seedlings. Mulch and herbicide treatments for moisture control resulted in significant stem volume increases over thecontrol treatment from 1997 to 1998. However, mulching was less effective than the herbicide treatment. There was no significant tree growth response resulting from fertilization during this same period.