Travis Idol

Characterization of coarse woody debris across a 100 year chronosequence of upland oak–hickory forests

In most forest ecosystems, the total amount of coarse woody debris and its distribution into decay classes change over time from harvest to old growth stages. The relationship of decomposition classes to substrate quality is important to determine the contribution of woody debris to ecosystem nutrient cycling and forest development. The two objectives of this study were: (1) to determine if down dead wood (DDW) nutrient content varied with decomposition class or forest stand age; (2) to determine if DDW decomposition classes were related to indicators of substrate quality. Volume, mass, and indicators of substrate quality, such as N content and lignin:N ratio, were determined for woody debris from several decomposition classes in upland hardwood forest stands of different ages in southern Indiana, USA. Results showed a large decrease in volume and mass of DDW from recently harvested to mature stands. The dominant decomposition class shifted from Class II to Classes III and IV with increasing stand age. No Class I woody debris was found within any of the study plots. Nutrient concentration (N, S, and P) and carbohydrate fractions (soluble, hemicellulose, cellulose, and lignin) all varied significantly among certain decomposition classes, but N and P concentration and the C:N ratio were the best indicators of decomposition class. Patterns of P retention in decomposition classes suggested a strong potential for immobilization of this nutrient in woody debris. Based on substrate quality groupings, there were three distinguishable decomposition classes: Classes II and III, Class IV, and Class V.

Fine root dynamics across a chronosequence of upland temperate deciduous forests

Following a major disturbance event in forests that removes most of the standing vegetation, patterns of fine root growth, mortality, and decomposition may be altered from the pre-disturbance conditions. The objective of this study was to describe the changes in the seasonal and spatial dynamics of fine root growth, mortality, and decomposition that occur following removal of standing forest vegetation. Four upland temperate deciduous forest stands in southern Indiana, USA were chosen for this study. The ages of the stands, as represented as the number of growing seasons since forest overstory removal, were 4, 10, and 29 years at the beginning of the study in 1995. A mature stand, about 80-100 years since last harvest, was chosen to represent the pre-harvest conditions. A combination of soil cores and ingrowth cores were used to assess stand-level rates of fine root growth, mortality, and decomposition. Results show that fine root growth increases significantly after harvesting, but declines as the stand matures. In all stands, fine root mortality and decomposition are nearly equal to or greater than fine root growth. Fine root growth in the A horizon (0-8 cm) is significantly greater than in the B horizon (8-30 cm) in the 4, 29, and 80-100-year-old stands. In the 4- and 10-year-old stands fine root growth in the A horizon peaks earlier in the year than in the B horizon. Fine root biomass recovers rapidly in these upland hardwood stands following forest removal due to high rates of fine root growth; however, the distribution of fine root growth between the A and B soil horizons differs from pre-harvest conditions during the first 10-30 years.

Ecosystem Services from Smallholder Forestry and Agroforestry in the Tropics

Smallholder forestry and agroforestry systems in the tropics provide essential products and services for millions of producers, their surrounding communities, national and international consumers, and global society. The diversity of products provided by these systems meet the needs of smallholder producers for fuelwood, food, animal fodder, and other household and farm needs; they provide additional income to supplement major commodity crops; and they offer flexibility in production and income to buffer against falling commodity prices, crop failure, or other sources of financial or economic difficulty. The sustainability of these systems is increasingly dependent upon sources of income beyond the sale of conventional products, such as price premiums from sustainability certification and agro- and ecotourism. Payments for ecosystem services (PES) programs have been developed at multiple levels to provide incentives for smallholders to conserve and enhance tree cover and management practices to provide ecosystem services such as watershed protection and carbon sequestration. Ecotourism provides an enterprise-based strategy to engage producers in conservation and enhancement of these services. This review evaluates the ability of smallholder systems to support the provision of ecosystem services (ES) and the capacity of smallholders to participate in support programs and take advantage of other emerging opportunities to support smallholder enterprises.

Indicators of forest ecosystem productivity and nutrient status across precipitation and temperature gradients in Hawaii

Precipitation and temperature are known to have important effects on forest productivity, but these effects may be strongly mediated through their influence on soil and leaf nutrients. We measured indicators of forest productivity and soil and leaf nutrients across independent gradients of precipitation and elevation/temperature in lower montane Hawaiian forests dominated by a single overstorey species, Acacia koa, situated on 1500-3000-y-old soils that were mixtures of volcanic ash and basalt. Stand basal area was highest at the wettest site, 2000 mm mean annual precipitation (MAP), and leaf N and P were lowest at the driest site, 1000 mm MAP. Soil N availability and leaf N concentration declined across an 8 50-m elevation gradient, but this was not correlated with stand basal area or soil organic matter content. Across all stands, basal area was negatively correlated with the exchangeable soil P fraction. As well, the soil C:N ratio was negatively correlated with both soil P availability and the size of the primary mineral P fraction. Soil P availability and weathering appear to be important determinants of soil organic matter quantity and quality. Overall, precipitation is the major driving force for forest productivity, but P weathering and availability play important roles in limiting productivity in wetter sites and in controlling soil organic matter dynamics in these N-fixing forests.

Differentiation of Acacia koa forest stands across an elevation gradient in Hawai‘i using fine-resolution remotely sensed imagery

Koa (Acacia koa) forests are found across broad environmental gradients in the Hawaiian Islands. Previous studies have identified important environmental factors controlling stand structure and productivity at the plot level, but these have not been applied at the landscape level because of small-scale spatial variability. The goal of this study is to compare the differentiation of koa forest types across an elevation/temperature gradient ranging from 1200 to 2050 m asl (17–13°C mean annual temperature (MAT)) through the analysis of field measurements of forest structure and fine-resolution remotely sensed imagery. Several vegetation indices (VIs) (atmospherically resistant vegetation index (ARVI), enhanced vegetation index (EVI), normalized difference vegetation index (NDVI), soil-adjusted vegetation index (SAVI), modified soil-adjusted vegetation index (MSAVI), simple ratio (SR) and modified simple ratio (MSR)) are calculated from IKONOS satellite imagery of these stands and analysed using supervised classification techniques. This procedure allows a clear differentiation of koa stands from areas dominated by grasses, shrubs and bare lava. Across the elevation gradient, VIs allow differentiation of three koa forest stand classes at upper, intermediate and lower elevations. In agreement with the image classification, analysis of variance (ANOVA) of tree height and leaf phosphorus (P) suggests that there are also three significantly different groups of koa stands at those elevations. A landscape-scale map of land cover and koa stand classes demonstrates both the general trend with elevation and the small-scale heterogeneity that exists across the elevation gradient. Application of these classification techniques with fine spatial resolution imagery can improve the characterization of different koa stand types across the islands of Hawai‘i, which should aid both the conservation and utilization of this ecologically important species.

Assessment of Acacia Koa Forest Health across Environmental Gradients in Hawai‘i Using Fine Resolution Remote Sensing and GIS

Koa (Acacia koa) forests are found across broad environmental gradients in the Hawai‘ian Islands. Previous studies have identified koa forest health problems and dieback at the plot level, but landscape level patterns remain unstudied. The availability of high-resolution satellite images from the new GeoEye1 satellite offers the opportunity to conduct landscape-level assessments of forest health. The goal of this study was to develop integrated remote sensing and geographic information systems (GIS) methodologies to characterize the health of koa forests and model the spatial distribution and variability of koa forest dieback patterns across an elevation range of 600–1,000 m asl in the island of Kaua‘i, which correspond to gradients of temperature and rainfall ranging from 17–20 °C mean annual temperature and 750–1,500 mm mean annual precipitation. GeoEye1 satellite imagery of koa stands was analyzed using supervised classification techniques based on the analysis of 0.5-m pixel multispectral bands. There was clear differentiation of native koa forest from areas dominated by introduced tree species and differentiation of healthy koa stands from those exhibiting dieback symptoms. The area ratio of healthy koa to koa dieback corresponded linearly to changes in temperature across the environmental gradient, with koa dieback at higher relative abundance in warmer areas. A landscape-scale map of healthy koa forest and dieback distribution demonstrated both the general trend with elevation and the small-scale heterogeneity that exists within particular elevations. The application of these classification techniques with fine spatial resolution imagery can improve the accuracy of koa forest inventory and mapping across the islands of Hawai‘i. Such findings should also improve ecological restoration, conservation and silviculture of this important native tree species.

Conservation Agriculture Practices in Rainfed Uplands of India Improve Maize-Based System Productivity and Profitability

Traditional agriculture in rainfed uplands of India has been experiencing low agricultural productivity as the lands suffer from poor soil fertility, susceptibility to water erosion and other external pressures of development and climate change. A shift toward more sustainable cropping systems such as conservation agriculture production systems (CAPSs) may help in maintaining soil quality as well as improving crop production and farmer’s net economic benefit. This research assessed the effects over 3 years (2011–2014) of reduced tillage, intercropping, and cover cropping practices customized for maize-based production systems in upland areas of Odisha, India. The study focused on crop yield, system productivity and profitability through maize equivalent yield and dominance analysis. Results showed that maize grain yield did not differ significantly over time or among CAPS treatments while cowpea yield was considered as an additional yield in intercropping systems. Mustard and horsegram grown in plots after maize cowpea intercropping recorded higher grain yields of 25 and 37%, respectively, as compared to those without intercropping. Overall, the full CAPS implementation, i.e., minimum tillage, maize–cowpea intercropping and mustard residue retention had significantly higher system productivity and net benefits than traditional farmer practices, i.e., conventional tillage, sole maize cropping, and no mustard residue retention. The dominance analysis demonstrated increasing benefits of combining conservation practices that exceeded thresholds for farmer adoption. Given the use of familiar crops and technologies and the magnitude of yield and income improvements, these types of CAPS should be acceptable and attractive for smallholder farmers in the area. This in turn should support a move toward sustainable intensification of crop production to meet future household income and nutritional needs.

Mycorrhizal colonization is compatible with exponential fertilization to improve tree seedling quality

ABSTRACT This study tested the ability of exponential fertilization to minimize the tradeoff of increased seedling size and nutrient concentration with good root colonization by mycorrhizae. Two native Hawaiian tree species were tested. Four rates of nitrogen (N) (0–3 g per seedling) were delivered by the method of exponential fertilization to seedlings with and without inoculation with a native strain of arbuscular mycorrhizal fungus. For both species, the highest growth and nutrient concentrations occurred with mycorrhizal colonization at 1–2 g N per seedling. Growth of inoculated seedlings was significantly lower at 3.0 g N per seedling, likely due to a large reduction in mycorrhizal colonization. Our results demonstrate that mycorrhizal colonization is not only compatible with exponential fertilization, combined they produce larger seedlings with higher nutrient content. This should improve outplanting success in degraded or challenging sites.