Recipient Organization
PURDUE UNIVERSITY
(N/A)
WEST LAFAYETTE,IN 47907
Performing Department
Forestry & Natural Resources
Non Technical Summary
Hardwood forests throughout the United States provide important ecological and economic benefits. With increasing population growth, however, there is tremendous pressure on these forests to supply timber, clean water, wildlife habitat, and recreation. The nation will increasingly turn toward plantations to help meet wood product needs. Concurrently, there is increasing interest in using plantations to help restore hardwood forest habitats for conservation purposes. Artificial forest regeneration through tree planting offers a means to control species composition, incorporate genetically improved (e.g., disease-resistant) stock, and apply intensive culture that may lead to enhanced tree growth and wood quality compared to natural forests. Additionally, tree plantations may aid in restoration of degraded areas (e.g., mine reclamation sites) or reintroduction of threatened native species, such as American chestnut (Jacobs et al. 2013). While extensive plantation research has been conducted with conifer species of the western and southeastern United States, regeneration issues in hardwood forests have received relatively little attention (Wilson and Jacobs 2006; Jacobs 2011).Establishment success of hardwood tree species is highly variable and factors such as herbivory, drought or nutrient stress, and vegetative competition result in many examples of failed plantations. In Indiana (Central Hardwood Region), for instance, survival of operationally planted hardwoods averages about 66%, with less than half of surviving seedlings deemed free-to-grow after five years (Jacobs et al. 2004). In other hardwood zones in the United States, lack of availability of appropriate hardwood nursery stock (i.e., species and stock quality) and pre- and post-planting management techniques limit operational regeneration success. This contrasts with conifer plantations in the western and southeastern United States, where survival is frequently above 90% and indicates the need for improvements in hardwood regeneration productivity.The Hardwood Tree Improvement and Regeneration Center (www.htirc.org) at Purdue University was founded nearly 20 years ago and has demonstrated that silvicultural to improve the quality of nursery seedlings, using appropriate planting techniques, and applying after-planting care to juvenile trees may significantly improve seedling establishment success and early productivity of hardwood regeneration (Jacobs 2011). Additionally, the Tropical Hardwood Tree Improvement and Regeneration Center (www.trophtirc.org) was established in 2010 to address overlapping priorities specific to Pacific Island hardwood tree species.Despite these strides, new threats are constantly emerging due to global change (e.g., invasive species, pests and pathogens, and a warmer climate; Jacobs et al. 2015). There is also an increased emphasis on restoration of degraded sites and conversion of abandoned conifer plantations to native hardwoods. This implicates the shifting and evolving nature of challenges that must be overcome to ensure forest productivity in hardwood-dominated forests.Thus, the basic function of this research project is to improve the regeneration of hardwood forests by identifying factors that limit successful forest regeneration and by formulating new silvicultural technologies to help overcome these constraints. We focus efforts on three important hardwood zones of the United States: the temperate Central Hardwood Forest Region, sub-temperate maritime forests along the southeastern Atlantic Coast, and tropical Hawaii. The outcomes of this endeavor promise to be of substantial economic and ecological benefit to the residents and environment of these regions.
Animal Health Component
70%
Research Effort Categories
Basic
30%
Applied
70%
Developmental
(N/A)
Goals / Objectives
The primary objective of this project is to enhance the regeneration and restoration success of native hardwood forest tree species in three important hardwood zones of the United States: the temperate Central Hardwood Forest Region, sub-temperate maritime forests along the southeastern Atlantic Coast, and tropical Hawaii. This will be addressed by improving knowledge of site-specific biotic and abiotic factors that limit establishment and juvenile development of hardwood forest regeneration. Simultaneously, management practices that promote hardwood plantation survival and growth will be identified and communicated. The specific project objectives are to:Evaluate influences of overstory light availability on eco-physiological responses of hardwood regeneration during site restoration.Determine the relative influence of animal browse on establishment of hardwood regeneration and identify cost-effective management options to control damage.Assess influences of competing vegetation control and nursery cultural treatments on establishment success of hardwood regeneration in afforestation and reforestation sites.Examine physiological and growth responses of hardwood regeneration to varying forms and application rates of nitrogen fertilizers.
Project Methods
To evaluate influences of overstory light availability on eco-physiological responses of hardwood regeneration during site restoration, we will evaluate complementary trials in three regions of study. In the temperate Central Hardwood Forest Region, we will evaluate conversion of introduced white pine (Pinus strobus) to native species including American chestnut (Castanea dentata) and northern red oak (Quercus rubra). These species are of high economic and ecological value in this region, yet are threatened by disease (chestnut) or poor regeneration in natural hardwood stands (oak). In sub-temperate maritime forests along the southeastern Atlantic Coast in Georgia, we will collaborate with a scientist at New Mexico State University to examine conversion of abandoned loblolly pine (Pinus taeda) plantations to the historically dominant maritime forests by planting live oak (Quercus virginia). Finally, in tropical Hawaii, we will collaborate with scientists at the University of Hawaii at Manoa to study conversion of the introduced Japanese tsugi pine (Cryptomeria japonica) to native koa (Acacia koa). In each of these regions, our overall objective is to evaluate effects of canopy shading on the morphological and physiological development of hardwood regeneration in order to aid species restoration. This will be accomplished by reducing overstory density to specific levels of residual tree basal area (white pine, loblolly pine; using a randomized complete block design with minimum 4 replications) or by incorporating existing patchiness (due to scattered mortality) that has created high variability in overstory tree density (tsugi pine; using a completely randomized design). We will measure survival and growth responses in all experiments but also evaluate physiological development of planted hardwood regeneration by measuring leaf water potential, gas exchange, and nutrient uptake. These results should help to provide important insight into the mechanisms controlling growth responses under the varying residual canopy overstory light conditions.We will use experimental trials in the three regions of study to determine the relative influence of animal browse on establishment of hardwood regeneration and to identify cost-effective management options to minimize this damage. Browsing damage, primarily from deer in all three regions of study, may be controlled by fencing but its use is limited in operation due to relatively high costs (Jacobs et al. 2004). Thus, experiments will be established to evaluate the relative efficiency of fencing, other direct forms of browse protection (e.g., plastic tree shelters or repellents), and techniques designed to allow escape from deer browse through promotion of rapid free-to-grow status of seedlings above the level of browse (e.g., field fertilization). We will plant live oak in Georgia and koa in Hawaii, while in Indiana the focus species will be oaks (Quercus spp.) and black walnut (Juglans nigra). Each experiment will be established as a randomized complete block design (minimum 4 replications). Field measurements including survival and growth will be recorded at the end of at least two growing seasons in each the study; level of browsing intensity will also be assessed during early-spring and late-fall. We will combine seedling responses in these studies with a report of estimated costs associated with the various alternative options to fencing. Collectively, these results will provide an assessment of the relative efficacy of varying browse control methods and serve as a guide to land managers in choosing options to best meet their objectives.Chemical site preparation and/or release treatments with herbicides are often used to promote establishment of native hardwoods, yet the potential for herbicide phytotoxicity is not well understood. Thus, to assess influences of competing vegetation control and nursery cultural treatments on establishment success of hardwood regeneration in afforestation and reforestation sites, we will install field experiments in each of the three study regions. The trials will include weed control (Georgia, Hawaii, Indiana) and/or use of high quality nursery stock (Hawaii, Indiana). Similar to objective two, we will focus on live oak in Georgia and koa in Hawaii, while in Indiana we will evaluate oaks and black walnut (Juglans nigra). Weed control treatments in all three study areas will consist of an untreated control, 1 year of weed control, or 2 years of weed control with herbicide (i.e., glyphosate) at recommended application rates. In Hawaii and Indiana, we will implement a factorial design with weed control treatments and varying nursery stocktypes (e.g., container vs. bareroot seedlings in Indiana; different container sizes and/or hardening regimes in Hawaii). Each experiment will be established as a randomized complete block design (minimum 4 replications). Field measurements including survival and growth will be recorded at the end of at least two growing seasons in each the study. Leaf water potential and nitrogen content will also be measured to quantify water stress and plant nutrient availability associated with weed control and/or nursery stocktypes. At the peak of vegetation cover (August), vegetation surveys will be conducted to evaluate competition. Through workshops, field days, and publications, these results will be communicated directly to land managers in each of the regions, providing relevant important to inform hardwood reforestation and restoration operations.To examine physiological and growth responses of hardwood regeneration to varying forms and application rates of nitrogen (N) fertilizers, we will establish controlled environment trials using black walnut in Indiana. Using the rare stable isotope 15N, these studies will determine relative efficiency of N uptake (i.e., Salifu et al. 2008, 2009b) from different N forms applied at varying phenological phases. This will be accomplished by installing factorial experiments with one-year-old black walnut seedlings transplanted into containers in a greenhouse and treated with four independent variables: N form (nitrate, ammonium, glycine), N concentration (3mM, and 12mM), and N form rate (equimolar, nitrate dominant, ammonium dominant and glycine dominant) at two different phenological stages (early spring and mid to late-summer). Nitrogen fertilizers will be labeled as 15N solutions to allow for direct quantification of uptake rates among the varying N treatments. Seedlings will be periodically evaluated for photosynthesis rates and chlorophyll content during active growth and destructively harvested at the end of the growing season. Seedlings will be divided into new stems and leaves, stems, coarse roots, and fine roots. These plant organs will each be analyzed for total N concentrations, and 15N/14N isotopic ratios, which will allow for determination of relative contributions of N uptake from soil vs. retranslocation of N from reserves in new growth of black walnut seedlings. Collectively, these results will allow for evaluation of how differences in N demand, photosynthetic rate, or internal N status may explain variation in N uptake rates within treatments and seasons. This research will also allow us to determine plant performance in response to varying N forms and potential interactions with soil N availability. Results from these experiments will be synthesized to provide recommendations for management systems that ensure the efficient use of high cost N fertilizer.