The Experts below are selected from a list of 18360 Experts worldwide ranked by ideXlab platform
Harold E. Burkhart - One of the best experts on this subject based on the ideXlab platform.
-
Survival Analysis of Loblolly Pine Trees With Spatially Correlated Random Effects
Journal of the American Statistical Association, 2015Co-Authors: Yili Hong, Ram Thapa, Harold E. BurkhartAbstract:Loblolly Pine, a native Pine species of the southeastern United States, is the most-planted species for commercial timber. Predicting survival of Loblolly Pine following planting is of great interest to researchers in forestry science as it is closely related to the yield of timber. Data were collected from a region-wide thinning study, where permanent plots, located at 182 sites ranging from central Texas east to Florida and north to Delaware, were established in 1980–1981. One of the main objectives of this study was to investigate the relationship between the survival of Loblolly Pine trees and several important covariates such as age, thinning types, and physiographic regions, while adjusting for spatial correlation among different sites. We use a semiparametric proportional hazards model to describe the effects of covariates on the survival time, and incorporate the spatial random effects in the model to describe the spatial correlation among different sites. We apply the expectation-maximization (EM...
-
predicting site index of plantation Loblolly Pine from biophysical variables
Forest Ecology and Management, 2014Co-Authors: Charles O Sabatia, Harold E. BurkhartAbstract:Concerns of the effect of climate change on forest productivity have impelled the need to accurately predict forest productivity from climate, physiographic and edaphic variables (biophysical variables). We fitted and evaluated random forest models and nonlinear least squares regression models for predicting plantation Loblolly Pine (Pinus taeda L.) site index from biophysical variables. Tree and stand location data were provided by the Virginia Tech Forest Modeling Research Cooperative. Climate data for each stand location were computed using the Oakridge National Laboratories’ daily surface weather prediction models, while soils data were extracted from the USDA Natural Resource Conservation Service SSURGO GIS database using GIS data extraction techniques. Separate models were fitted for non-intensively managed (Non-IMP) and intensively managed (IMP) Loblolly Pine plantations. Variable selection methods in both modeling approaches showed that the number of biophysical variables that were important in predicting site index of IMP Loblolly Pine was smaller than the number for Non-IMP stands. The non-parametric random forest models had better fit and prediction statistics than the least squares parametric models but exhibited the potential to give illogical predictions under extrapolation. Site index predictions from both modeling approaches exhibited a regression towards the mean.
-
Growth of young Loblolly Pine trees following pruning
Forest Ecology and Management, 2011Co-Authors: Ralph L. Amateis, Harold E. BurkhartAbstract:Pruning Loblolly Pine trees is sometimes practiced to improve wood quality even though reduced growth following treatment may occur. Two experiments were established in February 2000 in the Piedmont region of Virginia, USA, to examine the impact of timing and intensity of pruning on subsequent growth of young Loblolly Pine trees. Results of one study indicated that there is a window of opportunity during the early portion of stand development where up to 50% of the live crown length can be removed without a significant loss of long-term height or diameter growth. Within a year following pruning at ages 3, 6 and 9 (all pruning treatments occurred prior to crown closure), crown mass had been restored and growth comparable to an unpruned control resumed. By age 11 there were no significant differences in cumulative height or dbh of any of the one-lift pruning treatments and the control. Findings from a second study planted at closer spacings where pruning treatments occurred at crown closure (age 6) showed that pruning some of the trees in a Loblolly Pine plantation does not result in a loss of long-term height or diameter growth or crown dominance for the pruned trees as compared to their unpruned neighbors. For both studies, growth reductions following pruning were small and transitory.
-
Loblolly Pine Plantations in Southeastern US.
2004Co-Authors: James A. Westfall, Harold E. Burkhart, H. Lee AllenAbstract:Intensively managed Loblolly Pine stands are often subjected to a variety of silvicultural treatments at time of planting or shortly thereafter. However, most Loblolly Pine growth-and-yield models predict growth after crown closure has occurred. In this article, we describe the development and implementation of a system of equations designed to simu- late growth of Loblolly Pine before the onset of intraspecific competition. Treatment re- sponse functions were also developed for various site pre'paration, herbaceous weed con- trol, and fertilization practices. These functions modify the baseline model predictions to simulate the effects of treatments on tree growth and stand development. This system was incorporated into the PTAEDAZ growth-and-yield simulator to make growth projections from time of planting through rotation age for intensively managed stands of Loblolly Pine in the southeastern United States. Growth simulations specifying either bedding or disking showed increases in volume growth for both treatments. The shear-and-pile site-preparation method reduced growth rates slightly. Volume growth responses to herbaceous weed control were positive, with magnitude of increase largely depending on duration of treat- ment. Increases in volume attributable to fertilization at planting were related to types of element applied. The largest predicted response was for phosphorus fertilization, whereas application of potassium was the least effective fertilization treatment. Site preparation, weed control, and fertilization treatment combinations produced additional volume gains when compared to single treatments, while maintaining predicted values that are within biological limits for Loblolly Pine growth. Levels of response to treatments are consistent with results from published studies on intensive management practices. The addition of the precompetitive growth system did not significantly affect the predictive behavior of the PTAEDA2 model for untreated stands. FOR. SCI. 50(6):823-835.
-
Modeling the Effect of Density on the Growth of Loblolly Pine Trees
Southern Journal of Applied Forestry, 2002Co-Authors: Mahadev Sharma, Harold E. Burkhart, Ralph L. AmateisAbstract:Abstract Data from a set of Loblolly Pine spacing trials that have reached 16 yr since establishment were used to evaluate the effect of spacing on Loblolly Pine tree growth and stand development. Mean responses for six variables were evaluated: height, dbh, crown ratio, crown length, crown width, and survival. All response variables were affected by density, with dbh being the most affected and height the least affected over the 16 yr period. The rectangularity, or shape, of the growing space was not a significant factor in the development of any of these response variables. Models were constructed to characterize the development of the six response variables extrapolated over typical plantation rotation lengths of Loblolly Pine. South. J. Appl. For. 26(3):124–133.
C.d. Nelson - One of the best experts on this subject based on the ideXlab platform.
-
Post-fire resprouting of shortleaf Pine is facilitated by a morphological trait but fire eliminates shortleaf × Loblolly Pine hybrid seedlings
Forest Ecology and Management, 2016Co-Authors: J.c. Bradley, Rodney E. Will, John F. Stewart, C.d. Nelson, James M. GuldinAbstract:Abstract Concurrent with fire exclusion, shortleaf Pine × Loblolly Pine hybrids have increased throughout the southeastern USA and may threaten the genetic integrity of shortleaf Pine. Historically, fire favored shortleaf Pine over other southern Pine species, especially Loblolly Pine, with which it shares a broad sympatric natural range. Shortleaf Pine seedlings have a morphological adaptation (basal crook) that lowers dormant buds to the soil surface where they are presumably protected from fire to facilitate resprouting after topkill. To evaluate this presumption, we tested (1) the functional role of the basal crook in protecting dormant buds by measuring resprouting after exposing the lower stem of shortleaf Pine to fire and protecting from fire the lower stem (and dormant buds) of Loblolly Pine (which lacks a basal crook) and (2) the occurrence and importance of the basal crook morphological adaptation in F1 shortleaf × Loblolly Pine seedlings by comparing morphology and post-fire resprouting of the hybrids to both parents. Fire exposure of shortleaf Pine seedling dormant buds caused seedling mortality, while protecting Loblolly Pine dormant buds facilitated resprouting. Hybrid Pines have basal crooks intermediate to the strong crook of shortleaf Pine and Loblolly Pine’s non-crooked stem. Fire top-killed Loblolly Pine and shortleaf × Loblolly Pine seedlings, and they did not resprout, while 57% of shortleaf Pine resprouted after topkill during two dormant season and one growing season burns. This highly significant difference shows that the basal crook is important for shortleaf Pine resprouting after topkill by fire. Fire is an important tool to reduce shortleaf × Loblolly Pine hybrids, and to provide a competitive advantage to shortleaf Pine relative to Loblolly Pine, for ecosystem restoration and maintaining the genetic integrity of shortleaf Pine.
-
bidirectional introgression between Loblolly Pine pinus taeda l and shortleaf Pine p echinata mill has increased since the 1950s
Tree Genetics & Genomes, 2012Co-Authors: John F. Stewart, C. G. Tauer, C.d. NelsonAbstract:Hybridization between Loblolly Pine and shortleaf Pine has been shown in sympatric and allopatric portions of the species native ranges. In this study, we used 25 microsatellite markers to determine the hybrid status of 165 and 151 Loblolly Pine and shortleaf Pine trees sampled across their ranges, respectively, and to estimate population differentiation within these species. Estimated differentiation (Φ PT) for these current-day samples was significantly higher in both species—0.115 in Loblolly Pine and 0.146 in shortleaf Pine—than for trees planted from seed collected from the same locations in the 1950s. These increases are likely due to anthropogenic causes such as habitat fragmentation. In addition, the proportion of hybrids rose dramatically in both species: 27.3% hybrids in Loblolly Pine populations and 46.7% hybrids in shortleaf Pine populations compared to rates of 4.5% and 3.3%, respectively, in the 1950s populations. Our results suggest that shortleaf Pine and remnant naturally regenerated Loblolly Pine are at risk.
John F. Stewart - One of the best experts on this subject based on the ideXlab platform.
-
Post-fire resprouting of shortleaf Pine is facilitated by a morphological trait but fire eliminates shortleaf × Loblolly Pine hybrid seedlings
Forest Ecology and Management, 2016Co-Authors: J.c. Bradley, Rodney E. Will, John F. Stewart, C.d. Nelson, James M. GuldinAbstract:Abstract Concurrent with fire exclusion, shortleaf Pine × Loblolly Pine hybrids have increased throughout the southeastern USA and may threaten the genetic integrity of shortleaf Pine. Historically, fire favored shortleaf Pine over other southern Pine species, especially Loblolly Pine, with which it shares a broad sympatric natural range. Shortleaf Pine seedlings have a morphological adaptation (basal crook) that lowers dormant buds to the soil surface where they are presumably protected from fire to facilitate resprouting after topkill. To evaluate this presumption, we tested (1) the functional role of the basal crook in protecting dormant buds by measuring resprouting after exposing the lower stem of shortleaf Pine to fire and protecting from fire the lower stem (and dormant buds) of Loblolly Pine (which lacks a basal crook) and (2) the occurrence and importance of the basal crook morphological adaptation in F1 shortleaf × Loblolly Pine seedlings by comparing morphology and post-fire resprouting of the hybrids to both parents. Fire exposure of shortleaf Pine seedling dormant buds caused seedling mortality, while protecting Loblolly Pine dormant buds facilitated resprouting. Hybrid Pines have basal crooks intermediate to the strong crook of shortleaf Pine and Loblolly Pine’s non-crooked stem. Fire top-killed Loblolly Pine and shortleaf × Loblolly Pine seedlings, and they did not resprout, while 57% of shortleaf Pine resprouted after topkill during two dormant season and one growing season burns. This highly significant difference shows that the basal crook is important for shortleaf Pine resprouting after topkill by fire. Fire is an important tool to reduce shortleaf × Loblolly Pine hybrids, and to provide a competitive advantage to shortleaf Pine relative to Loblolly Pine, for ecosystem restoration and maintaining the genetic integrity of shortleaf Pine.
-
Recovery from topkill of shortleaf Pine × Loblolly Pine hybrids compared to their parent populations
Trees, 2013Co-Authors: Rodney E. Will, Curtis J. Lilly, John F. Stewart, Scott Huff, C. G. TauerAbstract:Hybrids between shortleaf Pine (Pinus echinata Mill.) and Loblolly Pine (Pinus taeda L.) have increased since the 1950s throughout the southeastern USA. Previously, greater sprouting capacity and the formation of a basal crook that lowers the height of dormant buds may have favored pure shortleaf Pine populations on fire prone sites. The objective of this study was to determine how seasonal timing of topkill by both fire and topclipping affect sprouting of shortleaf × Loblolly Pine F1 hybrids compared to their parent open-pollinated populations during their third growing season. A factorial combination of top-clipping (hand pruners) and girdling by fire (propane torch) was conducted on November 2010, January, March, and April 2011 and sprouting response was measured after the growing season. Survival of topkilled shortleaf Pine (94 %) was greatest followed by hybrid (78 %) and Loblolly Pine (35 %). However, species effects varied with topkill treatment and treatment date because survival was relatively lower for Loblolly and hybrid Pines in the burn-only as well as the November and April treatment dates while survival of shortleaf Pine was consistently high. The number of sprouts was greatest for shortleaf (32.3) intermediate for hybrid (23.8) and lowest for Loblolly Pine (12.0). Overall, 83 % of shortleaf Pine, 35 % of hybrid Pine, and 5 % of Loblolly Pine exhibited a basal crook. The height from ground line to the lowest sprout was shortest for shortleaf (3.5 mm), intermediate for hybrids (7.7 mm), and largest for Loblolly Pine (21.3 mm). While the hybrid saplings exhibited intermediate performance in survival, sprouting capacity, and crooking, pure shortleaf Pine were superior and are probably better suited to recover from fire.
-
bidirectional introgression between Loblolly Pine pinus taeda l and shortleaf Pine p echinata mill has increased since the 1950s
Tree Genetics & Genomes, 2012Co-Authors: John F. Stewart, C. G. Tauer, C.d. NelsonAbstract:Hybridization between Loblolly Pine and shortleaf Pine has been shown in sympatric and allopatric portions of the species native ranges. In this study, we used 25 microsatellite markers to determine the hybrid status of 165 and 151 Loblolly Pine and shortleaf Pine trees sampled across their ranges, respectively, and to estimate population differentiation within these species. Estimated differentiation (Φ PT) for these current-day samples was significantly higher in both species—0.115 in Loblolly Pine and 0.146 in shortleaf Pine—than for trees planted from seed collected from the same locations in the 1950s. These increases are likely due to anthropogenic causes such as habitat fragmentation. In addition, the proportion of hybrids rose dramatically in both species: 27.3% hybrids in Loblolly Pine populations and 46.7% hybrids in shortleaf Pine populations compared to rates of 4.5% and 3.3%, respectively, in the 1950s populations. Our results suggest that shortleaf Pine and remnant naturally regenerated Loblolly Pine are at risk.
James M. Guldin - One of the best experts on this subject based on the ideXlab platform.
-
Post-fire resprouting of shortleaf Pine is facilitated by a morphological trait but fire eliminates shortleaf × Loblolly Pine hybrid seedlings
Forest Ecology and Management, 2016Co-Authors: J.c. Bradley, Rodney E. Will, John F. Stewart, C.d. Nelson, James M. GuldinAbstract:Abstract Concurrent with fire exclusion, shortleaf Pine × Loblolly Pine hybrids have increased throughout the southeastern USA and may threaten the genetic integrity of shortleaf Pine. Historically, fire favored shortleaf Pine over other southern Pine species, especially Loblolly Pine, with which it shares a broad sympatric natural range. Shortleaf Pine seedlings have a morphological adaptation (basal crook) that lowers dormant buds to the soil surface where they are presumably protected from fire to facilitate resprouting after topkill. To evaluate this presumption, we tested (1) the functional role of the basal crook in protecting dormant buds by measuring resprouting after exposing the lower stem of shortleaf Pine to fire and protecting from fire the lower stem (and dormant buds) of Loblolly Pine (which lacks a basal crook) and (2) the occurrence and importance of the basal crook morphological adaptation in F1 shortleaf × Loblolly Pine seedlings by comparing morphology and post-fire resprouting of the hybrids to both parents. Fire exposure of shortleaf Pine seedling dormant buds caused seedling mortality, while protecting Loblolly Pine dormant buds facilitated resprouting. Hybrid Pines have basal crooks intermediate to the strong crook of shortleaf Pine and Loblolly Pine’s non-crooked stem. Fire top-killed Loblolly Pine and shortleaf × Loblolly Pine seedlings, and they did not resprout, while 57% of shortleaf Pine resprouted after topkill during two dormant season and one growing season burns. This highly significant difference shows that the basal crook is important for shortleaf Pine resprouting after topkill by fire. Fire is an important tool to reduce shortleaf × Loblolly Pine hybrids, and to provide a competitive advantage to shortleaf Pine relative to Loblolly Pine, for ecosystem restoration and maintaining the genetic integrity of shortleaf Pine.
Ralph L. Amateis - One of the best experts on this subject based on the ideXlab platform.
-
Crown-rise and crown-length dynamics: application to Loblolly Pine
Forestry: An International Journal of Forest Research, 2013Co-Authors: Harry T. Valentine, Ralph L. Amateis, Jeffrey H. Gove, Annikki MäkeläAbstract:The original crown-rise model estimates the average height of a crown-base in an even-aged mono-species stand of trees. We have elaborated this model to reduce bias and prediction error, and to also provide crownbase estimates for individual trees. Results for the latter agree with a theory of branch death based on resource availability and allocation. We use the improved model to estimate the growth and stem-profile development of a mean-tree in an even-aged stand of Loblolly Pine. Predictions show good agreement with data from a Loblolly Pine spacing trial.
-
Growth of young Loblolly Pine trees following pruning
Forest Ecology and Management, 2011Co-Authors: Ralph L. Amateis, Harold E. BurkhartAbstract:Pruning Loblolly Pine trees is sometimes practiced to improve wood quality even though reduced growth following treatment may occur. Two experiments were established in February 2000 in the Piedmont region of Virginia, USA, to examine the impact of timing and intensity of pruning on subsequent growth of young Loblolly Pine trees. Results of one study indicated that there is a window of opportunity during the early portion of stand development where up to 50% of the live crown length can be removed without a significant loss of long-term height or diameter growth. Within a year following pruning at ages 3, 6 and 9 (all pruning treatments occurred prior to crown closure), crown mass had been restored and growth comparable to an unpruned control resumed. By age 11 there were no significant differences in cumulative height or dbh of any of the one-lift pruning treatments and the control. Findings from a second study planted at closer spacings where pruning treatments occurred at crown closure (age 6) showed that pruning some of the trees in a Loblolly Pine plantation does not result in a loss of long-term height or diameter growth or crown dominance for the pruned trees as compared to their unpruned neighbors. For both studies, growth reductions following pruning were small and transitory.
-
Modeling the Effect of Density on the Growth of Loblolly Pine Trees
Southern Journal of Applied Forestry, 2002Co-Authors: Mahadev Sharma, Harold E. Burkhart, Ralph L. AmateisAbstract:Abstract Data from a set of Loblolly Pine spacing trials that have reached 16 yr since establishment were used to evaluate the effect of spacing on Loblolly Pine tree growth and stand development. Mean responses for six variables were evaluated: height, dbh, crown ratio, crown length, crown width, and survival. All response variables were affected by density, with dbh being the most affected and height the least affected over the 16 yr period. The rectangularity, or shape, of the growing space was not a significant factor in the development of any of these response variables. Models were constructed to characterize the development of the six response variables extrapolated over typical plantation rotation lengths of Loblolly Pine. South. J. Appl. For. 26(3):124–133.
-
Projecting the Growth of Loblolly Pine in a Changing Atmosphere
Southern Journal of Applied Forestry, 1999Co-Authors: Harry T. Valentine, Harold E. Burkhart, Ralph L. Amateis, Timothy G. Gregoire, David Y. Hollinger, David W. MacfarlaneAbstract:Abstract Recent findings regarding the magnitude of the influence of carbon dioxide concentration on the rate of photosynthesis in Loblolly Pine have been incorporated into Pipestem, a model of carbon allocation and growth. Pipestem translates photosynthetic rates into rates of change in stand basal area, quadratic mean diameter, tree density, average tree height, average crown length, dominant tree height, and woody dry matter. Projections of Loblolly Pine growth were run under the assumption that the atmospheric concentration of CO2 will continue to increase by 1.6 ppm/yr, the average rate of increase in the last 10 yr. Standing crops of woody dry matter in 20-yr-old Loblolly Pine stands in Buckingham County, Virginia, are projected to increase, on the average, by 9.8% in 20 yr. It is concluded that the CO2 effect should be accounted for in long-term projections of Loblolly Pine growth. South. J. Appl. For. 23(4):212-216.
-
Modeling individual tree growth for juvenile Loblolly Pine plantations
Forest Ecology and Management, 1996Co-Authors: Shaoang Zhang, Harold E. Burkhart, Ralph L. AmateisAbstract:Abstract Modeling juvenile growth of Loblolly Pine plantations is important for a better understanding of the whole process of stand development and helping to schedule appropriate silvicultural treatments for young stands. This paper evaluates spacing treatment effects on young Loblolly Pine trees and presents individual tree growth models for Loblolly Pine plantations. Using data from spacing trials (plot size ranging from 1.22 × 1.22 to 3.66 × 3.66 m2) for Loblolly Pine plantations, a generalized randomized block design (GRBD) analysis was conducted to test spacing treatment and site quality effects on young tree growth. It is shown that planting density and site quality have significant influence, and spacing rectangularity is negligible. Based on the Bertalanffy differential equation and biologically reasonable assumptions regarding density and site quality effects on tree growth, a general projection model for individual tree diameter and height was developed. A stochastic model for generalizing tree height predictions within each diameter class was proposed. Models for crown ratio, and initial diameter distribution were also developed. The models were estimated with spacing trial data from young Loblolly Pine plantations. Validation results for these models showed that they are appropriate for predicting the juvenile growth of Loblolly Pine plantations where competing vegetation has been controlled in a similar manner to these spacing trials.