Soil Science Society of America Journal, May 1, 1992
For many soils of the tropics, inputs of organic materials are essential to sustain soil fertilit... more For many soils of the tropics, inputs of organic materials are essential to sustain soil fertility and crop production. Research in the quality of organic inputs, a key factor controlling rates of decomposition and nutrient release, continues to guide selection and use of organic materials as nutrient sources. The relationship between decomposition patterns and the quality parameters of the fresh leaves of six agroforestry species: Sesbania sesban, Croton megalocarpus, Calliandra calothyrsus, Tithonia diversifolia, Lantana camara, and Senna spectabilis, was investigated in a litterbag study over a period of 77 days in the highlands of western Kenya. The litterbags were buried 1 cm below the soil surface and covered with soil of ca 1 cm thickness. Percent leaf mass and total N and P that remained with time strongly correlated with total P and C/P ratio (R 2 ϭ 0.60-0.90) during the first 35 days of study; but afterwards, correlation was stronger with the initial soluble polyphenolics (Pp)/P ratio (R 2 ϭ 0.69-0.92) than with total P and C/P ratio. Loss of leaf mass and release of N and P followed the exponential function, y t ϭ y 0 * e Ϫkt , from which the specific decay rate constants (k) were calculated for loss of leaf mass (k B) and release of N (k N) and P (k P). Among the plant species, the k values were lowest in Calliandra with k B ϭ 0.012/d, k N ϭ 0.017/d and k P ϭ 0.044/d. Lantana had the highest k values with k B ϭ 0.067/d and k P ϭ 0.119/d, but the highest k N value of 0.109/d occurred in Tithonia. The k B values for all organic materials were lower than their corresponding k N and k P values, suggesting that leaching of N and P from litters may have augmented the microbial mineralization of N and P. There was a strong correlation between the k B , k N , and k P values and total P (r ϭ 0.82-0.96; P Ͻ 0.01), but not total N, lignin (LIG), or Pp. Rates of N and P release followed the general trend: Tithonia Ͼ Senna Ͼ Lantana Ͼ Sesbania Ͼ Croton Ͼ Calliandra. The results indicated that, among the quality parameters studied, total P is the most important factor controlling rate of decomposition and N and P release from organic inputs in the area of study.
Genomic selection can increase genetic gain per generation through early selection. Genomic selec... more Genomic selection can increase genetic gain per generation through early selection. Genomic selection is expected to be particularly valuable for traits that are costly to phenotype and expressed late in the life cycle of long-lived species. Alternative approaches to genomic selection prediction models may perform differently for traits with distinct genetic properties. Here the performance of four different original methods of genomic selection that differ with respect to assumptions regarding distribution of marker effects, including (i) ridge regression-best linear unbiased prediction (RR-BLUP), (ii) Bayes A, (iii) Bayes Cp, and (iv) Bayesian LASSO are presented. In addition, a modified RR-BLUP (RR-BLUP B) that utilizes a selected subset of markers was evaluated. The accuracy of these methods was compared across 17 traits with distinct heritabilities and genetic architectures, including growth, development, and disease-resistance properties, measured in a Pinus taeda (loblolly pine) training population of 951 individuals genotyped with 4853 SNPs. The predictive ability of the methods was evaluated using a 10-fold, cross-validation approach, and differed only marginally for most method/trait combinations. Interestingly, for fusiform rust disease-resistance traits, Bayes Cp, Bayes A, and RR-BLUB B had higher predictive ability than RR-BLUP and Bayesian LASSO. Fusiform rust is controlled by few genes of large effect. A limitation of RR-BLUP is the assumption of equal contribution of all markers to the observed variation. However, RR-BLUP B performed equally well as the Bayesian approaches.The genotypic and phenotypic data used in this study are publically available for comparative analysis of genomic selection prediction models.
Two randomized complete block design experiments were used to study the effects of fertilization ... more Two randomized complete block design experiments were used to study the effects of fertilization and weed control treatments on the productivity of second rotation loblolly pine (Pinus taeda L.) plantations growing on poorly-drained Spodosols in north Florida. One experiment (actively managed retreated) received similar treatments as in the first rotation (Control, C; Fertilizer, F; Fertilizer + weed control, FW; Weed control, W), and the second was left untreated in the second rotation [untreated carryover (C-): C C , C F , C FW , and C W ]. Comparisons of total height and current annual increment across rotations indicated that the second-rotation stands were more productive than the first-rotation. In the current rotation of the untreated carryover experiment, treatments that received fertilizer in the first rotation (C F and C FW) accumulated significantly more aboveground biomass compared to the C C treatment [i.e. C F (63 Mg ha −1) = C FW (60 Mg ha −1) > C C (40 Mg ha −1)]. From the third to the fourth year, biomass accumulation in C F exceeded C FW , but by the fifth to the seventh years the two treatments were similar; a change that likely occurred because of root development into the lower solum for the C FW or increased understory competition in the C F treatment. In the actively managed retreated experiment, cumulative total aboveground biomass accumulation followed the trend: FW (90.6 Mg ha −1) > F (71.8 Mg ha −1) > W (55.1 Mg ha −1) > C (31.8 Mg ha −1). Comparison of upper quartile height gains due to fertilization between the first-and second-rotation experiments suggested that fertilizer added in the second rotation only provided growth gains after the fourth year. Our results suggest that management practices enhanced levels of productivity across treatments and rotations with some adjustment caused by carryover effects from past fertilization and weed control treatments.
Two randomized, complete block design experiments were established in north Florida to examine th... more Two randomized, complete block design experiments were established in north Florida to examine the inter-rotational effects of fertilization and herbicide applications on understory community responses in 2-year-old Pinus taeda L. stands. One experiment was left untreated (carryover [C]; C C , C F , C W , and C FW) and the second received the same first-rotation treatments-control (C), fertilizer (F), herbicide (W), and fertilizer and weed control (FW)-in the second rotation. In both experiments, herbicide applications alone and when combined with fertilization suppressed woody species such as Ilex glabra (L.) A. Gray and Serenoa repens (W. Bartram) Small (C FW : 0.26; FW: 0.01 Mg ha Ϫ1 biomass) but favored graminoids such as Andropogon virginicus L. var. glaucus Hack. and Dichanthelium acuminatum (Sw.) Gould & C.A. Clark (C FW : 3.1; FW: 1.1 Mg ha Ϫ1 biomass). Although the C W (0.99) and W (0.99) treatments did not affect understory diversity (HЈ), the C FW (0.45) and FW (0.5) treatments exhibited reductions compared with the C F (1.24) and F (1.33) treatments, respectively. In both experiments, fertilizer alone did not affect understory composition and diversity compared with the control. These results suggest that intensive additions of either herbicide alone or in combination with fertilization affected understory composition and diversity in the subsequent rotation.
Recent investigations on the mechanistic underpinnings for nutrient regulated organic matter deco... more Recent investigations on the mechanistic underpinnings for nutrient regulated organic matter decomposition suggest that micronutrients may limit microbial activity in nitrogen (N) enriched forest ecosystems. However, these nutrient limitations could be complex for managed pine plantations in the US South that received macroand micronutrient fertilization and weed control treatments. Soils and pine litter from second rotation loblolly pine stands were incubated to study the legacy effects of long-term silvicultural treatments [30+ years − Untreated Carryover (C) − Control (C C), Fertilization (C F), Fertilization + Weed control (C FW), Weed control (C W)] on microbial respiration and organic matter decomposition. These legacy treatment effects were contrasted with soils and litter corresponding to the current rotation's actively managed treatments that were the same as in the first rotation (Actively managed retreated-C, F, FW, W). In general, both past rotation (C F : 17.9 μg C g −1 soil day −1) and current rotation fertilizer treatments (F: 22.3 μg C g −1 soil day −1) resulted in higher microbial respiration rates compared to their respective controls (C C : 11.9 μg C g −1 soil day −1 ; C: 12.5 μg C g −1 soil day −1), which likely reflected an inherently higher soil carbon content. Carbon normalized microbial respiration rates during the incubation period followed exponential decay patterns, with lower decay rates in fertilized soils compared to the average among treatments. Furthermore, N + phosphorus (P) additions suppressed microbial respiration in the C F and F treatments, but accelerated it in the C C and C treatments. This observation suggests that during the early stages of decomposition, N and P were limiting to microorganisms in those soils without a silvicultural treatment history. Positive microbial respiration response to added Cu for the C C and C, and added Mn for the C C , C, and W treatments suggested micronutrient limitations to microbial decomposition processes. For soils without a fertilization history, Mn peroxidase activity response to Mn addition levels followed the trend: high level > low level = No addition (C C and C W : p = 0.0032; C and W: p < 0.0001), and significantly correlated with microbial respiration rates (r = 0.63). Overall, the carryover effects from past forest management practices altered soil microbial and decomposition responses to nutrient additions, including alleviation of nutrient limitations to soil extracellular enzyme production in a Florida Spodosol.
We present a new system of equations for slash pine plantations (Pinus elliottii Engelm. var. ell... more We present a new system of equations for slash pine plantations (Pinus elliottii Engelm. var. elliottii) that express the combined effects of CRIFF (Cooperative Research in Forest Fertilization Program) soil group and mid-rotation nitrogen (N) and phosphorus (P) fertilization on survival, basal area growth or yield, dominant height growth and the stand diameter distribution. A diameter growth model that accepts an initial diameter distribution (or tree list)provides the ability to predictfuture diameter distributions. Predictor variables include combinations of three mid-rotation fertilizer treatments: (1) no fertilizer; (2) N only (150 Ib/ac elemental), (3) N and P (150 Ib/ac and 50 Ib/ac elemental, respectively) and three CRIFF soil groups: (1) B soils (e.g., Arenic Paleaquult), (2) C soils (e.g., Ultic Haplaquod), and (3) D soils (e.g., Grossarenic Haplaquod). These models derive from analyses on data taken in 243permanent sample plots, some having been remeasured up to 6 times at 2 yr intervals, located in slash pine plantations on prepared sites. The models predict that fertilization with N and P at age 15 will result in around 30% (462 fta/ac) more cumulative merchantable growth by age 25for a typical site-index-60plantation growing on CRIFF soil group B. South.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution author... more The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.
This chapter focuses on loblolly pine (Pinus taeda) and considers the general features and proper... more This chapter focuses on loblolly pine (Pinus taeda) and considers the general features and properties in bioenergy production, genetics and breeding for bioenergy traits, silvicultural practices for bioenergy production, tree harvesting and chip processing, bioenergy opportunities and challenges, and sustainability of bioenergy production systems.
The effects of fertilization, weed control, and fertilization plus weed control on vegetation and... more The effects of fertilization, weed control, and fertilization plus weed control on vegetation and soil C and N pools were examined for a loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii var. elliottii Engelm.) forest at ages 18 and 26 years (at the end of rotation). The total C accumulated in fertilized forests without weed control was 20% (slash pine) and 40% (loblolly pine) greater than in the control forests at the end of rotation. Weed control increased pine C pools at 18 years, but by the end of rotation, weed control effectively resulted in no gain in ecosystem C. When the two treatments were combined, weed control slightly subtracted from the net C benefit produced by fertilization. This result occurred because of decreased forest floor and soil C in the weed control plots. Fertilization significantly increased stem, foliage, forest floor, and soil N pools, and N retention was 63% and 103% of the applied N in the slash and loblolly pine forests, respectively. Weed control with fertilization reduced ecosystem N retention efficiency, but weed control alone did not negatively affect ecosystem N accumulation. These results suggest that the optimal treatment for increasing C accumulation and N retention in these ecosystems is fertilization without weed control. Résumé : Les effets de la fertilisation et du désherbage, seuls ou combinés, sur la végétation ainsi que sur les réservoirs de C et de N du sol ont été étudiés dans des forêts de pin à encens (Pinus taeda L.) et de pin d'Elliott (Pinus elliottii var. elliottii Engelm.) âgées de 18 et 26 ans (fin de la rotation). Le C total accumulé dans les forêts fertilisées était 20 % (pin d'Elliott) et 40 % (pin à encens) plus élevé que dans les forêts témoins à la fin de la rotation. Le désherbage a augmenté les réservoirs de C du pin à 18 ans mais n'a pas entraîné de gain de C dans l'écosystème à la fin de la rotation. Lorsque les deux traitements étaient combinés, le désherbage a légèrement réduit le bénéfice net de C obtenu avec la fertilisation. Ce résultat est survenu à cause la diminution du C dans le sol et la couverture morte dans les parcelles désherbées. La fertilisation a significativement augmenté les réservoirs de N dans la tige, le feuillage, la couverture morte et le sol et la rétention de N a atteint respectivement 63 % et 103 % de N appliqué dans les forêts de pin d'Elliott et de pin à encens. Le désherbage combiné à la fertilisation a réduit l'efficacité de rétention de N de l'écosystème mais le désherbage seul n'a pas négativement influencé l'accumulation de N dans l'écosystème. Ces résultats indiquent que le traitement optimal pour augmenter l'accumulation de C et la rétention de N dans ces écosystèmes est la fertilisation sans désherbage.
Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for asse... more Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for assessing the potential for C sequestration of managed pine forests. This study used a sequential exclusion of aboveground litter inputs (L=litter exclusion) and above plus belowground inputs (LR= litter and root exclusion) to segregate C sources contributing to the development and maintenance of SOC in the surface soil supporting juvenile loblolly pine (Pinus taeda L.) in its rapid growth phase. The study spanned the 7 th to 10 th year of stand growth. Soil physical size fractions (>2 mm, ≤2mm, 2000-250 µm, 250-150 µm, 150-53 µm, and <53 µm) were used to investigate the change in native SOC over time in the untreated control plots (UC=untreated control) and the effects of exclusion treatments. An accretion rate of 4.6 Mg SOC ha-1 soil yr-1 was observed in the fine earth fraction (≤2 mm), reflecting the rapid phase of stand growth. The accretion was primarily observed in the upper 10 cm of the soil. Treatment effects were most apparent in soil bulk density, SOC of the fine earth, and 150-53 µm size fractions. In general, changes in SOC observed in the L treatment was an intermediate increase between the UC and LR treatments; where only the removal of roots provided no change in SOC and was significantly different from the control (p = 0.05). We conclude that a major contributor to the maintenance and increase of SOC in
In the 1950s, vast acreages of cutover forest land and degraded agricultural land existed in the ... more In the 1950s, vast acreages of cutover forest land and degraded agricultural land existed in the South. Less than 2 million acres of southern pine plantations existed at that time. By the end of the 20 th century, there were 32 million acres of southern pine plantations in the Southern United States, and this region is now the woodbasket of the world. The success story that is southern pine forestry was facilitated by the application of research results generated through cooperative work of the U.S. Department of Agriculture Forest Service, southern forestry schools, State forestry agencies, and forest industry. This chapter reviews the contributions of applied silvicultural research in land classification, tree improvement, nursery management, site preparation, weed control, and fertilization to plantation forestry in the South. These practices significantly increased productivity of southern pine plantations. Plantations established in the 1950s and 1960s that produced < 90 cubic feet per acre per year have been replaced by plantations established in the 1990s that are producing > 400 cubic feet per acre per year. Southern pine plantations are currently among the most intensively managed forests in the world. Growth of plantations managed using modern, integrated, site-specific silvicultural regimes rivals that of plantations of fast-growing nonnative species in the Southern Hemisphere. Additional gains in productivity are likely as clonal forestry is implemented in the South. Advances in forest biotechnology will significantly increase growth and quality of future plantations. It appears likely that the South will remain one of the major wood-producing regions of the world.
Intensive forest management (fertilization, weed control) and the planting of fast-growing famili... more Intensive forest management (fertilization, weed control) and the planting of fast-growing families of loblolly pine (Pinus taeda L.) can dramatically increase the rate of tree biomass accumulation, but it is unclear how tree genetics and management intensity interact to affect belowground processes. For 2.5 years in a 10-12-year-old plantation in north central Florida, we examined ecosystem carbon (C) accumulation, soil respiration (SR), total belowground C flux (TBCF), and litterfall in forests receiving different levels and types of fertilizer and weed control treatments that effectively reflected a contrast in 'high' vs. 'operational' management intensity. A fastgrowing family was compared with a slower-growing family using single-family block plots. Applying high intensity silviculture treatments significantly (p < 0.05) increased C accumulation in aboveground biomass on average by 55% (20.9 Mg C ha −1) relative to less intensive silviculture, and the fast growing family accumulated 14% (6.3 Mg C ha −1) more C than the slower growing family at the end of 12 years. For the organic layer C, the high intensity silvicultural treatments significantly (p = 0.02) increased C accumulation (9.0 Mg C ha −1) and biomass increment (p = 0.04, 0.7 Mg C ha −1 y −1); however, the family treatment was not significant (p > 0.05) for either annual increment or organic horizon C. In contrast, the response of belowground C dynamics to silvicultural intensity were family specific, with the fast-growing family having significantly (p < 0.001) greater SR and TBCF under the operational treatment, while the slow-growing family showed no change in allocation with silvicultural intensity. The faster growing family also concentrated SR on its mounded planting bed position under the low silvicultural intensity, potentially making it better adapted to receiving silvicultural treatments concentrated near the tree base. These results suggest that loblolly pine's C allocation belowground could be a characteristic to use for selecting pine families for greater growth potential, compatibility with silvicultural practices, or as a means to affect ecosystem C accumulation.
Silvicultural practices, particularly fertilization, may counteract or accentuate the effects of ... more Silvicultural practices, particularly fertilization, may counteract or accentuate the effects of climate change on carbon cycling in planted pine ecosystems, but few studies have empirically assessed the potential effects. In the southeastern United States, we established a factorial throughfall reduction (D) × fertilization (F) experiment in 2012 in four loblolly pine (Pinus taeda L.) plantations encompassing the climatic range of the species in Florida (FL), Georgia (GA), Oklahoma (OK), and Virginia (VA). Net primary productivity (NPP) was estimated from tree inventories for four consecutive years, and net ecosystem productivity (NEP) as NPP minus heterotrophic respiration (R H). Soil respiration (R S) was measured biweekly-monthly for at least one year at each site and simultaneous measurements of R S & R H were taken five to eight times through the year for at least one year during the experiment. Reducing throughfall by 30% decreased available soil water at the surface and for the 0-90 cm soil profile. Fertilization increased NPP at all sites and D decreased NPP (to a lesser extent) at the GA and OK sites. The F + D treatment did not affect NPP. Mean annual NPP under F ranged from 10.01 ± 0.21 MgC•ha −1 •yr −1 at VA (mean ± SE) to 17.20 ± 0.50 MgC•ha −1 •yr −1 at FL, while the lowest levels were under the D treatment, ranging from 8.63 ± 0.21 MgC•ha −1 •yr −1 at VA to 14.97 ± 0.50 MgC•ha −1 •yr −1 at FL. R S and R H were, in general, decreased by F and D with differential responses among sites, leading to NEP increases under F. Throughfall reduction increased NEP at FL and VA due to a negative effect on R H and no effect on NPP. Mean annual NEP ranged from 1.63 ± 0.59 MgC•ha −1 •yr −1 in the control at OK to 8.18 ± 0.82 MgC•ha −1 •yr −1 under F + D at GA. These results suggest that fertilization will increase NEP under a wide range of climatic conditions including reduced precipitation, but either NPP or R H could be the primary driver because F can increase stand growth, as well as suppress R S and R H. Moreover, D and F never significantly interacted for an annual C flux, potentially simplifying estimates of how fertilization and drought will affect C cycling in these ecosystems.
Soil Science Society of America Journal, May 1, 1992
For many soils of the tropics, inputs of organic materials are essential to sustain soil fertilit... more For many soils of the tropics, inputs of organic materials are essential to sustain soil fertility and crop production. Research in the quality of organic inputs, a key factor controlling rates of decomposition and nutrient release, continues to guide selection and use of organic materials as nutrient sources. The relationship between decomposition patterns and the quality parameters of the fresh leaves of six agroforestry species: Sesbania sesban, Croton megalocarpus, Calliandra calothyrsus, Tithonia diversifolia, Lantana camara, and Senna spectabilis, was investigated in a litterbag study over a period of 77 days in the highlands of western Kenya. The litterbags were buried 1 cm below the soil surface and covered with soil of ca 1 cm thickness. Percent leaf mass and total N and P that remained with time strongly correlated with total P and C/P ratio (R 2 ϭ 0.60-0.90) during the first 35 days of study; but afterwards, correlation was stronger with the initial soluble polyphenolics (Pp)/P ratio (R 2 ϭ 0.69-0.92) than with total P and C/P ratio. Loss of leaf mass and release of N and P followed the exponential function, y t ϭ y 0 * e Ϫkt , from which the specific decay rate constants (k) were calculated for loss of leaf mass (k B) and release of N (k N) and P (k P). Among the plant species, the k values were lowest in Calliandra with k B ϭ 0.012/d, k N ϭ 0.017/d and k P ϭ 0.044/d. Lantana had the highest k values with k B ϭ 0.067/d and k P ϭ 0.119/d, but the highest k N value of 0.109/d occurred in Tithonia. The k B values for all organic materials were lower than their corresponding k N and k P values, suggesting that leaching of N and P from litters may have augmented the microbial mineralization of N and P. There was a strong correlation between the k B , k N , and k P values and total P (r ϭ 0.82-0.96; P Ͻ 0.01), but not total N, lignin (LIG), or Pp. Rates of N and P release followed the general trend: Tithonia Ͼ Senna Ͼ Lantana Ͼ Sesbania Ͼ Croton Ͼ Calliandra. The results indicated that, among the quality parameters studied, total P is the most important factor controlling rate of decomposition and N and P release from organic inputs in the area of study.
Genomic selection can increase genetic gain per generation through early selection. Genomic selec... more Genomic selection can increase genetic gain per generation through early selection. Genomic selection is expected to be particularly valuable for traits that are costly to phenotype and expressed late in the life cycle of long-lived species. Alternative approaches to genomic selection prediction models may perform differently for traits with distinct genetic properties. Here the performance of four different original methods of genomic selection that differ with respect to assumptions regarding distribution of marker effects, including (i) ridge regression-best linear unbiased prediction (RR-BLUP), (ii) Bayes A, (iii) Bayes Cp, and (iv) Bayesian LASSO are presented. In addition, a modified RR-BLUP (RR-BLUP B) that utilizes a selected subset of markers was evaluated. The accuracy of these methods was compared across 17 traits with distinct heritabilities and genetic architectures, including growth, development, and disease-resistance properties, measured in a Pinus taeda (loblolly pine) training population of 951 individuals genotyped with 4853 SNPs. The predictive ability of the methods was evaluated using a 10-fold, cross-validation approach, and differed only marginally for most method/trait combinations. Interestingly, for fusiform rust disease-resistance traits, Bayes Cp, Bayes A, and RR-BLUB B had higher predictive ability than RR-BLUP and Bayesian LASSO. Fusiform rust is controlled by few genes of large effect. A limitation of RR-BLUP is the assumption of equal contribution of all markers to the observed variation. However, RR-BLUP B performed equally well as the Bayesian approaches.The genotypic and phenotypic data used in this study are publically available for comparative analysis of genomic selection prediction models.
Two randomized complete block design experiments were used to study the effects of fertilization ... more Two randomized complete block design experiments were used to study the effects of fertilization and weed control treatments on the productivity of second rotation loblolly pine (Pinus taeda L.) plantations growing on poorly-drained Spodosols in north Florida. One experiment (actively managed retreated) received similar treatments as in the first rotation (Control, C; Fertilizer, F; Fertilizer + weed control, FW; Weed control, W), and the second was left untreated in the second rotation [untreated carryover (C-): C C , C F , C FW , and C W ]. Comparisons of total height and current annual increment across rotations indicated that the second-rotation stands were more productive than the first-rotation. In the current rotation of the untreated carryover experiment, treatments that received fertilizer in the first rotation (C F and C FW) accumulated significantly more aboveground biomass compared to the C C treatment [i.e. C F (63 Mg ha −1) = C FW (60 Mg ha −1) > C C (40 Mg ha −1)]. From the third to the fourth year, biomass accumulation in C F exceeded C FW , but by the fifth to the seventh years the two treatments were similar; a change that likely occurred because of root development into the lower solum for the C FW or increased understory competition in the C F treatment. In the actively managed retreated experiment, cumulative total aboveground biomass accumulation followed the trend: FW (90.6 Mg ha −1) > F (71.8 Mg ha −1) > W (55.1 Mg ha −1) > C (31.8 Mg ha −1). Comparison of upper quartile height gains due to fertilization between the first-and second-rotation experiments suggested that fertilizer added in the second rotation only provided growth gains after the fourth year. Our results suggest that management practices enhanced levels of productivity across treatments and rotations with some adjustment caused by carryover effects from past fertilization and weed control treatments.
Two randomized, complete block design experiments were established in north Florida to examine th... more Two randomized, complete block design experiments were established in north Florida to examine the inter-rotational effects of fertilization and herbicide applications on understory community responses in 2-year-old Pinus taeda L. stands. One experiment was left untreated (carryover [C]; C C , C F , C W , and C FW) and the second received the same first-rotation treatments-control (C), fertilizer (F), herbicide (W), and fertilizer and weed control (FW)-in the second rotation. In both experiments, herbicide applications alone and when combined with fertilization suppressed woody species such as Ilex glabra (L.) A. Gray and Serenoa repens (W. Bartram) Small (C FW : 0.26; FW: 0.01 Mg ha Ϫ1 biomass) but favored graminoids such as Andropogon virginicus L. var. glaucus Hack. and Dichanthelium acuminatum (Sw.) Gould & C.A. Clark (C FW : 3.1; FW: 1.1 Mg ha Ϫ1 biomass). Although the C W (0.99) and W (0.99) treatments did not affect understory diversity (HЈ), the C FW (0.45) and FW (0.5) treatments exhibited reductions compared with the C F (1.24) and F (1.33) treatments, respectively. In both experiments, fertilizer alone did not affect understory composition and diversity compared with the control. These results suggest that intensive additions of either herbicide alone or in combination with fertilization affected understory composition and diversity in the subsequent rotation.
Recent investigations on the mechanistic underpinnings for nutrient regulated organic matter deco... more Recent investigations on the mechanistic underpinnings for nutrient regulated organic matter decomposition suggest that micronutrients may limit microbial activity in nitrogen (N) enriched forest ecosystems. However, these nutrient limitations could be complex for managed pine plantations in the US South that received macroand micronutrient fertilization and weed control treatments. Soils and pine litter from second rotation loblolly pine stands were incubated to study the legacy effects of long-term silvicultural treatments [30+ years − Untreated Carryover (C) − Control (C C), Fertilization (C F), Fertilization + Weed control (C FW), Weed control (C W)] on microbial respiration and organic matter decomposition. These legacy treatment effects were contrasted with soils and litter corresponding to the current rotation's actively managed treatments that were the same as in the first rotation (Actively managed retreated-C, F, FW, W). In general, both past rotation (C F : 17.9 μg C g −1 soil day −1) and current rotation fertilizer treatments (F: 22.3 μg C g −1 soil day −1) resulted in higher microbial respiration rates compared to their respective controls (C C : 11.9 μg C g −1 soil day −1 ; C: 12.5 μg C g −1 soil day −1), which likely reflected an inherently higher soil carbon content. Carbon normalized microbial respiration rates during the incubation period followed exponential decay patterns, with lower decay rates in fertilized soils compared to the average among treatments. Furthermore, N + phosphorus (P) additions suppressed microbial respiration in the C F and F treatments, but accelerated it in the C C and C treatments. This observation suggests that during the early stages of decomposition, N and P were limiting to microorganisms in those soils without a silvicultural treatment history. Positive microbial respiration response to added Cu for the C C and C, and added Mn for the C C , C, and W treatments suggested micronutrient limitations to microbial decomposition processes. For soils without a fertilization history, Mn peroxidase activity response to Mn addition levels followed the trend: high level > low level = No addition (C C and C W : p = 0.0032; C and W: p < 0.0001), and significantly correlated with microbial respiration rates (r = 0.63). Overall, the carryover effects from past forest management practices altered soil microbial and decomposition responses to nutrient additions, including alleviation of nutrient limitations to soil extracellular enzyme production in a Florida Spodosol.
We present a new system of equations for slash pine plantations (Pinus elliottii Engelm. var. ell... more We present a new system of equations for slash pine plantations (Pinus elliottii Engelm. var. elliottii) that express the combined effects of CRIFF (Cooperative Research in Forest Fertilization Program) soil group and mid-rotation nitrogen (N) and phosphorus (P) fertilization on survival, basal area growth or yield, dominant height growth and the stand diameter distribution. A diameter growth model that accepts an initial diameter distribution (or tree list)provides the ability to predictfuture diameter distributions. Predictor variables include combinations of three mid-rotation fertilizer treatments: (1) no fertilizer; (2) N only (150 Ib/ac elemental), (3) N and P (150 Ib/ac and 50 Ib/ac elemental, respectively) and three CRIFF soil groups: (1) B soils (e.g., Arenic Paleaquult), (2) C soils (e.g., Ultic Haplaquod), and (3) D soils (e.g., Grossarenic Haplaquod). These models derive from analyses on data taken in 243permanent sample plots, some having been remeasured up to 6 times at 2 yr intervals, located in slash pine plantations on prepared sites. The models predict that fertilization with N and P at age 15 will result in around 30% (462 fta/ac) more cumulative merchantable growth by age 25for a typical site-index-60plantation growing on CRIFF soil group B. South.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution author... more The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations.
This chapter focuses on loblolly pine (Pinus taeda) and considers the general features and proper... more This chapter focuses on loblolly pine (Pinus taeda) and considers the general features and properties in bioenergy production, genetics and breeding for bioenergy traits, silvicultural practices for bioenergy production, tree harvesting and chip processing, bioenergy opportunities and challenges, and sustainability of bioenergy production systems.
The effects of fertilization, weed control, and fertilization plus weed control on vegetation and... more The effects of fertilization, weed control, and fertilization plus weed control on vegetation and soil C and N pools were examined for a loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii var. elliottii Engelm.) forest at ages 18 and 26 years (at the end of rotation). The total C accumulated in fertilized forests without weed control was 20% (slash pine) and 40% (loblolly pine) greater than in the control forests at the end of rotation. Weed control increased pine C pools at 18 years, but by the end of rotation, weed control effectively resulted in no gain in ecosystem C. When the two treatments were combined, weed control slightly subtracted from the net C benefit produced by fertilization. This result occurred because of decreased forest floor and soil C in the weed control plots. Fertilization significantly increased stem, foliage, forest floor, and soil N pools, and N retention was 63% and 103% of the applied N in the slash and loblolly pine forests, respectively. Weed control with fertilization reduced ecosystem N retention efficiency, but weed control alone did not negatively affect ecosystem N accumulation. These results suggest that the optimal treatment for increasing C accumulation and N retention in these ecosystems is fertilization without weed control. Résumé : Les effets de la fertilisation et du désherbage, seuls ou combinés, sur la végétation ainsi que sur les réservoirs de C et de N du sol ont été étudiés dans des forêts de pin à encens (Pinus taeda L.) et de pin d'Elliott (Pinus elliottii var. elliottii Engelm.) âgées de 18 et 26 ans (fin de la rotation). Le C total accumulé dans les forêts fertilisées était 20 % (pin d'Elliott) et 40 % (pin à encens) plus élevé que dans les forêts témoins à la fin de la rotation. Le désherbage a augmenté les réservoirs de C du pin à 18 ans mais n'a pas entraîné de gain de C dans l'écosystème à la fin de la rotation. Lorsque les deux traitements étaient combinés, le désherbage a légèrement réduit le bénéfice net de C obtenu avec la fertilisation. Ce résultat est survenu à cause la diminution du C dans le sol et la couverture morte dans les parcelles désherbées. La fertilisation a significativement augmenté les réservoirs de N dans la tige, le feuillage, la couverture morte et le sol et la rétention de N a atteint respectivement 63 % et 103 % de N appliqué dans les forêts de pin d'Elliott et de pin à encens. Le désherbage combiné à la fertilisation a réduit l'efficacité de rétention de N de l'écosystème mais le désherbage seul n'a pas négativement influencé l'accumulation de N dans l'écosystème. Ces résultats indiquent que le traitement optimal pour augmenter l'accumulation de C et la rétention de N dans ces écosystèmes est la fertilisation sans désherbage.
Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for asse... more Quantifying soil organic carbon (SOC) inputs in the surface soil is a critical component for assessing the potential for C sequestration of managed pine forests. This study used a sequential exclusion of aboveground litter inputs (L=litter exclusion) and above plus belowground inputs (LR= litter and root exclusion) to segregate C sources contributing to the development and maintenance of SOC in the surface soil supporting juvenile loblolly pine (Pinus taeda L.) in its rapid growth phase. The study spanned the 7 th to 10 th year of stand growth. Soil physical size fractions (>2 mm, ≤2mm, 2000-250 µm, 250-150 µm, 150-53 µm, and <53 µm) were used to investigate the change in native SOC over time in the untreated control plots (UC=untreated control) and the effects of exclusion treatments. An accretion rate of 4.6 Mg SOC ha-1 soil yr-1 was observed in the fine earth fraction (≤2 mm), reflecting the rapid phase of stand growth. The accretion was primarily observed in the upper 10 cm of the soil. Treatment effects were most apparent in soil bulk density, SOC of the fine earth, and 150-53 µm size fractions. In general, changes in SOC observed in the L treatment was an intermediate increase between the UC and LR treatments; where only the removal of roots provided no change in SOC and was significantly different from the control (p = 0.05). We conclude that a major contributor to the maintenance and increase of SOC in
In the 1950s, vast acreages of cutover forest land and degraded agricultural land existed in the ... more In the 1950s, vast acreages of cutover forest land and degraded agricultural land existed in the South. Less than 2 million acres of southern pine plantations existed at that time. By the end of the 20 th century, there were 32 million acres of southern pine plantations in the Southern United States, and this region is now the woodbasket of the world. The success story that is southern pine forestry was facilitated by the application of research results generated through cooperative work of the U.S. Department of Agriculture Forest Service, southern forestry schools, State forestry agencies, and forest industry. This chapter reviews the contributions of applied silvicultural research in land classification, tree improvement, nursery management, site preparation, weed control, and fertilization to plantation forestry in the South. These practices significantly increased productivity of southern pine plantations. Plantations established in the 1950s and 1960s that produced < 90 cubic feet per acre per year have been replaced by plantations established in the 1990s that are producing > 400 cubic feet per acre per year. Southern pine plantations are currently among the most intensively managed forests in the world. Growth of plantations managed using modern, integrated, site-specific silvicultural regimes rivals that of plantations of fast-growing nonnative species in the Southern Hemisphere. Additional gains in productivity are likely as clonal forestry is implemented in the South. Advances in forest biotechnology will significantly increase growth and quality of future plantations. It appears likely that the South will remain one of the major wood-producing regions of the world.
Intensive forest management (fertilization, weed control) and the planting of fast-growing famili... more Intensive forest management (fertilization, weed control) and the planting of fast-growing families of loblolly pine (Pinus taeda L.) can dramatically increase the rate of tree biomass accumulation, but it is unclear how tree genetics and management intensity interact to affect belowground processes. For 2.5 years in a 10-12-year-old plantation in north central Florida, we examined ecosystem carbon (C) accumulation, soil respiration (SR), total belowground C flux (TBCF), and litterfall in forests receiving different levels and types of fertilizer and weed control treatments that effectively reflected a contrast in 'high' vs. 'operational' management intensity. A fastgrowing family was compared with a slower-growing family using single-family block plots. Applying high intensity silviculture treatments significantly (p < 0.05) increased C accumulation in aboveground biomass on average by 55% (20.9 Mg C ha −1) relative to less intensive silviculture, and the fast growing family accumulated 14% (6.3 Mg C ha −1) more C than the slower growing family at the end of 12 years. For the organic layer C, the high intensity silvicultural treatments significantly (p = 0.02) increased C accumulation (9.0 Mg C ha −1) and biomass increment (p = 0.04, 0.7 Mg C ha −1 y −1); however, the family treatment was not significant (p > 0.05) for either annual increment or organic horizon C. In contrast, the response of belowground C dynamics to silvicultural intensity were family specific, with the fast-growing family having significantly (p < 0.001) greater SR and TBCF under the operational treatment, while the slow-growing family showed no change in allocation with silvicultural intensity. The faster growing family also concentrated SR on its mounded planting bed position under the low silvicultural intensity, potentially making it better adapted to receiving silvicultural treatments concentrated near the tree base. These results suggest that loblolly pine's C allocation belowground could be a characteristic to use for selecting pine families for greater growth potential, compatibility with silvicultural practices, or as a means to affect ecosystem C accumulation.
Silvicultural practices, particularly fertilization, may counteract or accentuate the effects of ... more Silvicultural practices, particularly fertilization, may counteract or accentuate the effects of climate change on carbon cycling in planted pine ecosystems, but few studies have empirically assessed the potential effects. In the southeastern United States, we established a factorial throughfall reduction (D) × fertilization (F) experiment in 2012 in four loblolly pine (Pinus taeda L.) plantations encompassing the climatic range of the species in Florida (FL), Georgia (GA), Oklahoma (OK), and Virginia (VA). Net primary productivity (NPP) was estimated from tree inventories for four consecutive years, and net ecosystem productivity (NEP) as NPP minus heterotrophic respiration (R H). Soil respiration (R S) was measured biweekly-monthly for at least one year at each site and simultaneous measurements of R S & R H were taken five to eight times through the year for at least one year during the experiment. Reducing throughfall by 30% decreased available soil water at the surface and for the 0-90 cm soil profile. Fertilization increased NPP at all sites and D decreased NPP (to a lesser extent) at the GA and OK sites. The F + D treatment did not affect NPP. Mean annual NPP under F ranged from 10.01 ± 0.21 MgC•ha −1 •yr −1 at VA (mean ± SE) to 17.20 ± 0.50 MgC•ha −1 •yr −1 at FL, while the lowest levels were under the D treatment, ranging from 8.63 ± 0.21 MgC•ha −1 •yr −1 at VA to 14.97 ± 0.50 MgC•ha −1 •yr −1 at FL. R S and R H were, in general, decreased by F and D with differential responses among sites, leading to NEP increases under F. Throughfall reduction increased NEP at FL and VA due to a negative effect on R H and no effect on NPP. Mean annual NEP ranged from 1.63 ± 0.59 MgC•ha −1 •yr −1 in the control at OK to 8.18 ± 0.82 MgC•ha −1 •yr −1 under F + D at GA. These results suggest that fertilization will increase NEP under a wide range of climatic conditions including reduced precipitation, but either NPP or R H could be the primary driver because F can increase stand growth, as well as suppress R S and R H. Moreover, D and F never significantly interacted for an annual C flux, potentially simplifying estimates of how fertilization and drought will affect C cycling in these ecosystems.
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Papers by Eric Jokela