H. Lee Allen

Water quality impacts of forest fertilization with nitrogen and phosphorus

The drinking-water quality of streamwater in forests is typically very good, exceeding the quality of water in areas with other types of land use. Streams draining agricultural lands in the United States average about nine times greater concentrations of nitrate and phosphate than streams draining forested areas. Forest fertilization commonly increases nutrient concentrations in streamwater, and large increases could lead to unacceptable degradation of water quality. This review summarizes information from studies of forest fertilization around the world, and evaluates the responses of streamwater chemistry. In general, peak concentrations of nitrate-N in streamwater increase after forest fertilization, with a few studies reporting concentrations as high as 10‐25 (mg N)/l as nitrate. Increases in average concentrations of nitrate are much lower than the peak values, and the highest annual average nitrate-N concentration ever reported was 4 (mg N)/l. Relatively high concentrations of streamwater nitrate-N tend to occur with repeated fertilization, use of ammonium nitrate (rather than urea), and fertilization of N-saturated hardwood forests. Ammonium-N concentrations may also show large peaks following fertilization (up to 15 (mg N)/l), but annual averages remain 1 (mg P)/l, but annual averages remain <0.25 (mg P)/l. No evidence has been reported of detectable effects of forest fertilization on the composition or productivity of stream communities, but more detailed studies may be warranted (especially in relation to P fertilization). Major limitations in current knowledge include the effects of repeated fertilization in short-rotation plantations, fertilization of large landscapes rather than small stands, and the effects of fertilization on streamwater chemistry in tropical plantations. # 1999 Elsevier Science B.V. All rights reserved.

Short- and long-term effects of site preparation, fertilization and vegetation control on growth and stand development of planted loblolly pine

Abstract Short- and long-term effects of high and low site preparation intensity, fertilization at planting and vegetation control on growth and stand development were examined in a study that was established on six sites in southeastern USA. The study was established in 1979–1980, and growth after the 18th growing season is reported. The high-intensive site preparation improved long-term stand volume growth. Evidence suggests that the main long-term effect of the intensive site preparation was a reduction in competition from hardwoods. Herbicide treatment improved seedling establishment and early growth, but growth during the last period of measurements (14–18 years after planting) were lower in the herbicide-treated plots as compared to plots without herbicide treatment when herbicides were combined with intensive site preparation. Fertilization at planting, in combination with high-intensive site preparation, improved volume growth during the first 10 years after planting, while fertilization at planting in combination with low-intensive site preparation had little effect on volume growth. The hypothesis that low variability in the seedling stage due to intensive site preparation will lead to low variability in the mature stands with a subsequent reduction in self-thinning was examined. The low site preparation intensity had higher coefficient of variations of stem volumes, and higher mortality. However, the difference in mortality was probably partly a result of differences in competition from hardwoods, and it was not possible to separate the importance of reduced variability from reduced competition from hardwoods. Fertilized plots had lower variability than non-treated control plots but there was no significant difference in mortality between the two treatments. Therefore, it was concluded that reduced variability in the seedling stands, as a result of intensive regeneration methods that reduces environmental heterogeneity, reduces the variability in the mature stands. However, it could not be inconclusively proved that lower variability in the mature stands will result in reduced or postponed self-thinning.

Estimates of nutrient removal, displacement and loss resulting from harvest and site preparation of a Pinus taeda plantation in the piedmont of north Carolina

Abstract Biomass and nutrient removal and redistribution were estimated for combinations of two levels of harvest utilization (stem-only vs. complete tree) and two methods of site preparation (chop/broadcast burn vs. shear-pile/disk) in the Piedmont of North Carolina. Stem-only harvest removed 57 kg ha −1 N, 5 kg ha −1 P, 35 kg ha −1 K, 52 kg ha −1 Ca and 14 kg ha −1 Mg. Complete-tree harvest increased N, P, K, Ca and Mg removal over stem-only harvest by 216, 304, 152, 254 and 151%, respectively, although biomass removal was increased by only 65%. Estimated displacement of N and P into windrows during site preparation depended on harvest utilization, but generally exceeded harvest removals by at least 200%. Nutrient losses resulting from broadcast burning were small, primarily due to ineffectual burns. Removals, displacements and/or losses of nutrients during harvest and intensive site preparation were equal for both harvest utilization levels. These amounted to 714 kg ha −1 of total N in biomass and soil, and 46, 154, 481 and 88 kg ha −1 of P, K, Ca and Mg, respectively, in biomass and Mehlich III soil extractions.

Decomposition of roots in loblolly pine: Effects of nutrient and water availability and root size class on mass loss and nutrient dynamics

The decomposition of plant-derived organic matter exerts strong control over the cycling of carbon and nutrients in terrestrial ecosystems and may be significantly altered by increased precipitation and nitrogen deposition associated with global change. It was the goal of this study to quantify the rate of belowground decomposition in an intact loblolly pine forest, and determine how this was affected by increased availability of water and nitrogen. A randomized complete-block factorial of irrigation and fertilization treatments was installed in an 8 yr old loblolly pine plantation in Scotland county, North Carolina. Fresh root samples of three size classes were buried in fiberglass mesh bags in January, 1994 and recovered at two-month intervals for two years. Samples were analyzed for percent mass remaining and contents of macro-nutrients. Roots decomposed in a two stage process: early in the incubation mass loss was correlated to size class and nutrient concentrations, but this correlation disappeared later in the incubation when rates of mass loss converged for all size classes. Decomposition was seldom affected by the irrigation and fertilization treatments, due to the buffering capacity of soil moisture and complex ecosystem-level responses to fertilization. Net mineralization of N, P, K, Ca, and Mg occurred in the smaller size classes of roots providing a source of these nutrients to the aggrading plantation for an estimated 2 to 15 years. The largest size class of roots was a sink for N, Ca, and Mg for the duration of this study, and was a source of P and K for an estimated 20 and 4 years, respectively. It is concluded that in moist temperate ecosystems belowground decomposition will be less affected by the projected increases in moisture and nutrient availability than will decomposition of the forest floor due to the buffering capacity of the soil. Further, small roots provide important sources of macro-nutrients for several decades to aggrading forests after large-scale disturbances such as harvesting of aboveground biomass.

Direct and indirect estimates of Leaf Area Index (LAI) for lodgepole and loblolly pine stands

We compared direct and indirect estimates of leaf area index (LAI) for lodgepole and loblolly pine stands. Indirect estimates of LAI using radiative methods of the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) did not correlate with allometric estimates for lodgepole pine, and correlated only weakly with litter-trap estimates for loblolly pine. The PCA consistently under-estimated LAI in lodgepole pine stands with high LAI, and over-estimated LAI in the loblolly pine stands with low LAI. We developed a physical model to test the hypothesis that the PCA may under-estimate LAI in high leaf area stands because of increased foliage overlap and, therefore, increased selfshading. Radiative estimates of LAI using the PCA for the physical model were consistenly lower than allometric measures. Results from the physical model suggested that increased foliage overlap decreased the ability of the PCA to accurately estimate LAI. The relationship between allometric and radiative measures suggested an upper asymptote in LAI estimated using the PCA. The PCA may not accurately estimate LAI in stands of low or high leaf area index, and the bias or error associated with these estimates probably depends on species and canopy structure. A species specific correction factor will not necessarily correct bias in LAI estimates using the PCA.

Modeling tree growth in fertilized midrotation loblolly pine plantations

Diameter and height growth models for fertilized loblolly pine stands were developed using data from midrotation loblolly pine plantations across the southeastern United States. Tree growth in fertilized stands was predicted with a reference growth model multiplied by an equation predicting the relative growth response following fertilization. The temporal distribution of the growth response was modeled by the Weibull function. These equations for fertilizer growth response were developed to be compatible with individual-tree simulation models. Information about dose, nutrient elements, and time elapsed since fertilization are needed to predict the relative growth response following fertilization.

Light attenuation in a 14-year-old loblolly pine stand as influenced by fertilization and irrigation

Abstract We examined empirical and simulated estimates of canopy light attenuation at SETRES (Southeast Tree Research and Education Site), a 2×2 factorial study of water and nutrients. Fertilized plots had significantly lower under-canopy PAR transmittance (TC) when compared to non-fertilized plots. Light interception efficiency, as measured by the canopy cosine-corrected light extinction coefficient, G, was significantly lower in irrigated plots for all dates examined. Estimates of G ranged from a low of 0.36 in irrigated plots in September to a high of 0.64 in March for control plots. Study-wide analyses indicate that a G of 0.50 and a k (uncorrected light extinction coefficient) of 0.69 may be reasonable parameter estimates of canopy light extinction in intermediate-aged loblolly pine plantations across a range of stand conditions and seasons when site-specific data are unavailable. Simulated TC from our version of the BIOMASS model corresponded well to the empirical estimates. Varying the vertical distribution of foliage in simulations (from 10:60:30 to 40:40:10% in the upper, middle, and lower canopy positions, respectively) resulted in only a ±7% change in total PAR intercepted, whereas varying G from 0.3 to 0.7 resulted in a 67% and 31% increase in light intercepted for control and fertilized plots, respectively. Decreased G resulted in an increased proportion of beam radiation intercepted – 63–67% of total PAR intercepted – by the middle canopy where 55–60% of the foliage was found. We hypothesize that proportionally increased productivity observed in irrigated treatments may be attributed to increased beam radiation intercepted deeper into the canopy by a greater foliage area.

Quantity and timing of needlefall in N and P fertilized loblolly pine stands

Needlefall quantity and timing were examined for 1.5 years on three loblolly pine (Pinus taeda L.) stands from a nitrogen (N) and phosphorus (P) fertilization field study. Needlefall biomass increased following N fertilization on the two N-deficient stands. Needlefall biomass increased by as much as 75% (from 2088 to 3660 kg ha−1 year−1) on one of these stands, but on average increases were about 30%. On a high N quality stand, there was no needlefall biomass response to N fertilization. Phosphorus had no effect on needlefall biomass in any of the three stands. Across all stands, needlefall biomass was unrelated to stocking (as measured by basal area), but significantly correlated (r2 = 0.53; P<0.05) with foliar percent N. We hypothesized accelerated needlefall as a result of moisture stress during very dry periods in 1985 and 1986, particularly on plots which increased foliar biomass (and hence needlefall biomass) after N fertilization. Needlefall timing was affected by N fertilization on all stands, including a stand whose foliar biomass did not increase with N fertilization. In most cases, N fertilization resulted in an increased proportion of needlefall in early summer, and a decreased proportion of needlefall in late fall. This pattern suggests that other factors, such as shading or hormonal changes, may also be important in determining needlefall timing on fertilized stands.

Fertilization of Southern Pines at Establishment

Fertilization is a silvicultural practice used for increasing forestland productivity in the southern U.S. Effective operational use of fertilizers requires diagnostic systems, used individually or in combination, that accurately identify site nutrient status, needs, and potential responsiveness. Interactions of fertilization with other silvicultural practices such as site preparation and genetic tree improvement, and impacts of fertilization on pests, wood quality, and the environment, must be accounted for if fertilizer prescriptions are to be biologically effective and economically justified. This chapter introduces important concepts of forest nutrition and provides guidelines for fertilizing young, intensively managed southern pine plantations.

Economic returns from enhancing loblolly pine establishment on two upland sites: Effects of seedling grade, fertilization, hexazinone, and intensive soil cultivation

On two well drained Coastal Plain sites, early (4-year) and mid-rotation (12-year) performance of loblolly pine (Pinus taeda L.) was examined in relation to mechanical site preparation, herbaceous weed control, and fertilization with diammonium phosphate (DAP). In addition, seedling grade as determined by groundline diameter (GLD) was a fourth factor evaluated. Of the four factors examined, seedling grade was the only factor to consistently improve fourth-year survival. In Alabama, seedlings with a 2.5 mm GLD averaged 62% survival while 5.1 mm seedlings averaged 83% survival. In Virginia, 1.3 mm seedlings had 73% survival and 5.1 mm seedlings had 79% survival. Calculated volume gains from increasing seedling grade suggest that a 1 mm increase in GLD could amount to an additional 7 to 12 m3/ha at age 12. Seedling size and mechanical site preparation were partly exchangeable in influencing survival and growth. Use of hexazinone on late planted seedlings increased mortality at both sites. Applications of hexazinone increased volume/ha when combined with DAP fertilization. Fertilization with DAP increased 12-year volume/ha only when weeds were controlled with hexazinone or disking.