Nicholas B. Comerford

Effects of timber management on the hydrology of wetland forests in the Southern United States

Abstract The objectives of this paper are to review the hydrologic impacts of various common forest management practices that include harvesting, site preparation, and drainage. Field hydrological data collected during the past 5–10 years from ten forested wetland sites across the southern US are synthesized using various methods including hydrologic simulation models and Geographic Information Systems. Wetland systems evaluated include red river bottoms, black river bottoms, pocosins, wet mineral flats, cypress domes, and pine flatwoods. Hydrologic variables used in this assessment include water table level, drainage, and storm flow on different spatial and temporal scales. Wetland ecosystems have higher water storage capacity and higher evapotranspiration than uplands. Hydrologic impacts of forest management are variable, but generally minor, especially when forest best management practices are adopted. A conceptually generalized model is developed to illustrate the relative magnitude of hydrologic effects of forest management on different types of wetlands in the southern US. This model suggests that in addition to soils, wetland types, and management practice options, climate is an important factor in controlling wetland hydrology and the magnitude of disturbance impacts. Bottomland wetlands, partial harvesting, and warm climate usually offer conditions that result in low hydrologic impact.

Rhizosphere phosphatase activity and phosphatase hydrolyzable organic phosphorus in two forested spodosols

Abstract The cycling of organic phosphorus has a large effect on P availability in forest ecosystems. Organic P must be hydrolyzed to inorganic P before it can be utilized by plants. We examined the acid phosphatase activity in the rhizosphere of slash pine ( Pinus elliottii ) growing in A and Bh horizon soil from two forested Spodosols; and determined the amount of soluble organic P in these soils that could be hydrolyzed following the addition of an acid phosphomonoesterase. Significant acid phosphatase activity was observed in the A and Bh horizons of the two soils. Acid phosphatase activity was greater in the rhizosphere of the Leon A and Bh horizons and the Pomona Bh horizon soil. Phosphorus fertilization decreased the phosphatase activity in the rhizosphere soil. Soluble organic P comprised 15–25% of the total soluble P in the two A horizon soils and over 75% in the Bh horizon soils. Between 20 and 30% of the water-soluble organic P in the A and Bh horizons of the two soils was hydrolyzed when an acid phosphomonoesterase was added. Our results suggest that organic P may contribute to the P nutrition of slash pine growing on these soils.

Litter dynamics and monthly fluctuations in soil phosphorus availability in an Amazonian agroforest.

Abstract Commercial plantation agroforests offer a promising land-use alternative for small-scale farmers in tropical America because of their potential to produce high-value cash crops with less soil degradation than traditional annual cropping systems. In low- to no-input tree-based agroecosystems growing in tropical Ultisols and Oxisols, soil P availability depends heavily on factors that influence mineralization from decomposing litter. Using anion exchange resin membranes (AERMs), we monitored monthly fluctuations in soil solution P in an eight-year-old peach palm (Bactris gasipaes)–cupuassu (Theobroma grandiflorum) commercial plantation agroforest to determine if changes in P availability were related to environmental factors controlling organic matter decomposition (precipitation, soil moisture and temperature) and seasonal fluctuations in litterfall and fruit harvest. Decomposition and C, N, and P dynamics in leaf litter were also studied to determine if soil P availability might be related to species differences in litter quality (initial leaf C, N and P contents) and thus differing rates of P release or immobilization. Although AERMs acted as dynamic exchangers, they appeared adequately sensitive to detect fluctuations in monthly soil P availability, despite inherently low soil extractable P concentrations. Soil P availability was greatest early in the rainy season, when both litterfall and a cycle of soil-wetting and drying were initiated, decreasing during the mid-rainy season when fruit production peaked. AERM P was greatest in superficial palm root mats, where decomposing litter accumulates, and in mineral soil beneath palm litter. This corresponded with greater N and P release from more P-rich palm leaf litter. Phosphorus immobilization in initially P-poor cupuassu leaves appears to have contributed to lowered P availability in soil underlying this species’ litter. Phosphorus availability was lowest in bare mineral soil located agroforest alleys where litter accumulation was minimal. Greater overall P availability in peach palm litter-covered soil and root mats may contribute to observed higher productivity in this species.

Importance of weed control, fertilization, irrigation, and genetics in slash and loblolly pine early growth on poorly drained spodosols

Abstract Research reported here has evaluated interactions of factors limiting the biological potential of slash pine ( Pinus elliottii var. elliottii Engelm.) and loblolly pine ( P. Taeda L.). Water and nutrients were manipulated by irrigation, weed control, and intensive fertilization. Genetic factors were incorporated as (1) improved loblolly seedlings from a commercial clonal seed orchard and (2) slash seedlings from four fast-growing, open-pollinated seed-orchard clones. Three replications of a 2 × 2 × 2 factorial experiment were established on a Typic Haplaquod soil in northern Florida using four cultural treatments: no treatment (F0H0); weed control (F0H1); fertilizer (F1F0); and combination of weed control and fertilizer (F1H1) for each species. During the first year there were large, sustained responses to all cultural practices. Loblolly and slash pine showed similar growth responses and had a lengthened growing season (60–100 days). Slash pine growth was superior to that of loblolly. Growth responses observed during the first year continued. After 4 years, irrigation had no measurable effect on tree growth. Both pine species responded equally to F1H0 and F0H1, but slash retained a slight edge. Extra nutrients]available via fertilizer, reduced competition, or additional rooting space, increased slash-pine volume index from an average of 2.0 m 3 ha −1 (F0H0) to 11.90 and 13.59 m 3 ha −1 (F0H1 and F1H0, respectively). The F1H1 treatment produced the largest slash-pine response, diameter at breast height ( D bh ) averaged 9.84 cm, height reached 5.02 m, and volume index rose to about 22.94 m 3 ha −1 . With teh F1H1 treatment, average loblolly-pine height and volume exceeded that of the average slash pine. At age 4, the growth response due to increased nutrient supply was 13–29 times that of the best genetic response within F0H0 trees of the four slash-pine progenies. The best-growing slash-pine family (6–56) exceeded loblolly-pine growth under all four treatments and approximated the vigor shown by slash pine in the southern hemisphere.

Phosphorus mineralization and microbial biomass in a Florida Spodosol: effects of water potential, temperature and fertilizer application

Abstract Phosphorus mineralization and microbial biomass were measured in the surface 5 cm of a Spodosol (sandy, siliceous hyperthermic Ultic Alaquod) from north-central Florida. Soils from fertilized and unfertilized plantations of loblolly pine (Pinus taeda L.) were incubated at a range of water potentials (∼0, –3, –8, –10 and –1500 kPa) and temperatures (15  °C, 25  °C and 38  °C) for 14 days and 42 days. Increasing water potential and temperature increased specific P mineralization (mineralization expressed as a percentage of total P) regardless of fertilizer treatment. An increase in water potential from –10 kPa to –0.1 kPa resulted in an increase of between 38% and 239% in the concentration of KCl-extractable inorganic P, depending on incubation temperature and time. An increase in incubation temperature from 15  °C to 38  °C resulted in an increase of between 13% and 53% in KCl-extractable inorganic P. Changes in specific P mineralization with change in water potential or temperature were not affected by fertilizer application. This suggests that, although specific P mineralization was greater in the fertilized soils, environmental control of P mineralization was the same for both treatments. Specific P mineralization was most sensitive when soils were at higher water potentials, and decreased logarithmically to water potentials of between –3 kPa and –8 kPa. Specific P mineralization was relatively insensitive to changes in water potential when water potential was lower than –8 kPa. Microbial biomass C showed no consistent responses to changes of temperature or water potential and was not significantly correlated with specific P mineralization. Our results suggest that field estimates of P mineralization in these Spodosols may be improved by accounting for changes in soil water potential and temperature.

Non-destructive measurement of acid phosphatase activity in the rhizosphere using nitrocellulose membranes and image analysis

We developed a method using nitrocellulose membranes and image analysis to localise and quantify acid phosphatase activity in the rhizosphere of two plant species, one with cluster roots (Dryandra sessilis (Knight) Domin) and another with ectomycorrhizal roots (Pinus taeda L.). Membranes were placed in contact with roots and then treated with a solution of x, α-naphthyl phosphate and Fast Red TR. Acid phosphatase activity was visualised as a red imprint on the membrane. We quantified acid phosphatase activity by image analysis of scanned imprints. The method was used to estimate the spatial distribution of acid phosphatase activity within particular root classes (lateral roots, mycorrhizal roots, root clusters). Over 95% of the acid phosphatase activity of the root system of D. sessilis was associated with cluster roots, and between 20 and 32% of the root surface active. About 26 % of the acid phosphatase activity of the root system of P. taeda was associated with mycorrhizal roots and unsuberised white root tips and less than 10% of the root surface was active, irrespective of root type. This non-destructive method can be used for rapid, semi-quantitative assessment of acid phosphatase activity in the laboratory and in situ.

An exploratory analysis of phosphorus transformations in tropical soils using structural equation modeling

Abstract In the tropics, highly weathered soils with high phosphorus (P) fixation capacities predominate, reducing the P availability to plants. For this reason, understanding the cycle of P in the soil is important to develop management strategies that increase P availability to plants, especially in low-input production systems. The aim of this study was to apply structural equation modeling with latent variables, at an exploratory level, to test hypothetical models of the P cycle using data from the Hedley extraction method. Specifically, we evaluated interactions between the pools of P, and identified which pools act as a sink or source of P in unfertilized soils. The models of the P cycle for the tested soil were able to distinguish between the direct and indirect effects of labile and stable P on the available P pool. This approach led to a proposed distinction of functional P pools in the soil, and identifying the processes of P transformation in the soil between the pools based on a source–sink relationship. Based on these analyses, the organic pool consists of the bicarbonate organic phosphate (Po), hydroxide Po, and sonic Po fractions. The bicarbonate inorganic phosphate (Pi) and hydroxide Pi fractions formed the inorganic pool. The hydrochloride (HCl) Phot and residual P fractions formed the occluded pool, the HCl Pi fraction formed the primary mineral pool, and the resin Pi fraction constituted the most available P pool. Organic P pool was the major source to the available P pool.

Sensitivity of Pine Flatwoods Hydrology to Climate Change and Forest Management in Florida, USA

Pine flatwoods (a mixture of cypress wetlands and managed pine uplands) is an important ecosystem in the southeastern U.S. However, long-term hydrologic impacts of forest management and climate change on this heterogeneous landscape are not well understood. Therefore, this study examined the sensitivity of cypress-pine flatwoods hydrology to climate change and forest management by using the physically based, distributed hydrologic modeling system, MIKE SHE. The model was first calibrated and validated with a long-term data set, and then applied using several hypothetical scenarios developed in north central Florida. Our study showed that MIKE SHE could simulate the temporal and spatial dynamics of the shallow ground-water table. The model also identified and confirmed three horizontal ground-water flow patterns at this study site. The modeling results suggested that forest removal and climate change (i.e., warming and drying) would have pronounced impacts on the ground-water table during the dry periods, but these impacts may be minor under wet conditions at this typical flatwoods landscape. At the landscape scale, depressional wetlands may have higher responses to tree removal and climate change than surrounding uplands.

Alocação de nutrientes em plantios de eucalipto no Brasil

Forest management practices can alter nutrient exportation from the site. The purpose of this study was to estimate nutrient contents in the aboveground biomass of eucalyptus plantations in Brazil. The influence of key climatic variables on eucalypt productivity and nutrient content was evaluated, using the database from the Reserch Programa on Soil and Eucalyptus Nutrition of the Soil Science, Departament - Federal University of Vicosa, Minas Gerais State, Brazil. Climatic characteristics were an important component of the models. In regions with low water availability the nutrient accumulation in aboveground biomass as well as biomass production were lower. The highest proportion of all nutrients (68 % N, 69 % P, 67 % K, 63 % Ca, and 68 % Mg) was accumulated in the biomass within 4.5 years after planting for harvesting after approximately 6.5 years. After 4.5 years, the potential of fertilizer response was lower. Canopy and stem bark together accounted for 65 % N, 70 % P, 64 % K, 79 % Ca, and 79 % Mg in the aboveground biomass. Debarking in the field can therefore substantially reduce nutrient exportation and contribute to a more sustainable production in eucalyptus plantations.

Assessing Methods for Developing Phosphorus Desorption Isotherms from Soils using Anion Exchange Membranes

Developing desorption isotherms for inorganic phosphorus (P) is a time-consuming and non-standardized procedure. Anion exchange membranes (AEMs) have been successfully used in studies of P desorption kinetics and total membrane-desorbable P, but rarely have they been used for developing P desorption isotherms. Our study had two objectives: (1) to evaluate the suitability of using multiple strips of AEMs (termed the Multiple AEM Method) to develop P desorption isotherms; and (2) to compare the Multiple AEM Method with a sequential-extraction approach using AEMs (termed the Sequential AEM Method) to determine if the manner in which AEMs were used would influence the slope of the desorption isotherm, i.e. the partition coefficient. Both methods yielded well-defined, but numerically different desorption isotherms for all levels of sorbed P. However, estimated Kd values among methods were equivalent in the low and medium levels of P sorbed. The Multiple AEM method was quicker than the Sequential AEM method, but both gave similar Kd values in an agriculturally significant range of soil solution concentrations. These methods should be tested on a range of soil type to determine their suitability in developing P desorption isotherms and to move toward method standardization for desorption isotherms.