Daniel Markewitz

University of Georgia | UGA · Warnell School of Forestry and Natural Resources

Replacing long-lived, rarely disturbed vegetation with short-lived, frequently disturbed vegetation is a widespread phenomenon in the Anthropocene that can influence ecosystem functioning and soil development by reducing the abundance of deep roots. We explore how sources and fate of soil CO2 vary with organic substrate source, abundance of respiri...

After 4.5 billion years as an evolving and dynamic planet, the Earth continues to evolve but with human‐altered dynamics. Earth scientists have special opportunities and responsibilities to accelerate our understanding of Earth's changes that are transforming our most remarkable home.

Slash-and-mulch agroforestry systems can reduce greenhouse gas emissions by mulching the vegetation instead of burning it. This mulch layer then contains greater stocks of organic material than after burning, making it a potential source of N2O and CH4 efflux during decomposition. We examined N2O and CH4 efflux from slash-and-mulch AFS using a two-...

Land use changes and reforestation impact soil phosphorus (P) distribution over extended periods. This study examines P distribution in forest development from 1957 to 2017 at the Calhoun Critical Zone Observatory in South Carolina. Tracking changes in 0–60 cm mineral soil P fractions through six samplings in eight continuously uncut plots and eigh...

Non-industrial private forest landowners and foresters often rely on outdated site index models for forest productivity predictions, which hinders accurate assessment. To address this issue, 157 slash pine plots were established in the coastal plain of Georgia, USA, to collect tree and soil data. Using regression tree and linear regression models,...

Site productivity and forest management strategies hinge on intrinsic site resources such as soil water and nutrient availability. In this study, regression tree model and linear regression model approaches were employed to quantify the relationship between site index and soil parameters for loblolly pine plantations in the Coastal Plain. Both the...

Agriculture, and associated land-clearing, account for approximately 25% of global greenhouse gas (GHG) emissions, including trace gases nitrous oxide (N2O) and methane (CH4). Agroforestry systems (AFS) have been proposed to reduce GHG emissions of agricultural practices. Smallholding farmers of the global tropics often utilize slash-and-burn AFS t...

Atmospheric deposition of dissolved organic carbon (DOC) to terrestrial ecosystems is a small, but rarely studied component of the global carbon (C) cycle. Emissions of volatile organic compounds (VOC) and organic particulates are the sources of atmospheric C and deposition represents a major pathway for the removal of organic C from the atmosphere...

Soil health assessments require the establishment of soil indicators that are easy to measure and sensitive to changes in management practices. Despite the global demand for wood products and the intensification of silvicultural practices, very few indicators are currently used to monitor changes in soil properties and processes in managed forest p...

Large-scale quantification of soil physical properties is challenging due to their inherent spatial and temporal variability. This variability determines hydrologic and biogeochemical behavior of soils and influences their ecosystem responses. This study investigated electrical resistivity tomography (ERT) in an Artificial Neural Network (ANN) fram...

Soil P is present in multiple forms through the profile with plants potentially accessing different P pools at different depths through distinct pathways. Understanding P pool distribution and dynamics is necessary for sustainable forest management. Our research investigates soil P dynamics in clay (at 60–100 cm depth) and saprolite (at 450–500 cm...

Soil phosphorus (P) chemistry changes during ecosystem development and soil formation. These P transformations occur through both time and space as P is cycled into secondary compounds and translocated down slopes and through the soil profile by erosion and leaching. Over decades, the slow cycling of organic and occluded P fractions can modulate so...

Aboveground net primary productivity (ANPP) of an ecosystem is among the most important metrics of valued ecosystem services. Measuring the efficiency scores of ecological production (ESEP) based on ANPP using relevant variables is valuable for identifying inefficient sites. The efficiency scores computed by the Data Envelopment Analysis (DEA) may...

Tree plantations represent an important component of the global carbon (C) cycle and are expected to increase in prevalence during the 21st century. We examined how silvicultural approaches that optimize economic returns in loblolly pine (Pinus taeda L.) plantations affected the accumulation of C in pools of vegetation, detritus, and mineral soil u...

Human actions through land-use can alter soil phosphorus (P) distribution over time and space as vegetation is altered and added fertilizer P is translocated downslopes by runoff and erosion, or through the soil profile by leaching. In the southeastern US Piedmont, a more than 100-year period of human land-use of forest clearing and farming, which...

Net primary productivity (NPP) and net ecosystem production (NEP) are often used interchangeably, as their difference, heterotrophic respiration (soil heterotrophic CO2 efflux, RSH = NPP−NEP), is assumed a near‐fixed fraction of NPP. Here, we show, using a range‐wide replicated experimental study in loblolly pine (Pinus taeda) plantations that RSH...

Most terrestrial nutrient sources are hypothesized to shift in dominance from mineral- to organic matter (OM)-derived over millennia. We investigated how overlaying this hypothesis with plant rooting dynamics that can feedback to soil development offers insight into ecosystem functioning. To test the hypothesis that the nutritional importance of OM...

The critical zone encompasses terrestrial and aquatic systems that extend from local (soil pedon) to continental (watershed) scales, with heterogeneous fate and transport processes across these systems and scales. We present an exploratory analysis of carbon and nutrient fluxes on a Southeastern US landscape: from forest soils, subsurface transport...

Soil organic matter composition controls many microbial processes in the soil matrix. How these processes interact to drive carbon cycling through greenhouse gas fluxes or carbon stabilization through biochemical transformations continues to evolve. From laboratory incubations, it is clear that low molecular weight compounds (LMWCs; e.g. dextrose,...

The Piedmont region of the southeastern United States experienced a period of accelerated erosion in the 1800s. Clear-cutting of the forests coupled with soil tilling and inadequate erosion control practices led to substantial soil redistribution and loss. This redistribution exposed the subsoil clay (argillic) horizon in many locations and altered...

Expansion of agriculture in the Brazilian Amazon has been driven not just by demands from traditional, rural producers, but also large agriculture and cattle producers, both of whom have put considerable pressure on remaining forests and their watersheds. Monitoring of these watersheds has been a focus of intensive study for the past 20 years and a...

Row crop agriculture is a significant source of two major greenhouse gases (GHGs) (carbon dioxide [CO2] and nitrous oxide [N2O]) and the air pollutant precursor ammonia (NH3). Fluxes of these naturally occurring trace gases are often augmented by agricultural practices, such as fertilizer application and crop systems management. A living mulch syst...

Geomorphologists are quantifying the rates of an important component of bedrock's weathering in research that needs wide discussion among soil scientists. By using cosmogenic nuclides, geomorphologists estimate landscapes’ physical lowering, which, in a steady landscape, equates to upward transfers of weathered rock into slowly moving hillslope‐soi...

Biotically-mediated weathering helps to shape Earth’s surface. For example, plants expend carbon (C) to mobilize nutrients in forms whose relative abundances vary with depth. It thus is likely that trees’ nutrient acquisition strategies—their investment in rooting systems and exudates—may function differently following disturbance-induced changes i...

Forests in the Southeast USA are predicted to experience a moderate decrease in precipitation inputs over this century that may result in soil water deficiency during the growing season. The potential impact of a drier climate on the productivity of managed loblolly pine (Pinus taeda L.) plantations in the Southeast USA is uncertain. Access to wate...

Agroforestry systems are important, globally affecting 1.2 billion people and covering 0.6 billion hectares. They are often cited for providing ecosystem services, such as augmenting soil fertility via N accumulation and increasing soil C stocks. Improved-fallow slash-and-mulch systems have the potential to do both, while reducing nutrient losses a...

The pedosphere is the largest terrestrial reservoir of organic carbon, yet soil-carbon variability and its representation in Earth system models is a large source of uncertainty for carbon-cycle science and climate projections. Much of this uncertainty is attributed to local and regional-scale variability, and predicting this variation can be chall...

Slowly cycling P fractions have a significant role in soil P bioavailability in time scales longer than a growing season. The objective of this study is to evaluate P fractions and P bioavailability in Piedmont Ultisols that supported forest development from 1962 to 2017. Soil samples were collected from four depths (0-7.5, 7.5-15, 15-35, and 35-60...

To determine the effectiveness of forests in sequestering atmospheric carbon (C), we must know the amount of fixed carbon dioxide (CO2) that is subsequently lost due to heterotrophic microbial activity in the soil. Furthermore, the heterotrophic proportion of total soil respiration (Rs) must be quantified as it changes between different physiograph...

Management strategies for loblolly pine (Pinus taeda) plantations in the Southeastern USA can be adapted to fulfill both the demand for wood products and for bioenergy. This study quantifies the impact of plantation management choices on the cumulative carbon balance and the net present value of loblolly pine plantations at the stand level, as well...

Experimental warming of forest ecosystems typically stimulates soil respiration (CO2 efflux), but most warming experiments have been conducted in northern latitudes (> 40°N) with relatively young soils. We quantified the influence of experimental warming on soil respiration (RT) in two adjacent forest habitats—a mature, closed canopy forest and a g...

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...

We investigated the beneficial role of different concentrations of exogenous oxalic acid (OA) or citric acid (CA) for improving Pb tolerance and mitigating Pb-induced physiological toxicity in Changbai larch (Larix olgensis A. Henry) seedlings in northeast China. The seedlings were exposed to 100 mg·kg−1 Pb in soil alone or in combination with OA o...

Long-term environmental research networks are one approach to advancing local, regional, and global environmental science and education. A remarkable number and wide variety of environmental research networks operate around the world today. These are diverse in funding, infrastructure, motivating questions, scientific strengths, and the sciences th...

Carbon isotope composition (δ¹³C), intercepted photosynthetically active radiation (IPAR), foliar nitrogen (N) content and foliar N concentration are all factors related to stand growth and productivity. The relationships between these attributes and growth were studied in 15 and 16-year-old loblolly pine (Pinus teada L.) stands at planting densiti...

Collaborations between biologists and geologists are key to understanding and projecting how landscapes function and change over time. Such collaborations are stimulated by on-going scientific developments, advances in instrumentation and technology, and the growing recognition that environmental problems necessitate interdisciplinary investigation...

The role of biological nitrogen fixation (BNF) during secondary forest succession and in tropical pastures has been investigated and debated for several decades. Here we present results of a replicated experimental study in a degraded cattle pasture of eastern Amazonia using mass balance and a 15N tracer in lined soil pit mesocosms with three treat...

Forests in the Southeast U.S. are predicted to experience future changes in seasonal patterns of precipitation inputs as well as more variable precipitation events. These climate change induced alterations could increase drought and lower soil water availability. Drought could alter rooting patterns and increase the importance of deep roots that ac...

In the Southeast United States (U.S.), the climate is predicted to be warmer and have more severe drought in the summer. Decreasing rainfall in summer months should create more severe soil drying, which will eventually affect re-wetting cycles deeper in the soil profile. Changing drying-wetting cycles in this deeper portion of the profile may impac...

High productivity of fertilized loblolly pine (Pinus taeda L.) plantations in the southern United States is related to increased leaf area index (LAI), but higher evaporative leaf surface area may increase drought vulnerability. To determine if the benefits of fertilization are affected by water availability or the effects of drought are exacerbate...

The Calhoun Experimental Forest in the Piedmont of South Carolina has a history of forest clearing for agriculture, severe surface soil erosion, agricultural abandonment, and reforestation. This combination makes Calhoun a unique place to consider the landscape scale redistribution of P. The spatial distribution and chemical state (e.g., organic or...

Geomys pinetis (Southeastern pocket gopher) is a fossorial rodent historically associated with Pinus palustris (longleaf pine) communities. Conversion and fragmentation of longleaf pine communities have reduced quality and quantity of southeastern pocket gopher habitat. It is therefore important to determine characteristics of suitable habitat for...

The southeastern pocket gopher Geomys pinetis is absent from a large portion of its historical range. Translocation may represent a viable management technique to reestablish populations into suitable habitat. However, several aspects of the species’ ecology are poorly understood, making development of an effective translocation approach challengin...

To optimize sampling effort, knowledge of soil spatial variability is essential, but usually requires large and spatially detailed data sets. In this study, soils under secondary forests of four ages (1, 8, 15, 22 years) were compared within an agricultural landscape in the eastern Amazon (Igarapé Açu, eastern Pará state, Brazil). At three nested s...

CO2 effluxes from streams and rivers has been hypothesized to be a critical pathway of carbon flow from the biosphere back to the atmosphere. This study was conducted in three Amazonian small catchments to evaluate carbon evasion and dynamics, where land-use change has occurred on small family-farms. Monthly field campaigns were conducted from June...

The critical role streamside riparian zones play in mitigating the movement of nitrogen (N) and other elements from terrestrial to aquatic ecosystems could be threatened by residential development in the southern Appalachian Mountains. Many studies have investigated the influence of agriculture on N loading to streams but less is known about the im...

With large taper and biomass measurement datasets from destructively sampled loblolly pine trees, we developed weight-to-volume ratio equations and biomass allocation equations based on tree DBH and height. The weight-to-volume ratio equations were fitted simultaneously with stem green weight with bark and stem outside-bark volume equations or stem...

Due to its huge size and the difficulties of accessing remote forest areas it is a challenge to generate data about the hydrogeochemistry of small catchments in the Amazon Basin. A four year study of a stream in the FLONA do Tapajós has shown results that contribute to increase the knowledge about the hydrogeochemical processes in the region. These...

Exogenous organic acids are beneficial in protecting plants from the stress of heavy metal toxins (e.g., Pb) in soils. This work focuses on the potential role of organic acids in protecting Changbai larch (Larix olgensis) seedlings from the stress of growing in nutrient deficient soil. The seedlings were planted in a nutrient rich or deficient soil...

Small-holding farmers of the Brazilian Amazon often use a rotation of secondary forest, slash-and-burn land-clearing and fallow phase regeneration for agriculture. In recent decades reduction of the fallow phase from ~20 to ~5 years has limited nutrient accumulation by fallow vegetation to sustain future crop growth. Slash-and-mulch and improved fa...

Mechanical site preparation has been considered essential to southern pine plantation establishment since the 1950s. Although survival and early growth responses to site preparation are well documented, several factors often contribute to these responses, and the specific contribution of soil tillage is not well established. Soil moisture content,...

Soil erosion, particularly that caused by agriculture, is closely linked to the global carbon (C) cycle. There is a wide range of contrasting global estimates of how erosion alters soil-atmosphere C exchange. This can be partly attributed to limited understanding of how geomorphology, topography, and management practices affect erosion and oxidatio...

Accelerated soil erosion is an important element of the global carbon (C) cycle. Attempts to quantify the impact of erosion on C budgets are limited by the inability to systematically represent feedbacks between hydrological, geomorphological, and biogeochemical processes. For this purpose we use tRIBS-ECO (Triangulated Irregular Network-based Real...

Biomass estimation is a prerequisite for calculating biomass energy, carbon storage, and sequestration of forests and for examining forest productivity and nutrient cycling. With destructive biomass sampling data from 456 sampled trees on 114 plots of loblolly pine culture and density studies at ages 12, 15, and 16, two systems of nonlinear additiv...

The future climate of the southeastern USA is predicted to be warmer, drier and more variable in rainfall, which may increase drought frequency and intensity. Loblolly pine (Pinus taeda) is the most important commercial tree species in the world and is planted on ~11 million ha within its native range in the southeastern USA. A regional study was i...