About

Eric Kruger is a Professor and Department Chair in the Department of Forest and Wildlife Ecology at the University of Wisconsin-Madison. He specializes in tree physiology, focusing on the physiological basis of forest tree development and the factors affecting tree growth. Kruger has been a faculty member at UW-Madison since 1992, initially serving as an Assistant Professor, then as an Associate Professor, and currently as a Professor. His educational background includes a B.S. and M.S. in Forestry from the University of Minnesota, obtained in 1984 and 1986 respectively, and a Ph.D. in Forestry from the University of Wisconsin, earned in 1992. He teaches courses such as Tree Physiology, Integrated Resource Management, and Forest Resources Practicum, which involve resource management planning, field training, and exposure to forestry operations. Kruger's research and teaching contributions are centered on understanding forest tree physiology and applying this knowledge to resource management and conservation.

Research topics

• Geography
• Ecology
• Biology
• Environmental science
• Atmospheric sciences
• Geology
• Agroforestry
• Evolutionary biology
• Physics
• Remote sensing
• Botany
• Meteorology
• Demography
• Physical geography

Selected publications

• APTA Education Leadership Conference: A Reflection on Inclusion

  Journal of Physical Therapy Education · 2025-01-22 · 1 citations

  articleSenior author
  PublisherDOI

• Thinking Before Acting: Considerations on Directing DPT Programs Toward Competency-Based Education

  Journal of Physical Therapy Education · 2025-09-17

  article1st authorCorresponding
  PublisherDOI

• Quantifying foliar trait variation and covariation in sun and shade leaves using leaf spectroscopy in eastern North America

  Forest Ecosystems · 2024-01-01 · 4 citations

  articleOpen access

  Characterizing foliar trait variation in sun and shade leaves can provide insights into inter- and intra-species resource use strategies and plant response to environmental change. However, datasets with records of multiple foliar traits from the same individual and including shade leaves are sparse, which limits our ability to investigate trait-trait, trait-environment relationships and trait coordination in both sun and shade leaves. We presented a comprehensive dataset of 15 foliar traits from sun and shade leaves sampled with leaf spectroscopy, including 424 individuals of 110 plant species from 19 sites across eastern North America. We investigated trait variation, covariation, scaling relationships with leaf mass, and the effects of environment, canopy position, and taxonomy on trait expression. Generally, sun leaves had higher leaf mass per area, nonstructural carbohydrates and total phenolics, lower mass-based chlorophyll a + b, carotenoids, phosphorus, and potassium, but exhibited species-specific characteristics. Covariation between sun and shade leaf traits, and trait-environment relationships were overall consistent across species. The main dimensions of foliar trait variation in seed plants were revealed including leaf economics traits, photosynthetic pigments, defense, and structural traits. Taxonomy and canopy position collectively explained most of the foliar trait variation. This study highlights the importance of including intra-individual and intra-specific trait variation to improve our understanding of ecosystem functions. Our findings have implications for efficient field sampling, and trait mapping with remote sensing.

  PublisherDOI

• Herbaceous plant height is an early indicator of groundlayer response to an experimental manipulation of forest structure and deer pressure

  Forest Ecology and Management · 2023-03-10 · 4 citations

  article
  PublisherDOI

• Generality of leaf spectroscopic models for predicting key foliar functional traits across continents: A comparison between physically- and empirically-based approaches

  Remote Sensing of Environment · 2023-05-07 · 40 citations

  article
  PublisherDOI

• Genotypic variation rather than ploidy level determines functional trait expression in a foundation tree species in the presence and absence of environmental stress

  Annals of Botany · 2022-05-31 · 11 citations

  articleOpen accessSenior author

  BACKGROUND AND AIMS: At the population level, genetic diversity is a key determinant of a tree species' capacity to cope with stress. However, little is known about the relative importance of the different components of genetic diversity for tree stress responses. We compared how two sources of genetic diversity, genotype and cytotype (i.e. differences in ploidy levels), influence growth, phytochemical and physiological traits of Populus tremuloides in the presence and absence of environmental stress. METHODS: In a series of field studies, we first assessed variation in traits across diploid and triploid aspen genotypes from Utah and Wisconsin under non-stressed conditions. In two follow-up experiments, we exposed diploid and triploid aspen genotypes from Wisconsin to individual and interactive drought stress and defoliation treatments and quantified trait variations under stress. KEY RESULTS: We found that (1) tree growth and associated traits did not differ significantly between ploidy levels under non-stressed conditions. Instead, variation in tree growth and most other traits was driven by genotypic and population differences. (2) Genotypic differences were critical for explaining variation of most functional traits and their responses to stress. (3) Ploidy level played a subtle role in shaping traits and trait stress responses, as its influence was typically obscured by genotypic differences. (4) As an exception to the third conclusion, we showed that triploid trees expressed 17 % higher foliar defence (tremulacin) levels, 11 % higher photosynthesis levels and 23 % higher rubisco activity under well-watered conditions. Moreover, triploid trees displayed greater drought resilience than diploids as they produced 35 % more new tissue than diploids when recovering from drought stress. CONCLUSION: Although ploidy level can strongly influence the ecology of tree species, those effects may be relatively small in contrast to the effects of genotypic variation in highly diverse species.

  PublisherOA PDFDOI

• Motivational Interviewing Education and Utilization in US Physical Therapy

  Journal of Physical Therapy Education · 2022-11-16

  article1st authorCorresponding

  INTRODUCTION: In physical rehabilitation, motivational interviewing (MI) can improve treatment adherence and therapeutic outcomes. The objective of this study was to investigate the relationship between MI education and use of MI skills in physical therapy practice in the United States. REVIEW OF LITERATURE: Motivational interviewing is an empirically supported technique for facilitating behavior change. Numerous studies have examined its use in physical rehabilitation settings. No research has examined education and utilization of MI in physical therapy in the United States. SUBJECTS: Physical therapists (PTs) in the United States (N = 785) responded to an electronic survey distributed through the special interest academies and state chapters of the American Physical Therapy Association. METHODS: Descriptive, correlational, and group comparisons were used to analyze the survey responses about MI utilization in clinical practice, characteristics of MI training, and self-reported use of MI communication skills. RESULTS: Two-thirds of the sample reported using MI and half of the sample received training in MI. Motivational interviewing training was heterogeneous, with interactive elements superior to lecture alone. Interestingly, training received in PT education programs correlated negatively with the use of the MI skills assessed in this study. Use of MI skills significantly correlated with increased perceived patient adherence and decreased struggle with patients. DISCUSSION AND CONCLUSION: Incorporation of MI into physical therapy practice has the potential to improve patient care through increased therapeutic rapport, improvement of health outcomes associated with behavior change, and improved job satisfaction. Although MI is becoming more prevalent in physical therapy practice in the United States, the results of this study suggest that MI education should include dynamic components to increase the effective use of MI skills in clinical practice.

  PublisherDOI

• <i>Ixodes scapularis</i> density in US temperate forests shaped by deer, earthworms, and disparate factors at two scales

  Ecosphere · 2022-02-01 · 14 citations

  articleOpen access

  Abstract Forest and wildlife management can help regulate the risk of human exposure to tick‐borne pathogens by influencing the population density of host‐seeking ticks and the pathogen infection prevalence in tick populations. For the blacklegged tick ( Ixodes scapularis ), also known as the deer tick, the overall density of host‐seeking nymphs and the density of nymphs infected with Borrelia burgdorferi sensu stricto (which causes Lyme disease) are often closely and positively correlated. We sought to identify biotic and abiotic factors influencing nymph abundance in a multiscale assessment within and across forested landscapes in northern Wisconsin. On a set of randomly located plots within each of six mesic, hardwood‐dominated forests, we collected host‐seeking and on‐host ticks, observed two common mammal hosts (white‐tailed deer and mice), and characterized the structure and composition of the forest plant community. We also surveyed activity of exotic invasive earthworms, which are altering forest structure in the region. At the broader forest‐level scale ( n = 6), nymphal tick abundance was positively related to deer population density after accounting for the negative influence of forb cover. At the finer plot‐level scale ( n = 87), nymph abundance was positively correlated with the abundance of coarse woody debris and negatively correlated with the density of earthworm castings, an indicator of Lumbricid (nightcrawler) activity. Thus, we identified a suite of key factors, operating at different spatial scales, that shape the suitability of forest habitat for questing immature ticks. These findings inform our basic understanding of blacklegged tick ecology and also have important implications for managing tick‐borne pathogens in forest ecosystems and landscapes.

  PublisherDOI

• Genotypic variation rather than ploidy level determines functional trait expression in a foundation tree species in the presence and absence of environmental stress    

  2022-02-02 · 4 citations

  preprintOpen accessSenior author

  Background and Aims : At the population level, genetic diversity is a key determinant of a tree species’ capacity to cope with stress. However, little is known about the relative importance of the different components of genetic diversity for tree stress responses. We compared how two sources of genetic diversity, genotype and cytotype (i.e. differences in ploidy levels) influence growth, phytochemical, and physiological traits of Populus tremuloides in the presence and absence of environmental stress. Methods: In a series of field studies, we first assessed variation in traits across diploid and triploid aspen genotypes from Utah and Wisconsin under nonstressed conditions. In two follow-up experiments, we exposed diploid and triploid aspen genotypes from Wisconsin to individual and interactive drought stress and defoliation treatments and quantified trait variations under stress. Key Results: We found that 1) tree growth and associated traits did not differ significantly between ploidy levels under nonstressed conditions. Instead, variation in tree growth and most other traits was driven by genotypic and population differences. 2) Genotypic differences were critical for explaining variation of most of functional traits and their responses to stress. 3) Ploidy level played a subtle role in shaping traits and trait stress responses, as its influence was typically obscured by genotypic differences. 4) As an exception to the third conclusion, we showed that triploid trees expressed minimally higher levels of foliar defenses, photosynthesis, and rubisco activity under well-watered conditions, and displayed slightly greater drought resilience than diploids. Conclusion: Although ploidy level can strongly influence the ecology of tree species, those effects may be relatively small in contrast to the effects of genotypic variation in highly diverse species.

  PublisherOA PDFDOI

• Leaf spectroscopy reveals divergent inter‐ and intra‐species foliar trait covariation and trait–environment relationships across NEON domains

  New Phytologist · 2022-05-05 · 55 citations

  articleSenior author

  Concurrent measurement of multiple foliar traits to assess the full range of trade-offs among and within taxa and across broad environmental gradients is limited. Leaf spectroscopy can quantify a wide range of foliar functional traits, enabling assessment of interrelationships among traits and with the environment. We analyzed leaf trait measurements from 32 sites along the wide eco-climatic gradient encompassed by the US National Ecological Observatory Network (NEON). We explored the relationships among 14 foliar traits of 1103 individuals across and within species, and with environmental factors. Across all species pooled, the relationships between leaf economic traits (leaf mass per area, nitrogen) and traits indicative of defense and stress tolerance (phenolics, nonstructural carbohydrates) were weak, but became strong within certain species. Elevation, mean annual temperature and precipitation weakly predicted trait variation across species, although some traits exhibited species-specific significant relationships with environmental factors. Foliar functional traits vary idiosyncratically and species express diverse combinations of leaf traits to achieve fitness. Leaf spectroscopy offers an effective approach to quantify intra-species trait variation and covariation, and potentially could be used to improve the characterization of vegetation in Earth system models.

  PublisherDOI

Recent grants

• Doctoral Dissertation Research: Factors Determining Geographical Range Limits of Boreal and Temperate Tree Species

  NSF · $12k · 2008–2011

• Collaborative Research: Restricted Plasticity of Canopy Stomatal Conductance: A Conceptual Basis for Simpler Spatial Models of Forest Transpiration

  NSF · $47k · 2004–2007

Frequent coauthors

• Peter B. Reich

  University of Minnesota

  44 shared

• Philip A. Townsend

  University of Wisconsin–Madison

  27 shared

• Richard L. Lindroth

  University of Wisconsin–Madison

  19 shared

• B. E. Ewers

  16 shared

• D. S. Mackay

  University at Buffalo, State University of New York

  15 shared

• M. M. Loranty

  Colgate University

  15 shared

• Zhihui Wang

  Guangzhou Institute of Geography

  12 shared

• John C. Volin

  University of Maine

  11 shared

Labs

• Forest and Wildlife EcologyPI

Education

• Ph.D., Wildlife Ecology

  University of Wisconsin-Madison

  1995

• M.S., Wildlife Ecology

  University of Wisconsin-Madison

  1991

• B.S., Wildlife Ecology

  University of Wisconsin-Madison

  1988