Scientists & Staff

Todd Ristau

Todd Ristau

Research Ecologist / Director's Representative
335 National Forge Road
P.O. Box 267
Irvine, PA, 16329-0267
Phone: 814-563-1055

Contact Todd Ristau

Current Research

  • Influence of nitrogen deposition changes on black cherry seed production and seedling development in a changing environment following the reduced nitrate and sulfate emissions and deposition.
  • Recognizing silvicultural problems and opportunities during the early stem exclusion phase of stand development including competition and use of treatments such as herbicides and fertilizers to enhance seedling development.
  • Long term changes in old growth forests of the Allegheny Plateau region with focus on Hearts Content, Cook Forest and Tionesta Natural Area.
  • Enhancement of regeneration guidelines for northern hardwood forests, especially as related to herbicide and fertilizer use.

Research Interests

  • I am interested in how both woody and herbaceous plant communities respond to disturbances.
  • I am interested in understanding the conditions that result in monoculture following overstory removal and how to apply existing or novel silvicultural techniques to prevent monoculture and promote mixed species regeneration.
  • I am interested in how unmanaged old growth forests differ from or are similar to managed second growth forests in terms of  both woody and herbaceous species composition following disturbances.
  • I work to develop guidelines for forest management that are used in the SILVAH system of stand inventory, analysis and prescription used by many foresters in the northcentral and northeastern states use as a tool for forest management.

Why This Research is Important

Our mission is to enhance the basic understanding of Allegheny Plateau forest ecosystems while developing resource management guidelines. Understanding how management activities alter the herbaceous plant community in stands under a variety of management strategies is critical to the practice of ecosystem management. Understanding the competitive ability of species like black birch, black cherry, and pin cherry are important. Understanding establishment requirements and creating conditions favorable for a variety of species to become established where they are best suited is critical to achieving our mission goals.


  • The State University of New York, College of Env. Sci. and For., Ph.D. Plant Ecology, 2010
  • The Pennsylvania State University, M.S. Forest Science, 1997
  • Houghton College, B.S. Biology, 1991

Professional Organizations

  • Ecological Society of America (1995 - Present)
  • Torrey Botanical Society (1998 - Present)
  • Society of American Foresters (SAF) (1995 - Present)

Featured Publications & Products

Publications & Products

National Research Highlights

Upper panel: Black cherry raceme with individual flowers. Robert Long, USDA Forest Service
Lower panel: Mature black cherry seed at the base of a tree in fall 2010

Black cherry regeneration difficulties: Are They Related to Stand Age or Something Else?

Year: 2017

Forest managers report that black cherry regeneration is impeded by poor and erratic seed production. Tree stand age has been suggested as one of the causal factors affecting seed production. Forest Service scientists monitored black cherry seed production over seven years to see whether stand age affects seed production.

Photo 1:  Reid Garrison in a regenerating stand where black cherry seedlings are thriving after a nitrogen fertilizer treatment.
Photo 2:  Figures show increased species diversity in fertilizer treated stands.

Using fertilizer to promote diverse seedling development in Allegheny hardwood forests

Year: 2017

Fertilizing the forest understory slows the development of dominance by sweet birch, favors development of black cherry following overstory removal, and favors red maple in partial cut shelterwood stands.

This black cherry seedling is infected with black cherry leaf spot. Managers and scientists have observed this infection more frequently in recent years. Robert Long, U.S. Department of Agriculture Forest Service.

Changes in Black Cherry on the Allegheny Plateau

Year: 2016

Increased tree mortality, decreased seed production, and seedling growth. Managers and scientists have been observing these changes in black cherry on the Allegheny Plateau and are working together to sharpen the research focus and utilize long-term research to improve forest management.

Results of herbicide application using different surfactants with glyphosate to control striped maple and American beech. Bars with the same letter are not different at p < 0.05. U.S. Department of Agriculture Forest Service.

Fine-tuning Herbicide Prescriptions in Northern Hardwood Forests

Year: 2016

Fine-tuning existing herbicide prescriptions leads to better results for forest managers and landowners.

Ecoregions of Pennsylvania color-coded by the levels of similarity found between overstory and understory tree species composition in the Pennsylvania Regeneration Study data of 2001-2005. Todd Ristau, USDA Forest Service

Pennsylvania Regeneration Study Assesses Overstory and Understory Tree Species Communities

Year: 2014

In 2001, the Commonwealth of Pennsylvania and Forest Service's Forest Inventory & Analysis (FIA) program launched the "Pennsylvania Regeneration Study" to gain a better understanding of understory conditions across Pennsylvania. The landscape-level study was incorporated into a subset of the existing FIA sample locations. At each selected plot, composition and abundance of established tree seedlings and associated non-tree vegetation were recorded. Forest Service scientists analyzed the 2001 to 2005 data to determine whether overstory and understory species composition was similar by forest type or ecoregion and to test various hypotheses about causes for dissimilarity.

One of the common ground beetles Pterostichus melanarius that responded to lepidopteran outbreaks. Todd Ristau, USDA Forest Service

Scientists Study Long-term Response of Ground Beetle Communities to an Operational Herbicide Application

Year: 2013

Ground beetles comprise a large and diverse group of mostly predatory beetles that have long been recognized as a useful barometer of ecosystem health. As part of a long-term, large-scale study of the impacts of an operational herbicide-shelterwood treatment, Forest Service scientists found no treatment response by ground beetles as measured by abundance or diversity. However, their numbers and diversity were strongly correlated with natural outbreaks of forest lepidopterans, an order of insects that include moths and butterflies.

Deer browsing exerts top-down selection on plant communities, which over time ricochets back up the trophic web to affect insects and birds. Forestry Sciences Laboratory, Irvine, PA

Long-Term Differences in Forests With Different Deer Densities

Year: 2011

Thirty years after a study on the effects of deer on forest ecosystems established new forest stands at deer densities ranging from 10 to 64 deer per square mile, Forest Service scientists found that tree species diversity, canopy foliage density, insect density and bird density, all decreased significantly as the deer density at stand initiation increased. If deer densities were high initially, the effects carried over, even if densities were lower later.

Last modified: Monday, October 5, 2020