Mark Ashton

Mark S. Ashton

Senior Associate Dean of The Forest School; Morris K. Jesup Professor of Silviculture and Forest Ecology; Director of Yale Forests


Dr. Mark Ashton is the Morris K. Jesup Professor of Silviculture and Forest Ecology, and the Director of the Yale Forests. He has conducted over thirty-five years of research on the biological and physical processes governing the dynamics of natural forests and on the creation of their agroforestry analogs. His long-term research concentrates on tropical and temperate forests of the Asian and American realms. His field sites within these regions were selected specifically to allow comparison of growth, adaptation, and plasticity within and among close assemblages of species that have evolved within forest climates with differing degrees of seasonality. The results of his research have been applied to the development and testing of silvicultural techniques for restoration of degraded lands. He is the author of over 160 peer reviewed journal papers; an author of two field guides to tropical forest trees; an author of the primary silviculture textbook used throughout North America; and an editor or author to twelve other monographs and books concerning the management of forests for a variety of social values concerning agroforestry, watershed management and climate mitigation. Ashton has been recognized by fourteen university awards for his teaching and advising, the David M. Smith Award for Silvicultural Research by the Society of American Foresters, and the UNESCO Sultan Quaboos Award for tropical forest conservation.  

Understanding the regeneration dynamic as a basis for restoration and sustainable management of forests:
I foresee that upland forests in humid regions of the world, after two centuries of dramatic decline and degradation, will become critical resources for the sustenance of global services (water, climate amelioration, recreation) and products (genetic reservoirs of new products, specialty timber and nontimber products) demanded by society. My research concentrates on the ecological adaptations by which trees of various species of these complex forest types become established naturally after disturbances that make vacancies in the growing space. The kind of knowledge gained is a key part of the basis for developing silviculture that will sustain and augment the various forest values of the future.

The importance of big scale comparisons:
The regeneration period is a critical window of time during which the future composition and development of the forest is largely determined. It is also the period during which the silviculturist has the most opportunity to restore and guide forest growth. My research has focused on understanding the most important biological and physical processes governing regeneration of species-rich moist forests. The majority of my research has been centered for over twenty years at field sites in two primary upland forest regions: 1) the American temperate moist deciduous forests (oak-hickory) of southern New England, USA; and the Asian tropical wet-evergreen forest (mixed-dipterocarp) in Sri Lanka and Malaysia. For the last ten years I have also been working at three secondary field sites 1): the boreal spruce-aspen forests of Saskatchewan, Canada; 2) the moist mixed-conifer forests of interior British Columbia; and 3) the tropical seasonally-wet forests of Panama, Central America. Sites were selected to develop common methodological protocols that would enable a better understanding of the differences and similarities of regeneration within and across major forest biomes.

Long-term experimental rationale and framework: Building the basics:
Cladistic groups (at the genus level in particular) are largely the level at which species differentiation occurs in tree species-rich forests such as those of eastern North America and the Asian moist tropics. Co-occurring species within a genus may differ in value and the products that they yield, as well as in their spatial and temporal role in biodiverse plant assemblages. I have chosen to study a series of co-occurring species that are of the same cladistic group (and often of the same successional status), because their similar morphology and growth adaptations facilitate examination of differences. Identifying these differences and their variations can provide a better understanding of evolving species specialization in relation to environment. This, in turn, provides the ecological information necessary for restoration and sustainable management of moist tree species-rich forests.

Applying this knowledge to silviculture:
My work has immediate application for the development and testing of regeneration methods in natural forests, which I am pursuing at all my sites. I have long-term plots monitoring regeneration performance in experimental canopy openings that are intended to test hypotheses concerning forest resilience in relation to disturbance and site productivity. In the tropics I am using information gleaned from New England’s experience with deforestation, and together with my information on seedling regeneration ecology of the tropics (Panama, Sri Lanka), I have embarked on a series of sequential studies with collaborators on site reforestation. Much of this information has been summarized in two seminal textbooks on silviculture and agroforestry.


B.S., University of Maine, College of Forest Resources; M.F., Ph.D., Yale University

This professor is accepting doctoral students