Science of the Seasons

Spring 2019

Where astronomical spring is definite – it is on the calendar for March 20 – meteorological spring, and nature itself, weave into the season with a lot less confidence. A week may begin with temperatures slumping at 15 degrees below average and end with a rebound that shrinks the snowpack and fills basements over just a couple of days.  Welcome to spring!

This page brings together Northern Research Station science that relates to the spring season, along with links to other seasonal resources within the USDA Forest Service.  

Scientists Perspectives on the Seasons

Is it Spring Yet?

Bur oak branch in spring leaf out.On March 20, the calendar proclaims a new season, and a region battered by a polar vortex and snow and then more snow is more than ready for it. From the standpoint of a forest, spring is more subtle.

One could argue that the advent of “spring” is most evident in budbreak within tree crowns and the gradual expansion of leaves to produce green forest canopies. Research at Hubbard Brook Experimental Forest in New Hampshire has demonstrated that weather influences the timing and rate of canopy development in at least two significant ways:

  1. Temperature and precipitation events that melt the winter snowpack and allow for soil warming that then triggers initial tree biological activity – including budbreak.
  2. In addition, accumulations of warm air temperatures (e.g., often measured as warming degree days) help initiate budbreak and speed leaf expansion.

Weather events that slow the melting of snowpacks (e.g., protracted cold associated with the polar vortex) or speed snowmelt (e.g., high temperatures or excessive rain) will influence springtime soil warming and thus alter the initiation of tree biological activity. Once soils thaw, then the accumulation of warm temperatures become important in speeding budbreak and leaf expansion. This means that leaves gradually expand when temperatures are just a bit mild, but expand more rapidly when more intense warmth occurs.

Interestingly, short warm spells can initiate leaf expansion, but this process can stall if lower temperatures quickly return. These partially expanded leaves are very succulent and unusually vulnerable to frost injury relative to non-expanded buds or fully expanded leaves that are better protected from freezing injury.

-Paul Schaberg, Research Plant Physiologist, Northern Research Station

Trees Outside of Forests

[map:] Major Planting Areas of the Prairie States Forestry (Shelterbelt) Project, 1935-1942.The spring of 2019 is beginning with high water and concerns about even higher water. Eighty years ago, farmers in the Great Plains states were contending with the opposite extreme, a prolonged drought that led to dust storms that picked up so much parched topsoil that they blackened the sky. President Franklin D. Roosevelt began the Prairie States Forestry Project in 1935 as a way to reduce the velocity of the wind around farm fields and houses and, along with it, reduce soil erosion. Between 1935 and 1942, the project resulted in more than 220 million trees being planted in approximately 33,000 windbreaks that, if lined up end-to-end, would have measured more than 18,000 miles in length.

Windbreaks remain a familiar but not well-understood resource. While the USDA Forest Service’s Forest Inventory and Analysis Program monitors forests across the nation, windbreaks are usually not included because many do not meet the minimum width required to count as forest land. Two Forest Inventory and Analysis scientists in St. Paul, Minn., Dacia Meneguzzo and Greg Liknes formed the Trees Outside Forests Image-based Inventory (TOFii) team to develop methods for efficient mapping of tree cover as well as for identifying the ecosystem functions of trees in the Great Plains’ agricultural landscapes.

The TOFii team is expanding the Forest Service’s service to stakeholders by including trees outside of forests, and delivering key information to local land managers on the extent of tree resources and how they are changing over time.

Learn more at: Trees Outside Forests Image-based Inventory (TOFii)

Selected Research Stories

Selected Publications

The publications listed below do not represent every study related to spring; for a more complete list of NRS publications, please visit our Publications page at:

Russo, Nicholas J.; Elphick, Chris S.; Havill, Nathan P.; Tingley, Morgan W. 2019. Spring bird migration as a dispersal mechanism for the hemlock woolly adelgid. Biological Invasions. 48(6): 1-.

Asah, Stanley T.; Bengston, David N.; Westphal, Lynne M.; Gowan, Catherine H. 2018. Mechanisms of children's exposure to nature: Predicting adulthood environmental citizenship and commitment to nature-based activities. Environment and Behavior. 2018. 50(7): 807-836.

Duan, Jian J.; Schmude, Jonathan M.; Wang, Xiao-Yi; Watt, Timothy J.; Bauer, Leah S. 2018. Host utilization, reproductive biology, and development of the larval parasitoid Tetrastichus planipennisi as influenced by temperature: Implications for biological control of the emerald ash borer in North America. Biological Control. 125: 50-56.

Janowiak, Maria K.; D'Amato, Anthony W.; Swanston, Christopher W.; Iverson, Louis; Thompson, Frank R., III; Dijak, William D.; Matthews, Stephen; Peters, Matthew P.; Prasad, Anantha; Fraser, Jacob S.; Brandt, Leslie A.; Butler-Leopold, Patricia; Handler, Stephen D.; Shannon, P. Danielle; Burbank, Diane; Campbell, John; Cogbill, Charles; Duveneck, Matthew J.; Emery, Marla R.; Fisichelli, Nicholas; Foster, Jane; Hushaw, Jennifer; Kenefic, Laura; Mahaffey, Amanda; Morelli, Toni Lyn; Reo, Nicholas J.; Schaberg, Paul G.; Simmons, K. Rogers; Weiskittel, Aaron; Wilmot, Sandy; Hollinger, David; Lane, Erin; Rustad, Lindsey; Templer, Pamela H. 2018. New England and northern New York forest ecosystem vulnerability assessment and synthesis: a report from the New England Climate Change Response Framework project. Gen. Tech. Rep. NRS-173. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 234 p.

Ricciardi, Anthony; Blackburn, Tim M.; Carlton, James T.; Dick, Jaimie T.A.; Hulme, Philip E.; Iacarella, Josephine C.; Jeschke, Jonathan M.; Liebhold, Andrew M.; Lockwood, Julie L.; MacIsaac, Hugh J.; Pyšek, Petr; Richardson, David M.; Ruiz, Gregory M.; Simberloff, Daniel; Sutherland, William J.; Wardle, David A.; Aldridge, David C. 2017. Invasion Science: A Horizon Scan of Emerging Challenges and Opportunities. Trends in Ecology & Evolution. 32(6): 464-474.

Niemi, Gerald J.; Howe, Robert W.; Sturtevant, Brian R.; Parker, Linda R.; Grinde, Alexis R.; Danz, Nicholas P.; Nelson, Mark D.; Zlonis, Edmund J.; Walton, Nicholas G.; Gnass Giese, Erin E.; Lietz, Sue M. 2016. Analysis of long-term forest bird monitoring data from national forests of the western Great Lakes Region. Gen. Tech. Rep. NRS-159. Newtown Square, PA: U.S. Department of Agriculture, Forest Service, Northern Research Station. 322 p.


Stay Connected

Blog icon   Facebook icon  RSS icon  Twitter icon  YouTube icon

Environmental Education

Project Budburst logo
Discover your inner scientist with Project Budburst

Featured Podcast

Hot-Dry-Windy Fire Weather Index

Jon Yales talks with Jay Charney about a new fire weather index

The “Hot-Dry-Windy (HDW) Index,” uses three key factors affecting fire—temperature, moisture and wind--to predict days when weather conditions have the greatest chance of making wildfires erratic and especially dangerous.

Right click to download MP3 file (9 mb)

Download transcript


View our podcast archive

Last Modified: March 20, 2019