By: Jennifer Hushaw
March 20th marked the official First Day of Spring and in the ensuing weeks we have seen more and more evidence that spring has sprung in most of the country. It’s a beautiful time of year—fresh buds, vibrant blooms, new leaves with that particularly bright shade of green that is unique to spring foliage. But this isn’t a typical year. In fact, spring is arriving significantly earlier than average in large portions of the South, Great Plains, Great Basin, mid-Atlantic, Midwest, and parts of the Northeast, according to the National Phenology Network.
Spring Leaf Index Anomaly, April 20, 2017.
This is notable, but not exactly surprising. As average temperatures increase, we expect the timing of many seasonal processes to change. Phenology is the study of these seasonal rhythms of plants and animals, especially the timing as related to weather and climate, and it is a sensitive indicator of climate change. Shifts in phenology have far reaching implications for ecosystem processes, productivity, and even the global carbon budget.
Of course, people have been recording the timing of the seasons through plant phenology for centuries. The longest known records date back to the 9th century and describe the flowering of Japanese cherry trees, which are now blooming earlier than at any point in the last 1200 years1, but nowadays phenology has also become a prominent part of efforts to track the impact of a warming climate.
Over the past several decades, scientists have indeed documented earlier springs, later falls, and longer growing seasons, particularly in the Northern Hemisphere. In fact, the year 2012, which was the hottest year on record for the U.S., stands out as the earliest spring start to date. Although, that record may soon be broken because “2017 is shaping up to be two to three weeks earlier than 2012 in many parts of the country”2 and up to three weeks earlier than normal (compared to 1981-2010) in some locations in the southeast. The length of the growing season has also increased by as much as ten days since the 1980’s, with some parts of the country experiencing increases of up to 50 days in the period since 18953.
What do these changes mean for the health of our forests? Well, climate change presents a mix of opportunities and challenges. Longer growing seasons and reduced chance of frost damage will give some forests the opportunity for increased growth and productivity. On the other hand, many invasive species will also benefit from these changes and not all tree species can take advantage of the longer frost-free season, particularly those that rely more heavily on day-length than temperature to signal their seasonal cycles. There is an abundance of interesting and on-going research in this area, which we are monitoring through Manomet’s Climate Smart Land Network, and the March CSLN Bulletin examines this topic in more detail. You can read a one-page synopsis here or check out the full bulletin online for more information.
1 Primack, R.B., Higuchi, H., Miller-Rushing, A.J. 2009. The impact of climate change on cherry trees and other species in Japan. Biological Conservation. 142(9): 1943-1949.
2 National Phenology Network. 2017. How does the spring of 2017 stack up to the recent past? Accessed online at: https://www.usanpn.org/data/spring/2017comparisons.
3 EPA. 2016. Climate Change Indicators: Length of Growing Season. Accessed online at: https://www.epa.gov/climate-indicators/climate-change-indicators-length-growing-season.