Spring may come earlier to North American forests

Published: Tuesday, January 29, 2013 - 18:33 in Earth & Climate

Trees in the con­ti­nen­tal U.S. could send out new spring leaves up to 17 days ear­lier in the com­ing cen­tury than they did before global tem­per­a­tures started to rise, accord­ing to a new study by Prince­ton Uni­ver­sity researchers. These climate-driven changes could lead to changes in the com­po­si­tion of north­east­ern forests and give a boost to their abil­ity to take up car­bon dioxide. Trees play an impor­tant role in tak­ing up car­bon diox­ide from the atmos­phere, so researchers led by David Med­vigy, assis­tant pro­fes­sor in Princeton's depart­ment of geo­sciences, wanted to eval­u­ate pre­dic­tions of spring bud­burst -- when decid­u­ous trees push out new growth after months of win­ter dor­mancy -- from mod­els that pre­dict how car­bon emis­sions will impact global temperatures.

The date of bud­burst affects how much car­bon diox­ide is taken up each year, yet most cli­mate mod­els have used overly sim­plis­tic schemes for rep­re­sent­ing spring bud­burst, mod­el­ing for exam­ple a sin­gle species of tree to rep­re­sent all the trees in a geo­graphic region.

In 2012, the Prince­ton team pub­lished a new model that relied on warm­ing tem­per­a­tures and the wan­ing num­ber of cold days to pre­dict spring bud­burst. The model, which was pub­lished in the Jour­nal of Geo­phys­i­cal Research, proved accu­rate when com­pared to data on actual bud­burst in the north­east­ern United States.

In the cur­rent paper pub­lished online in Geo­phys­i­cal Research Let­ters, Med­vigy and his col­leagues tested the model against a broader set of obser­va­tions col­lected by the USA National Phe­nol­ogy Net­work, a nation-wide tree ecol­ogy mon­i­tor­ing net­work con­sist­ing of fed­eral agen­cies, edu­ca­tional insti­tu­tions and cit­i­zen sci­en­tists. The team incor­po­rated the 2012 model into pre­dic­tions of future bud­burst based on four pos­si­ble cli­mate sce­nar­ios used in plan­ning exer­cises by the Inter­gov­ern­men­tal Panel on Cli­mate Change.

The researchers included Su-Jong Jeong, a post­doc­toral research asso­ciate in Geo­sciences, along with Elena Shevli­akova, a senior cli­mate mod­eler, and Sergey Maly­shev, a pro­fes­sional spe­cial­ist, both in the Depart­ment of Ecol­ogy and Evo­lu­tion­ary Biol­ogy and asso­ci­ated with the U.S. National Oceanic and Atmos­pheric Administration's Geo­phys­i­cal Fluid Dynam­ics Laboratory.

The team esti­mated that, com­pared to the late 20th cen­tury, red maple bud­burst will occur 8 to 40 days ear­lier, depend­ing on the part of the coun­try, by the year 2100. They found that the north­ern parts of the United States will have more pro­nounced changes than the south­ern parts, with the largest changes occur­ring in Maine, New York, Michi­gan, and Wisconsin.

The researchers also eval­u­ated how warm­ing tem­per­a­tures could affect the bud­burst date of dif­fer­ent species of tree. They found that bud­burst shifted to ear­lier in the year in both early-budding trees such as com­mon aspen (Pop­u­lus tremu­loides) and late-budding trees such as red maple (Acer rubrum), but that the effect was greater in the late-budding trees and that over time the dif­fer­ences in bud­ding dates narrowed.

The researchers noted that early bud­burst may give decid­u­ous trees, such as oaks and maples, a com­pet­i­tive advan­tage over ever­green trees such as pines and hem­locks. With decid­u­ous trees grow­ing for longer peri­ods of the year, they may begin to out­strip growth of ever­greens, lead­ing to last­ing changes in for­est make-up.

The researchers fur­ther pre­dicted that warm­ing will trig­ger a speed-up of the spring "green­wave," or bud­burst that moves from south to north across the con­ti­nent dur­ing the spring.

The find­ing is also inter­est­ing from the stand­point of future changes in spring­time weather, said Med­vigy, because bud­burst causes an abrupt change in how quickly energy, water and pol­lu­tants are exchanged between the land and the atmos­phere. Once the leaves come out, energy from the sun is increas­ingly used to evap­o­rate water from the leaves rather than to heat up the sur­face. This can lead to changes in daily tem­per­a­ture ranges, sur­face humid­ity, stream­flow, and even nutri­ent loss from ecosys­tems, accord­ing to Medvigy.

Source: Princeton University


Latest Science Newsletter

Get the latest and most popular science news articles of the week in your Inbox! It's free!

Learn more about

Check out our next project, Biology.Net