Forests of the northeastern U.S. help maintain water and air quality by reducing losses of nitrogen (N) into nearby waterways and removing carbon dioxide (CO2) from the atmosphere. However, carbon (C) and N retention in northeastern forests may decrease in response to projected changes in climate, including reductions in winter snowpack and increased soil freezing. Together, these climatic changes may damage tree roots and alter soil processes. Few studies have investigated the extent to which snowpack and soil frost drive C and N fluxes during spring snowmelt, a biogeochemically important period. Similarly, little is known about how changes in winter climate affect above- and belowground CO2 fluxes to the atmosphere. My dissertation combines laboratory and field experiments to quantify the effects of reduced snowpack and increased soil freezing on C and N cycling in northeastern forests. I conducted a laboratory experiment to study the effects of soil freezing on C and N losses during snowmelt. Organic horizon soils collected from mixed Acer saccharum-Fagus grandifolia and Picea rubens-Abies balsamea forests were incubated in severe, mild, and no soil frost conditions prior to snowmelt. Results show that losses of N in leachate, as well as total C and N fluxes (gases + leachate), were reduced following severe soil frost, indicating the response to winter climate depends on both the presence and severity of soil frost. I also implemented a snow removal experiment in a mixed Quercus rubra-Acer rubrum forest at Harvard Forest, MA to quantify the effects of depth and duration of snowpack and soil frost on CO2 losses from tree stems and soils. This study provides evidence that reduced snowpack and increased soil freezing may increase annual soil CO2 efflux, but have no significant effect on tree stem CO2 efflux. Taken together, results from my dissertation highlight the importance of winter climate as a driver of C and N fluxes in northeastern forests and suggest that while soil frost reduces C and N losses during snowmelt, annual losses of CO2 may increase Future studies investigating controls on C and N cycling in northeastern forests should account for changes in winter climate.

Tjällossning är ett stort problem för våra vägar idag och det är något som återkommer varje år. Tjällossning för med sig följder som i sin tur kräver mycket tid och resurser för att kunna återställa dessa vägar till att återigen kunna användas för trafik. Varje år förekommer stora skador på bl.a. vägar, gånggator, parkeringar samt övriga trafikytor, vilket kräver enorma summor av pengar för att åtgärda problemet. Byggnader får sättningsskador och VA-ledningar täpps till av stora isklumpar eller så fryser de sönder, och bara detta visar vad för stora problem tjällossning kan åstadkomma. Det innebär att vägarna måste vara underhållna och skötta ganska ofta av entreprenörföretag, vilket i sin tur leder till oönskade ekonomiska konsekvenser. I värsta fall stängs den tjäldrabbade vägen av under en viss tid, som är nödvändig för många att transportera sig genom till sina destinationer. I Sverige räknar man med att ca 15 - 20.000km väg berörs av just sådana tjälproblem varje år och dessa avstängningar på den skadade delen av vägnätet leder varje år till stora kostnader för samhället till följd av dålig framkomlighet. Idag används olika metoder för att lösa problemet med tjällossning på vägar och därmed måste olika ekonomiska summor betalas. Och frågan blir vilken/vilka metoder är mest effektivast och användbara i dagsläget, samt med bäst ekonomiskt vinst? / Soil frost thawing is a big problem for our roads today, and its something that comes over again every year on different type of roads.  Soil frost thawing brings consequences, which in turn requires much time and resources to restore these roads to once again be used for traffic.Every year, big damages on the roads, streets, parking area, and ''traffic area'' usually occur and a great deal of money is spent to remedy these problems. Buildings are given damage-recompense 'and water and sewage pipes are closed off by big lumps of ice or they freeze until they break; this alone shows the extent of the problem that soil frost thawing can cause. This means that the roads must be maintained and managed quite frequently by entrepreneurial companies which in turn leads to great economic consequences and in worst case maybe the road has to shut down, that is very necessary for many people to transport themselves to their destinations during a period of time. In Sweden it is estimated that approximately 15 - 20.000km route affected by precisely such soil frost thawing every year, and these shutdowns on the damaged part of the road network leads every year to considerable costs for society due to poor accessibility.Today, they use different methods to solve the problem with the soil frost thawing on roads and thus have different economic sums paid. The question then becomes, which method is most effective and useful today as well as yields most economic profit?

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