Date of Award

5-2018

Document Type

Thesis

Department

Environmental and Forest Biology

Thesis Advisor

Ruth D. Yanai

Thesis Advisor

Colin M. Beier

Abstract

Excess nutrients in ecosystems may be altering deciduous tree phenological events. By having delayed autumn leaf abscission, the length of the growing season may be extended, which could increase forest productivity. Nitrogen (N) availability due to nitrogen deposition from anthropogenic pollution, in turn making phosphorus (P) limitation more likely. This study examines the effect of nitrogen and phosphorus additions on leaf retention at a community-level in hardwood forests and a species-level (American beech, sugar maple, red maple, paper birch, yellow birch, and pin cherry) located in 12 stands of different ages located in New Hampshire, USA. These stands were part of Multiple Element Limitation in Northern Hardwood Ecosystems (MELNHE), which contains plots that are either unfertilized or treated with N, P, or both N + P. Multiple leaf litter collections occurred four times in the fall of 2016 and once more in June of 2017. At a community-level, P-fertilized trees increased leaf retention by 16% (p = 0.01). Some species also experienced increased leaf retention due to P-additions: yellow birch trees increased leaf retention by 58% (p = 0.05) and pin cherry trees retained 24% more leaves (p = 0.05). N fertilization also increased leaf retention by 7% at community-level (p = 0.04), but promoted early leaf drop in American beech trees by 3% (p = 0.04). Both N and P fertilization caused sugar maple to retain less leaves than when fertilized by a single nutrient. Conversely, red maple trees fertilized with both N and P retained more leaves than a single nutrient addition. Increased nutrient availability from fertilization reduces the need for the trees to resorbed the foliar nutrients, as well as availability leads to longer leaf retention which may increase the length of the growing season and the total gain of carbon. This will have an impact on any forests experiencing nutrient influxes, which could alter their productivity.

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