Sap flow velocities of Acer saccharum and Quercus velutina during drought: Insights and implications from a throughfall exclusion experiment in West Virginia, USA.

Forest species composition mediates evapotranspiration and the amount of water available to human-use downstream. In the last century, the heavily forested Appalachian region has been undergoing forest mesophication which is the progressive replacement of xeric species (e.g.

Isotopic evidence for oligotrophication of terrestrial ecosystems.

Human societies depend on an Earth system that operates within a constrained range of nutrient availability, yet the recent trajectory of terrestrial nitrogen (N) availability is uncertain. Examining patterns of foliar N concentrations and isotope ratios (δN) from more than 43,000 samples acquired over 37 years, here we show that foliar N concentration declined by 9% and foliar δN declined by 0.6-1.

Imaging spectroscopy algorithms for mapping canopy foliar chemical and morphological traits and their uncertainties.

A major goal of remote sensing is the development of generalizable algorithms to repeatedly and accurately map ecosystem properties across space and time. Imaging spectroscopy has great potential to map vegetation traits that cannot be retrieved from broadband spectral data, but rarely have such methods been tested across broad regions. Here we illustrate a general approach for estimating key foliar chemical and morphological traits through space and time using NASA's Airborne Visible/Infrared Imaging Spectrometer (AVIRIS-Classic).

Spectroscopic determination of leaf morphological and biochemical traits for northern temperate and boreal tree species.

The morphological and biochemical properties of plant canopies are strong predictors of photosynthetic capacity and nutrient cycling. Remote sensing research at the leaf and canopy scales has demonstrated the ability to characterize the biochemical status of vegetation canopies using reflectance spectroscopy, including at the leaf level and canopy level from air- and spaceborne imaging spectrometers. We developed a set of accurate and precise spectroscopic calibrations for the determination of leaf chemistry (contents of nitrogen, carbon, and fiber constituents), morphology (leaf mass per area, Marea), and isotopic composition (δ15N) of temperate and boreal tree species using spectra of dried and ground leaf material.

Is the growth of temperate forest trees enhanced along an ambient nitrogen deposition gradient?

The extent to which atmospheric N deposition is enhancing primary production and CO2 sequestration along the ambient N deposition gradients found within many regional temperate forest ecosystems remains unknown. We used tree diameter measurements from 1984 and 2004, allometric equations, and estimates of wet N deposition from 32 permanent plots located along an ambient N deposition gradient in the Adirondack Park, New York, U.S.

The spatial pattern of nitrogen cycling in the Adirondack Park, New York.

Maps of canopy nitrogen obtained through analysis of high-resolution, hyperspectral, remotely sensed images now offer a powerful means to make landscape-scale to regional-scale estimates of forest N cycling and net primary production (NPP). Moreover, recent research has suggested that the spatial variability within maps of canopy N may be driven by environmental gradients in such features as historic forest disturbance, temperature, species composition, moisture, geology, and atmospheric N deposition. Using the wide variation in these six features found within the diverse forest ecosystems of the 2.

Foliar nitrogen responses to elevated atmospheric nitrogen deposition in nine temperate forest canopy species.

Despite its ecological importance, broad-scale use of foliar nitrogen as an indicator of ecosystem response to atmospheric N deposition has heretofore been obscured by its poorly understood intrinsic variability through time, space, and across species. We used a regional survey of foliar N conducted within a single growing season to observe that eight of nine major canopy tree species had increased foliar N in response to a gradient of N deposition in the Adirondack Park, New York. These results (1) add important foliar N evidence to support N saturation theory, (2) strongly reinforce the conclusion that N deposition is affecting the N status of forest ecosystems in the northeastern U.