Aboveground plant biomass for east of T-van, 1998 - 2004.

These data were used in the following related publication: Bowman, William D., Gartner, Julia R., Holland, Keri, and Wiedermann,
Magdalena. 2006. Nitrogen critical loads for alpine vegetation and terrestrial
ecosystem response - Are we there yet? Ecological Applications 16:1183-1193.
doi: 10.1890/1051-0761(2006)016[1183:NCLFAV]2.0.CO;2 Increases in the deposition of anthropogenic nitrogen (N) have been
linked to several terrestrial ecological changes, including soil biogeochemistry,
plant stress susceptibility, and community diversity. Recognizing the need to
identify sensitive indicators of biotic response to N deposition, we empirically
estimated the N critical load for changes in alpine plant community composition and
compared this with the estimated critical load for soil indicators of ecological
change. We also measured the degree to which alpine vegetation may serve as a sink
for anthropogenic N and how much plant sequestration is related to changes in
species composition. We addressed these research goals by adding 20, 40, or 60 kg
N.ha-1yr-1, along with an ambient control (6 kg N ha-1 yr-1 total deposition), to a
species rich alpine dry meadow for an eight-year period. Change in plant species
composition associated with the treatments occurred within three years of the
initiation of the experiment and were significant at all levels of N addition.
Using individual species abundance changes and ordination scores, we estimated the
N critical loads (total deposition) for (1) change in individual species to be 4 kg
N ha-1 yr-1 and (2) for overall community change to be 10 kg N ha-1 yr-1. In
contrast, increases in NO3 leaching, soil solution inorganic NO3, and net N
nitrification occurred at levels above 20 kg N ha-1 yr-1. Increases in total
aboveground biomass were modest and transient, occurring in only one of the three
years measured. Vegetative uptake of N increased significantly, primarily as a
result of increasing tissue N concentrations and biomass increases in subdominant
species. Aboveground vegetative uptake of N accounted for LT 40% of the N added. The
results of this experiment indicate that changes in vegetation composition will
precede detectable changes in more traditionally used soil indicators of ecosystem
responses to N deposition and that changes in species composition are probably
ongoing in alpine dry meadows of the Front Range of the Colorado Rocky Mountains.
Feedbacks to soil N cycling associated with changes in litter quality and species
composition may result in only short-term increases in vegetation N pools. NOTE: The LTER data portal display does not display important maintenance/log information or other EML metadata features. Please be sure to view the EML file (a text file that contains XML tags) which is included in the zip archive (click on "Download zip archive") pertaining to each dataset. The EML file name will have the following format: knb-lter-nwt.[3 digit dataset number].[version number].xml. Most web browsers can parse the EML so it's easier to read.