DOI: 10.5061/dryad.zcrjdfn9f
title: Data from: Divergent pathways of nitrogen-fixing trees through succession depend on starting nitrogen supply and priority effects

description: Nitrogen-fixing trees are a major potential source of nitrogen into
 terrestrial ecosystems. The degree to which they persist into older
 forests has considerable implications for forest nitrogen budgets. We
 characterized nitrogen-fixing tree abundance across stand age in the
 contiguous United States and analyzed a theoretical model to help
 understand competitive outcomes and successional trajectories of
 nitrogen-fixing and nonfixing trees. Nitrogen-fixing tree abundance is
 bimodal in all regions except the northeastern United States, even in
 older forests, suggesting that competitive exclusion (including priority
 effects) is more common than coexistence at the spatial scale of our
 analysis. Our model analysis suggests conditions under which alternative
 competitive outcomes are possible and when they are transient (lasting
 decades-centuries) vs. persistent (millennia). Critically, the timescale
 of the feedbacks between nitrogen-fixation and soil nitrogen supply, which
 is thought to drive the exclusion of nitrogen-fixing trees through
 succession, can be long. Therefore, the long-transient outcomes of
 competition are more relevant for real forests than the long-term
 equilibrium. Within these long-term transients, the background soil
 nitrogen supply is a major determinant of competitive outcomes. Consistent
 with the expectations of resource ratio theory, competitive exclusion is
 more likely at high and low nitrogen supply while intermediate nitrogen
 supply makes coexistence or priority effects possible. However, these
 outcomes are modified by the nitrogen-fixation strategy: Obligate
 nitrogen-fixation makes coexistence more likely than priority effects,
 compared to perfectly facultative fixation. These results advance our
 understanding of the successional trajectories of nitrogen-fixing trees
 and their effects on ecosystem development in secondary succession.
description: Data are from the Forest Inventory Analysis (version 5.1) and are
 publicly available in their raw form
 at https://www.fia.fs.fed.us/ In processing the data,
 we calculated the percent basal area of nitrogen (N)-fixing trees for each
 plot. These data (plot number and percent basal area of N-fixing trees)
 are displayed in our dataset together with the plot stand age, the
 absolute basal area of all trees in a plot, the absolute basal area of all
 N-fixing trees in a plot, the latitude and longitude of the plot, and the
 50 year age bin for the plot. Plantations and plots with harvest
 activities were excluded. N-fixing taxa were identified following Menge et
 al. (2017), which used actinorhizal and rhizobial N-fixing classifications
 from Huss-Danell (1997) and Sprent (2009), respectively. We used data for
 the contiguous United States. Literature
 cited: Huss-Danell, K. 1997. Actinorhizal symbioses and their N<sub>2</sub> fixation. New Phytologist 136:375–405. Menge, D. N. L., S. A. Batterman, W. Liao, B. N. Taylor, J. W. Lichstein, and G. Ángeles-Pérez. 2017. Nitrogen-fixing tree abundance in higher-latitude North America is not constrained by diversity. Ecology Letters 20:842–851. Sprent, J. I. 2009. Global Distribution of Legumes. Legume Nodulation: A global perspective.
description: Columns in the dataset are: pcn: Forest
 Inventory Analysis plot number stdage: Stand age of the
 plot pcn_sum_fix: Absolute basal area of N-fixing trees
 within each plot pcn_sum_all: Absolute basal area of
 all trees within each plot perc_fix: Percent basal area
 of N-fixing trees within each plot lat: Latitude of
 each plot lon: Longitude of each plot
 y50_bin: 50 year stand age bin of each plot