Ecological Archives E095-198-A1

Duncan N. L. Menge, Jeremy W. Lichstein, Gregorio Ángeles-Pérez. 2014. Nitrogen fixation strategies can explain the latitudinal shift in nitrogen-fixing tree abundance. Ecology 95:2236–2245. http://dx.doi.org/10.1890/13-2124.1

Appendix A. Theory-predicted N-fixing tree abundance in different habitats.

Table A1. Succession-weighted N-fixing tree abundances in N-limited habitats. Theory-predicted successional trajectories give N-fixing tree abundance at each stand age. To predict landscape-scale N-fixing tree abundance, we weighted these trajectories by distributions of stand age. The primary distribution, used in Fig. 4, is the stand age distribution of USA forests estimated from FIA inventory plots (Appendix B, Fig. B2). To evaluate the robustness of our results, we also examined cases where forests equatorward of 35° latitude had younger or older age distributions. These alternate stand age distributions rescaled the USA distribution by halving or doubling the reported stand age of each FIA inventory plot. Strategy: Symbiotic N fixation strategy.

Stand age distribution

Habitat type

Strategy

N-fixing tree abundance

USA forests

Severely N limited

Obligate

2.2%

USA forests

Moderately N limited

Obligate

1.5%

USA forests

Severely N limited

Facultative

92%

USA forests

Moderately N limited

Facultative

61%

USA forests, ages halved

Severely N limited

Obligate

5.4%

USA forests, ages halved

Moderately N limited

Obligate

2.8%

USA forests, ages halved

Severely N limited

Facultative

98%

USA forests, ages halved

Moderately N limited

Facultative

74%

USA forests, ages doubled

Severely N limited

Obligate

1.1%

USA forests, ages doubled

Moderately N limited

Obligate

0.9%

USA forests, ages doubled

Severely N limited

Facultative

77%

USA forests, ages doubled

Moderately N limited

Facultative

41%


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