Nitrogen-fixing trees inhibit growth of regenerating Costa Rican rainforests

BACKGROUND

Nitrogen fixing plants are the primary source of nitrogen in forests, and it is expected that more nitrogen fixers will bring in faster growth. Hence this study conducted, in a humid tropical rainforest North- East Costa Rica, challenged this notion. The area of study had similar dominant species, with P. macroloba being the most dominant Nitrogen fixer.

RESEARCH GOALS AND METHODS

17 consecutive years of data was used from eight, 1ha plots and 10m x10m sub plots that were set up to determine if Nitrogen fixers affect forest growth. 6 plots were in the regenerating forests ranging in stand age from 10 to 42 years old and two in the old- growth forests.  The effect of Nitrogen fixers on their neighbors at individual scale was also analyzed using Bayesian models. Trees were separated into fixers and non- fixers. All adult trees with a dbh of 5cm or more were tagged. 

CONCLUSIONS AND TAKEAWAYS

From the authors, although Nitrogen fixers are widely known to bring in Nitrogen into ecosystems, they may have strong negative interactions with other trees in a forest leading to their slow growth. This influences how tropical forests capture and store carbon to be able to predict future climate scenarios.