Understanding causes of tree growth response to gap formation: ∆13C-values in tree rings reveal a predominant effect of light
- 406 Downloads
Carbon isotope ratios in growth rings of a tropical tree species show that treefall gaps stimulate diameter growth mainly through changes in the availability of light and not water.
The formation of treefall gaps in closed canopy forests usually entails considerable increases in light and nutrient availability for remaining trees, as well as altered plant water availability, and is considered to play a key role in tree demography. The effects of gaps on tree growth are highly variable and while usually stimulatory they may also include growth reductions. In most studies, the causes of changes in tree growth rates after gap formation remain unknown. We used changes in carbon isotope 13C discrimination (Δ13C) in annual growth rings to understand growth responses after gap formation of Peltogyne cf. heterophylla, in a moist forest of Northern Bolivia. We compared growth and Δ13C of the 7 years before and after gap formation. Forty-two trees of different sizes were studied, half of which grew close (<10 m) to single treefall gaps (gap trees), the other half more than 40 m away from gaps (controls). We found variable responses among gap trees in growth and Δ13C. Increased growth was mainly associated with decreased Δ13C, suggesting that the growth response was driven by increased light availability, possibly in combination with improved nutrient availability. Most trees showing zero or negative growth change after gap formation had increased Δ13C, suggesting that increased water stress did not play a role, but rather that light conditions had not changed much or nutrient availability was insufficient to support increased growth. Combining growth rates with Δ13C proved to be a valuable tool to identify the causes of temporal variation in tree growth.
KeywordsCarbon stable isotopes Gap formation Tree growth Light availability Water availability Peltogyne
We thank Carmen Bürger of GeoForschungsZentrum in Potsdam, Germany, for her help with the analysis of the wood samples, Mart Vlam for his assistance during the sampling of wood in growth rings and two anonymous reviewers for their constructive and helpful comments. Peter van der Sleen and Pieter Zuidema were supported by the European Research Council (ERC grant #242955).
Conflict of interest
Authors declare that they have no conflict of interest.
- Baker TR, Phillips OL, Malhi Y, Almeida S, Arroyo L, Di Fiore A, Erwin T, Higuchi N, Killeen TJ, Laurance SG, Laurance WF, Lewis SL, Monteagudo A, Neill DA, Núñez Vargas P, Pitman NCA, Silva JNM, Vásquez Martínez R (2004) Increasing biomass in Amazonian forest plots. Philos Trans R Soc Lond B Biol Sci 359(1443):353–365PubMedCentralPubMedCrossRefGoogle Scholar
- Brienen RJW, Wanek W, Hietz P (2011) Stable carbon isotopes in tree rings indicate improved water use efficiency and drought responses of a tropical dry forest tree species. Trees Structure Function 25(1):103–113Google Scholar
- Hartshorn GS (1978) Tree falls and tropical forest dynamics. In: Tomlinson PB, Zimmermann MH (eds) Tropical trees as living systems. Cambridge University Press, New York, pp 617–638Google Scholar
- McCarroll D, Gagen MH, Loader NJ, Robertson I, Anchukaitis KJ, Los S, Young GHF, Jalkanen R, Kirchhefer A, Waterhouse JS (2009) Correction of tree ring stable carbon isotope chronologies for changes in the carbon dioxide content of the atmosphere. Geochim Cosmochim Acta 73(6):1539–1547CrossRefGoogle Scholar
- Toledo M, Poorter L, Peña-Claros M, Leano C, Bongers F (2008) Diferencias, en las características edáficas y la estructura del bosque, de cuatro ecoregiones forestales de Bolivia. Revista Boliviana de Ecología y Conservacíon Ambiental 24:11–26Google Scholar