Research published at the Public Library of Science on January 18, 2010, challenges the present models and concepts relating the loss of forest populations to nitrogen availability. The research indicates present models are over estimated and are proven to present a bias in predictions of future forest dynamics under climate warming.
A rigorous examination of the fossil evidence from the Holocene period indicates that change in forest species during a period of global warming far more extreme than the present is not nitrogen availability dependent.
The present theories are based on short term studies but this new research takes a long term view of over eight thousand years.
Forest ecosystems are not limited by the availability of nitrogen over long time frames.
“Contrary to current thinking, results from our study suggest that the nitrogen cycle was not a driver of secondary succession in this ecosystem during the period of rapid and significant climatic warming at the late-glacial/early postglacial transition “
“Our results demonstrated stability in ecosystem functioning across the interval of rapid climatic change and despite a change in the dominant tree species. Climate change was found to affect the rates of nitrogen cycling: following the threshold change in climate, our model indicated that there were higher rates of conversion of decaying biomass into available and total nitrogen.”
“It is important for future work to test the context-dependence of our findings by validation with other appropriate palaeoecological datasets of coniferous to deciduous forest transitions and changes in nitrogen cycling during the late-glacial warming period. Furthermore, in order for model-fitting and model-selection analysis of palaeoecological data to yield sufficient information to be useful for predictive modelling, this approach needs to be used to analyze a greater variety of transitions in dominant plant functional types. These caveats notwithstanding, results from this study demonstrate how the dynamics associated with ecosystem functioning can remain relatively stable following a major environmental perturbation.”
Classical ecological theory predicts that changes in the availability of essential resources such as nitrogen should lead to changes in plant community composition due to differences in species-specific nutrient requirements. What remains unknown, however, is the extent to which climate change will alter the relationship between plant communities and the nitrogen cycle. During intervals of climate change, do changes in nitrogen cycling lead to vegetation change or do changes in community composition alter the nitrogen dynamics? We used long-term ecological data to determine the role of nitrogen availability in changes of forest species composition under a rapidly changing climate during the early Holocene (16k to 8k cal. yrs. BP). A statistical computational analysis of ecological data spanning 8,000 years showed that secondary succession from a coniferous to deciduous forest occurred independently of changes in the nitrogen cycle. As oak replaced pine under a warming climate, nitrogen cycling rates increased. Interestingly, the mechanism by which the species interacted with nitrogen remained stable across this threshold change in climate and in the dominant tree species. This suggests that changes in tree population density over successional time scales are not driven by nitrogen availability. Thus, current models of forest succession that incorporate the effects of available nitrogen may be over-estimating tree population responses to changes in this resource, which may result in biased predictions of future forest dynamics under climate warming.
Stability in Ecosystem Functioning across a Climatic Threshold and Contrasting Forest Regimes
Elizabeth S. Jeffers 1*, Michael B. Bonsall 2*, Kathy J. Willis 3
1 School of Geography, University of Oxford, Oxford, United Kingdom
2 Department of Zoology, University of Oxford, Oxford, United Kingdom
3 Department of Biology, University of Bergen, Bergen, Norway
Citation: Jeffers ES, Bonsall MB, Willis KJ (2011) Stability in Ecosystem Functioning across a Climatic Threshold and Contrasting Forest Regimes. PLoS ONE 6(1): e16134. doi:10.1371/journal.pone.0016134
Funding: The work was supported by the Royal Society and the Natural Environment Research Council. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
Competing interests: The authors have declared that no competing interests exist.
Figure 1. Ecosystem dynamics
Tree population dynamics are represented by pollen accumulation rates (PAR) of pine (A) and oak (B). Nitrogen dynamics reflect changes in nitrogen availability inferred from stable nitrogen isotope analysis (C) and changes in total nitrogen (D) inferred from elemental analysis of bulk organic matter. Abrupt warming occurred at 11.7k cal. yrs. BP (dotted line).