Fighting over science

Most academic publications go ignored and poorly cited; fewer make an impact or controversy. I recently had the dubious honor of two papers being ‘debunked’ in the scientific literature.

My papers were focused on explaining the leaf economics spectrum – a global pattern that describes leaves use resources like carbon and nitrogen (Wright et al., Nature 2004).

My central hypothesis was that the leaf’s venation network is important in determining multiple aspects of the leaf’s functioning. One paper was published in Ecology Letters in 2011, and the other in Journal of Ecology in 2013

Screen Shot 2014-04-24 at 5.31.37 PM

Screen Shot 2014-04-24 at 9.58.51 PM.

A few months ago, Lawren Sack and colleagues published a paper in the Journal of Experimental Botany, in which they argued based on both empirical and theoretical grounds that venation networks were not a useful explanation for the leaf economics spectrum.

Screen Shot 2014-04-24 at 10.04.21 PM

They state in their abstract:

Leaf vein traits are implicated in the determination of gas exchange rates and plant performance. These traits are increasingly considered as causal factors affecting the ‘leaf economic spectrum’ (LES), which includes the light- saturated rate of photosynthesis, dark respiration, foliar nitrogen concentration, leaf dry mass per area (LMA) and leaf longevity. This article reviews the support for two contrasting hypotheses regarding a key vein trait, vein length per unit leaf area (VLA). Recently, Blonder et al. (2011, 2013) proposed that vein traits, including VLA, can be described as the ‘origin’ of the LES by structurally determining LMA and leaf thickness, and thereby vein traits would predict LES traits according to specific equations. Careful re-examination of leaf anatomy, published datasets, and a newly compiled global database for diverse species did not support the ‘vein origin’ hypothesis, and moreover showed that the apparent power of those equations to predict LES traits arose from circularity.

I’m not much for controversy, and this paper caught me by surprise – our research groups hadn’t had any behind-the-scenes discussions beforehand. But scientific criticism is healthy – it helps a field determine which ideas are worthwhile and supported by evidence. We read the criticism carefully, worried that it raised some points that would undermine our work. Our worry was not about our egos – more concern that we had done something unhelpful for the field of ecology.

Screen Shot 2014-04-24 at 5.12.20 PM

After a lot of thinking and re-analysis, we decided that Sack et al. raised some important points, but that their major criticisms were unfounded. We disagree about how to interpret empirical data, and also how to build a useful model – and we disagree about how to carry out certain calculations.

We just published a response in the same journal, saying:

Our model for the worldwide leaf economics spectrum (LES) based on venation networks (Blonder et al., 2011, 2013) was strongly criticized by Sack et al. (2013) in this journal. Here, we show that the majority of criticisms by Sack et al. are based on mathematical and conceptual misunderstandings. Using empirical data from both our original study as well as others in the literature, we show support for our original hypothesis, that venation networks provide predictive power and conceptual unification for the LES. In an effort to reconcile differing viewpoints related to the role of leaf venation traits for the LES, we highlight several lines of further investigation.

Screen Shot 2014-04-24 at 10.12.35 PM

Check out our response in the Journal of Experimental Botany and decide for yourself. We’re glad to share the debate with the whole field.

Leave a Reply