Wolf, A., W.R.L. Anderegg, and S.W. Pacala. “Optimal stomatal behavior with competition for water and risk of hydraulic impairment”. PNAS (2016). Print.Abstract

For over 40 y the dominant theory of stomatal behavior has been that plants should open stomates until the carbon gained by an infinitesimal additional opening balances the additional water lost times a water price that is constant at least over short periods. This theory has persisted because of its remarkable success in explaining strongly supported simple empirical models of stomatal conductance, even though we have also known for over 40 y that the theory is not consistent with competition among plants for water. We develop an alternative theory in which plants maximize carbon gain without pricing water loss and also add two features to both this and the classical theory, which are strongly supported by empirical evidence: (i) water flow through xylem that is progressively impaired as xylem water potential drops and (ii) fitness or carbon costs associated with low water potentials caused by a variety of mechanisms, including xylem damage repair. We show that our alternative carbon-maximization optimization is consistent with plant competition because it yields an evolutionary stable strategy (ESS)—species with the ESS stomatal behavior that will outcompete all others. We further show that, like the classical theory, the alternative theory also explains the functional forms of empirical stomatal models. We derive ways to test between the alternative optimization criteria by introducing a metric—the marginal xylem tension efficiency, which quantifies the amount of photosynthesis a plant will forego from opening stomatal an infinitesimal amount more to avoid a drop in water potential.

Weng, E.S., et al.Predicting vegetation type through physiological and environmental interactions with leaf traits: evergreen and deciduous forests in an earth system modeling framework. ”. Global Change Biology (2016). Print.Abstract

Earth system models are incorporating plant trait diversity into their land components to better predict vegetation dynamics in a changing climate. However, extant plant trait distributions will not allow extrapolations to novel community assemblages in future climates; that will require a mechanistic understanding of the trade-offs that determine trait diversity. In this study, we show how physiological trade-offs involving leaf mass per unit area (LMA), leaf lifespan, leaf nitrogen, and leaf respiration may explain the distribution patterns of evergreen and deciduous trees in the temperate and boreal zones based on (1) an evolutionary analysis of a simple mathematical model and (2) simulation experiments of an individual-based dynamic vegetation model (i.e. LM3-PPA). The evolutionary analysis shows that these leaf traits set up a trade-off between carbon and nitrogen use efficiency at the scale of individual trees and therefore determine competitively dominant leaf strategies. As soil nitrogen availability increases, the dominant leaf strategy switches from one that is high in nitrogen use efficiency to one that is high in carbon use efficiency or, equivalently, from high LMA/long-lived leaves (i.e. evergreen) to low LMA/ short-lived leaves (i.e. deciduous). In a region of intermediate soil nitrogen availability, the dominant leaf strategy may be either deciduous or evergreen depending on the initial conditions of plant trait abundance (i.e. founder controlled) due to feedbacks of leaf traits on soil nitrogen mineralization through litter quality. Simulated successional patterns predicted by LM3-PPA from the leaf physiological trade-offs are consistent with observed successional dynamics of evergreen and deciduous forests at three sites spanning the temperate to boreal zones.

Farrior, C.E., et al.Dominance of the suppressed: Power-law size structure in tropical forests”. Science 351.6269 (2016): , 351, 6269, 155-157. Print.Abstract

Tropical tree size distributions are remarkably consistent despite differences in the environments that support them. With data analysis and theory, we found a simple and biologically intuitive hypothesis to explain this property, which is the foundation of forest dynamics modeling and carbon storage estimates. After a disturbance, new individuals in the forest gap grow quickly in full sun until they begin to overtop one another. The two-dimensional space-filling of the growing crowns of the tallest individuals relegates a group of losing, slow-growing individuals to the understory. Those left in the understory follow a power-law size distribution, the scaling of which depends on only the crown area–to–diameter allometry exponent: a well-conserved value across tropical forests.

Pellegrini, A.F.A., et al.Convergence of bark investment according to fire and climate structures ecosystem vulnerability to future change.”. Ecology Letters 20 (2016): , 20, 307-316. Web. Publisher's VersionAbstract
Fire regimes in savannas and forests are changing over much of the world. Anticipating the impact of these changes requires understanding how plants are adapted to fire. In this study, we test whether fire imposes a broad selective force on a key fire-tolerance trait, bark thickness, across 572 tree species distributed worldwide. We show that investment in thick bark is a pervasive adaptation in frequently burned areas across savannas and forests in both temperate and
tropical regions where surface fires occur. Geographic variability in bark thickness is largely explained by annual burned area and precipitation seasonality. Combining environmental and species distribution data allowed us to assess vulnerability to future climate and fire conditions: tropical rainforests are especially vulnerable, whereas seasonal forests and savannas are more robust. The strong link between fire and bark thickness provides an avenue for assessing the vulnerability of tree communities to fire and demands inclusion in global models.
Farrior, Caroline E, et al.Decreased water limitation under elevated CO2 amplifies potential for forest carbon sinks”. Proceedings of the National Academy of Sciences (2015): , 201506262. Web. Publisher's Version
Dybzinski, Ray, Caroline E Farrior, and Stephen W Pacala. “Increased forest carbon storage with increased atmospheric CO2 despite nitrogen limitation: a game-theoretic allocation model for trees in competition for nitrogen and light”. Global change biology 21 (2015): , 21, 1182–1196. Web. Publisher's Version
Anderegg, WRL, et al.Pervasive drought legacies in forest ecosystems and their implications for carbon cycle models”. Science 349 (2015): , 349, 528–532. Web. Publisher's Version
Weng, ES, et al.Scaling from individual trees to forests in an Earth system modeling framework using a mathematically tractable model of height-structured competition”. Biogeosciences 12 (2015): , 12, 2655–2694. Web. Publisher's Version
Malyshev, Sergey, et al.Contrasting Local vs. Regional Effects of Land-Use-Change Induced Heterogeneity on Historical Climate: Analysis with the GFDL Earth System Model.”. Journal of Climate (2015): n. pag. Web. Publisher's Version
Wang, Shaopeng, et al.Density-dependent speciation alters the structure and dynamics of neutral communities”. Journal of theoretical biology 372 (2015): , 372, 128–134. Web. Publisher's Version
Rabin, SS, et al.Quantifying regional, time-varying effects of cropland and pasture on vegetation fire.”. Biogeosciences Discussions 12 (2015): n. pag. Web. Publisher's Version
Ogle, Kiona, et al.A model-based meta-analysis for estimating species-specific wood density and identifying potential sources of variation”. Journal of Ecology 102 (2014): , 102, 194–208. Web. Publisher's Version
Violle, Cyrille, et al.The emergence and promise of functional biogeography”. Proceedings of the National Academy of Sciences 111 (2014): , 111, 13690–13696. Web. Publisher's Version
Weng, ES, et al.Scaling from individuals to ecosystems in an Earth System Model using a mathematically tractable model of height-structured competition for light”. Biogeosciences Discussions 11 (2014): , 11, 17757–17860. Web. Publisher's Version
Chen, Anping, et al.Species-Independent Down-Regulation of Leaf Photosynthesis and Respiration in Response to Shading: Evidence from Six Temperate Tree Species”. PloS one 9 (2014): n. pag. Web. Publisher's Version
Sulman, Benjamin N, et al.Microbe-driven turnover offsets mineral-mediated storage of soil carbon under elevated CO2”. Nature Climate Change 4 (2014): , 4, 1099–1102. Web. Publisher's Version
Lichstein, Jeremy W, et al.Confronting terrestrial biosphere models with forest inventory data”. Ecological Applications 24 (2014): , 24, 699–715. Web. Publisher's Version
Wang, Shaopeng, et al.Why abundant tropical tree species are phylogenetically old”. Proceedings of the National Academy of Sciences 110 (2013): , 110, 16039–16043. Web. Publisher's Version
Shevliakova, Elena, et al.Historical warming reduced due to enhanced land carbon uptake”. Proceedings of the National Academy of Sciences 110 (2013): , 110, 16730–16735. Web. Publisher's Version
Farrior, Caroline E, et al.Competition for water and light in closed-canopy forests: a tractable model of carbon allocation with implications for carbon sinks”. The American Naturalist 181 (2013): , 181, 314–330. Web. Publisher's Version