• Energy Research

As Earth’s climate has varied strongly through geological time, studying the impacts of past climate change on biodiversity helps to understand the risks from future climate change. However, it remains unclear how paleoclimate shapes spatial variation in biodiversity. Here, we assessed the influence of Quaternary climate change on spatial dissimilarity in taxonomic, phylogenetic, and functional composition among neighboring 200-kilometer cells (beta-diversity) for angiosperm trees worldwide. We found that larger glacial-interglacial temperature change was strongly associated with lower spatial turnover (species replacements) and higher nestedness (richness changes) components of beta-diversity across all three biodiversity facets. Moreover, phylogenetic and functional turnover was lower and nestedness higher than random expectations based on taxonomic beta-diversity in regions that experienced large temperature change, reflecting phylogenetically and functionally selective processes in species replacement, extinction, and colonization during glacial-interglacial oscillations. Our results suggest that future human-driven climate change could cause local homogenization and reduction in taxonomic, phylogenetic, and functional diversity of angiosperm trees worldwide.

In a meta-analysis, we use an unprecedented dataset, representing 556 unique locations worldwide, distributed across 44 countries and six continents to show for the first time that lianas (woody vines) thrive relatively better than trees when forests are disturbed, temperature increase, precipitation decrease, and particularly in tropical lowlands. We demonstrate that liana dominance can persist for decades post-disturbance and hinder the recovery of disturbed forests, especially when climate favours lianas. With implications for the global carbon sink, our findings suggest that degraded tropical forests with environmental conditions favouring lianas should be the highest priority to consider for restoration management.

AbstractField courses, while generally considered as beneficial for students, are challenging to implement and can lead to strained relationships between local residents and visiting scientists. Thus, it is critical to both maximize the educational value of field courses and help students develop contextualized science communication skills. We report on the development of a science communication module, integrated into an existing field‐based ecology course, which aims to add value to an international field course enrolling students from multiple countries. Specifically, students surveyed local residents about their knowledge and perceptions of climate change, and then discussed their findings.

Understanding the relative influence of abiotic and biotic forces on ecosystem-level processes across broad scale remains a central question in global ecology (Schimel et al. 1996, Chapin et al. 1997, Kerkhoff et al. 2005). In their report, Piao et al. (2010) addressed how global-scale variation in annual terrestrial autotrophic respiration, Ra, varies across broad-scale gradients including temperature, biomass, and successionary age. In addition, they purported to test several predictions and observations from metabolic scaling theory, MST (West et al. 1997) on how temperature and autotrophic biomass influence rates of ecosystem metabolism and production (Enquist et al. 2007b). While I agree with Piao et al.’s emphasis on the need to assess variation in ecosystem processes across broad gradients, I question their methodology for comparing and standardizing rates of ecosystem production and disagree with their reading of MST. Issues of how to standardize flux measures in order to compare annual and instantaneous rates across sites are not just specific to Piao et al.’s study. These issues also apply to other studies assessing spatial variation in ecosystemmetabolism across broad spatial gradients (for example, see Beer et al. 2010) and are central to how we understand and quantify the relative influence of abiotic and biotic forces on the ecosystem-level processes across broad-scale gradients as well as how to use cross-site analyses to inform predictions for a warming world. There are four specific issues that can influence Piao et al.’s central conclusions: 1. Piao et al.’s methodology for comparing fluxes between sites is likely biased, because they did not correct for differences in growing season length or properly control for the scaling effects of biomass on ecosystem metabolism.—Piao et al. observed that the annual respiration of forests increased with temperature. Piao et al. also claimed that this finding is in contrast to the findings of Enquist et al. (2007b). However, one cannot compare these two studies because Piao et al.’s methodology does not follow that of Enquist et al. Specifically, Kerkhoff et al. (2005) and Enquist et al. (2007a) argued that in order to mechanistically assess the role of temperature on more instantaneous rates of ecosystem metabolism it is important to also correct for tree biomass and growing season length. Enquist et al. showed that these corrected rates of tree growth showed little to no signal with growing season temperature. There are several reasons why studies that use annual measures to compare differing sites in order to infer how climate influences ecosystem performance will be biased. By using annual temperature, the actual temperature under which most of the flux occurs will increasingly be underestimated for colder sites because biological activity is greatly reduced so that the flux is effectively ‘‘off’’ during the dormant season (see also Savage 2004). Next, any relationship between a rate, like autotrophic respiration, and some environmental attribute such as temperature depends on the timescale of measurement (see also discussion in Mahecha et al. 2010). Annual ecosystem fluxes, such as net productivity or respiration, are measured by summing more instantaneous measures throughout the year. Rates of ecosystem respiration are tightly coupled to rates of gross primary production (see Vargas et al. 2010). Similarly, the annual carbon balance of a site is constrained by the length of time autotrophs have to assimilate carbon during the year (Cannell and Thornley 2000, Vargas et al. 2010, Berdanier and Klein, in press). As a result, annual respiration measures will be limited by the gross production that occurs during the length of the growing season. The use of annual fluxes can underestimate instantaneous rate measures, especially when one does not account for the (sometimes appreciable) dormant season length (Chapin 2003, Allen et al. 2005, Kikuzawa and Lechowicz 2006). From these points, both the fluxes and temperatures of the colder sites used by Piao et al. will be underestimated by using annual values. Thus, the use of annual measures to assess physiologically based models, even one as simple as MST, will not be applicable. As a result, the methodology used by Piao et al. does not provide a strong assessment of physiologically based models such as MST, which focus on the controls on more instantaneous rates, and its application to the carbon balance of forests. To highlight the above issues I assessed growing season length and compiled ecosystem data across a similar temperature gradient presented by Piao et al. Across a broad latitudinal and temperature gradient, the length of the growing season changes (Fig. 1). Growing seasons vary from 12 months to as little as 4 months or Manuscript received 1 October 2010; accepted 14 January 2011; final version received 4 April 2011. Corresponding Editor: J. B. Yavitt. 1 Department of Ecology and Evolutionary Biology, University of Arizona, BioSciences West, Tucson, Arizona 85721 USA. 2 The Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501 USA. 3 E-mail: benquist@email.arizona.edu

Understanding energy and material fluxes through ecosystems is central to many questions in global change biology and ecology. Ecosystem respiration is a critical component of the carbon cycle and might be important in regulating biosphere response to global climate change. Here we derive a general model of ecosystem respiration based on the kinetics of metabolic reactions and the scaling of resource use by individual organisms. The model predicts that fluxes of CO2 and energy are invariant of ecosystem biomass, but are strongly influenced by temperature, variation in cellular metabolism and rates of supply of limiting resources (water and/or nutrients). Variation in ecosystem respiration within sites, as calculated from a network of CO2 flux towers, provides robust support for the model's predictions. However, data indicate that variation in annual flux between sites is not strongly dependent on average site temperature or latitude. This presents an interesting paradox with regard to the expected temperature dependence. Nevertheless, our model provides a basis for quantitatively understanding energy and material flux between the atmosphere and biosphere.

Plants are expected to differentially allocate resources to reproduction, growth, and survival in order to maximize overall fitness. Life history theory predicts that the allocation of resources to reproduction should occur at the expense of vegetative growth. Although it is known that both organism size and resource availability can influence life history traits, few studies have addressed how size dependencies of growth and reproduction and variation in resource supply jointly affect the coupling between growth and reproduction. In order to understand the relationship between growth and reproduction in the context of resource variability, we utilize a long‐term observational data set consisting of 670 individual trees over a 10‐year period within a local population of Bursera simaruba (L.) Sarg. We (1) quantify the functional form and variability in the growth–reproduction relationship at the population and individual‐tree level and (2) develop a theoretical framework to understand the allometric dependence of growth and reproduction. Our findings suggest that the differential responses of allometric growth and reproduction to resource availability, both between years and between microsites, underlie the apparent relationship between growth and reproduction. Finally, we offer an alternative approach for quantifying the relationship between growth and reproduction that accounts for variation in allometries.

Significance We explore an extended view of the tropical conservatism hypothesis to account for two often-neglected components of climatic stress: drought and the combined effect of seasonal cold and drought—the latter being a common feature of extratropical dry environments. We show that evolutionary diversity of angiosperm assemblages in extratropical dry biomes is even lower than in biomes subject to only one type of climatic stress. We further show that evolutionary diversity in many assemblages from eastern North America is higher or comparable to that of tropical moist forests, suggesting that some extratropical moist biomes have accumulated angiosperm lineages over deep evolutionary timescales with their flora assembled from lineages that represent the entirety of the angiosperm tree of life.