Browsing by Author "Reynolds, James F"

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Open Access
A mechanistic-bioclimatic modeling analysis of the potential impact of climate change on biomes of the Tibetan Plateau.
(Ecology, 2014-08) Ye, Jian-Sheng; Reynolds, James F; Li, Feng-Min
The Tibetan Plateau (TP) is experiencing high rates of climatic change. We present a novel combined mechanistic-bioclimatic modeling approach to determine how changes in precipitation and temperature on the TP may impact net primary production (NPP) in four major biomes (forest, shrub, grass, desert) and if there exists a maximum rain use efficiency (RUE(MAX)) that represents Huxman et al.'s "boundary that constrain[s] site-level productivity and efficiency." We used a daily mechanistic ecosystem model to generate 40-yr outputs using observed climatic data for scenarios of decreased precipitation (25-100%); increased air temperature (1 degrees - 6 degrees C); simultaneous changes in both precipitation (+/- 50%, +/- 25%) and air temperature (+1 to +6 degrees C) and increased interannual variability (IAV) of precipitation (+1 sigma to +3 sigma, with fixed means, where sigma is SD). We fitted model output from these scenarios to Huxman et al.'s RUE(MAX) bioclimatic model, NPP = alpha + RUE x PPT (where alpha is the intercept, RUE is rain use efficiency, and PPT is annual precipitation). Based on these analyses, we conclude that there is strong support (when not explicit, then trend-wise) for Huxman et al.'s assertion that biomes converge to a common RUE(MAX) during the driest years at a site, thus representing the boundary for highest rain use efficiency; the interactive effects of simultaneously decreasing precipitation and increasing temperature on NPP for the TP is smaller than might be expected from additive, single-factor changes in these drivers; and that increasing IAV of precipitation may ultimately have a larger impact on biomes of the Tibetan Plateau than changing amounts of rainfall and air temperature alone.
Open Access
Desertification is a prisoner of history: An essay on why young scientists should care
(Ecosistemas) Reynolds, James F
Since its origins, the concept of desertification has been shrouded in controversy and ambiguity. As a result, no single definition of the term has been acceptable; there is no agreement on its extent or seriousness; and the solutions proposed are often disparate and counterproductive. This essay suggests all of this is due to the concept of desertification being a permanent ‘prisoner of history’, a historical process led by the United Nations Convention on Desertification (UNCCD). In this essay, I describe why the prisoner of history narrative applies to the concept of desertification. To do this, I review the historical events that built a metaphorical prison for desertification; show why definitions of the term ‘desertification’ are products of this prison; describe how so much misunderstanding and confusion in this field has led to real, negative consequences; and lastly, provide recommendations to young scientists as to how to avoid becoming incarcerated in this prison.
Open Access
Earthworms modify plant biomass and nitrogen capture under conditions of soil nutrient heterogeneity and elevated atmospheric CO2 concentrations
(Soil Biology and Biochemistry, 2014-01-01) García-Palacios, Pablo; Maestre, Fernando T; Bradford, Mark A; Reynolds, James F
Earthworms modify the way roots respond to soil nutrient patchiness. However, few studies have evaluated the joint effects of earthworms and soil heterogeneity on plant community biomass and species dominance, and none of them have assessed the influence of different patch features and environmental conditions on such effects. We evaluated how soil nutrient heterogeneity, earthworms (Eisenia fetida), organic material quality (15N-labelled leaves and roots of contrasting C: N ratios) and elevated atmospheric CO2 concentrations (phytotron chambers) affected the resource-use strategy, biomass and species dominance of mixtures formed by Lolium perenne L. and Plantago lanceolata L. Soil heterogeneity decreased N capture from the organic material, especially in the presence of earthworms. Mixtures experienced a 26 and 36% decrease in shoot and root biomass when earthworms were added to the heterogeneous microcosms, but only with high quality organic material. The dominance of L. perenne was lower under conditions of elevated CO2, nutrient heterogeneity and earthworms. Our data suggest that earthworms can neutralize positive plant growth responses to soil heterogeneity by exacerbating decreases in the supply of N to the plant. Specifically, earthworms foraging for high quality patches may stimulate microbial N immobilization, translating into lower N capture by plants. Increases in casting activity under elevated CO2, and hence in microbial N immobilization, may also explain why earthworms modulated the effects of soil heterogeneity and CO2 concentrations on plant community structure. We show that earthworms, absent from most soil nutrient heterogeneity studies, mediate plant biomass responses to nutrient patchiness by affecting N capture. Future plant-foraging behaviour studies should consider the roles played by soil engineers such as earthworms, so that results can be better extrapolated to natural communities. © 2014 Elsevier Ltd.