Solar energy development is a significant driver of land‐use change worldwide, and desert ecosystems are particularly well suited to energy production because of their high insolation rates. Deserts are also characterized by uncertain rainfall, high species endemism, and distinct landforms that vary in geophysical properties. Weather and physical features that differ across landforms interact with shade and water runoff regimes imposed by solar panels, creating novel microhabitats that influence biotic communities. Endemic species may be particularly affected because they often have limited distributions, narrow climatic envelopes, or specialized life histories. We used experimental panels to simulate the effects of solar development on microhabitats and annual plant communities present on gravelly bajada and caliche pan habitat, two common habitat types in California's Mojave Desert. We evaluated soils and microclimatic conditions and measured community response under panels and in the open for seven years (2012–2018). We found that differences in site characteristics and weather affected the ecological impact of panels on the annual plant community. Panel shade tended to increase species richness on the more stressful caliche pan habitat, and this effect was strongest in dry years. Shade effects on diversity and abundance also tended to be positive or neutral on caliche pan habitat. On gravelly bajada habitat, panel shade did not significantly affect richness or diversity and tended to decrease plant abundance. Panel runoff rarely affected richness or diversity on either habitat type, but effects on abundance tended to be negative—suggesting that panel rain shadows were more important than runoff from low‐volume rain events. These results demonstrate that the ecological consequences of solar development can vary over space and time, and suggest that a nuanced approach will be needed to predict impacts across desert landforms differing in physical characteristics.

An explicit phylogenetic perspective provides useful tools for phytopathology and plant disease ecology because the traits of both plants and microbes are shaped by their evolutionary histories. We present brief primers on phylogenetic signal and the analytical tools of phylogenetic ecology. We review the literature and find abundant evidence of phylogenetic signal in pathogens and plants for most traits involved in disease interactions. Plant nonhost resistance mechanisms and pathogen housekeeping functions are conserved at deeper phylogenetic levels, whereas molecular traits associated with rapid coevolutionary dynamics are more labile at branch tips. Horizontal gene transfer disrupts the phylogenetic signal for some microbial traits. Emergent traits, such as host range and disease severity, show clear phylogenetic signals. Therefore pathogen spread and disease impact are influenced by the phylogenetic structure of host assemblages. Phylogenetically rare species escape disease pressure. Phylogenetic tools could be used to develop predictive tools for phytosanitary risk analysis and reduce disease pressure in multispecies cropping systems.

Forest communities with more distantly related trees have higher productivity, which is regulated by soil fungal pathogens.

Plant pathogens reduce the performance of their hosts and therefore may contribute to ecological mechanisms of coexistence. In Chesson’s framework, pathogens contribute to stabilizing mechanisms when they intensify negative intraspecific interactions, such as density‐dependent disease. Additionally, pathogens contribute to equalizing mechanisms when they reduce differences in performance among species. Life‐history trade‐offs predict higher susceptibility to pathogens in rapidly growing species, which could equalize performance among fast‐ and slow‐growing species in the presence of pathogens. In a coastal prairie in California, we studied the impact of leaf diseases on the performance of 17 co‐occurring species of Trifolium and Medicago (“clovers”). We transplanted clovers in randomized arrays into the natural prairie community in 3 years of common garden experiments. We quantified infection rates by isolating fungi from leaves, and we measured disease severity as per cent leaf area damaged. In a fungicide experiment, we measured the impact of infection on biomass and survival. We assessed whether disease on transplants was positively related to natural abundance of that species in the surrounding community, which we monitored over 5 years. We assessed life‐history trade‐offs by testing whether more rapidly growing species were more susceptible to pathogens. Rank abundance of clover species was stable over 5 years despite marked environmental fluctuations. Across hosts, fungal infection was not linearly related to density, although transplants of species that were locally absent showed lower and more variable infection. Disease severity was greater for more abundant species, but in only 1 of 3 years, and response to fungicide was not stronger in more abundant species. As predicted by life‐history trade‐offs, faster‐growing species experienced greater fungal infection. However, the impact of that infection was less negative, not more negative, on faster‐growing species. Our results suggest that life‐history trade‐offs in plant–pathogen interactions may influence equalizing mechanisms among species in this guild, but the combined effects of greater infection with greater tolerance may limit rather than promote coexistence. We also found modest evidence that density‐dependent disease may contribute to stabilizing mechanisms. Lack of host specificity, rapid evolution of host use and temporal variation in climatic conditions may all influence the role that pathogens play in coexistence of these closely related plants.

Political and economic initiatives intended to increase energy production while reducing carbon emissions are driving demand for solar energy. Consequently, desert regions are now targeted for development of large‐scale photovoltaic solar energy facilities. Where vegetation communities are left intact or restored within facilities, ground‐mounted infrastructure may have negative impacts on desert‐adapted plants because it creates novel rainfall runoff and shade conditions. We used experimental solar arrays in the Mojave Desert to test how these altered conditions affect population dynamics for a closely related pair of native annual plants: rareEriophyllum mohavenseand commonE. wallacei. We estimated aboveground demographic rates (seedling emergence, survivorship, and fecundity) over 7 yr and used seed bank survival rates from a concurrent study to build matrix models of population growth in three experimental microhabitats. In drier years, shade tended to reduce survival of the common species, but increase survival of the rare species. In a wet year, runoff from panels tended to increase seed output for both species. Population growth projections from microhabitat‐specific matrix models showed stronger effects of microhabitat under wetter conditions, and relatively little effect under dry conditions (lack of rainfall was an overwhelming constraint). Performance patterns across microhabitats in the wettest year differed between rare and common species. Projected growth ofE. mohavensewas substantially reduced in shade, mediated by negative effects on aboveground demographic rates. Hence, the rare species were more susceptible to negative effects of panel infrastructure in wet years that are critical to seed bank replenishment. Our results suggest that altered shade and water runoff regimes associated with energy infrastructure will have differential effects on demographic transitions across annual species and drive population‐level processes that determine local abundance, resilience, and persistence.