the GlobalChangeBiology blog

We quantified the photosynthetically active radiation (PAR) interception in a high-density (HD) and a super high-density (SHD) or hedgerow olive system, by measuring the PAR transmitted under the canopy along transects at increasing distance from the tree rows. Transmitted PAR was measured every minute, then cumulated over the day and the season. The frequencies of the different PAR levels occurring during the day were calculated. SHD intercepted significantly but slightly less overall PAR than HD (0.57 ± 0.002 vs. 0.62 ± 0.03 of the PAR incident above the canopy) but had a much greater spatial variability of transmitted PAR (0.21 under the tree row, up to 0.59 in the alley center), compared to HD (range: 0.34–0.43). This corresponded to greater variability in the frequencies of daily PAR values, with the more shaded positions receiving greater frequencies of low PAR values. The much lower PAR level under the tree row in SHD, compared to any position in HD, implies greater self-shading...

By averaging in time and/or space, models predict less variable light patterns under tree canopies than in reality. We measured light every minute in 24 positions in a grid under different chestnut orchards, for several clear and overcast days. We also modelled this light with a purposely created 3D, spatially explicit, ray-tracing light interception model, where canopy porosity was calibrated to match measured daily light. Finally, we used both the measured and modeled light patterns transmitted under the tree canopies to estimate the daily net photosynthesis (An) and radiation use efficiency (RUE) of an understory wheat leaf. As expected, modeled light was more uniform than measured light, even at equal daily light. This resulted in large overestimation of daily An and RUE of the understory leaf. Averaging light in time increased the overestimations even further. A sensitivity analysis showed that this overestimation remained substantial over the range of realistic values for leaf ph...

Exotic species that invade new areas cause economic loss annually nearly tenfold that of natural disasters. The economic impact of such biological invasions has been considerable also in agriculture, with many major agricultural pests being invasive species, which number is expected to increase given the combined action of climate warming and globalization, particularly in the Mediterranean Basin. This region is rich in natural and agricultural biodiversity but also considerably vulnerable to biological invasions that threaten key elements of Mediterranean agro-biodiversity such as the traditional perennial crops grape and olive. Currently, most major threats to grape and olive culture are invasive species - often vector borne diseases so serious that the only control method is removal and destruction of infected crop plants. However, how to assess the potential impact of such invasive threats, and hence how to manage them, remains an unresolved and largely unexplored problem. Gaps exi...

The Asian tiger mosquito ( Ae. albopictus ) is indigenous to the oriental region, but is now widespread throughout the world. It is an aggressive mosquito, which causes nuisance and is well known vector of important human disease. It is one of the world’s most invasive species and is now invading Europe by both natural means and human assisted dispersal. Currently, there is no consensus on the limits of its potential geographic distribution in Europe. For this reason, studying the role that environmental driving variables, mainly temperature, play in determining the spatial variation of the potential population abundance of the mosquito should be considered a high priority. To assess the risk posed by Ae. albopictus to Europe, a lattice model based on the temperature-dependent physiologically based demographic modelling approach has been developed and is being tested against field observations. The area of potential distribution of this insect is simulated as driven by current climate...

The invasive Asian citrus psyllid Diaphorina citri Kuwayama vectors the bacterial pathogen ‘Candidatus Liberibacter asiaticus’ that is the putative causal agent of citrus greening disease (Huanglongbing disease) in citrus in many areas of the world. The capacity to predict the potential geographic distribution, phenology and relative abundance of the pest and disease is pivotal to developing sound policy for their management. A weather-driven physiologically based demographic model (PBDM) system is developed that summarizes the available data in the literature, and used to assess prospectively the geographic distribution and relative abundance of citrus, the psyllid, its parasitoid ( Tamarixia radiata Waterston), and citrus greening disease in North America and the Mediterranean Basin. The potential for natural and biological control of citrus psyllid is examined prospectively. Gutierrez A.P., Ponti L., 2013. Prospective analysis of the geographic distribution and relative abundance...

Olive is of major eco-social importance for the desertification-prone Mediterranean Basin, a climate change and biodiversity hotspot of global relevance where remarkable climate change is expected over the next few decades with unknown ecosystem impacts. However, climate impact assessments have long been constrained by a narrow methodological basis (ecological niche models, ENMs) that is correlative and hence largely omits key impact drivers such as trophic interactions and the effect of water availability. To bridge this gap, mechanistic approaches such as physiologically-based weather-driven demographic models (PBDMs) may be used as they embed by design both the biology of trophic interactions and a mechanistic representation of soil water balance. Here we report progress towards assessing climate effects on olive culture across the Mediterranean region using mechanistic PBDMs that project regionally the multitrophic population dynamics of olive and olive fly as affected by daily wea...

The highly polyphagous light brown apple moth (LBAM) ( Epiphyas postvittana (Walk.): Tortricidae) is indigenous to Australia and was first found in California in 2006. It is currently found in 15 coastal counties in California, but nowhere has it reached outbreak status. The USDA projects the geographic range of LBAM will include much of Arizona and California and the southern half of the U.S., which together with economic estimates of potential crop losses have been used as the rationale for an eradication program in California. We report a temperature-driven demographic model to predict the likely distribution and relative abundance of LBAM using the detailed biology reported by W. Danthanarayana and colleagues, and climate data from 151 locations in California and Arizona for the period 1995 to 2006. The predictions of our model suggest that the near coastal regions of California are most favorable for LBAM, the northern Central Valley of California being less favorable, and the de...