Interacting Disturbances: Wildfire Severity Affected by Stage of Forest Disease Invasion

The presence of disease in wildfire prone areas has generated the assumption that increased disease outbreaks result in increased fire severity. Studies suggest that this relationship is in fact more complex and empirical data show that fuel loading and disease stage are more indicative than merely the presence of disease alone. One challenge when evaluating the effects of disease on fire severity is that often no pre-fire data exist in infected areas, so mapping post-fire characteristics that are induced by pre-fire forest conditions becomes speculative. Metz et al. (2011) had the unique opportunity to observe the effects of Sudden Oak Death (SOD) on wildfire severity on the California Central Coast. They examined results from the 2008 Basin Complex [fire] that had a perimeter encompassing 98 of the 280 plots established in 2006 and 2007 to monitor the effects of SOD on the forest. They found that there was generally minimal difference in fire severity in SOD infested and non-infested plots, except that the more concentrated dead fuel loading on the ground in SOD areas did increase the effects of fire on soil characteristics. Furthermore, the minor effect of SOD on fire severity was more observable in areas that were in the early stages of SOD infections because of the high presence of dead leaves and small diameter branches in the canopy that had not yet fallen to the understory. These “light flashy fuels” can be very volatile when ignited and can increase fire severity. –Lindon Pronto

Metz, Margaret R., Frangioso, Kerri M., Meentemeyer, Ross K., Rizzo, David M., 2011. Interacting disturbances: wildfire severity affected by stage of forest disease invasion. Ecological Applications 21, 313–320.

Food Security and Marine Capture Fisheries: Characteristics, Trends, Drivers, and Future Perspectives

In 2006, marine capture fisheries produce 82 million tons of fish a year and may have now reached up to 100 million tons, a possible upper limit.  An important source of protein, vitamins, and micronutrients, particularly for low-income populations in rural areas, fisheries, which include 32 million tons from inland aquaculture and 20 million tons from marine aquaculture, play a critical role in global food security.  While demand is high, marine populations are highly stressed by excessive fishing pressure, toxic contamination, pollution, costal degradation, and climate change.  How fisheries are governed and the success of related international and national policy will play a crucial role in ensuring that marine capture fisheries continue feeding the world.--Alyshia Silva

 

Garcia, S.M., Rosenberg, A.A., 2010. Food Security and Marine Capture Fisheries: Characteristics, Trends, Drivers, and Future Perspectives. Philosophical Transitions of the Royal Society 365, 2869–2880

How well do Predators Adjust to Climate-Mediated Shifts in Prey Distribution? A Study on Australian Water Pythons

The spatial relocation of many species’ vital resources has been attributed to climate change. These resources are often other terrestrial prey species. Therefore, predatory species’ resilience and survival in the face of climate change depends on their ability to shift their activities away from unsuitable territories to the new ranges their prey inhabits. Ujvari et al. (2011) monitored two spatially separate groups of Northern Australian water pythons (Liasis fuscus) that were tracking the movements of their primary prey, the dusky rat (Rattus colletti), during the wet season. One population of pythons inhabited an area (Beatrice Hill) that contained a large population of rats. The second group of pythons inhabited Fogg Dam, an area that had recently experienced a crash in rat numbers due to a severe flood. The authors measured the population size, the survival rate, and the residual body mass (RBM) of both python groups and found that food (rat) availability was correlated with python RBM. Therefore, the pythons’ lower RBM at Fogg Dam was attributed to limited prey availability. As a result, the population’s survival rate and size were greatly reduced through starvation, despite the presence of a close, large population of rats at Beatrice Hill. These results suggest that python migrations were signaled by habitat features that indicate prey availability—a life strategy that could inhibit the adaption of pythons to climate induced prey range shifts.—Megan Smith

Ujvari, B., Shine, R., Madsen, T., 2011. How well do predators adjust to climate-mediated shifts in prey distribution? A study on Australian water pythons. Ecology 92: 3, 777 – 783.

Sub-humid to Arid Zones of the World Experiencing increasing Groundwater Depletion and Withdrawals

From 1960 until 2000, the amount of groundwater withdrawn and depleted from climate changes has increased in sub-humid to arid areas of the world. Measures of groundwater depletion and withdrawal were found with data of decreasing volumes of water percolating back underground, and the amount of groundwater withdrawals, to calculate groundwater lost per year that is not recharged. Water volumes in two soil layers and the groundwater layer were all measured in these regions of the globe, separated into multiple cells. The results showed an increase of around 57 km³ per year in groundwater depletion. This consists of 36 (±10)% of the global groundwater withdrawn annually, 2(±0.6)% of the annual recharge, 0.8(±0.1)% annual global runoff, and 0.4(0.06)% of global evaporation. Though uncertain, this decrease in groundwater supplies is likely to present an added sea-level rise of 0.8(±0.1) mm per year.  This study compiled by Wada et al. concerns only regions of sub-humid to arid climates. –Darien Martin

Wada, Y. Van Beek, L., Van Kempen, C., Reckman, J., Vasak, Slavek., Bierkens, M., 2010. Global depletion of groundwater resources. Geophysical Research Letters 37, 1–5.

A Review of CO2 Enrichment Studies: Does Enhanced Photosynthesis Enhance Growth?

Plants typically only convert 2 to 4% of available energy into actual growth and this natural inefficiency provides a reason for scientists to attempt to increase the efficiency of the process by increasing photosynthesis. One of the most common methods, other than genetic modification, to increase photosynthesis is to increase ambient CO₂. Elevated CO₂ can lead to growth increases ranging from 10 to 50%, depending on the plant’s carbon sink capacity and nutrient availability. Previous studies show that elevated CO₂ inevitably leads to increased growth, but the magnitude of the growth varies with the photosynthetic capacity of the plant. Photosynthesis is an inefficient process with a maximum of 8 to 10% of the energy in sunlight being converted into chemical energy. Realistically, only 2 to 4% of energy in sunlight is converted. In this paper, Kirschbaum examines previous studies and conducts experiments of his own in order to summarize the current knowledge on CO₂ enrichment studies, focusing on the ability of increased photosynthesis to ultimately increase plant growth. Kirschbaum studies the factors that affect plant growth under elevated CO₂ in an attempt to determine if photosynthesis is the main factor increasing growth or if other factors are relatively more important.—Taylor Jones

Kirschbaum, M.U.F., 2011. Does Enhanced Photosynthesis Enhance Growth? Lessons Learned from CO₂ Enrichment Studies.  Plant Physiology 155, 117-124.