UC Berkeley News Service – Efforts to predict the emergence and spread of sudden oak death, an infectious tree-killing disease, have gotten a big boost from the work of grassroots volunteers. A joint study reveals the power of citizen science in SOD Blitz, a survey project in which volunteers are trained to identify symptoms of sudden oak death. Led by Matteo Garbelotto at UC Berkeley and Ross Meentemeyer at North Carolina State University, the study was published today (Friday, May 1) in the journal Frontiers in Ecology and the Environment.
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The Forest Mycology and Pathology Lab at UC Berkeley has developed a new method for sampling forest canopies. The Sampler Drone is a modified DJI Phantom 2 Vision quadcopter that is lightweight, compact, and exceptionally agile.
The Sampler Drone uses GPS positioning and gyroscopic axis stabilization to provide a stable aerial platform for collection of environmental samples. It is capable of hovering close to any portion of the canopy, taking samples, and returning them safely to the ground.
The forward-facing carbon fiber boom can be outfitted with a variety of modules for leaf, water, or air sampling and with a altitude ceiling of 400m, the drone is able to access trees of any height. The integrated HD camera, when combined with FPV headset goggles, allows the operator to pilot the quadcopter remotely from a first person view, in real time.
There are a number of common oak species in California including both tree species and shrub species.
Black Oak (Quercus kelloggii) Found in hilly regions between 2,000 and 6,000 feet. Typically associated with conifers and pines, firs, or incense cedars.
Blue Oak (Quercus douglasii) Found in the hot, dry interior foothills. Generally found below 3,500′.
Canyon Live Oak (Quercus chrysolepis) Evergreen oak found in foothills, steep canyons, and on slopes to 9,000′.
Coast Live Oak (Quercus agrifolia) Evergreen oaks found in coastal fog zones and in grassland savannas.
Engleman or Mesa Oak (Quercus engelmannii) Rare species found in scattered groups along the western edge of California deserts.
Interior Live Oak (Quercus wislizenii) Evergreen species usually found on uploand slopes below 5,000 feet , in low foothills and in hot dry canyons.
Island Oak (Quercus tomentella) Found on the Channel Islands off the coast. Typically in foggy areas often on north or north west facing slopes.
Oregon Oak (Quercus garryana) Found away from coastal fog on slopes and open valleys, usually between 1,000 and 5,000 feet
Shreve’s Oak (Quercus parvula var. shrevei) Similar in appearance, often found growing adjacent to, and may produce hybrids with Coast Live Oak.
Valley Oak (Quercus lobata) A deciduous tree species that can grow very large. Found typically inland from the coastal fog region, usually below 2,000 feet.
- SOD is an exotic disease caused by the microscopic pathogen Phytophthora ramorum, estimated to have been introduced into California 20-25 years ago from unknown region of the world.
- P. ramorum was unwittingly introduced into California’s natural landscape when infected ornamental plants, such as Rhododendrons and Camellias (which carry the disease), were outplanted into the environment. On many ornamental plants, as well as many native forest plants (including California bay laurels and tanoak), the pathogen causes a disease called ramorum blight. Ramorum blight is a foliar disease that often supports pathogen sporulation and spread, as the spores build up on the leaves and twigs of these hosts which can then be transferred to nearby oaks and tanoaks, causing sudden oak death. Ramorum blight is rarely lethal.
- In California, foliar infections on Bay Laurel leaves are mostly responsible for spreading the disease. Oaks and tanoaks are infected when in proximity of bay laurels. Oaks only get a stem infection; tanoaks can develop both stem and a foliar infection. Tanoaks are the only tree species that can spread the the disease and die from it as well. When P. ramorum infects oaks and tanoaks it destroys the cambium under the bark and effectively girdles the tree. Girdled trees are doomed, but can survive for 1 to 5+ years thanks to stored resources and their natural tolerance to drought.
- Besides Tanoaks, California Coast Live Oak, Black Oak, Shreve’s Oak, and Canyon Live Oak are known to be infected by P. ramorum. Oaks are not infectious in nature and do not spread the disease further, but oak wood may be infectious if carried to an uninfested area.
- P. ramorum can infect leaves and trunks of it’s hoasts without the need for wounds, but it does require rainfall and temperatures between 60 and 80F (25 to 27C). As a result most infections occur in the rainy season and in particular when spring temperatures rise (mid April to June).
- Yearly infection levels will depend on the presence of rainfall in the Spring; while tanoaks and bay laurels are infected yearly, oaks are normally infected only in years with abundant Spring percipitation.
- P. ramorum is dispersed aerially usually at short distances 100 yrds (100m) or less, but occasionally up to 1-2 miles (1.7-3.5km).
- Infectious airborne microscopic structures known as sporangia are produced during rain events on plant surfaces, primarily leaves, and can also accumulate in soil and stream water.
- Besides the natural spread of the pathogen, movement of infected plants or plant parts, soil, and water may lead to new infestations. Soil and plant material on tools and equipment may vector the disease.
- During dry periods, the pathogen survives within infected plant tissues, and by producing a thick walled resting structure called a chlamydospores. As a result SOD remains persistent in any site, but oak infection varies as it requires high infection levels of bay laurels.