Posts Tagged: Blue Oak
The Blue Oak
Finding an Ecological Niche: Selected Foothill Woodland and Chaparral Species, Part 1 of 3: The...
Thinning is an effective tool for management of blue oak woodlands
Researchers with UC Agriculture and Natural Resources (UC ANR) have worked with landowners for decades to help them manage these oak woodlands in ways that balance the ranchers' economic needs with ecological considerations.
In the late 1990s, Tulare County ranchers Jim and Gay Versteeg were interested in thinning their blue oak stands in order to improve biodiversity of the forage growing on the land. The family offered UC ANR researchers three acres to study blue oak tree management practices to better understand the impacts of various thinning practices.
For thousands of years, fire was an important part of California's oak woodlands. Native Americans and, more recently, ranchers set fires to improve habitat and enhance desirable vegetation. However, aggressive fire exclusion during the last 30 years has led to significantly denser stands of blue oak trees.
“We looked into the fire history on the Versteeg ranch,” said Richard Standiford, UC ANR Cooperative Extension specialist based at UC Berkeley. “It burned about every 13 years prior to 1965, but since then, there have been no fires at all.”
Standiford conducted the study with two San Joaquin Valley-based Cooperative Extension natural resources advisors, Neil McDougald of Fresno and Madera counties and Ralph Phillips of Kern County. One-third of the study area was moderately thinned, and one-third was heavily thinned. For comparison purposes, the researchers left one-third of the study area untouched. The study area excluded livestock, but it was accessible to deer and rodents.
“The Versteegs thought that, with more sunlight, the amount of native grasses would increase, but that wasn't the case,” Standiford said. “The vegetation in all the plots was mostly grasses and forbs that were introduced after Europeans began settling California, as it is in most oak woodland around the state.”
Thinning did result in the growth of younger trees from stump sprouting.
“We want the sprouts to come back to provide the next generation of trees so when the big ones die or blow over, there are young trees to take their places,” Standiford said. “The main way in which blue oaks regenerate is sprouting from stumps.”
Acorn production on a landscape scale was not impacted by thinning. Trees in the thinned plots produced more acorns per tree, however, because there were fewer trees, the same amount of acorns per acre was produced.
Standiford shared the results of the study with ranchers, land managers and researchers at the 7th California Oak Symposium in 2014; the research will be published in the symposium proceedings later this spring. He said the study results validate for landowners that thinning is an appropriate management practice on blue oak rangeland. Forage increases, the trees survive and grow back.
“If ranchers intend to thin every 15 years or so, moderate thinning is acceptable,” Standiford said. “If this is something they would do every 30 years, they could thin heavily.”
An initiative to maintain and enhance sustainable natural ecosystems is part of UC Agriculture and Natural Resources Strategic Vision 2025.
New Year, New Watershed Awareness Calendar
If you still need a paper calendar for 2013 and you cherish the many oak trees that beautify Napa...
Early Leaf-out a bit of a Mystery
Towards the end of January, an unusual phenomenon occurred in the Sierra foothills - some of the blue oaks began leafing out. While the vast majority of trees remained leafless, one could see occasional light-green canopies interspersed with their bare neighbors. This is unusual in that the earliest leaf-out most people recall observing doesn’t start until late February or early March.
So what is causing this? Clearly the weather pattern this past winter has been very unusual in terms of precipitation. There was abundant early rainfall in October and November, followed by a December and January that were some of the driest on record. However, dormancy and its subsequent breaking are much more controlled by temperature than by rainfall. That is, a significant period of cold is necessary before most temperate plants resume growth in the spring. Photoperiod – or the relative daily lengths of light and darkness - also often plays an important role but this obviously doesn’t vary from year to year.
Has the temperature pattern been abnormal? The CIMIS (California Irrigation Management Information System) long-term data was compared with this past winter’s averages and nothing stood out as particularly different, although there is apparent, large variability from year to year. There was a day or two of somewhat colder-than-average temperatures in mid-January, but below-freezing temperatures in the foothills occur almost every year. Therefore, at this point, the cause of early leaf-out remains a mystery.
What about the impacts? It is likely that some of these “early leafers” will suffer frost damage. This occurred several years ago in mid-spring when there was an unusually late freeze and many blue oaks had their foliage killed back. Most of this occurred at mid-elevations, presumably because trees at higher elevations hadn’t leafed out yet, and those at lower elevations were so far advanced that their foliage was hardier. While this certainly wasn’t good for the trees, they were able to recover and produce a new crop of leaves within a month or 6 weeks and no increase in mortality was noted. It seems likely that, as a species, blue oaks have evolved individuals that leaf out at different times of the year so that at least a portion of their population can take advantage of different weather conditions. The “risk takers” might get hammered now and then, but under the right conditions, they can take better advantage of unusual weather patterns than their more conservative colleagues. In the event of significant warming in California as a result of climate change, these may even be better adapted to survive and prosper in a changing environment.
Blue Oak Acorn Toxicity Risk in Cattle
Four head mature cows have been reported dead in Tulare County foothills from 2500 feet to 1000 foot elevations. All were in the vicinity of Blue Oaks with heavy crop of acorns.
Neil McDougald, Livestock Range Advisor of Madera County indicated that this year is similar to other years he has seen where there have been incidents of acorn toxicity. There is a very large acorn crop, and recent rains has led to some early green-up under Oak Trees which can result in some cows camping and eating an overload of acorns resulting in acorn poisoning.
Most cattle in California spend at least part of the year in areas where oak trees abound. Health problems due to ingestion of oak leaves or acorns are certainly not an everyday problem; however, when problems do occur they can be catastrophic. Several years ago, in a few northern California counties, about 2,700 cattle died due to oak toxicity1.
Some years have much higher production of oak acorns than others and this year, 2011 in the Foothill Ranges of the Southern Sierras, has been reported as one of the highest production years observed. In addition early rains may increase the risk of acorns by reducing the nutrient value of last year’s forage, as well as causing an early greening of grass under the oaks where acorns are accumulating.
During the week of October 10, 2011 four head mature cows were reported to be found dead in Tulare County foothills from 2500 feet to 1000 foot elevations. All were in the immediate vicinity of Blue Oaks with heavy crop of acorns. These cattle were not available for necropsy and cause of death was not confirmed, however oak acorn toxicity is suspected.
Oak toxicity symptoms usually appear when cattle eat 50% or more of their diet as oak (acorns, leaves, buds). Toxicity can be prevented by supplementing cattle with hay or other supplements when forage conditions are poor and acorns are abundant. A higher risk may occur if early or late snowstorms covers available forage and knocks down oak limbs with large amounts of buds and young leaves or acorns, be sure to start hay supplementation immediately. A delay of only a day or two could result in many deaths.
There are two recommendations to avoid cattle loss due to acorn toxicity. One is to provide supplement to draw cattle away from the acorns, so that their exposure decreases. The other is to remove cattle observed eating acorns from fields with high levels of acorns.
It is recommended that producers work with their local veterinarian and/or diagnostic laboratory, to be certain of the actual cause of death in all livestock losses. There are many other factors that can cause sudden death and although oak toxicity may be likely and immediate actions should be taken to prevent further deaths, a follow up with a veterinarian is often the best course of action to prevent further losses. For a more comprehensive discussion on identification and recommended actions for Oak Toxicity and Acorn Calf syndrome in cattle please refer to the link below.
Dr. John Maas, UC Davis Extension Veterinarian, informative article on oak toxicity (OAK TOXICITY UCD Vet Views California Cattleman, Jan 2001):
http://www.vetmed.ucdavis.edu/vetext/INF-BE_cca/INF-BE_cca01/INF-BE_cca0101.html.
Blue Oak Acorn
Cattle Pasture amongst Blue Oaks