- Posted By: Jaime Adler
- Written by: Adina Merenlender, CE Specialist
California’s hardwoods have so many virtues it is difficult to count them all. Only recently scientists have come to appreciate the influence that living hardwoods exert on stream channel shape as the key to providing good habitat for all aquatic species, including salmon in coastal California streams. It is well known that wood in streams provides habitat for a broad range of fresh water species and can influence the shape of the stream channel and important ecosystem processes, such as moving sediment and nutrient cycling. Wood also provides important habitat for fish by creating pools, providing shade and hiding places from predators, protection from high flows, food and shelter for invertebrates, woodjams that store spawning gravels and organic matter, and facilitates riparian plant regeneration. Wood is considered one of the most important habitat components for anadromous salmonids and with salmon on the decline it is important we ensure the presence of wood in California’s coastal streams.
Previously, scientists attributed all of these qualities to large pieces of dead wood from species that rot slowly such as the infamous California redwoods. But this begs the question: What is happening in streams lined by hardwoods such as California bay laurel, live oaks, alders, and willows commonly found in our mediterranean-climate woodlands? Field research conducted by Dr. Jeff Opperman, UC Berkeley alumnus now working for The Nature Conservancy, in 20 stream reaches in the northern parts of the San Francisco bay area, documents that living hardwoods are playing an essential role in California’s hardwood dominated streams by providing permanent structure that interacts with stream flow and gravel movement to create essential aquatic habitat for salmon and other native species (Figure 1).
Figure 1. Extracted from OPPERMAN, J. J. and A. M. MERENLENDER. 2007 Living trees provide stable large wood in streams. Earth Surface Processes and Landforms 32:1229-1238 (a) A red willow (Salix laevigata) that has fallen into Wildcat Creek (Aladmeda County, CA) but remains rooted and living (photo taken looking upstream).The lower arrow indicates sprouts growing from the lower branch of the willow. The upper arrow indicates a branch that has reoriented to become the primary source of photosynthesis for the fallen tree. A channel-spanning wood jam has accumulated upstream of this willow, which has contributed to the formation of the pool in the lower left portion of the picture. (b) The shaded areas denote all the wood that is still living within this wood jam.
As you can imagine trees that fall or grow over the stream and remain rooted and alive are more stable over time and and can withstand sizeable storms. After falling into the stream, hardwoods can often sprout new branches or bend into new shapes that result in vertical branches to capture more light for photosynthesis. A live tree spanning a creek with leaves on vertical branches creates significant shade and captures additional wood and organic material all to the benefit of the fish living below (Figure 1). These persistent hardwoods provide important in-stream structure in streams with riparian corridors that lack large conifers. In fact, in the 20 streams Jeff studied living hardwoods were the key piece of wood within a wood jam, the primary mechanism by which wood in?uences channel morphology, and had greater influence on channel morphology than larger pieces of dead wood found. Only 74% of the wood jams without live wood persisted to allow for scowering and pool formation in the stream over 1-2 years while 98% with living wood as a key piece remained in place for longer. Wood jams that span the entire channel provide the greatest influence over stream morphology and create complex habitat that maintains cooler safer waters for fish. Out of all the channel-spanning jams measured by Jeff, 44% had a living hardwood as key piece (Figure 2).
Figure 2. Extracted from OPPERMAN, J. J. and A. M. MERENLENDER. 2007 Living trees provide stable large wood in streams. Earth Surface Processes and Landforms 32:1229-1238 The proportion of all wood jams with a live key piece (shaded), dead key piece (white) or no key piece (black), based on channel position of the wood jam.
Clearly, California hardwoods are a necessary component within California’s fresh water aquatic ecosystems because they contribute to ?sh habitat by creating and maintaining wood jams, forming pools, and providing cover. Unfortunately, wood in streams is often removed by landowners, in some cases to protect property, but in other cases because of the desire for a clean stream or for easily accessible firewood. To stress the importance of maintaining wood in streams for fish habitat I, along with Jeff, and David Lewis a UCCE Watershed Management Advisor for Sonoma County, wrote a free publication for landowners titled “Maintaining wood in streams: A vital action for fish conservation.” Please click here to access the publication and learn more about this topic: http://ucanr.org/freepubs/docs/8157.pdf.
- Posted By: Richard B Standiford
- Written by: Rick Standiford, Forestry Specialist, UC Berkeley; Ralph Phillips, UCCE Livestock Advisor Emeritus; Neil McDougald, UCCE Natural Resource Advisor
Two thinning studies in the southern Sierra Nevada resulted in enhanced acorn production. A thinning experiment evaluating three levels of stocking for blue oak (Quercus douglasii Hook. & Arn.) was initiated in 1994 near California Hot Springs, California in Tulare County. The goal of the thinning was to evaluate how oak canopy overstory levels affected individual and stand tree growth, forage production, grassland diversity, and oak regeneration. The control level for the unthinned stand was close to 100 square feet per acre with a tree canopy level of 55 percent. The stands were thinned to 1/3 and 2/3 of the existing basal area level. In the first year after thinning, in addition to tree and grassland measurements, there was a measurement of acorn production by rating each tree using the four-class system developed by the Department of Fish and Game (see below).
|
Acorn Class |
Class Description |
Production (lbs./10 sq. ft. of canopy) |
|
1 |
No acorns visible on tree |
0.0 |
|
2 |
Acorns visible only after close examination. Maybe 1 or 2 acorns are observed |
0.1 |
|
3 |
Acorns are readily visible, but do not cover entire tree |
0.7 |
|
4 |
Acorns are readily visible, cover entire tree. Limbs appear to sag from weight of acorns. |
2.3 |
Figure 1 shows the impacts of the thinning on blue oak acorn production. For ease of presentation, we show the proportion of trees with no acorns (Acorn Class 1), to the proportion of trees with any acorns (Acorns Class 2, 3 or 4). This shows that for 5 of the 7 years we surveyed acorn production, the thinning treatments had a significant impact in increasing the proportion of blue oak trees with acorns. The two years with non-significance due to the thinning (1997 and 2002) were generally poor acorn years for the region.
Figure 1. Blue oak acorn production by thinning levels.
A second thinning study was carried out on interior live oak (Quercus wislizenii A. DC.) near North Fork, California in Madera County. This was a dense (close to 100 percent canopy cover) that developed after a wildfire 40 years previously. The same three thinning treatment levels were carried out, namely control/unthinned (75 square feet per acre), and a 1/3 and 2/3 thinning. In addition to tree growth, regeneration, and forage production data, acorn yields were also evaluated using the same procedure described above. Figure 2 shows the results of three years of observations on interior live oak acorn production. Thinning resulted in a significantly higher proportion of trees with acorns in all three years surveyed.
Figure 2. Interior live oak acorn production by thinning levels.
Discussion
We evaluated the fire history of the blue oak thinning area using fire scars, and found the fire return interval from 1851 to 1966 was 12.8 years (+2.3 years), with no fires on the site since 1966. We might speculate that the historical density of blue oak stands was much lower during the period of regular fires, and the thinning created more open conditions that mimic the effects of a period of frequent, low intensity fires. The live oak stands were quite dense, following 40 years of fire exclusion. The more open stand conditions created by the thinning for both species in these studies resulted in a higher probability that a tree would produce acorns. Blue oak produces acorns that mature in the fall of the first year after spring flowering, while interior live oaks produce acorns that mature in the fall of the second year after flowering. Despite the differences in the physiological processes guiding acorn formation between these two species, these two studies show that thinning may play a key role in the yield of acorns from our oak woodlands.
- Posted By: Jaime Adler
- Written by: Douglas D. McCreary
As everyone who lives in California knows, this has been a fairly unusual year weather-wise. In the fall there was abundant rainfall, but this was followed by a January when the tap shut off almost completely. Then in March it started raining and snowing almost continuously and has only recently stopped. There was a week or two of warm weather, but now in mid-April, it has turned cold again. Here at UC’s Sierra Foothill Research and Extension Center in Yuba County, almost all of the oaks have now leafed out. The trees are especially beautiful at this time of year since it seems that each of the different oak species has a distinctive color of green. However this new foliage is quite tender and vulnerable to frost damage. Damage to new foliage occurred in Northern California three years ago when there was a late frost and many trees had their new foliage killed. Interestingly it seemed to only occur at mid elevations between 1000 and 2000 feet. At lower elevations, temperatures were not cold enough to affect the foliage and at higher elevations, the trees were phenologically further behind and hadn’t yet leafed out. Fortunately oaks have evolved under conditions where leaf damage regularly occurs (also as a result of low intensity fires or insect defoliation) and normally suffer little long-term damage from late freezes.
Another risk at this time of year is cattle poisoning. Oak trees contain toxic chemicals in newly emerging foliage, including tannins and phenols, that can be lethal to cows if the foliage is a very high percentage of their diet. A couple of decades ago there was a late spring snowstorm that happened after the oaks had leafed out. In addition to knocking many limbs and branches to the ground, the snow covered up available grass so there was little for livestock to eat besides the young buds and foliage. As a result, about 2,700 cattle died due to oak toxicity. In the unlikely event such conditions occur again, livestock operators can prevent lethal damage by feeding their animals hay or other supplemental feed when the natural grass is covered up. But it is important to start hay supplementation immediately and not to wait until cattle get sick or die. A delay of only a day or two can easily result in many more deaths and ill cattle. If cattle are in conditions where toxicity is a longer-term possibility, the use of calcium hydroxide in a supplement can prevent sickness. The addition of 10% calcium hydroxide (hydrated lime) to a supplement will still be palatable to cattle. Then if the cattle will consume about two (2) pounds of this supplement per day it will prevent many cases of oak toxicity. This supplemental calcium hydroxide has to be consumed before exposure to be effective.*
* Information about oak toxicity was gleaned from an article by UC Extension Veterinarian, John Maas in the January 2008 issue of California Cattlemen’s Magazine.
- Posted By: Jaime Adler
- Written by: Douglas D. McCreary
For almost a century there has been concern that blue oak (Quercus douglasii Hook. & Arn.), a California endemic, is not regenerating adequately in portions of its range. For the last 20 years, there have been concerted efforts to develop successful procedures for artificially regenerating this species so that it can be planted in areas where natural regeneration is unsuccessful, or in areas where it once grew but has been lost. These efforts have been successful in identifying procedures that will work, but unfortunately, such procedures often require intensive management and are costly. Since 80% of the oak woodlands in California are privately owned and the principal activity is livestock grazing, many large woodland owners and managers have marginal incomes and are reluctant to spend a great deal to regenerate oak trees.
An alternative, but untested, approach is to use naturally regenerating oak seedlings and take measures to promote their advancement to the sapling stage. This could be critical since research has demonstrated that the bottleneck for successful regeneration is often getting seedlings to grow into saplings. If successful, using natural seedlings could result in considerable savings because no effort or cost would be expended to collect acorns, or to grow and plant seedlings. An additional advantage would be that only genetically adapted plant material would be used, alleviating concerns about using “offsite” planting stock. Because of these economic, ecologic, and low input (i.e., less work) advantages, the development of techniques to advance natural regeneration holds great promise for being adopted and implemented by landowners.
To test this strategy, a study was initiated in 2007 at six field sites in the range of blue oak throughout the state. At each site, 144 naturally occurring blue oak seedlings were identified. Half of these were under the canopy of onsite trees and half were in the open. In addition, treatments included protecting seedlings with tree shelters and controlling weeds. When the plots were established, the height of each seedling was recorded. Yearly assessments of survival and height growth have been made every fall since establishment to evaluate the efficacy of the treatments.
After three years, seedlings in treeshelters have consistently grown taller than unprotected seedlings. In addition, the survival of those receiving an annual weed treatment has been significantly higher than those not receiving it. These results suggest that utilizing existing natural seedlings could contribute to increased blue oak regeneration at lower cost, thus improving the chances that this important species can be managed sustainably and conserved for future generations.
- Author: Richard B Standiford
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