Your question is valid however there is no answer that can be used since oaks grow in some many diverse soils and climates. Additionally, because of the variety of oak species (both tree and shrub) form, no two species will react the same to similar growing conditions. For example, I once counted the tree rings in two blue oak trees (Quercus Douglassi), one was over 6” in diameter and was 103 years old; the second was 3” in diameter and was 97 years old. There is no correlation between size and age in oaks because of the edaphic influences they are exposed to. The only way to determine the growth rate of a particular tree or stand of trees is to core the trunks and count the rings….no easy task given the hardness of oak wood.
There are a variety of ways that oak canopy can be measured. From aerial photos, you can use a dot grid to determine what percent of the dots fall on canopy, and what percent falls on ground. That would give percent canopy cover for a given stand. It’s also possible to run a series of transects. I have used 100 foot tapes and determined where oak canopy overlaps the transect. The number of feet covered by canopy would translate to percent canopy cover. A third way would be to measure the crown radius in two dimensions of a tree in fixed radius plots (1/10 or 1/5 acre plot). Using the area of a circle formula for the average radius (pi x r squared) gives square feet of canopy cover per tree. Summing up all the trees on the plot, expanding to a per acre basis, and dividing by 43,560 square feet would give percent canopy cover. There are some measurement devices, looking like a periscope that can be used to determine what percent of observations intercepts tree canopy. I personally prefer to use the line transect approach to get percent canopy. There is an Extension publication that has some good ideas: “Monitoring California’s Annual Rangeland Vegetation”, Catalog # 21486.
I’m not aware of any fungicide that could be used as a topical treatment. The bark loss is most likely related to an infection by oak root fungus (Armillaria mellea) and there are no fungicides effective in the treatment of this pathogen. The general recommendation is to expose the root crown (trunk base) to air – to allow it to dry. This is done in pear orchards where infections have occurred and it has had a beneficial effect. The pathogen is not killed, but its development slows substantially. It is believed that the same effect occurs with oaks.
GSOB larvae continue to develop in infested, dying and dead trees with green wood including logs and firewood from recently killed trees. It is important to properly manage oak firewood harboring GSOB and limit the impact of the pest. Do not remove oak firewood from local infested areas to prevent the potential spread of GSOB. Without treatment, larvae in the cut would continue to be a threat to other susceptible oaks. As of right now there are currently there are no management options recommended for live oak trees infested with GSOB. So prevention, by not bringing in infested GSOB firewood, is the best option you have right now for keeping your trees free from GSOB. Once GSOB becomes established in a new location, an outbreak has the potential to kill most of the large-diameter oak trees, leading to dramatic reductions in aesthetic quality, property values, and value to wildlife. It may also result in unexpected and expensive tree removal and tree replacement costs. You can find more information about GSOB and prevention actions as well as a community preparedness plan at www.gsob.org
You are witnessing the “jumping oak galls” that are the nursery “cells” for small predacious wasps. The female wasps lays her eggs on the underside of the leaves, the eggs and the female produce chemicals that cause the tree to grow the “galls” around the egg. As they incubate and mature the larvae begin to move causing the jumping motion that you are witnessing. We once saw a similar thing sold in stores as “Mexican jumping beans” as a worm inside the beans caused them to “jump”. The wasps are predacious on aphids, whiteflies and other small insects that are commonly found on oaks. They cause no harm to the trees are a simply a part of the “living system” found living on oaks.
It’s always a bit tricky when irrigating around the base of established oaks. I’m glad that you recognize the need to be attentive to this practice. The greatest threat to the established trees is creating an environment conducive to the spread of oak root fungus (Armillaria mellea). Most newly established plantings will not require “deep watering” so this should not be a problem since you most likely will be providing limited water to your new plants frequently. The aim should be to provide just enough water to allow your new plants to survive, maybe a gallon to each, without the need to irrigate the entire area around the base of trees. Drip irrigation (various types) work good in this type of situation. In this way you can provide sufficient water to protect your new plantings but you won’t be creating an environment that allows the fungus to overwhelm your trees.
As a general rule of thumb 50% of a trees root system is found within the dripline, 50 % outside of the zone. For ease, the drip line is most often delineated as a circle around the outside of the existing dripline. The roots will remain static following pruning, I wouldn’t assume they move in and out in a reactionary mode following pruning. In other words, before any pruning when you establish the circle identifying the root zone it would remain the same after pruning.
By far the most effective method of protecting small trees from vole feeding is through the use of an exclusionary device. Most materials will work but the most commonly used products are the ones called “tree tubes” or “tree shelters”. I’m sure you have seen them used in protecting small orchard or vineyard crops. They are flesh colored and come in various lengths. Additionally, mowing, dicing or spraying a weed free area around the base of the tree is another very effective means of limiting vole damage. They’re small animals and prefer thick cover for hiding protection. A weed free area should be considered even when using a tree shelter. Any material can be used to make your own shelter. Window screening works well as it is pliable and the mesh is such that voles cannot slip through. Regardless of what you use, be sure and monitor the trees since voles are known to burrow beneath the shield.
I am not aware of any reasonable method of estimating age of oaks from visual measurements. Blue oaks in particular grow over such a large geographic area and under such extreme edaphic (soil and weather) conditions that it has not been possible to develop the type of graphic that you are asking for. The only approach would be to “core” local trees and count the rings (no easy task with oaks due to the hardness of their wood) or to count the rings of a tree once it has been cut. Another way may be “poll” local residents who may know a history of the site and see if they can help you determine if the trees have been present during their collective memory or if some historical event comes to mind to help estimate the age of the trees.
I’m not aware of any product that would inhibit blooming in oaks though I’ve pasted your question along to some who might. I’m sure that the blooming season has passed in Contra Costa County; I suspect it was in early March.
The problem may be related to summer irrigation of the oaks, which is highly conducive to oak root fungus infections and water mold root rot infections (Phytophthora spp). Many oaks decline as the result of summer irrigation – blue oak included. If the problem is related to summer irrigation, then it would be good to change the understory from irrigated landscape to mulch (wood chips, bark, or natural leaf and twig litter) or plants compatible with oaks. We identify such plants in chapter 5 of Oaks in the Urban Landscape (UC publication 3518) and give a fair amount of info regarding appropriate cultural practices for oaks. The key element to change is the irrigation – maintaining relatively dry conditions around the base of the trunk in the summer months is very important for CA native oaks.
Acorn production on the coast is relatively light this year. In most mixed species stands each species may have a few acorns but no one species appears to be dominating. Valley oaks (again on the coast) seem to be absent of nuts this year…not unusual since they are considered cyclic in their nut production. As for pre-contact issues, a.k.a. in the times before Costco, low acorn years meant people had to rely on other food sources for survival…as do all vertebrate species currently living in oak dominated landscapes. Often times, though it may be a “bad acorn year” one tree will have a relatively high concentration of nuts and was most likely an important resource for local people. The seasonality of acorns coincides with other seasonal foods within the oak range i.e. grasshoppers, grass seed heads, salmon, steelhead, suckers, sturgeon, and soft mast (berries). Folks would have had to have been resourceful to survive. You may wish to look up the book “Before the Wilderness” by Thomas Blackburn and Kat Anderson, Ballena Press, 1993.
Less is more when it comes to fertilizing mature oaks. I wouldn’t fertilize unless there was a significant reason for doing so — such as a lab report that says an element is deficient. You may want to check chapter 5 in UC publication #3518 “Oaks in the Urban Landscape” – there is a section on fertilization. We highlight this publication on our Urban Oak Care page.
You are right in that the two are coincidental and not related. Most likely the ants are attracted to the trees because of the presence of Homopterid insects (aphids, whiteflies, scale). The ants will tend these insects for the sugary honeydew that they produce and use it as a food source. The hollow trunks are most likely the result of fungi/bacteria, fire and time. In some cases past fire events can create an injury that over time will result in a hollowing of the interior heart wood from secondary pathogens. Likewise, fungi/bacteria can enter into the tree from a host of causes, wind damage, insects, etc. Most likely the trees with the hollows are quite old, regardless of size, and have been exposed to a number of pathogens that have impacted the wood.
During years of drought tree growth is usually arrested, if the drought persists for a prolonged period of time the encumbered water-related stress can lead to other secondary problems of pests and disease affecting both individual trees and stands of trees.
Tree selection – As you know some trees are more “drought resistant” than others. Usually this means they have some physiological characteristics that allow them to conserve water better than others. This can be observed by early leaf drop, leaf stomata being closed during daylight hours to reduce transpiration or even an evolutionary trait of going into summer dormancy.
Irrigation – is usually important in tree seedling establishment for the first summer or two. Most woody plants are relatively able to survive under “normal” precipitation regimes once established.
Landscape zones – if I understand the concept you are providing it usually means not mixes plants that have high irrigation needs with those who are irrigation sensitive. In the case of oaks, it is usually not recommended to plant turf grass around oaks since one (the grass) needs frequent summer irrigation while the tree (oak) may not need any.
I think you are mixing two concepts here. The “role” irrigation plays is it 1) establishes plants; or 2) keeps them alive. The conflict of water use between agriculture and urban needs has little to do with plant biology and is function of local, regional or statewide policy. In the case of limited or expensive water “a farmer” would have to make a personal choice on how extensive of planting they are able to consider on a yearly basis. In other words if a farmer wanted to plant 10 acres of trees they may have to plan to do the planting over period of time to accommodate both availability and costs. For example perhaps planting the 10 acres at a rate of 2 acres/year over the course of 5 years could be considered to meet these conflicting values.
The track record on oak transplants isn’t very strong. Key questions are: (1) how much of the oak woodland resource is actually transplanted to the new location; (2) what are the resources at transplant site, and how will they be impacted; and (3) is there a reason why oaks don’t occupy the transplant already, and will affect the success of the transplant. The cost varies with the size of the tree and the time they are held between removal and replanting, but 40 ft. trees cost between $10,000 to $15,000 each; and specimen or land mark tree range have ranged up to $350,000. In general, oak transplants leave behind most of the wildlife and plants associated with the original oak woodlands. Transplanted oaks need to lose much of their canopy and root systems to survive the stress of movement, and process challenges oak tree symbiotic organisms – live mycorrhizae. So the end result is a tree of small structure (15 to 20 ft. of sparse canopy) that slowly dies or is attacked by pests and pathogens. These can be nursed in a horticultural situation, but over 75% don’t survive in wildlands – even with some care and watering. Transplanting oaks into a disturbed site can be environmentally neutral, but past oak tree transplants have been placed onto coastal sage scrub, rare plant locations, archeological sites, and other sensitive resources with negative environmental consequences. There are places where oaks have failed to recolonize sites where they have been removed. But wildland locations without oaks are often places where oaks can’t grow. So oak transplants often fail to pass muster as mitigation; and the cost/benefits make them suspect for oak tree salvage or rescue. I can provide you with some results on transplanted oaks.
Certainly herbicide application to the stump or emerging sprouts can be effective. So if you measure “success” as dead stumps, then chemical treatment is a viable option. However, providing a suitable forage crop for deer may be desirable since I would think the shade provided from the remaining trees would constrain the stump growth. If the harvesting takes place this winter, you could delay any stump treatment until the following year to evaluate % sprouting, impacts of herbivory and it provides an opportunity to “replace” trees if the cutting is too heavy. A relevant study was conducted on sprouting in Shasta and Tehama Counties. The study has models of sprouting probability. Areas that had been treated to keep stumps from resprouting were tested, and a significant number still did sprout.
The seed source is not a factor when addressing these criteria. Wind resistance is a function of lignin in the wood which develops as a result of the young tree’s ability to “sway” in the wind. If a nursery specimen, or newly planted sapling, is staked too tightly it will grow as a vine, not a tree, and be wimpy (technical term). If allowed to sway over time, the nursery tree should have the same level of wind resistance as a naturally occurring acorn (allowing that the roots are able to develop normally).
First, you need to consider what factors are causing the old tree to “show its age.” Is it surrounded by asphalt, subject to intense heat and poor oxygen soil circulation? If the old tree grew in a “natural” setting, then it’s possible it could survive for many more years but would continue to decline. Urban trees pose liability problems when they begin to decline. It’s possible that any “new” tree will not be growing under optimum conditions and may last only ½ as long as the old tree before it starts to “show its age”.
Limit excessive summer water, minimize impacts/compaction within the root zone, prune out existing dead wood, minimize live wood pruning, clean cavities of duff and moisture, and limit human traffic beneath the canopy.
That number is fairly arbitrary. In the past, the arbitrary number to constitute a woodland has been suggested at 10% of the area covered by the tree’s canopy.
Decline, parasites and decay are part of a trees life cycle. If the tree is not in a position to cause damage to structures or people if a limb should fall then I would suggest simply leaving it. The mistletoe provides winter berries for birds, the dead branches provide for insects, even the decay provides habitat elements for other organisms.
The plants should be those that do not require extensive summer water. Obviously, California natives would be a good fit. Certainly he should avoid invasive ground cover plants such as English ivy, Vinca (periwinkle) that are very aggressive and can overtake a site quickly. I suggest that your brother contact the Bay Area Chapter of the California Native Plant Society to seek their advice.
Severe alteration of the root zone should always be avoided to protect the integrity of the tree. It would be difficult to assume that the rapid decline of the tree is simply a coincidence in this case if the alteration is what you describe. If one half of the roots of a large tree have been negatively impacted, then I would expect the tree to exhibit signs of stress.
First, Blue Oaks tend to be good sprouters. The sprouts can provide suitable browse for deer and also perches for rodents, like ground squirrels. If maintaining attractive wildlife forage and other habitat elements is desirable this may be a consideration. Leaving the stump will prove to be an obstacle if range seeding is desired in the future. The stump will eventually decompose into the soil. However, the loss of annual leaf fall has shown to affect soil productivity over time. The loss of annual leaf fall will affect grass productivity more that retaining the stump. Simply cutting down the tree and leaving in place is the least expensive. Removing the tree adds the cost of time and energy to transport the tree off site. Finally, removing the stump is another cost factor since heavy equipment will be needed to remove the stump, fill the hole and remove the stump from the site. All of the discussion points have merit.
You might also take a look at a recent article in Cal Ag on oak thinning in Shasta and Tehama Counties (Standiford, R.B. D.D. McCreary, S. Barry, L.C. Forero. 2010. Blue Oak Stump Sprouting on California’s Northern Sacramento Valley Hardwood Rangeland. California Agriculture 65(3):148-154.) The Guidelines for Managing California’s Hardwood Rangelands also has some good information about thinning recommendations for landowners.
Moving large trees is not the problem. Moving large trees and having them survive after the transplant is the problem. It’s a costly effort with unpredictable outcomes. Here are some considerations and consequences if you try to move oaks in wildland settings. Transplanting a wild oak will never recreate the original tree at a new location, or duplicate the resources it provided at its old location. A transplanted tree will usually lose a large part of its canopy. Severed root mass will disrupt water/nutrient uptake, as fine roots are damaged by the movement. It is also important to consider if transplantation site currently has oak trees. If oak trees are absent, it may indicate a lack of subsurface water, soil depth or insufficient soil chemistry to grow and maintain oaks. Therefore, even with a great deal of care there may not be a way that the new site can support an oak that developed in another, probably better location, as the oaks will be forced to respond to a completely different set of soil, substrate, and moisture conditions. The transplanted oak will be a dramatically altered resource, and you have to decide how much time and resources you want to put into the transplant process given a diminished and uncertain outcome. Tree spades are at the low end of commitment of transplanting effort, often with low rates of success and survivorship. Boxing the oak tree’s roots is a costly process that increases the probability of a tree living after transplant, but the success rate is still low.
These situations are always difficult to deal with since the prevention of this type of disturbance is what should have been done in the first place. Your approach sounds reasonable. The only other plausible idea would be to “clean up” any damage to the existing roots by using proper pruning techniques to eliminate any “frayed” ends that may have been damaged. Proper pruning is one of the best ways to minimize pathogens from getting started in open wounds.
There doesn’t appear to be any “standard” planting distance between oaks, and each species has different growth patterns. I do agree that 5-10 feet is too close for any species. However, another way to look at the situation may be to consider that not all of the plantings will survive. In addition, not all of the trees may have a desirable shape or degree of vigor and the plantings can be thinned after the trees have become established (3-5 years). Ultimately, spacing may be 15-30 feet between trees depending on your aesthetic or ecological future desired condition.
Care of oaks around a recreational center is not different than trees located in other high traffic areas. Simple steps can be considered to insure the long-term health of your trees e.g. do not over irrigate oaks during the summer, do not park vehicles or other heavy equipment under oaks, limit disturbance of soil between the trunk and the drip line, apply limited and proper pruning techniques only to achieve specific objectives. As for student assistance, you might want to check with your local community college’s horticulture or an instructor to see if any possibilities exist in your area.
The tubes are intended to provide increase CO2 concentrations to improve tree growth. If the new trees are seedlings, you can irrigate them weekly for the first summer and that will increase growth dramatically. After the first year monthly watering will increase growth. One question is to ask, “Protect the trees from what?” If the trees are in a secure location you may not need additional protection. Other screening materials can be used e.g. poultry wire, window screening, and milk cartons. Again, it depends on what is causing the risk to the trees. Providing a weed free zone around the young trees is also important. Manually scalping weeds, using mulch, or an herbicide to create a 2 to 4 foot weed free radius around the trees will help conserve moisture, and reduce rodent browsing pressure on the trees.
Yes, weed wacking is perfectly acceptable around the base of oak trees. One word of caution is to be careful that the trimming string does not strike and damage the bark as it could lead to other problems in the future. As for the poison oak, any means that works for you would be compatible with the oaks – hand pulling, chemical application, tilling, or goats.
Generally, in Orange County, there’s a problem with powdery mildew on coast live oak. Consequently, it’s recommended to prune in the summer, after new foliage has matured. Therefore, you can still prune your tree, but it is recommended that you identify specific reasons and/or goals for pruning and then select the appropriate pruning practices that will accomplish your goals. Tree maintenance guidelines, developed with the help of UC input, require that all pruning follow current ANSI and ISA guidelines. For oaks, avoid pruning unless necessary for safety, clearance, or the health of the tree. In Orange County, powdery mildew is generally not a problem, but summertime cankers are not uncommon. If you have concerns about canker-causing pathogens, then summer pruning would be best. If this is not a problem, then winter or summer will work. If you haven’t pruned this year, then I’d wait until summer and just do safety, cleaning, and clearance pruning. All “trimming” should be light selective cuts. The “best” time is when the trees are still dormant (at least in Northern California). In Orange County, you may be seeing bud break already, if that’s the case I would trim very lightly for now and wait until next winter for more extensive, but still selective trimming. If you want more info on this subject, see Chapter 5 of “Oaks in the Urban Landscape,” UC ANR Publication 3518.
A very effective mean of removing poison oak is with the use of grazing animals. Herbivory, or grazing, not only removes the above ground portions of the plant but over time, the roots will become starved of their carbohydrate stores and the plants eventually collapse. Sheep would also work but would require fencing, whereas goats could be tethered and moved around the property to target the plants. Another approach would be to severe the plants near the ground and spray the emerging sprouts with glysophate (Roundup®) when the shoots are very small. As long as the chemical does not come in contact with the oak leaves, there should not be any negative impacts.
Unfortunately, there isn’t a precise, clear answer. Tree density is a function of tree species, soil types, ground cover type, percent slope, aspect (north or south), and past land use practices (tree harvesting, grazing). The number you have (120 tpa) might well be an acceptable figure for some areas but I would not consider it a number that can applied across an entire county given the variables I mentioned.
In most cases, people would use available technologies (aerial imagery, Google Earth, etc.) or ground truthing to determine tree density for a particular area as you indicated for the ¼ acre. However, take caution when using that number for other sites unless more information was included. A source of county-based oak information is the Calfire Forest and Range Assessment Program (FRAP), at http://frap.cdf.ca.gov/ . I would suggest you search this site to see if you can find the type of information that may be useful for you.
As for reproductive maturity for oaks, again a number of factors come into play (i.e. species, soil, and age). Oaks have the ability to grow over such a large spectrum of soil types that there isn’t one set number that can be applied for either determining age or reproductive maturity. However, it has been estimated that oak maturity is about 30 years.
It is important to remember that both the above and below portions of the tree will grow proportionately over time. The prudent approach would be to select the spot that provides the most opportunity for the tree to grow with the greatest space available for root growth, trunk growth, and limb expansion. In addition, keep in mind that it may take 20-25 years for the tree to fill in the space you provide for it.