The drought conditions we have had the last two years, really most of the last decade, have caused some anxiety among landowners and foresters about how the drought will impact forestry and the productivity of our forests.Does drought impact forest productivity and forest management?I don’t think there is any question that it does.But those impacts can be minor and short-term, i.e. less than 100 years.Will drought prevent us from practicing forestry and kill forest productivity?No. I hope those are not the infamous “Famous Last Words.”
As we all have seen, drought leaves evidence. Some of it is easy to see, some not so easy.We’ve all see the evidence of drought.ClickWe see trees dying. We regularly get calls about yard trees dying, but as you drive the highways look at the forests. You’ll see trees dying there, too.ClickOne of the impacts that is more difficult to see is the reduced growth. Trees need water to grow. Drought = less water = less growthClickDrought impacts tree ring size and spacing which can impact wood quality.ClickWe also will see an increase in stress that forests have to deal with.
All of those impacts have consequences for our forests. As a result we should expect to see from drought:Stress – Drought causes stress for landowners when they become concerned about losing their forests. It also causes stress for forests which can lead to increased rates of pest infestation.ClickDrought results in decreased forest growthClickDrought results in some tree mortality within forests, so stocking rates may decreaseClickDrought results in changes in vegetation.Climate has implications for the vegetation that a site will support. Short-term climate changes cause changes in vegetation. The boundary between the Great Plains and the Eastern Deciduous Forest has always fluctuated. Our forest vegetation has not always been what it is now. That is the result of changes in rainfall patterns and other factors such as fire suppression.ClickCurrently we see plants requiring moist sites surviving on sites that historically have been dry. They are off-site. A little reduction in rainfall will push those plants over the edge.
Our weather patterns have been more stressful on trees than simple drought. At the Southwest Research and Extension Center we have seen:ClickTwo years of abnormally high rainfallclickWhen water is available, trees don’t produce as much root because they don’t need to.ClickThey also grow more crown because the water is available to support more crown.ClickTwo years of abnormally low rainfallClickWhen less water is available, trees need more root to get enough water; but they also need less crown.ClickA year of moderately low rainfallClickThe result of that combination of years is stress. Trees grew larger crowns when water was easy to get. Now they can’t support the larger crowns.Result is stress, pest infestation, and tree death.
In 2008 we recorded higher than normal rainfall at SWREC.By the end of the year we were about 10 inches above normal.
In 2009 we recorded much higher than normal rainfall.By the end of the year we were nearly 30 inches above normal.Trees were fat and sassy, putting on crown like the rain would never end.
Then in 2010 the rainfall stopped.20 inches below normal.
In 2011 rainfall was 15 inches below normal.
So far in 2012 at least in southwest Arkansas we are only a little below normal. Central Arkansas is in much worse shape than we are.The result of that particular rainfall pattern is about what we would expect.Increased stress on our forests. Greater risk of pest problems. Tree mortality.
Why is water so important to trees? Same reason it is important to us.Water is the solvent that allows physiological reactions (photosynthesis and respiration) to occur.Water also serves as a reactant in photosynthesis and respiration.Photosynthesis requires sunlight and water and contributes to energy storage in the tree.Respiration requires water and energy, but as the temperature increases so does the respiration rate, thus requiring more water and energy.Trees must maintain a positive energy balance, i.e. make more than they use. Negative energy balances for too long will result in tree death.
How much water does a tree need? Large yard trees can use as much as 250 gallons a day. Forest trees have smaller crowns, so they use less water.Where does that water go?Most of the water is used by and lost from the leaves because of photosynthesis.Photosynthesis requires carbon dioxide. That carbon dioxide must get into the leaf where it can be used.Leaves have small pores called stomates that allow gas exchange – CO2 in and O2 out. But the interior of the leaf must be moist for the CO2 to be absorbed by the leaf cells so that photosynthesis can occur.One of the consequences of having those stomates open so that gas exchange can occur is that water vapor can escape through the stomates. Trees can regulate how much water is lost through the stomates by opening or closing the stomates. When the stomates close to reduce water loss, that also reduces gas exchange which reduces photosynthesis which reduces the energy produced which creates a negative energy balance.Trees must strike a fine balance between water lost and energy produced.For trees to continue photosynthesis, water that is lost from the leaves must be replaced by water from the soil.Drought results in less available soil water.Drought can push a tree into a negative energy balance.
Drought impacts photosynthesis. When less water is available, less photosynthesis occurs.When less photosynthesis occurs, less carbohydrate is produced. Carbohydrates = energy.When less energy is available, less new growth is produced. That includes less root growth.Less energy also means less production of those chemicals, “natural pesticides,” that keep the pests at bay.
What do we mean by “stress” as it relates to forests?ClickStress is the result of changes the tree must make to deal with less than ideal growing conditions.ClickChanges that a tree must make to deal with less than ideal growing conditions result in strain. In a sense, it must start pushing uphill to get things done.ClickThere are two degrees of strain.ClickElastic strain is a strain from which the tree can recover. Example: plant in a flower pot. No water = wilt, water it and it recovers.ClickPlastic strain is a strain from which the tree cannot recover. Example: my prickly pear cactus that Mom killedClickAll trees at some point deal with elastic strain. Something strains the tree, strain is removed and the tree recovers.If we see trees hitting the point of plastic strain, the tree probably should not have been on that site to start with.
How does drought stress impact a tree’s ability to deal with pests?ClickRemember, we talked about the impact of stress on photosynthesis. Drought stress reduces photosynthesis and pushes the tree’s energy balance toward the negative.ClickThat means that less energy is available for those physiological process that help keep pests out of the tree.ClickThe weakened resistance results in an increase in successful attacks from pests.ClickThe resulting decline process can last from a few years to several decades.
We should expect to see an increase in several pests.ClickHypoxylon canker.ClickBark beetles.ClickAnd root weevils and leptographium fungus in the roots.
We can manage stands to help them survive drought.ClickKeep the stand healthyClickWe have two tools to accomplish that:ClickFirst – thin the stand when it needs thinning. Have your consulting forester examine the stand to determine whether it needs to be thinned to survive the drought.ClickSecond – control the vegetation that is competing for water with your crop.ClickRecognize that the time to harvest your stand depends on the financial maturity, i.e. how quickly that stand is gaining value. Drought will impact how quickly the stand gains value. Talk to your consulting forester about whether the stand is ready to harvest.
We’ve been talking about managing mature stands. Let’s change gears a bit and talk about planting seedlings.We’ve been getting questions about planting failures and about whether people should plant trees now.Should seedlings be planted at all during drought? The answer is it depends.ClickHow do we insure success?I’m going to point out some thing we can do.ClickDo we plan for failure during drought years?We might need to recognize that success will be limited on some sites or under some conditions.
The first consideration is seedling quality. During a stressful year, you won’t get good survival with poor quality seedlings.ClickPeople ask me sometime to recommend a nursery where they can buy the best seedlings. All of the nurseries in Arkansas produce good quality seedlings. All of them also produce some lesser quality seedlings. The quality depends partly on how much you want to spend. There isn’t one best nursery. Different seedling lines perform best on different sites. The seedling needs to be matched to the site. Talk to your consulting forester about what is best for you.ClickThere are some things you can look for that will indicate seedlings in good condition.ClickThe seedlings should have a well developed fibrous root system. A good tap root is not bad, but the fibrous roots absorb the water.ClickThe terminal bud needs to be well developed and in good condition.ClickThe seedlings needs to have developed secondary needles. You can identify the secondary needles because they will be in bundles of two or three. Primary needles are solitary.ClickThe seedlings need to have developed good diameter. Runts of the litter are less likely to survive.ClickThe seedlings need to be dormant – even pine seedlings. If the seedlings have started to grow before they are planted, their root system will not be able to supply the water a growing seedling will need.
We need to consider seedling storage. Part of properly handling seedlings is storing them properly. How is that done?ClickStore seedlings in a cooler. A refrigerated truck is nice, but most of us don’t have one.ClickOften a cooler will not be available at the planting site.ClickDon’t store seedlings in the sun. Remember, when the sun moves, the shade moves.ClickDon’t leave seedlings in a truck. Under a truck is Ok. In a truck is not so good.ClickWe emphasize keeping seedlings cool because when temperature increases, respiration increases. When respiration increases, energy reserves are used up.
We need to consider environmental conditions at the time we plant seedligns. Let proper planting conditions dictate your planting schedule.ClickDon’t plant when the soil is excessively dry. Seedlings need water. If it isn’t there, survival will be poor. Remember, earlier I said there might be times that you want to put off planting for a year.ClickDon’t plant trees on warm days. We like warm late winter days. Seedlings don’t.ClickDon’t plant on windy days. Wind dries out the seedling roots while the tree planters are handling them.
We need to consider how we handle seedllings. Seedlings need to be handled properly while they are being planted.ClickPlanters should remove only one tree at a time from the planting bag. When seedlings are out of the protection of that planting bag, the roots are exposed and will dry out.ClickNever prune or knock soil off the seedling roots. Over and over I’ve seen tree planters want to cut off some of the fibrous roots to make the seedling easier to plant. The seedling needs those roots. I’ve also seen tree planters beat the seedling roots over a truck bumper to knock the loose soil off. Both of those actions will damage roots and reduce seedling survival.
We need to consider how that seedling is being set in the soil.ClickThe critical factor for seedling survival is soil moisture. The deeper the seedling is planted, the more water is can get.Soil needs to be pressed firmly around the roots of the seedling. Roots in air pockets will not absorb water.ClickHow deep is too deep? As long as the terminal bud is above ground, you’re in good shape.Foresters used to recommend planting the seedling root collar 2 or 3 inches below the soil surface. Now we tell people that 6 inches is not too much.The critical factor is to get those seedling roots into soil that will stay moist through the summer.ClickJ-rooting used to be considered a death sentence for a pine seedling. Research has shown that it wasn’t the J-rooting itself that killed seedlings. The J-rooting resulted in shallow roots that dried out. ClickSeedlings need to be vertical in the planting hole. Angled seedlings have roots that are not planted deeply enough. Planters need to use dibbles that are in good condition and need to use them properly.
There are things we can do and choices we can make before and after the planting job to improve seedling survival.ClickGood site preparation improves seedling survival.Good site preparation does a couple of things for us.clickFirst, it gets debris out of the way so the tree planters can do a better job.clickSecond, tillage provides a volume of loose soil that the seedling can quickly grow roots into.ClickControl weedy competition. That makes more water available to the seedlings. Partial weed control can yield a 20 % increase in soil moisture. Complete weed control can yield a 50% increase in soil moisture.ClickConsider containerized seedlings. They are typically planted in late fall instead of late winter. They have 2 or 3 extra months to develop good root systems before the stress of spring sets in.
Sometimes people look for the easy way to successfully plant trees during a drought.ClickThe thinking is that planting more trees will compensate for lower survival rates. On the surface that makes some sense, but it is based on the assumption that survival rates will be lower. The reality is that survival rates might be lower or they might not.What happens if the rain starts and survival is good?ClickYou now have an overstocked stand that probably will require a precommercial thinning – an added expense before the stand can generate an income.You will be better off if you pay attention to the details of doing a proper planting job. If you can’t get good survival with a proper planting job, planting more seedlings won’t solve the problem.
Dr. Ford has developed an axiom to live by if you plant trees.Click[read]Click[read]
Does anyone have any questions?
Afa 2012 effects of drought jon
Effects of Drought on Tree Growth Dr. Jon Barry, RF Assistant Professor Southwest Research and Extension Center
Evidence ofDrought• Death• Less growth• Tree rings• Increased stress
Drought andEstablished Trees • Stress leading often to pest infestation • Decreased growth • Decreased stocking • Changes in vegetation - Ecotone movement between prairie and forest - Elimination of mesic species on xeric sites
Weather Patternfor SWREC • Two years of record rain - Decreased root growth during wet periods Increased top growth during wet - periods • Two years of severe drought - Need more roots and less top during drought • One year moderate drought • Result: Tree stress and pest infection
2008 Rainfall 70Inches 60 50 40 Cum Total 30 Cum Normal 20 10 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2009 Rainfall 90Inches 80 70 60 50 Cum Total 40 Cum Normal 30 20 10 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
2010 Rainfall 60Inches 50 40 Cum Total 30 Cum Normal 20 10 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Simple EnergyBalance Model Photosynthesis Respiration Te mp er atu re r Wate and Light Energy Storage
Water Flow Water Flow impacted by wind, temperature, and humidity. Water Flow controlled by stomates There is still ﬂow when stomates Water moves are closed through xylem Water Holding Capacity of Soil Depth of Soil
Effect of Droughton Photosynthesis • Decreasing water availability decreases photosynthesis • Decreasing production of carbohydrates • Less growth - Less roots • Less production of “natural pesticides”
What is Tree Stress• Trees subject to less than ideal growing conditions.• Strain (reduction or change in function) - Elastic Strain - Plastic Strain Off-site
Stress and Pests• Reduced photosynthesis and increased respiration lends to depleted energy• Lack of energy leads to the lack of resistance to pests• Trees succumb to repeated attacks or are not able to compartmentalize• pest Process can last decades
Stress and Pests• Hypoxylon canker• Bark beetles• Root weevils and leptographium
Managing OlderStands• Maintain vigor - Thin when thinning is needed - Control competing vegetation• Recognize financial and biological maturity
Seedlings andDrought• How do we insure success?• Do we plan for failure during drought years?
Seedling Quality• All nurseries in Arkansas produce quality seedlings.• What is a quality seedling? - Fibrous root system - Pronounced terminal bud - Secondary needles - Proper caliper - Dormant
Proper Storage• Stored in a cooler and planted directly from the cooler• If not kept in a cooler - Don’t leave in sun - Don’t leave in truck• Increasing temperatures increase respiration which decrease energy reserves
Proper PlantingConditions• Don’t Plant with Poor Soil Moisture.• Don’t Plant at Temperatures > 60o• Don’t Plant at Wind Speeds > 15 mph.
Proper Handlingin Field• One tree at a time• NO ROOT PRUNING
Planting• Tight and deep! - Beyond the root collar - As long as the terminal bud is above the ground - Don’t be over-concerned with root deformation - Vertical not at an angle
Strategy to ImproveSuccess• Site preparation - Debris removal - Tillage• Vegetation control - More water• Containerized seedlings - Fall planting
Poor DensityStrategy• Plant more trees - Overstocking
Ford’s Axiom• When environmental conditions are good, the little things matter a little.• When environmental conditions are bad, the little things matter a lot.