The Long & Winding Road (Regenerating Oaks Naturally) Patrick Brose USDA Forest Service Northern Research Station Irvine, PA
Acknowledgements Many of the details, graphs, and photos, I will present today come from my colleagues. Contributors include Bob Long, Aaron Stottlemyer, Gary Miller, Kurt Gottschalk, Tim Frontz, Scott Stoleson, Tom Waldrop, & probably somebody I overlooked.
So you want to create a new oak forest from an existing one? 100-year-old mixed oak stand on a better quality growing site. Plenty of red maple poles and saplings. No oak seedlings. Plan on a 10 to 20 year odyssey of aggravation and frustration. WHY?
The Oak Regeneration Process Flowering Seedling Development Acorn Development Seedling Establishment
Flowering Most oak species begin flowering between 15-25 years of age in forest stands. Oaks are monoecious (both flowers on same tree). Flower buds are formed in mid- to late summer of the previous year. A number of studies have shown that annual flower crops are surprisingly regular. Female flower Male catkins So if flower crops are regular, why aren t there regular acorn crops?
ACORN PRODUCTION IN WESTERN VIRGINIA, 1973-1995 90 Red oaks White oaks 80 70 60 50 40 30 20 10 0 1973 75 77 79 81 83 85 87 89 91 93 1995 Year
Flower and Bud Insects There are at least 46 species of insects that feed on oak buds, flowers, and pollen. These can reduce flower production, pollen production, and fertilization. Oak treehopper adult
Pollination Oak pollen is wind dispersed. Maximum pollen dispersal from an individual oak occurs over a 2-3 day period, but the oak pollen season may last 2-4 weeks. Optimal weather for pollination are warm, dry, breezy days. Cool, rainy, foggy weather substantially reduces pollen dispersal.
Frost The MAJOR Weather Problem
Acorn Development Slow at first then embryo growth accelerates in mid summer (1 st year for WO, 2 nd year for RO). Crown size, canopy position, and species are important factors in acorn development. Acorns are loaded with carbohydrates and fat. Also, some protein and minerals. A popular food for a wide array of insects while they are still in the tree.
INSECTS OF ACORNS GENUS Curculio 11 EASTERN SPP. (9 + Attack acorns) WEEVILS - CURCULIONIDAE Female chews hole in acorn and deposits a single egg before the acorns ripen PHOTO COURTESY FORESTRY IMAGES
INSECTS OF ACORNS WEEVILS - CURCULIONIDAE Larvae feed in the acorn for several weeks before cutting exit holes in the shell Larvae spend 1-2 years in soil before pupating Major portion of acorn crop may be destroyed, especially if co-infested by other insects. PHOTO COURTESY FORESTRY IMAGES
INSECTS OF ACORNS FILBERTWORM Melissopus latiferreanus Female lays egg on outside of acorn Larva bores into and feeds on acorn PHOTO COURTESY FORESTRY IMAGES
INSECTS OF ACORNS GALL WASPS - Callirhytis fructosa Stony gall Gall replaces the seed Several larvae per acorn PHOTO COURTESY FORESTRY IMAGES
Pip Galls caused by Cynipid Wasp Callirhytis operator Single larva per gall The galls themselves do not destroy the acorns
Squirrels cut the immature acorns in August and chew away the edge of the cap to get at the galls. So that they can feed on the cynipid wasp larvae inside the gall.
Other important acorn insects Weevils of the genus Conotrachelus Conotrachelus cannot infest a sound acorn. Acorn moth Valentinia glandulella Valentinia is a secondary invader. Acorn shell must be damaged.
Weather-Related Acorn Losses Generally, weather causes few losses to a developing acorn crop. The one exception drought. Oaks will abort acorns to protect against droughtincited decline and mortality.
Gypsy Moth
Aborted acorns due to gypsy moth defoliation
Pounds per Acre Effect of Gypsy Moth Defoliation Level on Sound Acorn Biomass Production (McConnell 1988) 400 1985 300 1986 200 100 0 None Moderate Heavy Defoliation Level
Acorns per Acre (1000's) Effect of Gypsy Moth Defoliation Level on Total Acorn Production (McConnell 1988) 700 600 500 400 300 200 100 0 Defoliation Level Undeveloped Partially Developed Fully Developed None Moderate Heavy
1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 Pounds per Acre Acorn Production in a Mature Mixed Oak Stand Huntingdon County, Penn. Game Commission (1995) 600 500 400 300 200 100 White Oaks N. Red Oak Other Red Oaks 0 Year (Years with Defoliation)
The Acorn Seedling Transition
Forest Floor Obstacles to Establishing Oak Seedlings Optimal seedbed is a thin O horizon (litter & rootmat). In this environment, an acorn is easily buried and can get the radicle into mineral soil. If litter and/or rootmat are > 2 inches thick, then these become obstacles to oak seedling establishment.
Insects and diseases will kill recently-fallen acorns A study of the 2001 acorn crop at Clear Creek SF in northern PA found that 33% of the acorns became infested or infected after they were on the ground.
Weather too Acorns must maintain 30 50% moisture content to remain viable. That same study found that nearly 50% of the acorns were killed by desiccation during the 2001-02 winter (cold, dry, & windy with little snow).
Fire too Several studies report 40 to 90% loss of viable acorns to fire.
Acorns as Wildlife Food Wildlife known to eat significant amounts of acorns:
Acorns in Wildlife Diets At least 90 species eat acorns in Mid-Atlantic region. The MAJOR hard mast source since the loss of the American chestnut. So important that mast crops significantly affect wildlife behavior. Numerous studies report wildlife consume from 5 to 95% of an acorn crop.
How Do Acorns Avoid Bugs, Crud, Desiccation, Fire, & Wildlife? With a little help from some friends. Blue jays and tree squirrels are scatter hoarders. They bury single acorns in edge areas and areas with thin leaf litter.
Germination Rate (%) NRO Germination Rates 120 110 100 90 80 70 60 50 40 30 20 10 0 B A L L/F L/HC L/F/HC B B/F B/HC B/F/HC Treatment
Oak Seedling Soil Requirements Forest floor and underlying mineral soil are both important, but often overlooked or minimized. Generally, oak seedlings grow fastest when there is adequate soil moisture and soil nutrients. Their exact needs are not well researched in forest environments.
Oak Seedling Soil Requirements Ectomycorrhizae are essential for oak seedling survival. Low soil ph and lack of soil calcium and magnesium (Acidic Deposition) implicated in loss of ectomycorrhizae and poor seedling growth. Long et al. 2012 COULD NOT substantiate the calcium & magnesium theory in a detailed, replicated study. Other soil nutrient needs not well researched in forest environments. New oak soil research underway on Tuscarora SF.
Seedling Root Diseases Damping-off fungi Pythium Rhizoctonia Phytophthora Cylindrocladium Root rotting fungi Armillaria spp. These attack and kill new germinants
Oak anthracnose Seedling Foliage Diseases This group of diseases are compound interest diseases with repeated cycles of spore production and infection if weather conditions are favorable (a cool, wet spring). In those years, an entire cohort of seedlings can be killed by anthracnose
Losses to Small Mammals New seedlings are clipped off just above the ground. Top of seedling is NOT eaten. Happens during the early summer. Looks like cutworm damage of vegetables. Seems to occur most frequently in areas with abundant woody debris. Not sure who the culprit is. In CA, gophers and voles kill thousands of oak seedlings in this manner.
Two major sources. Late frosts damage or kill the newly emerged leaves. Oak seedling does not yet have the root reserves to sprout from basal buds. Drought can wipe out new oak seedling cohorts before they have developed root systems and stress well established seedlings. Effects of both can linger for several years. Losses to Weather
Fire Small oak seedlings are virtually defenseless against fire because they haven t yet developed their root systems. Growing-season fires (after leaf expansion) are especially devastating to small oak seedlings.
Up to this point in the regeneration process, losses of acorns and oak seedlings can be small or substantial. However, substantial losses to these factors are often localized and temporary. Consequently, many oak forests will have a pool of small oak seedlings that continually recycles. The BIG oak regeneration problems are about to begin. Reality Check
The BIG 3 (CDL) Competition from other hardwoods and interfering vegetation Not Enough Light Excessive Deer Browsing
Seedling Competitive Reproduction Growing oak seedlings to a competitive size is the MAJOR bottleneck in the oak regeneration process for much of the eastern United States. Transition Involves growing oak root systems. Competitive size and oak root development are highly dependent on sunlight, site quality, composition of competing species, and deer browsing.
Root Collar Diameter (mm) Sunlight Effects on NRO Root Development 25 1 inch Full Sun 20 ¾ inch 15 50% Sun ½ inch 10 5 ¼ inch 15% Sun 5% Sun 0 1 2 3 4 5 6 7 8 Years Since Planting
Root Collar Diameter (mm) Sunlight Effects on Roots of Other Oaks 25 1 inch 20 ¾ inch 15 50% Sun ½ inch Full Sun 10 15% Sun 5 ¼ inch 5% Sun 0 1 2 3 4 5 6 7 8 Years Since Planting
Sunlight Effects on Oak Seedling Growth
Sunlight Effects on Oak Seedling Growth At 15% sun, oaks are small, but so too are the competitors (maple). At full sun, oaks are tall, but only half the height of the competitors (birch).
Deer Can Slow Or Stop Oak Seedling Development What? Don t blame me, its those darn coyotes fault!!!
Proportion of Surviving Seedlings (%) Sunlight & Deer Effects on Oak Seedlings Brose, Northwest PA Study 120 Control Fence Shelterwood Fence + Shwd 100 80 60 56% 40 20 0 2002 2003 2004 2005 2006 2007 2008 2009 28% 24% 2%
Percent Sunlight & Deer Effects on Oak Seedlings Gary Miller, WV Study 100 90 80 70 60 50 40 30 20 10 0 67% 36% 23% 14% Herbicide & Fence Fence Herbicide Control 0 1 2 3 4 5 Years since treatment
Feet Deer Effects on Oak Seedling Growth 0.5 0.4 0.3 Gary Miller, WV Study 0.2 0.1 Fenced Unfenced 0 High Medium Low Control Amount of Sunlight
The Oak Regeneration Process 10 to 20 years Can we do anything to speed up the process?
Make Use Of Oak Stump Sprouts Bypass the flowering, acorn development, and seedling establishment stages of the oak regeneration process and all their associated pitfalls. But, they come with their own set of regeneration problems.
Obstacles to Oak Coppice Silviculture Subject to several foliar diseases Not all oak stumps sprout Deer love to eat them Weak attachment Prone to ice, snow, and wind damage
Grow Oaks Where They Want To Grow The regeneration process is already underway (oak seedlings present). Generally, the drier sites do not have as severe of competition/interference issues as moister sites. Dense shade is less prevalent. Oak seedlings achieve competitive status at smaller sizes. (Dry Sites)
Dry Site Obstacles While this approach does potentially sidestep some of the oak regeneration obstacles, it still can encounter many of them. Thick Duff Deer Mountain laurel Bugs & Crud
Use Artificial Regeneration
QUESTIONS (ON NATURAL OAK REGENERATION)