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U. S. Department of Agriculture
Forest Service Research Paper 50-104
Natural Regeneration and Development
of Nuttall Oak and
Associated Species
Southern Forest Experiment Station Forest Service
U. S. Department of Agriculture
1975
Johnson, Robert L.
1975. Natural regeneration and development of Nuttall oak and associated species. South. For. Exp. Stn., New Orleans, La. 12 p. (USDA For. Servo Res. Pap. SO-104)
Nuttall oaks from a dense seedling catch survived for 5 to 10 years in complete shade and for 15 years with 1 or 2 hours of daily sunlight. They made little growth, but they responded well when released after periods of 1 to 9 years. Green ash, water hickory, and sugarberry survived equally well and outgrew the oaks after the overstory was removed. Additional keywords: Quercus nuttaUii, green ash, Fraxinus pennsylvanica, water hickory, Carya aquatica, sugarberry, Celtis laevigata, stand development.
Johnson, Robert L.
1975. Natural regeneration and development of Nuttall oak and associated species. South. For. Exp. Stn., New Orleans, La. 12 p. (USDA For. Servo Res. Pap. SO-104)
Nuttall oaks from a dense seedling catch survived for 5 to 10 years in complete shade and for 15 years with 1 or 2 hours of daily sunlight. They made little growth, but they responded well when released after periods of 1 to 9 years. Green ash, water hickory, and sugarberry survived equally well and outgrew the oaks after the overstory was removed. Additional keywords: Quercus nuttaUii, green ash, Fraxinus pennsylvanica, water hickory, Carya aquatica, sugarberry, Celtis laevigata, stand development.
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Natural Regeneration and Development Of Nuttall Oak and Associated Species
Robert L. Johnson '
Nuttall oaks from a dense seedling catch survived for 5 to 10 years in complete shade and for 15 years with 1 or 2 hours of daily sunlight. They made little growth, but they responded well when released after periods of 1 to 9 years . Time of release did not affect subsequent surviv al or growth. Green ash, water hickory, and sugarberry surv ived equally well and outgrew the oaks after the overstory was removed. After 15 years, the largest ashes were 5 to 10 feet taller and 1.5 to 2 times larger in diameter than most Nuttalls. On the better sites and where openings were one-fifth acre or larger, trees emerged from the vines in 5 to 10 years . Additional keywords: Quercus nuttallii, green ash, Fraxinus pennsylvanica, water hickory, Carya aquatica, sugarberry, Celtis laev igata, stand development.
Most bottom-land hardwood forests in the Midsouth are mixtures of many species and age or size classes. Conditions are the results of single-tree selection cutting in stands under some management and of diameter-limit cutting in unmanaged stands. In many forests, frequent harvesting has greatly decreased the proportion of oaks. This decline is significant, since oaks are the species most used by southern hardwood industries.
The study reported here offers strong evidence that silviculture must become more intensive than at present, if oaks are to continue to predominate in bottom-land hardwood forests. The data apply specifically to Nuttall oak (Quercus nuttallii Palmer), a red oak that is common to the Mississippi Delta and adjacent river bottoms. But ongoing research indicates that similar results can be expected with other oaks on other sites.
THE STUDY The study was in a mixed stand of uneven-aged hardwoods
on the Delta Experimental Forest near Stoneville, Mississippi. Soils were deep clay, classified as either Sharkey or Alligator. There 1 The author is Principal Silviculturist at the Southern Hardwoods Laboratory, which is maintained at Stoneville, Mississippi, by the Southern Forest Experiment Station, Forest Service--USDA, in cooperation with the Mississippi Agricultural and Forestry Experiment Station and the Southern Hardwood Forest Research Group.
were three major sites, differing mainly in elevation: ridges, with the sweetgum-water oak combination; flats, with the elm-ash-hackberry-Nuttall oak association; and sloughs, with the overcup oakbitter pecan type. On such sites, difference in elevation between ridges and sloughs may be no more than 6 feet, while ridges and flats are almost indistinguishable to the uninitiated.
Between November 1957 and May 1958, unusual circumstances resulted in the establishment of thousands of Nuttall oak seedlings directly under large seed trees. A very good crop of acorns matured in the fall of 1957, and rainfall from November through May was heavy. Water standing on the study area protected and stratified the acorns and provided a moist seedbed. High June temperatures triggered rapid germination before the surface soil dried and became unsuitable for seedling establishment ( fig . 1 ) .
Fifty stands of Nuttall reproduction were selected over a 40-acre area. All were directly under seed trees that averaged 60 to 80 years old, 100 feet tall, and 16 to 24 inches in d.b.h . A fully shaded 4-milacre plot, 13.2 by 13.2 feet , was located in each stand.
Figure l.-Typi cal dense stock i ng of I-year-old Nuttall oak seedlings on study plot s. Inset : Seedbed conditi ons w er e so favorable that some seedlin gs originated from acorns lying on the surface; normally acorns must germinate underground if seedlings are to become established.
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Plots had from 211 to 1,521 Nuttalls; the average was 552 , or the equivalent of 138,000 trees per acre.
Initially , five treatments were assigned at random: release after 1, 2, 3, and 4 years , and no release ( check plots ). Each treatment was applied to 10 plots. As the study progressed, however, three of the checks were found to have consistently heavier seedling stands than the other 47 plots. When it had become clear that 4-year-old Nuttalls would respond to release, these three plots were released after 9 years. In the rest of this paper, they are considered as a sixth treatment, and information about the check treatment is from seven plots only.
Annually for 12 years, and then after 15 years , trees on each plot were counted and tallied by species. Heights of the 12 tallest oaks per plot were measured and tagged. As other oaks became dominant , they too were tagged and measured. After the first year, plastic expansion rings were placed around the base of each oak in a plot to maintain identity of original trees.
After the fifth year , heights of the tallest tree of each competing species were tallied on each plot. Starting a year later, conditions in and around each plot were described. Noted were size of opening, interspecies competition, weed and vine competition , growth characteristics by species, depth of standing water (relative soil moisture conditions) , and rodent damage. In 2 separate years , size of opening was estimated by using a range finder to measure distance to the surrounding overstory.
Plots were released by cutting all competing trees 1 inch d.b .h . and larger during the dormant season . Diameter of the opening varied but usually was equal to at least half the height of the surrounding overstory.
RESULTS Released Plots
Except for one or two cottonwoods in each of three plots, practically no new seedlings became established after release. But it became apparent immediately that the Nuttalls would have to compete with advance reproduction and sprouts of green ash (Fraxinus pennsylvanica Marsh .), water hickory (Carya aquatica ( Michx. f.) Nutt .), sugarberry (Celtis laevigata Willd.) J and a scattering of other species. Usually the advance reproduction-of which ash was the most common-was lopped back to ground level when the overs tory was removed, but some trees 6 to 7 feet tall were left intact. While sprouts were mainly from cut reproduction, some were from saplings and poles ( fig . 2 ) .
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Figure 2.-Much of the green ash r eproduction originated as sprouts from stumps of cut trees. All sprouts in these photos are 6 y ears old. Note that the largest emerge from the largest stump.
A verage reduction in stocking followed a similar trend over time for stands released from 1 through 4 years ( fig . 3). Star ting with 125,000 to 150,000 trees per acre, stocking declined about 95 percent in 15 years-to 9,000 trees per acre, of which 6,000 were Nuttall oaks. Approximately three-fourths of the oak mortality occurred during the first 7 years . Trees of other species accounted for less than 1 percent of stocking in 1958 but for about one-third in 1972. Half of all trees greater than 10 feet tall in 1972 were of species other than Nuttall.
All plots followed a similar pattern of development. Within a year or two after release, they were invaded by vines, mostly peppervine (Ampelopsis arborea (L.) Koehne ) and trumpetcreeper (Campsis radicans ( L. ) Seem.). In 3 or 4 years, tree reproduction was completely covered by a dense mat of vines. The vines persisted until stands averaged 15 to 20 feet tall, or on the better sites for about 8 to 10 years after release. Plots with less than 10,000 trees per acre, those in openings of less than 1/ 5-acre, or those with poor moisture conditions were slow to emerge from the vines. Almost one plot in three was still in the vine stage 11 to 14 years after release.
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180r---------------------------------------------,
Figure 3.-Stand density (aU species) by year of release .
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Species varied in reaction to the vine competition. Nuttall oak and water hickory reproduction tended to be stout and slow to add height growth. Trees of these two species developed en masse, pushing the vines up until eventually the whole stand was clear. Both sprouts and advance reproduction of ash grew rapidly above the oaks and water hickory. Vines climbed individual ash trees and pulled the terminals over to within 3 or 4 feet of the ground. At this stage, it appeared that the ash would not survive or at best would develop very poor form. But within a year or two, a lateral became dominant at the point where the old terminal was bent over (fig. 4). The old terminal died and dropped off, and the bole had only a slight bend. Sugarberry reacted to vines about as ash did, but was not so consistent.
Figure 4.-This ash terminal (indicated by the machete point) was pulled over by vines. A new leader took over at point of bend. The old terminal win soon drop off, leaving the main stem with a curve so slight that it win be of little consequence when the tree is harvested.
Among the four most common species, green ash was the fastest grower and Nuttall oak the slowest. Growth varied considerably both within and between treatments (table 1). Eleven to 14 years after release, dominant ash were 30 to 35 feet tall and 3.0 to 3.5 inches d.b.h. or about 5 to 10 feet taller and 11;2 to 2 times larger
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Table I.-Average size and range: after 15 years, of the tallest Nuttall oak per plot and tallest tree among competing species
Age at Height Diameter at breast height r elease Plots
(years) Oak I Competitor Oak I Competitor
No. - - - - - - Feet - - - - - - - - - - Inches - - --
1 10 7.1 16.9 34.0 8.9 20.9 33.0 0.1 1.2 2.6 1.0 1.9 3.7
2 10 7.0 15.2 25.0 16.2 22.8 36.0 .2 1.0 1.9 1.0 2.0 3.4
3 10 7.1 13.5 19.3 8.8 20.5 31.0 .3 .8 1.3 .7 1.9 2.9
4 10 2.5 15.3 25.0 11.6 22.6 38.0 .0 1.0 1.9 .7 2.4 5.1
9 3 14.8 15.2 15 .5 19.5 22.7 25.5 .7 .8 1.0 1.6 2.4 3.6
Not r e leased 7 2.2 2.9 3.3 2.6 10.1 13.5
I Values in bold face are averages, others are ranges.
in d.b.h. than most Nuttalls (fig. 5). Ash was dominant on 44 percent of the plots, sugarberry on 15 percent, Nuttall oak on 13 percent, water hickory on 5 percent, and other species on 23 percent. When trees outside as well as on the plots were considered, ash was either dominant or codominant with one or more other species on 71 percent of the plots. Sugarberry was dominant or codominant on 24 percent, Nuttall oak on 10 percent, and water hickory on 7 percent.
Annual growth was not uniform by species, years, or plots. Oak seedlings changed crown positions almost annually, generally because of vine development or a sudden spurt of growth. Few oaks retained dominance throughout the study.
Growth was best on low plots where water usually stood from December to mid-Mayor early June and where openings were at least 100 feet in diameter (fig . 6 ) . Standing water on these plots probably had the same effect as in impoundments where, according to Broadfoot, diameter growth of Nuttall oak was increased by 38 percent when water was held until July 1. Broadfoot ascribed this effect to infiltration that increased the supply of soil moisture available after surface water was gone.'
Nine-year-old Nuttall oaks responded as well to release as Ito 4-year-olds did. The most notable difference was that some trees died back to 4 to 6 inches above ground level and resprouted. Trees released late underwent the same kind and degree of competition but grew as well as or better than trees released earlier. The three plots released after 9 years were low in elevation, a circumstance that may account for the better survival (fig. 3 ). Also, release of the 9-year-old trees was more complete than the average release 2 Broadfoot, W. M . Shallow-water impoundment increases soU moisture and growth
of hardwoods. Soil Sci. Soc. Am. Proc. 31: 562-564. 1967.
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Figure 5.-Typical stand 13 years after the overstory was cut. The large, clearly dominant tree is green ash; Nuttall oaks are no more than half the diameter of the ash and 5 to 10 feet shorter.
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Figure 6.-0pening in top photo, of approximately 1/1 O-acre, is too small for good development of reproduction. Opening in bottom photo is about ~ -acre, minimum recommended size. Both openings are 6 years old. Larger trees in bottom photo are green ash.
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given to 1- to 4-year-old trees; at least liz-acre was cleared around all three plots.
Check Plots
Stocking on the seven check plots averaged 150,000 trees per acre during the fall of 1958. Average survival was similar to that on released plots . Four of the seven plots still had living Nuttalls after 10 years, and two after 15 years. Oaks survived beyond 8 to 10 years only where they received an hour or two of direct sunlight from an opening somewhere in the canopy. Soil moisture supplies also appeared important, for plots where seedlings survived for 15 years usually had standing water into the growing season.
The trees grew from liz inch to 2 inches in height annually but did not die back and resprout. The largest living Nuttalls after 15 years were 3 feet tall. Diameters at the root collar were less than 0.5 inch, and growth rings could not be recognized. Root systems were small and in balance with tops. Except for the dark, rough appearance of the stems, 15-year-old Nuttalls resembled 1- to 2-year-old trees (fig. 7).
New Nuttall oak reproduction appeared in just two measurements, 1965 and 1966, and on only a few plots. None of the plots had more than 10 new trees.
Green ash, water hickory, and sugarberry demonstrated even more shade tolerance than the oaks by surviving in the understory for 15 years. In fact, most were older than 15 years, since they had been in the understory when the study began. Few new nonoak seedlings became established.
In complete shade, or with very little sunlight, green ash was the fastest-growing species, followed by water hickory and red maple. But even the ash did not exceed 6 inches of height growth in a year. Sugarberry survived but did not grow well in the understory. On some plots sugarberry was nipped back to the ground almost annually by rabbits. It was the only species to be so attacked.
There appeared to be a limit beyond which understory trees would not grow. Green ash and water hickory, for example, would reach 10 to 15 feet tall, then die back sometimes to the rootcollar, resprout, and regrow to about the same height.
DISCUSSION AND CONCLUSIONS It is important, silviculturally, that seedlings of several hard
wood species are highly tolerant of shade and will ultimately respond well to release. Advance reproduction of green ash, water hickory,
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Figure 7.-Nuttall oak on the left is 25 inches tall and has been i n the understory on a check plot 15 years; Nuttall on the r i ght is 21 inches tall and 1 year old from the nursery . The two trees di ffer considerably in color and texture of the bark.
and sugarberry can be stored in the understory for more than 15 years ; Nuttall oaks will endure for 5 to 10 years. All four species can be kept alive even longer by selective cutting of the overstory to allow 1 to 2 hours of daily sunlight to reach the understory. Green ash may grow up to 6 inches in height annually in the understory, whereas Nuttall may not exceed an inch or two . Root systems develop correspondingly. A larger root system supports the taller ash and results in more rapid shoot growth following release.
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Harvesting of the overstory can be postponed when there is advance .reproduction of tolerant species. Conversely, the new stand is already set, so that the type of harvesting or silvicultural system adopted will have little effect on the species composition that follows. New seedlings will be unimportant, since the few that become established grow too slowly to compete. The main consideration in selecting a harvesting system will be the size of opening created. An opening less than 1/ 5-acre is too small for good growth and development of reproduction. Moreover, small openings offer no advantage in reducing vines, since any opening large enough for tree growth will support vine growth. If tree development beyond 15 years is considered, openings of lh-acre or moreas recommended for upland hardwood forests in the Central States ' -would appear suitable.
If Nuttall oak is to be a favored species, reproduction must be established before the overstory is removed. Because a good stand occurred only once in 15 years during the present study, there appears to be ample reason to manage Nuttall properly when it does occur in the forest . On sites where the species does wen the forest manager has at least 5 years to release the reproduction. A single release may not suffice, since the seedlings grow more slowly than most common associates. After 11 to 14 years of release, sprouts of green ash, the most important competitor, may be two to three times as large in d.b .h. and nearly half again as tall as dominant oaks. The second release might best take place when dominant oaks average about 2 inches d.b.h. or, to judge from results in this study, in about 10 to 15 years on a moist site.
Microsites are important to species development but are difficult to recognize. Nuttall oaks will grow best in depressional areas where in a normal year water stands into the early part of the growing season. Condition of the larger Nuttalls is a good indicator of site potential. Data gathered in this study show that Nuttall oaks will sometimes start growing where they are not well suited. But when this happens, the young trees do not survive long with or without overstory release.
Vines are part of the ecological complex in bottom-land forests on Sharkey clay soil. They hinder, but do not halt, the development of reproduction. Species vary in their reaction to vines. Green ash and, to a lesser extent, sugar berry respond by sending up new leaders after the terminal has been pulled over. Nuttall oak and water hickory, which tend to grow more slowly, overcome the vines by sheer numbers. With good stocking, stands are usually out of the vine stage when dominants are 15 to 20 feet tall. ' Sander. I . L .. and F . B . Clark. Reproduction of upland hardwood forests In the Central States. USDA Agrfc. Handb. 405, 25 p . 1971.
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