Forest development after succesive clearcuts in the Southern Appalachians

Forest Ecology and Management, 13 (1985) 83--120

83

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

FOREST DEVELOPMENT AFTER SUCCESIVE CLEARCUTS IN THE SOUTHERN APPALACHIANS

DONALD

J. L E O P O L D

l, G E O R G E

R. P A R K E R

I and W A Y N E

T. S W A N K

s

~Department of Forestry and Natural Resources, Purdue University, W. Lafayette, IN 47907 (U.S.A.) ~Coweeta Hydrologic Laboratory, 999 Coweeta Lab Road, Otto, NC 28 763 (U.S.A.) (Accepted 13 June 1985)

ABSTRACT Leopold, D.J., Parker, G.R. and Swank, W.T., 1985. Forest development after succesive clearcuts in the Southern Appalachians. For. Ecol. Manage., 13: 83--120. A 16.l-ha watershed (Watershed 13, Coweeta Hydrologic Laboratory)was clearcut in 1939--1940 and again in 1962. Forest inventories were made in 1934, 1948, 1952, 1962, 1969, 1977 and 1984. Density, basal area, and size-class distribution of stems before the initial clearcut and during various stages of regrowth, were determined for each species. The even-aged, coppice forest of 1984 had a denstiy and basal area of 2330 stems ha -I and 20.83 m 2 ha -I, respectively, compared to 1934 values of 2632 stems ha -~ and 25.01 m ~ ha "~. Importance values, IV's [(relative density and relative basal area)/2 ], of mesic species, e.g., Betula lenta and Liriodendron tulipifera,have increased tremendously over the past fifty years due to their vital attributes (regeneration from sprouts and/or buried seeds, seed dispersal, fast growth, etc.) which have been favored by past disturbances, including clearcutting and chestnut blight. Importance values of Acer rubrum, Quercus coccinea and Q. prinus have increased moderately while IV's of Castanea dentata, C. pumila, Pinus rigida, Quercus alba and Q. rubra have decreased. The negative exponential function appropriately describes the size-class distribution of stems for all species combined for each census. Size-class distributions of individual species m a y (e.g.,Acer ru bruin ) or m a y not (e.g., Liriodendron tulipifera) fit this function for any inventory, primarily due to differences in shade tolerance and growth rate among species. Present (1984) composition and structure (including vertical structure) are also presented according to three community types within this watershed: Cove Hardwoods, Mixed Oak, and Oak-Pine.

INTRODUCTION

Little quantitative data have been published on the long-term effect of clearcutting on forest development in the high rainfall region of the Southern Appalachians. In contrast, there are thorough descriptions of the 'climax ~ forests of this region (Braun, 1950; Whittaker, 1956; Golden, 1981). Studies conducted in drier areas of the Southern and Central Appalachians (McGee and Hooper, 1970, 1975; Smith, 1979; Smith and Linnartz, 1980; Kochen-

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© 1985 Elsevier Science Publishers B.V.

84 derfer and Wendel, 1983; Mann, 1984) demonstrate the tremendous regenerative capacity of these forests, due to an array of species' vital attributes (sensu Noble and Slatyer, 1977, 1980), e.g., ability to root or stump sprout or regenerate from buried seeds; fast growth, and distant seed dispersal. Research done in areas of higher rainfall indeed show that clearcutting initiates forest regeneration by promoting various reproductive modes (Horn, 1980; Boring et al., 1981). However, how is forest composition and structure affected 10--20 years after treatment? What happens to forest development after a second clearcut? What vital attributes appear to be most important for a particular species? These questions are addressed in relation to successive clearcuts, 22 years apart, at the Coweeta Hydrologic Laboratory in western North Carolina. METHODS

Study area Coweeta Hydrologic Laboratory was established in 1934 by the U.S. Forest Service to study forest hydrology in the humid, montane region of the southeastern United States. The 1626-ha, bowl-shaped basin is in the Blue Ridge Province of the Appalachian Highlands physiographic region, within the Nantahala Mountains, and is about 16 km south of Franklin, 128 km southwest of Asheville, North Carolina. Individual watersheds have well-defined topographical boundaries. The average watershed relief and slope is about 300 m and 45%, respectively. Elevation ranges from 685 to over 1600 m. The Cherokee Indians used limited portions of the Coweeta Basin until the early 1840s, at which time white man began to settle the area (Dils, 1957). The Indians practiced spring and fall burning which was subsequently adopted by the white settlers and used until 1909 to improve grazing conditions. Grazing by cattle, horses, mules, sheep and hogs was common in some areas from 1847 to the early 1900s. In 1902, the Nantahala Co. acquired this land and all settlers were removed. The land was sold to the Ritter Lumber Co. of Ohio in 1906. Selective logging and controlled burning took place from 1909 to 1923 in accessible areas. In 1918, the U.S. Government purchased the land while the Ritter Lumber Co. retained rights to cut timber with a minimum diameter of 15 inches (38.1 cm) stump height. All burning and other anthropogenic perturbations ceased in 1924, except for the experimental watershed treatments. Chestnut blight, which began about 1925, has been a major disturbance in the Coweeta Basin. The basal area of Castanea dentata in permanent plots is now about 0.1% compared to 31.1% before the blight (Coweeta files, unpublished data). Prior to logging in 1919, these forests were predominantly composed of C. dentata, Quercus prinus, Q. alba, and Tilia heterophylla with about 5000 to 7000 bd-ft/acre (Kovner, 1955).

85 Geologically, this region has undergone great uplift, repeated and complex folding, and erosion. The underlying bedrock belongs to the Coweeta Group (Hatcher, 1979) which consists of a series of metasedimentary and possibly metaigneous rocks. Beneath this series are older rocks (pre-Cambrian origin) of the Tallulah Falls Formation, which has a minimum thickness of about 1000 m. The geology of this region is thoroughly discussed by Hatcher (1976, 1979). Soils differ throughout the Coweeta basin because of differences in parent material, topography and elevation. At lower elevations, the dominant soil series is Tusquitee, a member of the fine, loamy, mixed mesic family of the Humic Hapludults. The Chandler series is represented at higher elevations and along ridgetops, and is characterized into the coarse, loamy, micaceous, mesic family of Typic Dystrochrepts. Soil profiles are well-developed, particularly at lower elevations. Rock outcrops occur on steep slopes at high elevations. Surface horizons are low in bulk density and are highly permeable. Regolith depth over the entire basin averages about 7 m. Roots of mature trees extend mostly through the top meter of soil; however, some roots as deep as 6 m have been reported (Hewlett and Hibbert, 1961). The Coweeta Basin is situated in one of the highest precipitation zones of the United States. About 100 separate storms deposit nearly 2 m of water (1700 m at low elevations, 2500 mm at high elevations) over the basin annually (Hibbert, 1966). In most months, between 70 to 140 mm of rainfall is likely. October is typically the driest month, March the wettest. Less than 2% of the total precipitation is in the form of snow. The climate is typically marine, with cool summers and mild winters. Mean annual temperature is 13°C. Research reported here was done on Watershed 13 (Fig. 1) which is a 16.1-ha, northeast-facing catchment. Recent work by the Soil Conservation Service on this watershed (report on file at Coweeta Hydrologic Laboratory, fieldwork done 4 4 2 ) show two soil series are present: (1) Evard (lower slopes), a fine-loamy oxidic, mesic Typic Hapludults; and (2) Saluda (middle and upper slopes), a loamy, mixed, mesic, shallow Typic Hapludult. Midarea elevation is 808 m, mean land slope is 49% and mean annual precipitation is 1829 mm. Streamflow is perennial, with a narrow range for all months. Discharge is highest and most variable in late winter (particularly March), lowest and most stable in October. Quickflow or direct runoff amounts to less than 10% of the total precipitation. Overland flow has rarely been observed. A settler cleared about 1 ha of land in the center of Watershed 13, a disturbance which lasted from 1900 to 1903 (Kovner, 1955). The nature of selective logging on Watershed 13 prior to 1923 is not well known; however, this watershed has been relatively accessible. Kovner (1955) describes the timber here prior to the first clearcut as "... vigorous, second-growth, oakhickory pole stands with a scattering of larger-sized residuals from the logging operation."

86

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Fig. 1. Location of Watershed 13 within Coweeta Basin.

Watershed treatments All t r e e s and shrubs o n m e e n t i r e drainage w e r e f e l l e d and s c a t t e r e d in 1 9 3 9 - - 1 9 4 0 , and again in late 1 9 6 2 . N o f o r e s t p r o d u c t s w e r e r e m o v e d after

87 either clearcut and soil disturbance was minimal. No other treatments have occurred since 1934 other than these clearcuts. Cuts were made primarily to study the effect of forest clearing on various hydrological aspects of watersheds in this region (for hydrology results see Swank and Helvey, 1970; Swift and Swank, 1981; Swank et al., 1982).

Inventories Basal area values of important species on Watershed 13 have been reported elsewhere (Kovner, 1956; Swank and Helvey, 1970; Swift and Swank, 1981). Density values for selected species and inventories have also been published (Parker and Swank, 1982). A more detailed examination o f previous inventories is included here and some minor differences between the present and past analyses are apparent. The following changes were made for the inventory indicated: (1) 1934 -- S u m m a r y prepared by L. Jones {2-6-52) was used. (2) 1 9 4 8 - - S h r u b s (Clethra accurninata, Lindera benzoin, etc.) were excluded. (3) 1952 -- Plots number 33, 34 and 35 were omitted because the 1, 2 and 3 inch size~lasses were combined during data collection; and plot number 46 was deleted because one-third of plot was n o t on watershed. Total area excluded 0.32 ha. (4} 1962 --Transects 5 and 6 (ca. 0.59 ha total) were omitted because the 1, 2 and 3 inch size-classes were combined during data collection. (5) 1 9 7 7 - - K a l r n i a latifolia and Rhododendron maximum density and basal area values were excluded (as they were not included in summaries of earlier inventories). (6) Another difference with previously published data is with the number of years after either clearcut. Values listed here are based on full growing seasons, e.g., if an inventory was made in February, March or April of a given year, these months were n o t c o u n t e d as a new year. During the summer of 1981, 26 10 X 20 m plots were systematically located over Watershed 13. All tress with a diameter of 5.0 cm or greater at a b o u t 1.4 m aboveground (dbh) were measured in the entire plot and were tagged within one 10 X 10 m portion of each plot. Tags, consisting of aluminum strips and copper wire, were fastened to aluminum nails driven into each stem at a b o u t 30 cm aboveground. The location of dbh measurements was marked on each stem by white paint. These plots were established for annual assessment of tree growth, mortality and ingrowth. In March 1982, all trees which had already died within these plots were removed. Any signs of disease or insects were noted. Ages and diameters of the dead trees were determined from stem cross-sections made near ground level, and the pattern of growth (e.g., gradual or sudden suppression) was noted. Summaries o f forest inventory dates and characteristics are depicted in Tables 1 and 2. F o r all inventories e x c e p t 1984, tree diameters were record-

88 TABLE 1 Forest inventory and treatment dates on Watershed 13 Date

Event

Fall 1934--winter 1935 September 1939--January 1940 April 1948 August--September 1952 October 1962 November--December 1962 October 1969 May--June 1977 March 1984

Forest inventory Clearcut Forest inventory Forest inventory Forest inventory Clearcut Forest inventory Forest inventory Forest inventory

TABLE 2 Description of forest inventories on Watershed 13 Date

Minimum diameter a (cm)

Class interval (cm)

Plot size (ha)

Number of plots

Sampling method

1934--1935 1948 1952 1962 1969 1977 1984

1.27 1.27 1.27 1.27 0.25 0.25 5.00 e

2.54 b 2.54 2.54 2.54 2.54 d 1.27 f

0.08 0.01 0.08 0.08 0.01 0.05 0.02

23(11.4) c 20(1.2) 19(9.4) 36(17.9) 36(2.2) 35(10.9) 43(5.3)

Strip cruise Random plots Strip cruise Strip cruise Strip cruise Strip cruise Stratified systematic

aApproximately 1.37 m aboveground. bExcept first interval 7.62 cm wide. Cpercent of watershed sampled. dExcept first two intervals 1.27 cm wide. eExcept Kalmia latifolia and Rhododendron maximum, minimum diatemer = 1.0 cm. IActual diameter recorded to nearest 0.1 cm.

ed in the appropriate, generally 1-inch, interval class.However, in 1984 trees were measured with a metric diameter tape to the nearest 0.1 c m and the actual diameters were used in analyses.For the 1984 inventory, 17 additional 10 × 20 m plots were systematically located over the watershed in relation to the 26 established in 1981 to ensure adequate representation of the vegetation within three community types: Cove Hardwoods, Mixed O a k and Oak--Pine. These types were delineated based on aerial photographs (Ektachrome, color IR) supplied by the Aerial Photography Field Office, Agricultural Stabilization and Conservation Service (USDA); color aerial photographs taken by the author; and a field reconnaissance of the study area. Trees were measured in all 43 plots in 1984, but ingrowth and mortality data are based only on the original 26 plots.

89 Diameter measurements (dbh) were made for all inventories. Basal area and density values for Kalmia latifolia and Rhododendron maximum were excluded from all tree species calculations. Importance values for each arborescent species are sums of relative density and relative basal area, divided by two. Kalmia latifolia and R. maximum values are based on actual stem numbers in 1962, 1969 and 1977. However, for the 1984 inventory, due to the large number of coppice stems of both species on most plots, an average-size clump of each species was subjectively chosen, if present on a plot. All stems of these species, i> 1.0 cm at 15 cm aboveground, were counted and measured for the selected clump. All clumps of each species were counted on each plot and the appropriate multiplication factors yielded per hectare values. Basal area and density values obtained by this method seemed reasonable, given the uniform clump size and published values for these species at Coweeta (McGinty, 1972; Day and Monk, 1974). Tree and shrub heights were measured in March 1984 with a range pole (shrubs and trees ~< 4.0 m tall) or Haga and Suunto clinometers (trees > 4.0 m tall). Heights of species which comprised the dominant, codominant, intermediate and suppressed crown classes (Smith, 1962) were measured in all plots (over 730 tree and 160 shrub heights) except one due to an extremely dense R. maximum canopy which prevented viewing the tops of trees.

Growth Two increment cores from opposite sides of each tree were collected with a Djos increment borer (ca. 5.08 mm core diameter) at a b o u t 25--50 cm above ground, parallel to the slope whenever possible. Canopy dominant or codominant trees were cored in each of the 43 plots with the addition of some understory species, e.g., Carya spp. At least five trees were cored per plot (over 300 trees total). Additional cores of Liriodendron tulipifera (75) and Quercus prinus (24) were collected b e y o n d the plots. Ring widths of these cores were averaged with the totals of the c o m m u n i t y types for b o t h species. The actual number of cores measured for each species by community t y p e is given in Table 3. Only cores which were extracted intact (including bark) and either came near or reached the pith were measured. After extraction, cores were placed in plastic soda straws, coded and sealed in the field. Cores were air
90 TABLE 3 N u m b e r of i n c r e m e n t cores collected for each species by c o m m u n i t y type Species

Acer rubrum a Betula lenta Carya spp. Castanea dentata Fraxinus americana Liriodendron tulipifera Magnolia acuminata M. fraseri Oxydendrum arboreum P i n u s rigida Q u e r c u s alba Q. c o c c i n e a O. f a l c a t a

Q. m a r i l a n d i c a Q. p r i n u s Q. v e l u t i n a Robinia pseudoacacia Sassafras albidum Symplocos tinctoria Tilia h e t e r o p h y l l a Total

Community Type Cove Hardwoods

Mixed Oak

6 20 20 -4 127 2 1 2 --6

---0 --2 -4 18 6 50 2 24 2 6 2 -4 --

6 37 45 4 4 226 b 12 7 11 18

-10 8 4 6 -2

-17 25 4 -24 8 6 5 -4 64 --105 13 6 2 ---

218

283

120

720 d

-

Oak--Pine

Total

I0 120 2 24 141 c 27 12 8 4 2

a N o m e n c l a t u r e follows Little (1979). b I n c l u d e s 75 c o r e s c o l l e c t e d o u t s i d e o f p l o t s in 1 9 8 1 , 1 9 8 2 . c I n c l u d e s 24 c o r e s c o l l e c t e d o u t s i d e o f p l o t s in 1 9 8 2 . d I n c l u d e s 99 a d d i t i o n a l c o r e s o f L i r i o d e n d r o n t u l i p i f e r a a n d Q u e r c u s p r i n a s .

tific Corp., Chicago). British Imperial units were converted to millimeters subsequent to all analyses.

Data analyses The size-class structures of the forest and c o m p o n e n t species at various inventories were investigated by regression analysis using the negative exponential function Y = ke -aX (Meyer 1953), where Y is the number of trees per diameter class, X is the dbh class, e is the base of natural logarithms, and a and k are constants for a specific diameter distribution. Data were transformed logarithmically so that simple linear regression (Kim a n d K o h o u t , 1975a) could be used to calculate coefficients o f determination (r2). The negative p o w e r function, Y = k X - a was used only for the 1984 data since higher r 2 values resulted with the negative exponential function. Size-classes necessarily had narrow class widths so that comparisons among various inventories could be made.

91 Differences among mean tree diameters in 1984 were tested by ANOVA and Scheffe's multiple comparison test (Kim and K o h o u t , 1975b). Regression lines were tested for equality by the methods described in Neter and Wasserman (1974, pp. 160--165). RESULTS

Species composition Before the results are presented it should be reemphasized that the inventories to be discussed were not all made on the same plots over the 50-year period. Therefore, one should be prudent in the interpretation of the actual numbers. Tree density on Watershed 13 increased immediately and then gradually decreased after b o t h clearcuts (Table 4). The 1984 density is lower than the precut value which is a result of the higher diameter limit used in 1984 versus 1934 (5.0 vs. 1.3 cm dbh, respectively). Relative density decreases were greatest for Castanea dentata and C. pumila, n o t because of cutting treatments b u t due to the effect of chestnut blight. The combined relative density of these species declined from 26.0 to 0.2% b y 1984. Pinus rigida, Quercus alba and Q. rubra relative densities rose after the first clearcut b u t decreased after the second. Acer rubrum, Betula lenta, Liriodendron tulipifera, Oxydendrum arboreum, and Quercus prinus relative densities increased over the entire period. Relative densities of Carya spp., Cornus florida, Hamamelis virginiana, Nyssa sylvatica and Syrnplocos tinctoria fell markedly in the 1984 inventory, primarily due to the higher diameter limit. There are presently numerous individuals of these species below 5.0 cm dbh. The decrease o f Robinia pseudoacacia relative density over time after b o t h clearcuts can be attributed to the effect of Megacyllene robiniae, locust borer, which prevents this tree from attaining maturity at Coweeta (Boring and Swank, 1984). On Watershed 13 nearly all dead Robinia stems were riddled with holes caused by this insect. In 1982, the average age and diameter of all standing dead Robinia were 10.8 years and 5.8 cm, respectively. Of those alive in 1982 25.0% died by 1983, and 6.7% of the 1983 survivors died by 1984. Some species, e.g., Magnolia acuminata, M. fraseri and Symplocos tinctor/a were n o t present until after the first clearcut. Tilia heterophylla did n o t occur in any plots until after the second clearcut. Understory trees which increased in relative density after both clearcuts included Amelanchier arborea and Oxydendrum arboreum. Basal area of this forest appears to be accumulating more rapidly after the second clearcut (Table 5). T w e n t y ~ n e years after this cut, basal area is 80% of the precut (1934) value, versus 58% 23 years after the first clearcut. The 1984 basal area would have been higher than 80% of the precut value, if minimum diameters had been the same for b o t h years (5.0 vs. 1.3 cm dbh,

.

2632

-3(0.1 )

--

54(2.1) 230(8.7) 15(0.6) 90(3.4) 48(1.8) 58(2.2)

2(0.1)

189(7.2) 61(2.3) 61(2.3) 32(1.2) 158(6.0)

-. .

7(0.3) 242(9.2) 16(0.6) 3(0.1) 242(9.2) 410(15.6) 275(10.4) 320(12.2) 18(0.7) 2(0.1 ) 74(2.8) 22(0.8) .

7499

49(0.7) 1033(13.8) 143(1.9) 158(2.1) 361(4.8) 198(2.6) 213(2.8) ---

--

430(5.7) 79(1.1) 49(0.7) 25(0.3) 460(6.1)

--

89(1.2) 890(11.9) 64(0.9) 94(1.3) 722(9.6) 588(7.8) 134(1.8) 1166(15.5) 30(0.4) 15(0.2) 306(4.1) 203(2.7)

5068

1(0.0) 738(14.6) 63(1.2) 6(0.1) 442(8.7) 61(1.2) 84(1.7) 1014(20.0) 18(0.4) 4(0.1) 97(1.9) 94(1.9) 12(0.2) 3(0.1) 339(6.7) 246(4.9) 206(4.1) 70(1.4) 447(8.8) 5(0.1) 100(2.0) 496(9.8) 122(2.4) 168(3.3) 158(3.1) 71(1.4) --3(0.1) 3390

14(0.4) 426(12.5) 49(1.4) 59(1.7) 237(7.0) 13(0.4) 31(0.9) 655(19.3) 7(0.2) 7(0.2) 99(2.9) 88(2.6) 5(0.1 ) 4(0.1) 231(6.8) 206(6.1) 120(3.5) 39(1.1) 334(9.8) -68(2.0) 308(9.1) 45(1.3) 104(3.1) 77(2.3) 23(0.7) 75(2.2) Tb 66(1.9) 9518

683(7.2) 336(3.5) 189(2.0) 25(0.3) 20(0.2)

2600(27.3) | ~

61(0.6) 1397(14.7) 153(1.6) 122(1.3) 592(6.2) 269(2.8) -1769(18.6) 8(0.1) -172(1.8) 336(3.5) 50(0.5) 19(0.2) 275(2.9) 436(4.6) 6(0.1) "7-/

4697

37(0.8) 1004(21.4) 89(1.9) 101(2.1) 363(7.7) 38(0.8) -1184(25.2) --23(0.5) 182(3.9) 20(0.4) -161(3.4) 186(4.0) -39(0.8) 259(5.5) 23(0.5) 573(12.2) 32(0.7 ) 191(4.1) 119(2.5) 71(1.5) -2(0.0) --

14

7

23

8

13

Years after 2nd clearcut

Years after 1st clearcut

a Includes Acer saccharum, AInus serrulata, Carpinus caroliniana, Fagus grandifolia, Prunus serotina, and 7~uga canadensis. bLess than 1 stem ha -~.

Total

Miscellaneousa

Q. rubra Q. velutina Robinia pseudoacacia Sassafras albidum Symplocos tinctoria Tilia heterophylla

Q. pr/nus

Q. marilandica

Q. falcata

Acerpensylvanicum A. rubrum Amelanchierarborea Betula lenta Carya spp. Castanea dentata C. pumila Comus florida l~'ospyros pirginiana Fraxinus americana Hamamelis virginiana Liriodendron tulipifera Magnolia acuminata M. fraseri Nyssasylvatica O x y d e n d r u m arboreum Pinus rigida Quercus alba Q. coccinea

Precut (1934--1935)

Density (stems ha-') and relativedensity (in parentheses) of tree species on Watershed 13 following both clearcuts

TABLE 4

2330

90(3.8) 1(0.0) 5(0.2) 12(0.5) 316(13.6) 16(0.7 ) 10(0.4) 6(0.2) 136(5.8) 22(0.9) 8(0.3) 283(12.1) 1(0.0) 90(3.8) 465(20.0) 1(0.0) 78(3.3) 69(2.9) 27(1.1) 5(0.2) 6(0.2) --

3(0.1)

10(0.4) 401(17.2) 83(3.5) 121(5.2) 63(2.7) 2(0.1)

21

¢~ t~

25.01

0.02(0.1) 0.97(3.9) 0.03(0.1) 0.01(0.0) 1.47(5.9) 8.41(33.6) 0.61(2.4) 0.81(3.2) 0.04(0.2) T 0.15(0.6) 0.56(2.2) --0.70(2.8) 0.44(1.8) 2.95(11.8) 0.33(1.3) 2.11(8.4) T 0.33(1.3) 3.01(12.0) 0.24(1.0) 0.97(3.9) 0.63(2.5) 0.19(0,8) --0.03(0.1) 9.33

0.05(0.5) 1.09(11.7) 0.03(0.3) 0.06(0.6) 0.75(8.0) 0.95(10.2) 0.08(0.9) 0.70(7.5) 0.01(0.1) 0.02(0.2) 0.18(1.9) 0.48(5.1) --0.32(3.4) 0.12(1.3) 0.09(1.0) 0.01(0.1) 0.73(7.8) -0.10(1.1) 1.72(18.4) 0.20(2.1) 0.30(3.2) 1.10(11.8) 0.13(1.4) 0.11(1.2) ---11.04

Tb 1.28(11.6) 0.06(0.5) 0.01(0.1) 0.74(6.7) 0.06(0.5) 0.07(0.6) 0.95(8.6) 0.03(0.3) 0.01(0.1) 0.11(1.0) 0.77(7.0) 0.03(0.3) 0.01(0.1) 0.31(2.8) 0.50(4.5) 0.90(8.2) 0.19(1.7) 1.23(11.1) 0.02(0.2) 0.21(1.9) 2.03(18.4) 0.31(2.8) 0.60(5.4) 0.52(4.7) 0.09(0.8) --T 14.39

0.02(0.2) 1.18(8.1) 0.07(0.5) 0.30(2.4) 0.65(4.5) 0.01(0.1) 0.03(0.2) 0.89(6.2) 0.03(0.2) 0.02(0.2) 0.16(1.1) 1.35(9.3) 0.02(0.1) 0.01(0.1) 0.31(2.1) 0.66(4.6) 1.12(7.7) 0.25(1.7) 2.36(16.3) -0.26(1.8) 2.74(18.9) 0.46(3.2) 0.61(4.2) 0.57(4.0) 0.07(0.5) 0.05(0.4) T 0.19(1.4) 6.99

0.42(6.0) 0.15(2.2) 0.04(0.6) 0.02(0.3 ) 0.04(0.6)

2.57(36.8) | __[_

0.02(0.3) 0.71(10.2) 0.05(0.7) 0.07(1.0) 0.46(6.6) 0.15(2.2) -0.80(11.4) T -0.08(1.1) 0.85(12.2) 0.10(1.4) 0.03(0.4) 0.10(1.4) 0.33(4.7) T -'7-]

11.80

0.15(1.3) 0.96(8.1) -0.04(0.3) 2.45(20.8) 0.09(0.8) 0.60(5.1) 0.64(5.4) 0.17(1.4) -T --

--

0.05(0.4) 1.74(14.7) 0.09(0.8) 0.33(2.8) 0.50(4.2) 0.04(0.3) -0.84(7.1) --0.02(0.2) 2.57(20.9) 0.08(0.7) -0.16(1.4) 0.38(3.2)

14

7

23

8

13

Years after 2nd clearcut

Years after 1st clearcut

alncludes Acer saccharum, AInus serrulata, Carpinus caroliniana, Fagus grandifolia, Prunus serotina, and Tsuga canadensis. bless than 0.01 m 2 ha-'.

Total

Acerpensylvanicum A. rubrum Amelanchierarborea Betula lenta Carya spp. Castanea dentata C. pumila C o m u s florida Diospyros virginiana Fraxinus americana Hamamelis virginiana Liriodendron tulipifera Magnolia acuminata M. fraseri Nyssasylvatica O x y d e n d r u m arboreum Pinus rigida Quercus alba Q. eoccinea Q. falcata Q. marilandica Q. prinus Q. rubra Q.velutina Robiniapseudoacacia Sassafras albidum Symplocos tinctoria Tilia heterophylla Miscellaneous a

Precut (1934--1935)

Basal area ( m 2 ha -I ) and relative basal area (in parentheses) of tree species on Watershed 13 following both clearcuts

TABLE 5

20.83

o.01(0.o) 0.O7(O.4)

0.11(0.6)

0.42(2.0) 4.22(20.3 ) T 0.62(3.0) 0.67(3.2)

o.01(0.0)

0.74(3.6) 0.27(1.3) 0.04(0.2) 2.20(10.6)

o.o1(o.o)

0.24(1.2) T 0.02(0.1) 0.04(0.2) 7.29(35.0) 0.33(1.6) 0.08(0.4)

0.01(0.0)

0.04(0.2) 2.10(10.1) 0.28(1.3) 0.77(3.7) 0.23(1.1) 0.01(0.0)

21

¢.0 co

94

respectively). Liriodendron tulipifera and Quercus prinus account for 55% of the relative basal area in 1984. Pinus rigida relative basal area decreased considerably following both treatments. Although this P/nus sprouts as do the associated hardwoods (Fowells, 1965) P. rigida sprouts may be less competitive. Castanea dentata relative basal area declined from 33.6% to 0.0% from 1934 to 1984. There was a comparable relative basal area decrease for C. dentata on a nearby undisturbed watershed (Day and Monk, 1974). Relative density and basal area values for this species immediately after both clearcuts TABLE 6 I m p o r t a n c e values [(relative d e n s i t y + relative basal area)J2 ] o f t r e e s p e c i e s o n W a t e r s h e d 13 f o l l o w i n g b o t h c l e a r c u t s Precut (1934--1935)

Acer pensylvanicum A. rubrum Amelanchier arborea Betula lenta Carya s p p . Castanea dentata C. pumila Comus florida Diospyros virginiana Fraxinus americana Hamamelis virginiana Liriodendron tulipifera Magnolia acuminata M. fraseri Nyssa sylvatica Oxydendrum arboreum Pinus rigida Quercus alba Q. coccinea Q. falcata Q. marilandica Q. prinus Q. rubra Q.velutina Robinia pseudoacacia Sassafras albidum Symplocos tinctoria ~'lia heterophylla M i s c e l l a n e o u sa

Years after 1st clearcut

Years a f t e r 2nd clearcut

8

13

23

7

14

21

0.2 6.5 0.4 0.1 7.5 24.6 6.4 7.7 0.5 0.1 1.7 1.5

0.9 11.8 0.6 1.0 8.8 9.0 1.3 11.5 0.3 0.2 3.0 3.9

--

--

-5.0 2.0 7.0 1.3 7.2 0.1 1.7 10.4 0.8 3.7 2.2 1.5

-4.6 1.2 0.8 0.2 7.0 -0.9 16.1 2.0 2.7 8.3 2.0 2.0 ---

0.0 13.1 0.9 0.1 7.7 0.9 1.2 14.3 0.3 0.1 1.4 4.4 0.2 0.1 4.8 4.7 6.1 1.6 10.0 0.1 2.0 14.1 2.6 4.4 3.9 1.1 ----

0.3 10.3 0.9 2.0 5.7 0.2 0.5 12.7 0.2 0.2 2.0 6.0 0.1 0.1 4.5 5.3 5.6 1.4 13.0 -1.9 14.9 2.2 3.7 3:1 0.6 1.3 0.0 1.6

0.4 12.3 1.2 1.2 6.3 2.5 -14.9 --1.5 7.8 1.0 0.3 2.1 -4.6 -y/

0.6 18.1 1.3 2.5 6.0 0.6 -16.2 --0.3 12.4 0.5 -2.4 3.6 -1.0 6.8 -0.4 16.5 0.8 4.6 4.0 1.5 ----

0.3 13.6 2.4 4.5 1.9 0.1 0.1 2.5 0.0 0.2 0.3 24.3 1.1 0.4 0.1 4.7 1.1 0.3 11.4 0.0 2.9 20.1 0.0 3.1 3.1 0.7 0.1 0.3 --

--0.1

31.8 | .J_ 6.6 2.9 1.3 0.3 0.5

a I n c l u d e s Acer saccharum, Alnus serrulata, Carpinus caroliniana, Fagus grandifolia, Prunus serotina, a n d Tsuga canadensis.

95

suggest that Castanea responded vigorously to cutting. However, sprouts of this species were quickly reinnoculated by the causal agent of chestnut blight, Endothia parasitica. Mean diameter and age of dead Castanea by 1982 was 4.5 cm and 7.5 years, respectively. All dead stems exhibited the classic symptoms of chestnut blight. Changes in Importance Values (IV's) naturally parallel t h e t r e n d s in relative density and basal area. While the combined IV's for Castanea dentata and C. pumila dropped from 31.0 to 0.2%, the combined IV's of Amelanchier arborea, Betula lenta and Liriodendron tulipifera rose in the opposite manner (Table 6). The IV's of some species, e.g., Acer pensylvanicum, Fraxinus americana and Quercus falcata, fluctuated little over the 50 years. The two prevalent shrub species, Kalmia latifolia and Rhododendron maximum, were favored by the second clearcut (data prior to 1962 not available for these species). Basal area and density of both species increased since the second clearcut (Table 7). The 1984 values may seem especially high since the diameter limit this year was set at 1.0 cm dbh (versus 5.0 for tree species). However, these values appear reasonable compared to those reported for these species on a nearby, undisturbed watershed (Day and Monk, 1974). Much of Watershed 13 is covered by impenetrable thickets of these two species. Rhododendron establishment apparently is favored by disturbance (McGee and Smith, 1967). TABLE

7

Basal area (BA, rn2 ha -~ ) and density (D, stems ha -~ ) of Kalmia latifoliaand Rhododendron m a x i m u m for various inventories after the second clearcut (1962)

1962

1969

1977

1984

Species Kalmia latifolia Rhododendron maximum

BA

D

BA

D

BA

D

BA

D

0.83 0.52

1650 1034

0.05 0.03

806 703

0.21 0.65

984 1655

4.77 1.83

10212 2535

Size.class analysis The 1934 size-class structure of this forest by species is given in Table 8. The largest individuals were mostly Carya spp., Castanea dentata, Pinus rigida and Quercus spp. Many species such as Amelanchier arborea, Betula lenta and Liriodendron tulipifera were evident only in the smallest size-classes. The paucity of larger stems, especially of economically important timber species, e.g., C. dentata, L. tulipifera, Quercus alba and Q. rubra, is indicative of the selective logging that took place here prior to the mid-1920s. The number of C. dentata, L. tulipifera, P. rigida and Quercus spp. in the lower diameter classes suggests that this selective logging was intense enough to allow for the regeneration of these shade intolerant to mid-tolerant species.

3

2 12 7 31 2 10 8 2 7

208

10

16

27 116 41 166 22 65 27 55 373

2141

15

39

8

11

175

16 46 12

17

8.9

212 258 305

16 3

214

1.3 a

115

3 7 5 13 1 7 7 1 1

7

6

3

4

4 35 3

8

14.0

73

7 4 1

7 2 9

6

3

3

3 27

1

19.1

Size-class ( c m , l o w e r l i m i t )

aFirst class interval 7.6 c m wide, all others ~ 5.1 c m wide.

Totals

Others

Oxydendrum arboreum Pin us rigida Quercus alba Q. coccinea Q. marilandica Q. prinus Q. rubra Q. velutina Robinia pseudoacacia Sassafras albidum

Nyssa sylvatica

Acer rubrum Amelanchier arborea Betula lenta Carya spp. Castanea dentata Comus florida Liriodendron tulipifera

Species

N u m b e r o f s t e m s ha -1 in 1 9 3 4 , p r e t r e a t m e n t i n v e n t o r y

TABLE 8

36

4 1 6 1

4 2 6 2 1 47

6

5

1

2 9

1

29.2

6

4

1

2 16 1

2

24.1

21

4

2

4

5

2 3

1

34.3

21

2

2

2

5

1

2 7

39.4

9

1

1

3

1 3

44.5

6

2

2

2

49.5

6

2

4

54.6

1

1

59.7

3

1

2

64.8+

CD O~

97

The 1934 size-class distribution for all species combined is illustrated in Fig. 2 along with the predicted distribution based on the negative exponential model. The absence of stems greater than 65 cm dbh again demonstrates that this forest had been cut fairly heavily prior to its acquisition by the Forest Service.

ALL SPECIES-1934

100i

C-----C~

actual predicted

\

10( O J

\\ LU I-¢n It.

o

t,U

2:

10

\ 10

20

30

40

50

60

70

80

90

100

110

>120

SIZE CLASS, LOWER LIMIT (CM,DBH)

Fig. 2. Size-class distribution (stems ha -~), all species combined in 1934 (1st class interval 7.6 cm wide, others 5.1 cm).

98 TABLE 9

Size--classd i s t r i b u t i o n ( s t e m s h a -1) f o l l o w i n g first c l e a r c u t Species

Years after clearcut

Size classa:

Acer rubrum Ameianchier arborea Betula lenta Carya spp. Cas tanea den rata Comus florida Liriodendron tulipifera Magnolia acuminata Nyssa sylvatica Oxydendrum arboreum Pinus rigida Quercus alba Q. coccinea Q. marilandica Q. prinus Q. rubra Q. velutina Robinia pseudoacacia Sassafras albidum

8 1

2

3

4

13 1

5

608 64 84 474 297 1092 94

232

25

25

10 242 217 74 54

5 69

5

40

10

54 40 15

5 5 10

158 10 405 59 54 128 20 40

54 15 124 10 35 124

30

Others

371 35 25 25 242 25 494 74 69 79 178 748

Totals

5078

1812

521

85

5

5 10

5

2

3

4

5

6

418 48 2 239 46 753 25 5 263 101 57 30 161 36 133 55 47 37 46 150

206 15 4 149 13 248 18 3 69 91 53 18 125 43 139 32 52 66 18 54

88

20

5

44 1 12 9 2 7 50 51 12 79 17 107 26 37 33 7 9

8 i 1 10 1

2

2652

1416

591

4 31 7 73 4 87 5 23 16

8

9 1

14

7 !

7

8 3 6

5

1

3

1

3

2

3

24 3 6 3

3 3 1

1

74

28

9

2 293

7

6

a N u m b e r s r e f e r t o l o w e r l i m i t o f size-class b e g i n n i n g w i t h 1.3 c m . Size-class i n t e r v a l s are 2 . 5 4 e m w i d e . T A B L E 10 Size-class d i s t r i b u t i o n ( s t e m s h a -1) f o l l o w i n g s e c o n d c l e a r e u t Species

Years after clearcut 7 Size classa:

14

1

2

Acer rubrum 1019 Amelanchier arborea 131 Be tula fen ta 69 286 Carya spP. Cas tanea de n tara 194 1408 Comus florida Liriodendron tulipifera 56 Magnolia acuminata 11 Nyssa sylvatica 283 Oxydendrum arboreum 233 Pin us rigida 3 Quercus alba 880 Q. prinus J Q. coccinea l Q. marilandica 705 Q. rubra Q. velutina Ro bin iapse udoacacia 50 Sassafras albldum 261

3 355 22 58 289 69 861 117 17 42 183 3 628

680

Others

545

558 75 67

Totals

6592

8472

4

5

22

17 3

3

108 19

53 3

3

19 156

3

97

69

525

6

7 67

3

1

2

3

4

5

6

403 50 26 144 22 662 9 2 98 57

348 26 22 143 8 454 19 6 46 59

163 9 30 60 6 58 30 6 10 49

59 3 15 18 2 10 23 3 5 19

27

10 66 34 3 6 38 2 15 31

6 147 72 14 15 59 21 18 25

12 155 81 4 5 55 41 29 6

1678

1508

809

7 3 1 1 1

1

1 25 2 1 2

25 1 1

21

7 125 49 2 2 25 33 9 1

3 61 15

1 17 5

2 9 19

1 5 2 1

1 2

405

176

62

29

6 3

2 2

a N u m b e r s r e f e r t o l o w e r l i m i t of size-class b e g i n n i n g w i t h 0 . 3 c m . Size-class i n t e r v a l s a r e 2 . 5 4 can w i d e .

99

23 1

2

3

206 30 11 91 9 366 6 2 143 55 7 8 39 10 24 4 13 8 7 186

108 14 17 90 3 244 13 1 71 67 19 8 66 25 49 8 20 10 7 85

1225

925

4

5

55 4 12 38

40 1 8 12

44 15 1 14 54 28 8 86 22 68 11 36 20 7 25

2 19 2 26 27 8 77 12 77 6 22 23 2 11

548 3 7 5

6

7

8

9

10 11

11

5

1

1

6

4 1

1 1

1

9

3

5

4

14 1 22

4 1 7

4

3

32 6 5 6

12 1 2 2

8 3 1 1,

3

8 1 4 15 4 30 1 34 5 5 7

5

1

134 110

35

12

13

2

1

1

2

1

1

9

10

11

12

13

34 1

23 2

16 1

7

6

26

17

7

6

1

3

5 1

1

8

6

1 29

21 8

19

9

6

10

3

11

3

3 207 56 40 36 1 60 30 2 5 74 1 3 119 108 47 ! 26 10 14

4

5 84 12 34 I0

6

7

37

17

13 1

2 1

1 47 0

45 5

34 8 2 128 76 26

20 6 1 114 45 5

23 19 10 527

8 6

1

40 3

28 0

37 0

5 2

3

1

47 28 2

22 14

13 2

5 7

i0 21

7 10

2 5

1

2

326

176

85

57

43

1 21

5

3

3

867

100 Size-class distributions for each species following the first clearcut is shown in Table 9. The effect of chestnut blight on Castanea dentata is evident by the thirteenth year. By the twenty-third year, stem numbers remain concentrated in the smaller diameter classes of Amelanchier arborea, Cornus florida, Nyssa sylvatica, Oxydendrurn arboreum, and Sassafras albidum, among others. Liriodendron tulipifera, Pinus rigida, Quercus coccinea and Q. prinus stems occupied the larger classes. The negative exponential function describes very well the size-class distributions (Fig. 3) for all species combined, for the three inventories (r 2 values of 0.95, 0.99, 0.99 for 8, 13 and 23 years after the first clearcut, respectively; P < 0.05 for each value). Forest structure by individual species and all combined, after the second clearcut, is depicted by Table 10 and Fig. 4, respectively. There are much greater stem numbers in the mid to upper diameter classes for most species 21 years after the second clearcut compared to 23 years after the first. Many species m a y have regenerated from seed as well as advance regeneration after the first clearcut, and newly established species would grow slower than species which regenerated from stumps or preexisting stems. It seems very unlikely, though, that seedlings contributed m u c h to the regeneration of this forest after the second clearcut, because of the large n u m b e r of stems present prior to this cut. The potential for sprouting was also greater prior to the second clearcut because of the preponderance of small stems compared to a greater n u m b e r of larger stems before the first clearcut. The size-class structure after the second clearcut depicts the more rapid growth response of the sprout origin stems versus the first clearcut which apparently consisted of both seedling and sprout origin regeneration. Coefficients of determination (r 2) for the regression lines in Fig. 4 which represent the negative exponential function are again very high, although this forest is u n d o u b t e d l y even-aged (0.94, 0.98, 0.99 for 7, 14 and 21 years after the second clearcut, respectively; P ~< 0.05 for each). Regression lines for the first inventories after both clearcuts are n o t significantly different (P ~< 0.05), although there is a full growing season less for the first inventory after the second clearcut. Regression lines for the second and third inventories after each clearcut are significantly different primarily due to greater (less negative) slopes for linear regressions of forest structure following the second clearcut. By the third inventory after the second clearcut more stems are present in larger size-classes, even though this inventory was made two years before its counterpart after the first clearcut. Liriodendron tulipifera and Quercus spp. contributed greatly to the increase of stems in larger sizeclasses after the second clearcut. Size-class distributions were examined in greater detail for the 1984 inventory since actual diameters were recorded. Data were fit to both the negative exponential and negative power functions. Theoretically, the depletion of stems in larger diameter classes occurs at a constant rate for the negative exponential curve and at a declining rate for the negative power curve. The negative power function generally does not describe the size-class distribu-

101

\ YEARS AFTER Ist CLEARCUT

100(

o ¢,0 UlJ k,tf~ LL

Q 0¢

144 en

23

Z

10

13 8

\ 5.0

10.0

15.0

20.0

\ 25.0

30.0

SIZE CLASS, LOWER LIMIT (CM, DBH)

Fig. 3. Size-class distributions (stems ha-l), all species combined, 8, 13 and 23 years following first clearcut (2.5-cm class intervals).

102

YEARS AFTER 2nd CLEARCUT

1000

O -J tel

k-

t~ O tM

21

Z

10

~L

I

I 5.0

I

'l 10.0

I

L 15.0

4

I 20.0

I

t 25.0

I

I 30.0

SIZE CLASS, LOWER LIMIT [CM, DBH)

Fig. 4. Size-class distributions (stems ha-l), all species c o m b i n e d , 7, 14 and 21 years following second elearcut (2.5 cm class intervals).

103

T A B L E 11

Coefficients of determination (r 2) for negative exponential and negative power curve regressions of number of stems on size-class, in 1 9 8 4 . Only those species w i t h stems in at least five diameter classes (2 cm w i d t h ) were analyzed Species

Negative exponential curve d

Negative power curve e

Acer rubrum Betula lenta Carya spp. Liriodendron tulipifera Oxydendrum arboreum Pinus rigida Quercus coccinea

Robinia pseudoacacia

0.96 0.90 0.95 0.65 0.96 0.29 0.93 0.97 0.92 0.92 0.96 0.42

a b a a a c

0.88 b 0.94 b 0.96 b 0.45 b 0.87 b 0.34 0.82 b 0.93 b 0.78 b 0.90 a 0.86 a 0.28

All species c o m b i n e d

0.99 a

0.94 a

Q. marilandica Q. prinus Q. uelutina All Quercus spp. c o m b i n e d

ap < 0.0001;bp

a b b b b

< 0 . 0 1 ; c p < 0.10.

d y = ke-aX; e y = k x - a ; y is the number of stems in any size class, X is the size class and k a n d a are constants (k equals initial input into population at time zero and a is the depletion rate).

tions of individual species or all combined, as well as the negative exponential function (Table 11). However, coefficients of determination are very high for both functions. Illustrative examples of h o w Acer rubrum, Liriodendron tulipifera and all species combined fit these functions are shown in Figs. 5 and 6. Acer rubrum is representative of those shade tolerant and mid-tolerant species which are adequately described by either function, whereas neither are very appropriate for Liriodendron tulipifera and other intolerant species (Pinus rigida, Robinia pseudoacacia, etc.). In order that size~lass data will fit either function there must at least be larger numbers of stems in the smaller size-classes. This would happen either because of continued recruitment of individuals or due to persistence of individuals already present. The latter case explains why some species fit these functions and some do n o t because continued recruitment into this vigorous, dense coppice forest is unlikely. For example, small A. rubrurn stems c o m m o n l y do not become suppressed in the understory, at least at this age. Very few dead stems of this species have been noted during recent inventories, although some stumps have as many as 10 stem sprouts. In contrast, Liriodendron stems whose crowns do n o t reach the canopy, soon become suppressed and die. The dead Liriodendron stems which were examined in 1 9 8 2 had an average age and diameter of 12 years and 6.3 cm, respectively. Mortality of this species from 1982 to 1984 has been confined to the smallest diameter individuals.

-

OCN

Fig. 5. Size-class distributions (stems ha-‘), all species combined, Acer rubrum (REM) and Liriodendron tulpifera(YEP), 21 years after the second clearcut. Data fit to negative exponential function (2.0 cm class intervals).

-4

-

Fig. 6. Size-class distributions (stems ha-‘), all species combined, Acer rubrum and Liriodendron clearcut. Data iit to negative power function (2.0 cm. class intervals).

tulpifera

21 years after the second

REM

106 Only three species, Liriodendron tulipifera, Quercus prinus and Robinia pseudoacacia contributed to annual mortality in 1982 and 1983. The annual mortality rates for these years, all species combined, were 1.6% and 0.1%, respectively. Other species may have been included if smaller stems (< 5.0 cm dbh) had been initially tagged, and annual forest mortality rates would have been greater for these years. Two factors are predominantly responsible for the forest structure 21 years after the second clearcut. First, the large number of species and their lOOO-

It

•

t, 4----4

COVE HARDWOODS MtXED OAK

ID--.II

OAK - PiNE

0.--4

\

\

(r 2 for fit of data to negative exponential curve, p$0.01)

',

,,,

",,

lOO

%,, "r

t

~,, \

a. r 2 = 0.96 1 , , , ,

"I

"\\

\ '4

,\

~ r2:0.93

z

b

1(

7

I 5.0

I r.o

t 9.0

I 11,0

J T3.0

DIAMETER

I ls.o

t 17.0

) 19.0

I 2~.0

I 23.o

I 2s.o

t 27.0

I 29.0

I '~1.0

CLASS, LOWER LIMIT (CM)

Fig. 7. Size-class distributions, all species combined for each community type 21 years after the second clearcut (2.0 cm class intervals).

107

inherently distinct growth rates under various competition intensities cause the initial stratification of diameter sizes. Imposed upon these growth rates is the effect of a very heterogeneous habitat typical of this mountainous region. If the size-class distributions of particular stands on this watershed (equal to c o m m u n i t y types} are analyzed, the affect of this site diversity is lessened. Although the coefficients of determination are still high when community type size-class structure is fit to the negative exponential curve (Fig. 7) these values are lower than for the entire forest. Large numbers of small diameter individuals occur in the Oak--Pine type whereas the Cove Hardw o o d s have much larger diameter individuals.

Growth characteristics of species Differences in species growth characteristics since the second clearcut are specified in Table 12. Carya spp., Quercus marilandica and Sassafras albidum have few sprouts and those present have a small diameter. In contrast, Pinus rigida sprouts are large in diameter and few in number. Acer rubrum, Arnelanchief arborea and Oxydendrum arboreurn maintain large numbers of relatively small sprouts vs. Liriodendron tulipifera, which has many large sprouts. Regardless of species, stems which are part of a clump are greater in diameter than those which are solitary. Single stems were usually associated with a stump, i.e., m o s t smaller stems did not originate from seed after the second clearcut. Only one stem persisted on these stumps, due possibly to low vigor or/and greater shading from surrounding trees. Single stem individuals which originated from seed since the second clearcut were rarely discovered. T A B L E 12 S p r o u t i n g c h a r a c t e r i s t i c s f o r trees o n W a t e r s h e d 1 3 (having a d e n s i t y o f 1 5 or m o r e s t e m s ha -a) Species

Mean number sprouts

Mean sprout diameter a

M e g n single stem diameter

Overall mean diameter

Liriodendron tulipifera Magnolia aeuminata Pinus riglda Robinia pseudoacacia Quercus prinus Q. coccinea Q. velutina Betula lenta Oxydendrurn arboreum Acer rubrurn Quercus marilandica Sassafras albidurn Carya spp. Amelanchier arborea Cornt~s florida

3.1 2.7 2.1 2.5 2.8 2.7 2.4 2.6 3.6 3.2 2.2 2.8 2.0 3.3 2.5

16.1 17.6 12.0 10.9 10.5 9.8 9.7 8.8 8.1 8.0 7.7 6.7 7.1 6.5 5.7

12,8 (30) c 10.6 (7) 11.4 (5) 10.4 (29) 9.1 ( 1 1 4 ) c 8.8 '(108) c 8.9 (81) 7.6 (33) c 7.8 (29) 6.8 ( 8 6 ) c 6.8 (28) 7.6 ( 1 9 ) 6.4 (42) 5.8 ( 1 3 ) 5.8 (48)

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(286) b (9) (17) (40) (351) (175) (47) (88) (107) (315) (62) (8) (21) (70) (42)

a A l l cUameter m e a s u r e m e n t s in c m d b h . bNu~er o f s t e m s in e a c h g r o u p , h a -I. C S p r o u t and single s t e m m e a n d i a m e t e r s o f this s p e c i e s are s i g n i f i c a n t l y d i f f e r e n t , 0t = 0 . 0 5 , S t u d e n t ' s

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108

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Fig. 8. A v e r a g e d i a m e t e r s ( i n s i d e b a r k ) f o r s e l e c t e d s p e c i e s w i t h i n c o m m u n i t y t y p e s , a f t e r s e c o n d c l e a r c u t . K e y t o a b b r e v i a t i o n s : Y E P = Liriodendron tulipifera, SWB = Betula lenta, R E M = A c e r rubrum, HIC = Carya s p p . , B L O = Quercus velutina, S C O = Q. coccinea, C H O = Q. prinus, BJO = Q. marilandica, S O U = O x y d e n d r u m arboreum, PIP = Pinus rigi-

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Overall mean diameters for all trees measured in 1984 are also indicated in Table 12. Mean diameters of canopy dominant, codominant or intermediate (except some Carya spp. that were suppressed) trees for the three community types since the last clearcut are illustrated in Fig. 8. These diameters are based on annual ring analysis of increment cores taken close to ground level and do not include the contribution of bark to diameters. The amount of bark varied per core by species from 0.5 mm for Betula lenta and Carya spp. to 10.0 mm for Liriodendron tulipifera. Over the 21-year period, Liriodendron in the canopy became substantially larger than all other species in both the Cove H a r d w o o d s and Mixed Oak types (Fig. 8). Diameters of Carya spp. appear to reach a plateau in these types. Pinus rigida diameters are generally the largest of any species in the Oak--Pine t y p e whereas Quercus marUandica are the smallest. Mean annual radial growth, in 5-year intervals since the last clearcut, is given in Table 13. Although there was much variation within and between species for a specific year (standard deviations per year varied from 83% for Q. prinus to 120% for Liriodendron), all species exhibited a general decline in growth over the 21 years. This gradual decline of radial increment and variation on an annual basis is depicted in Fig. 9 for Carya spp., Liriodendron and Q. prinus. These results suggest that c a n o p y closure occurred 12-14 y e a r s after the cut. Radial increment appears to have stabilized for Carya spp. and Quercus prinus; however, Liriodendron growth is still erratic. TABL ~ Mean ahnual radial growth (ram) of tree species on Watershed 13, during 5-year intervals since last clearcut

Species

Acer rubrum Betula lenta Carya spp. Liriodendron tulipifera a Magnolia acuminata M. fraseri Oxydendrum arboreum t~'nus rigida Quercus alba Q. coccinea Q. marilandica Q. prinus b Q. velutina Robinia pseudoacacia Sassafras albidum

Interval 1964--1968

1969--1973

1974--1978

1979--1983

3.65 3.35 3.44 5.73 3.71 3.54 3.21 2.62 2.97 3.14 2.33 4.48 3.89 3.37 2.84

3.30 3.19 2.21 5.83 3.45 3.10 2.49 3.18 2.13 2.61 1.51 3.50 3.48 2.68 2.17

2.21 2.85 1.17 4.30 3.02 2.28 1.80 2.89 1.56 2.36 1.02 2.40 2.04 1.69 1.87

1.56 2.42 0.57 3.26 2.42 1.89 1.20 2.25 1.55 2.16 0.67 2.17 1.75 1.26 1.45

a Includes cores collected in 1981, 1982, 1983. blncludes cores collected in 1982, 1983.

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113

Present canopy structure Tree heights within the t w o most dissimilar c o m m u n i t y types, Cove Hardw o o d s and Oak--Pine are shown in Fig. 10. The majority of Liriodendron in the Cove H a r d w o o d t y p e are 17.5 m tall or greater after only 21 years. Nearly all Carya spp., Comus florida and Nyssa sylvatica were 12.5 m in height or less. Overall c a n o p y height is much lower in the Oak--Pine type as few c a n o p y dominants exceed 10 m in height. Within this type, relatively tall Pinus rigida are scattered among shorter Quercus spp. (primarily Q. coccinea and Q. marilandica) which constitute the main canopy. Few species actually occur in all three c o m m u n i t y types b u t for the few which do, there is a gradual decrease in height for such species, from the Cove H a r d w o o d s to Oak--Pine types as shown in Fig. 11 for A. rubrum and all Quercus spp. combined. DISCUSSION

Vegetation composition and structure One should be careful in comparing changes in species composition and structure over the 50-year period because repeated measurements were made on different plots. Another problem arises in relating these results to other regional studies because of different m i n i m u m diameter limits for sampling. Nevertheless, trends in forest dynamics are apparent and regional comparisons are stillvaluable as long as these limitations are recognized. Successive clearcuts apparently have not lowered forest productivity of Watershed 13. Presently the basal area is over 8 0 % of that before the first clearcut, and is about 8 0 % of the 1970 value for a nearby watershed, undisturbed (other than by chestnut blight) since the early 19208 (Day and Monk, 1974; m i n i m u m diameter 2.5 c m dbh). However, basal area was higher for forests of similar elevation and species composition in the Great S m o k y Mountains National Park (Whittaker, 1966; m i n i m u m diameter 1.0 c m dbh); values included 26.9, 35.0 and 53.2 m 2 ha "-Ifor a 'transitional'cove, mature chestnut oak and climax cove forests,respectively.Whittaker (1966) characterized the climax cove forests as having dominant trees aged 400 years or more, being 30--40 m tall and having diameters of 60--120 cm. Obviously the clearcut watershed in the present study is far from attaining such structural attributes. But it appears that clearcutting has made this watershed more productive, partly because of the nature of coppice stands (Smith, 1962, p. 517); and because the effects of past selective logging and chestnut blight have been minimized compared to stands in this region where the effect of these disturbances is stillevident. Research elsewhere in the Southern Appalachians demonstrates the benefit of m u c h lighter cuts in promoting ultimately higher productivity in otherwise degraded stands (Della-Bianca, 1983).

114 Outside of the southern section of the Blue Ridge Physiographic Province, forest basal area appears to be relatively lower. For example, within the Ridge and Valley Province, values for nine 60-year-old stands in an Appalachian oak forest averaged 23.0 m 2 ha -1 (McEvoy et al., 1980; all trees > 5.0 m height). Within the Cumberland Plateau, an old-growth and secondgrowth mixed mesophytic forest had basal areas of 27.8 and 24.6 m 2 ha-1, respectively (Muller, 1982; all stems/> 2.5 cm dbh). Mature forests throughout the eastern United States (Auten, 1941; Schmelz and Lindsey, 1965; Held and Winstead, 1975) average around 30.0 m 2 ha -1. Therefore the present study reiterates what others have concluded about the resilience of mesic forests to disturbance, i.e., these forests have a tremendous regenerative capacity (Marks and Bormann, 1972; Boring et al., 1981) even when recovery processes are initially inhibited by enforced devegetation (Likens et al., 1978; Kochenderfer and Wendel, 1983). Past disturbances have had different roles in the development of this forest. According to Kovner's description (1955), photographs taken during the first clearcut, and the 1934 stand structure, selective logging prior to 1923 apparently removed a substantial number of canopy trees. This allowed for reproduction of intolerant and midtolerant species (cf. Baker, 1949; Fowells, 1965), e.g., Betula lenta, Carya spp., Liriodendron tulipifera, Pinus rigida, Quercus spp. and Sassafras albidurn (Table 3) before the first clearcut. The first clearcut also promoted the regeneration of these species, especially the wind-dispersed species (B. lenta, L. tulipifera, and P. rigida). Additional individuals of Acer rubrum, B. lenta, L. tulipifera, Oxydendrum arboreum and P. rigida established particularly on lower to mid slopes because of openings created by dead or dying Castanea dentata. Liriodendron commonly had replaced Castanea on a nearby watershed at Coweeta (Nelson, 1955). Undoubtedly, Quercus spp. also established during this period. So, species density values prior to the second clearcut reflect the combined influences of selective logging in the early 1900s, chestnut blight beginning around 1930, and the first clearcut. Forest composition and structure at this time resulted due to new establishment of individuals and sprouting of existing stems. There is no evidence that tree species did not occupy all of the available growing space on Watershed 13 just before the second clearcut in 1962. Generally, no recruitment of stems appeared to be taking place at this time in the smallest size-classes of any species (Table 9). Rather, stems which had been in the lower-size classes in earlier inventories either grew into larger classes, became suppressed (e.g., Carya spp.), or died (especially C. dentata). In contrast to the regenerative mechanisms following the first clearcut, sprouting was the primary mechanism following the second clearcut, because if many seedlings initially regenerated, their survival against sprouts is doubtful. This is supported by hydrologic data {Swank and Helvey, 1970) and the predominance of stump origin stems. Not many stems were seen which had obviously not originated from a stump. Those few exceptions were found on

115 upper slopes where the canopy was less dense (Leopold and Parker, 1985). Therefore, the present forest resulted primarily from differential sprouting ability and growth among species. The substantial increase in L. tulipifera and Quercus prinus relative density and basal area is attributable to the large number of fast-growing sprouts (Table 12). Other species, e.g., A. rubrum and O. arboreum had greater numbers of sprouts which grew less rapidly. These species have been persistent at relatively high densities because of their tolerance to low light levels (Baker, 1949; Fowells, 1965). Quercus alba and Q. rubra sprouts apparently grew slower than associated species (Q. prinus and Liriodendron, respectively) because these Quercus spp. declined in importance due to both clearcuts. Although this forest is even-aged, the size-class structure resembles that depicted for all-aged, mature forests (Jones, 1945; Meyer and Stevenson, 1943; Meyer, 1952; West et al., 1981). Size-class distributions have been used for forest management decisions (Minckler, 1974; Trimble and Smith, 1976} and more questionably as an indicator of past stand disturbance (Schmelz and Lindsey, 1965; Johnson and Bell, 1975). Reasons why the negative exponential distribution could be more appropriate than the normal curve for even-aged, mixed species stands would include: (1} Clearcutting promotes regeneration from sprouts and new seedlings. Sprout growth is much faster than seedling growth (Renshaw and Doolittle, 1958; Roach and Gingrich, 1968; McQuilken, 1975). (2) Growth rates vary within a species at any particular age (McGee and Della~Bianca, 1967; Ford, 1975; Mohler et al., 1978). (3) Growth rates vary within a species over time (Oliver, 1978). {4) Growth rates vary between species (Fowells, 1965; Solomon and Blum, 1967; Trimble, 1969, Wendel, 1975). (5) Vertical stratification of shade tolerant species occurs (because of the three previous points) beneath intolerant canopy species which further contributes to different growth rates among species of these tolerance groups (Wilson, 1953; Bicknell, 1982; Lorimer and Krug, 1983; Marquis, 1983). (6} Forest age is young, therefore diameter classes are few and most stems occur in the smaller diameter classes (West et al., 1981). All of these statements, to various degrees, explain the present size-class distribution of this even-aged forest. Statement (1) probably is least significant, at least in relation to forest structural development after the second clearcut because of the predominance of sprout origin stems. Though statement (6) may be partially valid, especially for the earliest inventories after each clearcut, it can not explain the fit of the negative exponential function of older evenaged stands (Wilson, 1953; Putnam et al., 1960; Oliver, 1978; Muller, 1982). A more likely explanation for such diameter stratification in a single age class population has been implicit in previous statements, i.e., growth rates are indeed variable within and between species especially when species are distributed over such heterogeneous sites (Leopold and Parker, 1985} typical

116

of this mountainous region (Braun, 1950; Whittaker, 1956; Day and Monk, 1974; Golden, 1981). Relation to current ideas on forest development

These data support two generalizations on forest development following disturbance, recently discussed by Oliver (1981). In studies he reviewed, there was much evidence that even-aged forests often had diameter distributions typically associated with all-aged forests; and that most existing stems had established in a short period after disturbance. Inherent in the second point is a mechanism of old field succession proposed by Egler (1954), the "initial floristic composition," which suggests that most of the dominants throughout succession had actually invaded the site immediately after disturbance rather than at distinct successional stages. This concept is the foundation for the inhibition model of succession described by Connell and Slatyer (1977). In this model, species which dominate throughout succession had colonized the site soon after disturbance, and will continue to dominate unless destroyed. Continued dominance by those species on Watershed 13 is expected as proposed by the inhibition model. Of the four stages of stand development: stand initiation, stem exclusion, understory reinitiation and old-growth stages (Oliver, 1981}; the forest of Watershed 13 is still in the second stage. Stand initiation occurred primarily in the first growing season after the second clearcut, except on upper slope positions which have had slower canopy development. It is speculated that the stem exclusion stage will endure for at least an additional 25--50 years, barring any intervening large-scale disturbance. In the interim, space occupied by stems which die will be replaced by existing stems as canopies extend outward. Although the scenario of forest development illustrated by Oliver (1981) recognizes a shift in species dominance during the stem exclusion stage, this event appears unlikely at the present study area because of species heights and incremental growth data. For example, even though radial growth of the canopy dominant Liriodendron has gradually declined (Table 13, Fig. 9), which is a typical function of age (Assmann, 1970), growth of this species is still greater than any other over the same period. Because of its present canopy position (Fig. 10) and relatively fast growth rate, Liriodendron will continue to dominate these stands unless a severe disturbance such as drought occurs.

Thus far, the term "succession" has been purposely disparaged because it implies a sequence of changes in species and species assemblages (Drury and Nisbet, 1973). Such sequences have not been characteristic of at least the early stages of forest development in this study, and presumably will n o t be for quite some time until understory reinitiation and old-growth stages occur. Perhaps the term "forest regrowth" or "forest development" is more appropriate for circumstances as described here. "Forest development" has

117

a broader meaning, in that it encompasses simply regrowth or the more complex processes of succession. Regardless of terminology, forest dynamics after a disturbance result because of specific life history attributes {Noble and Slatyer, 1977, 1980) and population processes (Peet and Christensen, 1980). Species characteristics and processes are modified by competitive interactions over the environmental gradient, which eventually may become very stressful to a species. The outcome of these interactions determines the climax vegetation of a site, in the absence of further exogeneous perturbations. ACKNOWLEDGMENTS

We thank the following persons for their comments on this manuscript: W.R. Byrnes, W.R. Charley, B.C. Fischer, P.T. Sherwood, and J.S. Ward. This paper is a contribution from Purdue University Agricultural Experiment Station {Paper No. 10171). Research was supported by National Science Foundation Grant No. DEB-8012093.

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