Forest Ecology and Management, 14 (1986)293--304
Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands
REGENERATION AND SURVIVAL OF TREE SEEDLINGS AND SPROUTS IN TROPICAL DECIDUOUS AND SUB-TROPICAL FORESTS OF MEGHALAYA, INDIA
M.L. KHAN, J.P.N. RAI and R.S. TRIPATHI
Department of Botany, School of Life Sciences, North-Eastern Hill Univeristy, Shillong 793 014 (India) (Accepted 4 October 1985)
ABSTRACT Khan, M.L., Rai, J.P.N. and Tripathi, R.S., 1986. Regeneration and survival of tree seedlings and sprouts in tropical deciduous and sub-tropical forests of Meghalaya, India. For. Ecol. Manage., 14: 293--304. Species composition, regeneration status and survival of seedlings and sprouts of tree species were studied in tropical and subtropical forests of Meghalaya State in northeast India. The subtropical humid semi-evergreen forests at Upper Shillong and Mawphlang are dominated b y Manglietia insignis, Pinus kesiya, Quercus dealbata, Q. griffithii, Rhododendron arboreum, Schima khasiana and Prunus undulata whereas the tropical deciduous forest lying at lower altitude (Burnihat) is dominated by Artocarpus chaplasa, Duabanga sonneratoides and Shorea robusta. The species composition of the tree community at the periphery is different from that of the forest stand at the centre. In the forests at Upper Shillong and Burnihat 40% of the tree species regenerated through both seedlings and sprouts, whereas the percentage of such trees in the undisturbed forest at Mawphlang was only about 22%. Survival of seedlings and sprouts was higher at the forest periphery than under the dense canopy, signifying the role of light in forest regeneration. Although the seedling mortality occurred throughout the year, it was particularly high during winter season due to prevailing low temperature and high soil moisture stress. The sprouts, however, were less susceptible to adverse environmental conditions.
The ratio of forested land to total geographical area in Meghalaya State in north-east India is quite high. High rainfall, moderate temperature and wide variation in altitude and soilcharacters of the state provide a favourable environment for the luxuriant growth of humid tropical deciduous forests at lower altitudes (< 200 m) and sub-tropical evergreen forests at higher altitudes (> 900 m). The forest cover in the state has been reduced from 63.98% in 1975 to 55.39% in 1982 (National Remote Sensing Agency Report, Government of India, 1983), which is quite alarming. The increasing population pressure, prevailing shiftingcultivation (slash and burn agriculture
© 1986 Elsevier Science Publishers B.V.
locally called 'jhum') and other developmental activities in the region have also adversely affected the forest cover, ecological status of the forests and regeneration of the component tree species in these forests. Regeneration of tree species and survival and growth of their seedlings and sprouts depend upon the interactive influence of biotic and abiotic factors of the forest environment. Although the effect of certain factors like light intensity (Howard, 1973; Bazzaz and Pickett, 1980; Augspurger, 1984a,b,c; Burton and Mueller-Dombois, 1984; Connell et al., 1984), temperature (Sorensen and Ferrell, 1973), soft moisture (McLeod and Murphy, 1977; Mueller-Dombois et al., 1980; Schulte and Marshall, 1983), soil nutrients (Kliejunas and Ko, 1974; Mullin and Browdery, 1977; Mullin, 1978; Jamaluddin, 1978; Van Den Driessche, 1982) and pathogens (MuellerDombois et al., 1983; Augspurger, 1984a, b; Connell et al., 1984) has been studied on survival and growth of tree seedlings in other tropical, subtropical and temperate forests, there is conspicuous lack of studies on population behaviour of tree seedlings of this region. Keeping this in view, the present investigation was carried out to study the regeneration status of the forests and survival of naturally emerged seedlings and sprouts of the tree species in relation to their habitat conditions. MATERIALS AND METHODS
Characteristics of the study sites The three ecologically different natural forests occurring in Upper Shillong, Mawphlang and Burnihat in Meghalaya (25°15'--26°05'N and 89o56 ' 92°47'E) were selected for the study. (a) Forest at Upper Shillong. The forest at Upper Shillong represents a subtropical, humid, evergreen montane type (Champion, 1936). The vegetaTABLE 1 Physical and chemical attributes o f the study sites Sites
(lx x 103)
16.7 (6.9) a
aValues in parentheses refer t o light intensity in the forest stands in the centre.
295 tion is mixed broad leaved with oaks and laurels as dominant species. The forest stand on the bottom of the hill slope is dominated by Quercus dealbata, Quercus griffithii, Schima khasiana and Myrica esculenta with Rhododendron spp., Eurya japonica, Myrsine semierrata, Lindera pulcherrima and Symplocus spp. forming the under storey. Litsea spp., Dhaphne shillong, Lantana camara, Cinnamomum spp. are the c o m m o n shrubs and Osbeckia crinata, Eupatorium adenophorum, Coffea khasiana, Rubus spp. and some ferns and mosses represent the herbaceous ground flora. The soil is lateritic with a low organic m a t t e r and nitrogen content (Table 1). The forest is exposed to disturbances such as tree felling and burning. Shifting cultivation involving slashing and burning of forest vegetation is also practised in the area. As a result, the canopy is relatively sparse. (b) Forest at Mawphlang. This forest, representing relic climax vegetation, is 25 krn southeast of ShiUong, the capital t o w n of Meghalaya. The belief of the local people who maintain that the sylvan deities would be offended if trees are cut and flowers and fruits plucked, has given this forest the status of a 'sacred grove.' This forest, therefore, has remained more or less undisturbed for the last several centuries. It represents a typical subtropical humid semi-evergreen forest. The important tree species are Cory-
lopsis himalayana, Manglietia caveane, Quercus dealbata, Quercus griffithii, Manglietia insignis and Schima khasiana with an understorey consisting of Rhododendron spp. Eurya japonica, Urena lobata, Dhaphne shillong, D. bhalue and ferns and mosses. The soil is a light grey laterite and is rich in organic m a t t e r and nitrogen (Table 1). (c) Forest at Burnihat. The forest at Burnihat lies 90 k m northeast of Shillong and represents a successionally y o u n g forest of humid tropical deciduous type. The vegetation is rich in ground flora consisting o f Curcuma spicata,
Calocasia offenis, Costus specious, Draccana spicata, Dioscorea bulbifera, Fimbristylis dicotoma, Piper longum, Smilax ferox, Vernonia cinerea etc. The c o m m o n shrubs are Anoma wallichii, Alophylus serratus, Combretum decandrura, Mesua indica, Litsea khasiana, Randia densiflora and Sterculia cocinia. The dominant tree species are Artocarpus chaplasa, Amoora wallichii, Shorea robusta, Gmelina arborea, Castanopsis indica, Schima wallichii etc. The soil is a red loamy laterite and is very rich in organic matter and nitrogen (Table 1).
Clima te The climate is monsoonic (annual rainfall ca. 2500 ram) with over 85% of the rainfall occurring during May to September. The winter season (November to February) is characterized by low temperatures and occasional rain. The average m a x i m u m and minimum temperatures at Burnihat are 25 and 12°C respectively during winter and 34 and 23°C respectively for
5.88 39.20 8.58 52.95 14.63 56.49 3.79 61.58 9.83 48.32 2.08 62.14 4.79 97.57 3.21 82,61 1,75 48.25 0.58 88.83 0.33 200.00 1.79 130.32 0.92 200.00 5.58 37.24 3.00 99.48
9,92 12.76 15.38 33.45 19.92 30.48 6.38 40.47 13.33 27.86 3.54 59.32 6.58 75.17 5.38 63.57 3.00 50.31 1.00 97.18 0.54 200,00 4.21 84.78 1.25 200.00 10.58 22.47 4.79 89.28
6.83 22.09 13.17 67.28 24.75 64.43 3.67 28.26 17.92 67.50 3.17 67.54 6.83 83.14 2.00 44.62 2.71 71.30 1.67 49.67 0.46 176.59 5.21 110.62 1.13 190.25 8.88 67.84 4.29 83.13
9.83 23.97 19.13 37.43 28.54 51.95 5.38 38.26 19.33 60.32 4.46 65.49 9.21 69.96 3.08 59.95 3.96 73.92 2.29 38.66 0.50 178.47 8.08 57.89 1.21 182.07 13.46 36,66 5.67 68.56
10.54 17.43 26.00 26.23 51.42 28.88 6.00 52.26 24.42 46.20 4.54 64.64 27.00 85.50 2.75 66.85 2.63 69.43 3.25 77.94 1.92 71.18 7.92 64.33 7.54 84.58 13.92 55.11 12.08 74.66
13.83 4.06 32.58 13.75 54.88 26.43 7.67 46.32 26.50 44.21 6.17 63.96 28.38 81.23 3.50 58.45 3.71 73.98 4.17 72.37 2,46 65.59 9.71 59.44 9.04 77.09 17.38 49.67 15.21 67.02
• R ffi raw data; C ffi data corrected for loss o f root tips during processing. b CV ffi coefficient o f variation.
Total n u m b e r o f mycorrhizas (M51 and M52) CV b Total n u m b e r of myeorrhizal root tips (M51 and M52) CV T o t a l l e n g t h o f mycorrhizas (M51 and M52) (ram) CV Total n u m b e r o f M51 mycorrhizas CV T o t a i l e n g t h of M51 mycorrhizas ( m m ) CV Total n u m b e r o f M52 m y c o r r h i z u CV Total length o f M52 mycorrhizas (ram) CV N u m b e r of monopodial M51 mycorrhizas CV N u m b e r o f monopodial M52 mycorrhizas CV N u m b e r o f branched M51 mycorrhizas CV N u m b e r o f branched M52 mycorrhizas CV N u m b e r o f secondary tips (M51) CV N u m b e r o f secondary tips (M52) CV Total n u m b e r o f M51 m y c o r r h i z a l t i p s CV Total n u m b e r o f M52 mycorrhizal tips CV
5.63 60.06 9.29 25.68 16,67 20.22 3.83 69.66 12.54 32.95 1.79 40.46 4.08 26.77 2.63 123.92 1.50 48.01 1.21 49.57 0.29 28.57 3.17 80.51 0.50 60.86 7.00 27.97 2.29 35.32
8.92 30.92 15.88 12.37 20.88 15.91 6.08 40,13 15.42 21.41 2,88 11.95 5.46 19.37 3.75 96.73 2.33 19.34 2.29 63.23 0.54 46.15 5.71 60,14 1.25 73.43 11.75 14.72 4.13 29.76
Mean value• (per cm long root) for mycorrhizal characteristics o f Sitka spruce cuttings rooted in mistbeds and transplanted for a year to nursery transplant beds
297 the remaining months of the year. Upper Shillong and Mawphlang areas are characterized by colder climate (average maximum and minimum temperatures being 16 and 3°C respectively during winters and 22 and 15°C during the rest of the year).
Method of study In a given forest, species composition of the forest stands at the periphery and in the middle of the forest was separately studied in July, 1983. The two stands differed from each other in respect of light intensity and vegetation density. The light intensity at ground surface in the sparse forest stand at the periphery was 13000--17000 lx and in the dense forest stand in the middle it was 5000--8000 lx. Density of the trees and their seedlings was determined by laying 10 quadrats of 20 m × 20 m size in each of the above two stands in a given forest. For studying the seedling survival, 35--50 seedlings of those species which showed regeneration by seedlings were tagged with labelled aluminium foil. Survival of the seedlings was studied at bimonthly intervals on the two sites of the three forests over a period of one year. On each observation date, density of the ground frora was also determined in randomly laid ten 2 m × 2 m quadrats. Ten soil samples representing 0--10 cm soil depth were collected from a given stand on each observation date and the soil moisture content was determined following the method outlined by Piper (1947). The organic matter of the soil was determined by rapid titration method, soil nitrogen by microKjeldahl method (Jackson, 1962) and soil pH by a digital pH meter. For studying the survival of sprouts, ten stumps of a given species bearing 3--6 sprouts having 1 0 - 2 0 leaves were marked in the forest stands selected for study. The sprouts were tagged by labelled aluminium foil and their fate was followed at bimonthly intervals. RESULTS
Species composition The forests at Upper Shillong and Mawphlang representing a subtropical mixed semi~evergreen forest exhibited a few common tree species such as
Manglietia insignis, Myrica esculenta, Quercus dealbata, Q. griffithii, Rhododendron arboreum, Schima khasiana and Prunus undulata, whereas the species composition of the forest at Burnihat which is tropical deciduous is quite different (Table 2). The dominant species are Pinus kesiya and Quercus spp. in Upper ShiUong forest, Corylopsis himalayana, Manglietia caveane and Schima khasiana in Mawphlang forest and Artocarpus chaplasa and Duabanga sonneratoides in Bumihat forest. The species composition was also affected by light intensity. Exbucklandia populnea and Duabanga sonneratoides occur only at the periphery of the Mawpldang forest and
298 Bumhiat forest respectively. Contrastingly, a few species were exclusively p r e s e n t in t h e d e n s e f o r e s t s t a n d . S u c h s p e c i e s a r e D a p h n i p h y l l u m himalayense, Manglietia insignis and Prunus undulata (in U p p e r S h i l l o n g f o r e s t ) ,
Corylopsis himalayana, Manglietia caveane, Manglietia insignis, Myrica esculenta, P h y l l a n t h u s glaucus, Prunus undulata and Taxus baccata (in M a w p h l a n g f o r e s t ) a n d A m o o r a wallichii, Castanopsis indica a n d t w o s p e c i e s o f Terminalia in the f o r e s t o f B u r n ± h a t . A l t h o u g h m o s t o f t h e s p e c i e s t h a t w e r e p r e s e n t in b o t h d e n s e f o r e s t stand and f o r e s t s t a n d n e a r t h e p e r i p h e r y TABLE 3 Density (± S.E.) of tree seedlings and stumps bearing sprouts in the forests under study Location of the forest c o m m u n i t y
Density (ha -1 ) Seedlings
Upper Shillong Forest stand in the centre
Forest stand near the periphery
Mawphlang Forest stand in the centre
Forest stand near the periphery Burn±hat Forest stand in the centre
Forest stand near the periphery
A. nepalensis D. hirnalayense P. kesiya Q. dealbata Q. grifflthii S. khasiana A. nepalensis P. kesiya Q. dealbata Q. griffithii 8, khasiana M. caveane Q. dealbata Q. griffithii S. khasiana Q. dealbata Q. griffithii R. arboreum S. khasiana
80 ± 6.9
290 90 45 70
± ± ± ±
16.3 7.8 4.2 3.8
30 15 0 32 38 40
90 412 100 70 90
± ± ± ± ±
4.2 62.4 21.0 11.2 13.8
45 0 48 39 70
40 ± 3.6 42 ± 4.0 42 ± 2.8
40 14 13 12
± ± ± ±
64 98 90 102
± ± ± ±
6.3 9.8 10.0 12.2
A. wallichii 42 ± C. indica 46 ± S. wallichff 42 ± S. robusta 0 ± T. chebula 0 A. chaplasa 0 D. sonneratoides 52 * E. communis 0 G. arborea 61 ± S. wallichii 202 ± S. robusta 65 ±
8.2 2.7 3.0 4.0
6.7 9.0 41.2 13.7
± 3.2 ± 2.5 ± 3.0 ± 4.6 ± 3.2
± 4.9 ± 3.0 ± 6,9 4.2 2.2 2.4 1.2
38 ± 4.0 41 ± 2.8 0 72 ± 6.7 25 0 32 18 22 42 0 30 33 70 49
± 2.4 ± 4.2 ± 2.2 ± 3.2 ± 3.9 ± 4.2 ± 2.9 ± 4.5 ± 3.9
299 showed greater density in the former, species such as Eugenia communis in Burnhiat and Quercus griffithii, Rhododendron arboreum and Schima khasiana in Mawphlang forest showed higher density at the periphery (Table 2). Status of tree regeneration Out of 10 tree specie s in the forest at Upper Shillong, four (Alnus nepaelensis, Quercus dealbata, Q. griffithii and Schima khasiana) regenerated by both seedlings and sprouts. Daphniphyllum himalayense, however, regenerated only through sprouts and Pinus kesiya by seedlings. At Mawphlang forest only three species, viz. Quercus dealbata, Q. griffithii and Schima khasiana, regenerated by both seedlings and sprouts. Regeneration of Rhododendron arboreum was only by seedlings in the forest stand at the periphery and Manglietia caveane regenerated only through the sprouts in the dense forest. In the forest at Bumihat only four species showed regeneration through both seedlings and sprouts. Among these, Schima wallichii and Shorea robusta were present both in the dense forest stand and in the forest stand at the periphery. Conversely, Amoora wallichii and Gmelina arborea were restricted to the dense forest and the forest stand near the periphery respectively (Table 3). Amongst the species exclusive to a particular forest stand, Castanopsis indica regenerated through seedlings and Terminalia chebula by sprouts in the dense forest, whereas Duabanga sonneratoides regenerated through seedlings and Artocarpus chaplasa and Eugenia communis by sprouts in the forest stand near the periphery (Table 3). Seedling survival Survival of the tree seedlings was lowest during the winter months and it was relatively better during the rainy season and spring (Fig. i). The seedling population showed poor survival in the dense forest stands of all the three localities. Survival of the seedlings of Quereus spp. and Schima khasiana was nil in dense forest stands, while about 35% of seedlings of Quereus spp. and about 10% of Schima khasiana survived in the forest stands near the periphery at Upper ShiUong and Mawphlang. The seedlings of Quereus griffithiishowed better survival than that of Q. dealbata in the forests of both localities. In the forest at Burnihat, seedlings of Shorea robusta and Schima wallichii showed 100% mortality in the dense stand, whereas more than 2 5 % of the seedlings survived in the forest stand near the periphery (Fig. 1).
Survival of sprou ts The sprouts also exhibited a similar survival trend to that shown by the seedling population. However, mortality of the sprouts was far less than
300 Forest ~.tand at the Centre
Forest stand near the Periphery UPPER
~, neDaiensis, J- .~P. kesiya, o - o Q. dealbata ,l~eQ. ~ l r i f f i i h i i , H S . I0 C
J, - "....
0 MAWPHLANG Q. dealbata,#- - - Q_. 9 r i t f i t h i i , I - - I
R. a r b o r e u m ,
> Iz ul
tu Iz D 25~o Z .J
a---~ A . wallichil J---A C. indica e - - ~ .~. wal lichii
I - - i l G . # r b o r e a ,e--.~ 5 . r o b u s t a
~.~'~ ~ 25
25 0 JUL
MAR MAY 1984
MAR MAY 1984
Fig. 1. Survival of naturally emerged tree seedlings in the forest stand in the centre and near the periphery of the forests at Upper Shillong, Mawphlang and Burnihat. Dotted lines denote the soil moisture and vertical bars represent density (m -2) of under-canopy vegetation
that of the seedlings. The reduced light intensity under the dense forest stand resulted in greater mortality of the sprouts, especially in the forest at Mawphlang where about 20% of the sprout mortality in the two speices o f Quercus was observed to be due to reduced light intensity. In contrast to the seedling population, the sprout survival was better in Quercus dealbata than in Q. griffithii (Fig. 2). DISCUSSION
Species composition o f the forests at Upper Shillong and Mawphlang is more or less similar, which may be attributed to the similarity in altitude and climatic conditions o f these two localities. However, the forest at Bumihat, which is located at a lower altitude, shows a different species
a A. ne~len$is,
stand near Periphery
UPPER SHILLONG o _Q.de•lbata . • Q_. 9 ~ ,
• _D. i~imalaven~,e,
MAWPHLANG • Q. q r i f f i t h i i ,
BuRNiHAT Q A.chaol#~l. a _A.wallichii. I_E,communi~.o o 5. w a U i c h i i , •_T.~:hvl;)uI•
L E S P 1983
Fig. 2. Survival of naturally emerged tree sprouts in the forest stand in the centre and near the periphery of the forests at Upper Shillong, Mawphlang and Burnihat. composition. The difference between floristic composition of the forest stand having closed canopy and the stand occurring at the periphery as observed in the present study, is in agreement with the observations of Bainbridge et al. (1966), Howard (1973), Whitmore (1975), Hartshorn (1978, 1980), Brokaw (1980), Spurt and Barnes (1980), Lorimer (1983) and Augspurger (1984c). Exbucklandia populnea (in Mawphlang forest) and Duabanga sonneratoides (in the forest at Burnihat) grow only in well lighted areas and thus they may be considered as shade-intolerant and early successional species. Conversely, Daphniphyllum himalayense, Mang-
lietia insignis, Prunus undulata, Corylopsis himalayana, Manglietia caveane, Phyllanthus glaucus, Taxus baccata, Amoora waUichii, Castanopsis indica and two species of Terminalia which grow in dense stands (Table 2) may be regarded as shade-tolerant and late successional species. Density of trees in a forest is largely dependent upon the response of
302 the tree seedlings/sprouts to the prevailing microenvironment. The tree seedlings/sprouts showed better survival in the stand near the periphery than in the dense forest stands, which may be attributed to a lack of threshold light intensities for photosynthesis in the seedlings. This conforms with the observations of Whitmore (1975) Garwood (1979), Sasaki and Mori (1981), Abbott (1984), Augspurger (1984c), Langenheim et al. (1984) and Primack et al. (1985). Ekwebelam and Reid (1983) reported a substantial decrease in assimilates produced by pine seedlings under a low light regime. Lower seedling survival in the dense forest stands and poor regeneration in the 'Sacred grove' of Mawphlang, which is almost undisturbed and has a close canopy, may be ascribed to the decrease in assimilation. Boring et al. (1981) have emphasised the positive role of disturbances such as clearcutting of trees in improving the regeneration of forest. The peak mortality of tree seedlings during winter months may be due to prevailing low temperature and high soil moisture stress (Fig. 1). The detrimental effect of soil moisture stress on the survival of tree seedlings has also been reported by earlier workers (e.g. McLeod and Murphy, 1977; Pereira and Kozlowski, 1977; Mueiler-Dombeis et al., 1980; Schulte and Marshall, 1983). Significance of under-canopy vegetation in determining the size of seedling populations of trees through mortality has also been emphasised by Cross (1981), Eis (1981), Maguire and Forman (1983), Burton and MueUer-Dombois (1984) and Connell et al. (1984). The undercanopy vegetation may also influence seedling survival of tree species through their allelopathic effects, as has been reported by Rice (1974), Stewart (1975), Horsley (1977a,b), Willis (1980) and Ashton and William (1982). The possible effect of accumulated litter and its decomposition products on seedling survival also needs to be emphasised. The decrease in population size of the tree seedlings during the rainy season especially on the periphery of the forests is largely caused by the erosive action of the torrential rain received on the hill slopes of Meghalaya. ACKNOWLEDGEMENT This study was supported by the Department of Environment, Govt. of India under the Himalayan Eco-Development Programme.
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