Ecological Study of Bryophytes on Platanus orientalis L . Trees in Nainital ( Western Himalaya )

The bryophytic vegetation associated with Platanus orientalis trees were studied and compared with other important tree species of Nainital. In total 27 mosses and liverworts belonging to 14 families with three morphological groups formed the principle component of Platanus orientalis tree bark. Based on IVI (Important Value Index), Regmatodon orthostegius together with Brachymenium capitulatum formed the pioneer community, while Herpetineuron toccoae formed the climax community on the Platanus orientalis stems. Comparison of the bryoflora of P. orientalis with other dominant trees of this locality indicated that 15 species were common, while 12 species viz., Didymodon vinealis (Brid.) R.H., Bryoerythrophyllum dentatum (Mitt.) Chen, Gemmabryum apiculatum (Schwägr.), Ditrichum heteromallum (Hedw.) Britt., Entodon chloropus Ren. & Card., Cylindrothecium laetum (Griff.) Paris, Fabronia schensiana C. Muell., Lejeunea tuberculosa Stephani, Levierella neckeroides (Griff.), Regmatodon orthostegius Mont., Rhynchostegiella menadensis (Lac.) Bartr. and Stereophyllum fulvum (Harv.) Jaeg. were confined to the tree barks of P. orientalis.


Introduction
Epiphytic bryophytes constitute an important and integral part of forest communities in and around Nainital.Species richness and host specificity of bryophytes in relation to a large number of phorophytes have been studied in western countries [1]- [5].In India, epiphytic succession has been studied on tree trunks in a mixed oak-cedar forest in Kumaun Himalaya [6].Tewari and Pant [7] studied bryophyte diversity on four oak species and three gymnosperms and listed a total of 90 moss and 22 liverwort taxa from the bark of these phorophytes in Nainital.Similarly, Pande et al. [8] reported 21 bryophyte taxa from the bark of Aesculus indica in Nainital.Joshi [9] reported 19 species of bryophytes from the phorophytes at higher altitude forests of Kumaun Himalaya i.e., Quercus semecarpifolia, Abies pindrow, Aesculus indica and Acer cappadocicum.Awasthi et al. [10] reported 17 bryophyte taxa from bark of Erythrina arborescens and 8 mosses from endemic plant Trachycarpus takil of Kumaun [11].Bansal et al. [12] reported several bryophyte species on the bark of Thuja orientalis in Nagaland.Pande [13] studied the species richness and phytosociology of bryophytes in diverse habitats of Nainital.Pande and Joshi [14] [15] reported the species richness and phytosociology of bryophytes occurring on decaying logs at kharsu oak and silver fir forest.Nath et al. [16] studied the diversity of epiphytic moss flora of Pachmarhi Biosphere Reserve (Madhya Pradesh).Some other notable contributions on the ecological aspects of epiphytic bryophytes in Southern India and Western Ghats were made by Alam et al. [17] and Verma et al. [18].
The cool and humid climate of the Nainital supports a rich bryoflora on both evergreen and deciduous dominant tree species [8].Platanus orientalis L. trees (Platanaceae) planted along the lake side of Nainital comprise both young and mature trees.Though not a native to the place, it supports a rich bryoflora on its stem.The species is subjected to the vehicular pollution caused by the heavy pressure of vehicles on the Mall road.This study was aimed to identify the mosses and liverworts on the bark of these trees and to find out the successional trends of the bryoflora, if any.

Materials and Methods
The phytosociological analysis of the epiphytic bryophytes was made for 40 trees of P. orientalis classified into 5 girth classes i.e., the cbh (A: 0 -75 cm; B: 76 -150 cm; C: 151 -225 cm; D: 226 -300 cm and E: >300 cm) and each girth class consists of 8 trees.In each tree, 5 quadrats of 5 × 5 cm size were placed randomly for the sampling of bryophytes along with the underlying bark.The plants were separated according to their growth form, habit and other distinguishing field characters and voucher specimens were stored in the Bryology Laboratory, Department of Botany, D.S.B. Campus, Kumaun University, Nainital.Slides of leaves and other parts were prepared in gum-chloral mounting media [19] and plants were identified following Gangulee [20].Colour, texture and other characteristics of bark viz., pH and moisture content were also determined [21].The vegetation data were calculated for frequency, density and abundance [22].The Important Value Index of each species was determined as sum of relative frequency, relative density and relative abundance [23] [24].The data were also computed for Sorenson's Similarity Index (SI) [25] among trees of the 5 girth classes by using the following formula.SI = 2c/a + b; where c = number of species common to two girth classes, a = number of species at girth class 1, and b = number of species at girth class II.
Species composition of bryophytes on P. orientalis was compared with bibliographic data of bryophytes of other common and dominant phorophytes of Nainital [7] [8] [10].

Results
The physico-chemical characteristics of P. orientalis tree bark are given in Table 1.In general, the bark is mildly acidic.The moisture content of the bark ranged between 105% (girth class A) and 235% (girth class D).The barks of trees belonging to girth class E had almost neutral pH, high moisture content, rough surfaces with a large number of crack and crevices and supported maximum number of species (16 species).On the contrary, trees of lower CBH (girth class A) had acidic bark, low moisture content (105%), smooth surfaces and supported only a limited number of species (9 species).
Comparison of the bryoflora of P. orientalis with other dominant gymnosperm and angiosperm trees of this Based on percent frequency, Regmatodon orthostegius was the most frequent species in lower girth classes (% F = 42.5 and 32.5 in girth class A and B, respectively), while Herpetineuron toccoae was the most frequent species in higher girth classes (% F = 25 in C, 30 in D and 37.5 in E).On the basis of density, R. orthostegius dominated in lower girth classes (3950 ind.m −2 and 3508 ind.m −2 in girth class A and B, respectively).While in higher girth classes, C. laetum (1688 ind.m −2 , 2960 ind.m −2 and 2760 ind.m −2 in girth class C, D and E, respectively) was dominant (Table 4).

Phorophytes
Data of IVI indicated that only two types of bryophytic communities were formed across the girth classes (Table 4) The data on similarity index (Table 5) indicated that bryophytic vegetation of girth classes B and E had shown the maximum similarity (SI = 79%) followed by B and D (SI = 72%).The minimum resemblance was found between the vegetation at trees of girth classes A and C (SI = 41%).
The maximum number of species was represented by the family Bryaceae (5) followed by Entodontaceae (4) and Pottiaceae (4).Predominance of the acrocarpous mosses and more often of family Pottiaceae reveals the xeric nature of environment.The distribution pattern of the epiphytic bryophytes clearly exhibited that the number of species increased as the pH and moisture content increased along the successive girth classes (Table 4).
The study of epiphytes on trees of different ages within more or less same environment is a feasible method to study colonization and succession [29].The barks of the young trees (cbh less than 75 cm) had acidic nature (pH 5.5), low moisture content (105%) with smooth texture created a substrate not congenial and thus providing a limited chance for establishment and growth of propagules of some of the pioneer species.The occurrence of Entodon chloropus, Frullania muscicola and Lindbergia koelzii in only trees of girth class A where the moisture content of the substrate is low, allude the xeric nature of these species and their abilities to sustain in adverse environmental condition as also evident from certain morphological adaptations like presence of water sac (in Frullania) and concave leaves.On the contrary, the barks of mature trees of Platanus (girth class E) had almost neutral pH (6.7), high moisture content (235%) and rough in texture with a large number of cracks and crevices forming an ideal habitat for the establishment and growth of propagules of various species of bryophytes thus represent the climax association.At the tree barks of girth class E, 3 species namely, Plagiothecium, Stereophyllum and Rhynchostegiella invaded, exhibiting that these taxa are high moisture demanding.The old age trees having maximum cbh (girth class E) harbor maximum number of species.The number of species encountered in trees of different girth class was found in proportion to their respective moisture contents.Low moisture content of the barks of girth class D may be perhaps one of the reason that some of the species which invaded on barks of girth class C could not survive.The low moisture status of girth class D may be attributed to the dense canopy of the trees, inclination of the tree, so that the water flow could not trickle down to the base of the tree stems.The maximum value of similarity index in between trees of girth classes B and E denotes the transitional community association at the trees of girth class B and climax community at E. Coinciding, rough texture of the barks began from the trees of girth class B. It appears that moisture content and texture of the barks play key role in species distribution.Among the species encountered, four species viz., Brachymenium capitulatum, Cylindrothecium laetum, Herpetineuron toccoae and Lejeunea tuberculosa exihibited broad ecological amplitude as these were present in all the girth classes.Comparison of the bryoflora of P. orientalis with other dominant phorophytes of this locality (Table 3) revealed that only 12 species were confined to the Plantanus bark and also formed the predominant component of epilithic and terrestrial habitat of this locality.Remaining 15 species were common to other trees.The barks of Quercus sp. were found the most similar with Platanus in terms of number of common species probably because of same physical characteristic and acidic pH.On the other hand the barks of Aesculus indica and Erythrina arborescens represented the least similarity with Platanus in terms of number of common species among them probably because of difference in pH (acidic to neutral in Platanus and alkaline in former species).
A/F ratio of all the bryophyte species in all girth classes of trees show more than 0.05, thus reveal contagios distribution of all species [26].Distribution of Caduciella mariei, Conomitrium subpalmatum and Fabronia pusilla in all girth classes except girth class A clearly indicates that they prefer the habitat having high moisture content and mild acidic to neutral pH.On the basis of frequency, it can be stated that most of the species show rare (F = 10% -20%) or accidental (F < 10) occurrence.Regmatodon orthostegius in girth class A, Brachymenium capitulatum and Regmatodon orthostegius in girth class B, Cylindrothecium laetum in girth class C, Caduciella mariei, C. laetum and Herpetineuron toccoae in girth class D and E showed moderate or intermediate distribution.On the basis of IVI value, it can be stated Regmatodon orthostegius together with Brachymenium capitulatum formed the pioneer community, while Herpetineuron toccoae formed the climax community of epiphytic bryoflora on Platanus orientalis.Some of the mosses like Didymodon vinealis, Bryoerythrophyllum dentatum, Desmatodon gemmascens, Ditrichum heteromallum, Fabronia pusilla, Homalothecium neckeroides, Plagiothecium denticulatum and Stereophyllum fulvum may have their accidental presence in this habitat as their propagules or spores might be aggregated in bark by means of wind dispersal or any other factor as they show very low frequency and very small number of individuals.

Changes across the Girth Classes
Changes in epiphytic vegetation on tree stems, where bark peels off periodically are not the same as found in succession occurring in land.The tree girth and bark roughness increase continuously with time.A few patterns across girth classes which become easily apparent in epiphytic communities of the present study are as follows: 1) Across the girth classes, the species number gradually increases with increase in girth class.The only exception is in girth class D where the species number decreases from 15 (girth class C) to 13 (girth class D).We also found marked changes in species richness in time.
2) Distribution pattern of the moss species in relation to girth classes, in P. orientalis indicated that species like G. apiculatum, P. denticulatum, S. fulvatum, B. argenteum, F. schensiana and H. neckeroides showed their preferences to higher girth classes i.e.C, D and E and they may be considered as late successional species.While E. chloropus, L. koelzii and F. muscicola are considered as early successional species (early colonizers) as they disappeared in higher girth classes.
3) In the present study F. muscicola appeared as early successional species, while at higher altitudes this species appeared as late successional species in Acer cappadocicum stems [9].

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At trees of lower girth class (A and B), R. orthostegius together with B. capitulatum formed the community (IVI = 119.15and 73.02 in girth class A and B for R. orthostegius, while IVI = 64.86 and 54.37 in girth class A and B for B. capitulatum).At higher girth classes (C and D), C. laetum formed the community (IVI = 45.88 and 50.11 in girth class C and D, respectively) with co-dominant species H. toccoae (IVI = 45.33 and 45.67 in girth class C and D, respectively).At the trees of maximum girth class (E), H. toccoae (IVI = 44.96)forms the community with Caduciella mariei (IVI = 44.02).

Table 2 .
List of bryophyte species present on the Platanus orientalis tree.

Table 4 .
Vegetation data for the frequency (F), density (D), abundance (A) and Important Value Index (IVI) of the epiphytic bryophytes on different girth classes of Platanus orientalis trees.

Table 5 .
Similarity index among different girth classes.