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BIOLOGICAL CONSERVATION
ELSEVIER
Biological Conservation 85 (1998) 123-135
Effects of nature trails on ground vegetation and understory colonization of a patchy remnant forest in an urban domain Dinesh R. Bhuju *, Masahiko Ohsawa Laboratory of Ecology, Faculty of Science, Chiba University 1-33, Yayoicho, Inageku, Chiba 263, Japan Received 23 April 1997; accepted 25 August 1997
Abstract Effects of nature trails on understory vegetation was studied in a self recovering patchy forest remained in an urban sprawl of central Japan. An adverse impact of soil compaction at surface level, originating basically from human trampling, was found on root development and stem growth of understory colonizers implying a succession deterrence. Ground coverage was reduced with proliferated path web in trampled sites and a few species showed site preference. Management options such as demarcation of trek routes and their rotational use could help revitalize the colonization to further succession process. © 1998 Published by Elsevier Science Ltd. All rights reserved Keywords: Root configuration; Soil compaction; Trampling; Understory succession; Vegetation cover
1. Introduction As nature trails continue to have growing recreational values accompanied with ever-growing public pursuit of outdoor pleasure (Liddle, 1975; Bayfield, 1979), understanding impacts of human trampling has become even more important to both nature trail users and park managers. Trampling as an anthropogenic disturbance, not only brings about change in bio-community structure/vegetation composition but also reduces species richness and their coverage (Chappell et al., 1971; Liddle and Greig-Smith, 1975b) which are related to the amount of disturbance (Cole, 1987; Ikeda and Okutomi, 1990). The effects of human trampling has been reported to be much severe on the habitat of invertebrate fauna which can substantially decline their numbers and species (Duffey, 1975). Several researchers have recorded a marked alteration in soil structure, specifically increase in soil compaction at trampled sites which has assumed a causal relationship with vegetation degradation (Burden and Randerson, 1972; Liddle and Greig-Smith, 1975a; Weaver and Dale, 1978). Recent studies on impact of soil compaction due to trampling have been reported to reduce species richness/diversity (Gomez-Limon and de Lucio, * Corresponding author. Tel. and fax: 81 43 290 2815; e-mail: bbhuju@nature.s.chiba-u.ac.jp
1995) and retard successional development of plant communities (de Gouvenain, 1996). However, many of the works were focused on species responses to trampiing gradients leaving room to compare and document the relationship between species growth/establishment and soil characteristics in trampled habitats. Our objective of the present study was to elucidate the detrimental effects of nature trails on understory succession in a spontaneously recolonizing planted forest by assessing root configuration and growth pattern of some colonizing species with respect to the change in soil characteristics due to trampling. We also included a comparison of other vegetation properties coverage and diversity, between specified (confined) and unspecified (not confined) trails and under different canopy types to come out with some management options.
2. Study site The site of investigation, Sonno Shellmound Forest represents a remnant man-made forest located in Chiba City (35 ° 40' N, 140° 06' E) (annual mean temperature: 14.9°C, annual rainfall: 1218mm) of central Japan, in the warm temperate broad leaved evergreen forest zone (Government of Chiba City, 1987). The canopy is mainly composed of planted conifers--Cryptomeria japonica and Chamaecyparis obtusa comprising 70% of
0006-3207/98/$19.00 © 1998 Published by Elsevier Science Ltd. All rights reserved PII: S0006-3207(97)00148-1
124
D.R. Bhuju, M. Ohsawa/BiologicalConservation85 (1998) 123-135
the total by basal area, and some broad leaved components such as Quercus myrsinaefolia and Zelkova serrata (Bhuju and Ohsawa, 1996). This in combination with modification by natural and human disturbances has created a patchy environment in the forest. The management of the forest ceased for the last few decades enhancing a vigorous understory colonization by unplanted species; however, its proximity to city dwellers has added recreational burden to already existing human pressure by shellmound witnesses and shrine visitors.
a. Study site 0
~/
Tokyo"~
°/')0("Chiba ) ~~140" E35N b. Trails in sampled area
3. Methods
Trail routes were drawn on a recently prepared tree position map and patches of three different canopies were selected for the study, viz. Cryptomeria japonica, Chamaecyparis obtusa and Quercus myrsinaefolia, hereafter C J, CO and QM, respectively (Fig. l(a) and (b)). Each patch type consisted of disturbed and undisturbed habitats or sites with trails and without trails. Sites with trails were trampled while the sites without trails were untrampled and away from the human disturbances. Sites in each patch were either adjacent to each other as in CJ or located quite closely, less than 100 m, as in CO and QM. In C J, trails were specified or clearly demarcated while in CO and QM the trails were unspecified or not demarcated. For vegetation sampling, quadrates (quadrat size: 8x30m in CJ and 20x20m in CO and QM) were laid in the trampled and untrampled sites of each patch with intact canopy to reduce canopy differences. In each habitat of the three patches, herbaceous species were sampled in 12 sub-quadrates of 1x I m size. The cover percentage of each species was estimated and its mean height was measured. Dwarf bamboo (Pleioblastus chino), lianas and ferns were all treated as ground cover species. Seed dispersal forms of the species follow Numata and Yoshizawa, 1988. In case of the invading woody species (either shrub or tree which are not planted), all individuals below canopy (< 10 m height) were counted and their diameter at breast height (dbh) was measured where applicable. They were categorized into seedlings ( < 30 cm), saplings (30-150 cm) and high understories (> 150 cm). For growth analysis and root configuration, four most abundant broad leaved species, two deciduous (Aphananthe aspera and Celtis sinensis) and two evergreen type (Neolitsea sericea and Persea thunbergii) were selected. First year seedlings of each of four species of Aphananthe, Celtis, Neolitsea and Persea were carefully taken out (8 to 12 for each species) by removing soil and pressed on grid-paper keeping its original shape. Leaf area, stem length, root length (maximum depth), root diameter at base and tip (5 mm below) of the main root, and maximum root expansion (radius of major laterals)
N 0
50m
Fig. 1. (a) Map of central Japan showingstudysite. (b) Trails (dotted lines) and sampled sites. Bars in CO-TR and QM-TR indicate unspecifiedtrails. Abbreviations:CJ, Cryptomeriajaponicapatch; CO, Chamaecyparis obtusa patch; QM, Quercusmyrsinaefolia patch; TR, trampled; UN, untrampled.Figuremodifiedfromtree positionmap. were measured. Presence or absence of root bifurcation of main root within a length of 5 cm from base was also noted. Weight of leaves, stem and root was taken before and after drying at 80°C for over 24h. Shoot growth was estimated in saplings (100cm or c. 5 years old) of evergreen species by direct measurements of internodes. Samples of soil cores were obtained by driving metal cylinders (5cm deep with 5cm diameter) into soil at three levels--surface (0-5cm), middle (10-15cm) and deep (20-25 cm), and their wet weight and porosity were measured by three phases meter (DIK-1121, Daiki, Japan). The samples, 18 from each quadrates totalling 108, were oven dried at 105°C for over 24 h to calculate bulk density and soil water content. Samples were separately collected and sieved at 2 mm to estimate percent of nitrogen and carbon by CN corder (Yanaco MT
D.R. Bhuju, M. Ohsawa/Biological Conservation 85 (1998) 123-135
500). Soil hardness was measured by 10 random penetrations into surface soil at each sub-quadrates with PushCone (Daiki, Japan) and calculated in kgcm -2. Soil type, sandy or clay, was visually recorded during holing for soil collection. Soil samples were collected in October after three days of rainfall. Relative light intensity falling above ground vegetation was measured at four different corners in each sites--trampled and untrampled of the patches on a cloudy day of November.
4. Results
4.1. Canopy characteristics The selected patches of the study site--Cryptomeria (C J), Chamaecyparis (CO) and Quercus (QM)--were composed of or dominated by the respective species as their names already stand for. Compared to CO and QM, patch CJ had higher canopy density (1250nha -~, averaged between trampled and untrampled sites) and comprised younger or trees of small diameter class (mean diameter 19.7cm, averaged) (Table 1). The three patches, however, did not vary much in relative light intensity falling above ground vegetation that ranged from 3.4--5.7%. The differences in canopy measurements such as basal area, density, height and diameter were not consistent between trampled (TR) and untrampled sites (UN). In C J, basal area and density of trampled site were 37-2m2ha -j and 1333.3nha -~ while in untrampled the values were 43.24mZha -1 and l166.7nha -l, respectively. In CO, trampled had basal area 60.8 m2ha -~ and
125
density 566.7 n ha -~ with compared to 56.0 m 2 ha -~ and 666.7 n ha -~ in untrampled. Similarly, in QM, trampled site had basal area 57-4 m 2 ha-~ and density 700.0 n hawhile its untrampled site had 50.9m2ha -~ and 800.0 nha- ~, respectively. 4.2. Soil disturbance
Soil disturbance had been introduced mainly by the human trampling, sometimes associated with irregular sand surfacing. There were marked differences in soil characteristics such as hardness, bulk density, porosity and water content between sites with trails and without trails (Table 1, Fig. 2(a)-(c)). A soil profile showed that trampled sites in patches CO and QM had sand in the surface soil (0-5 cm ) indicating an artificial deposition which, at some particular spots, made up nearly 60% by volume. Such feature was, however, lacking in CJ and also in untrampled sites of all patches. In totality, soil hardness of the trampled site, measured at surface level was 12 times higher than in the untrampled, 5.04 and 0.43 kg cm -2, respectively (Table 1). Soil hardness among the three patches ranged from 4.51 (QM-TR) to 5-33 kgcm -2 (CO-TR) showing a less difference or suggesting almost an equal amount of passes. Differences were also found in total carbon and nitrogen percent, on average trampled sites had less C and N (C 5.58 and N 0.48%) with compared to the untrampled ones (C 11.5 and N 0.76%). From similar forests in the region, total C and N have been estimated about 8.34 and 0.63% respectively (Billore et al., 1995). However, the difference was only significant in CO and QM. A marked difference in bulk density of surface soil was found between the trampled and untrampled habitats,
Table 1 General characteristics of the studied patches Parameters/patch Area (ha) Canopy dimensions Basal area (m2ha J) Density (stem ha- 1) Mean height (m) Maximum height (m) Mean diameter (cm) Maximum diameter (cm)
Environmental measurements Relative light intensity Soil hardness (kgcm -2) Soil carbon percent Soil nitrogen percent Soil type (0-5,0 cm) Soil type ( > 5.0 cm) Trail route
Total (TT)
Cryptomeris patch (CJ)
Trampled Untrampled
Trampled Untrampled
0.84
52.9 833.3 14.3 20.0 26.2 54.5 4.42 ± 1-3 5.045:2.8 5.58 5:3.3 0.485:0.3
0.84
51.6 857.1 14.3 20-0 26-3 44.5 5.23 5:1.2 0.435:0.3 11.505:1,1 0.765:0.1
0-24
37.2 1333-3 12.9 16.0 18-3 32-0 5.02 5:1-2 5-29 ± 4-5 9.43 ± 2.7 0.82 5:0.3 Clay Clay
specified
0.24
43.5 1166.7 12.8 16.0 21 .I 35.0 5.13 5:1.3 0.255:0.1
11-47 ± 1.6 0.80±0.1 Clay Clay
absent
Chamaecyparis patch (CO) Trampled 0.30
60,8 566.7 18.1 20,0 35,9 54.5 4.80 5:1.6 5.335:2.1 3.805:1-2 0.365:0-1
Untrampled Trampled Untrampled 0.30
56-0 666.7 17-2 20.0 31-9 42.5
Clay
5.71 ± 1.5 0.645:0.4 10.62 ± 0.2 0.72 5:0-0 Clay Clay
unspecified
absent
Sandy
Quercus patch (QM)
0-30
57-4 700.0 13-4 19.5 30-4 47-5 3.44±1.1 4.51±1.0 3-51±0.0 0.26±0.0
Sandy Clay
unspecified
0.30
50.9 800.0 14.5 18-0 27-7 44.5 4.83 ± 1-0 0-41 ±0.3 12.39 ±0.6 0.77±0-0 Clay Clay
absent
126
D.R. Bhuju, M. Ohsawa/Biological Conservation 85 (1998) 123-135
CJ patch
Total 0.00 ,
0.40 t
I
,
0.80 ,
=
1.20 t
O.O0
0.40
0.80
1.20
1
a. Bulk demdly (g/cm 3)
0.5~
20.00
40.00
!
',
i
,o
0.40
0,80
120
0.00
0.40
0.80
1.20
....... ,
...........
,
0,00
,
........
0.00
QM patch
CO patch
O.O0
i1
2O.O0
I
O.O0
4O.OO
'
.....: ~4t
ii
20.00
40.09
0.00
! i.i ..
20.00
40.00
~ 3 0
I
...........................
........ i ........ i ........ !........ i4~-I oa
I is
Water
50,00 g
content
70,00
'
"
'
OI
I
(%1 90.00
fiO,O0
70.00
90.00
50,(]0
70.00
90.00
50.00
70.00
90.00
0-5 ........
.....
, ..... i . . . . ~.........
......... i ..........
i;..i
............
........i.......i ......! ............... c. Poroldty (%)
Fig. 2. Soil physical characteristics at three depths, 0-5, 10-15 and 20-25 cm at trampled (black) and untrampled (white) sites of three different patches. (a) Bulk density is high at surface (0-5 cm) in trampled sites, patches CO and QM have higher bulk density than CJ. (b) Soil water content is relatively low at trampled sites of CO and QM patches. (c) Porosity is lowest at surface of trampled sites and markedly increases towards the depth presenting a reverse pattern of bulk density. Patch abbreviations as in Fig. 1.
1.08 and 0.40gm -3, respectively (Fig. 2(a)). When compared among the three patches, bulk density of the trampled site was high in QM (1-26gcm -3) and CO (1.22gcm -3) than in CJ (0.72gcm -3) while it was nearly invariable among the untrampled sites of the same that ranged between 0-37 and 4,2gcm -3. The increased bulk density in the former two patches, QM and CO, is assumed to be intensified by the sand additions. Moreover, bulk density of the trampling sites decreased sharply at 5-10cm depth (0.62gcm -3 in average) and reached almost at the same level of the untrampled ones at 20-25 cm soil depth (0.52 g cm -3 in average) in all three patches indicating that the effective soil compaction by human trampling was confined on the surface. Soil porosity, also an indicator of compaction degree, was different in the trampled sites (58.5% in average) from those of the untrampled sites (83.1% in average) which, however, sharply increased with the depths (Fig. 2(b)). At 20-25 cm depth, the porosity of trampled and untrampled sites met at the same level (81% in average). Among the patches, porosity was lowest in Q M - T R (52.1%) followed by C O - T R (57.3%) and CJTR (71.1%) while it did not vary much among the untrampled patches (82.4-84.3%). When estimated for
trampling number, the CJ-TR porosity was comparable with soils receiving 1-4 trampling per day for times a week by one man (weight 65 kg) in Tokyo area (Ikeda and Okutomi, 1990). The soil water content of trampled and untrampled sites was not so distinct (Fig. 2(c)). However, its lower value in surface soil of trampled sites of CO and QM may indicate the faster water run off due to sand composition in their soil.
4.3. Ground vegetation In total, herbaceous coverage was high in the untrampled site than in the trampled one with ( 48.4 and 29-2%, respectively (Fig. 3(a)-(d)). Such difference was more pronounced in QM and CO suggesting its attribution to soil compaction and extended disturbance due to unspecified or many superfluous paths. In support, correlations of vegetation cover was established with bulk density and porosity at significant level, r=0.725 and r = 0.760, respectively (Fig. 4(a) and (b)). The total species richness of the ground vegetation was slightly higher in trampled site than in untrampled one with 18 and 16 species, respectively (Table 2). Some perennial herbs such as Achyranthes bidentata var.
D.R. Bhuju, M. Ohsawa/BiologicalConservation 85 (1998) 123-135 Herbaceous q)s 100
127
Woody sps
a.
lb.
75
a)
50 O "O
25
c
2 o 30-
20-
E
150 cm), 18 colonizing species (60%) were represented in the untrampled sites with total basal area of 214cm2/ 100m 2. In the trampled sites, only five species were present at this level with basal area of 21.7cm2/100m 2 which was only represented by CJ; no species was recorded from the trampled sites of CO and QM at this layer. Among untrampled sites of the three patches, QM (358-9cm2/100m 2) had the highest basal area followed
4.5. Root configuration The dissemination form of four colonizing species, Aphananthe and Celtis (deciduous type) and Neolitsea and Persea (evergreen type) was the same---endozoochorous or bird dispersed. Ratios of roots to stems were higher in the trampled sites than in untrampled ones (Table 5). Overall, root ratios of Aphananthe and Celtis were 3.9 and 4.6 in the trampled and 3.3 and 3-6 in the untrampled sites. Similarly, the root ratios of Neolitsea and Persea were 4.4 and 5.1 in trampled and 4.0 in untrampled sites.
Table 3
Density of seedlings ( < 30 cm) and saplings (30-100 cm) in trampled and untrampled sites of different patches Seedling density TT
Species by life-forms Total deciduous shrub Callicarpa japonica Viburnum dilataum Helwingia japonica A ralia elata Euonymus sp.
CJ
TR
UN
2 1 0
2 1 I 0
Total evergreen shrub Fatsiajaponica Ardisia japonica Aucubajaponica Ligustrum japonicum Trachycarpus fortunei Ardisia crenata llex crenata Mahonia japonica
16 5 4 3 3 1
Total deciduous tree/subtree Celtis sinensis Aphananthe aspera Carpinus tschonoskii Morus bombycis Prunus sp. Magnolia kobus Cornus controversa Clerodendron trichotomum Cornus brachypoda Mallotus japonicus
63 42 11 6 2 1
Total evergreen tree/subtree Quercus myrsinaefolia Neolitsea sericea Persea thunbergii Eurya japonica C innamomum japonicum Dendropanax trifidus Quercus acuta
163 105 46 11 1
All life forms
243
TR
15 1 9 3 1 1
14 7 5
9 5 3 1
UN
TR
QM UN
TR
32 7 16 4 5
22 12 3 2 5
15 1
10 3
7 2
4 2 1
5
0 0 1 0
142
CO
5 4 1
40 5 20 7 4 1 2 0 0
87 25 49 12 1
Sapling density
9 6 1
95 55 17 15 5 3
6 2 3 1
84 67 13 3 1
80
67 2 48 17
108
205
81 3 71 5 2
102
350 312 37 1
444
CO
QM
TR
UN
TR
UN
TR
UN
6 2 3 l
1 1 0
4 1 0 2 0 0
1 1
2
2 1 1
2 1
72 32 0 21 9 8 1 0
40 9
26 12 12
19 8 7
33 11 12
17 5 11
54 17 22
31 10 9
2 0
0 3 4 1
1
1 7 2 3
6 1
l 1
3
113 70 29 14
217
UN 7 1 1 5
1
31 15 10 4 3
TR
1 1
72 6 45 11 5 2 1 1 1
1
83 1 57 23 2
CJ
UN
l 1
1 1
56 3 43 9 1
TT
23 5 3
131 56 1 40 17 13 4
33 23
47 27
20 12
39 13
4 4 2
10 2 8
2 3 3
13 9 3 1
5 3 2
9 8 l
39 14 11
3 11
2
1
0 0
29 2 19 6 2
91 12 51 23 4
56 7 36 12
85 10 55 18 1
24
1
1 0
1
1
1
80
199
114
272
90
17 1 5
68 3 39 20 6
7 3 4
119 22 58 31 5 2 1
122
36
204
All values calculated per 100m 2. Value 0 indicates less than 1. Abbreviations: TT, total; CJ, Cryptomeria patch; CO, Chamaecyparis patch; QZ, Quercus patch; T R = trampled, U N = untrampled.
D.R. Bhuju, M. Ohsawa/Biological Conservation 85 (1998) 123-135
130
of all e x a m i n e d species--Aphananthe, Celtis, Neolitsea a n d Persea was deeper in the u n t r a m p l e d sites t h a n in the t r a m p l e d while their lateral e x p a n s i o n was just the reverse or low in u n t r a m p l e d a n d high in the trampled. The frequency of m a i n root bifurcation, o n the other h a n d increased in the t r a m p l e d sites a m o n g all the species. C o m p a r i n g the t r a m p l e d sites a m o n g the three different patches, r o o t depth tended to decrease from CJ
Such higher ratios of roots to stems became m o r e glaring in C O a n d Q M suggesting a response to increased soil c o m p a c t i o n . Likewise, d i s t i n g u i s h i n g features were revealed by the root c o n f i g u r a t i o n d a t a of the first year seedlings, viz. m a x i m u m d e p t h (length of m a i n root), m a x i m u m radial growth (lateral e x p a n s i o n ) a n d frequency of m a i n root b i f u r c a t i o n (Fig. 7). T h e soil p e n e t r a t i o n by m a i n root a°
125
C,
b. Evergreen tree/subtree
Deciduous tree/subtree
do
Deciduous shrub
i\
Evergreen shrub
100 E 875 ,_z,5 o -
~.
0 'TR UN=TR UN=TR UN' -C J- -CO- -QMPatch type
TR UNITR UN ITR UN I -CJ - -CO- -QM-
='Ill UN ITFI UN =TR UN I
-CJ -
-CO-
-QM-
Index [ ] Sapling [ ] Seedling
.ca
TR UN"rR UN tTR UN I -CJ- -CO- -QM-
Fig. 6. Density of seedlings (< 30 cm) and saplings (30-150 cm) of four different life-forms in trampled and untrampled sites of three different patches. Except evergreen shrubs, seedlings are relatively higher in trampled sites than in the untrampled while saplings are higher in untrampled sites than in trampled. Patch abbreviations as in Fig. 1. Table 4 Basal area (cm 100m-2) and density (stem 100m-2) of understory species TT-UN Species by life-forms
Basal area
CJ TR
Density Basal area
CJ-UN
Density Basal area
Density Basalarea
18.5 0.5 8-6 0-1 0.1 4.6 4.6
1.3 0-6 0.2 0.1 0.1 0. l 0.1
0.3 0.3
Evergreen tree/subtree Dendropanax trifidus Eurya japonica Neolitsea sericea Persea thunbergii Quercus acuta Quercus myrsinaefolia
189.4 0.2 0-5 165.2 19.9 0.6 3.1
17.0 0.1 0.2 14.3 1.9 0.1 0.4
15-2
1.7
20.4 0.7
9.6 0.4
191-9
10.3
14.2 0.3
0.8 0.4
19.0 0.3
8.3 0-4
183.9 2-7
9.7 0.3
0.7
0.4
0.3
0.4
5.3
0.3
Deciduous shrub Callicarpa japonica Sarnbuscus racemosa
1-0 0.4 0.6
0.2 0-1 0.1
Evergreen shrub Aucuba japonica Fatsiajaponica Ligustrum japonicum Trachycarpus fortunei
5.8 2.5 2.8 0-4 0.2
3.1 1.2 1.3 0.5 0.1
3.4 3.4
1.3 1.3
12.5 6.4 4-3 1,3 0.6
8.7 3.3 3.3 1-7 0.4
4.9 0.6 4.3
214.7
21.7
18.9
3.3
56.7
20.4
196.8
No understory growth in CO-TR and QM-TR. Abbreviations as in Table 3.
24.1 0.8 6.6 0.3 0.3 16.0
Density Basal area
QM-UN
Deciduous tree/subtree Aphananthe aspera Carpinus tschonoskii Celtis sinensis Cornus controversa Magnolia kobus Styrax japonica
All life-forms
0.4 0.4
CO-UN
2.5 0.8 0.4 0.4 0.4 0.4
Density
32.4 0.7 18.9
1.7 l-0 0.3
12.8
0.3
322.4
30.0
1.3 263.4 52.9 1.6 3.2
0-7 23,7 5.0 0.3 0-3
2.7 1.0 1.6
0-7 0.3 0.3
1-3 0.3 1.0
1.4 1.4
0.3 0.3
11.7
358-9
32-7
D.R. Bhuju, M. Ohsawa/Biological Conservation 85 (1998) 123-135
131
Table 5 Root configuration data of seedlings of selected species in trampled and untrampled sites of different patches
TT
CJ
CO
QM
Species TR
UN
TR
UN
TR
UN
TR
UN
Root to stem ratios Aphananthe aspera Celtis sinensis Neolitsea sericea Persea thunbergii
3-9 4.6 4.4 5.1
3.3 3.6 4.0 4.0
3.3 4.3 4.3 4.0
3.3 3.2 4.0 4.4
4-2 4.9 4.3 5.2
3.0 3.7 4.0 3.5
4.1 4-5 4.6 6.0
3-5 3-9 3.9 4.2
Maximum depth (cm) Aphananthe aspera Celtis sinensis Neolitsea sericea Persea thunbergff
7.2 7.5 6.2 9.2
9.5 12.9 10.5 14.2
8.6 12.7 7.9 10.0
10-8 16.8 10.5 14.4
6.8 6.6 6.3 8-4
8.5 7,8 10,8 12.8
6.1 7-0 4-5 10.1
9.8 14.4 9.2 16.0
Maximum radius (cm) Aphanan the aspera Celtis sinensis Neolitsea sericea Persea thunbergii
2.8 3.0 2,5 2.2
1.5 2.4 2-0 1-8
1.5 2.8 2-1 2-0
1.0 2.4 2.1 2.2
2.9 3-5 2.6 2.2
I. 8 2-3 1.8 1.5
4-1 2.6 2.8 2.5
1-8 2-5 2.2 2.0
59.4 51.8 63.6 37.5
7.8 8.9 14.2 27-5
40.0 33.3 50.0 25.0
0.0 0.0 16.7 20.0
71.4 63.6 69.2 37.5
14.3 16.7 10.0 25.0
66.7 58.3 71.4 50.0
9.1 10.0 15.8 16-7
Bifurcation (%) Aphananthe aspera Cehis sinensis Neolitsea sericea Persea thunbergii Abbreviations as in Table 3.
TR
UN
TR
'
UN
lJl
Neolitsea sericea
-
TR
~
1'
"
UN
TR
UN
IL
!,1
Per!ea thunbergii
Fig. 7. Root configuration of seedlings of four selected species in trampled site (TR, bulk density 1.25gcm 3) and untrampled site (UN, bulk density 0.40 g cm-3).
D . R . Bhuju, M . O h s a w a j B i o l o g i c a l C o n s e r v a t i o n 85 (1998,) 1 2 3 - 1 3 5
132 a. Maximum
L
b. M s x i m u m
Depth
b.
so.o "r............. ;'"r--~""-!""~
Radius
......~"""7 '" i '"'i-'i'"'~
12.0 4.0
•
i .......i.. I
3.0
8.0
E° 2oo ~o~ "
2.0 4.0 1.0-
Aphananthe aspera 0.o
! " '.'.
40.0
J
Patch i n d e x - e - - 11:t _o._ ON CJ
20.0
E r = 0.88g . . . . . .
.
=
.........
~ i
0.0
~ '
0"0/111t2
4.0
3
4 i i 5i 6
i i i ~ ~ 1 1 2 k31 4 ; 5 ; 6 ,
0.0
; i
Year
16.0
3.0-
~
~
=
Fig. 9. Growth pattern of (a) N e o l i t s e a sericea and (b) P e r s e a thunbergii in trampled and untrampled sites of different patches. Patch
12.0
abbreviations as in Fig. I.
2.0
8.0
Ce/t/s
r = 0.759
r = 0.768
slnensis
0.0
. . . . .
,
,
0.0
4.6. Growth measurements
1.0-
12.0
-
0.88.0-
0.60.4 4.0-
Neolltsea sericea
type. The effects of soil compaction on the root development were statistically significant (Fig. 8(a) and (b)).
1.0
4.0
Y
0.2 r= 0.906
r = 0,961
0.0
. . . . . . .
0.0
16.0 J
i
,
,
,
|
,
,
J
i
i
J
g
-~ zo.
12.0 -q
~ 1.s.
~ ,,r.
4.0.
1.0" 0.5.
Permea
r = 0.886
thunbergii 0.0
i
o
i
i
r= 0.696 i
i
~
i
0.0
0.20 0.40 1.20 Soil bulk density
i
0
i
i
0.20 0.40 1,20 Soil bulk d e n s i t y
Fig. 8. Simple regressions to show correlation between root configuration data (a) maximum depth, and (b) maximum radius of four selected species and soil bulk density (g cm-3).
(7.9-12.7cm) to CO (6.3-8.4cm) to QM (4.5-10.1 cm) corresponding with less to high soil compaction irrespective of the patch type; however, in comparing the untrampled sites, there was no such tendency though they did vary somewhat by species. In the same way, the maximum radius of lateral expansion was seen to increase from CJ (2.0°2.8 cm) to CO (2-2-3.5 cm) to QM (2.5-4.1cm) while their untrampled sites showed a minimal variation (1.0-2.8cm) irrespective of patch
The growth rate in both evergreen species Neolitsea and Persea, estimated by internode measurement of individuals of average 5 years, was higher in untrampled sites than in trampled (Table 6). In the untrampled sites, the average growth rate of Neolitsea and Persea was 8.9 and 7.6cm year -1, respectively, which was nearly 3 cm more with compare to trampled sites. By patch observation, the growth rate was much less, almost by half, in the trampled sites of CO (p=0.001) and QM (p =0.0001) where soil compaction was very high with compared to the untrampled sites. In C J, the growth rate did not show such a contrast between the trampled and untrampled sites (p = 0-01). The growth behaviour, the growth rate was not consistent for each year, but varied significantly (Fig. 9(a) and (b)). In the first year, supported by food reserves, seedlings showed relatively high growth rate with an average of 10cm year -~. The growth, however, was arrested in the following years. This phenomenon occurred in both trampled and untrampled types of habitat, but in the untrampled site, the growth rate recovered in the following years and plants gained height. For the deciduous species (Aphananthe and Cehis), the sapling density was very low in the trampled sites, those few which escaped the trampling were mostly confined to the base of canopy trees or refugia. Hence, comparative growth measurements were omitted.
Table 6 Average growth rate (cmyear ]) of selected species estimated by inter-node measurements in trampled and untrampled sites of different patches Total Species N e o l i t s e a sericea P e r s e a thunbergii
Cryptorneria patch
Charnaecyparis patch
Q u e r c u s patch
TR
UN
t
TR
UN
t
TR
UN
t
TR
UN
t
5.6 5.1
8-9 7.6
3.8"* 4.3**
6.2 6.7
9.3 8.6
3-4* 2-7*
5-6 4.7
8-5 7.2
3.6** 4.8**
4-9 3.9
9-0 6.9
5.0"** 5.6 *°°
Abbreviations: TR = trampled; UN = untrampled; t, t-test. *(p = O.Ol), **(p= 0.001), ***(p= O.O001).
D.R. Bhuju, M. Ohsawa/BiologicalConservation85 (1998) 123-135 5. Discussion
5.1. Changes in soil characteristics A consistent finding observed by many researchers is an increase of soil compaction--bulk density, penetration resistance and non-porosity, with increased amount of trampling (Chappell et al., 1971; Burden and Randerson, 1972; Liddle and Greig-Smith, 1975a; Weaver and Dale, 1978; Cole, 1987; Ikeda and Okutomi, 1990). Liddle, 1975 reviewed that vertical forces applied to the ground by a standing human can be over 200gcm -2 and dynamic forces may exceed 57 000 g cm -2. Bulk density in heavily used forest tracks or paths has been reported to range between 1.08 and 1.34gcm -3 (Chappell et al., 1971; Liddle and Greig-Smith, 1975a) and depending on soil type or slope it can be 0.250.68gcm -3 higher than in their adjacent natural sites (Dotzenko et al., 1967; Weaver and Dale, 1978). In our study, bulk density in the trampled sites varied between 0.72 and 1-26gcm -3 which was 0-3 to 0.9gcm -3 higher than in the untrampled sites. Much higher densities were recorded from plots where sandy soil was noticed; the sand is deposited to check soil erosion and to make convenient walking but paradoxically it has accentuated more lateral spread of the paths as was reported in British hill paths (Bayfield et al., 1988). Below the surface, however, bulk density drastically dropped to the same level of untrampled sites. The effects of trampling, thus, appears to be restricted to the surface soil (Ikeda and Okutomi, 1990). A few studies have included soil chemical properties and its relationship with trampling disturbance which is yet inconclusive (Chappell et al., 1971; de Gouvenain, 1996). In the present study, the carbon and nitrogen percents were quite low in trampled sites which may suggest a low accumulation of plant residues or low plant coverage. Moreover, the nutrients could have been barred from percolating the soil by the low porosity and high run off in the heavily trampled areas. However, our results are based on samples from surface soil for only forest site. 5.2. Vegetation response Experimental as well as field-based studies have shown that there is usually a reduction in the total coverage of ground vegetation and in the number of species in the trampled area (Bell and Bliss, 1973; Liddle and Greig-Smith, 1975b; Cole, 1987); however, the vegetation response to the trampling disturbance is quite variable among the species, some increase while others decrease or be neutral (Dale and Weaver, 1974; Bayfield, 1979). It has been suggested that trampling may reduce the vigour of the dominant components and help release tread communities from competitive suppression
133
(Grime, 1979; Ikeda and Okutomi, 1992) which, in turn, may increase species diversity. Overall, we found less vegetation cover in the trampled sites than in the untrampled ones and this was also true for the unconfined and confined paths. SolinskaGomicka and Symonides, 1996 have reported that biotopes were severely affected with the increase of footpath web in a preserved forest in Warsaw city. We also recorded a few annuals and perennial tread species (e.g. Plantago asiatica) from the trampled sites and common tread species of the region such as Eragrostis ferruginea, Eleusine indica, Setaria faberi, etc., were found in the open areas at the entrance of the studied forest (personal observation). The loss of species richness specially that of woody species was shown by the evergreen patch of Quercus (QM) with relatively a higher floristic diversity attributable to absence of single dominating species; in other patches the difference of.the number or diversity was not so glaring. It is reasoned that not only the trampling disturbances but also the canopy exerts effects upon the species number and diversity. 5.3. Growth inhibition Compaction of soil inhibits growth of woody plants because the increased soil strength restricts penetration by the radicles which in turn curtails the amount of water and minerals reaching the photosynthetic tissues (Kozlowski et al., 1991). In experimentally grown seedlings of Pinus radiata, Sands and Bowen, 1978 found that with an increase of bulk density the length of root decreased while the number of laterals and diameter increased. In the present study, similar results were obtained; in addition, there was higher frequency of main root bifurcation or lateral growths and higher root ratios to stems in all seedlings (Aphananthe, Celtis, Neolitsea and Persea) from the trampled sites. Pan and Bassuk, 1985 have also reported that soil compaction can induce taproots to grow into lateral roots in Ailanthus seedlings. Suppression of height and radial growth by artificially imposed surface compaction have been reported in saplings or juvenile trees belonging to broad-leaved as well as conifer species such as Acer rubrum and Quercus velutina (Donnelly and Shane, 1986) and Pinus ponderosa and P. contorta (Froehlich et al., 1986). de Gouvenain, 1996 studied on impact of soil trampling at subalpine elevations and suggested that trampling impacts on soils may have long-term effects on the successional development of plant communities beside affecting tree growth at the time of disturbance. In the present study, the growth rate as shown by the two colonizing evergreens (Neolitsea and Persea) did not differ much between the trampled and untrampled sites for the first one or two years but it was remarkably arrested in the trampled site in the following years. Foil
134
D.R. Bhuju, M. Ohsawa/ Biological Conservation 85 (1998) 123-135
and Ralston, 1967 reported that compaction exerted only limited effect on seed germination of Pinus taeda but the seedling establishment was reduced as much as 34%. We observed nearly 75% reduction in sapling density of woody species in the trampling sites that could be attributed not only to the increased bulk density and unrestricted paths but also to intact canopy except in patch CJ where the trampling disturbance was limited by single confined path. It is, hence, conceivable that trampling disturbance compounded with canopy induces more damage in the understory succession.
6. Conclusion The total loss of the understory stratum in two nature trail sites signifies the extent of trampling disturbance compounded by superfluous paths and occasional sand surfacing. Such successional suppression is due to soil compaction in the heavily trampled site that impedes root proliferation of seedlings of colonizing species and confines them to a few poor saplings under canopy refugia. With increased outdoor recreation, practical management options become essential. In our study site, attention has already been given to the ancient shellmound site located adjacent to the trampled area; an integrated conservation approach encompassing the fragile ecosystem as a whole will help bring back the lost woody species into the planted forest. Conceivably, such a scheme will take into account of in-detail plan such as confinement of paths, recovery plan, creating rest periods for recovery, public information etc. Given a well thought management plan, such a forest setting in many urban centres may perform a vital role to balance ecology and recreation.
Acknowledgements Dr. Pralad Yonzon, Resources Nepal thoroughly read the manuscript and provided the authors with valuable comments. The authors are also thankful to Dr. Liu Qi-Jin, Mr. S Miyazawa, Mr. T Shumiya and members of Laboratory of Ecology at Chiba University for their kind assistance during the investigation. This study was completed with a Monbusho (Ministry of Education, Japan) Grant. References Bayfield, N.G., 1979. Recovery of four montane heath communities on Cairngorm, Scotland from disturbance by trampling. Biological Conservation 15, 165-179. Bayfield, N.G., Watson, A., Miller, G.R., 1988. Assessing and managing the effects of recreational use of British hills. In: Usher, M.B., Thompson, D.B.A. (Eds.) Ecological Change in the Uplands. Blackwell, London, pp. 399-414.
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