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Ecology |
Institut National de la Recherche Agronomique (INRA), Laboratoire Franco-Chinois d'Informatique, d'Automatique et de Mathématiques Appliquées (LIAMA), Chinese Academy of Sciences—Institute of Automation (CASIA), P.O. Box 2728, Haidian District, 100080 Beijing, China; Ecole Nationale Supérieure d'Arts et Métiers (ENSAM), 151, Boulevard de l'Hôpital, 75013 Paris, France
Received for publication October 9, 2006. Accepted for publication May 23, 2007.
ABSTRACT
Bamboo is considered useful for controlling landslides, but we observed numerous shallow-slope failures in forests of big node bamboo (Phyllostachys nidularia) in Sichuan, China. Therefore, we inventoried landslide occurrence and vegetation type along one valley. To quantify bamboo root anchorage, we performed uprooting tests and measured plant morphological characteristics. Landslide occurrence was greatest at sites with bamboo and young trees. Culm failure was common because of the high length to diameter ratio (242 ± 6). Uprooting tests showed that the maximal force to cause failure was small (1615 ± 195 N). Uprooting force was strongly and positively regressed with a combination of the predictors lateral root number and volume (R2 = 0.92), and root systems were highly superficial (depth = 0.15 ± 0.12 m), contributing little to slope stability. In P. nidularia, which grows on landslide-prone slopes, surprisingly few resources have been allocated to anchorage. We suggest that this strategy puts this pioneer at an advantage on steep slopes, where it contributes little to slope stability and colonizes frequently formed gaps through vegetative regeneration. Fewer disturbances would result in subsequent secondary succession and dying back of this shade intolerant species.
Key Words: anchorage • disturbance ecology • Phyllostachys nidularia • root mechanics • vegetative reproduction
Land degradation through erosion and landslides has been listed as China's top environmental priority, and large-scale measures for controlling soil mass movement are needed (Liu and Diamond, 2005
). The use of vegetation to reinforce soil on unstable slopes or to control erosion is cost-effective and has been studied in detail over the last 10 years in several countries (Roering et al., 2003
; Barker et al., 2004
; Cammeraat et al., 2005
; Van Beek et al., 2005
; Stokes et al., 2007
). Nevertheless, the choice of species is essential when considering how to stabilize soil on a slope, and little information is available in China concerning the suitability of different species for correcting slope instability problems. Vetiver (Vetiveria zizanoides L.) grass is much cited as being useful in fixing soil in tropical and subtropical regions (World Bank, 1990
; Truong and Loch, 2004
), and Storey (2002)
, Zhou et al. (2005)
, and Chaulya et al. (1999)
promoted the use of bamboo species for preventing landslides on shallow slopes. Several studies have also quantified the way in which different species of bamboo control erosion. These studies have shown that beneficial effects of bamboo include modifications in soil chemical properties (Chen et al., 2002
; Tian et al., 2003
) and soil hydraulic conductivity (Ziegler et al., 2004
) and even an increase in soil and air moisture content (Storey, 2002
).
The most important parameters governing soil fixation with regard to shallow landslides appear to be rooting depth and root tensile strength (Wu, 1976
, 2007
). Recent studies have shown that to increase slope stability, roots must cross the slip surface (region within the soil where failure of the substrate is most likely to occur), which is located at a given distance beneath the soil surface (Cammeraat et al., 2005
; Van Beek et al., 2005
). Root tensile strength depends on diameter and cellulose content and usually increases with decreasing root diameter (Genet et al., 2005
). Other characteristics of root system morphology may also influence substrate mass movement but detailed data on this interaction is scanty (Wu, 2007
). With regard to controlling erosion, where soil loss is often very superficial, the density of roots near the soil surface and aerial cover are more important than rooting depth or tensile strength (Gyssels et al., 2005
).
Contrary to Storey (2002)
, Zhou et al. (2005)
, and Chaulya et al. (1999)
, in the Sichuan province of China shallow landslides often occur in forests of big node bamboo (Phyllostachys nidularia Munro, Poaceae) (A. Stokes, personal observations; X. Cai, Sichuan Academy of Forestry, personal communication). In a recent report on the 2006 flashflood and landslide disaster in Thailand, most shallow landslides occurred at sites where banana and wild bamboo were dominant, but species names were not given (ADPC, 2006
). Not only do landslides appear to be more frequent in these bamboo forests, but the plant culms themselves are often leaning or have buckled under their own weight (Fig. 1A). Big node bamboo is monopodial with a running rhizomatous type of root system (Fig. 1B); individual culms emerge at different distances along the shallowly rooted rhizome (http://www.americanbamboo.org). Rhizomes can grow quickly, thus ensuring rapid vegetative reproduction of this pioneer grass species. A second rooting form can also be found in sympodial bamboo species, in which clumps of culms are formed from a discrete rhizomatous root system (http://www.americanbamboo.org). Chaulya et al. (1999)
and Zhou et al. (2005)
did not describe whether the contribution of roots to soil fixation differs depending on the type of root system, but both studies discussed only clumping species; Chaulya et al. (1999)
studied Dendrocalmus strictus Roxb. and Zhou et al. (2005)
studied Bambusa vulgaris Schrad. and B. multiplex Lour.
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; Kappel et al., 2004
). Nevertheless, in big node bamboo, bending and buckling occur under natural conditions (Fig. 1A), and this phenomenon may also contribute to uprooting if the root systems are not firmly anchored. Anchorage of grasses and herbaceous species usually depends on a combination of root number, size, length, depth, and branching characteristics (Bailey et al., 2002
; Dupuy et al., 2005a
). The efficiency of root anchorage is also influenced by soil mechanical and physical properties (Ennos, 1990
; Dupuy et al., 2005b
) as well as by the ecological constraints placed on the plant, e.g., mechanical loading, grazing, or trampling (Read and Stokes, 2006
). The interaction with environment is highly complex, but local conditions largely determine root system depth and spread (Schenk and Jackson, 2002
). To determine whether landslides occurred more frequently in big node bamboo forest than in other types of vegetation, we inventoried the number, size, and type of vegetation growing around landslides along one valley located in the Sichuan province of China. Uprooting strength of big node bamboo was then quantified through winching tests, and root system morphology was measured on excavated or uprooted root systems.
MATERIALS AND METHODS
Site characteristics
The study site was a 4-km long valley located northwest of Chongzhou City on the eastern limits of the Tibet-Qinghai plateau, Sichuan province, China (30°48'104'' N, 103°24'732'' E). This plateau belongs to the middle segment of Longmen Mountain, the southeast offshoot of Qionglai Mountain. The area is mountainous, ranges from 960-3868 m a.s.l., and is characterized by gorges, steep hills and valleys. The few flat areas are located close to rivers and streams at the valley bottom. This area is situated in the moist monsoon (lasting from March to August) zone, and the climate is subtropical. Annual mean temperature is 12.3°C with minimum of 6.0°C in January and a maximum of 32.7°C in July and August. Average annual precipitation is 1300–1450 mm with 70% from June to August and only 5% from November to January. Climate is characterized by misty days, high humidity (annual average relative humidity 86%), little sunshine (average annual sunshine = 641.6 h), and low wind speeds (annual average wind speed = 1.4 m·s–1). Soil parent material consists mainly limestone, sandstone, and granite. The major soil type is a red clay soil accompanied by brown forest soil in mountainous regions. The soil thickness ranges from 0.5–1.3 m, with a humus layer of 0.01–0.03 m (Genet et al., 2006
). Average soil cohesion at a depth of 0.05 m is 10 kN·m2 and did not vary significantly along the valley (J. Ji, Beijing Forestry University, unpublished data).
The valley studied was extremely rich in flora, with over 300 different species inventoried (X. Cai, Sichuan Academy of Forestry, personal communication). The dominant vegetation comprised mixed and monospecific tree plantations of Cryptomeria japonica D. Don, Cunninghamia lanceolata Lamb., Metasequoia glyptostroboides Hu & Cheng., Betula luminifera H. Winkl., and Carya cathayensis Sarg. Major shrub species included Cornus controversa Helms., Trachycarpus fortunei H. Wendl., and Salix guebriantiana Schneid. Dominant grasses and herbs included big node bamboo (Phyllostachys nidularia Munro.), Phragmites communis Trin., Juncus effusus L., Plantago asiatica L., Iris tectorum Maxim., Pteridium latiusculum Desv. and Dobinea delavani Baill. Big node bamboo is a mountain bamboo endemic to southern China and is dominant on slopes with a gradient of 20–30° up to an altitude of 1800–2000 m a.s.l. in its natural habitat (Chen et al., 1999
; Zhu et al., 2003
) but can also be abundant on slopes up to 50°. In cultivated areas along the bottom of the valley in our study site, culms of big node bamboo are harvested every 3–4 yr and used for tools and furniture.
Landslides inventory
Along the 4-km valley, we characterized the vegetation growing adjacent to or around the scarp of superficial landslides that had occurred in the last 3 years. A period of 3 yr was chosen because little vegetation was present on the disturbed soil, making it easier to measure the area and depth of the landslide. The characteristics measured for each landslide included length, width, depth, slope angle, orientation, and geographic positioning system (GPS) coordinates (Table 1). Each landslide was small and could be accessed from a recently laid 3-m wide forest road running through the valley. Several of the landslides occurred just above the road, and its construction may have contributed to slope instability (Swanston, 1974
); therefore, the distance to the road was also noted. Surface area and volume of the landslide were calculated from the length, width, and depth. Because soil type did not differ along the valley (J. Ji, Beijing Forestry University, unpublished data), soil samples were not collected at the site of each landslide. The dominant plant species present on and around each landslide was determined. Using a classification system similar to that developed by Lee (2004)
, who inventoried landslides in Korea using satellite imagery and field surveys, we classed vegetation into six categories (bare soil; herbaceous and grass species; shrubs; trees < 0.1 m in diameter at breast height (BH); trees > 0.1 m in diameter at BH; and big node bamboo). The % cover of each category was determined visually within a distance of 5 m from the scarp and edges of the landslide.
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), the stem would have buckled before anchorage failure occurred. Therefore, we attached the sling near ground level and pulled plants downhill, which would mimic the mechanical action of a landslide on the stem base, although without the shearing action of the soil. Nevertheless, by pulling plants laterally and downhill, this type of uprooting is more representative of failure during a landslide than vertical uprooting, which is often used to examine root reinforcement on slopes (Mickovski et al., 2005
). Slope angle was measured at the culm base for each test. Force was measured using a load cell (K25H-20 kN, Scaime, S.A., France) and logged every second using a data logger (Almemo 2290–8, Ahlborn, Germany). Culm displacement was estimated by measuring the distance the winch cable was displaced during uprooting. The entire operation was also timed using a stopwatch.
Total plant height and culm basal and apical diameters were measured for each plant, so that the height : culm basal diameter (H : D) ratio, and volume of the whole culm (Vculm) could be determined. Samples (0.5 m long) were cut from the center of each culm, and the diameter at each end of the section was measured (Cucchi et al., 2004
). The fresh mass was then noted before drying in an oven at 80°C for 5 d, and dry mass was then measured. These data were used to estimate fresh and dry mass of the whole culm (Mculm), using the following equations based on those in Cucchi et al. (2004)
:
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| (1) |
Vculm and Vsample (either can be represented by V in Eq. 2) are both calculated using the equation:
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| (2) |
Root system morphology
In a preliminary study of root morphology, two intact blocks of soil (0.5 x 0.5 x 0.5 m) were removed and soaked in water for 3 d to soften the clay soil. Root systems, including rhizomes, were carefully washed and excavated. The total depth, number, length, basal diameter, and apical diameter of each first order lateral root per node were determined. Lateral root volume (Vroot) was determined using Eq. 3:
|
| (3) |
The same method was then applied to the first order lateral roots at the nodes along the rhizome. The diameter and distance between each node were also measured (Fig. 1B).
In plants that had been uprooted, the same technique was used to measure root morphology, but because roots were often broken during the uprooting tests, it was also noted whether the root was broken (hence root length and apical diameter corresponded to roots that were not whole) or whether the root had slipped out of the soil (in which case the root was considered as intact). The depth and diameter of the culm attachment to the rhizome (culm neck) and where it had broken were also noted.
Soil moisture content
To determine whether soil moisture content differed between the big node bamboo forest and mixed or monospecific forest nearby, as suggested by Storey (2002)
, soil moisture content was measured when anchorage tests were carried out on 4 July 2006 and also at three nearby sites on the same day. One site comprised a mixture of big node bamboo and 7-yr-old Cunninghamia lanceolata; the second and third sites were monospecific stands of Cryptomeria japonica aged 10 and 20 yr, respectively. Several fresh soil samples were removed at a depth of 50 mm from each site and immediately weighed. These samples were then dried at 80°C for 5 d, or until there was no further change in mass and weighed again. This drying temperature is standard in China (Anonymous, 1996
). Soil moisture content was expressed as a percentage (grams of water per 100 grams of dry soil).
Data analysis
Analysis of variance was used to determine whether differences in vegetation type or % cover and landslide characteristics differed between landslides located in the forest and those situated above the forest road (analyses were carried out using Minitab Statistical Software 13.20). The mean of slope orientation was calculated using circular statistics methodology (Batschelet, 1981
).
Cross-sectional areas (CSA) at each culm base, lateral root base (CSAbase), and apex (CSAapex) were calculated, because previous research suggested that uprooting resistance is a function of CSAapex of roots broken during uprooting (Toukura et al., 2006
). Root : shoot mass ratio was also calculated using the dry mass data. Regressions between maximal uprooting force and individual or combined plant morphological characteristics were carried out. Combined predictors (e.g., root number and length and basal diameter or volume) have been shown to be better indicators of pull-out resistance than single predictors (Bailey et al., 2002
; Dupuy et al., 2005a
).
Analysis of variance was used to test whether soil water content differed among the four sites. Data are presented as means ± SE.
RESULTS
Landslides inventory
Fifteen landslides were identified along the valley. All were superficial with a small surface area, and mean slope angle was quite steep (Table 1). Eight landslides were located just above the forest road. Big node bamboo was present at the scarp and adjacent to 60% of landslides, whereas young plantation tree species (<0.10 m diameter at breast height, DBH), especially C. japonica and C. lanceolata, were present adjacent to all landslide sites. Few landslides occurred adjacent to large trees (>0.1 m DBH), shrubs, or grasses (Table 1). When all landslides (natural and those probably due to forest road construction) were considered together, the percentage of cover with young plantation trees growing adjacent to the landslide was higher than that of big node bamboo but this difference was not significant (Table 1). However, the percentage of bamboo cover was significantly greater around the scarp or on the adjacent slope of natural landslides (48.6 ± 11.2%) than around landslides resulting from forest road construction (12.2 ± 6.7%) (F1,13 = 8.11, P = 0.014). Other vegetation types and slope angle did not differ significantly between natural landslides and those due to the construction of the forest road. No significant relationship existed between any type of vegetation cover and any landslide characteristic. During the inventory, we also observed that a high percentage of bamboo culms were leaning down slope, and in several cases, the culms had buckled (Fig. 1A).
Root system anchorage
As the bamboo was winched sideways, each culm quickly bent at the culm base and then buckled. When the culms buckled, uprooting began and individual roots could be heard breaking. If the sling slipped along the culm of the plant, the time at which this occurred was noted, so that in the uprooting vs displacement curves (Fig. 2), the slippage was not mistaken for root breakage. Mean uprooting resistance was 1615 ± 195 N when all plants were considered together.
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In uprooted plants, culms were long and thin with a very high mean H : D ratio (Table 2). Mean maximum rooting depth was only 153.3 ± 13.9 mm (Table 2), making the culm height : root depth ratio extremely high (38.3). Most roots were broken during uprooting, and only 17.6% of roots per plant slipped out of the soil rather than breaking during loading. The mean distance at which roots broke was 63.2 ± 2.2 mm (Table 2). Numerous lateral roots were present in each root system (Table 2), but root system dry mass was low compared to that of the shoot (Table 2). with a root : shoot dry mass ratio of 0.05 ± 0.01. Seven to eight nodes were usually present per root system. Lateral root number was highest at the culm base (15.0 ± 1.4) but decreased down the root system to only 6.0 ± 1.0 roots at node number 7. The CSA of lateral roots was lowest at the culm base (6.7 ± 0.7 mm2), increasing to 27.7 ± 0.9 mm2 at node number 7. Lateral roots were shortest at the culm base (33.3 ± 5.0 mm) but reached a mean length of 126.8 ± 21.4 mm at node number 7.
The diameter of the culm neck, which occurred at a mean depth of 50 ± 5 mm (Table 2), was slightly larger than those of lateral roots (Table 2). This attachment may fail in the final stages of uprooting. The outer cortex of the rhizome often delaminated, suggesting that the plant was torn off the rhizome rather than breaking cleanly.
Regressions of uprooting force with one or several variables of culm and root morphology showed that the best predictors for uprooting resistance were total lateral root volume and a combination of total lateral root volume with lateral root number (Table 3).
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Small and shallow landslides were often present in sites where big node bamboo and young plantation tree species, e.g., C. japonica and C. lanceolata, were present. Over half the landslides examined had occurred several meters above a narrow forest road, which was probably a major factor in the triggering of the landslide. When only natural (no road present) landslides occurred, big node bamboo was always the dominant species, even though young plantation trees were always present. The young trees were less than 0.1 m DBH and probably had few deep roots, thus contributing little to slope stability. All landslides occurred on quite steep slopes (49°), which are common in this region, and local foresters told us that the landslides observed had all taken place after major rains during the monsoon season. Although the number of landslides was small and all were measured in the same valley, data suggest that natural, shallow landslides do occur more in forests of big node bamboo than in the other plant communities examined.
Although measured on only one day during the monsoon season, soil moisture content was higher in pure big node bamboo plantations than in the mixed and monospecific forest sites. To obtain more accurate data about soil moisture in these different sites, it would be necessary to carry out long-term testing of hydrological properties. Nevertheless, our data suggest that, during the monsoon season, soil may indeed be wetter in sites where only bamboo is present, as stated by Storey (2002)
. This higher soil moisture content would mean that soil saturates faster in pure bamboo forest than in mixed forest or monospecific plantations. As landslides usually occur when the soil is saturated, the mechanism by which soil moisture is increased underneath bamboo culms (Storey, 2002
) might contribute to slope instability.
The extremely high culm H : D would explain the bending and buckling in culms. Although not entirely comparable with woody species, this ratio far exceeds the critical H : D of young trees (Holbrook and Putz, 1989
). To reach high light levels above the bamboo canopy, big node bamboo can be considered as taking "mechanical risks" (Sterck and Bongers, 1998
). The very low root : shoot biomass ratio of only 0.05 and high culm height : root depth ratio also implies that this species invests little in the root system. This unbalanced allocation of resources to shoots and roots may thus also lead to partial uprooting of the plant as the culm leans down slope. In such a situation, rainwater may collect in the space created by the uprooted plant and contribute to slippage of saturated soil.
Although uprooting tests were not vertical, as in previous studies (e.g., Bailey et al., 2002
; Mickovski et al., 2005
; Norris, 2005
; Toukura et al., 2006
), the lateral pulling tests simulated to a certain extent plant failure during a landslide. As the culms bent downward and buckled before root failure, it was not appropriate to transform uprooting data into bending moments, which are usually used to quantify mechanical behavior in self-supporting plants (Cucchi et al., 2004
). Few data have been published concerning uprooting strength for species comparable to big node bamboo. Mickovski et al. (2005)
found a mean uprooting resistance of 467 N in 2-yr-old plants of Vetiveria zizanioides, where mean total dry mass was only 41 g. In a study of uprooting resistance of several young riparian tree species ranging from 0.6–0.9 m in height and with a shoot dry mass between 20–27 g, Karrenberg et al. (2003)
found that uprooting resistance varied between 299–638 N. Therefore, the mean uprooting resistance of 1615 N observed in big node bamboo seems very low, considering that mean shoot dry biomass was 359 g.
The root morphology of the intact and uprooted plants was in general quite similar; therefore, root systems were not extensively damaged during uprooting. In agreement with Dupuy et al. (2005b)
, we found that the best predictors of uprooting resistance were total lateral root volume and a combination of the number of lateral roots and their volume. Unlike the individual plants studied by previous investigators (e.g., Ennos, 1990
; Bailey et al., 2002
; Toukura et al., 2006
), big node bamboo culms were attached to a running rhizome at a mean depth of 50 mm. The rhizomatous runners may play a role in anchorage, in that they and the associated lateral roots can be considered to act like guy ropes, holding the central, rigid element of the root system in place (Ennos, 1994
). Within the root system itself, the lateral roots can also be considered as acting like guy ropes, holding the rigid culm base in place. When plants failed during uprooting, the runners were left in the soil, indicating that the rhizome broke at the culm neck. The contribution of the culm neck to anchorage is difficult to quantify but seems to be the last structure to break. To measure the force needed to cause failure at this point of rhizome attachment, it would be necessary to carry out mechanical testing in the laboratory, using plants extracted from the soil medium.
Not only was anchorage of big node bamboo poor, but one of the most important parameters for controlling soil mass movement, the number of roots crossing the slip surface, was negligible. The slip surface was located at approximately 0.6 m depth, which corresponds to the mean depth of landslides in the valley. The maximal rooting depth of bamboo was very shallow (0.15 ± 0.12 m in uprooted plants), and therefore very few roots, if any, will cross the slip surface. To increase slope stability, root reinforcement at the slip surface is necessary (Cammeraat et al., 2005
; Van Beek et al., 2005
). In this bamboo species, which is subject to frequent heavy rains and consequent soil slippage, it appears that no mechanism has evolved to improve anchorage, and the plant allocates few resources to this fundamental function. The ecological context in which this plant grows may provide some clues as to why this may be.
Phyllostachys nidularia is a pioneer mountain species that dies back under shade. Patches in bamboo forest caused by landslides and other disturbances allow this species to colonize the newly formed gaps and hence grow in full light. Kajimoto et al. (2004)
also found in northern Japan that dwarf bamboo (Sasa kurilensis Rupr.) was able to grow profusely in microsites along avalanche paths, where large trees of Abies mariesii Mast. had failed during avalanches. In the valley we studied, once a shallow landslide has occurred, soil slippage above and around the landslide will continue, and debris flow may also commence. During a landslide or soil slippage, rhizomes will remain buried in the soil that is moved downhill. These rhizomes can rapidly grow in the newly disturbed soil, thus allowing fast colonization of the recently formed gap. If big node bamboo invested in a stiffer stem and well-anchored root system, which also better reinforced soil, species succession would result in trees eventually growing upwards and causing shade conditions detrimental to survival. Phyllostachys nidularia dies back after flowering, although the exact number of years between flowering is not known (Huang et al., 2002
). However, even though rhizomes persist in the soil, broadleaf tree species will quickly dominate the site, resulting in the next stage of succession. Flowering, although sporadic, ensures that population regeneration is maintained (Huang et al., 2002
), whereas vegetative reproduction through rhizome regeneration allows this pioneer species to quickly colonize newly formed patches in the landscape.
The ecology of colonization and vegetation succession on disturbed soil is well documented (Pickett and White, 1985
; Johnson and Miyanishi, 2007
), but species strategy with regard to frequent disturbance is less well studied. Disturbance has been defined as a relatively discrete event in time and space that alters the structure of populations, communities, and ecosystems and/or changes resources, substrate availability, or the physical environment (Pickett and White, 1985
). Frequent disturbances, e.g., landslides and avalanches (Kajimoto et al., 2004
), in the same area will permit native pioneer species to colonize patches in the landscape. Some species are able to colonize unstable slopes by various strategies. For example, the strong resprouting ability of Davidia involucrata Baill. allows this tree to grow and spread quickly on scree slopes where landslides occur frequently (Tang and Ohsawa, 2002
). Therefore, we suggest that the poor anchorage of P. nidularia gives this species a competitive advantage and thus may be considered as a mechanical strategy allowing this species to vegetatively reproduce and remain dominant within the landscape. Being endemic only to mountain slopes would have permitted this species, and possibly similar bamboo species, to evolve such a strategy. This phenomenon is contrary to that which is considered usual in terrestrial self-supporting plants, where adaptive growth usually occurs and root system anchorage improves if the plant is mechanically stressed, thus reducing uprooting and mechanical failure (Ennos and Fitter, 1992
; Stokes et al., 1995
; Telewski, 1995
; Read and Stokes, 2006
). Nevertheless, several aquatic and terrestrial species have been identified as possessing structurally altered or mechanically weak morphological zones. These modifications result in the facilitated breakage of organs leading to increased vegetative regeneration, hence contributing to species fitness (see review by Read and Stokes, 2006
). Although ecologists are beginning to examine the different mechanical mechanisms by which woody species ensure vegetative reproduction in different ecological niches (Beismann et al., 2000
; Karrenberg et al., 2003
), additional research is needed to better understand this phenomenon.
Our results suggest that P. nidularia is a suitable species for use in erosion control, because it produces a dense mat of roots, but is probably less useful in preventing mass movement of a substrate. Other rhizomatous species endemic to mountain slopes may behave in a similar way with regard to uprooting and regeneration strategy. Therefore, researchers and practitioners should be more precise when stating that such plants, in particular bamboo, are useful for reinforcing soil against landslides and should specify the exact species and rooting habit.
FOOTNOTES
1 The authors thank T. Fourcaud (CIRAD, France), N. Kokutse (Université Bordeaux I, France), S. B. Mickovski (University of Dundee, UK), L. Paquet (ENSAM, France), J. Ji (Beijing Forestry University, China), G. Hong (Chinese Academy of Forestry), and the Sichuan Academy of Forestry, China, for help with fieldwork and species identification. This project was funded by INRA (MRI AIP) and a LIAMA seed project. 
4 Author for correspondence (alexia.stokes{at}cirad.fr
; present address: Institute National de la Recherche Agronomique (INRA), Botanique et Bioinformatique de l'Architecture des Plantes (AMAP), TA A-51/PS2, Boulevard de la Lironde, 34398 Montpellier Cedex 5, France
5 Present address: Institute National de la Recherche Agronomique (INRA), Domaine de Vilvert- 78352 Jouy-en-Josas cedex, France
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