ecuador regeneration of natural landslides (ohl y bussman citado)

Feddes Repertorium 115 (2004) 3–4 , 248–264 DOI: 10.1002/fedr.200311041 Weinheim, August 2004

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 0014-8962/04/3-408-0248

Martin-Luther-University Halle-Wittenberg, Institute of Geobotany and Botanical Garden, Halle (Saale) University of Hawai’i Manoa, Institute of Botany, Honolulu

C. OHL & R. BUSSMANN

Recolonisation of natural landslides in tropical mountain forests of Southern Ecuador

With 2 Map; 4 Figures and 2 Tables

Summary

The regeneration of the vegetation of natural land-slides was studied at Estación Científica San Fran-cisco (ECSF) in a tropical mountain forest area of Southern Ecuador, north of Podocarpus National Park. The study focused on the process of regeneration on natural landslides and the vegetation change along an altitudinal gradient using space-for-time substitution. The most important plant families present on the landslides during the first stages of succession are Gleicheniaceae (Pteridophyta), Melastomataceae, Eri-caceae and Orchidaceae. Species of the genus Stiche-rus (Gleicheniaceae) are dominant, and species com-position varies with altitude and soil conditions. Colonisation of landslides is not homogeneous. Zones with bare ground, sparsely vegetated patches and densely covered areas may be present within the same slide. This small scale spatial heterogeneity is often created by local ongoing sliding processes and differ-ent distances towards undisturbed areas. Therefore, the duration of the successional process is highly variable. The initial stage of the succession is a com-munity of non vascular plants interspersed with scat-tered individuals of vascular plants. By means of runner-shoots they form vegetation patches which start growing into each other. The second stage is dominated by Gleicheniaceae (species composition varying in altitude and soil chemistry). In the third stage, bushes and trees colonise, sheltered by the ferns, and a secondary forest develops with pioneer species that are not found in the primary forest vegeta-tion. The common phenomenon of the natural land-slides leads to an increase in structural and species diversity on a regional scale.

Zusammenfassung

Rekolonisation auf natürlichen Hangrutschun-gen in tropischen Bergwäldern Südecuadors Im tropischen Bergwald Südecuadors (nördlich des Podocarpus Nationalparks im Gebiet der Estación Científica San Francisco, ECSF) wurden Artenzu-sammensetzung und Rekolonisationsprozesse früher Sukzessionsstadien entlang eines Höhengradienten auf natürlichen Hangrutschungen untersucht. Besonders Gleicheniaceae, Melastomataceae, Eri-caceae und Orchidaceae sind von Bedeutung. Arten der Gattung Sticherus (Gleicheniaceae) sind sehr zahlreich vertreten. Die Artenzusammensetzung wech-selt entlang des Höhengradienten und in Abhängigkeit von den Bodenbedingungen. Die mosaikartige Vertei-lung der Vegetation auf den Rutschungen (gänzlich unbedeckte bis stark überwucherte Zonen) ist auf häufige lokale Nachrutschungen sowie auf unter-schiedliche Geschwindigkeiten der Wiederbesiedlung entsprechend der Distanz zu ungestörter Vegetation zurückzuführen. Die Dauer der Sukzession ist daher sehr variabel. Das Initialstadium wird von Moosen und Flechten gebildet. Im weiteren Verlauf führt die überwiegend vegetative Ausbreitung einzelner Gefäß-pflanzen zum zweiten Sukzessionsstadium. Dieses ist durch die Dominanz von Gleicheniaceae gekenn-zeichnet, während im dritten Stadium im Schutze der Farne erste Büsche und Bäume heranwachsen und den Pionierwald bilden. Da diese Arten nicht im Primär-wald vertreten sind, kommt es regional zu einer be-trächtlichen Erhöhung der Artenzahl und der struktu-rellen Diversität.

Introduction

Landslides are extremely frequent in the tropi-cal mountain regions of Ecuador. Destruction

of roads and catastrophic events burying houses or even villages are common. Such slides, however, are usually initiated by human im-pact; most often by construction projects weak-

2041275 Feddes Repertorium 3-4/2004 FED0681u.doc WinXP: Patrick Ahlemann/Pfü. /Sch. Beitrag: 5 Diskettenartikel

C. OHL & R. BUSSMANN: Recolonisation of natural landslides in tropical mountain forests 249

© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Fig. 1 View of the research area. Note the high number of natural landslides

ening the underground and by deforestation accelerating erosion. At some distance from roadsides and settlements, dense forests still exist. Even in these untouched areas, landslides are a very common phenomenon (Fig. 1). Such natural slides are usually of smaller size than the anthropogenic slides. Little vegetation research has been done on landslides. Research on the regeneration of the plant cover of a single landslide in Northern Ecuador was carried out by STERN (1995). KESSLER (1999) studied succession on land-slides in Bolivia, and ERICKSON et al. (1989) in the central and southern Andes. In other tropi-cal mountain areas species colonisation on landslides was analysed by GARWOOD (1981 in Panama) and GUARIGUATA (1990 in Puerto Rico) and geomorphological processes by BATARYA & VALDIYA (1989 in the Lesser Himalaya in India). KEEFER (1984) studied earthquake triggered landslides all over the world.

In the present study natural slides in Ecua-dor were analysed for vegetation characteristics during regeneration, species composition at different altitudes, succession and the role of landslides for the biodiversity at the landscape level.

Study area

The research was done in the easternmost mountain chain (Cordillera de Consuelo) in the Southern Ecuadorian Andes (Cordillera de Numbala). The study area is part of the biologi-cal reserve “Estación Científica San Fran-cisco”. It is situated in the province Zamorra- Chinchipe (03°59′S, 79°04′W). Altitude ranges from 1800 m up to 3150 m. The well-known Podocarpus National Park borders the south of the site (Map 1). The southern part of the Ecuadorian Andes is the lowest part of the Andes near the equator.

250 Feddes Repert., Weinheim 115 (2004) 3–4


Map 1 The study site is located in southern Ecuador at the northern fringes of Podocarpus National Park between peak 3100 and ECSF (Estación Científica San Francisco) The substrate is built of pre-Creataceous to Tertiary material (HALL 1977; CLAPPERTON 1986). The geology of the study area varies. Strongly weathered clay to sand stones are common while phyllitic slates are abundant in the lowest areas (ZECH & WILCKE 1999, own obs.). The soils are mainly Aquic and Oxaquic Dystropepts (SCHRUMPF et al. 2001). The precipitation regime is bimodal as in the larger part of the Ecuadorian Andes. One peak of high rainfall occurs from February to May and the other from October to December (HOFSTEDE et al. 1998; BENDIX & LAUER 1992). The climate at 1950 m a.s.l. is semi-humid with 10 humid months, has a mean tem-perature of 15.5 °C and an annual precipitation of 2031 mm. Above 2200 m a.s.l. the climate is per-humid (EMCK, pers. comm.). The natural

landslides in the research area are predomi-nantly caused by steep relief, long and heavy rainfalls, occasional earthquakes and a sub-strate consisting mainly of highly weathered clay-stone; ideal conditions for the heavy wa-ter-logged organic layer to slip down. Roots rarely penetrate down to the mineral soil, and subsequently do not prevent the upper layers from sliding. The flora of Ecuador consists of approxi-mately 16000–20000 species of vascular plants (GENTRY 1977; JØRGENSEN & ULLOA ULLOA 1994; JØRGENSEN & LEON-YANEZ 1999). Given that Ecuador covers a relatively small area, it is one of the most species-rich floras of the world. This richness is not equally distrib-uted over the country. Only 10% of the coun-try’s surface falls into the altitudinal range of



900 to 3000 m a.s.l but it is at this altitude where about 50% of the species and 39% of the endemics are found (MADSEN & ØLLGAARD 1994). KESSLER (2002) counted 1138 endemic species in Ecuador at altitudes between 2500 and 3000 m. The altitudinal zonation of the vegetation in the study area is as follows:

< 2100 m: Montane Broad-leaved Forest 2100–2700 m: Upper Montane forest or Ceja Andina (2500–3100 m: Subalpine Elfin Forest or Yalca) > 2700 m: Grass-Páramo, in wind-protected areas Shrub-Páramo.

The Montane Broad-leaved Forest is cha-racterised by trees up to 30 m high, not exceed-ing this height at exposed sites. Epiphytes, especially ferns, Bromeliads and Orchids are highly abundant. Important taxa are Lauraceae (Ocotea, Nectandra, Persea), Melastomataceae (Miconia) and Rubiaceae (Psychotria, Pali-courea) (BUSSMANN 2001). The canopy is very dense and therefore herbal plants near the ground are less common than at higher alti-tudes. Philodendron (Araceae) and Cyat-heaceae dominate the shrub layer. The vegetation composition of the Upper Montane Forest and the transition towards the Yalca vegetation was studied in 1999 and 2000 by HOMANN. The zone up to about 2400 m is dominated by Purdiaea nutans (Cyrillaceae), a stunted growing tree, and Guzmannia vanvolx-emii (a terrestrial Bromeliaceae) building a dense ground-covering layer. Occasionally the latter is replaced by Neurolepis elata (Poaceae). Other important taxa include Clusiaceae, Me-lastomataceae and the genus Schefflera (Ara-liaceae). Above 2400 m Purdiaea nutans becomes less important while species of Melas-tomataceae become more abundant. Trees are between 5 and 10 meters high. In wind-exposed positions paramos occur as low down as 2700 m a.s.l.

Methods

23 landslides were selected between 2000 m and 2700 m a.s.l. Selection criteria were: accessibility, aspect and altitude. On each selected slide between 2 and 5 plots in homogenous zones were chosen for the vegetation survey. The plot size was generally

4 m2, as suggested by species area-curve analyses. Each plot was photographed. The cover of the floristic releves was estimated using the Londo scale (LONDO 1976). The vegetation table was sorted by hand and with the help of TWINSPAN (HILL 1979) according to floristic similarity (Table 1). The plots were sampled only once during the period between September and December 1999. The identification of plants was based on literature, and later compared to specimens in the “Herbario de la Estacion Cientifica San Francisco”, the “Herbario de la Universidad Nacional de Loja” (Loja) and in the “Herbario de la Pontifica Universidad Catolica” (QCA) in Quito. Angiosperm identification followed HUTCHINSON (1967), HARLING & SPARRE (1973–2000), KELLER (1996), BRAKO & ZARUCHI (1993), MADSEN & ØLLGAARD (1993), ULLOA ULLOA & JØRGENSEN (1993) and GENTRY (1996). Ferns have been identified according to the publications of TRYON & STOLZE (1989–1993), MACBRIDE (1930–1970), ØSTERGAARD (1995) and ØLLGAARD (1979). Non vascular plants were not identified. Nomencla-ture of higher plants follows JØRGENSEN & LEON-YANEZ (1999). Taxa missing in this work are named according to the QCA specimens. The collection of environmental data included soil texture of the upper mineral layer, and the soil pH. The depth of the humus layer was measured as an important indicator of successional age and ongo-ing erosion. The inclination and position on the slide was recorded as well as the altitude above sea level, the direction aspect and the geographical position of the landslide. Space-for-time substitution (PICKETT 1989) was employed to describe successional processes of initial stages. Knowledge about the history of the slides can be gained by studying the aerial pictures of the region from 1962, 1976, 1989 (Instituto Geographico Militar, Quito) and 1998. However, the time since the last major sliding event for the plots could not be assessed accurately because most of the landslide material is not displaced by one big event but by several consecutive slides. This type of land-slide has been called “ongoing slide” by STOYAN (2000). Further on, many of the slides were invisible at the aerial pictures due to their small size and the steep relief. Therefore, the vegetation table was organised according to their number of strata, in-creasing vegetation cover and height (Table 2). In this way the successional sequence can be inferred but not their duration. Patterns of succession in the early to intermediate stages were investigated in this study; however there are no samples in the late successional stage. This is due to the logistical prob-lem of finding well-grown slides, as they are invisi-ble in aerial pictures and hard to find by walking through the steep and dissected terrain.



Table 1 Vegetation types of landslides – frequency table, reduced to common and diagnostic species

Sticherus rubiginosus- type

Sticherus revolutus types

variant with Sticherus bifidus

variant with Sticherus melanoblastus

number of plots 13 31 32

Average altitude in m a.s.l. 2030 2290 2480

Sticherus rubiginosus V I I Elleanthus aurantiacus IV I II Diplopterygium bancroftii III I Sticherus arachnoideus II Isachne cf rigens II Andropogon bicornis II Ageratina dendroides II Munnozia senecionidis II I Sticherus bifidus I IV Purdiaea nutans II I Graffenrieda harlingii II I Sticherus melanoblastus IV Viola stipularis III Rhynchospora cf macrochaeta II Sticherus revolutus I V V Bejaria aestuans I V III Blechnum sp. I III V Brachyotum campanulare II II Disterigma acuminatum II II Baccharis genistelloides IV V V Lycopodiella glaucescens III V V Tibouchina lepidota III III III Pitcairnea trianae II III IV Lophosoria quadripinnata II IV III Rhynchospora cf vulcani II III III Cortaderia bifida I II II

Results

Floristic Composition

146 species of more than 40 families grew on the studied sites. 22 species belong to the Pteri-dophyta. Families with ten or more representa-tives in the data set are the Melastomataceae, Orchidaceae, Ericaceae, Asteraceae and Glei-cheniaceae (Pteridophyta). Poaceae, Bromeli-aceae and Rubiaceae are frequently found, too. 56 species were recorded only once. 75% of the total cover of vascular plants is composed of different species of Pteridophyta especially

Gleicheniaceae, of which nine species of Glei-cheniaceae were found. The genus Sticherus is the most important with seven species.

Vegetation: altitudinal and edaphic differentiation

Two major groups are recognisable in the vege-tation table classified according to floristic similarity (Table 1). One is dominated by Sticherus rubiginosus (Gleicheniaceae) while Sticherus revolutus (Gleicheniaceae) is com-mon in the other. The second group is clearly divided into two sub-clusters. The first is char-



acterised by Sticherus bifidus (Gleicheniaceae), the second by Sticherus melanoblastus (Glei-cheniaceae). Other species are frequently occurring all over the studied plots. These include Baccharis genistelloides (Asteraceae) and Lycopodiella glaucescens (Lycopodiaceae). Altitude is a major factor influencing the species composition of the landslides. Fig. 2 demonstrates the change of dominance of spe-cies of Gleicheniaceae at different altitudes. At low altitudes Sticherus rubiginosus dominates. At higher slides it is replaced by Sticherus revolutus accompanied by Sticherus bifidus or Sticherus melanoblastus. The latter species were never recorded both at the same slide. The landslides colonised by Sticherus bifidus (slide 3, 4, 5, 6, 7, 8, 9, 10 and 22) and Sticherus melanoblastus (slide 19, 20, 21 and 23) are located on different mountain ridges (Map 2). This shows that another environmental factor overlapping with the change in altitude is re-sponsible for this vegetation change. Slightly different pH-values and a different percentage of exchangeable Ca2+ (VALLADAREZ, pers. comm.; ZECH et al. 2000) are characteristic for the different ridges.

Vegetation: time factor

Table 2 shows a chronosequence of three suc-cessional stages. The first stage (Fig. 3) is ra-ther similar at all altitudes with mosses and lichens covering the ground. The percentage cover of the layer of lichens and mosses is highly dependent on the soil and water condi-tions at a very small spatial scale and therefore not useful as an indicator for succession. A few scattered vascular plants establish themselves. The duration of this stage is highly variable depending on the erosion of the site. The areas in the first stage of succession on the slides are freshly slipped parts, rocky parts, ever-eroding slopes or ever-accumulating zones with little inclination. Only some robust and runner-shoot building species can cope with strong erosion. In particular Baccharis genistelloides (As-teraceae) and Lycopodaceae are found. The duration of the first or early second stage is quite impossible to estimated, as ongo-ing erosion disturbs the successional sequence. The occasional presence of lignified plants

already on first stage sites points to an ad-vanced age of at least 5 to 10 years (for exam-ple Tibouchina lepidota, Vismia tomentosa or Bejaria aestuans in plot 5, 12, 15, and 16). The second stage (Fig. 4) develops with the exten-sion of the scattered plant individuals and ramets that established in the first stage of succession using vegetative propagation, espe-cially Gleicheniaceae (see upper left corner of Fig. 3) and Lycopodiaceae. Lycopodiella glaucescens and Lycopodium clavatum spread more quickly than the Gleicheniaceae with long looping runner-shoots but build stands of less density (8, 10, 17, 19, or 27). Locally Viola stipularis spreads successfully using runner shoots (plots 4, 20 and 21). The species compo-sition seems to be random up to the point when the patches meet and competitive effects occur. The month of October 1999 was a period of extremely dry weather conditions. Locally, entire populations of Lycopodiella or Sticherus vanished suddenly (leaving patches of dead above ground plant material) probably as a result of competition for water between the individuals, ramets and species. The second stage vegetation is made up by dense covers of Sticherus and Lycopodiaceae. Sticherus rubigi-nosus does not seem to have serious opponents at slides 1, 2, 11 and 12. Sticherus bifidus and Lycopodiella tend to take over the dominant role at slides 3–10. Sticherus revolutus pre- vails at slide 22 and Sticherus melanoblastus and Sticherus revolutus at slides 19–21, 23 and 13–18. The dominant role of Lycopo- diella glaucescens vanishes usually with in-creasing total vegetation coverage (plots 59, 70, or 75). Some species are equally present in early and later stages but never become dominant. Rhynchospora cf. vulcanii for example builds tufts and resists against the dominant species in low numbers from the first stage to the end of the second (plots 3, 11, 27, 38, or 70). Baccha-ris genistelloides does not build dense colonies, and due to its straight and narrow growth form, percentage cover is usually very low but there are some plots where it is of greater importance (plots 31, 43, 45, or 67). Seedlings of bushes like Tibouchina lepidota, Graffenrieda harlin-gii (both Melastomataceae) or Bejaria aestuans (Ericaceae) are frequently found under dense layers of Sticherus in the first herbal layer.



Sticherus rubiginosus

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Sticherus revolutus

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Sticherus bifidus

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Sticherus melanoblastus

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1900 2000 2100 2200 2300 2400 2500 2600 2700 2800 2900

altitude in m a.s.l.

dom

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Fig. 2 Altitudinal preference of some common Gleicheniaceae species on revegetating landslide plots Usually, these species are not found in primary forest but form the pioneer forests. Seedlings of Purdiaea nutans (Cyrillaceae), the dominant species in the upper primary forest, may be found but apparently never mature to shrubs or trees in any of the early successional stages (plots 17 or 29). The third stage: Vegetation development at the Sticherus rubiginosus-dominated sites does not show great variability. High stands of St. rubiginosus are covered with climbing Diplop-terygium bancroftii (plots 48, 49, or 50) which may locally dominate (plot 51); the mats of

undecomposed organic matter are very thick (plots 49, 50, and 51). The shady edges of the slides are dominated by either Sticherus arach-noideus, or St. tomentosus. The woody plants Ageratina dendroides (Asteraceae), Munnozia senecionidis (Asteraceae) and Liabum kingii (Asteraceae) are present. At the Sticherus melanoblastus or St. bifi-dus dominated sites Cortaderia bifida (Poa-ceae) climbs with long, looping runner-shoots through the dense layer, hardly ever touching the ground (59, 64, 65, or 71). In the upper strata Tibouchina lepidota (Melastomataceae)



Map 2 Position of the investigated landslides in the area. The landslides are aligned along three different mountain ridges

and other species build bushes or small trees. The fern Lophosoria quadripinnata (Lopho-soriaceae) grows up to 2 meters in height (plot 59).

Discussion

The first remarkable thing we noted when we were climbing around the landslides, was the ‘patchy’ distribution of vegetation. What is the reason for this? The slides are very similar in shape, being long and narrow, although they vary in size. The surface is smooth and very few rocks are present. Inclination changes step-

like, varying between about 30° and 80°. This leads to different erosive forces at different parts of the slide. Nevertheless, a direct correla-tion between vegetation cover and inclination or erosive energy would only partly account for the distribution of the vegetation. The study of soil cores of the slides under more, and less, dense vegetation did not produce results with significant differences in regard to soil texture, structure, colour and pH. This excludes the edaphic conditions as principal responsible factors. Landslide areas are colonised quickly either at the borders of the slide or around islands that slipped down without being overturned due to



Fig. 3 Aspect of a plot in late first stage. Sticherus bifidus is spreading in the upper left corner (scale on the right = 2 m) vegetative propagation from the undisturbed neighbouring areas and possibly due to a fa-vourable microclimate. Other patches of high vegetation cover are created by the clonal, looping runner-shoot building growth of most of the individual pioneers that managed to establish seedlings first (Gleicheniaceae, Lyco-podiaceae and Ericaceae). The majority of the abundant species are wind-dispersed and produce many seeds. The only frequent Angiosperm is Baccharis genis-telloides (Asteraceae) which flowers all year round, so fruits are permanently available. Under certain conditions freshly slipped slides do not last very long in the first stage and lichens and mosses do not develop well as the colonisation by higher plants starts already in the first year of succession. In addition to the 23 landslides studied in detail some sites of very recent origin were examined. On land-slides well protected against wind and direct sunlight, seedlings of the surrounding flora

established themselves after a few months. In contrast, a landslide exposed to wind and direct sunlight was bare of any vegetation about eight months after the slide event. Differences in vegetation along the altitudi-nal gradient have been found. The main flo-ristic change occurs at an elevation of about 2100 m. This altitude corresponds to the chan-ge in the vegetation zonation in the surrounding forests: from the Montane Broad-leaved Forest to the Upper Montane Forest (BUSSMANN 2001). On the landslides at higher altitudes some species typical for paramo vegetation are found (Paepalanthus meridensis – Eriocaula-ceae or Xyris subulata – Xyridaceae). Other distribution patterns do not correspond to vege-tation changes along the altitudinal gradient but show similar patterns to differences in soil chemistry. An explanation of the allopatric distribution of Sticherus bifidus and St. mela-noblastus by the altitudinal gradient alone is not possible, while the difference in altitude is



Fig. 4 Early stage 2, dominant species are Sticherus bifidus and Lycopodiella glaucescens too small and no transition zone with the pre-sence of both species was found. Contrarily, as described in the results, the influence of differ-ent soil chemistry combined with the influence of changing altitude would offer an explana-tion. Slightly different pH-values and a differ-ent percentage of exchangeable Ca2+ (ZECH et al. 2000) are characteristic for the different ridges. The amount of Ca2+ correlates negatively with the abundance of Al3+-ions which are toxic to plants and could therefore be responsible for the differences in floristic composition (LAN-DON 1991; ZECH & WILCKE 1999; WILCKE, pers. comm.). Correlations to other factors which could be responsible for the vegetation change such as aspect were not found. Landslides are a common phenomenon in most tropical mountain systems. STERN (1995) and KESSLER (1999) hypothesised that landsli-des maintain species diversity. STERN (1995)

compares the effect of landslides to the mean-dering rivers of the lowland ecosystems. They create secondary forests dominated by colonis-ing species which are not able to survive in mature stands. In this work species richness during the first two stages of regeneration is low due to the dominance of a few species of ferns. However, during the third stage of succession, species composition still differs somewhat completely to the surrounding forest, but diversity is high. The second stage with a dense cover of Gleicheniaceae has not been described from northern Ecuador (STERN 1995) but it was found on landslides in Bolivia (KESSLER 1999). There, the role of Gleicheniaceae seems simi-lar. Diplopterygium bancroftii and species of Sticherus dominate. In contrast, STERN (1995) found a dominant species of Chusquea, 3½ years after the slide event at the lower zone of a



landslide. She adds that the presence of the bamboo is especially noteworthy because under certain environmental conditions it can grow quickly and aggressively. Further on, she desc-ribes the great density of the bamboo, thereby having a profoundly limiting effect on the es-tablishment of other plant species. The bamboo occurred at sites with a reasonable upper layer of organic debris. Other interesting differences in her work are that species of the genus Equi-setum are important in the early stage and Blechnum dominates locally. No species of Gleicheniaceae were found. Reasons for those variations might be found in the obvious differ-ences in geological substrate (of quaternary volcanic origin) and the lower humidity and altitude of the site (1440 m). Gleicheniaceae do not hinder the establishment of bushes, though the time period from when seedlings of bushes appear to when they manage to break through the fern layer, varies. Different types of succes-sional models seem to correspond to the rege-neration processes at the slides studies by STERN on one hand and on the other hand the slides observed by KESSLER and the work on hand. Following the division of successional models according to CONNELL & SLATYER (1977) and PICKETT et al. (1987) the model of inhibition will have to be used to describe the situation in northern Ecuador as observed by STERN (1995). In contrast, the tolerance model combined with the facilitation model could be used to describe the situation in Bolivia (KESS-LER) and southern Ecuador. Little change in species composition but mainly a change in vegetation density or -height was observed due to local erosive energy, time elapsed since the last destruction, depth of the organic layer or the distance towards densely covered sites. Mosses and lichens are not only abundant dur-ing the first stage but also during the second and third stage (though we do not know if the species are similar) and Gleicheniaceae are present in the second and third stage though they loose importance as they are overgrown by the bushes and trees of the pioneer forests. Up to this point, the model of tolerance seems to fit while the missing of species of the primary forests during the third stage follows the facili-tation model. What is the main difference between the studied natural landslides and the human trig-

gered slides along the roads? Studies on the regeneration of the latter type of slides close to the research area have been carried out by HARTIG (2000). These slides are usually very extensive. The surface is not smooth but often rocky. Natural slides are mainly created by a heavy organic layer slipping over the mineral soil. If thick mats of organic material become water-logged due to long-lasting heavy rains, the weight of the material reaches a critical point when the adhesive strength gives in to gravity and a slide-event is initiated. The thres-hold in this area is very low as the adhesive strength is low due to the slippery mineral soil and the lack of a well developed root-system in the B-horizon which could help to fix the upper layers (own obs.; STERN 1995). The human triggered slides are usually initiated due to the weakened geological underground and have more in common with rock-falls. Succession differs between the two types of slides. Grasses largely replace the Gleicheniaceae and build a very dense layer often limiting the establish-ment of bush species. Succession seems to follow the inhibition model (CONNELL & SLA-TYER 1977; PICKETT et al. 1987). Especially the number of orchids is tremendous which leads to a very high diversity on man-made slides (GROSS 1998). In contrast, there are not many species of orchids found at the natural slides but in the few areas with rocky relief they be-come more abundant (see plot 21 or 48). The aerial pictures of the region show a very unequal distribution of the natural slides. One possible explanation for the clustered occurrence of the slides might be reached by studying the direction of the geological struc-tures. If the layers are aligned parallel to the slope, the risk of a slide-event arises. Consider-ing that on most of the slides the soil is not dragged down to the C-horizon, this explana-tion is probably not of great significance, but locally this certainly encourages or deters a sliding process. Probably, the heavy organic soil layer is responsible for the majority of sliding processes. Under mature forest organic layers build up, but due to evaporation and transpiration they will not get heavily water-logged. In contrast, comparable amounts of water do not transpire from senescent forest. A mosaic-like forest structure with younger and older forest stages is described in KESSLER



(1999) from the montane forest in the Bolivian Andes. He observed irregularly formed and spaced patches of senescent forest with single trees having already collapsed. This could explain the clustered occurrence of landslides as the risk of slipping in zones of senescent forest is higher than in zones of mature forest. In this case the effect of landslides in the eco-system would be very important for the natural regeneration of the system. At altitudes above 2100 m, especially under senescent forest, very dense layers of terrestrial Bromeliads are found. Germination of other species is very difficult under these circumstances. In contrast, a landslide provides light and a high availabil-ity of minerals for successful plant growth. There are still plenty of open questions concerning the governing factors and the pro-cesses going on at landslides in the research area. Further research will have to deal in parti-cular with the influence of the soil chemistry on species composition and succession and the development of the pioneer forests towards the climax stage.

Acknowledgements

We would like to express our cordial thanks to Prof. Dr. Ankea Siegl and Prof. Dr. Ulrich Deil for helpful discussions and revisions concerning this work and our Ecuadorian coun-terparts of the Universidad Nacionál Loja (Ing. N. Maldonado, Ing. W. Aplo, Dr. L. Loján), Herbario Reinaldo Espinosa Loja (Ing. Z. Aguirre , Ego. B. Merino, Dra. B. Kli tgaard), the herbaria QCA y QCNE in Quito, and ECSF, for all their collegial help at all times throughout the study. We thank INE-FAN for the research permit (now Ministerio de Medio Ambiente de Ecuador; no. 16-IC INEFAN DNAN VS/VS). We would also like to thank the Deutsche Forschungsgemeinschaft for financing the project (DFG, Be 473/28-1, Bu 886/1-1/2).

References

BATARYA, S. K. & VALDIYA, K. S. 1989: Landslides and erosion in the catchment of the Gaula River, Kumaun Lesser Himalaya, India. – Mountain Research and Development 9(4): 405–419.

BENDIX, J. & LAUER, W. 1992: Die Niederschlags-jahreszeiten in Ecuador und ihre klimadyna-mische Interpretation. – Erdkunde 46: 118–134.

BRAKO, L. & ZARUCHI, J. L. 1993: Catalogue of the flowering plants and Gymnosperms of Peru. – Monographs in Systematic Botany 45.

BUSSMANN, R. 2001: The montane forests of Reserva Biológica San Francisco. – Die Erde 132: 9–25.

CLAPPERTON, C. M. 1986: Glacial Geomorphology, Quaternary glacial sequence and palaeoclimatic inferences in the Ecuadorian Andes: 843–870. – In: V. GARDINER (ed.), Proceed. Intern. Conf. Geomorphology II. – Cluchester.

CONNELL, J. H. & SLATYER, R. O. 1977: Mechanisms of succession in natural communities and their role in community stability and organization. – Am. Nat. 111: 1119–1144.

DE NONI, G.; VIENNOT, M. & TRIJILLO, G. 1989–1990: Mesures de l‘erosion dans les Andes de l‘Equateur. – Cahier ORSTOM, Serie Pedologie 25(1–2): 183–196.

ERICKSON, G. E.; RAMIREZ, C. F.; CONCHA, J. F.; TISNADO, M. G. & URQUIDI, B. F. 1989: Land-slide hazards in the central and southern Andes: 111–117. – In: E. E. BRABB & B. L. HARROLD (eds.), Landslides: extend and economic signi-ficance. – Rotterdam.

GARWOOD, N. C. 1981: Earthquake-caused land-slides in Panama: recovery of the vegetation. – Res. Rep. Natl. Geogr. Soc. 21: 181–184.

GENTRY, A. H. 1977: Endangered plant species and habitats of Ecuador and Amazonian Peru: 136–149. – In: G. T. PRANCE & T. S. ELIAS (eds.), Extinction is forever. – The New York Botanical Garden, New York.

GENTRY, A. H. 1996: A field guide to the families and genera of woody plants of north-west South America (Colombia, Ecuador, Peru) with supple-mentary notes on herbaceous taxa. – Chicago, London.

GROSS, A. 1998: Terrestrische Orchideen einer Hangrutschung im Bergwald Süd-Ecuadors: Ver-teilung, Phytomasse, Phänologie und Blüten-merkmale. – Univ. Ulm, Diploma Thesis, unpubl.

GUARIGUATA, M. R. 1990: Landslide disturbance and forest regeneration in the upper Luquillo Mountains of Puerto Rico. – J. Ecol. 78: 814–832.

HALL, M. 1977: El volcanismo en el Ecuador. – Biblioteca Ecuador. – Quito.

HARLING, G. & SPARRE, B. 1973–2000: Flora of Ecuador. – Bot. Mus., Copenhagen.

HARTIG, K. 2000: Pflanzensoziologische Untersu- chungen von anthropogen gestörten Flächen im tropischen Bergwald Südecuadors. – Univ. Bayreuth, Diploma Thesis, unpubl.



HILL, M. O. 1979: TWINSPAN – a FORTRAN program for arranging multivariate data in an ordered two-way table by classification of the individuals and attributes. – New York.

HOFSTEDE, R.; LIPS, J.; JONGSMA, W. & SEVINK, Y. 1998: Geografia, ecologia y forestacion de la sierra alta del Ecuador. Revision de literatura. – ABYA-YALA, Quito.

HUTCHINSON, J. 1967: Key to the families of flowering plants of the world. – Oxford.

JØRGENSEN, P. M. & LEON-YANEZ, S. (eds.) 1999: Catalogue of the vascular plants of Ecuador. – Monographs in Systematic Botany from the Missouri Botanical Garden 75. – St Louis.

JØRGENSEN, P. M. & ULLOA ULLOA, C. 1994: Seed plants of the high Andes of Ecuador – a check-list. – Aarhus University (AAU) Reports 34.

KEEFER, D. K. 1984: Landslides caused by earth-quakes. – Geol. Soc. Amer., Bull. 95: 406–421.

KELLER, R. 1996: Identification of tropical woody plants in the absence of flowers and fruits. – Basel.

KESSLER, M. 1999: Plant species richness and endemism during natural landslide succession in a perhumid montane forest in the Bolivian Andes. – Ecotropica 5: 123–136.

KESSLER, M. 2002: The elevational gradient of Andean plant endemism: varying influences of taxon-specific traits and topography at different taxonomic levels. – J. Biogeogr. 29: 1159–1165.

LANDON, J. R. (ed.) 1991: Booker tropical soil manu-al. – Essex, New York.

LONDO, G. 1976: The decimal scale for releves of permanent quadrats. – Vegetatio 33(1): 61–64.

MACBRIDE, J. F. (ed.) 1930–1970: Flora of Peru. – Chicago.

MADSEN, J. E. & ØLLGAARD, B. 1993: Inventario preliminar de las especies vegetales en el Parque Nacional Podocarpus. – Ciencias agricolas de la Universidad Nacional de Loja 22–23(1–2): 66–87.

MADSEN, J. E. & ØLLGAARD, B. 1994: Floristic com-position, structure, and dynamics of an upper montane rain forest in Southern Ecuador. – Nord. J. Bot. 14: 403–423.

ØLLGAARD, B. 1979: Lycopodium in Ecuador – ha-bits and habitats: 381–395. – In: K. LARSEN & L. B. HOLM-NIELSEN (eds.), Tropical botany. – Proceed. sympos. Univ. Aarhus on 10–12 August 1978, organized on the occasion of the 50th anniversary of this university. – London.

ØSTERGAARD, E. 1995: Gleicheniaceae – en gruppe pioner plantenblandt tropiske bregner. Afdeling for Systematik Botanik. Specialerapport marts 1995. – Biologisk Institut Aarhus Universitet, Aarhus.

PICKETT, S. T. A. 1989: Space-for-time substitution as an alternative to long-term studies: 110–135. – In: G. E. LIKENS (ed.), Long-term studies in ecology. – New York.

PICKETT, S. T. A.; COLLINS, S. L. & ARMESTO, J. J. 1987: Models, mechanisms and pathways of succession. – Bot. Rev. 53: 335–371.

SCHRUMPF, M.; GUGGENBERGER, G.; VALAREZO, C. & ZECH, W. 2001: Tropical montane rain forest soils: development and nutrient status along an altitudinal gradient in the south Ecuadorian Andes. – Die Erde 132: 43–59.

STERN, M. J. 1995: Vegetation recovery on earth-quake-triggered landslide sites in the Ecuadorian Andes: 207–220. – In: S. P. CHURCHILL; H. BALSLEV; E. FORERO & J. L. LUTEYN (eds.), Biodiversity and conservation of neotropical montane forests. – New York.

STOYAN, R. 2000: Aktivität, Ursachen und Klassifi-kation der Rutschungen in San Francisco/Süd-ecuador. – Univ. Erlangen, Diploma Thesis, un-publ..

TRYON, R. M. & STOLZE, R. G. 1989–1993: Pterido-phyta of Peru I–V. – Fieldiana (Botany). N.S. – Chicago.

ULLOA ULLOA, C. & JØRGENSEN, P. M. 1993: Arbo-les y arbustos de los Andes del Ecuador. – Aarhus University (AAU) Reports 30.

ZECH, W. & WILCKE, W. 1999: Einfluß der Land-nutzung auf Bodeneigenschaften sowie auf die Wasser- und Elementflüsse in Bergwäldern Süd-ecuadors. – Bericht zum bodenkundlichen Teil-projekt des Projektverbunds „Ökosystemare Kenngrössen gestörter und ungestörter tropischer Bergwälder“. Zwischenbericht. – Univ. Bay-reuth, unpubl.

ZECH W.; WILCKE, W. & VALAREZO, C. 2000: In-fluencia del uso de la tierra en los propiedades del suelo y en los flujos de aqua y de elementos en los bosques montanosos del Ecuador del sur. Zwischenbericht. – Univ. Bayreuth, unpubl.

Addresses of the authors: Dr. Constanze Ohl (corresp. author), Martin-Luther-Universität Halle-Wittenberg, Institut für Geobotanik und Botanischer Garten, Am Kirchtor 1, D-06108 Halle, Deutschland e-mail: [email protected] Dr. R. Bussmann, University of Hawai’i Manoa, 3860 Manoa Road, Honolulu, Hawai’i, [email protected], USA.

Manuscript received: September 29th, 2003/revised version: December 15th, 2003.

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