Catastrophic Influences on the Vegetation of the Valdivian Andes, Chile*

Vegetatio Vol. 36, 3: 149-167,1978

CATASTROPHIC INFLUENCES ON THE VEGETATION OF THE VALDIVIAN ANDES, CHILE*

Thomas T. VEBLEN’,**, *** & David H. ASHTON

‘Facultad de Ingenieria Forestal, Universidad Austral, Valdivia, Chile 2School of Botany, University of Melbourne, Parkville, Victoria, Australia

Keywords: Andes, Catastrophic events, Chile, Colonization, Fire, Forest structure, Nothofagus forest, Succession, Vulcanism

Introduction sands of debris avalanches, landslides, and mudflows which occurred in a 300 by 100 km area of the Andes On Sunday afternoon 22 May 1960 sixty percent of the from ca. 39” to 42”s (Fig. 1). buildings of the city of Valdivia in southern Chile were In the scientific inquest which followed this disaster, either destroyed or seriously damaged by an earthquake the profound long-term geomorphic and pedological ef- measuring 8.75 on the Richter scale. This was one of a fects of such catastrophic phenomena in south-central series of eleven shocks of an earthquake swarm, each Chile were assessedby Wright & Mella (1963), Davis & measuring over 6 on the Richter scale, which rocked Karzulovic (1963), Saint-Amand (1962), and Weischet south-central Chile from approximately latitude 37” to (1960, 1963). There is no doubt that mass movements, 43% from 21-25 May. It also resulted in a 10 m tidal largely triggered by.seismic activity, have also had a wave which destroyed numerous settlements along the profound influence on the vegetation of the Valdivian Chilean coastline as well as in Hawaii and Japan (Anon. Andes. We suggest that at low and middle elevations 1974). North of about 38”3O’S the Chilean coastline was (i.e. below ca. 1000 m) No&o&us-dominated forest uplifted 0.75-1.8 m while in the southern area it subsi- types represent successional phases which are very wi- ded 1.5 m resulting in the inundation by seawater of despread in the Andes of South-central Chile as a con- approximately 40,000 ha (Wright & Mella 1963). During sequence of a long history of catastrophic phenomena. this period Volc&n Puyehue (40”35’S, 72”OB’W) erupted It follows that in the absence of periodic catastrophic ash and viscous lava for six weeks. In the following year disturbance much of the Nothofagus overstorey would Vol& Calbuco (41”2O’S, 72”37’W) erupted ash and gradually be replaced by other tree species in the mid- lava intermittently for several months (Saint-Amand montane zone of the Valdivian Andes. 1962). Associated with this seismic activity were thou- The evidence presented to support this view includes: (1) the historical frequency of catastrophic phenomena similar to those which occurred in 1960, (2) the pattern *Nomenclatural authoritiesare given at the first mention of the. speciesin Tables6,7, and 9, or at their first mention in the text of colonization of the surfaces exposed by the 1960 mass for those speciesnot included in the tables. movements, and (3) the structure of the existing forest **Part of this work was supported by Celulosa Panguipulli vegetation. Ltda. We are grateful to Dr. C. Ramirez of the Universidad Austral for checking our initial plant identifications, to Dr. J. Diaz-Vaz of the Universidad Austral for identifying charcoal samples, and to Dr. F. Schlegeland Dr. J. Schlatter of the The Valdivian Andes Universidad Austral for discussingwith us some aspects of vegetation and soils in south-central Chile. We thank A. Ve- Physical environment blen for assistingin the field and critically reading the manus- cript. Dr. J. Schlatterprovided analysesof soil samples. ***Sponsored by the Smithsonian-PeaceCorps Environmen- The Valdivian Andes, i.e. the extent of the Andean tal Program. Cordillera occurring in the Province of Valdivia, extend

149 active in Recent and historic times and have deposited thick ash layers on top of the extensive Pleistocene till and glacio-fluvial deposits (Illies 1970). Physiographi- tally, this zone is a labyrinth of peaks averaging 2000 m and valleys with extensive lakes arranged in a step-like pattern’ in glacially scoured troughs at altitudes of 70-230 m. The steep slopes rising from these lakes are mantled with a meter or more of pale orange to reddish-, brown porous volcanic ash described as scoriaceous coarse gravel (Wright & Mella 1963) or pumiceous lapilli (Weischet 1960). The soils are polymorphic since pumiceous lapilli forms the subsoil and fine tuff and dust (principally from volcanoes Villarrica and Mocha) form the topsoils. The abundance of colluvial rock fragments (both sedimentary and plutonic) in soil profiles suggest instability of slopes during the soil-forming process. The climate of the Province of Valdivia is characteri- LLANQUIHUE zed by a high annual precipitation, mild wet winters, and short dry summers and is classified in the Koppen system as an oceanic west coast climate with a mild Medi- terranean influence (Cfsb) (Thomasson 1963). There are gradients of increasing precipitation from north to south and eastwards from the Central Depression up the western flanks of the Andes. Except in local rain-shadow valleys. annual precipitation in the Valdivian Andes generally exceeds 3000 mm and at the higher altitudes on west-facing slopes is well over 4000 mm (Table 1). Above altitudes of 1000 m much of the winter precipitation is in the form of snow, and altitudes greater than 2000 m are perpetually snow-covered. Temperature data for this region are nearly entirely lacking except for the 1970-71 data (from the Instituto de Geografia y Geologia de la Universidad Austral) for Futrono (125 m) Fig. 1. Sketch-map of southern Chile from 39” to 43”s. Asterisk which is located in the Central Depression a few km indicates the valley of the Rio Pillanleuftl. Locations of large west of the Valdivian Andes. Here the average mini- mass movements (hatching) which occurred in 1960 are shown only for the area north of 41”15’S. Based on Wright Meha (1963), Weischet (l%O), Herve et al. (1974a), and Saint- Table 1. Precioitation in the Yaldivian Andes. sources: Anon. 1994, Amand (1%2), and field observations. from 39”25’ to 40”4O’S and encompass a mountainous zone 70 by 130 km (Fig. 1). This is a geologically com- plex region in which Cretaceous-Tertiary sedimentary, metamorphic, and granitoid rocks underlie extensive areas of Upper Tertiary to Recent volcanic rocks (He& et al. 1974b). The volcanic rocks include extensive andesitic and basaltic lava flows, pyroclastic mate- rial, and volcanic mudflow deposits. Several of the volcanic cones which are aligned in a north-south axis to the west of and parallel to the main Cordillera have been

150 mum temperature of the coldest month (August) is 5.072 Province of Valdivia, Brun (1975) classifies the forest and the average maximum of the warmest month (Fe- vegetation of the Valdivian Andes into six types (Table bruary) is 2O.O”C; the average annual temperature is 2). These forest types represent altitudinal zones greatly ll.O”C. In the mountain basins, frosts are frequent modified by the influences of topographic position, as- year-round. pect, and disturbances of the vegetation. All except the Nothofagus pumilio type are characterized by both an Vegetation upper and an intermediate tree layer. Land-clearance for agriculture, timber production, and pastoral purposes The vegetation of the Chilean Lake District of which the has nearly eliminated all of the lower altitude virgin Valdivian Andes constitute the northern part has been forests. Thus, for the Nothofagus obliqua and Eucryp- partially described by Neger (1899), Reiche (1934), Ober- hia cordifolia types, only highly disturbed stands were dorfer (1960), Schmithtisen (1956, 1960), Thomasson encountered. In the remnant stands of these forest types (1963), and Heusser (1966, 1976). at altitudes belobca. 500 m, the climbing bamboo, Schmithtisen (1956) has classified the vegetation of Chusquea quila Kunth., proliferates following distur- Chile into twelve vegetation regions. The Valdivian bance of the tree cover and often makes the vegetation Andes lie mostly within the temperate evergreen rainfo- impenetrable. Above altitudes of ca. 500 m, C. coleu, rest and summer-green deciduous forest regions. The which reaches heights of over 7 m, typically dominates temperate evergreen rainforests are composed of the understorey of disturbed forests and sites beneath broad-leafed evergreen trees among which Nothofagus gaps in the forest canopy. Wiry lianas, such as Mitraria dombeyi predominates; these forests are rich in species coccinea, Boquila trtfoliata, Lapageria rosea, and Lu- and display a luxuriant development of lianas and epip- zuriaga radicans, and the robust liana, Hydrangea inte- hytes. The summer-green deciduous forest is less rich in gerrima, are very abundant in the lower and middle species and is characterized by the deciduous N. obli- elevation forest types but gradually diminish in impor-‘_ qua or N. alpina (Poepp. et Endl.) Oerst. as well as by tance above ca. 850 m. Most of the remaining virgin evergreen trees such as Laurelia sempervirens and Per- forests are of the Nothofagus dombeyi type although as sea lingue. recently as 1952 forests dominated by the highly prized Based on data from a 1952 forest inventory of the N. alpina were also very extensive. These two very similar types are differentiated primarily by the propor- tion of the two dominant Nothofagus spp. in the upper stratum which often reaches 45 m or more. In both types the intermediate tree layer consists of Laurelia philippiana and Saxegothaea conspicua and to a lesser extent Dasyphyllum diacanthoides and Weinmannia trichosperma. The shrub and ground layers in these types are characteristically very sparse, the most important species being Chusquea coleu. In the Valdivian Andes the Araucaria araucana-Nothofagus pumilio type is found only in the north on the slopes of VoUin Quetrupillan and along the Argentine border at Paso Carirriiie where it forms the upper forest limit on all but slopes of a southerly aspect. Elsewhere in the Valdivian Andes the uppermost forest type consists of pure N. pumilio stands; this type forms the upper forest limit at b. L. phllippiana, S. cbnspicua, W. trichosperma, D. diaczmthoide.3 1400-1700 m depending on aspect and recency of disturbance by volcanic activity.

151 Catastrophism in the Valdivian Andes

Mass movements

On aerial photographs (scale 1 : 20,000) taken less than a year following the severe 1960 earthquake, fresh scars PH f 4.90 + 0.05 (ll=12) of the many mass movements are readily identifiable in ac XI 9.16 + 0.52 the Valdivian Andes. Numerous eyewitnesses testify (n=12) aNt 0.61 + 0.05 that nearly ah of the many scars present today in the (ll=9) C/N 15.26 + 0.12 zone date from 1960. Thirty of the 173 air photos cover- G9, Bulk density 0.48 + 0.03 ing the Valdivian Andes were randomly selected and the (gm/c& $ (n=9) Pore volume S1.80 + 1.26 percentage area of mass movements was estimated with (a) (n=9) a grid over-lay. The results indicated that at least 2.8% of the total area of this zone, or over 25,000 ha of land x ICC1 0.M (1:s). ILX Oxidation with potassium dichromate and calorimeter determination surface, slid in 1960. Since this surface was determined t Kjeldahl titration. + Mercury pycnometer. by measuring distances over very rugged topography only in the horizontal plane, it is an underestimate of the total surface area affected. The zones of greatest concentration of slides are mapped in Fig. 1 as are the locations of major faults and fracture zones. The three zones of concentration of landslides in the Valdivian Andes are: (1) the steep slopes bordering the head of Lake Calafquen and surrounding Lake Pellaifa, (2) the rolling hills in the valley a few km southeast of Lake Neltume, and (3) the northern two-thirds of the valley of the Rio Pillanleufi (southeast of Volcan Mocha). These three zones in the Valdivian Andes lie 20-25 km east of the topographic limit of the Cordillera in the northern portion of the Reloncavi fault zone where mass movements occurred in thousands of localities in 1960 (Saint-Amand 1962, Weischet 1963). Even in areas distant from fault zones, many of the slopes of the Valdivian Andes were, and still are, in a very tenuous equilibrium due to the oversteepening of the glacial valleys and to the characteristics of the successive layers of volcanic ash which mantle them. Co- vering these slopes - even those steeper than 40” - are successive layers of very porous pumiceous lapilli; (Ta- ble 3). Frequently between these porous water-holding layers is a layer of fine andesitic ash!weathered to a stage high in allophane (Wright & Mella 1963). Allophane is an amorphous hydrated alumino-silicate gel characteristic of young, well-drained soils derived from volcanic ash (Brady 1974). It can absorb a large amount of water which is subsequently expressed when shaken under Fig. 2. Mass movementsat the eastern end of Lake Pellaifa. pressure, producing a thixotropic phenomenon resem- The deciduous trees near the summit of the slope (top center- left of photo) are Northofagus pumilio and the dominants of the bling liquefaction (Wright & Mella 1963). This noncrys- forests below are mostly N. dombeyi and Eucryphia cordifolia. talline allophane-rich layer when moist serves as a lu- Note in the foreground the dead trees which were inundated bricant for the movement of the pumiceous lapilli and when the lake’s egress was blocked by slide debris in 1960. overlying soil and vegetation, and under certain condi- occur where the forest cover was intact. tions whole hillsides may collapse. Approximately 12km southeast of Lake Neltume on a The location and general characteristics of the mass ridge to the southeast of Volcan Mocha, a mudflow movement sites studied are summarized in Table 4. (III-F) over 200 m wide flowed ca. 1 km into the south- These mass movements are debris avalanches, landsli- western side of the basin of Pilmaiquen. Again, several des, and mudflows which represent a gradient from layers of lapilli were exposed which must have been relatively dry to highly saturated masses. The extensive saturated at the time of the 1960 earthquake, providing debris avalanches and landslides at the head of Lake the moisture for the mudflow. In this case the original Calafquen and surrounding Lake Pellaifa blocked the slope did not exceed 15”. For adistance of ever 10km to effluent stream connecting the two lakes and raised the the south in the valley of the Rio Pillanleufu, the devas- water level of Lake Pellaifa several meters (Fig. 2). The tation is the most extensive of anywhere in the Valdivian effects of these slides were studied at Site I, 3 km west of Andes - as much as one-fourth of the land surface of this the western end of Lake Pellaifa, where an 850 by 300 m area slid in 1960 (Fig. 3). Here the slopes of the valley debris avalanche had occurred on a northwest-facing walls are very steep (usually over 40”). Some forests slope. The large debris avalanche which extends from such as the remnant Nothofagus dombeyi forest studied an altitude of 900 to 350 m exposed both lapilli and (III-D) escaped destruction despite being surrounded bedrock (Sites I-B and I-C respectively in Table 4). on all sides by debris avalanches. The underlying rock Prior to 1960 this surface appears to have been occupied debris indicates that this remnant forest had developed by a forest dominated by Nothofagus obliqua and Eu- on a site previously affected by a debris avalanche. The ctyphia cordifolia (I-D) in the lower portion and by N. tributary valleys were similarly affected by landslides; dopnbeyi (I-A) above; the presence of a large number of fans of rock debris such as at Site III-A are frequently old spars indicates a past tire, which according to local encountered where they join the principal valley. Such inhabitants occurred at leasta decade prior to 1960. The debris dammed the Rio Pillanleufu at several sites and original slope is estimated at ca. 25-30”. Many of the when finally breached produced catastrophic floods surrounding slopes which are as steep or steeper did not which buried the forests in the narrow valley floor with slide where there was an undisturbed forest cover. deposits up to 4 m (Fig. 4). Wright & Mella (1963) also observed a greater fre- South-central Chile is one of the most seismically- quency of slides on slopes with disturbed forest cover. active parts of the world. The historical record indicates On the opposite side of this small valley, on a northeast- that catastrophic mass movements similar in magnitude facing slope of ca. 20-25”, the original forest cover had to those of 1960 have affected south-central Chile se- been cleared. Here a limited landslide ca. 50 by 100 m in veral times in the past five centuries. From 1520 to 1946 extent occurred in 1960 exposing deep layers of lapilli. there have been forty-seven notable earthquakes be- The surrounding slopes of 15-20” which were forested in tween Santiago and ChiloC Island (ca. 42%); seven of 1960, although somewhat disturbed by fire and cutting, these earthquakes have been roughly comparable in remained intact. magnitude to the main shock of 22 May 1960 (Saint- Approximately 25 km further south along this axis to Amand 1962). The city of Valdivia was partially de- the southeast of Lake Neltume, the low rolling hills are stroyed in 1575, 1737, 1837, and 1907 by earthquakes also mantled by several layers of pumiceous lapilli ex- similar in their effects to the seismic shocks of 1960 tending to depths of 4 m between which are fossil soils (Weischet 1960, Guarda 1953). In association with these and finer ash deposits. Several landslides, the largest of major earthquakes, large mass movements were repor- which is ca. 80 by 150 m, occurred in 1960 on the slopes ted in the south-central Andes (Fonck 1896). For exam- of an estimated orginal inclination of 15-20”. In all cases ple, four and half months after the 16 December 1575 the vegetation cover in 1960 was pasture (II-A) which, earthquake, a catastrophic flood destroyed a large part due to the lack of the binding effect of deep tree roots, of the city of Valdivia (Weischet 1960). Subsequent probably contributed to the numerous landslides on re- investigation revealed that the flood resulted from the Iatively gentle slopes. Elsewhere, root penetration to breaching of a dam formed by a huge mudflow blocking over 4 m into the lapilli indicates the potential impor- ‘the egress of Lake Riiiihue to the Rio San Pedro. This tance of a tree cover in stabilizing slopes.On surroun- sequence of events was almost repeated in 1960 when a ding slopes of ca. 25-30” (II-C and D), slides did not 30 million m3 mudflow again blocked the egress of Lake

153 Table 4. Summary of site samples.

site vegetation substrate type and observations I. Lake Pellaifa (39'33'S, 71'56'W) I-A N. dombeyi forest Relatively undisturbed; located on less steep slope above debris avalanche. I-B Very sparse shrub cover Lapilli exposed by 1960 debris avalanche. I-C Sparse shrub cover Bedrock and rock debris exposed by 1960 debris avalanche. I-D Young forest of N. obliqua Burned several decades ago. I-E Pasture Surrounding area of 1960 landslide. I-F Very sparse herbaceous cover Lapilli exposed by 1960 landslide; limited grazing by cattle has occurred. I-G Eucryphia cordifolia forest Stumps indicate recent selective cutting; evidence of a fire several decades ago. I-H Young N. obliqua forest Cut and burned since 1960 II. Southeast of Lake Neltume (39'49'S, 71°5S'W) II-A Pasture Borders area of 1960 landslide on the northwest. Very sparse herbaceous and Lapilli exposed by 1960 landslide; moderately 11-B1 , 2 33 shrub cover grazed by cattle. II-C N. obliqua forest Cut and burned prior to 1960. II-D N. obliqua-L. philippiana No evidence of recent disturbance. forest III. Valley of the Rio Pillanleufd (40°06tS, 71'59'W) III-A Shrub cover Rock debris deposited at base of slope by 1960 debris avalanche. Valley of the Rio Pillanleufd (40006'S, 71'5S'W) III-B Very sparse shrub cover Bedrock exposed by 1960 debris avalanche. Shrub cover Bedrock and rock debris exposed by 1960 debris 111-c112 avalanche. III-D N. dombeyi forest Forest remnant which escaped destruction by the 1960 debris avalanche. III-E Sparse shrub cover Sand and gravel deposited at the foot of the slope by the 1960 debris avalanches; heavily grazed Valley of the Rio Pillanleufu (39O57'5, 71°55'W) III-F Very sparse herbaceous and Lapilli exposed by 1960 mudflow; heavily shrub cover grazed until recently. III-G N. dombeyi-Saxegothaea No evidence of disturbance. conspicua forest PII-H Dense young stand of N. Gn lapilli exposed by 1960 mudflow and border- dombeyi and shrubs ing the remaining forest. III-I Relatively young N. dombeyi Not affected by 1960 mudflow. forest

154 Rinihue; however, the excavation of artificial channels Table 5. Volcanic eruptions during recent historic tmes in the "aldivinn Andes. Sources: casertano (1963), Illies averted another flood (Davis & Karzulovic 1963). (1970), Martin (19231, Stone & lngerson (193% Hervh et al. (1974b3

volcano location dates of eruptions Vulcanism (S) (W) Yillarrica 39O25' no57 1922, 1899, 1874, 1976, 1893, 1908, 1920, 1958-59, PIId 1970-n* Numerous recently active volcanoes are found in the RGihue group: ChOShUSlCO 39O55' do3 1869. 1893, and 1907. Valdivian Andes or in close enough proximity so that MOChO 39%' 7Z002' their activity may affect the vegetation occasionally. In Nilah"e group: CarrPn 40% 5 7Z006 1 1907 and 1955 Table 5 the significant eruptions of these volcanoes Riiiinahue 40°28 7AO' during the past two centuries are listed. While none of P"yeh"e 40°35' 72°08' 1907, 1921-22, 1926, and 1960. the known historic eruptions have been large-scale ex- * Should read 1971-1972. plosions, the numerous lava flows have destroyed thousands of ha of vegetation on the flanks of the volcanoes. Rio Pillanleufu and ca. 10 km southeast of the Pilmai- Ash showers from these eruptions have affected much quen basin, an 8 m roadcut at an altitude of ca. 700 m more extensive areas, the ash from the 1960 eruption of provided the opportunity for close examination of the Volcan Puyehue falling as far as 125 km away on the stratigraphic evidence of catastrophic volcanic activity coast of Valdivia. in this zone (Fig. 5). The stratigraphy indicates three In Sector Las Canoas (40”03’S, 71”55’W) east of the major eruptions of scoriaceous gravel (lapilli) followed

Fig. 3. The valley of the Rio F’illanleti where the forest vegetation was stripped off of extensive areas by numerous mass movements.

’ 155 % N

n Silt and Cloy (< 0.02mm dlametrr) q PH q Lapllli m Vciconlc Tuff 0 Caarw Froprmntr fl Charcoal (>2.0mm dlomrtw) Fig. 4. Remnantsof forests in the valley of the Rio F’illanleufti q Send (0.02-2.0mm \vhich were buried by severalmeters of flood depositsresulting dlamrtrr) from the damming of the main river and its tributaries by the debris of the 1960mass movements. Fig. 5. Profile of roadcut and the variation of some chemical and physicalproperties in the soils and ash depositsat Las by the deposition of finer ash (tuft) and soil develop- Canoas. ment. The positions of the fossil soils are clearly indicated in Fig. 5 by the higher nitrogen and clay-silt cpntents likely a Myrtaceae (J. Diaz-Vaz, pers. comm. 1975). and the lower pH’s. At a depth of 152-156 cm is a layer Since the only large trees near the sample site were N. of charcoal on the surface of the uppermost buried soil. dombeyi, the charcoal sample is not from a burned root From several sites over a horizontal distance of ca. 5 m, of a living or recently living tree. Thus, the only logical samples of charcoal were taken for a radiocarbon age interpretation is the origirial one that the sample was determination. The 14CI assay yielded a date of less than from the vegetation burned at the time of deposition of 200 radiocarbon years B.P. which did not differ signifi- the youngest lapilli layer. This interpretation assumes cantly from the Modern Standard (Sample GX-4183 as- that the age of this lapilli deposit is at most a few hund- sayed at Geochron Laboratories, Cambridge, Mass.). red years. Such a young age is remarkable because of the presence While the regional extent of this uppermost lapilli on this surface ofN. dombeyi of nearly 1.5 m in diameter layer has yet to be determined for the Valdivian Andes at breast height; ring counts on stumps at several sites at in general, an age of only a few hundred years is accep- comparable altitudes in the Valdivian Andes indicate ted for this ash deposit in the zone of Pilmaiquen and that this IV. dombeyi could have an age of anywhere Las Canoas. This interpretation calls for exceptionally from 200 to 350 years. The structure of the charcoal rapid soil formation and vegetation development on the sample was studied in the Wood Technology Labora- volcanic ash. On the basis of the degree of soil develop- tory of the Universidad Austral de Chile in Valdivia and ment as indicated by the pH and carbon and nitrogen was found not to be of a species of Nothofagus but most contents of the A-horizon, an age of 200 years for this

156 uppermost lapilli layer is feasible (Birkeland 1974). The of the surrounding vegetation were taken using the same combination of annual precipitation in excess of 4000 sized belt transects. Due to the steepness and instability mm and the relatively mild, temperatures of this zone as of the slopes, only a small fraction of most of the slide well as the porous nature of the ash deposits would favor surfaces was accessible and relatively few samples of rapid weathering and soil formation. High rates of an- the vegetation on the exposed bedrock could be taken. nual forest litter production (5.4 metric tons per ha) In each quadrat, all vascular plant species, bryophytes, measured in a nearby virgin Nothofagus-dominated fo- and lichens were assessed in percentage categories of rest at Trafun (Burschel et al. 1976) further demonstra- less than 1, l-5,6-25,26-50,51-75, and 76-100 (Tables tes that conditions are favorable for rapid biochemical 6 and 7). Where the slope of the landslide surface per- processes and rapid soil formation. mitted, the densities of the regeneration of shrub and tree species were determined in larger quadrats. In such Fire

Fire is another catastrophic influence which has had an important impact on the vegetation of the Valdivian Andes, at least during recent historic times. Eriksen (1975) refers to frequent fires in the Andean region of the Chilean-Argentine border during the early twentieth century. Wright & Mella (1963) report that during the three consecutive very dry summers of 1942, 1943, and 1944, several large fires occurred in the Valdivian An- des. The frequent occurrence of burned spars in this region clearly indicates the past importance of fire. Al- though most recent fires have been started by human carelessness, natural tires may also be, important. When the large populations of the several Chusquea spp. flower synchronously and die within the following two years, a huge quantity of dry fuel becomes available, thereby making natural tires possible in this wet climate. Similarly, vulcanism could have caused forest fires in the Valdivian Andes before the arrival of man.

Dynamics of the vegetation

Colonization of surfaces affected by the 1960 mass movements

Methods

Vegetation on and surrounding the sites affected by the 1960 mass movements was sampled at several sites in the Valdivian Andes (Table 4). The substrate types exposed by the mass movements were classified as bare bedrock, pumiceous lapilli, and rock debris; within each of these substrate types, a randomly located 1 by 10 m belt transect subdivided into ten 1 by 1 m quadrats was used to sample the vegetation. This size of sample area was found to be well above the so-called minimal area for the vegetation on the slide surfaces; several samples cases, 10-20 m parallel belt transects were located at fixed intervals from the foot of the slide towards the top and the numbers of each shrub or tree species were counted in each 1 by 1 m subdivision of the belt transect. As will be described below, in several instances other methods of sampling the structure and floristic composition of the surrounding vegetation were employed.

Results riable having a similarity coefficient of only 38.7. Floris- To assessthe degree of similarity of the vegetation from tically, the lapilli sites are especially variable. The vege- one site affected by a mass movement to another, So- tation on the bedrock and rock debris sites is substan- rensen’s similarity coefficients (Mueller-Dombois & El- tially more similar but still shows considerable varia- lenberg 1974) were calculated (Table 8). Considered tion. The most notable difference between the bedrock together the vegetation on the landslides is quite va- and lapilli sites is the relative scarcity of N. dombeyi in the latter. This is partially explained by the limitation of the sampling to the central portion of the lapilli sites which were located over 100 m from any seed sources for N. dombeyi; apparently the relatively heavy winged seeds dispersed much shorter distances than the smaller seeds of E. cordifolia and many of the shrub species. A fringing thicket of N. dombeyi at Site III-F had developed on the lapilli adjacent to the forest edge demonstra- ting its capacity to grow vigorously on this substrate type in spite of its scarcity in the central portion of the exposed lapilli. Also, because of summer drought, N. dombeyi may establish in larger numbers towards the edges of surfaces of the very porous iapilli where partially shaded by the adjacent forest. Similarly, the scarcity of the large-leaved Gunnera chilensis - a plant characteristic of moist habitats in southern Chile - on the lapilli sites in contrast to its abundance on the bedrock and debris sites may reflect the lower moisture levels in the lapilli during the summer. The desiccation of the lapilli surface and the greater heterogeneity of the bedrock and debris sites are also reflected by the larger number of species on the latter sites. On the six lapilli sites sampled (Table 7) the mean number of vascular plant species present was 15 which is significantly less (PYO.001) than the mean of 23 for the six bedrock and -debris sites (Table 6). On the exposed lapilli sites are a large number of cosmopolitan species (both arable weeds and ruderal species), many introduced to Chile either intentionally or accidentally by man; these include Plantago lanceolata, Juncus effusus, Aira ca- ryophylla, Trifolium repens, T. dubium, Hypochoeris iadicata, Poa pratensis, Holcus lanatus, Lotus uligino- sus, Taraxcum officinale, Prunella vulgaris, and Rumex * for ‘auriantaca’ read ‘aurantiaca’. acetosella among others. It is of considerable significance that the dominant young stages of the surrounding stands on long undis- trees in the surrounding mature forests such as Eucryp- turbed sites. Both on the 1960 slide surfaces and in the hia cordifolia, Nothofagus obliqua, and N. dombeyi are virgin forests, the dominants are E. cordifolia and N. also the common colonizers of the surfaces exposed by dombeyi. Due to the capacity of the seedlings of the the 1960 mass movements (Table 9). Also noteworthy is tolerant species to establish and grow once the intole- the absence or relative scarcity of the tolerant trees rants have formed a relatively dense canopy, the tole- which characteristically form an intermediate stratum rants are likely to increase in abundance as the E. cordi- such asLaurelia philippiana, L. sempervirens, Aextoxi- folia and Nothofagus-dominated stands develop. The con punctatum, Saxegothaea conspicua, Dasyphyllum near absence of the tolerants from the 1960 slide surfa- diacanthoides, and Persea lingue. The vegetation now ces may be due to a combination of reduced dispersal established on the 1960 slide surfaces appears to be capacity and poor establishment under completely open conditions. For example, the fruits ofA. punctatum and P. lingue are relatively large drupes and disperse slowly while Laurelia spp., D. diacanthoides, and S. conspicua which produce small light seeds apparently do not establish in large numbers due to their inability to tole- rate the environmental conditions associated with completely openesites. Although some cryptogams and a large number of herbaceous species establish early on the slide surfaces, there is no indication that they modify the micro- environment in a manner which greatly affects the subsequent establishment of forest trees and shrubs. On the bedrock sites the shrubs and trees were rooted in the crevices and, judging by their age, established there within a year or two following exposure of the slide surfaces. Shrub and tree establishment is equally as early but more uniform on rock debris and lapilli sites. Clearly, the low nitrogen level in the lapilli (Table 3) slows down the growth rate of the non-nitrogen-fixing plants and, with the establishment of a plant cover in- cluding probable hosts for nitrogen-fixers such as Gun- nera chilensis and Coriaria ruscifolia, insufficient nitrogen would become less of a limiting factor. Neverthe- less, despite the initially poor soil conditions woody plants establish in large numbers as illustrated by the shrub and tree densities determined for several lapilli and bedrock and debris sites (Table 10). The common shrub species on the slides are generally the same species which are common in this zone in secondary succession related to the abandonment of agricultural land and to forest felling and burning. These include Aristotelia chilensis, Fuchsia magellanica, Co- riaria ruscifolia, Baccharis racemosa, Ribes puncta- turn, Buddleia globosa, Embothrium coccineum, Be- rberis spp., and Pernettya spp. among others. The major.difference between the primary successions on the slide surfaces and the secondary successions in this region is the almost total absence in the former of the

159 populations gregariously flower, produce seed, and die. Although these bamboos spread relatively effectively by means of an extensive rhizome system, unless a local population has recently flowered and produced seed, they are slow to invade sites where the vegetation and topsoil have been entirely removed - such as the slide surfaces. If Chusquea seeds do not germinate quickly after falling they are probably consumed by rodents 5 5 3 whose populations grow rapidly following seed production (Urban 1934). Thus, it is unlikely that Chusquea 203 10 seed persists after the seed-producing year. Studies of Chusquea abietifolia in Jamaica (Seifrez 1950) have

13 shown that this species flowers gregariously at 33 year

10 intervals; a similarly lengthy interval between seed pro- ductions would account for the absence of Chusquea large native bamboos, Chusquea spp. The dominance of spp. from the surfaces exposed by the 1960 mass move- Chusquea spp. in the understories of the disturbed fo- ments in the Valdivian Andes. rests is so great that it impairs tree regeneration (Bur- schel et al. 1976, Rosenfeld 1972). The absence of the Forest structure in relation to catastrophism rapidly growing Chusquea spp. from the slide surfaces is not surprising if their life cycle is considered. At long In the Valdivian Andes two general types of forest strut- intervals - probably of a decade at the least - local ture involving Nothofagus spp. are commonly found.

18 i

n Saxegothaea conspicua q Dasyphyllum diacanthoides 0 Weinmannia trichosperma q Nothofagus dombeyi

6-10 II-20 21-30 31-40 41-50 51-60 61-70 71-80 81-90 9j7 1017 Ill, 121, 131, 141, 151, 100 II0 120 130 140 I50 160 DIAMETER AT BREAST HEIGHT IN CM. Fig. 6. The distribution of diameters-at-breast-height in a mature Nothofagus dombeyi-dominated forest adjacent to the large 1960 mudflow in F’ilmaiquik basin. N. dombeyi accounted for 75% of the total basal area, Saxegothaea conspicua for 17%, Weinmannia trichosperma for 6’%, and Dasyphyllum diacanthoides for 2%.

160 The first type is the mature Nothofagus-dominated beyi was present while replacement is indicated by the stands with an intermediate stratum of shade-tolerant population structure of Saxegothaea conspicua which trees. The second type is the pure stands of young is the most abundant of the three species forming the even-aged Nothofagus dombeyi. intermediate tree layer. Intensive timber harvesting and agricultural activity Although mature N. alpina-dominated stands are in the lower altitudes (especially below 600 m) have now very rare, the few observed are characterized by a nearly eliminated the virgin forests in which Eucryphia structure very similar to that described for the mature cordtfolia or Nothofagus obliqua dominate. However, N. dombeyi stands. At ca. 700 m in Sector Las Canoas, at higher altitudes a few virgin forests dominated by N. several mature stands were inspected in which N. al- dombeyi or N. alpina- remain and the analysis of their pina and N. dombeyi in about equal numbers dominate structure is instructive. One such forest is located in the the upper stratum at heights in excess of 35 m and with zone known as San Pablo de Tregua (37”07’S, 72”02’W) diameters at breast height of 1.5 m or more. Not quite as at an altitude of ca. 950 m. In this forest dominated by N. large is the abundant L. philippiana; D. diacanthoides is dombeyi, density and basal area of trees taller than 3 m also common while Weinmannia trichosperma is rare. were determined by means of the wandering quarter The dominant of the understorey is Chusquea coleu method (Mueller-Dombois & Ellenberg 1974); for both which is over 5 m tall and dense beneath gaps in the the understorey and overstorey species, cover was de- forest canopy. Again, no regeneration of the Nothofa- termined by randomly locating five 1 by 10m quadrats in gus spp. was observed while root suckers and seed the 1 ha stand (Table 11). Compared to the surrounding regeneration of L. philippiana were present suggesting forest, the dominance and density of N. dombeyi in the that the successional trend of this stand is towards the stand sampled are relatively great. While there is no latter species. regeneration of N. dombeyi, regeneration of Laurelia In a study of a mature forest dominated by N. dom- philippiana, Dasyphyllum diacanthoides, and Saxego- beyi and N. alpina in Traftin at 1100 m, Burschel et al. thaea conspicua is indicated by the presence of indivi- (1976) describe a similar stand structure in which there duals in all size classes. This structure suggests that is an absence of Nothofagus regeneration and an abun- given a long disturbance-free period, these species dance of regeneration of L. philippiana primarily by root would eventually replace the presently do- suckering and secondarily from seed. Brun (1975) pre- minant N. dombeyi. This type of forest structure is the sents the diameter at breast height distribution of the norm for mature N. dombeyi-dominated stands in the common Nothofagus spp. and three of the shade- Valdivian Andes. In a mature N. dombeyi forest at ca. tolerants based on his analysis of 225 0.1 ha plots of 900 m adjacent to the huge mudflow at the edge of the ‘undisturbed’ forest from the 1952 forest inventory. Pilmaiquen basin (III-G), the diameters at breast height These distributions show abundant individuals in all of all trees over 3 m tall were measured in an 18 by 2.5m diameter classes for L. philippiana, A. punctatum, and plot. As indicated in Fig. 6 no regeneration of N. dom- S. conspicua in contrast to the scarcity of individuals of N. dombeyi, N. alpina, and N. obliqua in the small diameter classes. Thus, the structure of these stands suggests that over an extensive area in the Valdivian Andes there exists a successional trend from the intolerant Nothofagus spp. toward the tolerant tree species.

cable 12. ~~~~~rt$ional trends in the Valdivian Andes; the altitudinal ranges are approximations.

present forest types: successional trends towards forests dominated by: Lover altitudes (below ~a. 500 m) Nothofagus obliqua type .4extoxicon punctatlm, Eucrypbia cordifolia type ~aurelia sempervirens, and L. philippiana Higher altitudes (ca. 500-1100 m) Nothofagus obliqua type L. philippiana, Saxegothaea Eucrypbia cordifolio type COLISPICUP, Dasyphyllum dia- Nathofagus alpina type canthoides, and Weinmannia Nothofagus dombeyi type trichosperma

161 This regional successional trend would be expected to N. dombeyi, only a few virgin forests in which it domi- vary with altitude as indicated in Table 12. Only small nates have escaped destruction by man’s activities. patches of non-Nothofagus forest are today found in the The second type of forest structure which appears to Valdivian Andes. These probably represent the forest be related to past slides is the frequently encountered mosaic which would develop over most of the Valdivian pure younger stands of N. dombeyi which are conspi- Andes in the absence of catastrophic influences. Al- cuously even-aged. For example, the eastern side of the though gaps in the forest canopy produced by the death large mudflow at Site III-F is bordered by an even-sized of old trees might permit the regeneration of an occasio- stand of N. dombeyi (III-I) whose structure was analy- nal Nothofagus, the overwhelming predominance of zed by means of a 700 m2 plot in which all diameters at Nothofagus spp. at middle elevations today in the Val- breast height of trees 3 m or taller were recorded. The divian Andes is attributable to catastrophic disturbance. only tree species in this stand was N. dombeyi; 80% of The role of Eucryphia cordifolia in the forest dynamics the individuals were in the size class 16-45 cm and none of this region is not as clear as that of the Nothofagus were less than 11 cm in diameter. Such stands must spp. While it is very common on slide surfaces and at the develop on surfaces which abruptly become available lower altitudes appears to play a role analogus to that of for colonization such as a slide surface. The absence of

Fig. 7. Forestsat the southernend of the PiImaiquCnbasin. The uniform canopytexture on the mid-slopes are.even-aged Nothofugus dombeyi. Upslope are mature forests of N. dombeyi with the characteristic intermediate layer of shade-tolerant trees. Debris from the large 1960 mudflow is visible in the foreground.

162 E. cordifolia from this stand is probably a result of the 1972). The capacity of N. dombeyi to grow very rapidly relatively high altitude (850 m). The surrounding slopes under high light levels gives it a considerable advantage are characterized by numerous relatively young even- in the formation of pure even-aged stands. aged N. dombeyi stands interfingering with mature forests of N. dombeyi containing an intermediate layer of Conclusions S. conspicua, D. diacanthoides, L. philippiana, and W. trichosperma (Fig. 7). This pattern is best explained by The long history of frequent mass movements and cata- landslides occurring on these slopes several decades or strophic vulcanism has very likely contributed to the more ago. The invasion of shrub and tree species along a large percentage of forest dominated by N. dombeyi in 50 m wide band on the northwest edge of the lapilli the Valdivian Andes. While mass movements have had exposed by the 1960 mudflow (III-H) indicates the pos- the greatest impact on the vegetation during the past few sible origin of such an even-aged N. dombeyi stand. centuries, volcanic ash showers have also been impor- Here tree and shrub heights and frequencies were re- tant in opening up forest canopies by breaking limbs and corded by means of eight parallel 10 m line transects felling old trees, thus creating favorable conditions for located at 5 m intervals from the edge of the sparsely the regeneration of the relatively shade-intolerant trees covered lapilli to the edge of the unaffected N. dombeyi such as Nothofagus spp. and Eucryphia cordifolia. The mature forest. The composition of this thicket is indica- overall effect of periodic fires, most likely associated ted in Table 13. The heights of all the N. dombeyi were with vulcanism, would also have increased the relative within the range of 0.6-3.0 m with a mean of 1.85 m (* importance of the rapidly growing intolerant trees. Both 0.52 S.D.). Thus, the colonization of the border of the vulcanism and catastrophic mass movements account lapilli surface is strongly dominated by N. dombeyi of for the great extent of what is a relatively young succes- uniform height and is, by implication, of uniform age; sional phase - namely, the Nothofagus-dominated fo- this situation may be regarded as a precursor to the rests of shade-tolerant subdominant trees at middle ele- even-aged N. dombeyi forest described above. vations in the Valdivian Andes. This interpretation is consistent with what little is This interpretation is supported by: (1) the demon- known of the ecological behavior of the dominant forest strated ability of N. dombeyi to colonize the 1960 slide species of this region. For example, Brun (1975) reports surfaces, (2) the lack of N. dombeyi regeneration in old that stem analyses show that the intolerant species have virgin forests, and (3) the frequency of pure even-aged substantially faster growth rates than the tolerants; stands of N. dombeyi. The original importance of N. thus, the faster growth rates of the Nothofagus spp. alpina in the vegetation of this zone is also probably due would give them the capacity to form the dominant tree to the opening up of closed vegetation by catastrophic layer above the slower growing tolerants. Similarly, the events. While never as abundant as N. dombeyi, where greater abundance of N. dombeyi versus N. alpina is seed sources are nearby, N. alpina is found in small partially explained by the more rapid growth of the numbers on the 1960 slide surfaces. It is likely however former where the forest canopy is disturbed (Rosenfeld that the cutting of N. alpina has so greatly reduced the seed source for this species that its relative capacity to Table 13. Relative frequencies of tree and shrub species on lapilli surface in the colonize slide deposits cannot be judged. The few re- Pilmaiqu& basin (Site III-H) colonized since 1960. maining virgin stands of N. alpina in the Valdivian An- des are in very remote areas such as along the border species rel.freq. (%I with Argentina. Similarly, although the destruction of Trees the lower altitude forests makes it difficult to evaluate Nothofagus dombeyi 73.8 the role ofE. cordifolia, the available evidence suggests Weimannia trichosperma 2.4 Dasyphyllum diacanthoides 1.2 that its role at altitudes below ca. 600 m is analogous to Nothofagus antarctica (Forst.)Oerst 1.2 that of N. dombeyi. Shrubs While the collection of data for this study was restric- Pernettya poeppigii 9.5 ted to the middle elevations of the Valdivian Andes, the Baccharis sp. 7.1 Chusquea coleu 2.4 influence of catastrophism on the vegetation of south- Escallonia rubra 1.2 central Chile is much more widespread (Veblen et al. in Discaria crenata (Clos.)Regel 1.2 press). In the southern part of the Lake District (Fig. 1)

163 in the areas surrounding Lakes Puyehue, Rupanco, succession seems to be trending in the Valdivian Andes Llanquihue, and Todos Los Santos, numerous debris occur over an extensive area on the western side of the avalanches, landslides, and mudflows were observed to Coastal Cordillera. Geologically, the Coastal Cordillera bear a vegetation very similar to that studied in the is made up of Paleozoic and Precambrian metamorphic Valdivian Andes. The majority of these slides also oc- rocks and the western side has not been greatly affected curred in 1960 (Saint-Amand 1962, Wright & Mella by Recent vulcanism (Ruiz et al. 1966, Illies 1970). Nei- 1963). Similarly, extensivelandslides, some as large as 5 ther is it as affected by catastrophic mass movements as km long, usually associated with major earthquakes are is the Andean Cordillera. It is tempting to attribute the reported for the Lake District and Chiloe Island during absence of Nothofagus from the western side of the the eighteenth and nineteenth centuries (Fonck 1896). Coastal Cordillera to the relative lack of catastrophic Quaternary mudflow deposits which were probably as- vulcanism and mass movements. However, the milder sociated with either glaciation or earthquakes are pre- temperature ranges and probably greater humidity cha- sent in the Central Depression as far north as Santiago racteristic of these slopes (Weinberger 1973) as compa- (33”3O’S)(Heusser 1966). At least as far south as Laguna red to the Valdivian Andes must also be considered. San Rafael (46”4O’S), avalanche scars are common While the vegetation of much of the world’s moun- along the front of the Andes and, consequently, the tainous areas (especially those of humid climates) is vegetation is highly disturbed (Heusser 1964). The in- known to be influenced by frequent mass movements terpretation of the Nothofagus-dominated forests of (Robbins 1950, Flaccus 1959, Langenheim 1956), there shade-tolerant subdominant trees as a relatively early seem to be few areas where the regional importance of successional phase can tentatively be applied to much of slides is as great as it is in the Andes of south-central the western side of the Andes from 39” to 41”3O’S. Ho- Chile. The greatest parallels with the slide/vegetation wever, within this zone the Nothofagus pumulio forest relationships in south-central Chile are found in the type (above ca. 1200 m) which forms the uppermost humid mountainous regions of New Zealand. In the forest limit cannot be considered a successional phase Tararua Range of the North Island in the region of because of the absence of other tree species which could forests of Nothofugus menziesii Oerst., landslides are replace it; nevertheless, this forest type is frequently frequently triggered by earthquakes (Franklin 1967, P. affected by catastrophic vulcanism and snow avalan- Wardle 1962). In Fiordland on the South Island, the ches. At altitudes greater than 1050 m Laurelia philip- forests of the steep slopes are periodically devastated piana and Dasyphyllum diacanthoides are generally ab- by immense slides. The resulting seral vegetation is sent and Saxegothaea conspicua is much reduced in dominated by N. menziesii although N. solandri var. vigor and height. Thus, in the narrow transitional zone cliffortioides (Hook. f.) Poole is usually also present from forests dominated by N. dombeyi and N. alpina to (Holloway 1954, J. Wardle 1970). As in south-central those dominated by N. pumilio, there is no tendency for Chile, Nothofugus spp. are both the early colonizers of Nothofagus spp. to be replaced by other three species. the slide surfaces and the dominants of the mature fo- Similarly, at more southerly latitudes (south of ca. 42”s) rests. N. solandri var. cliffortioides characteristically on the western side of the Andes the pure as well as forms one, two, or three age class monotypic stands mixed N. pumilio and N. betuloides (Mirb.) Bl. forests which are the result of regeneration following a cata- do not necessarily represent early successional phases. strophic influence on the vegetation (J. Wardle 1974). At low to middle elevations on the western side of the Thus, the relationship of forest dominance by Nothofa- Coastal Cordillera of Chile at ca. 4O”S,Nothofugus spp. gus spp. and catastrophic influences appears to be more are generally absent except for a few N. obliqua near sea than a local Chilean phenomenon. However, in Victo- level (Philippi 1865). This region contains the most ex- rian and Tasmanian cool temperate rainforest of sou- tensive undisturbed Valdivian rainforest remaining in theastern Australia, regeneration of Nothofugus cun- Chile. These forests are dominated by the same shade- ninghamii Oerst. can occur in the absence of disturban- tolerant trees which are the subdominants of the Notho- ce. Although even-aged stands may follow crown fires fugus forests of the Valdivian Andes; these include Aex- under certain conditions, this species may be eliminated toxicon punctatum, Laurelia philippiana, Dasyphyllum from the site in favor of giant light-demanding Eucalyp- diacanthoides, Weinmanniu trichosperma, and Saxego- tus spp. if disastrous fires are repetitive (Howard & thaea conspicua. Thus, the forest types towards which Ashton 1973).

164 The slide/vegetation relationships described for outcrops by climax woody species with little influence south-central Chile are of interest within the context of of cryptogamic or herbaceous communities in succes- successional theory. Although there is little uniformity sions leading towards Pinus ponderosa forest on xeric in detail, it is generally implied in the ecological litera- sites andAbies concolor forest on mesic sites. Similarly, ture that in climatic areas capable of supporting a forest in the White Mountains of New Hampshire, Flaccus cover primary succession progresses iinearly from co- (1959) has reported the early colonization by several lonization by cryptogams through herbaceous and tree species of surfaces affected by landslides and the shrub communities to an eventual ‘climax’ forest com- relative unimportance of herb and shrub stages in suc- munity; the establishment of each later stage depends on cessions leading towards forests ofAbies balsamea and the physical and biotic changes brought about by the Picea rubens. These studies, as well as the present one, previous stage (Odum 1969, Mueller-Dombois & Ellen- suggest that primary succession is not as strongly com- berg 1974, Whittaker 1953). In two of the most widely munity controlled as previously believed. used ecology texts it is strongly emphasized that suc- Steady-state vegetation refers to that vegetation cession is ‘community controlled’ in the sense that the which would maintain itself on the same site if not modification of the physical and biotic environment by disturbed (Whittaker 1975) and is considered an impro- the plants of early stages permit the establishment and vement over the much maligned climax terminology growth of the plants of subsequent stages (Odum 1975, (Whittaker 1953, Drury & Nisbet 1973). In such self- Whittaker 1975). This is known as the concept of ‘reac- maintaining vegetation there must be a balance between tion’ and is attributable to F.E. Clements (1916). The the birth and death rates; the plants which make up nature of the colonization of the landslide surfaces of the steady-state forest vegetation must be able to reproduce Valdivian Andes contrasts somewhat with this interpre- and grow in the shade of the plants already present. tation of succession. In this wet climate the dominant Thus, the forest types dominated by shade-intolerants forest trees of the surrounding vegetation establish on such as Nothofagus dombeyi, N. alpina, N. obliqua, the slide surfaces soon after exposure. Cryptogams, and E. cordifolia cannot be considered the steady- state herbs, and shrubs establish at the same time but the vegetation of the Valdivian Andes. The Nothofagus- establishment of the dominant trees does not appear to dominated forests (below the altitude of the N. pumilio be dependent on their prior modification of the site. type, ca. 1200 m) which account for the major portion of However, the contribution of the cryptogams and herbs the plant cover of the Valdivian Andes appear to be to soil development probably does increase the rate of slowly undergoing directional changes in terms of spe- stand growth. Furthermore, the similarity of the domi- cies dominance and floristic composition. However, the nants of the young vegetation on the slides to those of frequency of catastrophic phenomena and the slowness the surrounding vegetation illustrates the importance of of succession involving the replacement of the long- the ‘initial florstic composition’ of primary succession lived intolerant tree species prevents the development sites (Egler 1954). In general, the nature of revegetation over large areas in the Andes of south-central Chile of a of the 1960 slides corresponds well with the view of steady-state vegetation consisting of shade-tolerant successional phenomena presented by Drury & Nisbet trees. (1973) in which they challenge the concept of reaction as the driving force of succession and, in its place, empha- size the importance of differential growth, differential Summary survial, and differential dispersal of species adapted to grow at different points on stress gradients. The capa- In association with a devastating earthquake in 1960, city of the dominant forest species to establish immedia- thousands of debris avalanches, landslides, and mud- tely on primary bare surfaces has been documented in flows occurred in the Andes of south-central Chile. several parts of the world. In Hawaii, Atkinson (1970) Catastrophic mass movements associated with seismic has shown that Metrosideros collina is the dominant activity have affected the Andes of south-central Chile climax forest species on incipiently weathered lava and several times in the past 400 years and have profoundly is also one of the first colonizers on sterile outcrops. In intluenced the regional vegetation. the southern Sierra Nevada of California, Rundell The most widespread forest types in the Andean Cor- (1975) has documented the early colonization of granite dillera of the Province of Valdivia (latitude 39”25’ to

165 40”4O’S) are dominated by Nothofagus spp. and Eu- Fonck, F. 1896. Viajes de Fray Francisco Menendez a La cryphia cordifolia and characteristically have an inter- Cordillera. C.F. Niemeyer, Valparaiso, Chile. 528 pp. mediate layer of shade-tolerant trees. These forest ty- Frankin, D.A. 1967. The synecology of the Tararua indigenous forests. New Zealand Forest Service, Tech. Paper No. 53, pes represent relatively early successional phases follo- 39 PP. wing forest destruction by catastrophic phenomena. Guarda G., F. 1953. Historia de Valdivia 1552-1952. Imprenta The supporting evidence for this interpretation inclu- Cultural, Santiago, Chile. 360 pp. des: (1) the nature of the colonization of the surfaces HervC A., F., H. Moreno H., & M. Parada R. 1974a. Grani- tojds of the Andean range of Valdivia Province, Chile. Pac. exposed by the 1960 mass movements, (2) the structure Geol. 8: 3w5. of the existing forest vegetation, (3) the ecological cha- Hervd A., F., H. Moreno H., & M. Parada R. 1974b. Nuevos racteristics of the dominant trees, and (4) the historical antecedentes sobre la geologia de 10s Andes de la Provincia frequency of similar catastrophic events in the Andes of de Valdivia. Dept. Geol. Univ. Chile, Santiago (mimeogr.). south-central Chile. 13 PP. Heusser, C.J. 1964. Somepohenprofilesfromthe Lagunade San Rafael Area, Chile. Ancient Pacific Floras, 95-114. Univ. Hawaii, Honolulu. References Heusser, C.J. 1966. Late-Pleistocene pollen diagrams from the Province of Llanquihue, southern Chile. Proc. Amer. Phil. Almeyda A., E. & F. Saez S. 1958. Recopilacion de Datos Sot. 110: 269-305. Climaticos de Chile y Mapas Sin6pticos Respectivos. Min. Heusser, C.J. 1974. Vegetation and climate of the southern de Agric., Santiago. 19.5pp. Chilean Lake District during and since the last interglacia- Anon. 1964. Climatologia en Chile, Fasciculo I, Valores Nor- tion. Quat. Res. 4: 290-315. males de 36 Estaciones Seleccionadas, Period0 191G-1945. 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Accepted 30 June 1977

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