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 assessed by 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 authorities are 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. Schlegel and 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 sys- tem 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 wes- tern 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 philip- piana and Saxegothaea conspicua and to a lesser extent Dasyphyllum diacanthoides and Weinmannia trichos- perma. 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.

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