Early Vegetation Recovery After the 2008-2009 Explosive Eruption Of

bioRxiv preprint doi: https://doi.org/10.1101/746859; this version posted October 8, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 1 Early vegetation recovery after the 2008- 2 2009 explosive eruption of the Chaitén 3 Volcano. 4 5 Ricardo Moreno-González1*, Iván A. Díaz2, Duncan A. Christie2,3, Rafael E. Coopman2,4, 6 Antonio Lara2, 3 7 8 1. Department of Palynology and Climate Dynamic, University of Göttingen, Germany. 9 2. Instituto de Conservación, Biodiversidad y Territorio, Universidad Austral de Chile, 10 Valdivia, Chile. 11 3. Center for Climate and Resilience Research (CR)2 12 4. Marilyn Ball's Lab, Plant Science Division, Research school of Biology, The Australian 13 National University 14 * Corresponding author: Ricardo Moreno González 15 E-mail: [email protected] 16 17 bioRxiv preprint doi: https://doi.org/10.1101/746859; this version posted October 8, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 18 Abstract 19 In May 2008, Chaitén volcano entered in eruptive process, one of the world largest eruptions 20 in the last decades. The catastrophic event left different type of disturbance and caused diverse 21 environmental damage distributed heterogeneously in the surrounding areas of the volcano. We 22 went to the field to assess the early vegetation responses a year after the eruption, in September 23 2009. Particularly, we evaluated the lateral-blast disturbance zone. We distributed a set of plots 24 in three disturbed sites, and one in an undisturbed site. In each of these sites, in a plot of 1000m2 25 we marked all stand tree, recording whether they were alive, resprouting or dead. Additionally, 26 in each site 80 small-plots (~4m2) we tallied the plants regeneration, its coverage, and the log- 27 volume. We described whether the plant regeneration was growing on mineral or organic 28 substrate. In the blast-zone the eruption created a gradient of disturbance. Close to the crater 29 we found high devastation marked by no surviving species, scarce standing-dead trees and logs, 30 as well as no tree regeneration. On the other extreme of the disturbance gradient, the trees with 31 damaged crown were resprouting, small-plants were regrowing and seedlings were more 32 dispersed. The main regeneration strategy was the resprouting of trunks or buried roots, while 33 few seedlings were observed in the small plots and elsewhere in disturbed areas. However, the 34 assessment was too soon after the eruption and updated monitoring is required to confirm 35 observed patterns. The main findings of this study are: i) a mosaic of pioneering-wind dispersed 36 species, scattered survivors regrowing and spreading from biological legacies, and plant species 37 dispersed by frugivorous birds, likely favored by the biological legacies; (ii) the early 38 succession is influenced by the interaction of the species-specific life history, altitudinal 39 gradient and the different intensity of disturbance. 40 bioRxiv preprint doi: https://doi.org/10.1101/746859; this version posted October 8, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 41 Keywords: 2008-Chaiten Volcano, Volcanic disturbance, vegetation dynamics, Nothofagus 42 dynamics, South American temperate rainforest, early succession. 43 44 1. Introduction 45 Volcanic eruptions are large-scale disturbance that modify the composition, the structure and 46 ecosystems processes (Swanson et al., 2013; Turner and Dale, 1998; Turner et al., 1997). As 47 volcanoes enter in eruptive phase complex mechanism involve the events in a gradient of 48 multiple type of disturbances such as explosive blasts, thermal and toxic chemical waves, 49 landslides, glowing avalanche deposits, debris flows, lava flows, and air falls of volcanic tephra 50 (Dale et al., 2005; Swanson et al., 2013). A volcanic eruption could have effects at very large 51 spatial and temporal scales (Peet, 1992; Robock and Oppenheimer, 2003), yet directly on 52 surrounded forest throughout burning, burying and/or blowing down trees or other plants (Dale 53 et al., 2005). However, since this kind of large disturbance are infrequent (Turner et al. 1998) 54 or have been seldom monitored (Chrisafully and Dale, 2018), our understanding of vegetation 55 responses is still limited. Despite the importance of volcanic eruptions, few studies have 56 analyzed the effect of eruptions short after the event (Dale et al., 2005; Chrisafully and Dale 57 2018). On the other hand, the effect of volcanism has been studied by comparing different 58 stands in chronosequences assuming that different forest patches would reflect the successional 59 stage after the disturbance (e.g. Drury and Nisbet 1973; Franklin and Swanson, 2010; Pickett 60 1988; Walker et al 2010). 61 62 Forest recovery is considerably slow following disturbances that heavily impact soils as well 63 as aboveground vegetation (Chazdon, 2003). Despite volcanoes are considered as catastrophic 64 disturbance event, it is possible that diverse biological legacies can remain after the event. The bioRxiv preprint doi: https://doi.org/10.1101/746859; this version posted October 8, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 65 persistence and heterogeneous distribution of these biological legacies might modulate and help 66 the recolonization of the plants (Foster et al., 1998; Franklin et al., 1985; Turner et al., 1998). 67 For example, the life-history traits of the pre-disturbed community will result in particular 68 survivors perhaps able to re-colonize and expand over the new conditions on the disturbed 69 environment (Foster et al., 1998; Turner et al., 1998). Therefore, the arrange and the amount of 70 the biological legacies would drive the rate and the pathways of the new colonizers. 71 72 One of the most active tectonic and volcanic areas in the world correspond to the subduction 73 area of the Nazca and the South American plate (e.g., Stern, 2004), which also originated the 74 longest and the second highest mountain range in the world, the Andes. The volcanoes in the 75 Chilean Andes are quite active. The Southern and Austral Volcanic Zones comprise 74 active 76 volcanoes since the Post-Glacial up to the present and at least 21 have had one large explosive 77 eruption (Fontijn et al., 2014). In the southern portion of the Andes, it is located the South 78 American Temperate rainforest (SATR) (Armesto et al., 1998). This cordillera plays a critical 79 role in SATR dynamics, where current successional models after volcanic disturbance suggest 80 the Nothofagus are dominant pioneer trees that benefit from disturbances to persist (Veblen et 81 al., 2016). The SATR represent a biogeographical island, rich in endemic species and 82 dominated by evergreen, broad-leaved species (Armesto et al., 1996; Villagran and Hinojosa, 83 1997, Arroyo et al., 2004). South of 40°S, extensive areas of old-growth forest dominate the 84 mountainous landscape. These forest are not directly disturbed by modern human activity, and 85 represent one of the last pristine areas with pre-industrial biogeochemical conditions (Perakis 86 and Hedin 2002) 87 On May 1st 2008 started the last eruption of the Chaiten Volcano (42° 50’S), near the small 88 town of Chaiten, in southern Chile. This eruption was the largest rhyolite eruption since the bioRxiv preprint doi: https://doi.org/10.1101/746859; this version posted October 8, 2019. The copyright holder for this preprint (which was not certified by peer review) is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under aCC-BY-NC 4.0 International license. 89 great eruption of Katmai Volcano in 1912, being the first rhyolite eruption in which some 90 attributes of its dynamics and impacts have been monitored (Major and Lara, 2013). The 91 eruption consisted of an approximately 2-week-long explosive phase that generated as much as 92 1 km3 bulk volume tephra (~0.3 km3 dense rock equivalent) followed by an approximately 20- 93 month-long effusive phase that erupted about 0.8 km3 of high-silica rhyolite lava that formed a 94 new dome within the volcano’s caldera (Major and Lara, 2013). Chaiten volcano was 95 surrounded by extensive old-growth undisturbed forest by humans, providing a unique 96 opportunity to evaluate the effects of volcanism over undisturbed landscape, then providing an 97 opportunity to understand how volcanism may have affected the forest, under pre-industrial 98 conditions. 99 100 In this study, we characterized the early establishment of the vegetation after the eruption of 101 the Chaitén volcano along a disturbance gradient one year after the eruption started, from 102 nearby the crater to the closest old-growth forest with vegetation completely alive. We predict 103 that plant species diversity and the number of living trees decrease close to the crater, and 104 pioneering Nothofagus species are colonizing the areas affected by the eruption. Our objectives 105 included the creation of a baseline for further long-term monitoring of vegetation recovering, 106 and to identify and analyze the importance of biological legacies for forest recovery.

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