(2019). Tree-Ring-Based Reconstruction of Larch Budmoth Ou
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Research Article ii FF o o r r e e s s t t doi: 10.3832/ifor2533-012 Biogeosciences and Forestry vol. 12, pp. 289-296 Tree-ring-based reconstruction of larch budmoth outbreaks in the Central Italian Alps since 1774 CE Riccardo Cerrato (1), The larch budmoth (Zeiraphera diniana Gn. – LBM) offers a unique example of Paolo Cherubini (2-3), cyclic fluctuations in insect populations. During regular LBM mass outbreaks, (2-4-5) defoliation of European larch (Larix decidua Mill.) subalpine trees results in Ulf Büntgen , distinct ring-width reductions in the host trees. Although several observations, Anna Coppola (1), reconstructions and models suggest that LBM outbreaks travel from the south- Maria Cristina Salvatore (1-6), west to the northeast along the Alpine arc, gaps in the underlying data still (1-6) hamper our mechanistic understanding of the spatio-temporal system dynam- Carlo Baroni ics. Evidence of historical LBM outbreaks before 1964 is generally associated with uncertainty and is particularly scarce for the Central Italian Alps. Here, we introduce four new larch ring-width chronologies from Val di Sole in the Central Italian Alps and use time-series analyses and comparisons with non- host trees (Picea abies Karst.) to reconstruct LBM mass outbreaks. We identify distinct fingerprints of 15 spatially-synchronized LBM events that occurred be- tween 1774 and 1964 CE. Our results are important for improving qualitative space-time models to simulate travelling wave dynamics of insect populations, and for correcting ring-width-based summer temperature reconstructions from this part of the Alpine arc. Keywords: European Larch, Insect Outbreaks, Larch Bud Moth, Tree-rings, Zeiraphera diniana Gn. Introduction patterns are affected by cyclic outbreaks of and climate (Baltensweiler 1993, Ginzburg Tree growth at high-latitude and high-ele- the larch bud moth (Zeiraphera diniana Gn., & Taneyhill 1994, Berryman 1996, Turchin et vation sites is mainly limited by low sum- LBM hereafter – Weber 1997, Baltensweiler al. 2003). The diet of LBM larvae is based mer temperatures. Tree-ring width (TRW) & Rubli 1999, Esper et al. 2007, Büntgen et on the raw fiber and protein in new larch series from such sites have therefore been al. 2009). The spatio-temporal identifica- foliage (Baltensweiler & Fischlin 1988, Ber- used to reconstruct temperature changes tion of past LBM outbreaks is necessary to ryman 1996, Turchin et al. 2003). The first over different spatio-temporal scales interpret the climatic signal of tree-ring effect of larvae feeding is defoliation. In (Fritts 1976, Esper et al. 2016, 2018). How- chronologies. the following two to three years, reduced ever, forest natural disturbances, such as The LBM, a moth belonging to Lepidop- needle length and a lower nitrogen con- wildfires, windstorms and geomorphologi- tera and characterized by periodic cyclic tent are typically observed (Baltensweiler cal events and processes, as well as biotic population fluctuations (Dormont et al. et al. 2008). The decrease in crown mass attacks, such as insect outbreaks and fun- 2006), has been studied since the early reduces photosynthetic rates, and the re- gal diseases, may also influence tree 1960s in the Engadin valley (Switzerland), lated lower carbohydrate production and growth (Schweingruber 1988). European and reports of outbreaks in several Alpine accumulation decrease TRW and maximum larch (Larix decidua Mill.) is one of the most areas date back to 1815 (Baltensweiler & latewood density, leaving a typical finger- commonly used species for dendroclimatic Rubli 1999). LBM population cycles are print in the tree-ring series (Baltensweiler reconstructions in the Alps (Büntgen et al. driven by trophic and non-trophic factors, et al. 2008). LBM population dynamics are 2005, 2006, 2011, Frank & Esper 2005, Co- such as host-parasite interactions, food influenced by site characteristics, and a rona et al. 2010), although larch tree-ring quality, maternal effect, population density clear periodicity of outbreaks every 8-10 years is typically observed within the LBM (1) Dipartimento di Scienze della Terra, University of Pisa, Pisa (Italy); (2) WSL Swiss Fed- optimum elevation belt between 1700 and eral Research Institute, Birmensdorf (Switzerland); (3) Department of Forest and Nature Con- 2000 m a.s.l. (Baltensweiler & Rubli 1999, servation, Faculty of Forestry, University of British Columbia, Vancouver BC (Canada); (4) De- Johnson et al. 2010). In the French Alps, the partment of Geography, University of Cambridge, Cambridge (United Kingdom); (5) Czech- history of LBM outbreaks from 1750 to Globe and Department of Geography, Masaryk University, Brno (Czech Republic); (6) CNR- 1994 was reconstructed (Rolland et al. IGG, National Research Council - Institute of Geosciences and Earth Resources, Pisa (Italy) 2001) and compared with climate (Saulnier et al. 2017) and land use changes (Batti- @ Riccardo Cerrato ([email protected]) paglia et al. 2014). Tree-ring analyses con- ducted at the border between the Italian Received: Jun 23, 2017 - Accepted: Apr 02, 2019 and French Alps were used to reconstruct LBM outbreaks that occurred from 1760 to Citation: Cerrato R, Cherubini P, Büntgen U, Coppola A, Salvatore MC, Baroni C (2019). Tree- 1999 (Nola et al. 2006), and in the Löt- ring-based reconstruction of larch budmoth outbreaks in the Central Italian Alps since 1774 schental, Switzerland, a 1200-year tree-ring CE. iForest 12: 289-296. – doi: 10.3832/ifor2533-012 [online 2019-05-27] density chronology was used to recon- struct LBM outbreaks well back into me- Communicated by: Emanuele Lingua dieval times (Esper et al. 2007). While the presence of LBM was found to © SISEF https://iforest.sisef.org/ 289 iForest 12: 289-296 Cerrato R et al. - iForest 12: 289-296 y r (FUMO) on the southern part of the same t s massif, and “Val Comasine” (ANBO) on the e r southern part of the Ortles-Cevedale group o (Fig. 1). All valleys are N-S oriented. Two F cores (five mm in diameter) were collected d n from each individual using an increment a borer (Haglöf, Sweden). All trees were s e cored at breast height, perpendicular to c n the slope direction, to minimize the occur- e i rence of reaction wood in the samples c s (Schweingruber 1988). Trees showing scars o caused by mechanical disturbances, such e g as debris flows and avalanches, or other in- o i juries were avoided. B – t Sample preparation and chronology s development e r The cores were sanded with progres- o F sively finer sand paper (P80, P150, P240, i P400, P800 and P2000) to highlight the an- nual ring boundaries. TRW was measured using a sliding table (LINTAB™ mod. 3, RIN- NTECH®, Heidelberg, Germany), with a res- olution of 0.01 mm, and TSAPWin Scientific 4.69h software (RINNTECH®). The individ- ual TRW series were then visually com- pared and cross-dated, also against a pub- lished larch reference chronology (Bebber 1990). The visual cross-dating was addition- ally verified using the COFECHA program (Grissino-Mayer 2001) and the “dplR” pack- age in R (Bunn 2010, R Core Team 2019). The raw TRW series were power trans- formed in order to attenuate the variance, Fig. 1 - Location map of the study area. The dotted circle, triangle, square and penta- and standardized indexes were then calcu- gon represent ANBO, BARC, PALP and FUMO, respectively. lated as a ratio using a cubic smoothing spline with a 50% frequency cut-off at 32 be synchronous at the valley scale, a wave al. 2008). years (Cook & Kairiûkštis 1990). Four site pattern from west to east with a calculated The climate of the study area is inner- standard chronologies were formed as a bi- velocity of 219.8 km · year-1 along the Alpine alpine, with cold winters and temperate weighted mean of standard index series, arc was described (Bjørnstad et al. 2002, summers. The mean annual temperature of and residual chronologies were formed us- Johnson et al. 2004, 2010). Temporal and 0 °C is found at 2540 m a.s.l. Baroni et al. ing pre-whitening. These splines enabled spatial data are essential to understand the (2004) calculated a mean vertical tempera- the removal of medium and low frequen- dynamics of the LBM populations and to ture gradient of 0.59 °C / 100 m elevation. cies due to age and long-term climatic develop outbreak wave models. However, The total amount of precipitation in the trends while preserving the signal related in some regions, such as the Central Italian area spans from 810 mm to 1504 mm and is to the pattern of LBM outbreaks, which Alps, LBM data from before 1964 are gen- positively correlated with elevation and was characterized by high-frequency rap- erally lacking (Baltensweiler & Rubli 1999). negatively correlated with latitude (Baroni id growth variations (Cook & Kairiûkštis Here, we develop four new TRW chro- et al. 2004). 1990). Owing to the uneven sample depth, nologies from high-elevation sites in the The valley floors of the study area are the analyses were performed on the por- Central Italian Alps and use statistical ap- dominated by Norway spruce (Picea abies tion of the chronology that presented an proaches to analyze them in order to high- [L.] Karst.) forests, which transition to Expressed Population Signal (EPS) value light the years characterized by anomalous mixed forest stands (with European larch) higher than 0.85 (Wigley et al. 1984, Cook growth. The aim is to reconstruct LBM out- above 1500 m a.s.l. Above 1900 m a.s.l. Eu- & Kairiûkštis 1990). breaks that occurred in this area in the past ropean larch becomes the dominant spe- centuries, thus contributing to knowledge cies and is associated with green alder (Al- Identification of pointer years of the LBM cycle at locations above the nus viridis [Chaix] D.C.).