Decrease in growth increment of Populus euphratica upon defoliation by Lepidopteran larvae in a Central-Asian floodplain forest Philipp Sch € afer a , Murad Saleh b , Ruide Yu c, d , Ximing Zhang c , Frank M. Thomas a, * a University of Trier, Faculty of Regional and Environmental Sciences, Geobotany, Campus II, Behringstraße 21, 54296 Trier, Germany b Friedrich-Wilhelm-Gymnasium Trier, Olewiger Str. 2, 54295 Trier, Germany c Chinese Academy of Sciences, Xinjiang Institute of Ecology and Geography, 40 South Beijing Road, 830011 Urumqi, China d Chinese Academy of Sciences, Xinjiang Institute of Ecology and Geography, Sino-German Joint Research Center for the Management of Ecosystems and Environmental Changes in Arid Lands (MEECAL), 818 South Beijing Road, 830011 Urumqi, China article info Article history: Received 20 January 2017 Received in revised form 7 June 2017 Accepted 27 June 2017 Available online xxx Keywords: Allometry Catocala Insect infestation River run-off Tarim basin Tugai forest abstract Populus euphratica is a constitutive tree species of the mostly monospecific forests along Central-Asian rivers. In the hyper-arid climate along the Tarim River, Xinjiang, NW China, these trees are phreato- phytes with continuous access to the groundwater. Those poplar stands are often moderately to completely defoliated by Lepidopteran larvae in spring. In a P. euphratica stand at the middle reaches of the Tarim River, which grew close to the river and to the water table, we tested whether severe defo- liation significantly reduces the trees' radial stem increment and their production of above-ground wood biomass even at ample water supply by the river. Tree-ring analyses and allometric regressions revealed a drastic decrease in radial stem increment and annual above-ground wood production upon complete defoliation even in a period of ample water supply, which otherwise would have allowed maximum productivity. The loss of above-ground pro- duction by herbivory amounted to approximately 44% relative to the high production rate of the year before complete defoliation. During the recent decade, however, only the amount of river discharge e but not the estimated intensity of defoliation e was (marginally) significantly correlated with the stem increment. We conclude that in P. euphratica forests growing close to the river and to the groundwater, tree growth is mainly related to the amount of river discharge, but can be significantly reduced in years with complete defoliation. Therefore, defoliation events should be considered in assessing the produc- tivity of these riparian forests. © 2017 Elsevier Ltd. All rights reserved. 1. Background, study design, sampling and data evaluation A substantial part of the vegetation along the rivers of Central Asia's arid regions consists of floodplain (tugai) forests (Walter and Box, 1983). Along the Tarim River at the northern and eastern fringe of the Taklamakan Desert in the Tarim Basin (Xinjiang, north- western China), these forests are almost exclusively formed by the Euphrates poplar (Populus euphratica Oliv.; syn. P. diversifolia Schrenk) (Wang et al., 1996). In this hyper-arid region, P. euphratica is a phreatophyte, which relies on permanent access to the groundwater for survival and growth (Gries et al., 2005; Thomas et al., 2006). Accordingly, a previous study has shown that the radial stem increment of trees growing at a short distance to the groundwater and to the river is significantly related to the river discharge of the respective preceding year (Lang et al., 2016). In contrast, the small annual amount of precipitation (<100 mm) is irrelevant to the growth of this species. In the poplar forests of the Tarim Basin, several infestations by Lepidopteran species have been recorded during the past 20 years (1996e2012), with larvae of Apocheima cinerarius Erschoff (Geo- metridae) and Catocala remissa Staudinger (Erebidae) being the most prominent defoliators (Weisgerber, 2000; Zheng et al., 2014). These infestations, which generally occur from mid-April to May, resulted in moderate to complete defoliation of entire P. euphratica stands, which, however, are capable to recover by forming new leaves during a time period from mid-May to June. We hypothe- sized that in addition to the water supply by the river, defoliation * Corresponding author. E-mail addresses: schaefer@uni-trier.de (P. Sch€ afer), adisal1474@gmail.com (M. Saleh), yuruide@sina.com (R. Yu), zhxm@ms.xjb.ac.cn (X. Zhang), thomasf@ uni-trier.de (F.M. Thomas). Contents lists available at ScienceDirect Journal of Arid Environments journal homepage: www.elsevier.com/locate/jaridenv http://dx.doi.org/10.1016/j.jaridenv.2017.06.002 0140-1963/© 2017 Elsevier Ltd. All rights reserved. Journal of Arid Environments xxx (2017) 1e4 Please cite this article in press as: Sch€ afer, P., et al., Decrease in growth increment of Populus euphratica upon defoliation by Lepidopteran larvae in a Central-Asian floodplain forest, Journal of Arid Environments (2017), http://dx.doi.org/10.1016/j.jaridenv.2017.06.002