Citation: Özçelik, M.S.; Tomášková, I.; Surový, P.; Modlinger, R. Effect of Forest Edge Cutting on Transpiration Rate in Picea abies (L.) H. Karst. Forests 2022, 13, 1238. https:// doi.org/10.3390/f13081238 Academic Editor: Filippo Giadrossich Received: 29 June 2022 Accepted: 3 August 2022 Published: 5 August 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Effect of Forest Edge Cutting on Transpiration Rate in Picea abies (L.) H. Karst. Mehmet S. Özçelik 1 , Ivana Tomášková 2 , Peter Surový 2 and Roman Modlinger 2, * 1 Faculty of Forestry, Isparta University of Applied Sciences, 32260 Isparta, Turkey 2 Faculty of Forestry and Wood Sciences, Czech University of Life Sciences, 16500 Prague, Czech Republic * Correspondence: modlinger@fld.czu.cz Abstract: A field study was conducted to investigate the effect of forest-edge cutting on the transpira- tion rates of individual Picea abies (L.) H. Karst. trees regarding their susceptibility to bark-beetle Ips typographus (L.) infestation. The study period, spanning from 2019 to 2020, involved two treatment plots (T p ) and two control plots (C p ). Sap-flow sensors working according to the trunk-heat-balance method were set up on selected sample trees from T p and C p . Calibration equations were established after a one-year monitoring period between C p and T p , followed by 50-meter-long forest edges created at T p . The changes in the daily sap flow rates were determined as the differences between the measured and predicted values derived from the calibration equations. The results showed that the created forest-edge clearance caused an increase of up to 16% in the sap flow of trees positioned near the new edge. There was a positive correlation between the increase in the sap flow of the trees and the decreased canopy density of the surroundings. The results of this study indicated that forest-edge clearance and forest fragmentation significantly affect the responses of forest-edge trees to new microclimatic conditions. Keywords: sap flow; forest edge; forest fragmentation; bark beetle; stand canopy density 1. Introduction The physiological stress caused by temperature anomalies and drought as a result of global climate change makes forests more vulnerable to dieback worldwide [1,2]. This threat is increasing when combined with biotic stresses, such as forest pests, and, as a result, significant damage is caused to forests, both ecologically and economically [3,4]. The Czech Republic suffers from one of the most aggressive bark-beetle species, Ips typographus (L.) of Eurasia. This species damaged 3.1–5.4% of the Norway spruce (Picea abies (L.) H. Karst.) growing annually across the country in 2017–2019, with economic losses of EUR 260 million [5]. Due to the broad application of sanitation felling and the traditional management strategy against bark beetles [6], the forests in the outbreak areas remain considerably fragmented. These patched forest stands create many forest margins, with a specific microclimate characterized by higher temperatures, increased solar radiation, wind exposure, higher evaporative demand, greater vapor-pressure deficit, and lower soil-water potential [7–12]. The altered microclimate on the forest edges is also expected to affect the physiological responses of the trees, e.g., sap flow [13,14]. Fresh forest edges are favorable sites for the aggregation of bark beetles [15], with a higher predisposition to infestation [16]. In general, significant predisposition factors are the distance from previous infestations [16], the presence of wind-thrown trees [17], expo- sure [18], the age structure of stands [19], the stand density, and spruce representation [20]. However, the forest-stand predisposition to spruce-bark-beetle infestation is a complex process that shows no monocausal relationship. The high density of spruce stands, triggered by economic goals, causes the lower availability of sunlight, precipitation, or nutrients. As a result, it has a negative effect on trees and causes intensive stress [21–23]. Forests 2022, 13, 1238. https://doi.org/10.3390/f13081238 https://www.mdpi.com/journal/forests