High-intensity thinning treatments in mature Pinus halepensis plantations experiencing prolonged drought

Abstract

Pinus halepensis plantations are widespread throughout semiarid-subhumid landscapes of the Mediterranean. Recently, drought-induced decline has often been reported raising concerns with regard to the future of these man-made ecosystems. The study was set out to investigate thinning as a means to alleviate water stress and improve performance of mature P. halepensis plantations experiencing prolonged drought. The study was conducted in a 40-year-old P. halepensis forest in the Jerusalem Mountains of Israel (rainfall: 550 mm year -1 ). Declining stands (stand basal area increment, BAI stand & -3 % year -1 ) were treated by thinning: (1) intense thinning-tree density, BA stand , and leaf area index (LAI) reduced by 81, 68, and 59 %, respectively; (2) moderate-56, 48, and 26 %, respectively;(3) control (*560 tree ha -1 ). Plots of 70 9 70 m were used in four replicates. Individual tree-to stand-level variables were monitored during 4 years through stem and leaf area metrics alongside with predawn shoot water potential (w PD ) and tree mortality. Thinning ameliorated drought stress, reduced mortality, and improved individual tree growth (w PD = -1.7, -1.8, and -2.0 MPa; mortality = 0.2, 2, and 5 % year -1 ; BAI tree = 3.4, 2.0, and 1.4 % year -1 in intense, moderate, and control treatments, respectively). Thinning effects became more pronounced with time. LAI and individual tree leaf area (LA tree ) fluctuated with association to annual rainfall. Higher LA tree caused by thinning reflected a ''selection effect'' while increased leaf area efficiency (BAI per unit LA tree ) was attributed to a ''release effect'' of thinning.

Forest management for adaptation to climate change in the Mediterranean basin: A synthesis of evidence

“…There is increasing evidence that the implementation of a given management practice may be beneficial for reaching a specific objective but, at the same time, it can impair the consecution of other objectives or induce negative impacts on untargeted ecosystem components (Bradford and D'Amato, 2012). In a Mediterranean context, for instance, managers may seek forest resistance to droughts by releasing competition after thinning (Calev et al, 2016), but such treatments can reduce the benefits for carbon storage (Ameztegui et al, 2017;Ruiz-Peinado et al, 2013) or modify the habitat conditions needed for some forest-dwelling species (De La Montaña et al, 2006).…”

Adjacency to a harvest trail increases drought resistance of interior Douglas-fir (Pseudotsuga menziesii var. glauca) in partially harvested stands in central British Columbia

“…Studies from other dry regions suggest that thinning may mitigate the increased drought stress 51 introduced by climate change (Calev et al 2016), but no information is available on the net effect of 52 clustered distributions on drought response in a dry environment. The percentage of gross rainfall lost to 53 interception has been found to progressively decline with increased thinning intensity in established 54 plantations in mesic and xeric systems (Molina and del Campo 2012).…”

Disturbance history and its influence on drought tolerance of interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beisn.) Franco) in the Cariboo-Chilcotin region of British Columbia, Canada

“…Mortality resulting directly from moisture deficit is expected to increase under such climate change (Allen et al, 2010), while disturbances from insect pests and pathogens are expected to become more frequent (Currano et al, 2008;Woods et al, 2010). Stand thinning has been recommended as a means of reducing these risks (Mitchell et al, 1983;Sohn et al, 2013) while maintaining productivity in the short-to mid-term (Elkin et al, 2015;Calev et al, 2016). Thinning reduces canopy interception of rainfall and inter-tree competition for soil moisture, resulting in greater moisture availability to residual trees (Stogsdili et al, 1992;Bréda et al, 1995).…”

“…Studies from other regions suggest that thinning may mitigate the increased drought stress introduced by climate change (Elkin et al, 2015;Calev et al, 2016), but there is no information available on the net effect of clustered distributions on drought response in a dry environment. The percentage of gross rainfall lost to interception has been found to progressively decline with increased thinning intensity in established plantations in mesic and xeric systems (Teklehaimanot et al, 1991;Molina & del Campo, 2012).…”

“…Thinning has been found to increase drought tolerance of managed stands in a number of ecosystems (Sohn et al, 2013;Elkin et al, 2015;Calev et al, 2016), with increased precipitation throughfall and decreased competition for available moisture identified as underlying mechanisms (Stogsdili et al, 1992;Mazza et al, 2011;Nanko et al, 2016).…”