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Resin is a renewable forest resource that can increase the economic value of some forests in rural areas. Resin production is associated with climatic conditions. However, its impact on trees' growth remains unclear. Here, we studied radial growth in six Portuguese Pinus pinaster forests that had been resin tapped for 5–7 years along a latitudinal and climatic gradient to understand whether resin tapping affects tree growth, and how it is affected by climate, stand and tree traits. Tree-ring width (TRW) on tapped and untapped trunk sides was compared before and during the tapping period. Tree-ring width decreased in the three youngest populations (< 30 years), with no changes in older populations (> 40 years), while TRW increased after resin harvesting began in the oldest stand (> 55 years). Annual resin-tapping impact (RTI), calculated as the ratio between TRW during tapping years and the 5-year average TRW before tapping, was below and above 1 in the younger and older stands, respectively. Among stand characteristics and across sites, RTI was negatively correlated with tree competition and positively correlated with TRW, cambial age, and tree height. Climatic conditions had a minor role on tree growth response to resin tapping. Our main conclusion is that the effect of resin extraction on growth is age-dependent. Our results encourage the co-production of resin and wood on maritime pine stands over 40 years old where resin extraction impact on growth is negligible. [ABSTRACT FROM AUTHOR]

Key message: Primary growth is less sensitive than secondary growth to water and phloem blockage in maritime pine saplings, with variations in radial growth resulting from tracheid production without altering their size. In plants, primary and secondary growth is regulated by internal and external factors. However, apical and cambial meristems may not respond in the same way. In this study, we disentangle the role of carbon and water availability on stem growth (primary and secondary) and on anatomical tracheid features by investigating the effect of stem girdling (phloem blockage vs. no phloem blockage) and water availability (control vs. drought) in three-year-old Pinus pinaster saplings. We found that primary growth was similar among treatments, while secondary growth was affected by both treatments. Tree ring-width increment in saplings subjected to drought corresponded to half of that on control plants, and phloem blockage enhanced ring width under guidelines soil water conditions. These differences in the radial growth resulted mainly from an increase in tracheid production, which also increased with phloem blockage (above the girdling), regardless the water regime. However, the seasonal pattern of tracheid features was mainly explained by individuals and to a less extent by the water regime and girdling. Contrasting seasonal patterns between treatments were found only on cell wall thickness, showing a faster decrease with increasing water constrains in the drought group than in the control one. The absence of treatment effects on primary growth in P. pinaster saplings suggests a trade-off between the priority in plant development and meristem sensitivity to environmental conditions. [ABSTRACT FROM AUTHOR]

Widespread tree mortality associated with drought has been observed on all forested continents and global change is expected to exacerbate vegetation vulnerability. Forest mortality has implications for future biosphere-atmosphere interactions of carbon, water and energy balance, and is poorly represented in dynamic vegetation models. Reducing uncertainty requires improved mortality projections founded on robust physiological processes. However, the proposed mechanisms of drought-induced mortality, including hydraulic failure and carbon starvation, are unresolved. A growing number of empirical studies have investigated these mechanisms, but data have not been consistently analysed across species and biomes using a standardized physiological framework. Here, we show that xylem hydraulic failure was ubiquitous across multiple tree taxa at drought-induced mortality. All species assessed had 60% or higher loss of xylem hydraulic conductivity, consistent with proposed theoretical and modelled survival thresholds. We found diverse responses in non-structural carbohydrate reserves at mortality, indicating that evidence supporting carbon starvation was not universal. Reduced non-structural carbohydrates were more common for gymnosperms than angiosperms, associated with xylem hydraulic vulnerability, and may have a role in reducing hydraulic function. Our finding that hydraulic failure at drought-induced mortality was persistent across species indicates that substantial improvement in vegetation modelling can be achieved using thresholds in hydraulic function.