Vegetative propagation techniques such as grafting can be used, in conjunction with field studies, to decouple the relative effects of age and size on tree metabolism and growth. Despite interest in this approach, little attention has been paid to the best metrics for assessing the growth performance of grafted plants over time. Based on an analysis of the grafting literature and our own data, we show that the choice of metrics to assess tree growth can entirely change the conclusions reached about the relative importance of age versus size. We recommend that absolute as well as relative rates of growth are calculated and that scion size be standardized as much as possible at the start of the experiment. Once proper metrics are chosen, all of the available published evidence is largely concordant with two concepts: (1) age-mediated controls of tree growth are likely to be important during the first few years of a tree's life (before phase change); and (2) after the first few years of a tree's life, size-mediated factors largely prevail over age-mediated factors in determining tree growth rates. We found no support for theories invoking age-mediated sink limitations in old trees.

Urban green areas present a lucid example for the harmonious co-existence of the artificial and natural environments best illustrated by their interdependence and interconnection in urban spaces. Urban green areas are essential for the health and wellbeing of citizens. The present study aimed to investigate those multiple benefits for citizens that arise through the existence of urban green areas, as well as important policy dimensions that should be considered when designing the expansion of urban green spaces in urban development. The study was based on a literature review to examine for available evidence on the benefit levels derived by the existence of urban green areas. An extended literature review was followed by a structured review, based on specific inclusion and exclusion criteria, which partly followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. The search was conducted in two databases, and a total of 1674 articles and abstracts were identified through the database searches. After removing 114 duplicates, 1560 records were initially screened based on title and Following inclusion and exclusion criteria, 14 articles were incorporated in the structured review and a total of 47 in the extended review. The extended literature review identified 33 additional articles examining aspects of benefits that did not fall under the pre-established inclusion and exclusion criteria used in the structured review, such as health benefits and other social parameters associated with urban green spaces. The selected studies were allocated in five principal groups according to study types: three of the them consisted of studies employing “willingness to pay” (WTP) methods, five were based on property values, two studies assigned monetary values, while another two assigned CO₂ values, and, finally, two studies were based on qualitative criteria. The results indicated benefits to citizens and increased welfare levels gained by the existence of urban green areas. The conducted review revealed a number of findings and recommendations that could direct future research and urban policy. Those hints could assist local authorities as well as stakeholders in order to measure and assess the benefits of green spaces and urban parks and promote measures and programs to assist their further deployment.

Summary: Variations in water tension in a transpiring tree cause elastic changes in stem diameter. To better understand the dynamics of these variations, stem diameter changes and sap flow rates were monitored simultaneously in trees from two Scots pine chronosequences in Scotland. Tree below‐ground hydraulic conductance (k_bg) was estimated from the relationship between leaf‐specific sap flow rates and the difference between stem and soil water potentials estimated from diameter variations in the stem. In a given tree, k_bg varied both within and among days, with conductance increasing as a function of sap flow and evaporative demand. These patterns could be explained in terms of a composite model of root water transport and possible changes in the gating of aquaporins. We interpreted these trends of increasing k_bg with evaporative demand as a mechanism to enhance the ability of trees to control leaf water potential and keep it within physiologically acceptable limits, with potential implications for our general understanding of plant water relations, and for the estimation and modelling of ecosystem water fluxes. Across trees, k_bg declined with increasing tree age/size, but the proportional contribution of below‐ground to whole‐tree hydraulic resistance also declined. This is consistent with an increase in below‐ground carbon allocation in old/tall trees and a partial acclimation of tall trees to hydraulic limitations. It is argued that these trends have to be considered when discussing the importance of tree height for water transport and growth.

Aleppo pine (Pinus halepensis Mill.) is widespread in most countries of the Mediterranean area. In Greece, Aleppo pine forms natural stands of high economic and ecological importance. Understanding the species’ ecophysiological traits is important in our efforts to predict its responses to ongoing climate variability and change. Therefore, the aim of this study was to assess the seasonal dynamic in Aleppo pine gas exchange and water balance on the leaf and canopy levels in response to the intra-annual variability in the abiotic environment. Specifically, we assessed needle gas exchange, water potential and δ¹³C ratio, as well as tree sap flow and canopy conductance in adult trees of a mature near-coastal semi-arid Aleppo pine ecosystem, over two consecutive years differing in climatic conditions, the latter being less xerothermic. Maximum photosynthesis (A_max), stomatal conductance (g_s), sap flow per unit leaf area (Q_l), and canopy conductance (G_s) peaked in early spring, before the start of the summer season. During summer drought, the investigated parameters were negatively affected by the increasing potential evapotranspiration (PET) rate and vapor pressure deficit (VPD). Aleppo pine displayed a water-saving, drought avoidance (isohydric) strategy via stomatal control in response to drought. The species benefited from periods of high available soil water, during the autumn and winter months, when other environmental factors were not limiting. Then, on the leaf level, air temperature had a significant effect on A_max, while on the canopy level, VPD and net radiation affected Q_l. Our study demonstrates the plasticity of adult Aleppo pine in this forest ecosystem in response to the concurrent environmental conditions. These findings are important in our efforts to predict and forecast responses of the species to projected climate variability and change in the region.