Size-mediated effects of climate on tree growth and mortality in Mediterranean Brutia pine forests

The Eastern Mediterranean Basin is experiencing long-term drought conditions that affect the growth and mortality of many forest tree species. We analysed tree rings from 113 Pinus brutia (living and dead) trees of different age (<50, 50-85, >85 years old) and size to study how climatic variation during the 20th century has shaped their radial-growth and mortality patterns. We selected the pine forest on the island of Lesvos (Greece) representing the largest continuous P. brutia forest on the Aegean islands, to develop a chronology that could provide a bridge between the available tree-ring data sets from the Western and Eastern Mediterranean region. The analysis of the novel chronology captured well-known drought events during the 20th century, such as those in 1949, 1990 and 2007, and provided an equation to reconstruct the intensity of droughts (10 month time scale). P. brutia tree-growth indicated a positive trend from the beginning until the 3rd quarter of the 21st century and then flattened for living trees. Trees that eventually died between 2010 and 2019, were characterized by a much lower growth than surviving trees and also illustrated a long-lasting negative growth trend. Precipitation and water availability (inferred from the SPEI drought index) were positively related to the growth of living and dead trees, mainly in the middle and old age classes. Temperature effect on tree growth shifted from negative to positive with increasing age of living trees, but remained always negative across all age classes in trees that eventually died. Our findings verify the positive effect of water availability on tree growth and survival of Mediterranean pines and highlight a size-mediated effect of temperature on tree growth, probably coupled with individual-tree access to underground water resources. Increased air temperatures during various time periods related to tree physiological activity seem to negatively affect tree survival across all age classes, in Mediterranean P. brutia forests, highlighting their potential vulnerability to global warming conditions.

Converting treatment wetlands into "treatment gardens": Use of ornamental plants for greywater treatment

Nowadays, the use of constructed wetlands for on-site greywater treatment is a very promising option. The successful application of this nature-based solution at full scale requires public acceptance, economic feasibility and the production of high-quality treated greywater. This work focuses on the use of ornamental plants as vertical flow constructed wetland (VFCW) vegetation for greywater treatment, aiming to improve aesthetic and acceptability of the system. The performance and economic feasibility of the proposed green technology were examined during a 2-years study. Results show that Pittosporum tobira and Hedera helix can grow in VFCW operating with greywater without any visible symptoms. These species tolerated both drought and flooding conditions, making them ideal for use not only in residential buildings but also in seasonal hotels and holiday homes. In contrast, partial defoliation of Polygala myrtifolia plants was observed during the winter period. High average removal efficiencies were observed for BOD (99%), COD (96%) and TSS (94%) in all examined VFCWs including unplanted beds. Phosphorus removal gradually decreased from 100% during first months of operation to 15% during second year of operation. In addition, total coliforms concentration reduced by 2.2 log units in the effluent of all planted systems, while lower removal efficiency was observed in the absence of plants. The mean concentration of BOD and TSS in the treated greywater met the standards for indoor reuse (<10 mg/L). Cost payback periods for the installation of the proposed technology in a multi-family building, a single house and a hotel in Greece were found 4.7, 16.6 and 2.5 years, respectively. Overall, the "treatment gardens" proposed in this study provide a technically and economically feasible solution for greywater treatment, with the additional benefit of improving the aesthetic of urban, semi-urban and touristic areas.