Climate Change Challenges: The Effect of Shade and Herb Competition on the Regeneration of Quercus Suber L. and Quercus Rotundifolia Lam

• Main Author: Portugal, Francisco Soares
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022
• Subjects: Climate Change; Forestry; Forests; Trees
• ISBN: 9798383490167

Low recruitment of Quercus suber L. (cork oak) and Quercus rotundifoliaLam. (holm oak) woodlands are a consequence of inadequate land-use practices and ongoing climatic changes, threatening the ecological and economical sustainability of Mediterranean ecosystems. Increasing evidence shows the critical positive role of the canopy nurse effect on seedling survival, however the role of herb vegetation in seedling establishment is seldom understood. Aiming to address the effect of canopy and herb vegetation on cork and holm oak recruitment dynamics, 18 plots were established in 2003 under different combinations of canopy cover (present, open) and herb vegetation (present, removed). Height and diameter were measured periodically, and growth rate was calculated. Survival analysis was performed using Cox Regression for 2004-2006 and 2004-2015 time periods, considering SPEI (Standardized Precipitation Evapotranspiration index). This study shows that nurse tree canopies and high SPEI values have a positive effect on cork and holm oak seedling survival ratio, especially for cork oak. Canopy also positively affected trees, considering the period 2004-2015, and canopy interaction with herb vegetation did not significantly affect tree survival in any of the conditions tested. Our results show that open conditions and high SPEI (high moisture level) had a beneficial effect on growth (height). Presence of herb vegetation had a negative effect on tree growth rate, particularly in early development stages and when SPEI values were low, and more clearly for cork oak. The results suggest that higher growth rates predominate for cork oak in early stages, while holm oak grows at a higher rate for later stages. Only by ameliorating the causes of adult mortality and improving regeneration by management practices (e.g., active management of herb vegetation, promoting healthy tree canopy) will it be possible to assure the permanence of this valuable and important part of the natural and cultural heritage.