Augusta Costa

Analysis of spatial patterns of oak decline in cork oak woodlands in Mediterranean conditions

Abstract• Cork oak mortality is a recurrent problem in southwestern Portugal. Despite the perception of increasingly visible damage in oak woodlands on drought-prone sites, the role of the various environmental factors in their decline is not clear.• To describe the spatial patterns of cork oak (Quercus suber L.) mortality, a cork oak mortality index (MI) was determined for each landscape feature (agroforestry system, soil type, slope and aspect) using a GIS approach. To achieve this goal, a logistic regression model was formulated analyzing interactions between landscape attributes and allowing a prediction of cork oak mortality.• Maximum values of MI were found in (i) shrublands and open woodlands with shrub encroachment (MI 6 and 3, respectively), where competition for soil water between tree and understory increases; and (ii) on lower slopes in the rounded hilltops and smooth hillsides or shallow soils where access to groundwater resources during summer drought is difficult.• The model highlighted the importance of the agroforestry systems on cork oak mortality and may be used to identify sensitive areas where mitigation actions should be employed in a scenario of increasing drought severity in these Mediterranean ecosystems.Résumé• La mortalité du chêne liège est un problème récurrent dans le sud-ouest du Portugal. Malgré la perception de dommages de plus en plus visibles dans les forêts de chênes sur les sites propices à la sécheresse, le rôle des différents facteurs environnementaux dans leur déclin n’est pas clair.• Pour décrire les schémas spatiaux de la mortalité du chêne liège (Quercus suber L.), un indice de mortalité des chênes lièges (MI) a été déterminé pour chaque élément du paysage (système agroforestier, type de sol, pente et exposition) en utilisant une approche SIG. Pour atteindre cet objectif, un modèle de régression logistique a été formulé pour analyser les interactions entre les attributs du paysage et permettre une prédiction de la mortalité du chêne liège.• Les valeurs maximum des MI ont été trouvées dans (i) les zones arbustives et les forêts claires avec empiètement d’arbustes (MI 6 et 3, respectivement), où la concurrence pour l’eau du sol entre les arbres et le sous-bois s’accroît ; et (ii) dans le bas des pentes du sommet des collines arrondies et les pentes douces de coteaux ou sur les sols peu profonds où l’accès aux ressources souterraines en eau est difficile en période de sécheresse estivale.• Le modèle a mis en évidence l’importance des systèmes agroforestiers dans la mortalité des chêneslièges et peut être utilisé pour identifier les zones sensibles où des actions de mitigation devraient être employées dans un scénario d’augmentation de la sévérité des sécheresses dans ces écosystèmes méditerranéens.

A dendroclimatological approach to diameter growth in adult cork-oak trees under production

Abstract. The diameter growth of mature cork oaks under cork production in southwestern Portugal was studied during a 9-year cork-production cycle in relation to fluctuations in precipitation and temperature, and to drought indices combining the two variables. A dendroclimatological approach was applied to the series of 8 complete years contained in the cork-production cycle and growth effects were removed by standardization and calculation of annual growth indices. The most important factor positively influencing diameter growth was cumulative precipitation in the growing season (January–June) and in the previous autumn and winter (October/November of the previous year–June). The monthly temperature is a less influential factor, negatively correlated with diameter growth in high summer drought (August) and positively correlated at the beginning of physiological activity (March).

Patterns and Drivers of Scattered Tree Loss in Agricultural Landscapes: Orchard Meadows in Germany (1968-2009)

Scattered trees support high levels of farmland biodiversity and ecosystem services in agricultural landscapes, but they are threatened by agricultural intensification, urbanization, and land abandonment. This study aimed to map and quantify the decline of orchard meadows (scattered fruit trees of high nature conservation value) for a region in Southwestern Germany for the 1968 2009 period and to identify the driving forces of this decline. We derived orchard meadow loss from 1968 and 2009 aerial images and used a boosted regression trees modelling framework to assess the relative importance of 18 environmental, demographic, and socio-economic variables to test five alternative hypothesis explaining orchard meadow loss. We found that orchard meadow loss occurred in flatter areas, in areas where smaller plot sizes and fragmented orchard meadows prevailed, and in areas near settlements and infrastructure. The analysis did not confirm that orchard meadow loss was higher in areas where agricultural intensification was stronger and in areas of lower implementation levels of conservation policies. Our results demonstrated that the influential drivers of orchard meadow loss were those that reduce economic profitability and increase opportunity costs for orchards, providing incentives for converting orchard meadows to other, more profitable land uses. These insights could be taken up by local- and regional-level conservation policies to identify the sites of persistent orchard meadows in agricultural landscapes that would be prioritized in conservation efforts.

Fragmentation patterns of evergreen oak woodlands in Southwestern Iberia: Identifying key spatial indicators

Mediterranean evergreen oak woodlands (composed of Quercus suber L. and Quercus rotundifolia Lam.) are becoming increasingly fragmented in the human-modified landscapes of Southwestern Portugal and Spain. Previous studies have largely neglected to assess the spatial changes of oak woodlands in relation to their surrounding landscape matrix, and to characterize and quantify woodland boundaries and edges. The present study aims to fill this gap by analyzing fragmentation patterns of oak woodlands over a 50-year period (1958-2007) in three landscapes. Using archived aerial imagery from 1958, 1995 and 2007, for two consecutive periods (1958-1995 and 1995-2007), we calculated a set of landscape metrics to compare woodland fragmentation over time. Our results indicated a continuous woodland fragmentation characterized by their edge dynamics. From 1958 to 2007, the replacement of open farmland by shrubland and by new afforestation areas in the oak woodland landscape surrounding matrix, led to the highest values for edge contrast length trends of 5.0 and 12.3, respectively. Linear discriminant analysis was performed to delineate fragmented woodland structures and identify metric variables that characterize woodland spatial configuration. The edge contrast length with open farmland showed a strong correlation with F1 (correlations ranging between 0.55 and 0.98) and may be used as a proxy for oak woodland mixedness in landscape matrix. The edge dynamics of oak woodlands may result in different patterns of oak recruitment and therefore, its study may be helpful in highlighting future baselines for the sustainable management of oak woodlands.

Insights into the Responsiveness of Cork Oak (Quercus suber L.) to Bark Harvesting

Insights into the Responsiveness of Cork Oak ( Quercus suber L.) to Bark HarvestingThe cork oak (Quercus suber L.) is harvested for its bark (cork), a highly valuable non-timber forest product. Recurrent cork harvesting is practiced over the lifetime of the tree and constitutes a stressful action that, while artificially promoting cork growth, may severely deplete tree vigor after an exploitation time span. To date, few long-term studies have been conducted regarding the effect of recurrent cork harvests on cork growth rates, and there is a complete lack of knowledge on the effect of the stress, induced by cork harvesting, on the vigor of the cork oak. In this study we propose to address the resilience of the cork oak to cork harvesting, using cork-ring width as an indicator of tree vigor. We use dendrochronological methods to develop an extended cork-ring width series that was analyzed by autoregressive integrated moving average modeling with an intervention analysis approach. We show that cork harvesting represents a human-induced loss of tree resilience only after six consecutive harvests, and that only after a single stochastic cork-harvesting event may trigger a sudden collapse in cork oak vigor. Our results also suggest that the tree (optimum) exploitation period of 110–120 years, which includes more than nine consecutive harvests, extends more than 35 years beyond the tree vigor breakpoint (occurring at the sixth consecutive harvest). Within this time frame, the tree is producing cork instinctively to survive, and its vulnerability to other (a)biotic stresses may increase, leading to untimely cork oak decline. These results suggest that there is a great potential in the time-series analysis of cork-ring widths for the development of tools that may enhance typical cork oak management planning by addressing both economic and ecological objectives.Compreender a capacidade de resposta do sobreiro ( Quercus suber L.) ao descortiçamentoO sobreiro (Quercus suber L.) distingue-se das outras árvores pelas características singulares da sua espessa casca suberosa, a cortiça. Atualmente, a cortiça é considerada um importante produto não-lenhoso da floresta da região Mediterrânica, com elevado valor comercial. A extração da cortiça (descortiçamento) é feita periodicamente ao longo da vida da árvore, em sucessivos ciclos de produção de cortiça. Após um descortiçamento, a camada geradora de cortiça (felogene) morre e a árvore tem a capacidade de regenerar uma nova que, quase imediatamente, começa a formar novas camadas de cortiça. A longo prazo, os sucessivos descortiçamentos, do mesmo modo que “forçam” a árvore a produzir novas camadas de cortiça, afetam decisivamente os processos fisiológicos da árvore. Apesar de bem estudadas, as reações fisiológicas imediatas do sobreiro ao descortiçamento e a curva crescimento de cortiça num ciclo de produção, nada se sabe sobre como a árvore reage a sucessivos descortiçamentos, ao longo da sua vida.Neste estudo, apresenta-se uma abordagem inovadora para obter informação sobre a variação da resiliência do sobreiro ao descortiçamento. Assume-se que a largura do anel de crescimento da cortiça é um indicador do vigor vegetativo da árvore e efetuou-se uma análise dendrocronológica de séries temporais extensas da largura dos anéis para modelar o crescimento da cortiça. Os resultados obtidos mostraram que a resposta da árvore ao descortiçamento é diferente ao longo da sua vida. A partir de determinado descortiçamento, a árvore tem um colapso da sua resiliência ao descortiçamento, reduzindo drasticamente a largura do seu anel de crescimento da cortiça. A explorabilidade económica da árvore estende-se muito para além deste colapso na sua resiliência ao descortiçamento, a partir do qual poderá aumentar a vulnerabilidade da árvore a outros agentes nocivos (a)bióticos e a promover a sua morte prematura.

Post Hoc Assessment of Stand Structure Across European Wood-Pastures: Implications for Land Use Policy

ABSTRACT Europes woodland and savanna rangelands, often part of silvopastoral systems known as wood-pastures, are deteriorating because of abandonment that leads to return to a forested state or lack of tree regeneration from overgrazing or tree and shrub removal. Despite numerous local studies, there has been no broader survey of the stand structure of European wood-pastures showing which systems are at risk of losing their semiopen character. This overview aims to 1) show some of the differences and similarities in wood-pastures from landscapes across Europe and 2) identify which of these wood-pastures are at risk of losing their semiopen character. We collated a dataset of 13 693 trees from 390 plots in wood-pastures from eight different European regions (western Estonia, eastern Greece, northern Germany, Hungary, northern Italy, southern Portugal, central Romania, and southern Sweden), including tree diameters at breast height, tree density, management type, and tree species composition. On the basis of their structural characteristics, we classified wood-pastures using principal component analysis (PCA) and cluster analysis. The PCA showed a gradient from dense wood-pastures with high levels of regeneration (e.g., in Estonia) to sparse wood-pastures with large trees but a lack of regeneration (e.g., in Romania). Along this gradient, we identified three main groups of wood-pastures: 1) sparse wood-pastures with mostly big trees; 2) dense wood-pastures composed of small trees, and 3) wood-pastures containing a wide range of tree ages. Our results show a large structural gradient in European wood-pastures, as well as regeneration problems varying in their severity, highlighting the importance of social-ecological context for wood-pasture conditions. To maintain the ecological and cultural integrity of European wood-pastures, we suggest 1) more comprehensively considering them in European policies such as the Common Agricultural Policy and EU Habitats Directive, while 2) taking into account their structural characteristics and social-ecological backgrounds.

Climate Signal in Cork-Ring Chronologies: Case Studies in Southwestern Portugal and Northwestern Algeria

Abstract In temperate regions, the analysis of climate signals encoded in the wood rings allows assessing tree sensitivity to climate and its potential effects on growth and yield. In Mediterranean regions, the cork oak (Quercus suber L.) has received limited attention for dendrochronological studies because tree rings are faint and cork rings with a clear annual banding have been rather neglected. We analyzed the climatic signal of cork-ring chronologies for AD 1996–2010 from distinct regions in western Algeria [a mountain oak forest called Hafir-Zarieffet] and in southern Portugal [a peneplain wood-pasture called Benavente]. The goal was to evaluate the strength and consistency of climate signal and to assess cork growth sensitivity to climate variables (precipitation and temperature). Our results suggest that cork growth encodes a climatic signal. Trends of cork growth, via correlation analysis, including climate variables (on a monthly and seasonal basis) and Langs index (on an annual basis) were successfully assessed. Drought-driven cork growth reduction is a threshold function of a P-T ratio, and with expected increase in the drought occurrence under changing climate, cork growth is likely to be similarly affected in both regions.

Differential DNA Methylation Patterns Are Related to Phellogen Origin and Quality of Quercus suber Cork

DNA methylation is thought to influence Quercus suber cork quality, which is the main constraint for its economic valorisation. However, a deep knowledge of the cytosine methylation patterns disclosing the epigenetic variability of trees with different cork quality types is totally missing. This study investigates the hypothesis that variations in DNA methylation contribute to differences in cork cellular characteristics directly related to original or traumatic phellogen activity. We used MSAPs (Methylation Sensitive Amplified Polymorphism) to assess DNA methylation patterns of cork and leaf tissues of Q. suber adult trees growing in three cork oak stands. The relationship between the detected polymorphisms and the diversity of cork quality traits was explored by a marker-trait analysis focusing on the most relevant quality characteristics. Populations differed widely in cork quality, but only slightly in degree of epigenetic differentiation. Four MSAP markers (1.3% of the total) were significantly associated with the most noteworthy quality traits: wood inclusions (nails) and porosity. This evidence supports the potential role of cytosine methylation in the modulation of differential phellogen activity either involved in localized cell death or in pore production, resulting in different cork qualities. Although, the underlying basis of the methylation polymorphism of loci affecting cork quality traits remain unclear, the disclosure of markers statistically associated with cork quality strengthens the potential role of DNA methylation in the regulation of these traits, namely at the phellogen level.

Comparing cork quality from Hafir-Zarieffet mountain forest (Tlemcen, Algeria) vs. Tagus basin Montado (Benavente, Portugal)

Abstract In the southwestern Mediterranean Basin, cork oaks (Quercus suber L.) are periodically harvested for their cork. This natural product is valued by its homogeneity which heightens the importance of characterizing cork tissue discontinuities, or cork pores. Cork porosity profile in natural cork planks has been reported to be affected by forest management practices but, so far, has been scarcely addressed. We characterize the cork porosity profile in two contrasting cork oak woodland; at a mountain forest, in Western Algeria (absence of forest management) and at a peneplain “montado,” in southern Portugal (intensively managed toward the optimization of cork production). Image analysis techniques were applied on transverse sections of more than 40 cork samples from both woodland, and a stepwise discriminant analysis was used to discriminate between the cork pore features data-sets. Cork porosity profiles were similar between regions but; in the cork samples from Algeria, cork pores were having higher values for linear dimensions of pores (length and perimeter) and contrasting shape values (roundness) which depreciate cork quality, when compared to the cork samples from Portugal. However, improved woodland management strategies at Algeria should ensure adequate cork homogeneity and suitability for more valuable cork products.