Reyes Alejano

Influence of pruning and the climatic conditions on acorn production in holm oak (Quercus ilex L.) dehesas in SW Spain

Acorn production by Quercus ilex L. ssp. ballota (Desf.) Samp. in SW Spain was assessed, and variations between years and the influence of pruning on it were examined. To this end, an experimental study was conducted at two different sites (Calañas and San Bartolomé, in the province of Huelva) where trees were subjected to traditional (light, moderate or heavy) pruning and also to a new (crown-regeneration) pruning method. Acorn yield was quantified over a period of 5 years in the Calañas plot and 4 in the San Bartolomé plot, and found to average at 95.61 ± 0.76 g DM/m2, which is equivalent to 6.5 ± 0.05 kg DM/tree; however, yield figures varied markedly between years depending on the particular climatic conditions. The average acorn production was correlated with the water potential in mid summer (end of July); the annual, spring and autumn rainfall; and the actual evapotranspiration for the period from September (previous year) to August. No significant differences in acorn production between traditional pruning intensities were detected; in fact, there were only hints that heavy pruning might result in decreased acorn yields. The new pruning method used, crown-regeneration, seems promising with a view to increasing acorn yield; however, it should be tested on larger sample sizes before any final conclusions can be drawn in this respect. Based on the results, the present health status of holm oaks in southwestern Spain (a result of sustained decline) and the low value of firewood — which used to be a very important source of income from pruning a few decades ago -, the authors recommend reducing the frequency and intensity of pruning in the dehesas of the study area.RésuméLa production de glands par Quercus ilex L. ssp. ballota (Desf.) Samp. dans le sud ouest de l’Espagne a été mesurée, et l’influence de la taille sur les variations interannuelles a été examinée. Dans ce but, une étude expérimentales a été conduite dans deux sites (Calañas et San Bartolomé dans la province de Huelva) où des arbres ont été soumis à une taille traditionnelle (légère, modérée ou forte) et aussi à une nouvelle méthode de taille (régénération de couronne). La production de glands a été quantifiée sur une période de 5 ans sur le site de Calañas et de 4 ans sur celui de San Bartolomé et était en moyenne de 95,61 ± 0,76 g de matière sèche/m2, ce qui équivaut à 6,5 ± 0,05 kg de matière sèche/arbre. Cependant la production a varié de façon marquée entre années en relation avec les particularités climatiques. La moyenne de production de glands était corrélée avec le potentiel hydrique au milieu de l’été (fin juillet); avec les précipitations annuelles, du printemps et de l’automne, et avec 1’évapotranspiration pour les périodes allant de septembre (année précédente) à août. Aucune différence significative de production de glands n’a été détectée, entre les intensités de taille traditionnelle. La nouvelle méthode utilisée est prometteuse et permet une augmentation de la production de glands; cependant elle devra être testée sur des lots d’arbres plus importants avant d’arriver à des conclusions définitives sur ce sujet. Sur la base de ces résultats, en prenant en compte de l’état de santé actuel du chêne vert dans le sud ouest de l’Espagne (résultat d’un déclin prolongé) et la faible valeur actuelle du bois de feu qui était habituellement une source très importante de revenus provenant de la taille il y a quelques dizaines d’années, les auteurs recommandent la réduction de la fréquence et de l’intensité de la taille dans les dehesas.

Do ecological and silvicultural factors influence acorn mass in Holm Oak (southwestern Spain)

The effect of orientation, location, year, and pruning treatment on mean acorn mass in two open woodland experimental locations (Huelva, South-Western Spain) of Holm Oak (Quercus ilex L. subsp. ballota [Desf.] Samp.) was analyzed during 2001–2006. Data were analyzed by using a mixed linear model, where the covariates were tree size parameters (circumference at 80 cm height, crown size), topographic position (wet index and flow length), intraspecific competition, total acorn crops per tree (weight and number), and climatic parameters. Average estimated acorn mass was 3.17 g acorn−1 in the Calañas location and 4.12 g acorn−1 in the San Bartolomé location, with significant differences between locations, among individual trees and across years. Acorns from the south sides of trees were significantly heavier than those at other positions. The effect of pruning treatment and the interactions location × treatment and treatment × year were not significant. Our study provides no evidence that pruning affects acorn mass. None of the analyzed covariates related to tree size, topographic position and intraspecific competition explained the difference among trees, suggesting that heritable factors play an important role. Specific climatic parameters during September, the most important month for acorn growth, may explain the effects of year and location × year on acorn mass. In addition, there appeared to be a “trade-off” between acorn mass and number of acorns.

Acorn Production Patterns

Acorns—the fruits of oaks—are a key resource for wildlife in temperate forests throughout the Northern Hemisphere. Acorns are also economically important for extensive livestock rearing, and as a staple food have supported indigenous human populations. Consequently, differences in how individual trees and populations of oaks invest in acorn production, both in terms of the size of the acorn crop and of the size of individual acorns, are of interest both ecologically and economically. Acorn production by oaks in both California and Spain tends to be highly variable and spatially synchronous. We summarize studies conducted in the two regions that investigate the factors influencing acorn production. One hypothesis explored is that, as a consequence of management, acorn production tends to be affected by different environmental factors in the two regions; another hypothesis is that acorn production in oaks in Spanish dehesas produce larger and more predictable acorn crops than trees in less managed Spanish forests or in California woodlands. Other factors potentially influencing acorn production are summarized, including biotic factors, trade-offs with growth, trade-offs with acorn size, and pollen limitation. We conclude with a discussion of spatial synchrony and acorn production at the community level. There remain many questions concerning the mating systems of oaks, trade-offs between different oak life-history characters, and the patterns and drivers of spatial synchrony. Environmental conditions in the two regions are similar, but understanding how their subtle differences influence acorn production is likely to yield important insights about the proximate and ultimate factors affecting acorn production and masting behavior.

El potencial de crecimiento radical en planta de vivero de Pinus halepensis Mill. Influencia de la fertilización

Dado el interes que posee el atributo Potencial de Crecimiento Radical de la planta de vivero como predictor de la respuesta postrasplante, este trabajo analiza el efecto de varios tratamientos de fertilizacion en vivero (5g/L de Osmocote 15-8-11; 3, 5, 7 g/L de Osmocote 9-13-18, idem de Osmocote 17-10-10) sobre el Potencial de Crecimiento Radical de planta de pino carrasco de una savia, concluyendose la existencia de diferencias significativas que discriminan grupos de formulaciones a favor de las tres dosis de 9-13-18, que produjeron los mejores resultados (hasta 74 raices mayores de 1 cm en promedio para 7 g/L). Sin embargo, no se han encontrado relaciones univariables significativas entre atributos morfologicos o fisiologicos de la planta y Potencial de Crecimiento Radical. Por otra parte, todos los tratamientos sobrevivieron en plantacion con valores superiores al 70 por ciento en condiciones de semiaridez, indicando un buen estado de vigor de todos los lotes ensayados, incluidos los de menor expresion del potencial de formacion de nuevas raices (17 raices > 1cm).

Effect of ecological factors on intra-annual stem girth increment of holm oak

Key messageThe intra-annual stem girth increment ofQuercus ilex is mainly driven by water availability and secondly by temperature. Tree size and competition modulate the growth response to climate.AbstractHolm oak (Quercus ilex ssp. ballota [Desf.] Samp.) is the most widespread species in the Iberian peninsula, being one of the most representative trees in forests and open woodlands. The analysis of stem girth increment of holm oak may provide valuable information about how Mediterranean ecosystems will respond to the forecasted climate changes. However, due to the variability of the Mediterranean climate, the knowledge of intra-annual patterns of growth is needed for a better understanding of the influence of the climatic variables at this scale. To this end, we used band dendrometers to measure monthly stem girth increments of 96 holm oak trees from 2003 to 2010, located in open woodlands and dense Mediterranean forests in southwestern Spain. We assessed the effects of climate, competition, topography, and initial stem diameter on stem girth increment. The major stem increment periods were in spring and autumn whereas increment rates were very low or even negative in winter and summer. Spring was not every year the season with the higher stem increments, but autumn when spring was very dry. Higher precipitation, soil moisture, and relative humidity had significant positive effects on stem increment, whereas higher temperature, reference evapotranspiration, and solar radiation had significant negative effects. Initial tree diameter and competition from nearby trees partly explained significant differences in stem increment of individual trees. Therefore, the forecasted climatic changes, in which decreased rainfall in spring and increased summer drought are expected in the Mediterranean region, may be a significant threat to the Q. ilex ecosystems.

Tree rings reflect growth adjustments and enhanced synchrony among sites in Iberian stone pine (Pinus pinea L.) under climate change

Key MessageWe used tree ring analysis to assess the response ofPinus pineato climate change in South Iberia. Climate–growth relationships changed over time, with greater sensitivity in recent years due to increasing aridity. A common dendroclimatic signal among sites was found, suggesting that climate change is the main responsible for the observed variation in tree growth.ContextUnderstanding the response of Mediterranean forests to climate change is required to assess their vulnerability and to develop measures that may limit the impact of future climate change.AimsWe analyzed the sensitivity of several populations of Pinus pinea (Stone pine) in Southern and Central Spain and Portugal to climate and identified some responses to climate change.MethodsWe constructed tree ring chronologies and studied the dendroclimatic signal over the last century.ResultsThere were similarities in tree ring growth and response to climate among sites. Growth was enhanced after precipitation during the previous autumn and the current spring and was limited by water shortage. In recent decades, aridity increased in the study region and the sensitivity of tree ring growth to water availability increased at all study sites. We also observed an enhanced growth synchrony among chronologies as well as an increase in ring width variability during the last decades.ConclusionThe radial growth of P. pinea indicated strong effects of climate change. The climatic signal in tree ring chronologies suggested a plastic growth response to climate of this species, although the enhanced growth synchrony and variability in recent years suggest the presence of conditions that are limiting for growth. This study provides the first assessment of the responses of Iberian populations of P. pinea to changes in climate.

Assessment and Comparison of the Visual Survey Method for Estimating Acorn Production in Holm Oak (Quercus ilex ssp. ballota) Open Woodland of Southwestern Spain

We assessed the accuracy of a visual survey method for quantification of acorn production in Holm oak in two plots located in the Huelva province of southwestern Spain during three acorn dissemination periods from 2007 to 2010. At the end of September during each period, visual surveys were used to estimate acorn numbers. Four seed traps were placed beneath the crowns of the same trees at the north, south, east, and west positions to determine acorn weight and number on a fortnightly basis during the mast seeding period (October to January). The accuracy of the visual survey was assessed by linear regression and correlation analysis. The results indicated a significant positive correlation of the two methods during all the three time periods. The resulting regression equations allowed estimation of acorn production based on visual surveys. These results suggest that the visual survey method is a simple and precise method that can be used to predict acorn production in Holm oak landscapes.

Tree patch distribution drives spatial heterogeneity of soil traits in cork oak woodlands

Key messageSpatial heterogeneity of soil resources is linked to tree patch distribution in Mediterranean cork oak woodlands. Tree patch distribution modifies soil traits by varying litterfall inputs due to different tree covers.ContextThe spatial heterogeneity of soil resources affects the structure and functioning of the different plant communities on ecosystems. In Mediterranean oak woodlands, the scattered trees play a key role in this spatial heterogeneity and might strongly influence ecosystem functioning and its productivity.AimsTo assess the influence of the spatial pattern of trees and litter nutrient content on the spatial heterogeneity of soil properties.MethodsWe used a combination of geostatistical techniques and a linear mixed model to evaluate the spatial heterogeneity of soil and the seasonal and spatial variability of litter nutrient content, respectively.ResultsSoil parameters showed a high spatial heterogeneity. Tree cover was positively related with soil pH, and the organic matter, N, K, and Ca soil content. The return of nutrients to the soil via leaf fall had a marked seasonality and a high spatial variability, but this spatial variability had no effect on the spatial pattern of soil resources.ConclusionThe spatial heterogeneity of soil in cork oak woodlands is mainly driven by tree patches distribution. The importance of the spatial heterogeneity of soil resources and the spatial pattern of trees on the functioning of the dehesa ecosystem makes it necessary to include them in plant nutrition studies and modeling approaches in these ecosystems.