Dario Martin-Benito

Growth response to climate and drought in Pinus nigra Arn. trees of different crown classes

Tree-ring chronologies were examined to investigate the influence of climate on radial growth of Pinus nigra in southeastern Spain. We addressed whether drought differentially affected the ring-widths of dominant and suppressed trees and if our results supported the hypothesis that, in a Mediterranean climate, suppressed conifer trees suffer greater growth reductions than dominant trees. Climate–growth relationships were analyzed using response and correlation functions, whereas the effect of drought on trees growth was approached by superposed epoch analysis in 10 dry years. A cool, wet autumn and spring, and/or mild winter enhanced radial growth. Latewood was the most sensitive ring section in both kinds of trees and it was primarily influenced by current year precipitations. Earlywood was mostly influenced by climatic conditions previous to the growing season. In general, May was the most influential month. Pinus nigra was shown to be very drought sensitive tree in the study area. Tree-rings in suppressed trees showed lower growth reductions caused by drought than those of dominant trees. However, dominant trees recovered normal growth faster. Dominant trees showed a more plastic response, and suppression appeared to reduce the effect of climate on tree radial growth. Some possible causes for these effects are discussed. Our results support the essential role of the balance between light and moisture limitations for plant development during droughts and show that it is not appropriate to generalize about the way in which suppression affects climate-growth relationship in conifers.

Forest disturbances under climate change

Forest disturbances are sensitive to climate. However, our understanding of disturbance dynamics in response to climatic changes remains incomplete, particularly regarding large-scale patterns, interaction effects and dampening feedbacks. Here we provide a global synthesis of climate change effects on important abiotic (fire, drought, wind, snow and ice) and biotic (insects and pathogens) disturbance agents. Warmer and drier conditions particularly facilitate fire, drought and insect disturbances, while warmer and wetter conditions increase disturbances from wind and pathogens. Widespread interactions between agents are likely to amplify disturbances, while indirect climate effects such as vegetation changes can dampen long-term disturbance sensitivities to climate. Future changes in disturbance are likely to be most pronounced in coniferous forests and the boreal biome. We conclude that both ecosystems and society should be prepared for an increasingly disturbed future of forests.

Influence of drought on tree rings and tracheid features of Pinus nigra and Pinus sylvestris in a mesic Mediterranean forest

We investigated the influence of climate on the ring width and xylem anatomy of two co-occurring pines (Pinus nigra Arn. and P. sylvestris L.) in the mountains of east-central Spain in order to test their utility for dendroclimatic reconstructions. We developed chronologies of ring width, mean lumen diameter and mean cell-wall thickness (in the earlywood, latewood, and the total annual ring) and the number of cells between 1960 and 2006. Drought, expressed as the standardized precipitation-evapotranspiration index (SPEI), was the main climatic driver of tree radial growth, although trees were also sensitive to temperature (negative effect in previous autumn and current summer) and precipitation (with a general positive effect). P. sylvestris response was stronger to climate of the current year, whereas the effect of previous-year climate was more important for P. nigra. Warm and dry summers reduced ring width, tracheid lumen, and wall thickness in both species, whereas warm winter-spring temperatures had the opposite effect, primarily for P. sylvestris. Previous-year or early-season conditions mainly affected earlywood features, whereas latewood was more responsive to summer climate. Overall, climate appeared to be a stronger limiting factor for P. sylvestris. During periods of drought, cell-wall thickness was reduced while lumen width increased in the latewood of P. sylvestris. This could compromise its hydraulic safety against drought-induced cavitation as our site was close to the southern and dry edge of the species distribution area. Our results suggest that anatomical variables record different and stronger climate information than ring width variables, especially in P. sylvestris. Reconstruction models for SPEI at the 3-month scale were developed for July–August and September–October using principal components regression. The best models included anatomical and width variables of both pine species suggesting that tracheid chronologies can be useful for drought reconstructions especially at mesic sites or with species that encode a mixed drought and temperature-precipitation signal.

Climate-growth variability in Quercus ilex L. west Iberian open woodlands of different stand density

Abstract• We present the longest tree-ring chronology (141 y) of Quercus ilex L. (holm oak), and discuss the species climate-growth relationships and the influence of stand density on tree sensitivity to climate.• Similarly to Quercus suber L., the most influential climatic variables upon holm oak growth were late spring and early summer precipitation, which enhanced growth, and high temperatures in the previous August and current July, which negatively affected growth.• High density stands responded to similar climatic factors as low density stands, but their response was generally weaker. Holm oak sensitivity to climate has increased in recent decades, which might be related to increasing temperatures in the region. Sensitivity was higher in low density stands. Additionally, the effect of summer stress on growth seems to have increased during the same period, similarly to other species in the Iberian Peninsula, suggesting that trees are more vulnerable to climatic changes.• Stand density could buffer the response to climate by smoothing climatic extremes. Nevertheless, the effect of competition might reverse this positive effect at the individual tree level. Precautions should be taken before providing management guidelines regarding the effect of climate change and stand density on holm oak.Résumé• Nous présentons la plus longue chronologie de cernes (141 ans) de Quercus ilex L. (chêne vert) comme et nous discutons les relations climat-croissance chez cette espèce et l’influence de la densité du peuplement sur la sensibilité des arbres au climat.• De façon similaire à Quercus suber L., les variables climatiques les plus influentes sur la croissance du chêne vert ont été les précipitations de la fin du printemps et du début de l’été, qui ont augmenté la croissance, et les températures élevées d’août de l’année précédente et du mois de juillet de l’année, qui ont affecté négativement la croissance.• Les peuplements de densité élevé ont répondu à des facteurs climatiques similaires que les peuplements de faible densité mais leur réponse a été généralement plus faible. La sensibilité du chêne vert au climat a augmentée au cours des dernières décennies, elle pourrait être liée à l’augmentation des températures dans la région. Cette sensibilité est plus élevée dans les peuplements de faible densité. En outre, le effet du stress estival sur la croissance semble avoir augmenté au cours de la même période, de la même façon que pour d’autres espèces dans la péninsule Ibérique, ce qui suggère que les arbres sont plus vulnérables aux changements climatiques.• La densité du peuplement pourrait amortir la réponse au climat en lissant les extrêmes climatiques. Néanmoins, les effets de la concurrence pourraient inverser cet effet positif au niveau des arbres individuels. Des précautions doivent être prises avant de fournir, pour le chêne vert, des lignes directrices de gestion concernant les effets du changement climatique et de la densité.

Black pine (Pinus nigra Arn.) growth divergence along a latitudinal gradient in Western Mediterranean mountains

Abstract• Most studies of tree-growth and climate report positive responses to global warming in high latitudes and negative responses at lower ones.• We analyzed tree-ring width of Pinus nigra Arn. along a 500 km latitudinal transect in the Iberian Peninsula to study the temporal trend and climate forcing in tree radial growth during the last century.• Tree growth was enhanced by cool summers and moist cold seasons. Increased moisture stress has decreased tree growth rates. However, we present evidence of growth increases in some trees in all sampled populations after 1980’s. Climate change negatively (positively) affected between 72% (5%) of trees in the southern populations and 40% (25%) in the north Trees with positive growth trends were favored by winter temperatures and their abundance was inversely correlated with forest productivity.• Our findings add evidences of tree growth divergence in the Mediterranean basin and show the gradual transition between forests where positive (temperate and boreal) and negative (Mediterranean) growth trends dominate.Résumé• La plupart des études sur la croissance de l’arbre en relation avec le climat rapportent des réponses positives au réchauffement climatique dans les hautes latitudes et des réponses négatives dans les basses latitudes.• Pour étudier l’évolution temporelle et le forçage climatique dans la croissance radiale des arbres au cours du siècle dernier, nous avons analysé la largeur des cernes chez Pinus nigra Arn. le long d’un transect latitudinal de 500 km dans la Péninsule Ibérique.• La croissance des arbres a été augmentée par des étés frais et des saisons froides humides. L’augmentation du stress hydrique a diminué les taux de croissance des arbres. Cependant, nous présentons la preuve de l’augmentation de la croissance de certains arbres dans toutes les populations échantillonnées après 1980. Le changement climatique a négativement (positivement) affecté entre 72 % (5 %) des arbres dans les populations du Sud et 40 % (25 %) dans les arbres du Nord avec des tendances de croissance positives qui ont été favorisées par les températures hivernales et leur abondance étaient inversement corrélée à la productivité forestière.• Nos résultats ajoutent des preuves de la divergence de croissance des arbres dans le bassin méditerranéen et montrent la transition progressive entre les forêts où les tendances positives (zones tempérées et boréales) et négatives (zone méditerranéenne) de croissance dominent.

Climate remains an important driver of post‐European vegetation change in the eastern United States

Department of Geography, University of Wisconsin-Madison, 550 North ParkStreet, Madison, WI 53706, USAThe influence of climate on forest change during thepast century in the eastern United States was evalu-ated in a recent paper (Nowacki & Abrams, 2014)that centers on an increase in ‘highly competitivemesophytic hardwoods’ (Nowacki & Abrams, 2008)and a concomitant decrease in the more xerophyticQuercus species. Nowacki & Abrams (2014) con-cluded that climate change has not contributed sig-nificantly to observed changes in forest composition.However, the authors restrict their focus to a singleelement of climate: increasing temperature since theend of the Little Ice Age ca. 150 years ago. In theirstudy, species were binned into four classifications(e.g., Acer saccharum – ‘cool-adapted’, Acer rubrum –‘warm-adapted’) based on average annual tempera-ture within each species range in the United States,reducing the multifaceted character of climate into asingle, categorical measure. The broad temperatureclasses not only veil the many biologically relevantaspects of temperature (e.g., seasonal and extremetemperatures) but they may also mask other influ-ences, both climatic (e.g., moisture sensitivity) andnonclimatic (e.g., competition).Understanding the primary drivers of forest changeis critically important. However, using annual tem-perature reduces the broad spectrum of climaticinfluence on forests (e.g., Jackson & Overpeck, 2000;Jackson et al., 2009) to a single variable. Tsuga canad-ensis illustrates one example of the complex interac-tion between trees and temperature. In the southernpart of its range, Tsuga canadensis growth is weakly,but positively correlated with early growing-seasontemperature. However, this relationship becomesstronger and shifts to later in the season toward thenorthern part of its range (Cook & Cole, 1991). More-over, Tsuga canadensis growth is significantly andnegatively correlated with just May temperaturesduring the current growing season in the northeast-ern United States (Cook, 1991; Cook & Cole, 1991;Vaganov et al., 2011), while in the southeastern Uni-ted States it is strongly and negatively correlatedwith summer (June–August) temperatures (Hart et al.,2010). Trees can also be sensitive to diverse and ofteninteracting climate variables at various stages of theirlife cycles (Jackson et al., 2009). Interactions betweenprecipitation and temperature are clearly important(Harsch & Hille Ris Lambers, 2014; Martin-Benito &Pederson, accepted), and often lead to counterintui-tive responses. For example, some plant species thatwould have been expected to move north and ups-

Dendrochronological Dating of the World Trade Center Ship, Lower Manhattan, New York City

Abstract On July 2010, archaeologists monitoring excavation at the World Trade Center site (WTC) in Lower Manhattan found the remains of a portion of a ships hull. Because the date of construction and origin of the timbers were unknown, samples from different parts of the ship were taken for dendrochronological dating and provenancing. After developing a 280-year long floating chronology from 19 samples of the white oak group (Quercus section Leucobalanus), we used 21 oak chronologies from the eastern United States to evaluate absolute dating and provenance. Our results showed the highest agreement between the WTC ship chronology and two chronologies from Philadelphia (r  =  0.36; t  =  6.4; p < 0.001; n  =  280) and eastern Pennsylvania (r  =  0.35; t  =  6.3; p < 0.001; n  =  280). The last ring dates of the seven best-preserved samples suggest trees for the ship were felled in 1773 CE or soon after. Our analyses suggest that all the oak timbers used to build the ship most likely originated from the same location within the Philadelphia region, which supports the hypothesis independently drawn from idiosyncratic aspects of the vessels construction, that the ship was the product of a small shipyard. Few late-18th Century ships have been found and there is little historical documentation of how vessels of this period were constructed. Therefore, the ships construction date of 1773 is important in confirming that the hull encountered at the World Trade Center represents a rare and valuable piece of American shipbuilding history.

Missing Rings, Synchronous Growth, and Ecological Disturbance in a 36-Year Pitch Pine (Pinus rigida) Provenance Study

Provenance studies are an increasingly important analog for understanding how trees adapted to particular climatic conditions might respond to climate change. Dendrochronological analysis can illuminate differences among trees from different seed sources in terms of absolute annual growth and sensitivity to external growth factors. We analyzed annual radial growth of 567 36-year-old pitch pine (Pinus rigida Mill.) trees from 27 seed sources to evaluate their performance in a New Jersey Pine Barrens provenance experiment. Unexpectedly, missing rings were prevalent in most trees, and some years—1992, 1999, and 2006—had a particularly high frequency of missing rings across the plantation. Trees from local seed sources (<55 km away from the plantation) had a significantly smaller percentage of missing rings from 1980–2009 (mean: 5.0%), relative to northernmost and southernmost sources (mean: 9.3% and 7.9%, respectively). Some years with a high frequency of missing rings coincide with outbreaks of defoliating insects or dry growing season conditions. The propensity for missing rings synchronized annual variations in growth across all trees and might have complicated the detection of potential differences in interannual variability among seed sources. Average ring width was significantly larger in seed sources from both the southernmost and warmest origins compared to the northernmost and coldest seed sources in most years. Local seed sources had the highest average radial growth. Adaptation to local environmental conditions and disturbances might have influenced the higher growth rate found in local seed sources. These findings underscore the need to understand the integrative impact of multiple environmental drivers, such as disturbance agents and climate change, on tree growth, forest dynamics, and the carbon cycle.

Low-Hanging DendroDynamic Fruits Regarding Disturbance in Temperate, Mesic Forests

Temperate, mesic forests (TMFs) are generally viewed as being in a shifting-mosaic or a kind of dynamic equilibrium at broad spatial scales. Gaining insight to the potential dynamics of TMFs at large-scales is crucial because these species-rich, highly productive forests are important drivers of regional water and carbon cycles for approximately one billion people.