Bryan A. Black

Local Stressors Reduce Coral Resilience to Bleaching

Coral bleaching, during which corals lose their symbiotic dinoflagellates, typically corresponds with periods of intense heat stress, and appears to be increasing in frequency and geographic extent as the climate warms. A fundamental question in coral reef ecology is whether chronic local stress reduces coral resistance and resilience from episodic stress such as bleaching, or alternatively promotes acclimatization, potentially increasing resistance and resilience. Here we show that following a major bleaching event, Montastraea faveolata coral growth rates at sites with higher local anthropogenic stressors remained suppressed for at least 8 years, while coral growth rates at sites with lower stress recovered in 2–3 years. Instead of promoting acclimatization, our data indicate that background stress reduces coral fitness and resilience to episodic events. We also suggest that reducing chronic stress through local coral reef management efforts may increase coral resilience to global climate change.

USE OF BOUNDARY-LINE GROWTH PATTERNS AS A BASIS FOR DENDROECOLOGICAL RELEASE CRITERIA

Identifying releases from suppression represents one of the most fundamental dendroecological procedures for quantifying forest disturbance histories. In tree-ring series, releases are typically defined as pulses in percent growth change that exceed a minimum threshold. Past methodologies have applied fixed growth-change thresholds that may overly generalize the ability of a tree to respond to a disturbance event. In this study, we develop a more precise method that scales each release by its maximum release potential as defined by prior growth rates, using an old growth hemlock (Tsuga canadensisL.) forest in central Pennsylvania as an example. On average, tree age, diameter, and crown class appear to influence the magnitude of release response. However, differences in release response be- tween age, diameter, and crown classes are largely an artifact of the more fundamental relationship between release response and growth immediately prior to release. Specifically, maximum percent growth change declines at a steep, negative exponential rate as prior growth levels increase. Slow-growing hemlocks can exceed 800% growth increases while fast-growing hemlocks do not exceed growth increases of 20%. This negative exponential threshold, or boundary line, represents the maximum percent growth change that is phys- iologically possible at a given level of prior growth. Thus, release potential is relative to prior growth rate. This relationship between prior growth and release potential is species specific and is demonstrated in 24 additional hemlock stands. We propose new criteria based on prior growth in which moderate and major releases are those falling within 20- 49.9%, and 50-100% of the boundary line, respectively. Effects of short, moderate, and long-term climate events are mitigated by the percent-growth-change calculation and the high growth-change threshold applied to slow-growing trees. In addition, we demonstrate that similar boundary lines occur in Pinus strobusL and Quercus prinusL., and interspecific variations in boundary line configuration reflect differences in understory tolerance. Overall, this approach provides a more theoretically sound and flexible approach to developing disturbance histories, and we believe it will ultimately have broad applications in a variety of forest types.

Establishing highly accurate production-age data using the tree-ring technique of crossdating: a case study for Pacific geoduck (Panopea abrupta)

We apply the tree-ring technique of crossdating to generate highly accurate age data and evaluate error in annual growth increment (annual growth zone) counts for long-lived Pacific geoduck (Panope...

Constructing long-term proxy series for aquatic environments with absolute dating control using a sclerochronological approach: introduction and advanced applications

The possibility of applying absolute dating techniques to annual growth increments from the hard parts of aquatic animals was examined. This was done using the theory of cross-dating, which was adopted from dendrochronological principles. Using two mollusc species as examples, the practical issues of the method were demonstrated. Empirical data were used to evaluate the different time series analysis techniques as follows. Biological growth trends were first captured from original time series using cubic splines. Dimensionless growth indices were obtained by extracting the observed growth values from the values of spline curves as ratios. The common growth signal among the index series was quantified visually and statistically. In statistical analysis, correlations between all possible pairs of indexed sample series and, alternatively, between sample series and master chronology (the average of all other remaining time series) were calculated. It was demonstrated that sample–master correlations were consistently higher than sample–sample correlations. Sclerochronologically cross-dated time series were proved to provide absolute dating of high-resolution proxy records that assessed environmental change in marine and freshwater settings. The wider applicability of the associated techniques is discussed, and it is suggested that use of the term ‘sclerochronology’ be restricted to refer only to material or studies for which careful cross-dating has been successfully applied.

The value of crossdating to retain high-frequency variability, climate signals, and extreme events in environmental proxies

High-resolution biogenic and geologic proxies in which one increment or layer is formed per year are crucial to describing natural ranges of environmental variability in Earths physical and biological systems. However, dating controls are necessary to ensure temporal precision and accuracy; simple counts cannot ensure that all layers are placed correctly in time. Originally developed for tree-ring data, crossdating is the only such procedure that ensures all increments have been assigned the correct calendar year of formation. Here, we use growth-increment data from two tree species, two marine bivalve species, and a marine fish species to illustrate sensitivity of environmental signals to modest dating error rates. When falsely added or missed increments are induced at one and five percent rates, errors propagate back through time and eliminate high-frequency variability, climate signals, and evidence of extreme events while incorrectly dating and distorting major disturbances or other low-frequency processes. Our consecutive Monte Carlo experiments show that inaccuracies begin to accumulate in as little as two decades and can remove all but decadal-scale processes after as little as two centuries. Real-world scenarios may have even greater consequence in the absence of crossdating. Given this sensitivity to signal loss, the fundamental tenets of crossdating must be applied to fully resolve environmental signals, a point we underscore as the frontiers of growth-increment analysis continue to expand into tropical, freshwater, and marine environments.

Disturbance history and climate response in an old-growth hemlock-white pine forest, central Pennsylvania

Abstract Bryan A. Black and Marc D. Abrams (203 Forest Resources Laboratory, University Park, PA 16802). Disturbance history and climate response in an old growth hemlock forest, central Pennsylvania. J. Torrey Bot. Soc. 132: 103–114. 2005.—Radial growth patterns are examined in relation to the historical development, disturbance history, and climate responses of an old-growth hemlock forest located in central Pennsylvania. Hemlock recruited continuously from the mid 1700s through 1890 with a sharp pulse of regeneration between 1860 and 1870, while white pine formed an even-aged cohort in a narrow interval between 1865 and 1870. No recruitment of any species occurred in the 20th century, likely because of deer browsing. Isolated pulses in radial growth occurred in almost every decade of the chronology, indicating a high frequency of small-scale disturbances. Major stand-wide pulses in hemlock radial growth occurred around 1810 and 1850. The 1850 event corresponds with the date of two intense windstorms and was the only disturbance event large enough to recruit white pine. Long-term effects of climate were apparent in the 20th century in which periods of low radial growth occurred in the cool, dry periods of 1910–1930 and 1965–1970. Correlations and response function analysis revealed that hemlock radial growth was limited by drought in winter and early fall, and by low March temperatures.

Spatial variability in growth-increment chronologies of long-lived freshwater mussels: implications for climate impacts and reconstructions.

Abstract: Estimates of historical variability in river ecosystems are often lacking, but long-lived freshwater mussels could provide unique opportunities to understand past conditions in these environments. We applied dendrochronology techniques to quantify historical variability in growth-increment widths in valves (shells) of western pearlshell freshwater mussels (Margaritifera falcata). A total of 3 growth-increment chronologies, spanning 19 to 26 y in length, were developed. Growth was highly synchronous among individuals within each site, and to a lesser extent, chronologies were synchronous among sites. All 3 chronologies negatively related to instrumental records of stream discharge, while correlations with measures of water temperature were consistently positive but weaker. A reconstruction of stream discharge was performed using linear regressions based on a mussel growth chronology and the regional Palmer Drought Severity Index (PDSI). Models based on mussel growth and PDSI yielded similar coefficients of prediction (R2Pred) of 0.73 and 0.77, respectively, for predicting out-ofsample observations. From an ecological perspective, we found that mussel chronologies provided a rich source of information for understanding climate impacts. Responses of mussels to changes in climate and stream ecosystems can be very site- and process-specific, underscoring the complex nature of biotic responses to climate change and the need to understand both regional and local processes in projecting climate impacts on freshwater species.

Otolith oxygen isotopes measured by high‐precision secondary ion mass spectrometry reflect life history of a yellowfin sole (Limanda aspera)

RATIONALE The oxygen isotope ratio (δ(18)O value) of aragonite fish otoliths is dependent on the temperature and the δ(18)O value of the ambient water and can thus reflect the environmental history of a fish. Secondary ion mass spectrometry (SIMS) offers a spatial-resolution advantage over conventional acid-digestion techniques for stable isotope analysis of otoliths, especially given their compact nature. METHODS High-precision otolith δ(18)O analysis was conducted with an IMS-1280 ion microprobe to investigate the life history of a yellowfin sole (Limanda aspera), a Bering Sea species known to migrate ontogenetically. The otolith was cut transversely through its core and one half was roasted to eliminate organic contaminants. Values of δ(18)O were measured in 10-µm spots along three transects (two in the roasted half, one in the unroasted half) from the core toward the edge. Otolith annual growth zones were dated using the dendrochronology technique of crossdating. RESULTS Measured values of δ(18)O ranged from 29.0 to 34.1‰ (relative to Vienna Standard Mean Ocean Water). Ontogenetic migration from shallow to deeper waters was reflected in generally increasing δ(18)O values from age-0 to approximately age-7 and subsequent stabilization after the expected onset of maturity at age-7. Cyclical variations of δ(18)O values within juvenile otolith growth zones, up to 3.9‰ in magnitude, were caused by a combination of seasonal changes in the temperature and the δ(18)O value of the ambient water. CONCLUSIONS The ion microprobe produced a high-precision and high-resolution record of the relative environmental conditions experienced by a yellowfin sole that was consistent with population-level studies of ontogeny. Furthermore, this study represents the first time that crossdating has been used to ensure the dating accuracy of δ(18)O measurements in otoliths.

Integrated Assessment of Wind Effects on Central California’s Pelagic Ecosystem

Ecosystem-based management requires integrated physical studies on biological functions. In this study, we hypothesized that seasonal variation in upwelling-favorable winds has differential influences on species of the central California Current pelagic ecosystem. To test this hypothesis, we developed multivariate indicators of upwelling and species’ responses using wind and sea surface temperature (SST) data from buoys and growth and reproductive data for 11 species of fish and seabirds. From previous work, we predicted that winds and SST could be decomposed into winter and spring/summer ‘modes’ of variability, but only a single mode of “winter/spring” environmental variability was observed. We attribute this difference from expectations to the local and shorter-term measurements of winds and SST used in this study. Most species responded to winds and SST variability similarly, but SST was a better predictor of most biological responses. Both SST and wind were better predictors than the traditional upwelling index. Notably, Pacific sardine (Sardinops sajax) was disassociated with the other biotic measurements and showed no relationships with coastal upwelling. The multivariate indicators developed here are particularly appropriate for integrated ecosystem assessments of climatic influences on marine life because they reflect both structure and processes (upwelling and timing/growth/productivity) known to determine functions in marine ecosystems.

Properties of boundary-line release criteria in North American tree species.

Abstract• Boundary line release criteria are increasingly applied to evaluate forest disturbance histories from tree-ring data. However, a number of important properties central to the technique have not been evaluated, including: (i) the ability of boundary line release criteria to standardize releases across various sites, species, and tree life stages (ii) the minimum sample sizes necessary for developing boundary lines, and (iii) the degree to which the criteria can resolve the degree of crown exposure following a disturbance event.• In an analysis of eleven North American tree species, boundary line release criteria do not fully compensate for declines in release response a tree experiences with increasing age and size, with the exception Tsuga canadensis.• A bootstrapping analysis indicates that approximately 50 000 ring width measurements are necessary to develop boundary line release criteria for a given species.• In a Quercus prinus stand, boundary line release criteria better predict the degree of crown exposure following a disturbance than an earlier running mean technique.• Despite certain limitations, boundary line release criteria have the potential to standardize release calculation across most life stages of a tree, and possibly among sites and species.Résumé• Les lignes limites de dégagement sont des critères de plus en plus appliqués pour évaluer l’historique des perturbation des forêts à partir des données des cernes des arbres. Toutefois, un certain nombre de propriétés importantes au cœur de la technique n’ont pas été évaluées, y compris : (i) la capacité du critère de la ligne limite de dégagement pour standardiser les dégagements à travers différents sites, espèces et stades de la vie des arbres, (ii) la taille minimale des échantillons nécessaires pour le développement de lignes limites, et (iii) le degré avec lequel les critères peuvent résoudre le degré d’exposition de la couronne suite à un événement perturbant.• Dans une analyse de onze espèces d’arbres d’Amérique du Nord, les critères de ligne limite ne compensent pas entièrement la baisse de réponse au dégagement d’un arbre en relation avec l’âge et la dimension, à l’exception Tsuga canadensis.• Une analyse bootstrap indique que près de 50 000 mesures de largeur sont nécessaires pour développer des critères de ligne limite de dégagement pour une espèce donnée.• Dans un peuplement de Quercus prinus, les critères de ligne limite de dégagement permettent de mieux prédire le degré d’exposition de la couronne à la suite d’une perturbation que la technique de la moyenne courante.• En dépit de certaines limitations, les critères de ligne de limite de dégagement ont le potentiel de standardiser les calculs de dégagement dans la plupart des étapes de la vie d’un arbre et, éventuellement, entre les sites et les espèces.