This study presents a summer temperature reconstruction using Scots pine tree-ring chronologies for Scotland allowing the placement of current regional temperature changes in a longer-term context. ...‘Living-tree’ chronologies were extended using ‘subfossil’ samples extracted from nearshore lake sediments resulting in a composite chronology >800 years in length. The North Cairngorms (NCAIRN) reconstruction was developed from a set of composite blue intensity high-pass and ring-width low-pass filtered chronologies with a range of detrending and disturbance correction procedures. Calibration against July–August mean temperature explains 56.4% of the instrumental data variance over 1866–2009 and is well verified. Spatial correlations reveal strong coherence with temperatures over the British Isles, parts of western Europe, southern Scandinavia and northern parts of the Iberian Peninsula. NCAIRN suggests that the recent summer-time warming in Scotland is likely not unique when compared to multi-decadal warm periods observed in the 1300s, 1500s, and 1730s, although trends before the mid-sixteenth century should be interpreted with some caution due to greater uncertainty. Prominent cold periods were identified from the sixteenth century until the early 1800s—agreeing with the so-called Little Ice Age observed in other tree-ring reconstructions from Europe—with the 1690s identified as the coldest decade in the record. The reconstruction shows a significant cooling response 1 year following volcanic eruptions although this result is sensitive to the datasets used to identify such events. In fact, the extreme cold (and warm) years observed in NCAIRN appear more related to internal forcing of the summer North Atlantic Oscillation.
•Radial-growth averaging and absolute-increase had fewer type I and II errors.•Radial-growth averaging require the least a priori data.•Time-series produces information on magnitude and duration of ...release events.•False positives were more common in forests with infrequent and low severity disturbance.•Yearly binning performs better to identify local maxima indicating disturbance.
The retrospective study of abrupt and sustained increases in the radial growth of trees (hereinafter ‘releases’) by tree-ring analysis is an approach widely used for reconstructing past forest disturbances. Despite the range of dendrochronological methods used for release-detection, a lack of in-depth comparison between them can lead researchers to question which method to use and, potentially, increases the uncertainties of disturbance histories derived with different methods.
Here, we investigate the efficacy and sensitivity of four widely used release detection methods using tree-ring width series and complete long-term inventories of forest stands with known disturbances. We used support vector machine (SVM) analysis trained on long-term forest census data to estimate the likelihood that Acer rubrum trees experiencing reductions in competition show releases in their tree-ring widths. We compare methods performance at the tree and stand level, followed by evaluation of method sensitivity to changes in their parameters and settings.
Disturbance detection methods agreed with 60–76% of the SVM-identified growth releases under high canopy disturbance and 80–94% in a forest with canopy disturbance of low severity and frequency. The median competition index change (CIC) of trees identified as being released differed more than two-fold between methods, from −0.33 (radial-growth averaging) to −0.68 (time-series). False positives (type I error) were more common in forests with low severity disturbance, whereas false negatives (type II error) occurred more often in forests with high severity disturbance. Sensitivity analysis indicated that reductions of the detection threshold and the length of the time window significantly increased detected stand-level disturbance severity across all methods.
Radial-growth averaging and absolute-increase methods had lower levels of type I and II error in detecting disturbance events with our datasets. Parameter settings play a key role in the accuracy of reconstructing disturbance history regardless of the method. Time-series and radial-growth averaging methods require the least amount of a priori information, but only the time-series method quantified the subsequent growth increment related to a reduction in competition. Finally, we recommend yearly binning of releases using a kernel density estimation function to identify local maxima indicating disturbance. Kernel density estimation improves reconstructions of forest history and, thus, will further our understanding of past forest dynamics.
Climate and disturbance alter forest dynamics, from individual trees to biomes and from years to millennia, leaving legacies that vary with local, meso and macroscales. Motivated by recent insights ...in temperate forests, we argue that temporal and spatial extents equivalent to that of the underlying drivers are necessary to characterize forest dynamics across scales. We focus specifically on characterizing mesoscale forest dynamics because they bridge fine‐scale (local) processes and the continental scale (macrosystems) in ways that are highly relevant for climate change science and ecosystem management. We revisit ecological concepts related to spatial and temporal scales and discuss approaches to gain a better understanding of climate–forest dynamics across scales.
•We present a new method for detecting past canopy disturbances in tree rings.•Disturbances were reconstructed for forests with known prior events.•Combined step and trend interventions outperformed ...pulse interventions.•This method isolates a disturbance signal, quantifying subsequent growth.•This signal provides broad applications by estimating growth, volume, or carbon.
Time series analysis can identify outliers in tree-ring widths that may not only indicate past disturbances, but may also estimate the subsequent effects of these disturbances on tree growth. Finding a way to isolate these disturbance signals from tree-ring time series could have broad applications in forest ecology and management. Time series outliers may be expressed as pulse, step, or trend interventions, but few dendroecological studies have explored how well these different types of interventions express the response of tree-ring widths to a canopy disturbance resulting in a release event. This study addresses that question by comparing two different time series approaches for detecting release events: a pulse intervention approach and a new combined step and trend (CST) intervention approach. These methods are tested against tree-ring collections with known historical canopy disturbance events: northern red oaks (Quercus rubra) in New York released by the chestnut blight during the early 1920s, eastern hemlocks (Tsuga canadensis) in Pennsylvania released by adjacent selective logging in 1910, and northern red oaks and chestnut oaks (Quercus montana) in West Virginia released through an experimental thinning in 1982. Clusters of CST interventions, but not pulse interventions, were detected for all three collections during and immediately after the known disturbance events, showing that a CST intervention approach consistently reconstructs these release events. In addition, a CST intervention approach isolated canopy disturbance signals from tree-ring widths as disturbance-growth indices. Detrending disturbances from tree-ring widths provides an alternative approach to reconstruct climate in closed-canopy forests; however, just as importantly, disturbance-growth indices created through this method can also reconstruct changes in tree growth rates, biomass, or carbon resulting from a past disturbance event or forest thinning.
ABSTRACT
A detailed understanding of past temporal patterns and spatial expression of temperature variations is important to place recent anthropogenic climate change into a longer term context. In ...order to fill the current gap in our understanding of northwest European temperature variability, point‐by‐point principal component regression was used to reconstruct a spatial field of 0.5° temperature grids across Scotland. A sequence of reconstructions utilizing several combinations of detrending and disturbance correction procedures, and a selection of tree‐ring parameters including ring width (RW), maximum latewood density (MXD) and blue intensity (BI) was used in an evaluation of reconstruction skill. The high resolution of the reconstructed field serves also as a diagnostic tool to spatially assess the temperature reconstruction potential of local chronologies. Best reconstruction results, reaching calibration r2 = 65.8% and verification r2 = 63.7% in central Scotland over the 1901–1976 period, were achieved using disturbance‐corrected and signal‐free detrended RW chronologies merged with BI data after low‐pass (high‐pass) filtering the RW (BI) chronologies. Calibration and verification r2 > 50% was attained for central, north and east Scotland, >40% in west and northwest, and >30% in southern Scotland with verification of nearly all grids showing some reconstruction skill. However, the full calibration potential of reconstructions outside central Scotland was reduced either due to residual disturbance trends undetected by the disturbance correction procedure or due to other climatic or non‐climatic factors which may have adversely affected the strength of the climate signal.
Accurately capturing medium- to low-frequency trends in tree-ring data is vital to assessing climatic response and developing robust reconstructions of past climate. Non-climatic disturbance can ...affect growth trends in tree-ring-width (RW) series and bias climate information obtained from such records. It is important to develop suitable strategies to ensure the development of chronologies that minimize these medium- to low-frequency biases. By performing high density sampling (760 trees) over a ~40-ha natural high-elevation Norway spruce (Picea abies) stand in the Romanian Carpathians, this study assessed the suitability of several sampling strategies for developing chronologies with an optimal climate signal for dendroclimatic purposes. There was a roughly equal probability for chronologies (40 samples each) to express a reasonable (r = 0.3–0.5) to non-existent climate signal. While showing a strong high-frequency response, older/larger trees expressed the weakest overall temperature signal. Although random sampling yielded the most consistent climate signal in all sub-chronologies, the outcome was still sub-optimal. Alternative strategies to optimize the climate signal, including very high replication and principal components analysis, were also unable to minimize this disturbance bias and produce chronologies adequately representing climatic trends, indicating that larger scale disturbances can produce synchronous pervasive disturbance trends that affect a large part of a sampled population. The Curve Intervention Detection (CID) method, used to identify and reduce the influence of disturbance trends in the RW chronologies, considerably improved climate signal representation (from r = 0.28 before correction to r = 0.41 after correction for the full 760 sample chronology over 1909–2009) and represents a potentially important new approach for assessing disturbance impacts on RW chronologies. Blue intensity (BI) also shows promise as a climatically more sensitive variable which, unlike RW, does not appear significantly affected by disturbance. We recommend that studies utilizing RW chronologies to investigate medium- to long-term climatic trends also assess disturbance impact on those series.
Questions: We evaluate the role of past land use on long-term forest succession and ask fundamental questions: (i) are successional patterns along a chronosequence consistent through time; (ii) is ...past land use or physiography a greater driver of forest composition; and (iii) does forest composition converge with age? Location: Thomas Jefferson's Monticello plantation, Virginia Piedmont, USA. Methods: Combining dendroecology, historical documents and a repeated vegetation survey from 1934, we reconstruct forest histories along a chronosequence that retains a temporal dimension. Tree-ring data indicate initial canopy status and canopy release events using time series analysis with intervention detection. Results: Forest extent was lowest during Jefferson's tenure; however, tree ring and documentary evidence revealed the location of Jefferson's timber zone. Jefferson-era trees in this zone are largely on the west slope with scattered Pinus recruitment starting in the late 18th century, followed by Quercus species. Pinus cohorts also recruited into former agricultural fields on south and east slopes in two chronosequence stages from the 20th century. Synchronized release events were observed during the early 1800s, 1850s-1860s and 1960s, indicating periods of intense forest use. Ordination of repeated vegetation surveys showed a progression in forest age that explained more variation in forest composition than elevation and slope. The forest age gradient is also evident independently from tree-ring data, but the ordination does not show convergence in composition with forest age. Conclusion: Past land use is a greater driver of forest composition than an inferred soil moisture gradient. The composition of the most recent chronosequence stage suggests that future forest dynamics may be novel compared to the prior two centuries because of differences in land use and species availability. These land-use legacies demonstrate how colonial-era agricultural decisions at Monticello continue to impact forest growth and composition more than two centuries later.
Landscape-scale alterations that accompany urbanization may negatively affect the population structure of wildlife species such as freshwater turtles. Changes to nesting sites and higher mortality ...rates due to vehicular collisions and increased predator populations may particularly affect immature turtles and mature female turtles. We hypothesized that the proportions of adult female and immature turtles in a population will negatively correlate with landscape urbanization. As a collaborative effort of the Ecological Research as Education Network (EREN), we sampled freshwater turtle populations in 11 states across the central and eastern United States. Contrary to expectations, we found a significant positive relationship between proportions of mature female painted turtles (Chrysemys picta) and urbanization. We did not detect a relationship between urbanization and proportions of immature turtles. Urbanization may alter the thermal environment of nesting sites such that more females are produced as urbanization increases. Our approach of creating a collaborative network of scientists and students at undergraduate institutions proved valuable in terms of testing our hypothesis over a large spatial scale while also allowing students to gain hands-on experience in conservation science. Las alteraciones a escala de paisaje que acompañan a la urbanización pueden afectar negativamente a la estructura poblacional de las especies silvestres como las tortugas de agua dulce. Los cambios en los sitios de anidación y las altas tasas de mortalidad causados por colisiones con vehículos y el incremento poblacional de depredadores pueden afectar particularmente a las tortugas inmaduras y a las tortugas hembras maduras. Supusimos que las proporciones de hembras adultas y de tortugas inmaduras en una población se correlacionan negativamente con la urbanización del paisaje. Como un esfuerzo colaborativo de la Investigación Ecológica como Red Educativa (EREN, en inglés) muestreamos las poblaciones de tortuga de agua dulce en once estados del centro y el este de los Estados Unidos. Contrario a lo esperado, encontramos una relación positiva significativa entre las proporciones de hembras maduras de Chrysemys picta y la urbanización. No detectamos una relación entre la urbanización y la proporción de tortugas inmaduras. La urbanización puede alterar el ambiente térmico de los sitios de anidación de tal forma que se producen más hembras conforme incrementa la urbanización. Nuestra estrategia de crear una red colaborativa de científicos y estudiantes en instituciones universitarias resultó ser valiosa para probar nuestra hipótesis a lo largo de una gran escala espacial mientras permitió también que los estudiantes ganaran experiencia de primera mano en la ciencia de conservación.
The detection of release events in the annual growth increments of trees has become a central and widely applied method for reconstructing the disturbance history of forests. While numerous ...approaches have been developed for identifying release events, the preponderance of these methods relies on running means that compare the percent change in growth rates. These methods do not explicitly account for the autocorrelation present within tree-ring width measurements and may introduce spurious events. This paper utilizes autoregressive integrated moving-average (ARIMA) processes to model tree-ring time series and incorporates intervention detection to identify pulse and step outliers as well as changes in trends indicative of a deterministic exogenous influence on past growth. This approach is evaluated by applying it to three chronologies from the Forest Responses to Anthropogenic Stress (FORAST) project that were impacted by prior disturbance events. The examples include a hemlock (Tsuga canadensis (L.) Carriere) chronology from New Hampshire, a white pine (Pinus strobus L.) chronology from Pennsylvania, and an American beech (Fagus grandifolia Ehrh.) chronology from Virginia. All three chronologies exhibit a clustering of step, pulse, and trend interventions subsequent to a known or likely disturbance event. Time-series analysis offers an alternative approach for identifying prior forest disturbances via tree rings based on statistical methods applicable across species and disturbance regimes.
Acid deposition is a major biogeochemical driver in forest ecosystems, but the impacts of long‐term changes in deposition on forest productivity remain unclear. Using a combination of tree ring and ...forest inventory data, we examined tree growth and climate sensitivity in response to 26 years of whole‐watershed ammonium sulfate ((NH4)2SO4) additions at the Fernow Experimental Forest (West Virginia, USA). Linear mixed effects models revealed species‐specific responses to both treatment and hydroclimate variables. When controlling for environmental covariates, growth of northern red oak (Quercus rubra), red maple (Acer rubrum), and tulip poplar (Liriodendron tulipifera) was greater (40%, 52%, and 42%, respectively) in the control watershed compared to the treated watershed, but there was no difference in black cherry (Prunus serotina). Stem growth was generally positively associated with growing season water availability and spring temperature and negatively associated with vapor pressure deficit. Sensitivity of northern red oak, red maple, and tulip poplar growth to water availability was greater in the control watershed, suggesting that acidification treatment has altered tree response to climate. Results indicate that chronic acid deposition may reduce both forest growth and climate sensitivity, with potentially significant implications for forest carbon and water cycling in deposition‐affected regions.
Plain Language Summary
While acidifying nitrogen and sulfur pollution has substantially declined in the eastern United States due to the Clean Air Act and its amendments, the legacy of acidification on forest ecosystems is projected to be long‐lasting. However, it is often difficult to discern the effects of air pollution on forests without controlled experiments, since changes in pollution have occurred alongside other long‐term environmental changes (e.g., climate change and rising atmospheric CO2 concentrations). At the Fernow Experimental Forest in West Virginia, we examined the growth and climate sensitivity of trees in a watershed that has received 26 years of experimental acidification treatments to trees in an adjacent control watershed. Trees responded to treatment in species‐specific ways, but growth of three of four examined hardwood species was greater in the control watershed. Also, trees in the acidified watershed were less sensitive to interannual variation in water availability, suggesting that forests that have experienced high levels of acid deposition respond differently to precipitation than forests that have been less impacted. However, given that trees respond to acid deposition in species‐specific ways, the impacts on changes in air pollution on forests will largely depend on the species composition in a given region.
Key Points
Experimental whole‐watershed acidification treatments reduced covariate‐adjusted tree growth in three of four hardwood species examined
For most species, tree growth responded positively to growing season water availability and spring temperatures and negatively to vapor pressure deficit
Trees in the treated catchment were less sensitive to interannual variation in water availability than those in the control catchment
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