Rapid Early Growth Rates Research Articles

Integration of dendrochronological and palaeoecological disturbance reconstructions in temperate mountain forests

Disentangling the long-term changes in forest disturbance dynamics provides a basis for predicting the forest responses to changing environmental conditions. The combination of multidisciplinary records can offer more robust reconstructions of past forest disturbance dynamics. Here we link disturbance histories of the central European mountain spruce forest obtained from dendrochronological and palaeoecological records (fossil pollen, sedimentary charcoal, bark beetle remains and geochemistry) using a small glacial lake and the surrounding forest in the Šumava National Park (Czech Republic). Dendrochronological reconstructions of disturbance were created for 300-year-long records from 6 study plots with a minimum of 35 trees analyzed for the abrupt growth increases (releases) and rapid early growth rates, both indicative of disturbance events. High-resolution analysis of lake sediments were used to reconstruct 800-year long changes in forest composition and landscape openness (fossil pollen), past fire events (micro- and macroscopic charcoal), bark beetle occurrence (fossil bark beetle remains), and erosion episodes (geochemical signals in the sediment) potentially resulting from disturbance events.Tree-ring data indicate that disturbances occurred regularly through the last three centuries and identify a most intensive period of disturbances between 1780 and 1830 CE. Geochemical erosion markers (e.g. K, Zr, % inorganic) show greater flux of catchment sediment and soils in the periods 1250–1400 and 1450–1500 CE, before a substantial shift to a more erosive regime 1600–1850 and 1900 CE onwards. Pollen records demonstrate relatively small changes in forest composition during the last 800 years until the beginning of the 20th century, when there was decrease in Picea. Fossil bark beetle remains indicate continuous presence of bark beetles from 1620s to 1800s, and charcoal records suggest that more frequent fires occurred during the 18th century. Each of the dendrochronological, palaeoecological and sedimentological records provide a unique perspective on forest disturbance dynamics, and combined offer a more robust and complete record of disturbance history. We demonstrate that sedimentary proxies originating from the lake catchment mirror the forest disturbance dynamics recorded in the tree-rings. The multidisciplinary records likely record forest disturbances at different spatial and temporal scales revealing different disturbance characteristics. Integrating these multidisciplinary datasets demonstrates a promising way to obtain more complete understanding of long-term disturbance dynamics. However, integrating datasets with variable spatial and temporal influence remains challenging. Our results indicated that multiple disturbance factors, such as windstorms, bark beetle outbeaks and fires, may occur simultaneously creating a complex disturbance regime in mountain forests, which should be considered in forest management and conservation strategies.

Disturbance history of an old-growth subalpine larch forest in the Qinling Mountains, north-central China

Knowledge on how historical disturbances shaped the long-term development of forests is essential for understanding the present forest structure and for predicting the future forest ecosystem dynamics. In this study, dendroecological methods were used to reconstruct the disturbance history of an old-growth subalpine larch (Larix chinensis) forest in the Qinling Mountains of north-central China. Growth patterns of 690 and 582 increment cores extracted respectively from two climatically and topographically different larch stands in the northern and southern slope of the Qinling Mountains were examined for abrupt increases in radial growth indicating formation of past canopy gaps and for rapid early growth rates indicating recruitment in former canopy gaps. The findings demonstrated that there were no large-scale, stand-replacing disturbances during the past more than two centuries. Low- and medium-severity disturbance events predominated, which were probably caused by windthrows due to strong winds. The stand was unevenly aged, and the recruitment pulses associated with disturbance peaks could be distinguished. There were considerable spatio-temporal differences in disturbance dynamics of the subalpine larch stand between the topographically and climatically different sites, manifesting that the larch stand in the northern slope experienced frequent moderate but rare major disturbance events, contrasting with frequent major and moderate disturbance events in the southern slope. This study provided strong evidences that there were substantial variations in the intensity and frequency of disturbance dynamics, leading to considerable differences in the size and age structures of the subalpine larch forest.

Weed Suppression and Tolerance in Winter Oats

A crops ability to both suppress weed growth and tolerate weed competition is a key consideration when taking an agroecological approach to weed management. Amongst other cereals, oats are widely considered to have superior weed competitiveness yet studies examining competitive ability of oat varieties are rare. We investigated the ability of oats to suppress weeds and yield in the presence of competition from weeds in trials involving five husked and three naked oat varieties at an organic site in the east of England over four trial years (2009-13). We identified a number of key traits that were important for weed suppression including establishment rate, tillering ability, and early leaf area index (LAI) which highlight the importance of rapid early growth rate. Furthermore, taller varieties tended to be more weed tolerant but not necessarily more suppressive. Trade-offs between competitive traits and yield were not found in this study. Crop tillering ability was highlighted as an important trait for selection due to its beneficial effects on weed suppression as well as grain yield and also its high heritability.

Incubation temperature and clutch effects on initial body sizes and growth rates in green iguana hatchlings (Iguana iguana)

Large initial body size and rapid early growth rate are important in many species, both because predation rates decline as individuals grow and because females that attain a larger adult body size are more fecund. To identify possible factors contributing to size and growth rate variation in hatchling green iguanas, we artificially incubated six clutches at three constant temperatures to test for effects of incubation temperature and/or clutch effects on initial size and growth rate. Higher incubation temperatures resulted in significantly shorter incubation periods but did not influence initial body size. There were significant differences among clutches in egg size, and also in initial hatchling body size, even after correcting for differences in egg size among clutches. A subset of hatchlings from each nest was reared in semi-natural conditions for four months, with individuals from the high incubation temperature condition exhibiting the slowest longer-term growth rates. No clutch effects were detected in the growth rate analyses. The observed variation in early growth rate of juvenile iguanas seems to be selectively important and this variation may be due in part to the conditions the eggs experience during incubation, but clutch effects in this study were limited to egg size and initial hatchling body size variation, but were not found for subsequent growth rates.

Frequent severe natural disturbances and non-equilibrium landscape dynamics shaped the mountain spruce forest in central Europe

Disturbances shape forest structure and composition, but the temporal dynamics of disturbance patterns, their influence on dynamics of forest structural complexity, and the potential impacts of ongoing climate changes are not fully understood. We addressed these issues by focusing on (1) long-term, landscape level retrospective analysis of disturbance dynamics of mountain Norway spruce (Picea abies) forest; (2) testing for the prevailing disturbance agent; and (3) the detection of disturbance drivers, particularly site conditions, using a dendrochronological approach.We had a unique opportunity to sample a large area of natural forest (in otherwise altered region) in Bohemian Forest, that was recently affected by extensive and severe wind and bark beetle disturbances raising management concerns. Tree-ring series of a minimum of 35 trees on each of the 26 study plots were analysed for signals of past disturbances that were indicated either by release from suppression (rapid growth increase) or rapid early growth rate (gap origin).A broad range of disturbance severities were detected across the landscape, but severe disturbances (>50% trees responded), with a short rotation period of 174years, best characterize the area. Reconstructed disturbances were associated with historically documented windstorms and bark beetle outbreaks. They were distributed across the landscape and affected its large portions with spatially variable severity. Over the last five centuries, disturbances peaked in the 1820s, but were rare after 1880. This non-equilibrium dynamics resulted into mature landscape structure at the end of 20th century and contributed to the large extent of disturbances in the last two decades. Disturbances were more frequent on wind-exposed locations such as mountain ridges and flatter terrain.Frequent disturbances did not allow the forest to develop into an old-growth phase; rather disturbance events of variable severities created structures important for biodiversity and could also preserve key early-seral phases in the landscape. We anticipate that potential future increase of disturbance intensities will not lead to comparable regime shifts in forests shaped by high-severity disturbances that kill largely mature trees (e.g., wind and bark beetle), because such disturbances are followed by resistant forest structure. Conservation areas should be large enough to allow for a wide range of disturbances. Emphasizing ecological functions needs understanding of biological legacies of natural disturbances and managers could partly rely on natural events to restore natural features into cultivated forests.

Landscape‐level variability in historical disturbance in primary Picea abies mountain forests of the Eastern Carpathians, Romania

AbstractQuestionsHow have the historical frequency and severity of natural disturbances in primary Picea abies forests varied at the forest stand and landscape level during recent centuries? Is there a relationship between physiographic attributes and historical patterns of disturbance severity in this system?LocationPrimary P. abies forests of the Eastern Carpathian Mountains, Romania; a region thought to hold the largest concentration of primary P. abies forests in Europe's temperate zone.MethodsWe used dendrochronological methods applied to many plots over a large area (132 plots representing six stands in two landscapes), thereby providing information at both stand and landscape levels. Evidence of past canopy disturbance was derived from two patterns of radial growth: (1) abrupt, sustained increases in growth (releases) and (2) rapid early growth rates (gap recruitment). These methods were augmented with non‐metric multidimensional scaling to facilitate the interpretation of factors influencing past disturbance.ResultsOf the two growth pattern criteria used to assess past disturbance, gap recruitment was the most common, representing 80% of disturbance evidence overall. Disturbance severities varied over the landscape, including stand‐replacing events, as well as low‐ and intermediate‐severity disturbances. More than half of the study plots experienced extreme‐severity disturbances at the plot level, although they were not always synchronized across stands and landscapes. Plots indicating high‐severity disturbances were often spatially clustered (indicating disturbances up to 20 ha), while this tendency was less clear for low‐ and moderate‐severity disturbances. Physiographic attributes such as altitude and land form were only weakly correlated with disturbance severity. Historical documents suggest windstorms as the primary disturbance agent, while the role of bark beetles (Ips typographus) remains unclear.ConclusionsThe historical disturbance regime revealed in this multi‐scale study is characterized by considerable spatial and temporal heterogeneity, which could be seen among plots within stands, among stands within landscapes and between the two landscapes. When the disturbance regime was evaluated at these larger scales, the entire range of disturbance severity was revealed within this landscape.

Dendrochronological reconstruction of the disturbance history and past development of the mountain Norway spruce in the Bohemian Forest, central Europe

Disturbances play a major role in shaping forest structure and composition. However, the effects of disturbances on forest ecosystems in central Europe are poorly understood, despite the importance of this information for forest management (e.g., for managing recent, large-scale, high-severity disturbances in the region). Using the tree-ring approach, this work investigates the past development, disturbance history and historical range of variability of the old mountain Norway spruce (Picea abies) forest stand in the high elevation Bohemian Forest (Protected Landscape Area Šumava) in the Czech Republic.The goals of the study were threefold: (1) to reconstruct the historical disturbances of the forest, (2) to describe the recruitment strategy of trees in response to disturbance, and (3) to describe the subsequent development of trees by their growth trends.We cored all stems within three 0.25ha plots. The growth series were surveyed for events indicative of past tree mortality: (1) abrupt, sustained and rapid increases in growth (releases from suppression) and (2) rapid early growth rates (gap origins). We then conducted a cluster analysis of individual growth trends by fitting splines to the power-transformed and age-filtered (RCS-method) tree ring series.High-severity disturbances were identified in the 1820s and 1860s. Less severe disturbances also occurred every 10–50years. The disturbances were synchronised among plots and consistent with data from distant locations in the Bohemian Forest. Most disturbances were explained by known historical windstorms; some by bark beetle outbreaks. Most trees regenerated shortly before or after disturbance and exhibited evidence of 1–3 disturbance events in their growth chronologies. A smaller proportion of trees was suppressed before disturbance for more than 10years. The cluster analysis of growth trends revealed five types of tree behaviour classified according to their growth rate during (1) stand initiation and (2) later development.We conclude that disturbances (including large, high-severity and low-frequency disturbances) contribute to the broad range of variability of central European mountain spruce forests. Sustainable management strategies should therefore incorporate described disturbances and their biological legacies, as many species likely depend on them. In addition, the development trajectory of stands following stand-replacing disturbance, as described here, can be used to predict future development of presently disturbed stands.

Disturbance history of an old‐growth sub‐alpine Picea abies stand in the Bohemian Forest, Czech Republic

AbstractQuestionsWhat historical natural disturbances have shaped the structure and development of an old‐growth, sub‐alpine Picea abies forest? Are large‐scale, high‐severity disturbances (similar to the recent windthrow and bark beetle outbreaks in the region) within the historical range of variability for this forest ecosystem? Can past disturbances explain the previously described gradient in stand structure that had been attributed to an elevation gradient?LocationŠumava National Park (the Bohemian Forest) of the southwest Czech Republic.MethodsWe reconstructed the site's disturbance history using dendroecological methods in a 20‐ha study plot, established to span an elevation gradient. Growth patterns of 400 increment cores were screened for: (1) abrupt increases in radial growth indicating mortality of a former canopy tree and (2) rapid early growth rates indicating establishment in a former canopy gap.ResultsSpatial and temporal patterns of canopy accession varied markedly over the 20‐ha study area, resulting in disturbance pulses that corresponded to an elevation gradient. On the lower slope of the plot, the majority of the trees reached the canopy during two pulses (1770–1800 and 1820–1840), while most trees on the upper slope accessed the canopy in one pulse (1840–1860). Historically documented windstorms roughly coincide with peaks in our disturbance reconstruction.ConclusionsOur study provides strong evidence that these forests were historically shaped by infrequent, moderate‐ to high‐severity natural disturbances. Our methods, however, could not definitively identify the agent(s) of these disturbances. Nevertheless, the recent mid‐1990s windstorm and the ensuing spruce bark beetle outbreak may provide an analogue for past disturbance, as the duration and severity of these events could easily explain past patterns of growth response and recruitment in our results. Thus, it seems reasonable to assume the interaction of windstorms and bark beetles seen in the contemporary landscape has occurred historically. Finally, our results suggest that the previously documented elevation gradient in forest structure may not be related to elevation per se (lower temperatures and shorter growing season) but rather to changes in disturbance severity mediated by elevation.

Transpiration along an age series of Eucalyptus globulus plantations in southeastern Australia

Many of the world's Eucalyptus plantations are grown on short rotations of 15 years or less, which often covers the most rapid phase of stand development and peaks in growth rates and leaf areas. Since transpiration is related to stand leaf area these short rotations that make use of rapid early growth rates, may also maximise plantation water use, which has implications for predicting their water requirements and impacts on catchment hydrology. This study examined the transpiration, leaf area and growth rates of Eucalyptus globulus Labill. plantations aged 2–8 years. Transpiration ( E), estimated using the heat pulse technique, increased from 0.4 mm day −1 at age 2 years to a peak of about 1.6–1.9 mm day −1 in stands aged 5–7 years. This was associated with similar trends for stand leaf area index (LAI) and periodic annual increments of aboveground biomass, which both peaked at about age 4–6 years resulting in a linear relationship between E and LAI. While stand sapwood areas were continuing to increase at age 8 years, E was already declining due to reductions in sap velocity, from 13.5 cm h −1 at age 2 years to 6.3 cm h −1 at age 8 years and reduced sapwood area growth rates. Trees compensated for this reduction in sap velocity with declines in the leaf area ( A L) to sapwood area ( A S) relationship ( A L :A S) with age. There was also a reduction in growth efficiency (aboveground biomass increment per LAI) with age. However, reductions in WUE were small after age 4 years, which explained the linear relationship between E and LAI. If E continues to decline successive short rotation lengths may not only make use of rapid early growth rates but could also increase plantation water use compared to longer rotations over the same period of time.

Metabolic Disorders: Limitations to Growth of and Mineral Deposition into the Broiler Skeleton after Hatch and Potential Implications for Leg Problems

Metabolic diseases are associated with a rapid early growth rate in poultry, especially in broilers, and their incidence can be decreased by slowing early growth. Leg problems seen in the absence of infectious agents are often the result of fast early growth and thus can be related to metabolic diseases. At hatch, the broiler skeleton is poorly mineralized; growth and mineralization occur most rapidly in the first 2 wk of life. Except for Ca, the embryo has limited access to minerals. Most minerals in the egg cannot be influenced by maternal diet, but embryo mineral uptake can be improved by dietary mineral source selection. The use of management tools to reduce metabolic diseases that rely primarily on decreasing feed consumption, without increasing prestarter mineral density, may have negative unintended consequences on skeletal development. Incidence of losses due to leg problems during growout and processing have decreased since the early 1990s, in part due to breeding programs, but not enough information is available to estimate the proportion of losses related to metabolic diseases. This information is needed if improvements are to be made.

Influences of Freshwater and Marine Growth on the Egg Size–Egg Number Tradeoff in Coho and Chinook Salmon

How to partition a finite amount of energy into progeny is an important issue in evolutionary biology. Salmonids produce a small number of large eggs compared with other teleost fishes, and there are positive correlations between female size and both the size and number of eggs produced. We examined the temporal variation in reproductive investment (gonad mass, fecundity, and egg size) of coho salmon Oncorhynchus kisutch and Chinook salmon O. tshawytscha at the University of Washington hatchery over the last three to five decades. During this period, fish growth rates in freshwater and at sea varied greatly, allowing us to test the hypotheses that rapid early growth rate results in high fecundity and that hatchery populations evolve high fecundity over time. In the coho salmon, reductions in length, condition factor, and size-adjusted fecundity over the past decades combined to reduce overall average fecundity to only about half its former level. In Chinook salmon, age at maturity decreased as smolt size increased, so average size decreased over time but size at a given age did not decline. Reproductive investment (gonad size, corrected for body size) decreased for the coho salmon but not for the Chinook salmon. Egg size (adjusted for variation in fish size) did not vary with growth rate for either species or environment. Size-adjusted fecundity did not increase with increasing freshwater growth for either species, but it did increase with marine growth for the coho and age-3 Chinook salmon. These results contradict the prediction that females adjust egg size depending on the perceived quality of the juvenile habitat. Egg size is probably determined much later in life, corresponding to the number of remaining eggs and the energetic constraints at maturity. The results are also inconsistent with the hypothesis that hatchery populations will evolve small eggs and high fecundity as a result of a relaxed selection for large fry.

The influence of drought on red oak group species growth and mortality in the Missouri Ozarks

The effects of drought on growth of red oak group species were studied by examining basal area increment and ring width index patterns of dominant Quercuscoccinea Muenchh. (scarlet oak) and Quercusvelutina Lam. (black oak) trees sampled in 1990–1991 on 62 continuous forest inventory plots located across the southeastern Missouri Ozark Mountains. Trees of both species were older on plots that had suffered high mortality and showed post-1979 reductions in growth rate compared with trees growing on low-mortality plots. Quercuscoccinea trees from high-mortality plots that were dead at the time of sampling exhibited a distinct flattening in growth rate after the mid-1930s, although death did not occur for many years. Severe droughts in 1980 and 1986–1988 were associated with further accentuated reductions in growth rate in dead trees. Dead Q. coccinea that had grown on plots with lower mortality showed comparable reductions in basal area index and similar post-1979 growth patterns, but the departure in basal area index between living and dead trees occurred 2 decades later and was associated with a severe drought during 1953–1956. Additionally, dead trees on lower mortality plots grew faster than living trees for many years before the 1953–1956 drought, suggesting that rapid early growth rates may predispose trees to early death under certain conditions. The ring width index chronologies of both species growing on high- and low-mortality plots were significantly correlated with Palmer drought severity index values, further emphasizing that drought has an important influence on growth of red oak group species in the Missouri Ozarks. Analysis of first differences of ring width index chronologies indicated that severe drought had an additional persistent effect involving long-term reductions in the sensitivity of growth to climate. The results are consistent with previously hypothesized mechanisms of stand dieback and emphasize the role of severe droughts in predisposing trees to eventual death.

Yield prediction models and comparative growth rates for six eucalypt species

Summary Stand stem volume yield prediction models are presented for six eucalypt species Eucalyptus regnans F. Muell., E. obliqua L'Her., E. delegatensis R. Baker. E. pilularis Smith, E. grandis Hill ex Maiden and E. diversicolor F. Muell. The data set used was collected over many years by eight of the major forestry agencies of Australia. It included data only from fully stocked, monospecific stands which had received no major natural or unnatural disturbance throughout their life-times. The bulk of the data was collected from regrowth forest, but some data from plantation forest were also included. The data did not sample formally or fully the entire area of natural occurrence of the six species. These data limitations must be borne in mind when applying the models. A site-index equation is developed for each species and these are then used in developing the stand stem volume yield prediction models which were based on the commonly used Schumacher model. The models are then used to compare growth rates of these species. It is shown that E. diversicolor has the most rapid early growth rate in stem volume and E. pilularis has the slowest. The other species are intermediate in growth rate between these two and do not differ greatly between each other.