Impact of Climate Trends and Drought Events on the Growth of Oaks (Quercus robur L. and Quercus petraea (Matt.) Liebl.) within and beyond Their Natural Range

Due to predicted climate change, it is important to know to what extent trees and forests will be impacted by chronic and episodic drought stress. As oaks play an important role in European forestry, this study focuses on the growth response of sessile oak (Quercus petraea (Matt.) Liebl.) and pedunculate oak (Quercus robur (L.)) under contrasting climatic conditions. Analyses cover both site conditions of their natural occurrence (Southern Germany and Northeast Italy) and site conditions beyond their natural range (South Africa). The sites beyond their natural range represent possible future climate conditions. Tree-ring series from three different sites were compared and analysed using dendrochronological methods. The long-term growth development of oak trees appears to be similar across the sites, yet the growth level over time is higher in the drier and warmer climate than in the temperate zone. When compared with previous growth periods, growth models reveal that oak trees grew more than expected during the last decades. A recent setback in growth can be observed, although growth is still higher than the model predicts. By focusing on the short-term reactions of the trees, distinct drought events and periods were discovered. In each climatic region, similar growth reactions developed after drought periods. A decline in growth rate occurred in the second or third year after the drought event. Oaks in South Africa are currently exposed to a warmer climate with more frequent drought events. This climatic condition is a future prediction also for Europe. In view of this climate change, we discuss the consequences of the long- and short- term growth behaviour of oaks grown in the climate of South Africa for a tree species selection that naturally occurs in Europe

LEDA (Eucalyptus Deglupta Blume) Increment on Various Dimensions of Growth

Setting stands to produce the optimal growth of Leda (Eucalyptus deglupta Blume) is necessary to achieve maximum and sustenable results. The study aims to determine the growth and accretion of growth (increment) of Leda (Eucalyptus deglupta Blume) stands. The research was conducted in the area of Industrial Forest Plantation Inhutani Company Gowa-Maros, South Sulawesi, on Leda stands aged 1 year, 2 years, 3 years, 5 years, and 7 years. The research was conducted using survey methods and purposive sampling techniques that chose age-class stands at the research site. The data was gathered through the 15 sample plots, each measuring 0.04 ha (20 x 20 m), by striving in a particular way so that the sample plot represents the growth conditions of the stand. The growth analysis of the Leda stands used Richard’s Model equation, which was then extrapolated to obtain the increment values of CAI and MAI at the dimensions of height, diameter, and area of the based area. The results showed that the growth of the 7-year-old Leda reached a height of 17.20 m, with a Mean Annual Increment (MAI) of 2.46 m and a Current Annual Increment (CAI) of 2.00 m. The diameter of the 7-year-old Leda’s trunk reached a diameter of 14.60 cm, with a Mean Annual Increment (MAI) of 2.09 cm and a Current Annual Increment (CAI) of 2.30 cm. The basal Area (BA) of 7-year-old Leda reached 15.6 cm2. The mean accretion of the based area (MAI) was 2.23 cm2, and the annual accretion of the based area (CAI) was 2.40 cm2. The diameter of the 10-year-old Leda’s trunk reached tree level with a trunk diameter of 21.1 cm

Radial Growth of Qilian Juniper on the Northeast Tibetan Plateau and Potential Climate Associations

There is controversy regarding the limiting climatic factor for tree radial growth at the alpine treeline on the northeastern Tibetan Plateau. In this study, we collected 594 increment cores from 331 trees, grouped within four altitude belts spanning the range 3550 to 4020 m.a.s.l. on a single hillside. We have developed four equivalent ring-width chronologies and shown that there are no significant differences in their growth-climate responses during 1956 to 2011 or in their longer-term growth patterns during the period AD 1110–2011. The main climate influence on radial growth is shown to be precipitation variability. Missing ring analysis shows that tree radial growth at the uppermost treeline location is more sensitive to climate variation than that at other elevations, and poor tree radial growth is particularly linked to the occurrence of serious drought events. Hence water limitation, rather than temperature stress, plays the pivotal role in controlling the radial growth of Sabina przewalskii Kom. at the treeline in this region. This finding contradicts any generalisation that tree-ring chronologies from high-elevation treeline environments are mostly indicators of temperature changes

Estimation of Biomass Increase and CUE at a Young Temperate Scots Pine Stand Concerning Drought Occurrence by Combining Eddy Covariance and Biometric Methods

The accurate estimation of an increase in forest stand biomass has remained a challenge. Traditionally, in situ measurements are done by inventorying a number of trees and their biometric parameters such as diameter at the breast height (DBH) and height; sometimes these are complemented by carbon (C) content studies. Here we present the estimation of net primary productivity (NPP) over a two years period (2019–2020) at a 25-year-old Scots pine stand. Research was based on allometric equations made by direct biomass analysis (tree extraction) and carbon content estimations in individual components of sampled trees, combined with a series of stem diameter increments recorded by a network of band dendrometers. Site-specific allometric equations were obtained using two different approaches: using the whole tree biomass vs DBH (M1), and total dry biomass-derived as a sum of the results from individual tree components’ biomass vs DBH (M2). Moreover, equations for similar forest stands from the literature were used for comparison. Gross primary productivity (GPP) estimated from the eddy-covariance measurements allowed the calculation of carbon use efficiency (CUE = NPP/GPP). The two investigated years differed in terms of the sum and patterns of precipitation distribution, with a moderately dry year of 2019 that followed the extremely dry 2018, and the relatively average year of 2020. As expected, a higher increase in biomass was recorded in 2020 compared to 2019, as determined by both allometric equations based on in situ and literature data. For the former approach, annual NPP estimates reached ca. 2.0–2.1 t C ha−1 in 2019 and 2.6–2.7 t C ha−1 in 2020 depending on the “in situ equations” (M1-M2) used, while literature-derived equations for the same site resulted in NPP values ca. 20–30% lower. CUE was higher in 2020, which resulted from a higher NPP total than in 2019, with lower summer and spring GPP in 2020. However, the CUE values were lower than those reported in the literature for comparable temperate forest stands. A thorough analysis of the low CUE value would require a full interpretation of interrelated physiological responses to extreme conditions

Assessing Site Productivity in Tropical Moist Forests: A Review

Reliable estimates of site productivity are essential for improved predictions of timber yields and for meaningful simulation studies. Few suitable techniques exist for tropical moist forests. Conventional indices such as site index cannot be estimated reliably for stands with many species or indeterminate ages. Emerging techniques require two steps: calibration and validation with permanent sample plots, and correlation with easily measured stand parameters. One promising index for the tropical moist forest is based on the expected diameter increment of individual trees adjusted for tree size and competition. Measures of stand height such as maximum stand height, canopy height and the height-diameter relationship may also prove useful. Proposed measures should satisfy four criteria: they should be reproducible and consistent over long periods of time; indicative of the site, and not unduly influenced by stand condition or management history; correlated with the site's productive potential; and at least as good as any other productivity measures available

Invasion of winter moth in New England: Effects of defoliation and site quality on tree mortality.

Abstract Widespread and prolonged defoliation by the European winter moth, Operophtera brumata L., has occurred in forests of eastern Massachusetts for more than a decade and populations of winter moth continue to invade new areas of New England. This study characterized the forests of eastern Massachusetts invaded by winter moth and related the duration of winter moth defoliation estimated using dendrochronology to observed levels of tree mortality and understory woody plant density. Quercus basal area mortality in mixed Quercus and mixed Quercus-Pinus strobus forests in eastern Massachusetts ranged from 0-30%; mortality of Quercus in these forests was related to site quality and the number of winter moth defoliation events. In addition, winter moth defoliation events lead to a subsequent increase in understory woody plant density. Our results indicate that winter moth defoliation has been an important disturbance in New England forests that may have lasting impacts

Dynamics of P. pinea and P. pinaster forests: Implications for adaptive management in a climate change context

Over the last decades, climate change has been particularly severe in the Mediterranean basin, where the intensity and frequency of drought events had a significant effect on forest dynamics. As a consequence, tree allometry is modified, reducing tree and stand growth, provoking tree or stand decay and dieback and altering plant recruitment. In this context, differences in structural and physiological strategies of tree species, could mitigate the damage inflicted by climate change and reduce risk. Programs aiming to adapt forests to climate-changing conditions should take profit from the knowledge of these strategies, and propose a set of actions oriented to emulate or enhance the inherent capacity of the forest for adaptation. Between these actions, this thesis highlights the promotion of natural regeneration or the increase of intra and interspecific diversity. A most diverse ecosystem could help to reduce vulnerability and increase resistance against the lack of water availability. In addition, tree species interactions could lead to complementary effects during low-growth years by the optimization of resources. This thesis provides a variety of methodologies based on analyzing how different factors control the response dynamics of P. pinea and P. pinaster in mixed and monospecific Mediterranean forests throughout stand development, from regeneration to adult stages. The main hypothesis was that species responses, could help to cope with climatic variability and that the composition, mixed or monospecificic, could attenuate these responses. The thesis used data from a network of 1936 plots of 0.02 ha to study natural regeneration, and a network of 75 mixed and monospecific temporal plots on adult stands, both installed in the Northern Plateau of Spain. In this last group of plots, the use of tree-ring width series permitted us to evaluate species-mixing effects on inter-annual and intra-annual tree growth dynamics.Doctorado en Conservación y Uso Sostenible de Sistemas Forestale