Tree growth as indicator of tree vitality and of tree reaction to environmental stress: a review

The intensive monitoring plots (Level II) of ICP Forests serve to examine the effects of air pollution and other stress factors on forest condition, including tree vitality. However, tree vitality cannot be measured directly. Indicators, such as tree growth or crown transparency, may instead be used. Tree growth processes can be ranked by order of importance in foliage growth, root growth, bud growth, storage tissue growth, stem growth, growth of defence compounds and reproductive growth. Under stress photosynthesis is reduced and carbon allocation is altered. Stem growth may be reduced early on as it is not directly vital to the tree. Actual growth must be compared against a reference growth, such as the growth of trees without the presumed stress, the growth of presumed healthy trees, the growth in a presumed stress-free period or the expected growth derived from models. Several examples from intensive monitoring plots in Switzerland illustrate how tree-growth reactions to environmental stresses may serve as vitality indicator. Crown transparency and growth can complement each other. For example, defoliation by insects becomes first visible in crown transparency while stem growth reaction occurs with delay. On the other hand, extreme summer drought as observed in large parts of Europe in 2003 affects stem growth almost immediately, while foliage reduction becomes only visible months later. Residuals of tree growth models may also serve as indicators of changed environmental conditions. Certain stresses, such as drought or insect defoliation cause immediate reactions and are not detectable in five-year growth intervals. Therefore, annual or inter-annual stem growth should be assessed in long-term monitoring plots. An erratum to this article can be found at     

Potential spread of the pine processionary moth in France: preliminary results from a simulation model and future challenges

Context

Some forest insect pests are currently extending their range as a consequence of climate warming. However, in most cases, the evidence is mainly based on correlations and the underlying mechanism is not clearly known.

Aims

One of the most severe pests of pine forests in Europe, the pine processionary moth, Thaumetopoea pityocampa, is currently expanding its distribution as a result of climate warming and does not occupy entirely its potential habitat. A model describing its spread was developed to simulate its potential range in France under various climate change scenarios.

Methods

The spread model was divided into several sub-models to describe the growth, survival and dispersal of the species. The model was validated on the observed change of species distribution, its sensitivity was tested, and spread scenarios were simulated for the future.

Results

The model shows that climate warming initiated the species range expansion in France since the early 1990s. The spread is now limited by dispersal capability, but human-mediated dispersal could accelerate the range expansion.

Conclusion

Species range expansion is an indicator of climate change. However, time lags can appear due to limited dispersal capabilities, and human-mediated dispersal could create satellite colonies and artificially accelerate the spread.     

A case of habitat complementation in forest pests: Pine processionary moth pupae survive better in open areas

Little attention has been given to the relevance of habitat complementation concept to the population dynamics of insect herbivores. Late instar larvae of the pine processionary moth (PPM) Thaumetopoea pityocampa move in late winter from pine stands, their feeding habitat, to neighbouring habitats where they pupate until next summer. They search for sunny exposed soil which they can find in open areas. We investigated the effect of both forest cover and soil origin, with three matching types (pine stand, broadleaved stand and open area) on the survival of PPM pupae. The microclimatic soil variables which significantly differentiated cover types and soil origins were the maximum temperature and the mean relative humidity in spring, soon after pupation has occurred. A significant effect of the cover type, but not of the soil origin, was detected on the proportion of dead, emerged or diapausing pupae. Open areas were more suitable for pupae survival than forest covers (pine or broadleaved stands), due to warmer and more humid soil conditions. In this study, we provide one of the first examples of habitat complementation for an insect herbivore, as PPM population can benefit from the combination of pine habitats for the feeding of larvae with open habitats for pupation. The presence of broadleaved stands next to pine stands might also represent an ecological trap for PPM pupae, as broadleaved habitats may turn to be less suitable for pupae survival in spring when the apparition of leaves creates cooler conditions.     

Frost heaving of forest tree seedlings: a review

Soil frost heaving is the result of the formation of ice lenses in the soil caused by a segregation of the soil water. Ice lenses are growing from below and pushed upward. Seedlings heave when they are pushed out of the ground by the ice sheet formed at the surface of the soil. Frost heaving may greatly reduce growth and survival of forest tree seedlings particularly in regions where freezing and thawing are accompanied by high soil moisture. Resistance to frost heaving increases with size of seedling as the ability of a seedling to anchor itself increases. A few methods, such as fertilizing, choice of planting spots, sowing or planting at the proper time, shading, and use of mulches, appear to be effective in controlling frost heaving. Shade from natural plant cover can greatly reduce frost heaving.     

Testing a process-based model of tree seedling growth by manipulating

A model was developed that simulated photosynthesis, growth and allocation in tree seedlings. The model was parameterized with data from experiments on seedlings of sycamore (Acer pseudoplatanus L.), Sitka spruce (Picea sitchensis (Bong) Carr.) and young birch trees (Betula pendula Roth.). In these experiments, CO2 concentration ([CO2]) and nutrient addition rate were varied. Parameters quantifying nutrient uptake, translocation and starch synthesis were fitted, based on data from control treatments. Elevated [CO2] and low-nutrient treatments were then used to test the predicted response of growth and allocation against observations. The model accurately predicted total seedling growth in the elevated [CO2] treatments. A response of growth to elevated [CO2] was seen in the birch and sycamore experiments, but not in the Sitka spruce, because of photosynthetic down-regulation. Predictions of allocation were reasonably accurate in the birch and Sitka spruce experiments, but were notably poorer in the sycamore experiments, possibly because of differences in sink strength between root and shoot. In the birch and sycamore experiments, little change in allocation with elevated [CO2] was observed or predicted. This was ascribed to the relative values of K(Tc) and K(Tn), the translocation coefficients that determine the sensitivity of allocation to carbon and nitrogen uptake rates, respectively. Growth and allocation in the low-nutrient treatments were poorly predicted by the model. In Sitka spruce, it was suspected that the photosynthetic parameters measured in August 1994 had been higher earlier in the season, before nutrients became depleted. In sycamore, the discrepancies were thought to relate to differences in sink strength between root and shoot that could not be described by the model.     

Biotechnology of the multipurpose tree species Arbutus unedo: a review

Arbutus unedo L. (strawberry tree, Ericaceae) is a woody species with a circum-Mediterranean distribu-tion. It has considerable ecological relevance in southern...     

植物生长调节剂对林木生长的控制

用植物生长调节剂处理樟子松。丁香幼苗。实验表明,经处理后的幼苗。高径生长提高１５％￣３０％。樟子松小苗造林成活率平均提高１９．８７％。     

Extending a physiological forest growth model by an observation-based tree competition module improves spatial representation of diameter growth

One of the pivotal objectives in forestry research is to estimate the response of silvicultural target variables to climate change scenarios at high temporal resolution in order to consider within-year feedbacks between growth and environmental conditions. To meet this challenge, models are needed which support and complement the widely used observation-based decision systems in forest management and consulting. Physiological models in particular provide the fundamental prerequisites to reflect the impact of various simultaneously changing environmental conditions. However, a physiological representation at the individual tree level is computationally very expensive and sensitive to uncertain initializations. We thus propose an approach that combines a modern representative of the physiological cohort model type, MoBiLE-PSIM, with the individual tree competition concept of a distance-dependent empirical growth simulator (SILVA). The resulting hybrid provides a key feature for the consideration of forest management in long-term simulations at high computational efficiency. The extended model was evaluated with growth-diameter distributions obtained from core-boring at two beech (Fagus sylvatica L.) forest sites in south-west Germany that differ in exposure and soil conditions. The mean bias of annual stand-scale growth from 2001 to 2007 decreased from ?0.59 to ?0.41 mm at one evaluation plot and from ?0.55 to ?0.24 mm at the other when the competition module was coupled in. Inclusion of the SILVA-based individual tree module into MoBiLE-PSIM improved the size-dependent representation of competition and growth on five-year and even annual timescale. This was particularly the case where the spatial distribution of dominant trees was clustered.     

造林密度对杨树生长的影响

该文对欧美杨107、雄性毛白杨1319、窄冠白杨3个无性系密度试验林连续6a的定位观测资料进行了分析研究。结果表明:3个无性系6a生时在树高生长、胸径生长、单株材积生长上存在显著差异。密度对3个无性系的胸径生长、单株材积生长影响极为显著。6a生时,单位面积上的林分蓄积量为2m×3m(1667株/hm2)2m×4m(1250株/hm2)4m×6m(417株/hm2)。通过对3个无性系在3个不同密度的生长进程、连年生长量分析,提出了初次间伐的合理年限。     

How climate change might affect tree regeneration following fire at northern latitudes: a review

New Forests - Climate change is projected to increase fire severity and frequency in the boreal forest, but it could also directly affect post-fire recruitment processes by impacting seed...     

Adapting a growth equation to model tree regeneration in mountain forests

Management and risk analysis of protection forests depend on a reliable estimation of regeneration processes and tree growth under different site conditions. While the growth of forest stands and thus the average growth of larger trees is well studied and published in yield tables as well as embodied in numerous simulation models, there is still a lack of information about the crucial initial stages of tree growth. Thus, we evaluated juvenile tree growth for different site conditions in the Swiss Alps and developed an approach to model both the early and later stages of growth based on the Bertalanffy equation. This equation is physiologically well founded and requires only two parameter estimates: a maximum tree height and a growth parameter. Data for the parameter estimation were available from studies of tree regeneration at a range of sites in Switzerland: growth patterns of larch (Larix decidua) were available from a high-elevation afforestation experiment. For spruce (Picea abies), data were obtained from a blowdown area in the Alps. The growth equation was fitted to the observed data and we found a good correlation of the fitted curves with the observed data. The parameter estimates were validated with independent data sets. The extrapolated growth curves, calculated with the estimated growth rates, correspond well to the validation data. Thus, it is possible to use the Bertalanffy equation to model both the early and later stages of growth. With this approach, we provide a basis for modelling the growth of juvenile and mature trees of different tree species in mountain forests of the European Alps.     

Fertilization—Effects on deciduous tree growth and browsing by moose

Knowledge of plant–herbivore interactions is fundamental for understanding foraging patterns of herbivores and their effects on the ecosystem as well as the human use of natural resources. The nutrient resources available for plants may determine not only growth rate, but also the amounts of secondary compounds in the plant tissues. As a consequence, browsing pressure on plant communities by large herbivores can be affected by fertilization and nitrogen deposition. We conducted a field fertilization experiment to test the hypothesis that fertilization leads to increased sapling growth and increased browsing by a large herbivore, the moose (Alces alces). The study was conducted on fertilized and unfertilized plots (50 m × 50 m) in northern Sweden. The plots were located in Scots pine (Pinus sylvestris) stands of young succession stages with an intermixture of deciduous species. Fertilization with 600 kg calcium–ammonium–nitrate per ha (=200 kg N ha⁻¹), was conducted in spring on one of the plots in each of 25 paired plots. The other plot in each pair was kept as control. The effect of fertilization on plants and browsing pressure was evaluated on five deciduous tree species in June and August the year after fertilization. Both browsing from preceding winter (bites) and current summer (leaf strips and bites) was recorded. Shoot size and other shoot variables increased with fertilization. Fertilization increased winter browsing for most species, but few differences were statistically significant. The late summer recording (August) showed pronounced differences in browsing pressure (leaf strips and bites) between control and treatment. In June, only a trend of increased browsing (leaf strips) was found for all species on fertilized plots. Generally, the pressure of leaf stripping was low in June, probably due to the short time the annual shoots had been exposed to moose browsing. Number of summer bites (recorded in August) was significantly higher on fertilized plots for the Betula spp., and the trend was similar for the other tree species. Within species, there was no difference in strip length between the treatments. The result indicates that fertilization can be used as a habitat improvement for ungulates within wildlife management. But, fertilization is also likely to lead to an increased risk of browsing damage, which is undesirable if forests are being fertilized for increased forest production.     

Influence of several tree traits on rainfall partitioning in temperate and boreal forests: a review

? In forests, rainfall is partitioned into intercepted water (IW), throughfall (TF) and stemflow (SF). We reviewed the majority of published works comparing water flows among tree species in temperate and boreal forests to test the effect of several tree traits on water flows.

? We hypothesized that water flows differed between evergreen and deciduous species, and according to successional status and bark roughness. We also investigated that water flows would be explained by stand variables such as basal area.

? Linear mixed models fitted on reviewed data showed that evergreens had a lower TF than deciduous trees (decrease of 13.9% of total precipitation year-round and 8.4% over the growing period). Similar results were found for conifers compared to broadleaves. TF also declined with the successional status from pioneer to late-successional tree species. SF decreased with bark roughness from smoother to rougher bark. Evergreens had water flows that were dependent on age of the stand, especially for TF which increased by 15.6% of total precipitation from young to adult forests.

? The large scale of TF differences between tree genera together with specific transpiration amounts and rooting features highlighted in other studies should result in significant differences in soil water content among tree species. This may have consequences on stand fitness and growth, and understory vegetation.

     

Admixing broadleaved to coniferous tree species: a review on yield, ecological stability and economics

For several reasons the conversion of mono-species into mixed-species forests is presently a major concern of forest management and policy in Central Europe. Although it is possible to show a clear trend in favour of mixed-species forests, private forest owners and some forest economists have often not favoured mixed forests, assuming that they are less profitable. The trend towards mixed forests seems mainly for ecological reasons, while sound economic analysis of mixed forests is still rare. Based on this background the objective of the study is to answer the following four questions: (1) Does the yield of mixed-species forests differ from that of pure forests? (2) Does the mixing of tree species influence the ecological stability of forests? (3) Is the economic value of a mixed forest less than that of a monoculture? (4) How do forest economic models integrate the findings on yield and ecological stability of mixed forests? To answer these questions a literature review was conducted on the possible impacts of mixed-species forests. In comparison to pure stands a greater yield is not necessarily given in mixed stands. Yet, mixed-species stands are better able to compensate disturbances than monocultures. Moreover, there is substantial evidence that mixed-species stands are more resistant against biotic and abiotic disturbances. Applying an extended forest economic model, it was possible to demonstrate that mixing large blocks of native broadleaf species into pure conifer forests may lead to a significant reduction of financial risk. From a risk-averse perspective the economic value of a mixed-species forest may thus be greater than that of a mono-species forest. Yet, it became clear that forest economists do not often integrate the research findings on yield and ecological stability of mixed stands in modelling, but rather apply simple bioeconomic modelling. Moreover, in the context of mixed forests economists also largely ignore even classical financial approaches, which consider risk and risk preferences. We concluded that forest economics has to close substantial research gaps. Firstly, the knowledge of how to integrate biophysical properties of mixed forests in bioeconomic modelling is still an open question. Secondly, forest economists have to adopt the modern approaches of financial theory and management science to value mixed forests.     

Drought tolerance and rainforest tree growth on a North Queensland rainfall gradient

Three instrumented sites were established in 1985 along a 160-km transect from coastal evergreen rainforest on lowlands near Cairns, through rainforest on the Atherton Tableland, to semideciduous vine forest southwest of Mount Garnet. Mean annual rainfall graded from 2800 mm at coastal site (1), through 1400 mm on Atherton Tableland (2), to 760 mm at inland site (3). Each site was equipped with scaffold towers to provide regular access to upper and middle canopy.

Two shade-intolerant rainforest tree species which occurred at all three sites were used to compare tree growth and water relations; these were Acacia aulacocarpa (brown salwood) which was evergreen, and Melia azederach var. australasica (white cedar) which was leafless during onset of drought. Drought responses from coastal to inland sites were qualitatively different between Acacia and Melia. While Acacia foliage endured persistent low-moisture status, the deciduous habit of Melia provided a means of drought-avoidance.

Mean minimum leaf water-potential for deciduous Melia varied from −1.7 MPa to −2.3 MPa across all sites and seasons. By contrast, evergreen Acacia experienced increasing seasonal drought stress from coast to inland, reducing dry-season water-potentials from −2.1 Mpa to −6.4 Mpa, respectively.

Annual patterns of growth in stem cross-sectional area also varied according to species and site. For Acacia, current annual increment ( ) was 54.1 and 56.9 cm² year⁻¹ for coastal and tableland sites respectively. Acacia at the inland site was only 3.1 cm² year⁻¹.

Present results are relevant to species selection criteria in the tropics, where establishment of rainforest species can be limited by seasonal drought.     

Black locust (Robinia pseudoacacia L.) as a multi-purpose tree species in Hungary and Romania: a review

Black locust(Robinia pseudoacacia L.) was the first North-American tree species imported to Europe at the beginning of the seventeenth century. It is commonly planted worldwide because of its adaptability to environmental stresses, its valuable wood, easy propagation, frequent and abundant seed production, excellent coppicing,high seedling survival, and relatively high wood yield. In Europe, Romania and Hungary have the most highly-developed black locust growing techniques and experiences.As a result of increasing interest in black locust in many countries, this review aims to provide a comprehensive overview of state-of-the-art site requirements, propagation, improvement and management(including growth and yield as well as use in energy plantations).     

Effects of water, nutrients and their interactions on tree growth, and plantation forest management practices in Australasia: A review

The amount and distribution of rainfall throughout the year is used to highlight climatic differences between Australia and New Zealand. Plantation forest growth is strongly influenced by both available moisture and nutrients. Practices such as cultivation and mounding (bedding) are used on wet sites, whereas cultivation, ripping, weed control, mulching andheavier thinning regimes are recommended for dry sites.

Management of nutrients to improve growth includes some of the practices listed above which enhance moisture relationships. Nutrient conservation measures and the selection of planting stock with better root systems to explore the soil are suggested as methods to improve growth, along with the direct application of nutrients in fertiliser, sewage effluents and wastes.

Responses to a questionnaire distributed to the major forestry enterprises in Australia showed that practices with very conspicuous benefits (e.g. weed control) had generally been accepted, but the lead-time for implementation of positive research and development was still excessive. A number of other promising practices (e.g. mycorrhizal inoculation of nurseries) had only received minimal or at best a moderate acceptance by managers.

In reviewing the positive impact of recent past research on management practices, we suggest that more information on the interaction of moisture availability and nutrition along with detailed research on both positive and negative effects of cultivation is required. The potential benefits from the use of wastes and effluents within forests to supply both water and nutrients will ensure the development of this practice. Experiments should be designed to explore the interactions between genetically improved stock, sites and cultural treatments, as well as physiological processes determining growth.     

Deep BarkID: a portable tree bark identification system by knowledge distillation

Species identification is one of the key steps in the management and conservation planning of many forest ecosystems. We introduce Deep BarkID, a portable tree identification system that detects tree species from bark images. Existing bark identification systems rely heavily on massive computing power access, which may be scarce in many locations. Our approach is deployed as a smartphone application that does not require any connection to a database. Its intended use is in a forest, where internet connection is often unavailable. The tree bark identification is expressed as a bark image classification task, and it is implemented as a convolutional neural network (CNN). This research focuses on developing light-weight CNN models through knowledge distillation. Overall, we achieved 96.12% accuracy for tree species classification tasks for ten common tree species in Indiana, USA. We also captured and prepared thousands of bark images—a dataset that we call Indiana Bark Dataset—and we make it available at https://github.com/wufanyou/DBID.