Effect of selective logging on stand structure and tree species diversity in a subtropical evergreen broad-leaved forest

?Context

Selective logging followed by natural regeneration is rarely employed for restocking subtropical evergreen broad-leaved forests in East Asia compared with the use of clear-cutting.

?Aims

To clarify the succession of these forests, the effects of selective logging on stand structure, species diversity, and community similarity were studied in a mature and regenerating forest in Okinawa, Japan.

?Methods

Four study plots were established, and trees ≥1.2 m height were identified by species name, tree height, and diameter at breast height.

?Results

The results showed that the species composition of regenerating forest was similar to mature forest; however, the former had a greater species density and Shannon–Wiener index than the latter. Castanopsis sieboldii and Distylium racemosum, the predominant trees in the mature forest, continued to dominate the regenerating forest, with a broad layer distribution. High Sørensen and Jaccard community similarity indices for mature and regenerating forest indicated that the regeneration occurred in a progressive succession.

?Conclusion

The similar species composition and stand structure for both mature and regenerating forest, and the higher species diversity for the latter, provided no evidence of forest degeneration and suggested that the regenerating forest may develop into a stand similar to preselective logging forest.     

Individual vulnerability factors of Silver fir (Abies alba Mill.) to parasitism by two contrasting biotic agents: mistletoe (Viscum album L. ssp. abietis) and bark beetles (Coleoptera: Curculionidae: Scolytinae) during a decline process

? Context

In recent decades, there have been increasing reports of forest decline, especially in Mediterranean forest ecosystems. Decline in tree vitality is usually due to complex interactions between abiotic factors and biotic agents that attack weakened trees.

? Aims and methods

Estimating dendrometrical characteristics [basal area increment (BAI), age at DBH from tree ring counting, social status, height, and diameter], tree health status, and a competition index, we investigated the individual vulnerability of a French declining silver fir forest to both mistletoe (Viscum album L. ssp. abietis) and bark beetles (Pityophthorus pityographus Ratz., Pityokteines vorontzovi Jac., and Pityokteines spinidens Reitt.).

? Results

BAI was negatively correlated with both mistletoe infection (via mistletoe biomass) and bark beetle attack (number of insects per square meter), but there was evidence of divergence in tree choice between two groups of parasites. Mistletoe preferentially infected isolated and dominant trees that showed higher past growth rates than non-infected ones. Conversely, bark beetles mainly attacked defoliated and preferably declining trees with diameter (DBH) lower than 44.5 cm and slower past growth.

? Conclusion

While successive severe drought periods are thought to greatly weaken southern silver fir populations, mistletoe and bark beetles may contribute actively to their decline processes as inciting and contributing factors, respectively.     

Multi-coefficient goal programming in thinning schedules to increase carbon sequestration and improve forest structure

Context

Current decision analysis techniques are ineffective for planning thinning operation to improve the forest structure.

Aims

The purpose of this study is to use multi-coefficient goal programming (GP) to plan a thinning schedule that allows more carbon sequestration and diverse forest structure.

Methods

A multi-coefficient GP is applied to plan a thinning schedule for a 2,633-ha plantation forest.

Results

This technique efficiently fine-tunes the thinning schedule to obtain 420,500 tons of carbon sequestration which was a little higher than the result by a multi-segment goal programming (MSGP). Moreover, a fixed-ratio multi-coefficient GP is applied to efficiently generate mosaic of thinned areas with various thinning intensities. Although the captured carbon by a fixed-ratio multi-coefficient GP is lower, the thinned areas can provide various habitats for forest life with multiform contrasting edges.

Conclusion

The use of a multi-coefficient GP allows practicable planning of better thinning alternatives to increase carbon sequestration and forest structure.     

Genotypic parameters of wood density and fiber traits in triploid hybrid clones of Populus tomentosa at five clonal trials

? Context

A clear understanding of the genetic control of wood properties is a prerequisite for breeding for higher wood quality in Populus tomentosa Carr. hybrid clones.

? Aims

The experiments aimed at unraveling genetic and environmental effects on wood properties among triploid hybrid clones of P. tomentosa.

? Methods

We used 5-year-old clonal trials established in Northern China to assess the heritability of wood density and fiber traits. Two hundred seventy trees from nine clones were sampled in five sites.

? Results

Site had a very significant effect on all recorded traits. Despite this large site effect, a tight genetic control was detected and clonal repeatability varied between 0.53 and 0.95. Significant genotype?×?environment interactions were detected for most of the traits. Moderate to tight correlation were evidenced among traits but they were not consistent with that in several cases that were site-dependent.

? Conclusions

Our results revealed a tight genetic control over several wood properties and therefore breeding programs might be able to improve wood density, fiber length, and coarseness in these hybrids.     

Phenotypic plasticity and climatic adaptation in an Atlantic maritime pine breeding population

Context

Pinus pinaster Ait. is found in the Iberian Peninsula under Mediterranean and Atlantic conditions. Both climates encounter each other in Galicia (NW Spain), where two bioclimatic regions can be differentiated: coastal and inland. A breeding program was launched in the coastal area, with two breeding and deployment areas delimited.

Aims

We analyse plasticity patterns across regions in a coastal breeding population to assess the suitability of current breeding areas and how genetic material will likely respond to future climate.

Methods

Total height at ages 3 and 8?years was assessed in 16 trials established along the coast and in inner Galicia. Clustering of environments with similar genotypic performance, family sensitivities to climatic factors and stability analyses were performed.

Results

Sizeable genetic variation in plasticity was found among families, and crossover genotype-by-environment interactions were detected within and between regions. It was unfeasible to regionalize Galicia into alternative areas of stable genotypic performance. Only the cold regime was found to noticeably underlie the array of phenotypic responses to changing environmental conditions.

Conclusions

Results suggest that previous delimitation in two breeding areas is pointless and indicate reduced effects of a changing climate towards Mediterranean conditions on decreasing population fitness.     

Growth response to climate and drought change along an aridity gradient in the southernmost Pinus nigra relict forests

Context

Tree populations at the rear edge of species distribution are sensitive to climate stress and drought. However, growth responses of these tree populations to those stressors may vary along climatic gradients.

Aims

To analyze growth responses to climate and drought using dendrochronology in rear-edge Pinus nigra populations located along an aridity gradient.

Methods

Tree-ring width chronologies were built for the twentieth century and related to monthly climatic variables, a drought index (Standardized Precipitation–Evapotranspiration Index), and two atmospheric circulation patterns (North Atlantic and Western Mediterranean Oscillations).

Results

Growth was enhanced by wet and cold previous autumns and warm late winters before tree-ring formation. The influence of the previous year conditions on growth increased during the past century. Growth was significantly related to North Atlantic and Western Mediterranean Oscillations in two out of five sites. The strongest responses of growth to the drought index were observed in the most xeric sites.

Conclusion

Dry conditions before tree-ring formation constrain growth in rear-edge P. nigra populations. The comparisons of climate-growth responses along aridity gradients allow characterizing the sensitivity of relict stands to climate warming.     

European oak powdery mildew: impact on trees,effects of environmental factors,and potential effects of climate change

? Context

Powdery mildew is one of the most common diseases of oaks in Europe. After alarming reports in the beginning of the twentieth century following the presumed introduction of the invasive fungus, the disease has become familiar to foresters. However, its impact may vary greatly according to intrinsic and extrinsic factors.

? Aims

We aimed at providing updated and synthesised information on the impact of powdery mildew on oak and on the effects of environment on disease.

? Methods

A comprehensive literature review was performed, including old reports of the early epidemics to more recent data.

? Results

Tree growth patterns are of critical importance to explain the severity of the disease and the differences between juvenile and mature trees. A critical element, especially for infection of mature trees, is the availability of spores during the production of the first leaf flush. High disease impact is often related to modified growth patterns, either by environmental factors (insects or frost) or silvicultural practices (e.g., coppicing).

? Conclusion

Powdery mildew can have important impacts in natural oak regenerations and a significant role in decline of mature trees. Climate change might influence the disease severity mainly by altering the host pathogen phenological synchrony. Process-based models are required for reliable predictions.     

Influence of cambial age and climate on ring width and wood density in Pinus radiata families

? Context

The correlation between tree ring width and density and short-term climate fluctuations may be a useful tool for predicting response of wood formation process to long-term climate change.

? Aims

This study examined these correlations for different radiata pine genotypes and aimed at detecting potential genotype by climate interactions.

? Methods

Four data sets comprising ring width and density of half- and full-sib radiata pine families were used. Correlations with climate variables were examined, after the extraction of the effect of cambial age.

? Results

Cambial age explained the highest proportion of the ring to ring variation in all variables. Calendar year and year by family interaction explained a smaller but significant proportion of the variation. Rainfall had a positive correlation with ring width and, depending on test site, either a negative or positive correlation with ring density. Correlations between temperature during growing season and ring density were generally negative.

? Conclusion

Climate variables that influence ring width and wood density can be identified from ring profiles, after removing the cambial age effect. Families can be selected that consistently show desirable response to climate features expected to become prevalent as a result of climate change.     

Influence of tree size, reduced competition, and climate on the growth response of Pinus nigra Arn. salzmannii after fire

Context

After wildfire, surviving trees are of major ecological importance as they can help in the post-fire regeneration process. Although these trees may be damaged, they may also benefit from reduced fuel hazard and competition. However, little is known about the long-term growth response of surviving trees.

Aims

This study aims to explain short- to long-term variations in the postfire growth of surviving black pines in an area burnt in 1994, focusing on levels of fire severity and tree sizes.

Methods

Relative basal area increments were used to detect time-course variations in postfire radial tree growth depending on fire severity. Linear mixed-effects models were used to describe the factors affecting postfire ring growth.

Results

In the short term, fire caused stronger reduction in growth in small trees with increasing bole char height. However, as time since fire increased, a positive effect of fire on growth due to reduced competition counteracted the short-term fire impacts. Indeed, small surviving trees demonstrated a surge in growth 15 years after the fire.

Conclusion

It was concluded that reduced competition might offset the short-term negative effects of fire in surviving black pines.     

Storm damage of Douglas-fir unexpectedly high compared to Norway spruce

Context

Since storm damage has a large impact on forest management in Central Europe, we investigated the main storm risk factors for two important conifer species, Douglas-fir (Pseudotsuga menziesii [Mirbel] Franco) and Norway spruce (Picea abies [L.] Karst.).

Aims

We compared general storm damage levels of Douglas-fir and Norway spruce, the latter being known to have high storm risk among European tree species.

Methods

Generalized linear mixed models and boosted regression trees were applied to recorded storm damage of individual trees from long-term experimental plots in southwest Germany. This included two major winter storm events in 1990 and 1999. Over 40 candidate predictors were tested for their explanatory power for storm damage and summarized into predictor categories for further interpretation.

Results

The two most important categories associated with storm damage were timber removals and topographic or site information, explaining between 18 and 54 % of storm damage risk, respectively. Remarkably, general damage levels were not different between Douglas-fir and Norway spruce.

Conclusion

Under current forest management approaches, Douglas-fir may be considered a species with high storm risk in Central Europe, comparable to that of Norway spruce.     

The effects of N-enriched rain and warmer soil on the ectomycorrhizae of black spruce remain inconclusive in the short term

Context

Warmer temperatures and anthropogenic N depositions are altering soil nutrient cycles and plant nutrition worldwide and are projected to rise dramatically in the future, particularly at the high latitudes. How much will such alterations affect symbiotic organisms such as ectomycorrhizae (ECM)?

Aims

The aim was to investigate the short-term effects of warmer soil temperatures and N-enriched precipitations on roots and ECM.

Methods

A field experiment was established during 2008–2010 in two black spruce (Picea mariana) stands of the boreal forest of Quebec, Canada. The ECM of 12 trees per site were counted and identified by morphotyping.

Results

After 3 years, soil heating markedly modified the proportions of vital root tips and ECM in the colder stand, while no effect of the N-enriched rain was observed on soil chemistry and consequently on roots and ECM. Density and ramification of root tips were not affected by the treatments.

Conclusion

The hypothesis that the treatments would alter the ECM was confirmed only partially in the colder stand. The type of application and amount of N supplied were unable to substantially modify in the short-term growth conditions of roots and ECM, explaining the observed results.     

A tree distance-dependent growth and yield model for naturally regenerated pure uneven-aged maritime pine stands in central inland of Portugal

? Context

Maritime pine (Pinus pinaster Aiton) is one of the most important Portuguese species, growing in pure stands ranging from even-aged to multi-aged structures. Current growth and yield models were developed only for even-aged, managed stands and/or for very specific regions of Portugal.

? Aims

This paper focuses on the validation of the existing size-class model PBRAVO, adapted to even-aged stands, and on the subsequent development of a single tree distance-dependent growth and yield model (PBIRROL), both in distance-independent and distance-dependent versions, for uneven-aged stands.

? Methods

The new model is composed of four modules, each with a set of sub-models for: tree variable prediction, tree volume prediction, future tree list prediction and growth projection.

? Results

The evaluation of the PBRAVO and PBIRROL models showed that the new model gives more accurate predictions. Moreover, medium-term simulations provided consistent and logical predictions.

? Conclusion

It was verified that individual tree models are more suited to simulate poorly managed uneven-aged stands than diameter distribution models. No clear superiority of distance-dependent models was found over models using just distance-independent measures of inter-tree competition.     

Within-population variability in architectural traits and suitability to forestry conditions in Nothofagus nervosa (= N. alpina; Nothofagaceae)

? Context

There is evidence that Nothofagus nervosa (= N. alpina) is suitable for timber production in temperate regions due to its wood quality and fast growth. However, high intra-specific variability in the architectural traits of this species limits its usefulness.

? Aims

This study was aimed at evaluating intra-specific variability in the architecture of N. nervosa trees at the population level, with emphasis on traits related to the suitability of trees for timber production.

? Methods

The size of 13-year-old trees installed in an experimental field population and the extent of differentiation between trunk and branches were compared among families (trees derived from different mother trees).

? Results

The large majority of trees exhibited architectural features indicative of high suitability for timber production: clear differentiation between trunk and main branches and few occurrences of permanent trunk forks, apex deaths, and sylleptic branching. Trees belonging to different families differed in height and trunk diameter. Micro-environmental conditions had a very significant effect on most architectural traits, including the trunk differentiation.

? Conclusions

N. nervosa emerges as a suitable option for timber production in temperate regions. Trunk growth seems to be under both environmental and genetic control in this species.     

The incorporation of extreme drought events improves models for beech persistence at its distribution limit

Context

Projections of species distribution models under future climate are usually based on long-term averages. However, singular extreme drought events presumably contribute to the shaping of distribution limits at the retreating low-elevation xeric limits.

Methods

The objectives of this study were to set up a distribution model based on extreme drought events (EDM), which uses sanitary logging information as a proxy of vitality response of beech, and compare it with the results of classical species distribution models (SDMs).

Results

Predictions of the EDM for 2025 were in agreement with those of the SDM, but EDM predicted a more serious decline in all regions of Hungary towards the end of the century.

Conclusion

These results suggest that the predicted increase in frequency and severity of drought events may further limit the distribution of beech in the future.     

Assessing genetic variation to improve stem straightness in Eucalyptus globulus

Context

Stem straightness is an important trait for growers and processors of Eucalyptus globulus logs for solid-wood products.

Aims

The aims of the study were to determine the extent of genetic variation in stem deviation from straightness in E. globulus and assess the utility of a six-point subjective scoring method as a selection criterion for stem straightness.

Methods

Two E. globulus progeny trials, grown under solid-wood product regimes, were studied. At age 9 years (post-thinning), stem straightness was measured using both image analysis and a six-point subjective scale. Diameter at breast height (DBH; 1.3 m) was measured at both age 5 (pre-thinning) and age 9 years.

Results

Significant additive genetic variation was observed. Strong, positive and significant additive genetic correlations were observed between the stem straightness assessment methods and between DBH at ages 5 and 9 years. Significant positive genetic correlations were shown between subjectively scored stem straightness and DBH at both ages 5 and 9 years.

Conclusion

The six-point subjective scoring method is a cost-effective selection criterion for stem straightness in E. globulus. The image measurement technique may be applied where objective estimates of stem straightness are required, for training purposes and to verify subjective scores.     

Nutrient concentration and allometric models for hybrid eucalyptus planted in France

Context

Short rotation coppice (SRC) of hybrid Eucalyptus has been developed in France for almost 30 years for the production of pulp and paper and, since a few years, for energy purposes. In the traditional pulp production, only the stems are harvested, whereas the whole biomass may be harvested for energy purposes. Thus, a range of different harvest scenarios need to be considered with higher plantation densities or younger age of harvest for example.

Aims

The objective of this study was to build models to estimate biomass and nutrient content of eucalyptus at different ages and so to estimate the production and the nutrient exportation of a SRC, depending on the different harvest scenarios.

Methods

Over 250 trees were sampled in 16 stands at ages from 1 to 15 years. For each tree, biomass of different compartments and nutrient contents were recorded.

Results

A complete set of equations for the four compartments (wood, bark, branches, and leaves) of aboveground biomass and for nutrient concentration was set up.

Conclusion

Biomass and its allocation to different compartments and nutrient concentrations depended on the dimension and/or the age of the tree. In particular, nutrient concentration decreased with increasing tree diameter.     

Ectomycorrhizal communities associated with silver fir seedlings (Abies alba Mill.) differ largely in mature silver fir stands and in Scots pine forecrops

Context

The requirement for rebuilding forecrop stands besides replacement of meadow vegetation with forest plants and formation of soil humus is the presence of a compatible ectomycorrhizal (ECM) fungal community.

Aims

This study aims to assess ectomycorrhizal fungi diversity associated with silver fir (Abies alba Mill.) seedlings regenerating in silver fir stands and Scots pine forecrops.

Methods

One-year-old seedlings were sampled in six study sites: three mature fir forests and three pine forests. ECM fungi were identified by polymerase chain reaction amplification and sequencing of the internal transcribed spacer of rDNA.

Results

The mean mycorrhizal colonization exceeded 90 %. Thirty-six ectomycorrhizal taxa were identified in fir stands and 23 in pine forecrops; ten out of these species were common to both stands. The fungal communities were different between study sites (R?=?0.1721, p?=?0.0001). Tomentella stuposa was the only species present at all sites.

Conclusion

Silver fir seedlings in Scots pine forecrops supported smaller ECM fungal communities than communities identified in mature silver fir stands. Nevertheless, fungal colonization of seedling roots was similar in both cases. This suggests that pine stands afforested on formerly arable land bear enough ECM species to allow survival and growth of silver fir seedlings.     

Thinning increases cone production of stone pine (Pinus pinea L.) stands in the Northern Plateau (Spain)

Context

Edible stone pine (Pinus pinea L.) nut is a forest product which provides the highest incomes to the owners of stone pine forests.

Aim

The objective of this work is to evaluate the effect of first thinning on growth and cone production in an artificially regenerated stand in order to determine optimum intensity.

Methods

A thinning trial was installed in 2004 to compare two thinning regimes (heavy and moderate) and a control treatment. From 2004 to 2012, six inventories of forest attributes were carried out, and the cone crop was harvested annually. We evaluated the effect of thinnings on growth using repeated measures analysis of variance with a mixed model approach. With regards to cone production, we first estimated the probability of finding cones in a tree by applying a generalized mixed model and then estimated cone production by using a mixed model, including climatic variables.

Results

We found that thinning had a positive influence on tree diameter increment. Thinning increased the probability of finding cones and cone production. However, significant differences between heavy and moderate thinnings were not found.

Conclusion

We recommend early silvicultural treatments in stone pine stands to favor the development of trees and larger edible pine nut production.     

US strategy for forest management adaptation to climate change: building a framework for decision making

Context

Recent policy changes in the USA direct agencies managing federal forests to analyze the potential effects of climate change on forest productivity, water resource protection, wildlife habitat, biodiversity, and other values.

Aims

This paper describes methods developed to (1) assess current risks, vulnerabilities, and gaps in knowledge; (2) engage internal agency resources and external partners in the development of options and solutions; and (3) manage forest resources for resilience, not just in terms of natural ecosystems but in affected human communities as well.

Methods

We describe an approach designed to characterize certain climate change effects on forests, and estimate the effectiveness of response options ranging from resistance to a realignment of management objectives.

Results

Field testing on a 6,300 km² area of conifer forest in the northwestern USA shows this decision model to be useful and cost-effective in identifying the highest sensitivities relating to vegetation management, biological diversity, water resources and forest transportation systems, and building consensus for adaptive strategies and actions.

Conclusions

Results suggest that this approach is an effective means for guiding management decisions to adapt to the effects of climate change, and provides an empirical basis for setting budgetary and management priorities.     

Oak powdery mildew changes growth patterns in its host tree: host tolerance response and potential manipulation of host physiology by the parasite

Context

Parasites can induce strong effects on their host’s growth, not only as a result of host resource exploitation (growth loss) but also with a potential adaptive value for host (tolerance response) and themselves (increased transmission).

Aims

We assessed these three types of phenotypic changes in oak seedlings infected by powdery mildew.

Methods

A manipulative field experiment with three levels of parasite inoculum was designed in order to tease apart infection from genetic effects on oak growth. Seedlings were monitored during 3 years for height growth, phenology and infection.

Results

Powdery mildew infection induced both significant growth loss and qualitative changes in plant architecture. The most striking and unexpected change was increased growth polycyclism in infected seedlings. This benefitted both the host as a form of compensation for infection-caused height loss, and the pathogen, by increasing sporulation.

Conclusion

The study highlights the effect of parasites in the expression of plant phenotypic traits, such as phenology and ultimately tree architecture. Both host tolerance and parasitic manipulation may be involved in the observed changes in growth patterns. These results suggest a complex interplay between development and defence in trees and emphasize the need to better assess tolerance mechanisms when considering the defence strategies of trees against pathogens.