Tracing drought effects from the tree to the stand growth in temperate and Mediterranean forests: insights and consequences for forest ecology and management

European Journal of Forest Research - How drought affects tree and stand growth is an old question, but is getting unprecedented relevance in view of climate change. Stress effects related to...     

Response of species and stand types to snow/wind damage in a temperate secondary forest,Northeast China

Snow/wind damage is one of the important natural disturbances in forest ecosystems, especially in a montane secondary forest. However, the effects of snow/wind damage remain unclear which affects the management of these forests. Therefore, we investigated the responses of species, individual tree traits and stand structure to snow/wind damage in a montane secondary forest. Results show that, amongst the canopy trees, Betula costata exhibited the most uprooting, bending and overall damage ratio (the number of damaged stems to the total number of stems in a plot); Quercus mongolica showed the highest breakage ratio and Fraxinus mandshurica and Juglans mandshurica the least overall damage ratios. Among the subcanopy trees, Carpinus cordata, Acer mono, Acer tegmentosum and Acer pseudo-sieboldianum showed the least uprooting and breakage, and the most bending damage. A. pseudo-sieboldianum demonstrated the lowest breakage and highest bending damage ratios. These findings indicate that different species have various sensitivities to snow/wind damage. Larger trees (taller, wider crowns) tend to break and become uprooted, while smaller trees are bent or remain undamaged, suggesting that tree characteristics significantly influence the types of damage from snow and wind. Stands of Q. mongolica and B. costata had the highest damage ratios, whereas A. pseudo-sieboldianum had the lowest snapping ratio. In summary, the severity and type of snow/wind damage are related to individual tree attributes and stand-level characteristics. Therefore, selection of suitable species (e.g., shorter, smaller with deep root systems, hard wood, bending resistance and compression resistance) and appropriate thinning are recommended for planting in the montane secondary forests.     

Functional traits and plasticity in response to light in seedlings of four Iberian forest tree species

We investigated the differential roles of physiological and morphological features on seedling survivorship along an experimental irradiance gradient in four dominant species of cool temperate-Mediterranean forests (Quercus robur L., Quercus pyrenaica Willd., Pinus sylvestris L. and Pinus pinaster Ait.). The lowest photochemical efficiency (F(v)/F(m) in dark-adapted leaves) was reached in deep shade (1% of full sunlight) in all species except Q. robur, which had the lowest photochemical efficiency in both deep shade and 100% of full sunlight. Species differed significantly in their survival in 1% of full sunlight but exhibited similar survivorship in 6, 20 and 100% of full sunlight. Shade-tolerant oaks had lower leaf area ratios, shoot to root ratios, foliage allocation ratios and higher rates of allocation to structural biomass (stem plus thick roots) than shade-intolerant pines. Overall phenotypic plasticity for each species, estimated as the difference between the minimum and the maximum mean values of the ecophysiological variables studied at the various irradiances divided by the maximum mean value of those variables, was inversely correlated with shade tolerance. Observed morphology, allocation and plasticity conformed to a conservative resource-use strategy, although observed differences in specific leaf area, which was higher in shade-tolerant species, supported a carbon gain maximization strategy. Lack of a congruent suite of traits underlying shade tolerance in the studied species provides evidence of adaptation to multiple selective forces. Although the study was based on only four species, the importance of ecophysiological variables as determinants of interspecific differences in survival in limiting light was demonstrated.     

Species traits as generalized predictors of forest community response to human disturbance

During the past decade, substantial effort has been aimed at identifying a group of easily measured, widely applicable plant traits that could serve as a metric to predict temporal change in plant communities. Traits that transcend regional differences in species composition and ecological conditions through their consistent response to disturbance would give managers a simple tool for tracking ongoing and future forest change in response to human disturbance. Although a wide range of plant traits has been associated with human disturbance, consistent traits have not emerged in the literature. However, this may due to differences in methodology among studies. Previously collected data from two eastern deciduous forest floras of North America (Iowa and Massachusetts) allowed us to evaluate whether such traits emerged, while controlling for methodological differences. We created a plot × traits matrix for each site and ordinated them used using principal components analysis (PCA) to identify disturbance gradients. We then assessed how well the traits most strongly associated with the disturbance gradients corresponded. The data sets shared only 4 of the 12 traits associated with disturbance and 6 of 12 traits associated with undisturbed sites. We did not find a consistent association between dispersal limitation and undisturbed sites or high dispersal capacity associated with disturbed sites. However, in both data sets degree of habitat specialization was an important variable on both ends of the disturbance gradient. Habitat generalists were associated with disturbance and habitat specialists were associated with more pristine sites in both data sets. These results agree with the findings of a wide range of site-specific studies, and we therefore propose that this variable is a promising candidate trait to provide a signal of forest community response to human disturbance. Our results are should be particularly encouraging for managers because in many regions morphological trait data are not readily available, and compiling such data is a very time-intensive task and unlikely to be feasible for most managers to undertake. With a list of species and a published flora, upwards of several hundred species can quickly be coded for degree of habitat specialization and used to track the impact of current disturbance, to predict future impacts, and to target specific species for reintroduction or restoration.     

Effects of environmental factors on plant functional traits across different plant life forms in a temperate forest ecosystem

New Forests - Plant functional traits have been shown to vary with environmental conditions. However, we lack empirical data on how plant functional traits of different plant life forms respond to...     

Belowground competition in a broad-leaved temperate mixed forest: pattern analysis and experiments in a four-species stand

We investigated fine root biomass and distribution patterns in a species-rich temperate Carpinus–Quercus–Fagus–Tilia forest and searched for experimental evidence of symmetry or asymmetry in belowground competition. We conducted extensive root coring and applied the recently introduced in situ-root growth chamber technique for quantifying fine root growth under experimentally altered intra- and interspecific root neighbourhoods in the intact stand. In 75% of all soil cores, fine roots of more than two tree species were present indicating a broad overlap of the root systems of neighbouring trees. Quercus trees had more than ten times less fine root biomass in relation to aboveground biomass or productivity (stem growth) and a much higher leaf area index/root area index ratio than Carpinus, Fagus and Tilia trees. The root growth chamber experiments indicated a high belowground competitive ability of Fagus in interspecific interactions, but a low one of Quercus. We conclude that (1) interspecific root competition is ubiquitous in this mixed stand, (2) root competition between trees can be clearly asymmetric, and (3) tree species may be ranked according to their belowground competitive ability. Fagus was found to be the most successful species in belowground competition which matches with its superiority in aboveground competition in this forest community.     

Abiotic and biotic drivers of species diversity in understory layers of cold temperate coniferous forests in North China

Understory plants are important components of forest ecosystems and play a crucial role in regulating community structures, function realization, and community succession. However, little is known about how abiotic and biotic drivers affect the diversity of understory species in cold temperate coniferous forests in the semiarid climate region of North China. We hypothesized that(1) topographic factors are important environmental factors affecting the distribution and variation of understory strata,and(2) different understory strata respond differently to environmental factors; shrubs may be significantly affected by the overstory stratum, and herbs may be more affected by surface soil conditions. To test these hypotheses, we used the boosted regression tree method to analyze abiotic and biotic environmental factors that influence understory species diversity, using data from 280 subplots across 56 sites in cold temperate coniferous forests of North China.Elevation and slope aspect were the dominant and indirect abiotic drivers affecting understory species diversity, and individual tree size inequality(DBH variation) was the dominant biotic driver of understory species diversity; soil water content was the main edaphic factors affecting herb layers. Elevation, slope aspect, and DBH variation accounted for 36.4, 14.5, and 12.1%, respectively, of shrub stratum diversity. Shrub diversity decreased with elevation within the range of altitude of this study, but increased with DBH variation; shrub diversity was highest on north-oriented slopes. The strongest factor affecting herb stratum species diversity was slope aspect, accounting for 25.9% of the diversity, followed by elevation(15.7%), slope(12.2%), and soil water content(10.3%). The highest herb diversity was found on southeast-oriented slopes and the lowest on northeast-oriented slopes; herb diversity decreased with elevation and soil water content, but increased with slope. The results of the study provide a reference for scientific management and biodiversity protection in cold temperate coniferous forests of North China.     

Species divergence in seedling leaf traits and tree growth response to nitrogen and phosphorus additions in an evergreen broadleaved forest of subtropical China

Tree competitiveness generally depends on trait plasticity in response to environmental change.The effects of nitrogen(N) and phosphorus(P) on leaf trait variability by species is poorly understood,especially in China’s subtropical forests.This study examined the seedling leaf traits and net primary productivity of all trees >5 cm DBH of two dominant species,Schima superba and Castanopsis carlesii,in an evergreen broadleaved forest fertilized with nitrogen(+N),phosphorus(+P),and nitrogen plus...     

大青山米老排树干径向生长变化及其对环境因子的响应

【目的】研究南亚热带大青山林区乡土珍贵树种米老排径向生长日变化特征及对环境因子的响应,为理解米老排生长-气候响应的生理机制、森林培育和保护等提供基础数据。【方法】利用点状树木径向生长变化记录仪对米老排径向生长变化进行连续观测,采用气象站同步测量辐射总量、土壤含水量、相对空气湿度、空气温度等环境因子数据。通过径向生长与环境因子的相关分析,研究米老排生长季第一个高峰期(5月)的不同分化等级径向生长日变化规律、不同天气条件下生长变化及径向生长-环境因子相互关系。【结果】1)不同分化等级米老排5月份的径向生长日变化量优势木(17.08μm)>平均木(13.94μm)>被压木(-1.81μm),差异极显著(P<0.01),且不同阶段的起始时间、阶段时长、变化量也有所不同。2)不同天气条件下,三种分化等级米老排径向日净生长量和日变化幅度均表现为雨天>晴天>阴天,受雨水影响,雨天条件下径向变化量远超其自身生长量;同种天气条件下,径向日净生长量优势木最大,日变化幅度则表现为平均木最大。3)不同分化等级米老排径向生长与相对空气湿度、降雨量呈极显著正相关关系,与气温、总辐射呈极显著负相关关系,而20 cm土壤含水率无显著性相关,且各影响因子均存在不同时间滞后效应。【结论】不同分化等级米老排由于林木生长状况的差异,导致其受到环境因子影响程度的不同,进而使得其径向生长变化量产生差异。     

Main biotic drivers of tree growth in a developing Juniperus thurifera stand in central Spain

Over the last few decades, abandonment of traditional management practices in Spain has led to widespread stand densification and has favoured the expansion of some forest species that previously exhibited more restricted ranges. Spanish juniper (Juniperus thurifera L.) woodlands are experiencing this phenomenon due to agricultural land abandonment and a decrease in the livestock pressure. Yet the main drivers underlying stand structure and dynamics at this novel scenario are poorly understood. In this study, we investigate the main biotic drivers of tree growth in a high-density stand of the dioecious J. thurifera at an early developmental stage (mean tree age of 32, ca. 50 years after land abandonment). Tree growth was measured by coring 299 individuals of different reproductive classes (male, female and non-reproductive). Neighbourhood models were used to assess the relative importance of tree size and neighbourhood competition on tree growth of each reproductive class in the study plot. We found that tree size had the strongest effect on tree growth, whereas the effect of intraspecific competition was negligible. We observed differences in growth patterns among reproductive classes along trunk diameter sizes. Thus, at smaller sizes, the three reproductive classes presented identical patterns of growth. However, at bigger sizes, females were the fastest growing individuals, followed by males and non-reproductive individuals. Overall, our results suggest that in young J. thurifera monospecific forests, where self-thinning processes may have not undergone yet, tree size and the reproductive class could play a relatively more important role than competition as drivers of tree growth. These findings constitute new information which contributes to understanding growth dynamics at early developmental stages in this dioecious species. Furthermore, our results provide guidelines for silvicultural managing, suggesting that at these young juniper stands thinning would likely not translate into enhanced growth on remnant trees.     

Decreased mushroom production in a holm oak forest in response to an experimental drought

A holm oak forest located in the Prades mountains (north-eastSpain) was subjected to an experimental drought, reducing soilwater moisture by 15 per cent by the use of plastic strips andfunnels that partially excluded rain throughfall and by ditchexclusion of water runoff. We monitored mushroom productionper plot once a week during 1999 and 2000. Drought treatmentdid not delay mushroom appearance, but reduced mushroom productionby 62 per cent on average. This suggests that in a drier environment– as predicted for Mediterranean areas in the near future– there is likely to be a decrease in mushroom production,and as a result, changes in some ecological parameters suchas soil organic matter decomposition, and also a reduction inthe economic and recreational value of these Mediterranean forests.     

Age and growth of a fire prone Tasmanian temperate old-growth forest stand dominated by Eucalyptus regnans, the world's tallest angiosperm

Forests are key components of the global carbon cycle, with deforestation being an important driver of increased atmospheric carbon dioxide. Temperate old-growth forests have some of the highest above ground stores of carbon of any forest types on Earth. Unlike tropical forests, the ecology of many temperate forests is dominated by episodic disturbance, such as high intensity fire. An exemplar of a particularly carbon dense temperate forest system adapted to infrequent catastrophic fires is the Eucalyptus regnans forests of south eastern Australia. Knowledge of the growth and longevity of old-growth trees is crucial to understanding the carbon balance and fire regimes of these forest systems. In an old-growth E. regnans stand in the Styx Valley in southern Tasmania we used dendrochronological techniques and radiocarbon dating to determine the age and stem growth of E. regnans and Phyllocladus aspleniifolius, an understorey rainforest conifer. Our analysis revealed that an even-aged cohort of E. regnans and P. aspleniifolius established in 1490–1510AD, apparently after a stand-replacing fire. The stem growth rates of E. regnans in the first 100 years were very rapid compared to the co-occurring P. aspleniifolius. That the longevity of E. regnans is >500 years challenges the suggested 350–450 year timeframe proposed for the widely held model of succession from eucalypt to rainforest. These forests not only have the potential to store vast amounts of carbon, but can also maintain these high carbon densities for a long period of time. Estimates of the capacity of these forests to sequester and store carbon should explicitly consider past harvesting and fire regimes and the potential increases in the risk of fire associated with climate change.     

Tree mortality in a natural mixed forest affected by stand fragmentation and by a strong typhoon in northern Japan

Windthrow is recognized as an extremely significant disturbance in many forests. Its effects are increased by stand fragmentation, which exposes the stand to strong winds. In this study, we investigated the change in tree mortality in fragmented stands with the distance from the stand edge, in a conifer–broadleaved mixed forest in northern Japan. We set out experimental plots having three stand sizes (400, 1,600, 6,400 m²) and examined the stand dynamics over 10 years. Tree mortality tended to be higher in smaller stands, although an effect of stand size was found only in the first 5 years of the study. Distance-dependent individual mortality was obvious in Abies sachalinensis, the most vulnerable major tree species, again in the first 5 years, suggesting that wind-risk management should emphasize the area within ca. 20 m from the stand edge. No distant-dependent effect was found, however, in the latter 5 years, in which there was a strong typhoon; tree deaths occurred throughout the stand (irrespective of distance within) as a result of this event. We conclude that the severity of wind can cause the features of wind-induced damage to differ; stand edge effects peculiar to a small forest are unlikely to occur with particularly strong winds, and the effect of fragmentation might therefore be clear only in weaker disturbances.     

Soil organic matter in European forest floors in relation to stand characteristics and environmental factors

Published data on the quantities of organic matter in the forest floor (SOM_fl) of European forest stands were collated. Studies of SOM_fl were included if the total sampled surface was at least 0.15 m², the surface of a single sample was at least 100 cm², live material was sorted out, and ash or carbon content was determined. Data from 59 forest stands were compared with regard to stand characteristics and environment. Using a single variable, tree genus was most important for the amount of SOM_fl (R ² _adj = 0.34). The amounts in spruce stands (41 × 10³ kg ha^?1) were significantly higher than those in larch, Douglas fir, oak and birch stands (4–11 × 10³ kg ha^?1). The best significant multiple model was genus combined with stand age and basal area (R ² _adj. = 0.72). The importance of litter quantity and quality for differentiating the tree genera is discussed.     

Differential response to soil drought among co-occurring broad-leaved tree species growing in a 15- to 25-year-old mixed stand

? Introduction

In the context of global environmental changes, better understanding of tree response to soil drought in young mixed species stands is needed to anticipate forest adaptation and management practices for the future.

? Materials and methods

We investigated the functional response of five co-occurring broad-leaved tree species growing in a 15- to 25-year-old mixed stand in northeastern France during the 2006 summer drought. We measured functional traits related to water acquisition (phenology, rooting pattern and vulnerability of xylem to cavitation) and the ecophysiological response (sap flux density, leaf water potential) of these species to soil water shortage.

? Results

Our study highlights contrasted drought response strategies among these species and a trade-off between leaf phenology, resistance of xylem to cavitation and root system depth.

? Conclusion

At this site, a deep root system seemed to be a key functional trait for the species to cope with drought. Quercus robur and Salix capreae can be characterised as drought-avoidance species as they possess a deep root system and therefore did not strongly experience soil drought. Despite deep rooting capacity, Betula pendula did not really avoid soil drought and strongly regulated transpiration during dry periods. Nevertheless, the earliness of budburst of this species contributes to high annual growth rate. In contrast, Carpinus betulus and Fagus sylvatica both displayed typical characteristics of drought-sensitive species.     

The forest vegetation and its differentiation under disturbance in a temperate mountain, China

Composition and structure of the main forest types, as well as the species changes under disturbance, were described as the representation of the forest vegetation in the north slope of Changbai mountain, northeast China. There were 3 forest zones from 600 m to 2,000 m asl, (1) broad-leaved-conifer mixed forest zone, 600–1,100 m asl, dominated byPinus koraiensis, Tilia amurensis, Acer mono, Ulmus japonica, (2) coniferous forest zone, 1,100–1,700 m asl, dominated byPicea jezoensis var.komarovii, P. koraiensis, Abies nephrolepis, and (3)Betula ermanii forest zone, 1,700–2,000 m asl, dominated byBetula ermanii, except for the east slope which was occupied byLarix olgensis. The evergreen component increased with elevation up to the upper limit of the coniferous forest zone (1,700 m), but disappeared in theB. ermanii zone. Species richness was significantly related to elevation. Towards higher elevation, the lapse rate of species-number was 1.6 species per 100 m, and it was only one species near the timberline. Species richness was reduced sharply under intensive disturbance, such as clear cutting, windfalletc. The species diversity was very low in the early stage of succession, and high in the later.     

Early response of stand structure and species diversity to strip-clearcut in a subtropical evergreen broad-leaved forest in Okinawa Island, Japan

Natural regeneration by strip-clearcut has rarely been used for restocking of evergreen broad-leaved forests in the East Asia. To contribute to a better understanding of the likely reasons for either the successful recovery of these forests or failure, the early response of stand structure and tree species diversity to strip-clearcut were studied in Okinawa Island, southwest Japan. The 4,000 m² study area was divided into 10 adjacent sections of equal area with a 10 m × 10 m sampling plot in the center, of which five sections were strip-clearcut while the remaining five sections uncut. Eight-year secondary succession following strip-clearcut showed that the density of woody stems, tree species diversity increased significantly not only in the regenerating stands but also in the residual stands compared to the primary stands. The primary dominant target species, Castanopsis sieboldii, continued to dominate both the regenerating and residual stands although colonizing species invaded abundantly in the stands, occupying approximately one-third of total tree species in each treatment. The community similarity analyses showed that the species composition were similar between the primary stands and the regenerating stands or residual stands reflected the high similarity amongst the primary stands and the regenerating stands or the residual stands. The similar stand structure, high tree species diversity and greater community similarity after strip-clearcut provided no evidence of forest degeneration, suggesting that the regenerating stand might gradually develop into stand similar to that prior to strip-clearcut.     

Dynamic response to climate change in the radial growth of Picea schrenkiana in western Tien Shan,ChinaOA

Forests are important ecosystems for economic and social development. However, the response of tree radial growth to climate has produced ‘divergent problems’ at high latitudes under global warming. In this study, the response stability and trend of Picea schrenkiana radial growth to variability in climate factors were analyzed in the mid-latitudes of the western Tien Shan Mountains. Radial growth of P.schrenkiana was mainly limited by minimum and mean temperatures. The divergent responses of ra...     

Ten years of fluxes and stand growth in a young beech forest at Hesse, North-eastern France

? Water and carbon fluxes, as measured by eddy covariance, climate, soil water content, leaf area index, tree biomass, biomass increment (BI), litter fall and mortality were monitored for 10 successive years in a young beech stand in Hesse forest (north-eastern France) under contrasting climatic and management conditions.

? Large year-to-year variability of net carbon fluxes (NEE) and to a lesser extent, of tree growth was observed. The variability in NEE (coefficient of variation, CV = 44%) was related to both gross primary production (GPP) and to variations in total ecosystem respiration (TER), each term showing similar and lower interannual variability (CV = 14%) than NEE. Variation in the annual GPP was related to: (i) the water deficit duration and intensity cumulated over the growing season, and (ii) the growing season length, i.e. the period of carbon uptake by the stand. Two thinnings occurring during the observation period did not provoke a reduction in either GPP, water fluxes, or in tree growth. Interannual variation of TER could not be explained by any annual climatic variables, or LAI, and only water deficit duration showed a poor correlation. Annual biomass increment was well correlated to water shortage duration and was significantly influenced by drought in the previous year.

? The relationship between annual NEE and biomass increment (BI) was poor: in some years, the annual carbon uptake was much higher and in others much lower than tree growth. However this relationship was much stronger and linear (r ² = 0.93) on a weekly to monthly time-scale from budburst to the date of radial growth cessation, indicating a strong link between net carbon uptake and tree growth, while carbon losses by respiration occurring after this date upset this relationship.

? Despite the lack of correlation between annual data, the NEE and BI cumulated over the 10 years of observations were very close.

? On the annual time-scale, net primary productivity calculated from eddy fluxes and from biological measurements showed a good correlation.