Estimating water use of sclerophyllous species under East-Mediterranean climate: III. Tabor oak forest sap flow distribution and transpiration

The annual course of daily transpiration and the hydrological balance of a Tabor oak forest were determined. The study was done in a representative forest within the natural geographical range of the species in the lower Galilee region of Israel. The climate is sub-humid with a rainless dry season from May to October. A partial water balance of a 0.1 ha area supporting an average of 14 trees was calculated from: (a) soil water content (SWC) measured by a Neutron Probe at depths of from 0.2 to 8 m, and (b) daylight transpiration rate measured with sap flow sensors by the heat pulse technique.Soil–bedrock complex water content (%) in the first 2 m of the profile fluctuated strongly between 5 and 20% depending on the season. The water content increased with depth from about 10% at 2.0 m depth to more than 20% at 5.0 m depth. For depths exceeding 5.5 m seasonal fluctuations in water content were negligible and water content ranged from 30 to 35%. After a dry winter, water content generally decreased within the main root zone down to about 2.0 m depth. Monthly changes in water content (mm) were greatest at depths of 0.35–1.0 m. Only minor changes in the soil–bedrock complex water content were recorded at greater depths. After a very rainy winter (2002/2003), decreases in soil–bedrock complex water content in the upper 2 m were much larger than after a dry winter. Fluctuations of soil–bedrock complex water content in deeper regions were larger in the wetter year, probably the result of drainage.Sap velocity was measured at six depths in the sapwood, from 4 to 44 mm, at 8 mm intervals. Sap velocity declined with depth, hence, sap flux density too.Based on sap velocity measurements performed during 4 years, the annual average daily transpiration (T) was 0.796 mm/day. This sums up to 239 mm during ∼300 days of leaf carriage, i.e. 41.3% of the 578 mm average annual rainfall for the area in the last 50 years. In a relatively dry year (rainfall of 432.7 mm) total water withdrawal from the 8 m soil–bedrock profile was 81% of the annual rainfall; of this amount 69% were transpired by the oak trees (239.0 mm), or 55% of the annual rainfall. In a relatively wet year (annual rainfall 801.4 mm) total water withdrawal was 67%; of this amount 45% would be transpired by the oak trees, or 30% of the annual rainfall.     

Drivers of bryophyte diversity allow implications for forest management with a focus on climate change

Understanding the major drivers of diversity in forests is crucial for ecologists, conservationists, and particularly forest managers. In most forested habitats, bryophytes are diverse and important primary producers. Here we report the first study of the relative importance of regional macroclimate as compared to local variables on abundance, species richness, and community composition of bryophytes growing in soil and in dead wood in a mountain temperate forest. Using PCA axes, we built predictor sets for macroclimate, microclimate, soil attributes, and dead wood availability. The explanatory power of each set was tested using variance partitioning. Abundance and species richness of soil bryophytes was best explained by microclimate, whereas the community composition did not distinctively differ between the environmental sets. In contrast, dead wood bryophyte abundance, species richness, and community composition was clearly driven by macroclimate. Among the single axes, the component represented best by soil moisture was the main driver for soil bryophyte abundance. In contrast, dead wood bryophyte abundance was mostly affected by components correlated with minimum global radiation and minimum temperatures as well as by the component represented by dead wood. The component represented by canopy openness was superior in explaining the community composition of both soil and dead wood bryophytes. We conclude that (1) dead wood amounts should be increased in closed stands to act as a buffer during climate changes, and (2) open canopy, which provides important habitats for soil-inhabiting bryophytes, should be provided by management with slow reforestation after natural or logging openings.     

Variation in the radial patterns of sap flux density in pubescent oak (Quercus pubescens) and its implications for tree and stand transpiration measurements

Radial variation in sap flux density across the sapwood was assessed by the heat field deformation method in several trees of Quercus pubescens Wild., a ring-porous species. Sapwood depths were delimited by identifying the point of zero flow in radial patterns of sap flow, yielding tree sapwood areas that were 1.5-2 times larger than assumed based on visual examinations of wood cores. The patterns of sap flow varied both among trees and diurnally. Rates of sap flow were higher close to the cambium, although there was a significant contribution from the inner sapwood, which was greater (up to 60% of total flow) during the early morning and late in the day. Accordingly, the normalized difference between outer and inner sapwood flow was stable during the middle of the day, but showed a general decline in the afternoon. The distribution of sap flux density across the sapwood allowed us to derive correction coefficients for single-point heat dissipation sap flow measurements. We used daytime-averaged coefficients that depended on the particular shape of the radial profile and ranged between 0.45 and 1.28. Stand transpiration calculated using the new method of estimating sapwood areas and the radial correction coefficients was similar to (Year 2003), or about 25% higher than (Year 2004), previous uncorrected values, and was 20-30% of reference evapotranspiration. We demonstrated how inaccuracies in determining sapwood depths and mean sap flux density across the sapwood of ring-porous species could affect tree and stand transpiration estimates.     

Expansion potential of invasive tree plants in ecoregions under climate change scenarios: an assessment of 54 species at a global scale

Climate change may increase expansion risk of invasive tree plants (ITPs) worldwide. Ecoregions are the power conservation tool for the management of ITPs. However, few studies have investigated the relationship between ITP expansion and ecoregions at the global scale under climate change scenarios. Here, we provided a method to evaluate the expansion potential of 54 representative ITPs in ecoregions specifically under influences of the changing climate at the global scale. We found that climate change due to increasing greenhouse gas (GHG) concentration plays a positive role on the expansion of ITPs. We determined two of the most important ecoregion hotspots of ITP expansion potential, such as New Zealand and South Africa. In addition, ITPs were likely to have a large potential to expand in ecoregions of five different biomes, like temperate broadleaf and mixed forests. The potential expansion of ITPs would increase obviously in ecoregions of Boreal Forests/Taiga and Tundra. More importantly, the ecoregions of high elevation belonging to Tropical and Subtropical Coniferous Forests were expected to experience the higher expansion risk in the low GHG concentration scenario. Given our estimates of ITP expansion for ecoregions, management for the prevention and control for ITPs is urgent at the global scale.     

Predicting the distributions of suitable habitat for three larch species under climate warming in Northeastern China

The larch (Larix) genus is the most important species group in the forest ecosystems in Northeastern China, occupying about 25% of the forest areas. The high tolerance to coldness and relatively fast growth rate make this genus the main species group for forestation. According to the predictions of the global circulation model CGCM3, temperature could rise by 2–4 °C over the next 100 years. Few studies have been conducted on the response of larch species to climate warming in Northeastern China. Such studies are becoming increasingly needed due to the economic and ecological significance of this genus. This paper studies the potential distribution ranges of three larch species under the current and the warming climate conditions. A new classification and regression tree technique, Random Forest, was used to investigate the potential distributions of three larch species, based on 18 environmental variables which reflect the climate, topography and soil conditions of Northeastern China. The results showed that the biological coldness index (BCI) is the most important factor for Dahurian larch, annual precipitation (AP) is the most important factor for Korean larch and elevation (DEM) is the most important factor for Prince Rupprecht larch.     

Deciphering the ozone-induced changes in cellular processes: a prerequisite for ozone risk assessment at the tree and forest levels

Key message

Ozone, one of the major atmospheric pollutants, alters tree growth, mainly by decreasing carbon assimilation and allocation to stems and roots. To date, the mechanisms of O₃ impact at the cellular level have been investigated mainly on young trees grown in controlled or semi-controlled conditions. In the context of climate change, it is necessary to introduce a valuable defence parameter in the models that currently predict O₃ impact on mature trees and the carbon sequestration capacity of forest ecosystems.

Context

Air pollution is an important factor that affects negatively forest ecosystems. Among oxidative air pollutants, ozone is considered as the most toxic in terms of impact on vegetation.

Aims

This paper focuses on the negative impacts of ozone on trees in controlled conditions or in their natural environment. The current knowledge of the responses at cell level is presented and ways to improve their use for ozone risk assessment of forest stands are discussed.

Methods

Information was collected from original papers or reviews, providing an overview of the research conducted over the last 60 years.

Results

The negative effects of ozone on carbon assimilation and tree biomass production were reviewed and discussed, with a focus on effects on cell processes implied in cell defence, including stomatal regulation, detoxification, signalling, and biosynthesis of wood compound.

Conclusion

In the context of increasing significance of O₃ flux approach, this review intends to shed light into the black box of defence processes, which are playing a crucial part within the effective O₃ dose modelling. Today, it is recognized that tropospheric ozone inhibits tree growth and its role on the future carbon sink of the forest ecosystem is discussed along with the combination of other environmental factors like elevated temperature, water, and nitrogen supply, likely to be modified in the context of climate change.

     

Predicting the activity of Heterobasidion parviporum on Norway spruce in warming climate from its respiration rate at different temperatures

We studied the effect of climate warming on Heterobasidion root rot in boreal forests by measuring respiration activity of pure cultures of Heterobasidion parviporum in Norway spruce (Picea abies) sawdust and by linking these data to temperature data obtained from three spruce forests located along a north‐south transect stretching from northern Germany to northern Finland. The pure cultures applied in this investigation were homokaryotic, but in a separate investigation, we found no significant difference between the activity of homo‐ and heterokaryotic isolates. We also found that the temperature response curves of growth and respiration rates of this fungus were similar and propose that respiration reflects the general activity of H. parviporum. The respiration data were scaled up to annual cumulative respiration activity using daily temperature measurements from soil and air in the spruce forest sites. The annual respiration activity of H. parviporum showed a linear relationship with the average annual air temperature. An increase in the annual air temperature by 5°C would raise the annual activity of H. parviporum in spruce roots in northern Finland, southern Finland and northern Germany by 91%, 53% and 40%, respectively. This increase remains below the predicted increase in forest growth in northern Finland but exceeds considerably the predictions for southern Finland. According to the previous literature, a number of other decay fungi show a similar activity response to temperature as H. parviporum, suggesting that this result can be generalized to decay fungi with similar ecological habits.     

Phenological and water-use patterns underlying maximum growing season length at the highest elevations: implications under climate change

Consequences of climate change on tree phenology are readily observable, but little is known about the variations in phenological sensitivity to drought between populations within a species. In this study, we compare the phenological sensitivity to temperature and water availability in Abies pinsapo Boiss., a drought-sensitive Mediterranean fir, across its altitudinal distribution gradient. Twig growth and needle fall were related to temperature, precipitation and plant water status on a daily scale. Stands located at the top edge of the distributional range showed the most favourable water balance, maximum growth rates and little summer defoliation. Towards higher elevations, the observed delay in budburst date due to lower spring temperatures was overcome by a stronger delay in growth cessation date due to the later onset of strong water-deficit conditions in the summer. This explains an extended growing season and the greatest mean growth at the highest elevation. Conversely, lower predawn xylem water potentials and early partial stomatal closure and growth cessation were found in low-elevation A. pinsapo trees. An earlier and higher summer peak of A. pinsapo litterfall was also observed at these water-limited sites. Our results illustrate the ecophysiological background of the ongoing altitudinal shifts reported for this relict tree species under current climatic conditions.     

Knowledge update in adaptive management of forest resources under climate change: a Bayesian simulation approach

Context

We develop a modelling concept that updates knowledge and beliefs about future climate changes, to model a decision-maker’s choice of forest management alternatives, the outcomes of which depend on the climate condition.

Aims

Applying Bayes’ updating, we show that while the true climate trajectory is initially unknown, it will eventually be revealed as novel information become available. How fast the decision-maker will form firm beliefs about future climate depends on the divergence among climate trajectories, the long-term speed of change, and the short-term climate variability.

Methods

We simplify climate change outcomes to three possible trajectories of low, medium and high changes. We solve a hypothetical decision-making problem of tree species choice aiming at maximising the land expectation value (LEV) and based on the updated beliefs at each time step.

Results

The economic value of an adaptive approach would be positive and higher than a non-adaptive approach if a large change in climate state occurs and may influence forest decisions.

Conclusion

Updating knowledge to handle climate change uncertainty is a valuable addition to the study of adaptive forest management in general and the analysis of forest decision-making, in particular for irreversible or costly decisions of long-term impact.     

Spatial distribution of the fruiting bodies of Agaricales in a Japanese red pine (Pinus densiflora) forest

To examine the effect of the spatial distribution of litter and intergeneric interaction on the spatial distribution of agaric fruiting bodies, we surveyed spatial distribution of fruiting bodies of Agaricales in a mixed forest dominated by Pinus densiflora (Sieb et Zucc.) from July 1999 to July 2002. Three 10 × 10-m plots with different vegetation and positions on a slope were established: Top-Mixed, Top-Pinus, and Bottom-Pinus. Litter thickness in the Top-Mixed plot was the thinnest among the three plots. During the study, we counted 3563 fruiting bodies in 27 genera from 13 families. The dominant genera were Collybia, Marasmius, Mycena, Rhodophyllus, and Lactarius, and showed an intrageneric aggregated distribution at a quadrat size of 1 m². Collybia and Lactarius formed fruiting bodies in arcs. The spatial distribution of Collybia, Marasmius, and Lactarius fruiting bodies tended to overlap in two consecutive years. In the Top-Mixed plot, the number of Marasmius fruiting bodies increased with increasing litter thickness, while that of Lactarius decreased with litter thickness. Values of C′_δ indicating degree of overlap were calculated for particular pairs of dominant fungal genera and the values differed between plots and years: for example, fruiting bodies of Marasmius and Mycena in the Bottom-Pinus plot were distributed aggregately in 1999 and 2000, but randomly in 2001, while they were distributed segregatedly in the Top-Pinus plot every year. Our study suggests that the spatial distribution of fungal fruiting bodies is affected by the distribution of litter in and between plots and that fungal flora is affected by vegetation.     

Current status and predicted impact of climate change on forest production and biogeochemistry in the temperate oceanic European zone: review and prospects for Belgium as a case study

Reviews of the current statuses of forests and the impacts of climate change on forests exist at the (sub)continental scale, but rarely at country and regional levels, meaning that information on causal factors, their impacts, and specific regional properties is often inconsistent and lacking in depth. Here, we present the current status of forest production and biogeochemistry and the expected impacts of climate change on them for Belgium. This work represents a case study for the temperate oceanic zone, the most important bioclimatic zone in northwestern Europe. Results show that Belgian forests are mainly young, very productive, and have a high C-sequestration capacity. Major negative anomalies in tree vitality were observed in the 1990s and—as result of disturbances—in the last decade for sensitive species as poplars and European beech. The most severe disturbances were caused by extreme climatic events, directly (e.g. storms) or indirectly (e.g. insect outbreaks after a mild autumn with an early/severe frost). Because of atmospheric deposition and soil fertilization (due to the previous use of the land), nutrient stocks of Belgian forests are likely to sustain the future enhancement in productivity which is expected to follow the increase in atmospheric CO₂ concentration that will occur in years to come. However, in the long term, such (enhanced) forest production is likely to be limited by nutrient deficiencies at poor sites and by drought for sensitive species such as beech and (particularly) Norway spruce. Drought conditions will likely increase in the future, but adverse effects are expected on a relatively limited number of tree species. The potential impacts of windstorms, insects and fungi should be carefully investigated, whereas fires are less of a concern.     

Assessing forest vulnerability and the potential distribution of pine beetles under current and future climate scenarios in the Interior West of the US

The aim of our study was to estimate forest vulnerability and potential distribution of three bark beetles (Curculionidae: Scolytinae) under current and projected climate conditions for 2020 and 2050. Our study focused on the mountain pine beetle (Dendroctonus ponderosae), western pine beetle (Dendroctonus brevicomis), and pine engraver (Ipspini). This study was conducted across eight states in the Interior West of the US covering approximately 2.2 million km² and encompassing about 95% of the Rocky Mountains in the contiguous US. Our analyses relied on aerial surveys of bark beetle outbreaks that occurred between 1991 and 2008. Occurrence points for each species were generated within polygons created from the aerial surveys. Current and projected climate scenarios were acquired from the WorldClim database and represented by 19 bioclimatic variables. We used Maxent modeling technique fit with occurrence points and current climate data to model potential beetle distributions and forest vulnerability. Three available climate models, each having two emission scenarios, were modeled independently and results averaged to produce two predictions for 2020 and two predictions for 2050 for each analysis. Environmental parameters defined by current climate models were then used to predict conditions under future climate scenarios, and changes in different species’ ranges were calculated. Our results suggested that the potential distribution for bark beetles under current climate conditions is extensive, which coincides with infestation trends observed in the last decade. Our results predicted that suitable habitats for the mountain pine beetle and pine engraver beetle will stabilize or decrease under future climate conditions, while habitat for the western pine beetle will continue to increase over time. The greatest increase in habitat area was for the western pine beetle, where one climate model predicted a 27% increase by 2050. In contrast, the predicted habitat of the mountain pine beetle from another climate model suggested a decrease in habitat areas as great as 46% by 2050. Generally, 2020 and 2050 models that tested the three climate scenarios independently had similar trends, though one climate scenario for the western pine beetle produced contrasting results. Ranges for all three species of bark beetles shifted considerably geographically suggesting that some host species may become more vulnerable to beetle attack in the future, while others may have a reduced risk over time.     

Correction to: Climatic factors controlling stem growth of alien tree species at a mesic forest site: a multispecies approach

European Journal of Forest Research -     

Temperature variation and distribution of living cells within tree stems: implications for stem respiration modeling and scale-up

Few studies have examined variation in respiration rates within trees, and even fewer studies have focused on variation caused by within-stem temperature differences. In this study, stem temperatures at 40 positions in the stem of one 30-year-old Norway spruce (Picea abies (L.) Karst.) were measured during 40 days between July 1994 and June 1995. The temperature data were used to simulate variations in respiration rate within the stem. The simulations assumed that the temperature-respiration relationship was constant (Q10 = 2) for all days and all stem positions. Total respiration for the whole stem was calculated by interpolating the temperature between the thermocouples and integrating the respiration rates in three dimensions. Total respiration rate of the stem was then compared to respiration rate scaled up from horizontal planes at the thermocouple heights (40, 140, 240 and 340 cm) on a surface area and on a sapwood volume basis. Simulations were made for three distributions of living cells in the stems: one with a constant 5% fraction of living cells, disregarding depth into the stem; one with a living cell fraction decreasing linearly with depth into the stem; and one with an exponentially decreasing fraction of living cells. Mean temperature variation within the stem was 3.7 degrees C, and was more than 10 degrees C for 8% of the time. The maximum measured temperature difference was 21.5 degrees C. The corresponding mean variation in respiration was 35% and was more than 50% for 24% of the time. Scaling up respiration rates from different heights between 40 and 240 cm to the whole stem produced an error of 2 to 58% for the whole year. For a single sunny day, the error was between 2 and 72%. Thus, within-stem variations in temperature may significantly affect the accuracy of scaling respiration data obtained from small samples to whole trees. A careful choice of chamber position and basis for scaling is necessary to minimize errors from variation in temperature.     

Evolution of soil organic matter composition and edaphic carbon effluxes following oak forest clearing for pasture: climate change implications

This research encompasses soil CO₂ emission studies from forest and pasture couplets located in northwestern Spain, where two mature oak forest ecosystems partially cleared for pasture 5 or 50?years ago were selected to monitor soil C effluxes during 2?years. The CO₂ exchanges in the soil–atmosphere interphase of forest and pasture plots were seasonally determined using portable infrared gas analysers. At the same time, soil samples from both forest and pasture ecosystems were used to carry out long-term incubations under laboratory conditions. Solid-state ¹³C-NMR with cross-polarization/magic angle spinning was applied to determine the deforestation effects on soil organic matter (SOM) composition. Pasture implantation caused a notable decline of the labile C pool and a decrease in the total soil C, with an increase in both the SOM humification and the relative concentration of phenolic and carboxyl C. After only 5?years, the deforestation caused a general decrease in the soil CO₂ emissions with reduced seasonal fluctuations, these effects being even more intense 50?years after clearing. The correlation observed in oak forests between the CO₂ measured in situ and the soil temperature, is masked in pasture ecosystems by the high summer soil dryness. After the partial disappearance of soil C stocks caused by deforestation, a new long-term C input/output equilibrium seems to be established, probably due to the joint adaptation of both SOM and microbial communities in the old pasture soil; however, the entire soil C retention capacity remains still degraded as compared with the original uncleared forest ecosystem.     

Young conifer stands form a deer browsing refuge for an oak admixture: silvicultural implications for forest regeneration under herbivore pressure

There is little knowledge how ungulate pressure on forest regeneration may be mitigated by silvicultural methods. The knowledge is especially needed for artificially regenerated, deciduous tree species. We studied factors affecting browsing incidence by deer in the Pisz Forest District in Poland, an area where 10,000 ha of forest was damaged by a 2002 hurricane. In 2006, we established three experimental plots (in total, 22.6 ha), in which the main species was Scots pine (Pinus sylvestris) admixed with pedunculate oak (Quercus robur). The data on browsing were collected in 2008–2015. In general, oak browsing incidence was unrelated to oak planting density. On a plantation scale, it was significantly affected by the pine age. Although in each variant all the oaks were browsed for four consecutive years (2009–2012), in 2013 browsing incidence began to decrease. When the pines grew higher and formed a physical barrier, it was harder for deer—roe deer (Capreolus capreolus), red deer (Cervus elaphus) and moose (Alces alces)—to move through and locate the oaks. Moreover, within plantations, oak browsing incidence was higher in the patches with shorter pines. Browsing of individual saplings or small groups of saplings was also negatively affected by the height of neighbouring pine saplings. Oak density influenced deer selectivity depending on the tree height. In a low oak tree density, browsing incidence was unrelated to oak height, while in higher tree density, deer selected oaks of the height between 40 and 100 cm. We postulate that deciduous admixture in a coniferous (unattractive) stand can be planted with a few year delay. Older coniferous trees should impede locating of attractive tree species by deer and the browsing incidence.     

Seasonal variation of soil respiration in a Pinus cembra forest at the upper timberline in the Central Austrian Alps

Soil respiration (R) of a 95-year-old Pinus cembra L. forest at the alpine timberline was measured continuously from October 2001 to January 2003 with an automated multiplexing gas exchange system. There was significant spatial variability in soil respiration, and R at a soil temperature of 10 degrees C (R10) decreased by about 20% m(-1) with increasing distance from the trunk. Needle litter and fine root density also decreased. The spatially averaged annual soil CO2 efflux was 35 g C m(-2) year(-1) in 2002. About 70% of the temporal variation in soil respiration could be explained by variations in soil temperature, whereas the influence of soil water potential and thus soil water content was negligible because soil water availability was supra-optimal.