Screening species-rich communities for the variation in functional traits along environmental gradients may help understanding the abiotic drivers of plant performance in a mechanistic way. We ...investigated tree leaf trait variation along an elevation gradient (1000-3000 m) in highly diverse neotropical montane forests to test the hypothesis that elevational trait change reflects a trend toward more conservative resource use strategies at higher elevations, with interspecific trait variation decreasing and trait integration increasing due to environmental filtering. Analysis of trait variance partitioning across the 52 tree species revealed for most traits a dominant influence of phylogeny, except for SLA, leaf thickness and foliar Ca, where elevation was most influential. The community-level means of SLA, foliar N and Ca, and foliar N/P ratio decreased with elevation, while leaf thickness and toughness increased. The contribution of intraspecific variation was substantial at the community level in most traits, yet smaller than the interspecific component. Both within-species and between-species trait variation did not change systematically with elevation. High phylogenetic diversity, together with small-scale edaphic heterogeneity, cause large interspecific leaf trait variation in these hyper-diverse Andean forests. Trait network analysis revealed increasing leaf trait integration with elevation, suggesting stronger environmental filtering at colder and nutrient-poorer sites.
•Fagus sylvatica, Europe’s most important temperate hardwood tree species, is drought sensitive.•This review analyses drought responses from the molecular physiological to the whole-tree level.•The ...large leaf area and the fine root system, rather than the hydraulic architecture, are most sensitive.•Beech suffers from recent growth reductions in large parts of its distribution range.
European beech (Fagus sylvatica) is the dominant tree species of Central Europe’s natural forests and one of the continent’s most important timber species. This highly competitive species is known to be drought-sensitive and thus may increasingly be threatened by climate change-related heat waves and drought in part of its distribution range. Tree responses and tolerance to drought are complex processes that are best understood by adopting a multi-level analysis spanning from the molecular physiological to the tree and stand levels. Here I review recent progress in our understanding of beech drought responses in all relevant fields of research, notably adjustments in cellular biochemistry, responses of photosynthesis, stomatal regulation and leaf water status, the vulnerability of the hydraulic and phloem systems, adaptive responses of the fine root system, leaf area adjustments, long-term declines in radial growth, and drought-induced tree mortality. A special focus is on population differences in drought tolerance as the basis for the selection of drought-hardier provenances. The evidence from the different research fields is brought together with the aim to develop a multi-disciplinary perception of beech drought response, to identify weak components in the species’ drought response strategy, and to suggest future research efforts to close knowledge gaps.
Aim In order to investigate the relative importance of ecological (habitat specialization) and biogeographical (speciation, geographical dispersal limitation) processes as causes of non-random ...spatial distribution of tree species in the mountain forests of Malesia, we analysed the elevational change in the taxonomic and phylogenetic diversity of tree assemblages in different biogeographical subregions. Location Malesia (Borneo, Java, Sulawesi and the Philippines). Methods Tree inventory data of 12 old-growth forests from a wide elevational range (650–3080 m a.s.l.) were taxonomically harmonized and standardized (50 random draws of 245 individuals each per plot), and the phylogeny of 204 genera was resolved and scaled to its evolutionary origin. The taxonomic and phylogenetic diversities were calculated using effective generic measures, and the diversity patterns analysed by regression, ordination and classification. Results The primary factor determining the diversity patterns of the tree assemblages was elevation, whereas the influence of region was surprisingly low. This results in common elevational patterns in taxonomic and phylogenetic community structure across western and central Malesia. The major clades of the contemporary mountain forest trees must therefore have evolved before the formation of the Malay Archipelago in its present form (sympatric speciation). Taxonomic richness and phylogenetic diversity exhibited opposite trends with elevation. Generic richness decreased linearly with elevation; the phylogenetic structure of high-elevation forests revealed overdispersion, indicating convergent trait evolution towards higher elevations, whereas the submontane and colline assemblages showed clustering with a considerable number of confamilials. The upper montane forests of Borneo and Sulawesi were characterized by the dominance of Southern Hemisphere conifers, which differentiated them from lower-elevation communities. Main conclusions Our results indicate that ecological, evolutionary and biogeographical processes (environmental filtering, sympatry and long-distance dispersal) have shaped the contemporary community structure of Malesian mountain forests. Wallace's Line may represent a significant barrier between the lowland tree floras of Borneo and Sulawesi, but this is not true for those at higher elevations. The uniqueness of high-elevation forests in terms of their high phylogenetic diversity and of their unusual structure calls for a high priority in conservation programmes.
•Three common sap flow measuring techniques were compared and calibrated.•Thermal dissipation probes underestimated gravimetric flow by 23–45%.•Species-independent re-parameterization significantly ...improved accuracy.•Heat field deformation system overestimated flux density by ∼11%.•At low to medium flow rates, heat ratio method showed highest accuracy.
Sap flow probes are routinely used in forest and horticulture hydrology for estimating tree water use. This requires unbiased measurements when upscaling from tree to stand level, but accuracy and comparability of different thermometric methods have been questioned. Three sap flow measuring techniques were compared against gravimetric flow measurement in cut stem segments: ‘Granier-type’ thermal dissipation probes (TDP; three different sensor types), the heat field deformation method (HFD), and the heat ratio method (HRM). For the empirical methods (TDP and HFD), new calibration parameters were estimated using a nonlinear hierarchical modelling approach. 66 stem segments from five temperate, diffuse-porous tree species (9–16cm stem diameter, 100cm stem length) were exposed to a wide range of flux densities by applying subatmospheric pressure (−50 to −650hPa) analogous to natural flow conditions in the field.
All TDP probes underestimated flux density by 23–45% when calculated with Granier's original calibration parameters, with the deviation increasing with flux rate. The accuracy was significantly improved by estimating new calibration parameters, especially for probes differing from Granier's original sensor design. Species-specific parameters further improved accuracy, although the species differences might partially be explained by variation in the observed ranges of sap flux. The HFD sensor overestimated gravimetric flow by ∼11%; empirical calibration did not improve its accuracy compared to the manufacturer's equation. At low to medium flow rates, the HRM system achieved higher accuracy than the other probes (0.8% underestimation), while performing poorly at high flux rates under our measurement settings (energy input of 25J). Both for TDP and HFD sensors, we observed a surprisingly large variability in calibration parameters between different stems of the same species.
We conclude that (i) TDP and HFD sensors require species-specific calibration to measure sap flux with high accuracy, (ii) the original Granier equation cannot be used for TDP probes with deviating design, and (iii), at low to medium flow rates, the highest accuracy can be achieved with HRM sensors. Our results help to increase the accuracy of tree sap flow measurements with thermal dissipation probes, and to assess various levels of errors related to the different thermometric methods. This is important when synthesizing forest transpiration data on regional and global scales.
Key message
In the five temperate tree species, leaf turgor loss point and the stringency of stomatal regulation are not related to each other and to the drought sensitivity of radial growth, ...suggesting that additional factors exert a large influence on the species’ drought tolerance.
Context
How trees are responding to drought will largely determine their fitness and survival in a warmer and drier world. Much of our understanding of the drought response strategies of woody plants has been based on the study of either plant hydraulics or leaf water status dynamics or stomatal behavior, while the interaction of these components is less often studied.
Aims
To examine the relatedness of leaf tissue osmotic and elastic properties to the isohydry–anisohydry syndrome in adult trees of five co-occurring broadleaf tree species (
Acer pseudoplatanus
L.,
Carpinus betulus
L.,
Fagus sylvatica
L.,
Fraxinus excelsior
L., and
Tilia cordata
Mill.), which differ in the stringency of stomatal regulation.
Methods
Adult trees of the five species were accessed with a mobile canopy lift and pressure–volume (p-v) curves of sun leaf tissue analyzed for species differences and seasonal change in p-v curve parameters. The extent of seasonal fluctuation in daily leaf water potential (Ψ
l
) minima served to position the species along the isohydry-anisohydry continuum.
Results
The five species differed greatly in the bulk modulus of elasticity (
ε
) (12 MPa to 33 MPa) and, to a lesser extent, in leaf water potential at turgor loss (
π
tlp
) (− 2.3 MPa to − 2.9 MPa), exhibiting species-specific combinations of p-v parameters with the extent of Ψ
l
fluctuation. However,
π
tlp
and
ε
were only weakly, or not at all, related to the species’ position along the isohydry–anisohydry continuum. Anisohydric
Fagus sylvatica
with high
ε
and relatively low
π
tlp
had a more drought-sensitive radial growth than the fairly isohydric
Tilia cordata
with low
ε
and relatively high
π
tlp
.
Conclusion
The five coexisting tree species exhibit largely different drought response strategies, which are partly determined by species differences in leaf tissue elasticity and the stringency of stomatal regulation.
Despite a large body of studies investigating soil organic carbon (SOC) stocks and potential influencing factors, the impact of contrasting parent material, particularly in the subsoil, has received ...little attention. To reveal potential effects varying parent materials exert on SOC stocks, we investigated chemical (14C content and overall chemical composition via 13C NMR spectroscopy) and plant/microbial related parameters (root mass, amino sugars) of bulk soil and soil organic matter fractions from topsoil, subsoil, and rhizosphere soil at three European beech stands (Fagus sylvatica L.) only differing in parent material (Tertiary sand, Quaternary loess, and Tertiary basalt).
The results suggest that the clay fraction, its amount being largely dependent on the respective parent material, took a central role in shaping differences in SOC stocks among the investigated sites by affecting soil organic matter stabilization via organo-mineral association and aggregation. This fraction was particularly relevant in the subsoil, where it accounted for up to 80% of the bulk soil SOC stocks that decreased with decreasing amounts of the clay fraction (basalt > loess > sand site). Determining the soil's nutrient composition, parent material likely also indirectly affected SOC stocks by changing rhizosphere traits (such as fine root density or mortality) and by attracting root growth (and thus organic matter inputs) to subsoil with higher nutrient contents, where in situ root inputs in the form of rhizodeposits were likely the prime source of plant-derived SOC. However, root inputs also contributed in large part to topsoil SOC stocks and were associated with higher abundance of microbial compounds (amino sugars), whose relative importance increased with increasing soil depth.
Independent of soil depth and site, amino sugars and the amount of the clay fraction, combined with parameters related to the input of organic matter (root mass and amount of the particulate organic matter fraction) explained more than 90% of the variability in SOC stocks, indicating a key role of these measures in impacting SOC stocks. Because parent material directly or indirectly influenced these parameters, we demonstrate the necessity to consider differences in parent material when estimating and predicting SOC stocks.
Display omitted
•The clay fraction, particularly in the subsoil, shaped differences in SOC stocks.•In the topsoil, the relevance of the clay fraction was attenuated by root inputs.•Microbial residues were constant or slightly increased with soil depth.•Amino sugars, root mass, clay and POM explained ∼90% of variation in SOC stocks.
With increasing elevation, trees in tropical montane forests have to invest larger fractions of their resources into their fine roots in order to compensate for increasingly unfavorable soil ...conditions. It is unclear how elevation and related edaphic changes influence the variability in tree fine root traits and belowground functional diversity. We measured six fine root traits related to resource acquisition on absorptive fine roots of 288 trees from 145 species along an elevational gradient from 1000 m to 3000 m a.s.l. in tropical montane forests of the Ecuadorian Andes. We analyzed trait relationships with elevation and soil nutrient availability, and tested whether root functional diversity varied along these gradients. Fine roots at higher elevations and at more nutrient‐poor sites were thicker, had higher tissue densities, and lower specific root length and nutrient concentrations than at lower elevations. These trends were diluted by the coexistence of tree species with a broad range of different root traits within communities particularly towards lower elevations, where root functional diversity was significantly higher. We conclude that nutrient limitation and potentially further adverse conditions at higher elevations are strong environmental filters that lead to trait convergence towards a conservative resource use strategy, whereas different trait syndromes are equally successful at lower elevations.
•The first repeated terrestrial canopy gap inventory in a Eur. beech virgin forest.•We found a significant decrease in gap fraction and changes in gap size pattern.•High rates of gap closure were ...found that strongly dominated over gap formation.•There was a shift in the dominant gap filling process with increasing gap size.•Gaps released a heterogeneously structured understory and promoted its height growth.
Canopy gaps play a crucial role for forest dynamics processes, as they largely determine light transmission to lower canopy strata, thereby controlling the turnover of tree individuals in the stand. Even though their functional importance is undisputed, quantitative data on the rate of gap creation and gap closure, and the temporal change in gap size distribution patterns in temperate virgin forests are scarce. We used a repeated inventory (line-intercept sampling) of gap size frequency and fraction in a virgin beech (Fagus sylvatica) forest in the Slovakian Carpathians over a 10-year interval (2003–2013) to test the hypotheses that (i) disturbance intensity and thus gap creation and gap closure rate change only little over time, (ii) gaps persist or even expand, until they are filled primarily by vertical ingrowth of trees from lower strata, and (iii) gap creation promotes the height growth of released saplings and sub-canopy trees. In the 2003 and 2013 inventories, 37 and 30 gaps >20 m2 size were mapped along a total of 3217 m transect line investigated. The large majority of gaps was <100 m2 in size; large gaps >500 m2 were very rare. Gap fraction decreased significantly from 13.6% in 2003 to 8.2% in 2013 (associated with a reduction in mean gap size from 261 to 96 m2), indicating considerable variation in disturbance intensity in the past decades. Before 2003, both large gaps (probably caused by wind throw) and small gaps (from dying trees) have been formed, while only small gaps developed in the period 2003–2013. Small gaps were closed within a few years through rapid horizontal canopy expansion of neighboring beech trees, while vertical gap filling through ingrowth of lower canopy layers and regeneration was the dominant process in larger gaps. Saplings and trees in lower canopy layers formed a heterogeneous understory in large parts of recently formed gaps and responded to this process with increased height growth. We conclude that, despite considerable variation in disturbance intensity over time, this beech virgin forest responds to gap formation with high resilience through rapid lateral canopy expansion in small gaps and ingrowth of saplings and sub-dominant tree layers in larger gaps.
Aim To assess the consequences of agricultural intensification since the 1950s for Central Europe's plant communities of arable plants. Location Central Germany. Methods We employed a semipermanent ...plot design to analyse changes in 392 field interiors for 10 study regions, including sandy, limestone and loamy sites between the 1950s/60s and 2009. Results The analysis revealed a reduction in the regional species pool during the 50-year period of 23% (from 301 to 233 vascular species) and dramatic losses in plot-level diversity (from medians of 24 to 7). Median cover of spontaneously growing arable plants decreased from 30% to 3%. Losses were disproportionally larger on limestone sites while sandy sites maintained a larger fraction of the original diversity. Archaeophytes, neophytes and most Poaceae (including some aggressive weeds) showed similarly strong losses as indigenous plants. This contradicts the assumption that grasses and neophytes are generally profiting from agricultural intensification. Crop diversity decreased from 25 crop plants present in the 1950s/60s to only 16 in 2009, while crop cover generally increased. Winter cereals, oilseed rape and maize are dominant today, while all other crop types showed strong declines. Main conclusions Vegetation change over time depended on soil substrate with once markedly different arable communities now showing more homogenized community structure. Increasing Ellenberg indicator values for nitrogen and pH point to N fertilization as a major driver of change. New conservation measures such as the establishment of field flora reserves and agri-environment schemes with less intensive land use are thus urgently needed especially on limestone substrates to bring an end to the decline of this functionally distinct and increasingly threatened component of the Central European flora.
1. Optimal resource partitioning theory predicts that plants should increase the ratio between water absorbing and transpiring surfaces under short water supply. An increase in fine root mass and ...surface area relative to leaf area has frequently been found in herbaceous plants, but supporting evidence from mature trees is scarce and several results are contradictory. 2. In 12 mature Fagus sylvatica forests across a precipitation gradient (820-540 mm yr⁻¹), we tested several predictions of the theory by analysing the dependence of standing fine root biomass, fine root production and fine root morphology on mean annual precipitation (MAP), the precipitation of the study year, and stand structural and edaphic variables. The water storage capacity of the soil (WSC) was included as a covariable by comparing pairs of stands on sandy (lower WSC) and loam-richer soils (higher WSC). 3. Fine root biomass, total fine root surface area, fine root production and the fine root : leaf biomass production ratio markedly increased with reduced MAP and precipitation in the study year, while WSC was only a secondary factor and stand structure had no effect. 4. The precipitation effect on fine root biomass and production was more pronounced in stands on sandy soil with lower WSC, which had, at equal precipitation, a higher fine root biomass and productivity than stands on loam-richer soil. 5. The high degree of allocational plasticity in mature F. sylvatica trees contrasts with a low morphological plasticity of the fine roots. On the more extreme sandy soils, a significant decrease in mean fine root diameter and increase in specific root area with decreasing precipitation were found; a similar effect was absent on the loam-richer soils. 6. Synthesis. In support of optimal partitioning theory, mature Fagus sylvatica trees showed a remarkable allocational plasticity as a long-term response to significant precipitation reduction with a large increase in the size and productivity of the fine root system, while only minor adaptive modifications occurred in root morphology. More severe summer droughts in a future warmer climate may substantially alter the above-/below-ground C partitioning of this tree species with major implications for the forest C cycle.
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