Genetic structure and phylogeography of <Emphasis Type="Italic">Juniperus phoenicea</Emphasis> complex throughout Mediterranean and Macaronesian regions: different stories in one

Key message

The genetic structure of Juniperus phoenicea in the Mediterranean Basin is inferred using amplified fragment length polymorphism markers (AFLP) markers. As other Mediterranean conifers, J. phoenicea populations show moderate levels of genetic diversity and interpopulational differentiation. The pattern of distribution of genetic diversity seems highly influenced by the climatic fluctuations which occurred in the Pleistocene.

Context

It has been stated that the genetic structure of Mediterranean conifers is mediated by the historical climatic changes and the geological rearrangements which occurred in the Mediterranean Basin. J. phoenicea provides an excellent example to test how its genetic structure is influenced by these events.

Aims

In this work, we study the amount and distribution of genetic diversity of J. phoenicea complex, in order to evaluate its taxonomic status and to reveal underlying phylogeographic patterns.

Methods

The molecular diversity was analyzed for 805 individuals from 46 populations throughout its distribution range using AFLP markers. Principal coordinate analysis, analysis of molecular variance (AMOVA), and Bayesian-based analysis were applied to examine the population structure.

Results

AFLP markers revealed moderate levels of intrapopulation genetic diversity, pairwise genetic differentiation, and a clear pattern of isolation by distance. Bayesian analysis of population structure showed five clusters related to the taxonomic status of J. phoenicea and J. turbinata, and a geographic pattern of genetic structure in J. turbinata.

Conclusion

All the analysis separate J. phoenicea from J. turbinata. For J. turbinata, up to four groups can be distinguished from a phylogeographic point of view. The genetic structure of J. turbinata seems highly influenced by climatic and geologic fluctuations occurring since the Oligocene.

     

A review of the development of Mediterranean pine–oak ecosystems after land abandonment and afforestation: are they novel ecosystems?

Context

Mediterranean landscapes are composed of different interacting vegetation patches. Pine and oak ecosystems form contiguous patches within these landscapes, in pure stands, or as mixed pine?Coak ecosystems. During the nineteenth century, pine forest distribution in the Mediterranean Basin increased dramatically as a result of large-scale re-forestation and spontaneous forest regeneration. At the same time, secondary succession of abandoned agricultural land allowed development of pine and oak ecosystems. Consequently, a pine?Coak mosaic has developed, which created opportunities for cross-colonization, i.e. species colonization from one ecosystem in the reciprocal system. Pines shed their wind-dispersed seeds and colonize Mediterranean oak vegetation. Oaks regenerate in different ecosystems, including pine forest understories.

Research question

This paper reviews fire-free landscape-scale dynamics of pine?Coak Mediterranean mosaics and analyze how landscape-scale interactions are leading to pine?Coak ecosystems by different processes.

Results

Published information from the Mediterranean Basin illustrates pathways of pine?Coak ecosystems formation. Using Mediterranean literature, I try to elucidate the factors that (1) control colonization potential and (2) modulate the resistance to colonization, in different habitats, land uses, and landscape settings.

Conclusion

Management implications for these mixed pine?Coak ecosystems are suggested. The question of whether they are novel ecosystems is discussed.     

Survival to prescribed fire of plantation-grown Corsican black pine in northern Portugal

Context

The current fire regime threatens black pine (Pinus nigra Arn.) persistence in the Mediterranean Basin, which recommends larger-scale fuel treatments. Prescribed burning is an option for stand protection but its use in young stands (which are particularly at risk) is hindered by the scarce knowledge on post-fire tree survival.

Aims

The objectives were to characterize bark thickness as a fire-resistance trait in P. nigra and to describe how post-fire tree survival responds to tree size and fire effects in a 16-year-old plantation.

Methods

Bark thickness was related to diameter at breast height and height in the stem. Metrics describing tree size and stem and crown damage were measured 1?year after prescribed burning in 259 trees. Tree survival was modeled with logistic regression and Classification and Regression Tree analysis.

Results

Bark thickness increased linearly with diameter at breast height (dbh) and decreased with height in the stem. Tree survival was primarily a function of crown injury. Stem damage was an influent factor in small trees.

Conclusion

Due to thinner bark and lower tolerance to crown damage, young P. nigra trees are less fire-resistant than other Mediterranean pines, e.g., Pinus pinaster. Prescribed fire should not be attempted if dbh <10?cm. Mechanical clearing is the treatment of choice in young stands with a significant shrub layer.     

Genetic diversity and genotypic stability in <Emphasis Type="Italic">Prunus avium</Emphasis> L. at the northern parts of species distribution range

Key message

Large genetic variation was found in Prunus avium L. populations from the northern parts of the species distribution range. The ranking of genotypes in terms of growth was stable when tested at three trial sites within the northern parts of the species distribution range.

Context

Peripheral populations especially those in the leading edge are isolated from rest of the areas in the species distribution range. This can make them less genetically diverse yet genetically distinct from the rest of the populations in the species distribution range. Evaluation of their genetic diversity is thus crucial in understanding the local adaptation potential of a species.

Aims

We investigated the genetic diversity and genotype by environment interaction at the northern parts of the distribution range of P. avium.

Methods

Quantitative genetic variation of growth, stem form, and spring phenology were assessed in progenies from 93 plus trees of P. avium selected from 43 locations at the north of the species distribution range in Sweden and tested at two Swedish sites and one Danish site.

Results

We find large quantitative genetic variation in growth and phenology at the northern part of the distribution range of P. avium. Only a limited genotype by environment interaction was observed with no clear indication of local adaptation at the northern parts of the species distribution.

Conclusion

We conclude that P. avium harbors a high level of genetic diversity at the north of its distribution range. Present patterns therefore reflect more likely the recent introduction of the species and dispersal dynamics rather than a long-term loss of diversity along South-North ecological clines during the Holocene. With no indications of genetic depletion in growth or phenology, the gene pool in the breeding program is considered suitable for the future propagation of the species in the tested area.

     

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.     

<Emphasis Type="Italic">Quercus suber</Emphasis> forest and <Emphasis Type="Italic">Pinus</Emphasis> plantations show different post-fire resilience in Mediterranean north-western Africa

Key message

In the African rim of the Western Mediterranean Basin, cork oak forests and pine plantations coexist. Under similar fire regimes, cork oak forest is more resilient in terms of habitat structure (canopy, understory, and complexity of vegetation strata) than pine plantation. By contrast, both woodland types show similar resilience in plant species composition. Resilience in habitat structure varies between the two woodland types because of the resprouting and seeding strategies of cork oak and pine species, respectively. These differences can be relevant for the conservation of biodiversity of forested ecosystems in a future scenario of increased fire frequency and scale in the Mediterranean basin.

Context

Wildfires have major impacts on ecosystems globally. In fire-prone regions, plant species have developed adaptive traits (resprouting and seeding) to survive and persist due to long evolutionary coexistence with fire. In the African rim of the Western Mediterranean Basin, cork oak forest and pine plantation are the most frequently burnt woodlands. Both species have different strategies to respond fire: cork oak is a resprouter while pines are mostly seeders.

Aims

We have examined the hypothesis that pine plantations are less resilient in habitat structure (canopy, understory, diversity of vegetation strata) and plant composition than cork oak woodlands.

Methods

The habitat structure and plant species composition were measured in 30 burnt and 30 unburnt 700-m transects at 12 burnt sites from north-western Africa, where the two forest types can coexist. Habitat structure and plant species composition were compared between burnt and unburnt transects from cork oak and pine plantation woodlands with generalized linear mixed models and general linear models.

Results

The results showed significant interaction effect of fire and forest type, since cork oak forest was more resilient to fire than was pine plantation in habitat structure. By contrast, both forest types were resilient to fire in the composition of the plant communities, i.e., plant composition prior to fire did not change afterwards.

Conclusion

The higher structural resilience of cork oak forest compared to pine plantation is related to the resprouting and seeding strategies, respectively, of the dominant tree species. Differences in the responses to fire need to be considered in conservation planning for the maintenance of the Mediterranean biodiversity in a future scenario of changes in fire regime.

     

Is the private forest sector adapting to climate change? A study of forest managers in north Wales

? Context

Two-thirds of Britain’s forest area is privately owned. Thus, understanding private forest owners and managers, and their attitudes to uncertainty and change, is essential for the success of climate change adaptation policies.

? Aim

The aims of this study are to (1) assess how beliefs in climate change in the private sector have influenced forest management practices; (2) identify constraints related to changes in species choice and silvicultural systems; (3) analyse the implications for implementing climate change policy in forestry.

? Method

Semi-structured interviews with key informants who provide advice to, or manage woodlands in, the private forest sector in north Wales.

? Results

Woodland managers and some advisers are not generally convinced of a need to adapt. They feel the future is uncertain, more usually in relation to tree disease than to climate change itself. Species choice is the principle focus of adaptation activities and reveals a deep divide in opinion. Commercial advisors look to new exotics but are inhibited by absence of markets, while small-scale owners rely more on native genetic diversity.

? Conclusions

Findings that are likely to apply widely include: the influential role of forest agents in forest management decisions including species choice; lack of confidence in climate change predictions, and in markets; more immediate concerns about tree pests and diseases; demand for leadership from the public sector, and for engagement amongst the private sector. Further research is needed across a wider area to test the variability in relationship between attitudes and behaviours, and local conditions including climate change predictions.     

The role of cold storage and seed source in the germination of three Mediterranean shrub species with contrasting dormancy types

Context

The use of native species in ecological restoration is highly recommended but, in practice, it is often impaired by knowledge gaps in the germination ecology of suitable species.

Aims

This study aimed to assess the role of storage conditions and seed source on the germination of three Mediterranean shrub species with contrasting types of dormancy.

Methods

Ripe fruits were harvested at two or three distant locations in mainland Portugal. Seeds were subjected to three treatments consisting in different storage conditions: cold storage at low and high moisture conditions, plus a control. Five replicates of up to 30 seeds were placed under constant temperature conditions and germination was monitored weekly during 14 weeks.

Results

The effect of cold storage at high moisture on germination differed between the three species and seed source played a significant role in the germination of all three species. In the case of the species with dormancy, the observed differences in germination could reflect changes in the species’ dormancy degree or sensitivity to dormancy breaking factors across their geographical range. In the case of Pistacia lentiscus (no dormancy), the results suggested a possible adaptation of the northern seed source to high moisture conditions.

Conclusions

The observed differences between species agreed well with their dormancy types, and the seed source-related differences could be adaptive features, as they seemed related with local climate conditions.     

Beneath the mistletoe: parasitized trees host a more diverse herbaceous vegetation and are more visited by rabbits

? Key message

Parasitism by mistletoe increases the cover and diversity of herbaceous vegetation under the host tree and attracts the activity of rabbits in comparison to control trees. Thus, the effects on forest community go beyond the parasitized tree.

? Context

Mistletoes are a diverse group of aerial hemiparasitic plants and are considered keystone species in forest ecosystems around the world. They produce nutrient-enriched litter, which exerts a substantial effect on soil-nutrient concentration, and the enriched nutrient patch alters the vegetation at the site as well as the associated fauna.

? Aims

Our goal is to ascertain whether mistletoe (Viscum album) parasitism of pine forest of a Mediterranean mountain favors herbaceous vegetation and attracts mammalian herbivores.

? Methods

We recorded in Sierra de Baza (SE Spain) the composition of the herbaceous vegetation under pines with and without mistletoe parasitism, and estimated the rabbit activity at the same sites by collecting their excrements.

? Results

An effect on herbaceous vegetation, especially in grasses belonging to the family Poaceae, was reflected in a notable increase in soil cover, species richness, and species diversity beneath parasitized pines with respect to unparasitized ones. As a consequence, parasitized pines attract the activity of rabbits, as shown by a fivefold quantity of excrement with respect to control ones.

? Conclusion

Parasitism by mistletoe, by creating patches of greater nutrient availability under the host canopy, extends its effects beyond the host tree to other members of the forest community, such as herbaceous plants and associated herbivorous animals, which in turn contribute to environmental heterogeneity with their activity.

     

Local-scale diversity and adaptation along elevational gradients assessed by reciprocal transplant experiments: lack of local adaptation in silver fir populations

Key message

Silver fir transplantations along elevational gradients revealed a high diversity but no local adaptation. Populations displayed similar abilities to adapt to new environments including those due to climate change.

Context

The sustainability of forest stands depends on the ability of species and communities to adapt by combining plasticity and genetic evolution. Although well-documented at the scale of species distributions, the variability and adaptation of forest tree genetic resources are less understood at the short-distance scale.

Aims

We analysed the effects of genetic and environmental factors on the local-scale phenotypic diversity of traits related to adaptation in Abies alba. We also sought to highlight local adaptation, revealing past selection.

Methods

Six adaptive traits related to growth, phenology and survival were measured on seedlings from 57 half-sib families collected from 15 provenances and planted in a nine-site reciprocal transplant experiment distributed along three elevational gradients.

Results

Most part of the phenotypic variability was attributed to the environmental factors. Provenances and families had also significant effects on seedling performances, but the genetic variability was mostly attributed to the families. No pattern of local adaptation was observed, except in the presence of lateral branches in the driest garden.

Conclusion

The absence of local adaptation suggests a similar ability of all silver fir populations to develop in the various environments. This result provides favourable conditions for coping with the ongoing climate change without exotic resources enrichment.

     

Site-specific growth responses to climate drivers of Pinus pinea L. tree rings in Italian coastal stands

Context

Six Pinus pinea stands growing under the Mediterranean type climate in Italy along the Tyrrhenian and Sardinian coasts.

Aims

To identify the main climatic factors driving variability in growth responses to contrasting climate conditions at local and regional scales using tree-ring analysis.

Methods

Common growth patterns in tree rings were explored with clustering techniques. Local and regional growth responses to climate were examined using a dendroclimatic analysis. To remove the age-dependent trend we decomposed the tree ring width data into age-bands, thereafter standardised and recombined into a single mean site chronology.

Results

The main grouping of tree ring series reflected climate-driven growth patterns, with a clear separation between stands from wetter and drier sites. The most interesting results were found at a seasonal scale and showed i) a shift of the main precipitation inputs from previous autumn-winter to current early-spring period, and ii) a bimodal pattern of sensitivity to water availability, when increasing drought conditions.

Conclusion

Our findings suggest that water deficit limits P. pinea growth also during late summer months in drier sites. In view of the projected increases in the frequency and duration of summer droughts in the Mediterranean basin, detecting differences in growth responses to site-specific climate patterns may allow selection of more appropriate mitigation and conservation strategies across most of its present range.     

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.     

Genetic monitoring of traditional chestnut orchards reveals a complex genetic structure

Key message

This study presents the results of a systematic genetic analysis between wild and cultivated chestnuts in an orchard in southern Spain, highlighting a complex structure and considerable genetic diversity and opening the possibility to generalize this approach to other Mediterranean orchards.

Context

Tree genetic monitoring offers a good opportunity to evaluate populations and preserve their long-term adaptive evolutionary potential. Chestnut is a multipurpose species of high economic importance in the Mediterranean basin and considered an example of integration between natural and man-driven distribution of diversity under changing environmental and historical conditions. Due to its multipurpose characteristics, man influenced its populations (grafting/sexual propagation) and a complex genetic structure is expected.

Aims

We monitored the trees of a chestnut orchard for studying the genetic diversity and relationship in grafts and rootstocks and detecting possible response in its adaptive potential.

Methods

For this, morphological traits and genomic and genic microsatellite markers were used.

Results

Chestnut trees showed considerable genetic structure, with high level of clonality in the varieties and genetic diversity in rootstocks. The similarity analysis revealed a different clustering pattern for varieties, detecting higher variability for genomic microsatellite markers. Rootstocks harboured a high level of diversity, not previously described, and not contained in the genetic information from populations and varieties from the same region.

Conclusion

Results contribute to understanding the human role in the management of chestnut and demonstrate that rootstocks constitute an unexploited reservoir of variation valuable for conservation strategies against stress factors and future and unpredictable environmental changes.

     

Decline of genetic diversity of sessile oak at the retracting (xeric) limits

Context

Genetic diversity of sessile oak (Quercus petraea) populations in Hungary was assessed close to the retracting, low-elevation, low-latitude (xeric) distribution limits.

Objective

We aimed at tracing an assumed effect of climatic factors on genetic diversity, particularly at the southern, low elevation limits of distribution.

Methods

Genetic diversity at isozyme-coding loci was analysed in populations, and related to the climate of the sites where the populations grow. A locus-wise analysis proved to be essential to follow responses.

Results

A climate-related cline was found at seven isoenzyme-coding gene loci. Declining allelic numbers and heterozygosity indicated lower diversity at warmer and drier sites. The majority of loci were responsive to precipitation factors, others to temperature. Genetic clustering was neither related to geographic distance nor to random or historic effects.

Conclusions

The results suggest that climatic stress may elicit a genetic diversity loss in populations, which may reduce their plasticity and adaptive potential. The selective pressure may override historic effects and gene flow. With respect to expected climate change, the correlation of diversity with some climatic factors gains specific importance. If supported by further investigations, the results might be utilised for reconsidering conservation strategies and rules for use of forest reproductive material.     

Freezing injury in primary and secondary needles of Mediterranean pine species of contrasting ecological niches

? Pine seedlings show a marked ontogenetic difference between primary and secondary needles, the latter prevailing with a different timing among species.

? Using the electrolyte leakage method following an artificial freezing test, we aimed at (1) determining the differences in freezing tolerance between primary and secondary needles in eight pines of contrasting thermal habitats: P. canariensis, P. pinea, P. halepensis, P. brutia, P. pinaster, P. nigra, P. sylvestris and P. radiata, (2) evaluating the relation between freezing tolerance and sclerophylly and (3) relating freezing tolerance with the climate of origin.

? Primary needles were significantly more sensitive to freezing than secondary needles in Pinus halepensis, P. brutia, P. pinaster and P. nigra, whereas no differences were found in P. canariensis, P. pinea and P. radiata. LT50 was uncorrelated with needle sclerophylly but very highly correlated with the mean temperature of the coldest month at the seed source.

? Results support an adaptive role of secondary needles in the mountain Mediterranean pines P. nigra, P. pinaster and P. brutia, while the more complex responses in coastal Mediterranean pines can be interpreted in the light of seedling ontogeny and species’ ecological niches.

     

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.     

The role of developmental stage in frost tolerance of Pinus pinea L. seedlings and saplings

Context

Although drought is generally considered the main environmental constraint in Mediterranean environments, the ability to acclimate to and tolerate frost in early developmental stages can be a determinant for seedling survival of many Mediterranean tree species like stone pine (Pinus pinea L.).

Aims

The aim of this study was to assess the impact of the developmental stage of naturally regenerated stone pine individuals on tolerance to low temperature (LT) from summer to late autumn and in spring, at a highly continental site in central Spain. Specifically, we tested to what extent the differences in tolerance are related to shoot heteroblasty.

Methods

We assessed LT tolerance of needles from individuals at three age classes (class C1: seedlings, class C2: 4- to 8-year-old saplings and class C3: >9-year-old saplings) over nine dates from summer to spring.

Results

LT tolerance displayed severe seasonal trends and differed between age classes. It usually increased with sapling age. Such differences were tightly related to heteroblasty of the shoots. Our results point to a higher LT tolerance associated with larger leaf dry mass per unit area (LMA) values. No impact of late frosts on shoot growth rates was detected during this study.

Conclusions

Developmental changes during early plant growth seem to play a role in frost tolerance of stone pine seedlings, a finding which furthers our understanding of regeneration dynamics in this species in areas with continental influence.     

Regeneration strategies influence ground bryophyte composition and diversity after forest clearcutting

Context

Natural regeneration with broadleaved species and reforestation with coniferous trees are two widely practiced forest regeneration strategies after timber harvesting. They lead to different tree species composition and may cause different understory biodiversity, but the effects on ground bryophyte composition and diversity are not well-known.

Aims

We tested whether natural regeneration with broadleaved species and reforestation with spruce induced different diversities of the ground bryophyte populations 20–40 years after old-growth spruce forest clearcutting in the subalpine regions of southwestern China.

Methods

Differences between natural stands and plantations were compared through the analysis of 13 paired stands, with 78 plots, 390 shrub/herb quadrats, and a total of 1,560 bryophyte quadrats.

Results

Naturally regenerated forests were characterized by lower density and cover and lower tree height but higher herbaceous plant height, shrub cover, and bryophyte diversity. They also harbored many more ground bryophytes. The species richness of pleurocarpous mosses and fans, mats, and turfs were significantly higher in naturally regenerated forests. Frequency difference analysis demonstrated that more bryophyte species preferred ground habitats in naturally regenerated forests than in plantations (116 vs. 48 species). The canonical correspondence analysis indicated that stand structure attributes were more important determinants of ground bryophyte diversity and abundance.

Conclusion

Natural regeneration and reforestation resulted in large differences in ground bryophyte populations. A larger diversity was observed in the former case, and natural regeneration practices can be an effective measure for the protection of ground bryophyte diversity after clearcutting.     

Assessing temporal variation of primary and ecosystem production in two Mediterranean forests using a modified 3-PG model

Context

Forest ecosystem carbon uptake is heavily affected by increasing drought in the Mediterranean region.

Aims

The objectives of this study were to assess the capacity of a modified 3-PG model to capture temporal variation in gross primary productivity (GPP), and ecosystem net carbon uptake (NEE) in two Mediterranean forest types.

Methods

The model was upgraded from a monthly (3-PG) to a daily time step (3-PG_day), and a soil water balance routine was included to better represent soil water availability. The model was evaluated against seasonal GPP and NEE dynamics from eddy covariance measurements.

Results

Simulated and measured soil water content values were congruent throughout the study period for both forest types. 3-PG_day effectively described the following: GPP and NEE seasonal patterns; the transition of forest ecosystems from carbon sink to carbon source; however, the model overestimated diurnal ecosystem respiration values and failed to predict ecosystem respiration peaks.

Conclusions

The model served as a rather effective tool to represent seasonal variation in gross primary productivity, and ecosystem net carbon uptake under Mediterranean drought-prone conditions. However, its semi-empirical nature and the simplicity inherent in the original model formulation are obstacles preventing the model working well for short-term daily predictions.     

Light transmissivity of tube shelters affects root growth and biomass allocation of Quercus ilex L. and Pinus halepensis Mill

Context

Tube shelters have been shown to enhance field performance of several Mediterranean species, but responses of newly planted seedlings to the microenvironment induced by shelter walls with different light transmissivity are still poorly documented.

Aims

We studied effects of a range of shelters with varying light transmissivity on post-planting seedling responses during the wet season establishment phase for two Mediterranean trees of contrasting functional ecology.

Methods

Root growth, biomass allocation, water potential, and chlorophyll fluorescence of Quercus ilex and Pinus halepensis seedlings were evaluated across shelters varying in light transmissivity (80, 40, 20, and 10 % plus a mesh shelter) with irrigation.

Results

Plants in dark tubes (20 and 10 % light transmissivity) had less above- and belowground growth and more than two times greater leaf to protruding roots mass ratio, with shoot growth response of Q. ilex being less plastic. Ratio of leaf area/protruding roots area decreased when light transmissivity increased, although no differences were found at ≥40 % transmissivity. Xylem water potential indicated lack of water stress, and high maximum photosynthetic efficiency (F _v/F _m) values show no photoinhibition symptoms irrespective of light transmissivity.

Conclusion

Shelter transmissivity ≥40 % promotes rapid and vigorous root growth immediately after planting for these species. This minimum transmissivity should be considered as a target when designing shelters to help root development and improve water balance of Mediterranean seedlings.