Oak Species Research Articles

Influence of Anthropogenic Activities on Forest Carbon Stocks—A Case Study from Gori Valley, Western Himalaya

Carbon stock assessment in various ecosystems is vital for monitoring the health of these ecosystems and national accounting for the United Nations convention on climate change. The influence of various anthropogenic drivers on carbon stock in different ecosystems has not been examined comprehensively. This study aims to determine the impact of anthropogenic pressures (lopping, cutting, grazing) on soil physico-chemical properties and carbon stock in four temperate broadleaf forests dominated by different species of oak, viz., Banj oak (Quercus leucotrichophora), Rianj oak (Quercus lanuginosa), Moru oak (Quercus floribunda) and Kharsu oak (Quercus semecarpifolia) along an elevation gradient from 1700–3000 m asl in Gori valley, western Himalaya. Biomass data were collected from 120 quadrats of 10 × 10 m size at three distinct altitudes (4 forest sites × 3 altitudes × 10 quadrats) and analysed for carbon stock, whereas soil samples were randomly collected in triplicate from three depths of each altitude of the forest site and further analysed for their physico-chemical properties. A total of 767 individual trees with a diameter of ≥31 cm were measured at twelve sites and standing biomass was estimated following the growing stock volume equations. Mean carbon stock was highest in Moru oak (396.6 ± 29.5 Mg C ha−1) and lowest in Banj oak forest (189.3 ± 48.6 Mg C ha−1). We also found soil to be the largest pool of forest carbon (43.0–59.7%) followed by aboveground biomass (31.5–45.0%), belowground biomass (8.4–11.7%) and litter (0.4–0.5%). The basal area showed significant effect on altitude and carbon stock, whereas disturbance showed significant (p < 0.05) negative correlation with the total carbon stock. Soil nitrogen exhibited a significant positive correlation (R2 = 0.60) with the basal area, indicating that nitrogen enhances tree growth and forest carbon stock. However, anthropogenic disturbance showed a significant negative impact on the basal area, soil nutrients and carbon stock of oak forests. This concludes that forest structure, anthropogenic pressure and soil parameters contribute to the carbon stock of the area. Considering the significance of these overexploited oak forests, it is recommended to conserve the old-growth forest species in the study area, since they have the highest carbon accumulation potential.

THE BUCF HERBARIUM DATABASE OF ALLOCHTHONOUS OAKS

The BUCF Herbarium stores 253 specimens of allochthonous oaks species belonging to 33 accepted taxa. Amongst the representatives, Quercus rubra has the most recordings. Moreover, three species classed as near threatened on the IUCN Red List were identified. The most significant contribution was made by the botanist S. Pașcovschi who amassed approximately one-third of the collection. The specimens were collected between 1872 and 1987, with a maximum activity between 1940 and 1949. The majority of the specimens were sampled from dendrological parks and botanical gardens in Romania, the Bazos Dendrological Park remarking itself with one of the most diverse collections of cultivated oaks. A considerable number of specimens were received from donations and exchanges with several herbaria. Most of the herbarium material is very well-preserved having high potential for future investigations.

Restoring bigcone Douglas-fir post-fire in drought-stricken Southern California: Assessing the effects of site choice and outplanting strategies

IntroductionForest restoration is a powerful tool to combat the dual threats of drought and fire, both of which have been increasing in frequency and severity in recent years in the Western United States. The hard-hit region of Southern California is home to the endemic bigcone Douglas-fir, Pseudotsuga macrocarpa (Vasey), whose abundance and range have been impacted by multiple large fires within the last two decades.MethodsTo better understand the ecology of these trees, and thereby improve the potential for restoration in light of predicted future conditions, we outplanted 1,728 seedlings into burned areas with varying levels of pre-planting fire severity and proximity to water (near canyon bottom and upslope). Within each planting area, seedlings were planted into one of four microhabitats; under conspecifics, under the codominant oak species [Quercus chrysolepis (Liebm)], in the open (no woody canopy), or in the open within a microsite feature such as a log, rock or a small shaded hole. At each site and within each microhabitat, half the seedlings were treated with oak-soil amendments (soil from under the oak) and half with spring watering (4 months after planting). To better understand the influence of outplanting conditions, we tracked the survival of the seedlings over the next two years.Results and discussionShort-term (March to June) survivorship following planting was quite high and the most significant die-off of seedlings occurred during the first dry season (June to November) despite strong droughts in the second and third dry seasons. Overall, only 7.3% (127 of 1,728) of seedlings survived. Seedling success depended strongly on the microhabitat and summer watering, though not in necessarily intuitive ways. Seedlings that received supplemental water during the first summer did worse than unwatered seedlings. The most successful microhabitats for planting were open sites with microsite features and sites underneath canyon live oak, while sites under mature bigcone Douglas-firs had the lowest rates of survival. Position on the slope had no effect on outcomes and soil amendment had a weak negative effect on seedling survival.

Fertilisation and irrigation have no effects on growth of oak (Quercus robur, Q. petraea) stands on abandoned farmland in southwest Sweden

Low nutrient availability often limits productivity in northern forests. In a nutrient optimisation trial, we investigated the effects of fertilisation and irrigation on soil moisture, leaf area index (LAI) as well as height and radial growth in 25-year-old stands of pedunculate and sessile oak (Quercus robur L., Q. petraea (Matt.) Liebl.) growing on abandoned farmland in southwestern Sweden. Control (C), fertilisation (F), irrigation (I), and irrigation + fertilisation (IF) treatments were arranged in a randomized complete block design. End of growing season analysis of foliar nutrients guided the quantitative composition of next year’s fertiliser mix. Volumetric soil moisture (VWC) was significantly higher in the I and IF treatments compared to the C and F treated stands of both oak species. We did not observe a fertiliser-related reduction in VWC (except for 2015, when VWC in F-treated Q. robur stands was significantly lower than the control by about 18 %). This is in line with the unaffected LAI estimates (5.3–5.9) suggesting no stimulation of leaf production that could drive increases in transpiration with subsequent soil moisture depletion. There was no treatment × year interaction for any of the growth-related variables. Treatments had no significant effects on basal area growth, which increased annually by 1.72 and 1.54 m2 ha−1 on average for Q. petraea and Q. robur, respectively. Pre-treatment height differences in Q. petraea stands (7–12 % taller trees in the C and IF plots) persisted throughout the study resulting in significant effects, while no significant differences in height occurred in Q. robur. Periodic annual volume increment varied more strongly following drier periods but there were no significant differences among treatments.Our findings indicate that fertilisation causes no or only minor increases in oak water use, suggesting that nutrient addition in oak stands within this precipitation regime does not require simultaneous irrigation. Most importantly, our data implies that the soil nutrient legacies of past agricultural use suffice to maximise the productivity of oak stands on abandoned farmland typical of the main oak growing region in southwestern Sweden.

Tick abundance and diversity are substantially lower in thinned vs. unthinned forests in the New Jersey Pinelands National Reserve, USA

Forest thinning is a management tool used in the New Jersey Pinelands and elsewhere to improve forest health and resilience, mitigate wildfire risk, and manage for wildlife. Forest thinning leads to warmer drier microclimates, which have been shown in both field and laboratory studies to reduce tick survival and reproduction. To directly assess the effects of forest thinning on the abundance and diversity of ticks and on the prevalence of tick-borne human pathogens, we sampled ticks weekly from March to November 2021 at three replicated pairs of thinned and unthinned forest sites composed primarily of pitch-pine, shortleaf pine, and various oak species. We characterized microclimate in the understory and forest floor at each sampling plot by deploying multiple data loggers to monitor temperature and relative humidity throughout the study period. As expected, we found that thinned plots were significantly drier and warmer than unthinned plots. We also found that average questing tick abundance was 92% lower in thinned as compared with unthinned plots. Of the three main tick species collected in unthinned plots (Amblyomma americanum, Ixodes scapularis, and Dermacentor albipictus) only A. americanum and a single I. scapularis were collected in thinned plots. Prevalence of Ehrlichia species in A. americanum did not differ between treatments, and the sole I. scapularis collected in a thinned plot was infected with Borrelia burgdorferi sensu lato. However, the significant and much lower tick abundance in thinned plots indicates a lower risk of human-tick encounters. Our results add to the growing evidence that landscape and forest management can reduce local tick abundance, thereby reducing tick-borne disease risk.

Comparative ecology of two closely associated scrub-dominating oaks in South Florida: Quercus myrtifolia and Q. geminata (Fagaceae)

Recent authors have developed a detailed perspective on the parallel sympatric radiation into similar habitats throughout North America of oak species (Quercus, Fagaceae) representing different sections, including prominently Florida. Quercus myrtifolia and Q. geminata are a localized example of that radiation: two species in different sections codominating scrub habitats in the coastal Southeast Florida study area. Within that context the two are usually encountered at shrubby sizes almost without spatially related habitat differentiation, raising the question of how they coexist in essentially the same niche. The present project addresses this pronounced niche overlap with two different approaches: first, field exploration to discern local exceptions to the apparent near-inseparability of the two oaks, and second, to identify environmentally related differential growth responses. Exploring several scrub sites in Palm Beach and Martin counties, Florida, the study found three deviations from the usual intimate shrubby-site association having Q. myrtifolia proportionally dominant. Those deviations are: 1. Shrubby-sized Q. geminata tends proportionally to dominate dune bases vs. Q. myrtifolia dominating higher dune slopes. 2. Tree-sized Q. myrtifolia proportionally dominates sheltered scrub dune localities. 3. Tree-sized Q. geminata proportionally dominates exposed scrub dunes. During site maturation the two species diverge in relative abundance depending on sheltered shade vs. open exposure until fire or hurricanes restart succession from their intermixed subterranean portions. When young and shrubby, in exposed conditions as opposed to in partial shade, Q. geminata tends toward reduced leaf blade areas and increased marginal curling parallel to the long axis. By contrast, Q. myrtifolia in exposed conditions tends toward broad diversity in three-dimensional foliar conformations. Different foliar morphotypes characterize different Q. myrtifolia clumps.

Dependence of flower-bearing on trunk size and trunk origin in four tree species of the subgenus Quercus

ABSTRACT We investigated the flower-bearing properties of four sympatric oak species in the subgenus Quercus commonly grown in semi-natural forests in western Honshu Island, Japan. Quercus variabilis and Quercus acutissima belong to the section Cerris and Quercus serrata and Quercus aliena belong to the section Quercus. The timing and pattern of flower-bearing varied among the four oaks, but were synchronized between the male and female inflorescences within each species. Trunk size was the primary factor affecting the flower-bearing properties; more flowers were borne on thicker trunks. Threshold trunk sizes for flower-bearing, below which no flowers were borne, were identified in the two Cerris section oak species; in contrast, the two Quercus section oak species bore flowers even on the smallest trunks. The smallest flower-bearing trunk sizes of the Quercus section oaks were extremely small compared with the other tall tree species distributed in the temperate zone of Honshu Island. The flowering probability was not clearly influenced by whether the stem originated from a seedling or a sprout, except for the male inflorescences of Q. aliena, which rather showed a positive relationship between sprout-origin and flower-bearing. Thus, no trade-off relationship between sprouting and flowering was observed.

Vehicle pollution is associated with elevated insect damage to street trees

Abstract Vehicle pollution is a pervasive aspect of anthropogenic change across rural and urban habitats. The most common emissions are carbon‐ or nitrogen‐based pollutants that may impact diverse interactions between plants and insect herbivores. However, the effects of vehicle pollution on plant‐insect interactions are poorly understood. Here, we combine a city‐wide experiment across the Sacramento Metropolitan Area and a laboratory experiment to determine how vehicle emissions affect insect herbivory and leaf nutritional quality. We demonstrate that leaf damage to a native oak species (Quercus lobata) commonly planted across the western US is substantially elevated on trees exposed to vehicle emissions. In the laboratory, caterpillars preferred leaves from highway‐adjacent trees and performed better on leaves from those same trees. Synthesis and applications. Together, our studies demonstrate that the heterogeneity in vehicle emissions across cities may explain highly variable patterns of insect herbivory on street trees. Our results also indicate that trees next to highways are particularly vulnerable to multiple stressors, including insect damage. To combat these effects, urban foresters may consider planting trees that are less susceptible to insect herbivory along heavily travelled roadways.

Higher growth synchrony and climate change‐sensitivity in European beech and silver linden than in temperate oaks

AbstractAimClimatic changes affect the growth dynamics of temperate trees, but these effects might differ between co‐occurring ring‐ and diffuse‐porous species as well as between mesic and xeric rear‐edge populations. We explore whether recent climate warming has increased the climate sensitivity and within‐stand synchrony of growth in these groups differently.LocationThe natural beech–oak ecotone in Western Romania at the dry margin of beech occurrence.TaxaThree ring‐porous oak species (Quercus petraea, Q. frainetto and Q. cerris), and diffuse‐porous European beech (Fagus sylvatica) and silver linden (Tilia tomentosa).MethodsWe correlated tree‐ring records with monthly and seasonal climate data (period 1940–2017). Regional growth synchrony was assessed through the analysis of inter‐series correlation of growth within populations and among populations using mixed models.ResultsIn all five species including two south‐east European oak taxa and silver linden, water availability in summer was the most important climatic determinant of radial growth. This factor has gained in importance since the onset of rapid warming after 1980, while the impact of other climate factors in spring and summer has decreased. Within‐population growth synchrony as a measure of overall climatic stress has increased, or remained stable, since 1980 in beech and silver linden, but has decreased in the oak species, matching declining growth trends in beech and linden and increasing (or stable) trends in the oaks.Main ConclusionsThe patterns of growth synchrony provide valuable information on tree species' drought susceptibility in efforts to select suitable tree species for climate change‐adapted forestry. The climate vulnerability of beech is higher than that of the more drought‐resistant oak species due to its marked summer‐drought sensitivity of growth.

The distinct fruit size and physical defense promote divergent secondary seed dispersal strategies of three oak species

Secondary seed dispersal is one of the most important factors contributing to the co-existence of plant species. Variations in fruit properties including fruit size, physical defense and chemical composition influence seed foraging and secondary dispersal, but the details remain unclear. Here, we focused on three common nut-bearing tree species (Quercus aliena Blume, Q. dentata Thunb., and Q. variabilis Blume), which often co-occur in mixed deciduous forest in northern China. We estimated their acorn properties and evaluated their effects on the secondary dispersal patterns. We found similar chemical profiles but different acorn sizes and physical defense among these three species. Moreover, we detected distinct secondary seed dispersal strategies in relation to their acorn properties: Q. dentata produced the smallest-sized acorns with the lowest physical defense, which had shorter dispersal range but the highest survival rate; Q. variabilis generated the largest-sized acorns with the highest physical defense, which suffered the lowest survival rate but benefited from the longer dispersal range; and an intermediate survival rate existed in Q. alienawith the intermediate-sized acorns. In addition, Père David’s rock squirrel (Sciurotamias davidianus Milne-Edwards, Sciuridae) and brown rat (Rattus norvegicus Berkenhout, Muridae) are secondary seed dispersal agents for three oak species. Brown rats not only disperse more acorns than Père David’s rock squirrels, they also create different dispersal distance for the acorns of three species, which enhance three species’ niche separation. Our results therefore revealed that differentiations in acorn properties have derived distinct trade-offs in secondary seed dispersal strategies, likely facilitating the coexistence of the three examined species.

Thinning improves growth and resilience after severe droughts in Quercus subpyrenaica coppice forests in the Spanish Pre-Pyrenees

During the past years, growth and productivity of different oak species have been constrained by water shortage in seasonally dry regions such as the Mediterranean Basin. Thinning could improve oak radial growth in these drought-prone regions through the reduction of tree competition for soil water in summer. However, we still lack adequate, long-term assessments on how lasting are thinning treatments effects and to what extent they contribute to oak growth recovery after drought. Here we aim: (i) to study the radial growth sensitivity to drought of Quercus subpyrenaica in the Spanish Pre-Pyrenees, and (ii) to verify if thinning represents a suitable option to enhance growth resistance to drought and post-drought growth recovery. We analysed basal area increment (BAI) trends in the period 1960–2020 of formerly coppiced oak stands thinned in 1984 and compared them with unthinned plots and also with coexisting Scots pine (Pinus sylvestris) growing in thinned plots. We used the Standardized Precipitation Evapotranspiration Index (SPEI) to estimate the severity of droughts and we also assessed climate-growth relationships. Oaks in thinned plots showed higher BAI (369 mm2) than those in unthinned plots (221 mm2). Growth rates remained higher in thinned than in unthinned plots also under severe drought stress. A severe summer drought in 1986 caused abrupt BAI reductions in both oaks (- 40.5%) and pines (- 40.1%). The positive effect of thinning on growth lasted for over 20 years and slightly declined as canopies closed. In the thinned plots, trees with smaller diameter showed the greatest growth release. Oaks in unthinned plots and Scots pine were more sensitive to short-term droughts in terms of growth reduction than oaks in thinned plots, while long term droughts have similar effects on oaks from both thinned and unthinned plots. Oaks were resilient to drought, showing recovery periods lasting from 1 to 2 years in both thinned and unthinned plots. However, intense and prolonged droughts could strongly reverse the expected growth enhancement of thinned plots, and a greater frequency of droughts would limit coppice growth and productivity thus lengthening the rotation periods.

A climate-sensitive mixed-effects tree recruitment model for oaks (Quercus spp.) in Hunan Province, south-central China

Tree recruitment is an essential component and plays a fundamental role in forest management decision-making. However, the existing tree recruitment models for oak (Quercus spp.) species have been developed using traditional modeling functions, and have neglected the effects of climate, which do not apply to long-term projections of future forest composition under a climatic change scenario. In this study, we developed tree recruitment models based on the data of 548 permanent sample plots distributed in Hunan Province, south-central China. Five commonly used recruitment approaches (negative binomial model, zero-inflated Poisson, zero-inflated negative binomial model, Hurdle-Poisson model, and Hurdle-negative binomial model) were employed to analyze the data. Then the random effects of the regions were included to develop the nonlinear mixed-effects models and account for spatial and temporal correlations. Among the various candidate predictors tested including stand characteristics, site conditions, and climate, stand basal area (BA), quadratic mean diameter (QMD), basal area of the species (Bai), cosine of the slope combined with the natural logarithm of elevation (CIE), and mean annual temperature (MAT) had significant effects on oak recruitment. The zero-inflated negative binomial model was selected as the optimal model compared to the other four basic models. The performance of the models improved significantly when the random effects were added. These results and knowledge of adaptive management will be useful for developing practical forest management plans.

Wildfire Variable Toxicity: Identifying Biomass Smoke Exposure Groupings through Transcriptomic Similarity Scoring.

The prevalence of wildfires continues to grow globally with exposures resulting in increased disease risk. Characterizing these health risks remains difficult due to the wide landscape of exposures that can result from different burn conditions and fuel types. This study tested the hypothesis that biomass smoke exposures from variable fuels and combustion conditions group together based on similar transcriptional response profiles, informing which wildfire-relevant exposures may be considered as a group for health risk evaluations. Mice (female CD-1) were exposed via oropharyngeal aspiration to equal mass biomass smoke condensates produced from flaming or smoldering burns of eucalyptus, peat, pine, pine needles, or red oak species. Lung transcriptomic signatures were used to calculate transcriptomic similarity scores across exposures, which informed exposure groupings. Exposures from flaming peat, flaming eucalyptus, and smoldering eucalyptus induced the greatest responses, with flaming peat grouping with the pro-inflammatory agent lipopolysaccharide. Smoldering red oak and smoldering peat induced the least transcriptomic response. Groupings paralleled pulmonary toxicity markers, though they were better substantiated by higher data dimensionality and resolution provided through -omic-based evaluation. Interestingly, groupings based on smoke chemistry signatures differed from transcriptomic/toxicity-based groupings. Wildfire-relevant exposure groupings yield insights into risk assessment strategies to ultimately protect public health.

Adaptability responses to drought stress in the oak species Quercus petraea growing on dry sites

We studied sessile oak (Quercus petraea) growing on six dry sites to understand adaptability responses to drought stress. Pedunculate oak (Quercus robur) on a moderately dry site was tested in parallel. We analyzed accessions from mostly dry sites that were less sensitive to soil drought and found that the growth performance ranking was not the same before and after treatment. We used phenological plasticity approaches to study seed development and plant development before and after drought: the treatments included stem length, root length, and collar diameter, as well as dry above- and below-ground biomass performance. Additionally, after drought treatment, osmolytes and root surface were tested in Q. petraea. According to the analyses and results, the ranked sites did not maintain their ranking status, with Q. petraea exhibiting different rates of growth during each developmental stage from seed development until the end of the treatment of plant material. The smallest seeds came from the driest site, which may indicate more adaptability to drought stress. After drought treatment, large differences were found between the dry biomass performance, stem length, root length, and collar diameter of oaks grown on different sites. The osmolality of Q. petraea on most of the dry sites was higher under the reduced treatment than under the optimal treatment, but not significantly. After drought treatment, all accessions – and especially those from the driest site – showed large differences in growth performance between the treatments. The relationship between seed weight and seedling development before and after drought treatment differed according to the developmental stage.

Drivers of site productivity for oak in Poland

The site index (SI) is the most commonly used and representative measure of the phytocentric approach; it evaluates the site productivity based on the stand height and age. In the case of mixed stands with complex structures, phytocentric methods are very limited, while in non-forest areas, they are not ap­plicable. In situations where the applicability of phytocentric methods is limited, the site productivity is de­termined by geocentric methods. Geocentric methods allow direct modelling of site productivity, expressed by SI predicted from various environmental variables. The aim of this study was to develop a geocentric model for oak. Site productivity expressed by SI was described by the environmental variables and stand characteristics. To develop the SI model, we used the data from 2490 NFI plots with dominant oak species (Quercus sessilis and Quercus robur). A generalized additive model was used in modelling site productivity. We documented a significant relationship between SI and the environmental variables, age of stands and stand density. Furthermore, the site productivity for oak is shaped by climate factors, soil type, geology, and altitude. The model developed based on the geocentric method, explained 55.1% of the variation of SI

Bimodal and unimodal radial growth of Mediterranean oaks along a coast-inland gradient

Wood formation during the growing season is shaped by the intra-annual variability of climatic conditions. In the Mediterranean, the cambial activity is seasonally constrained by winter low temperature and summer drought, resulting in bimodal growth patterns. Although bimodal growth is an ecologically important adaptation of woody species to seasonally dry environments, its variability across space and among species remains unclear. We combined direct monitoring of intra-annual radial growth using dendrometers and xylogenesis micro-sampling with indirect wood formation modeling to assess growth bimodality for two coexisting oak species across six sites in North-Eastern Spain. We focused on species with two contrasting life strategies, evergreen with diffuse-porous wood (Quercus ilex) and winter deciduous with ring-porous wood (Q. faginea/Q. pubescens). Study sites spanned from oceanic areas with high autumn precipitation to dry continental inland regions. We hypothesized that growth bimodality reflects the interaction between local precipitation patterns and species-specific traits. Our results revealed cambial activity in autumn after summer quiescence across the entire region and for both oak species. However, growth bimodality and the relative contribution of the autumn growth peak to the total annual growth was geographically structured and species-specific. Growth was unimodal under continental and Atlantic conditions. By contrast, growth bimodality was significant along the Mediterranean coast, where precipitation showed a bimodal pattern. Moreover, evergreen Q. ilex showed more growth bimodality compared with deciduous Q. faginea/Q. pubescens at Mediterranean sites. Different intra-annual distribution of radial growth could facilitate coexistence of both oak species through temporal niche partitioning. The growth bimodality helps to compensate for reduced growth in summer by autumn cambial resumption and, therefore, the differences in its intensity between sites and species may determine divergent responses of forest ecosystems to ongoing climate change.

Changes in land use of temperate forests associated to avocado production in Mexico: Impacts on soil properties, plant traits and insect-plant interactions

CONTEXTTemperate forest ecosystems harbor great biodiversity and provide key ecosystem services. However, in Mexico they have been deforested for use in avocado orchards, which represents a major threat to ecosystems functioning and the conservation of biodiversity. OBJECTIVEWe evaluated the changes in soil chemical properties in a fragmented landscape of avocado agrosystems and forests in Mexico and the effects on plant quantity and quality (leaf area, canopy cover, DBH and chlorophyll content), leaf morphology, herbivory and fluctuating asymmetry in Quercus castanea and Q. obtusata. METHODSEight study sites were selected: i) areas with a more proportion of forest and less of avocado orchards, ii) areas with equal proportion of both forest and orchards, iii) areas with more proportion of orchards. In all sites, 15 adult trees at the edge and 15 trees in the interior of each fragment were selected for each oak species. Soil samples were also collected in all study sites to analyze their chemical properties. RESULTS AND CONCLUSIONSWe found higher concentration of Mg2+, NO3− and SO42− in soils of sites with more proportion of orchards. Total leaf area, canopy cover and DBH, as well the herbivory and FA levels were higher in these sites and in the edges of fragments for both oak species. Chlorophyll content was higher at forest edges than in the interior of fragments for all sites analyzed. Leaves of both oak species were more elongated and wider in sites with more proportion of orchards, as well in forest edges. Plant traits, herbivory and FA were related to chemical soil properties according to the proportion of forest and orchards, indicating that the mechanisms driving this interaction are scale-dependent and vary among habitat types according to proportion of forest. Herbivory was positively correlated with leaf area, DBH, chlorophyll content and FA for both oak species, indicating that herbivory increase as resource availability and quality increased along mosaic of avocado agrosystems. Our results showed that land use change of forest to avocado orchards, creates fragments with intense edge effects changing chemical soil properties, which in turn affect quantity and quality of resources to insect herbivores, as well as leaf morphology and FA levels of Q. castanea and Q. obtusata individuals. SIGNIFICANCEOur study is the first to denote the importance of the maintenance and conservation of temperate forest ecosystems and their potential functional and ecological benefits to avocado cultivation.

Effects of exogenous bacterial quorum-sensing signal molecule/messenger N-hexanoyl-L-homoserine lactone (C-HSL) on acorn germination and plant growth of Quercus robur and Q. rubra (Fagaceae)

The effect of pre-sowing priming with N-hexanoyl-L-homoserine lactone (C6-HSL) solution (300 mg/L) on acorn germination and morpho-phenological characteristics of Quercus robur and Q. rubra was studied under laboratory conditions. After priming, 93.4% of Q. robur acorns germinated that exceeded the control by 32.2%, while the number of sprouted acorns of Q. rubra increased within error limits by 5% more than the control and amounted to 90%. According to morphological characteristics, the 47-day-old plants of Q. robur were divided into the following groups: germinated acorns, sprouts and seedlings with juvenile leaves, whereas among the plants of Q. rubra, sprouts and seedlings with true leaves were selected. A group of plants with juvenile leaves was detected only in the samples primed with C6-HSL. Priming induced differential changes in cotyledon biomass of both species and accelerated nutrient utilization by Q. robur seedlings. We observed a positive effect on the growth and biomass accumulation of Q. robur plants and a negative effect, except for plants of the third group, on those of Q. rubra. The dry weight of seedling roots of Q. robur and shoots of Q. rubra increased, respectively, by 103% and 153%. Priming of acorns with C6-HSL solution induced an increase in number, length, biomass and total area of leaves. These changes were more pronounced in Q. rubra seedlings. Alterations in the root system architecture towards formation of numerous additional lateral roots were recorded for both species. Thus, priming with C6-HSL solution activated acorn germination and stimulated growth of Q. robur plants and decelerated growth of plants of Q. rubra. Exogenous C6-HSL did not eliminate the syndrome of unfriendly seedlings of both studied oak species, but improved the viability of acorns and increased the number of seedlings.

Acute oak decline (AOD) new complex disese on holm oak (Quercus ilex L.) and possibilities of spread on other oak species in Croatia

U radu se prikazuje pregled dosadašnjih saznanja o Akutnom odumiranju hrastova (AOH), u svijetu opisanom kao AOD (Acute oak decline). Ova polimikrobna bolest je nedavno otkrivena u Hrvatskoj (2021. godine) na poluotoku Pelegrin (otok Hvar), gdje se na stablima hrasta crnike zadnjih nekoliko godina javljaju tipični simptomi: sušenje vrhova krošnje koje prate uzdužne raspukline kore, gdje istodobno ispod kore dolazi do odumiranja tkiva u obliku crnih nekroza. U kasnijoj fazi javljaju se i tekline te se vide izlazne rupe kukaca, a stablo nakon 3-4 godine odumire. Bolest se širi sa stabla na stablo, a krajnja posljedica je masovno sušenje. Uzročnici odumiranja tkiva pod korom su patogene bakterije Brenneria godwinii, Gibbsiella quercinecans i Lonsdalea britannica, a njihovi mogući prijenosnici su krasnici Agrilus sulcicolis i A. olivicolor. AOH je do sada opisana u Ujedinjenom kraljevstvu, Latviji, Španjolskoj, Iranu i Švicarskoj. Važnost prvog nalaza AOH u Hrvatskoj je što hrast crnika kao autohtona vrsta ima posebno značenjej za Mediteranske šume, a k tome su po prvi puta nađene i vrste krasnika koje do sada nisu potvrđene kao vektori AOH. Posebno se naglašava rizik prijelaza AOH na kontinentalne šume hrasta lužnjaka i kitnjaka, jer za razliku od svih dosadašnjih nalaza AOH u svijetu, lužnjakove i kitnjakove šume u Hrvatskoj su jedine koje su već godinama izložene napadima hrastove mrežaste stjenice (Corythucha arcuata). Moguća kombinacija hrastove mrežaste stjenice i AOH mogla bi biti iznimno opasna. Stoga se naglašava promptna primjena mjera zaštite, posebice preventivnih te važnost znanstvenih istraživanja.

The LGM refugia of deciduous oak and distribution development since the LGM in China

The distribution development of oak has significant effects on ecosystems and society. Long-term forest distribution studies can help to better understand the vegetation dynamics under climate change or human activities in the future. In this study, we integrated different methods (i.e., palaeoecology, phylogeography, and species distribution models) to investigate the likely locations of glacial refugia and the postglacial development of the main deciduous oak species (i.e., Quercus variabilis, Q. mongolica, Q. dentata, Q. aliena, Q. acutissima and Q. liaotungensis). The results indicated that mountains such as the Changbai, Qinling, and Dabie Mountains acted as the refugia in northern and central China during the Last Glacial Maximum (LGM). The present Quercus in northern China could be the result of local dispersal during the postglacial period rather than only that of long-distance migration from south to north. Climate was the main influencing factor for oak migration, while human activities did not show much influence on this widespread genus. The topography acted as a buffer and made the mountains to act as refugia under a deteriorated climate. Compared with other main tree genera (e.g., Pinus and Betula), the refugia locations and migration routes of deciduous oak species were different because of their physiological differences. The individual migration dynamics of these three genera need to be considered when modelling their dynamics.