Intra and inter-annual variation in seed rain in a secondary dry tropical forest excluded from chronic disturbance

Domestic livestock grazing and firewood extraction are chronic and pervasive disturbances in dry secondary forest that reduce diversity and modify composition. Exclosure of such disturbances may allow the reestablishment of original diversity. To investigate potential vegetation recovery following 30 years of perturbation, seed rain was evaluated monthly during 3 years in 96 0.78 m² seed traps located in eight exclosures established in 2006 in a species-poor secondary dry forest in central Mexico. Twelve additional seed traps were located outside the exclosures in 2010 for comparison purposes. Baseline diversity of seed sources (trees, ?5 cm DBH) was recorded to compare standing tree composition with seed rain. Also, baseline diversity of potential primary (birds) and secondary (ants) dispersal vectors were registered to infer current plant-animal interactions. Total seed rain over 3 years within the exclosures comprised 180,375 seeds from 61 woody species, an average of 1.12 seeds/m²/month. Half of these species (31) and 95% of the seeds falling within the exclosures belonged to trees typical of perturbed sites. Sixty percent of all recorded seeds belonged to an early-successional, bird-dispersed shrub (Hamelia patens Jacq., Rubiaceae). Seed rain at one non-excluded plot was dominated by the wind-dispersed early-successional tree Heliocarpus sp. (Tiliaceae). Richness and seed density increased significantly in the second year of exclusion; however, by the third year, richness remained constant while seed density decreased. Seed rain was richer and more abundant during the dry season and was dominated by wind-dispersed species. Phenology, successional status and the dispersal modes of woody species explained most variance in richness and seed density of seed rain in early-successional dry forest. Seeds of early-successional species were dispersed in equal measure by abiotic and biotic vectors, whereas biotic vectors dispersed a higher density of late-successional seeds. The amount and timing of fall of abiotically dispersed seeds of the three most abundant species in the standing tree community may prolong their current domination of the landscape. However, even when richness in the seed rain within exclosures remained constant through time, composition was gradually shifting towards animal-dispersed species which may start a positive feedback producing an increase in animal visitation and a further increase of richness.     

Saproxylic beetle assemblages in the Mediterranean region: Impact of forest management on richness and structure

Forests cover almost 30% of the Mediterranean region today, yet forest management activities have influenced structure and composition of both natural and planted forests. To date no study has been conducted to evaluate the impact of forest management on saproxylic beetle assemblages, although it is known that the Mediterranean is a biodiversity hotspot with a long-lasting human pressure on natural habitats. We provide an overview of saproxylic beetle assemblages of three forest types (mature Pinus halepensis forests, mature Pinus brutia forests, young Quercus calliprinos forests) in the East Mediterranean region using a one-year sample from 12 forest plots located in the north of Israel.     

小陇山不同经营措施下次生锐齿栎天然林物种多样性研究

采用固定样地和样方法调查了小陇山林区百花林场3个实施不同经营措施的锐齿栎天然林林分特征和物种组成,运用4种常用的物种多样性指数对调查林分的乔木层、灌木层和草本层的物种多样性进行对比分析,结果表明:3种类型锐齿天然林的灌木层相对于其乔木层和草本物种组成丰富,多样性高;长期封育后的锐齿栎天然林群落在3种天然林类型中物种组成最丰富,乔木层、灌木层和草本层的Shannon-Wiener指数、Pielou指数和Margalef指数值在3个林分中最高;近自然技术单株经营后的锐齿栎天然林各层次的物种组成相对较少,多样性较低,但其林分中保留的乔木树种个体较大;结构优化抚育后的锐齿栎天然林的物种组成和多样性介于二者之间.抚育经营措施对林分的影响与抚育经营强度密切相关,适当的抚育经营强度能够促进林分多样性提高,否则会带来不利的影响,结构化森林经营技术是一种有效的经营方法.     

Effects of grazing exclusion and environmental conditions on the soil seed bank of a Mediterranean grazed oak wood pasture

Large seed banks in the soils of Mediterranean wood pastures can allow the composition of the understorey vegetation to adapt to changing conditions such as under-grazing, grazing exclusion and climate change. This three year study investigated the effect of grazing exclusion on the transient and persistent seed banks of 23 areas of a Mediterranean wood pasture of Quercus suber L., Q. ilex L. and Q. pubescens Willd. A canonical correspondence analysis was used to determine the effect of topo-climatic (elevation, aspect, slope, rainfall, temperature, tree coverage), soil (pH, soil texture, and soil nitrogen, phosphorus, lime and organic carbon content) and biodiversity (Shannon index, species richness index, and Pastoral Value) variables on the soil seed bank under grazed and ungrazed conditions. The size of the persistent seed bank increased with rainfall, grazing, and the available phosphorus content of the soil. Specific site by site grazing regimes could increase the abundance of legumes in the soil seed bank and the species richness and diversity of the understorey vegetation. These results can help guide the conservation management of this silvopastoral area.     

甘肃小陇山灌木林不同改造模式天然更新研究

用样方法,研究了小陇山林区5种典型灌木林地改造模式的乔木树种天然更新幼苗的密度和多样性。结果表明:5种灌木林地改造模式的乔木树种天然更新情况总体良好,小于50 cm高度级幼苗数量相对较少,大于50 cm高度级幼苗的存活率较高;5种改造模式天然更新树种以锐齿栎为主,其中,全面割灌改造日本落叶松(模式3)更新幼苗物种丰富度最高,全面割灌改造油松模式(模式2)天然更新树种丰富度最小;带状割灌改造模式(模式4和模式5)和全面割灌改造华山松模式(模式1)的更新树种多样性较高,各树种分配均匀,优势树种的集中性较低;改造树种华山松的天然更新能力较油松日本落叶松强,带状割灌改造模式更有利于华山松天然更新。     

Characteristics of a 20-year-old evergreen broad-leaved forest restocked by natural regeneration after clearcut-burning

? To elucidate the application of natural regeneration to the restocking of evergreen broad-leaved forests in the subtropics, the characteristics of a 20-year-old evergreen broad-leaved forest restocked by natural regeneration after clearcut-burning were studied in Okinawa, Japan. Within a 0.87 ha clearcut area with four 10 m × 10 m sampling plots, two burned and two unburned ones, the tree composition, tree species diversity and vegetation changes were investigated.

? The results showed that the species diversity, basal area and density of woody stems ? 1.0 m in height differed significantly among phanerophyte types, while they were not significantly different between the burned and unburned treatments. A vegetation census also revealed no obvious differences between the treatments.

? The primary dominant species, Castanopsis sieboldii, continued to dominate the secondary forest with a broad height distribution.

? The structural complexity and high tree species diversity of the regenerating forest after clearcut-burning provides no evidence of degeneration. We can predict that the regeneration forest may gradually develop into stands similar to pre-clearcut primary forest, and that natural regeneration may restore the high tree species diversity of the evergreen broad-leaved forests in Okinawa.

     

Effects of selection cutting on the forest structure and species diversity of evergreen broad-leaved forest in northern Fujian, southern China

The short-term effects of selection cutting of different intensities on the forest structure and species diversity of evergreen broad-leaved forest in northern Fujian Province were investigated and analyzed. The results showed that selection cutting of low and medium intensities caused little variation in the forest structure. After cutting, the dominant species retained their leading status in the community. However, the community structure changed significantly following selection cutting of high and extra-high intensities;the status of the dominant species of the community declined dramatically. Some tree species began to disappear from the sampling plots. Except for extra-high intensity cutting, the diversity of tree species did not change significantly for the other three cutting intensities. However, the evenness of the stands was very different among the four kinds of cutting plots. For low and medium intensity selection cutting, the evenness declined slightly. For extra-high intensity selection cutting, the evenness increased to some extent,which might be due to a more even distribution of tree species after cutting. Cutting operations resulted in some adverse reactions to development of arborous species diversity of evergreen broad-leaved forest, particularly serious damage to the forest canopy. But the rational selection cuttings, which may benefit the restoration and maintenance of species diversity over a long period and may come about from the variations in environmental factors such as sunlight, temperature and humidity.     

The sustainability of selection cutting in a late successional broadleaved community forest in Bhutan

This study assessed the sustainability of selection cutting in a community forest (CF) in Bhutan. The harvesting approach differed from cable crane logging operations in an adjacent commercially managed forest by creating much smaller canopy openings. This had many implications for natural regeneration of preferred species. The study was conducted in a late successional broadleaved CF containing 32 genera of tree species dominated by Quercus and Castanopsis and managed for timber, firewood, non-wood forest products and forest grazing. The study was based on a comparison of two forest inventories to assess forest structure and regeneration, a study of stumps to quantify harvesting intensities, and a household survey to quantify livestock holdings and grazing patterns. The study examined different intensities of selection cutting in three blocks of the CF and found that higher intensities of selection cutting did not have a negative impact on: (a) natural regeneration of seedlings and saplings of preferred timber species; (b) the diameter distribution of all species and use categories except for Quercus; (c) the diversity of tree genera; and (d) the percentage of remaining trees with favorable bole shape and form. These results contrasted with findings in the adjacent commercially managed forest. Community management of broadleaved forests with selection cutting appeared to be sustainable and avoid some of the unresolved silvicultural problems associated with commercially managed forests in Bhutan. However more research is needed on the sustainable management of Quercus spp.     

Acacia cyanophylla for forage and fuelwood in North Africa

Forage and wood yield of Acacia cyanophylla, also known as Acacia saligna, was studied in a 300–400 mm precipitation zone in Tunisia. Yields were measured during and after drought. This short (2–8 m) evergreen leguminous tree is used as a forage drought reserve in frost free regions where mean annual precipitation exceeds 250 mm. The standing crop of leafy forage builds up year after year for at least four years or until the tree is cut. It rapidly regrows after cutting from coppice shoots. The leaves provide high protein forage for sheep and goats during the long dry summer season typical of the Mediterranean climate as well as emergency forage during drought. The tree is used to stabilize moving sand dunes, and as a windbreak to protect cropland. It also provides fuelwood and increasaes soil nitrogen by fixation. The need for supplemental irrigation during establishment is a major constraint. Research in the 350 mm precipitation zone of Tunisia found 3.2 year old trees to yield over 1400 kg of forage standing crop per hectare after a severe drought. Trees harvested at 2.5 years of age in May, during the worst drought in over 30 years, yielded a standing forage crop of 724 kg per hectare. Forage regrowth 8 months after cutting and 4 months after rains returned was 700 kg/ha. The forage standing crop for trees harvested only once during the 3.2 year period was double the amount of forage regrowth from trees harvested the previous year, but mean annual forage yield similar. This demonstrates that it is possible for forage to be conserved as a living forage reserve for later use during drought. Total wood yield was only 1621 kg/ha for trees cut twice compared to 3683 kg/ha for trees cut only once. Annual cutting will substantially reduce the amount of forage available during drought and reduce the production of fuelwood. It may also reduce the vigor, productivity and life of the tree. Acacia cyanophylla alley cropped on cereal farmland can protect the soil from erosion, protect the associated crop from wind damage, fix nitrogen, provide fuelwood and provide a reserve of high quality forage for use during drought. This work was supported by the Government of Tunisia and the U.S.A.I.D. Tunisia Range Development and Management Project (664-0312.8).     

Establishing grazing and grazing-excluded patches increases plant and invertebrate diversity in a Mediterranean oak woodland

Grazing is a global, dominant land use affecting biodiversity and ecosystem processes. In Mediterranean ecosystems grazing is a major ecological and evolutionary driver but, surprisingly, there is little information on the use of grazing as a tool to manage biodiversity in these ecosystems. We conducted an experiment to assess if establishing grazing and small scale grazing-excluded areas would increase plant and invertebrate diversity in a Mediterranean evergreen oak woodland. Plant community traits were different between treatments. Biomass of herbs (176.7 ± 18.3 g m⁻²vs 100.4 ± 10.6 g m⁻²) and litter (291.0 ± 38.3 g m⁻²vs 186.8 ± 26.4 g m⁻²), as well as the total cover of legumes (0.83 ± 0.05 vs 0.91 ± 0.03) were higher, and the proportion of bare ground (0.83 ± 0.05 vs 0.91 ± 0.03) was lower, in ungrazed plots. There were no differences in the number of plant species between treatments. Some plant species and invertebrate taxa were recorded exclusively in grazed or ungrazed plots. Invertebrate detritivores and sap sucking insects were more abundant in ungrazed plots. Ant assemblages were functionally different between treatments: Honeydew-gatherer ants were associated with ungrazed and higher plant biomass plots, and seed-eaters as well as aggressive predator ant species were associated with grazed, open habitat, plots. Management practices that maintain grazing and small scale grazing-excluded areas can increase habitat heterogeneity and promote herbaceous plant and invertebrate diversity at the local level.     

Persistent Acacia savannas replace Mediterranean sclerophyllous forests in South America

Mediterranean ecosystems are global hotspots of biodiversity threaten by human disturbances. Growing evidence indicates that regeneration of Mediterranean forests can be halted under certain circumstances and that successional stages can become notoriously persistent. The Mediterranean sclerophyllous forest in central Chile is been largely transformed into savannas dominated by the invasive legume tree Acacia caven as result of interacting management and ecological factors. We used multi-temporal satellite imagery to study the transition dynamics of these major vegetation types over the last four decades (1975-2008). Vegetation changes were related to indicators of resource availability (topography, water availability, solar radiance), potential propagule availability (distance to forest remnant patches) and disturbance regimes (grazing, fire occurrence and distance to roads and cities). During this study period, forests were mostly converted into Acacia savannas (46.1%). Acacia savanna was the most persistent natural vegetation type. The probability of sclerophyllous forest degradation into Acacia savanna increased on drier northern-exposed slopes, close to roads and further away from forest remnants. In contrast, forest regeneration from Acacia savanna was higher on moister southern-exposed slopes and closer to forest remnants. Acacia savannas are increasingly being converted into cultivated land on the moister locations or switching into a bare soil state in locations close to cities and further away from forest remnants. These results highlight the vulnerability of diverse sclerophyllous forests and its increasing conversion into persistent Acacia savannas in the Mediterranean region of central Chile and identify the ecological conditions for successful conservation and restoration of the native sclerophyllous forest vegetation that can be used for sensible land use planning.     

Forest patches in Imperata grassland and prospects for their preservation under agricultural intensification in Northeast Luzon, The Philippines

Frequent burning and grazing and cultivation of cash crops increasingly threaten forest patches in hilly grassland in Northeast Luzon, yet their importance as a resource with multiple environmental functions and forest products persists. The aim of this study is to identify different types of forest patches, and their condition under present land-use intensification, and discuss prospects for their integration into sustainable local farming systems. Five types of forest patches are distinguished, both natural and planted ones, including rows of trees, woody patches, gallery forests, hill-slope forests and homegarden conglomerations. Natural woody patches and gallery forests in Imperata grassland are subject to degradation and land-use conversion under conditions of agricultural intensification. Woody patches in grassland affected by frequent burning and grazing cover small areas (66% below 50 m² as opposed to 28% in protected grassland) and contain relatively few woody plant species (25 woody species in total as opposed to 82 where protected). Yet where well managed, they may provide a variety of products for sale and subsistence, covering emergency needs and giving off-season cash income to rural communities. Moreover they serve like the gallery forest various ecological functions, carrying valuable indigenous tree species, retaining soil base nutrients, providing a continuous supply of organic matter and intercepting fine earth soil particles removed from bare surfaces. It is suggested that forest-patch management systems may be developed, taking into account both patch diversity and the diverse needs of rural communities, and to strengthen existing and undervalued functions of forest patches as permanent elements in an agricultural landscape.This revised version was published online in November 2005 with corrections to the Cover Date.     

Specific gravity of some woody species in the Srinagar Valley of the Garhwal Himalayas, India

In this study, we investigated the specific gravity of wood samples collected from a total of 31 woody species, consisting of 20 trees, 10 shrubs and one species of bamboo from sub-tropical regions of Garhwal Himalayas, India. Results show that among these woody species, the specific gravity of trees ranged from 0.34 for Erythrina suberosa to 0.83 for Albizia procera. For shrub species the specific gravity of Ricinus communis was 0.39 and that of Dodonaea viscosa 0.93. The average specific gravity of trees was 0.58 and of shrubs 0.66.     

Effect of exclosure ages on woody plant structure,diversity and regeneration potential in the western Tigray region of Ethiopia

Exclosure is a method of rehabilitating degraded lands by protecting them from the interference of animals and from human encroachment, and is used to regenerate native vegetation as a way to reduce soil erosion, increase rain water infiltration and provide fodder and woody biomass in degraded grazing lands. Therefore, we studied woody plant structure, diversity and regeneration potentials in 5- and 10-year grazing exclosures in comparison with open grazed sites in a semi-arid environment. Data on species diversity, abundance, structure, basal area, frequency, density, and regeneration status were collected from 270 sample plots. Forty-one woody species representing 20 families were identified, with 18, 28 and 38 species found in open grazed areas, and in 5- and 10-year grazing exclosures, respectively. The 10-year grazing exclosures had a higher (P < 0.05) species richness and plant densities compared to the 5-year grazing exclosures and the open grazed areas. The population structure and regeneration status of woody species in both grazing exclosures showed an inverted J-shape, indicating a healthy regeneration status, whereas hampered regeneration was observed in open grazed areas. The establishment of grazing exclosures had positive effects in restoring woody plant diversity and improving vegetation structure and regeneration potentials of degraded grazing lands.     

Woody understory plant diversity in pure and mixed native tree plantations at La Selva Biological Station,Costa Rica

Tree plantations can be an important tool for restoration of abandoned pasturelands in the tropics. Plantations can help speed up secondary forest succession by improving soil conditions, attracting seed-dispersal agents, and providing shade necessary for understory growth. In this study, abundance and richness of understory regeneration was measured in three native tree plantations 15–16 years of age at La Selva Biological Station in the Costa Rican Caribbean lowlands. Each plantation contained tree species in pure plots, a mixture of the species, and natural regeneration plots (no trees planted). The greatest abundance of regeneration was found in the understory of pure plots of Jacaranda copaia (Aubl.) D.Don., Vochysia guatemalensis Donn.Sm., Dipteryx panamensis Benth, Vochysia ferruginea Mart., and in two mixed stands, while the lowest was found in the natural regeneration treatments with about half the values as in the plantation stands. There was a significant negative correlation between percent canopy openness and abundance of regeneration in the understory. Two distinctive clusters separated the regeneration treatments from the mixed and pure plantations at a very low Bray–Curtis similarity value. The natural regeneration treatments are separated from mixed and pure plantations in the two-dimensional ordination. The lack of difference between the understory make-up of pure and mixed plantations in abundance, species richness, and seed-dispersal syndromes of understory species suggests that planting mixed stands is not necessarily superior to planting pure stands for promoting understory diversity of woody species. While regeneration of woody species can be faster under pure- or mixed-species plantations than in open pastures, the abundance, richness and species composition depends on each plantation species, or species assemblages in case of the mixtures.     

Dynamics and determinants of Quercus alba seedling success following savanna encroachment and restoration

The scattered tree layer that defines savannas is important for structuring the understory community and determining patterns of overstory recruitment. However, encroachment by woody plants has altered overstory tree densities and regeneration dynamics. We characterized seedling success of the savanna-forming species Quercus alba within Midwestern (USA) oak savannas that had been degraded by encroachment (control; n = 4) or experimentally restored by removal of encroaching woody vegetation (treatment; n = 4). In early 2004, 981 seedlings were transplanted along transects radiating from tree boles of overstory Q. alba trees to inter-canopy gaps and monitored for three growing seasons. Seedlings in restored sites had greater survival (>2×), height growth (by >50%), and basal diameter growth (by >20%). In general, seedling survival and growth parameters increased with distance from overstory trees and were greatest in inter-canopy gaps of restored sites. By the final growing season (2006), the seedling survival-by-distance from tree correlation was stronger in control (r² = 0.25) than treatment sites (r² = 0.18), due to relatively uniform (and greater) survival at all distances from trees in treatment sites. In 2006, growth parameters (seedling height, diameter, Δ height, Δ diameter, and # leaves) were significantly (and more strongly) positively correlated with distance from trees in treatment sites. However, seedling herbivory was also greater after treatment and increased with distance from overstory trees. To understand seedling/microenvironment relationships, we created logistic (survival) and linear regression models (Δ height, Δ basal diameter, # leaves in 2006). Control seedling models had consistently greater predictive power and included more variables, suggesting that savanna restoration may decouple seedlings from their microenvironments, potentially by decreasing competition for limiting resources. Encroachment of the savannas in this study is limiting regeneration of Q. alba, suggesting substantially altered regeneration dynamics from those under which these savannas originally formed. Initial responses from our test of restoration, however, were promising and mechanical encroachment removal may be a means to promote overstory regeneration of this species. Finally, the savannas in this study appear inherently unstable and a scattered canopy tree configuration is unlikely to persist without regular disturbance, even in the restoration sites. Repeated mechanical thinning treatments with selected retention of recruiting Q. alba individuals or reintroduction of understory fire or grazing animals may be potential mechanisms for promoting long-term persistence of savannas at these sites.     

Secondary forest floristic composition, structure, and spatial pattern in subtropical China

Secondary evergreen broadleaved forests are precious remnants for biodiversity conservation and templates for sustainable management of natural forests in subtropical China. Floristic composition, size structure, and spatial pattern of dominant tree species have been investigated for a subtropical secondary evergreen broadleaved forest in the Huitong Yingzuijie National Forest Reserve, Hunan, China. The location of all trees greater than 4 cm in diameter at breast height (DBH) were mapped within a 0.96-ha plot in which species, DBH, and total tree height were recorded. Ripley’s K(t) function was used to analyze spatial patterns and associations. The secondary forest consisted of 74 tree species and 1,596 stems per hectare. A reverse-J shaped DBH classes distribution was observed for all stems and trees of later seral species whereas trees of earlier successional species were distributed irregularly. Significant aggregated spatial patterns were observed for all trees within the forest and for conspecific trees of each dominant species. This result, and a repulsive spatial pattern for interspecific trees of Choerospondias axillaries and Cyclobalanopsis glauca against other dominant tree species, support segregation hypothesis. Contributions of seed dispersal, topographic heterogeneity, and competition to spatial patterns of conspecific trees vary depending on tree species. Attractive spatial pattern among interspecific trees of Liquidambar fortunei, Liquidambar formosana, and Pinus massoniana reflects stochastic colonization of pioneer tree species and a facilitation relationship. Although deciduous species are long-lived and persist over long successional processes, they will eventually be replaced by late seral evergreen species within the secondary forest if no disturbance events occur.     

哀牢山植物多样性垂直分布格局

以设于哀牢山各植物群的样地调查材料为依据,分析了哀牢山东、西坡不同海拔高度地带性植物群落乔木层林木的高、径垂直分布特征,植物群落生物多样性指数的垂直分布态势。结果表明:该山地植物群落乔木层和灌木层的植物物种多样性沿海拔梯度呈单峰型分布格局,以中山湿性常绿阔叶林乔木层林木的最大和平均树高、最大胸径值和物种多样性指数最大;而灌木层植物物种多样性指数最大值出现在中山湿性常绿阔叶林带下的季风常绿阔叶林和半湿性常绿阔叶林带内;而草本层植物的物种多样性指数则沿海拔梯度上升呈整体减小的趋势;累加其植物群落乔、灌、草3层植物的物种多样性指数,哀牢山东、西坡植物群落的Shannon-Weiner指数和物种丰富度最大值出现在海拔高度2000 m左右。在相同海拔高度处,西坡植物群落的植物物种多样性高于东坡,季风常绿阔叶林的物种多样性大于半湿性常绿阔叶林,而山顶苔藓矮林的植物物种多样性最小。     

Fingerprinting and genetic variability in cork oak (Quercus suber L.) elite trees using ISSR and SSR markers

Quercus suber L., is a socially, economically and ecologically important forest species in rural areas of the Mediterranean basin. Fifty three elite-trees from nine stands of four provenance regions in the Community of Extremadura (Spain) were analysed with the aim to establish their DNA-fingerprinting and the genetic relationships among them. Two types of molecular markers, microsatellites and intermicrosatellites, were used for tree genotyping. Microsatellite markers could distinguish 94% of the trees. Observed and expected heterozygosities, and effective number of alleles were correlated with the polymorphism information content (PIC). Intermicrosatellite patterns were used to construct a dendrogram. They showed high levels of genetic diversity in these elite trees, without any clear relationship with provenance regions. Both types of markers detected a high level of intra-stand variability, which is common in Quercus species, probably due to its mating system, the low distance among stands and the small size of stands. Others factors that could affect this result, such as introgression between Q. suber L. and Q. ilex L., are also commented. The high level of genetic variability detected in these elite trees can be useful for improvement programs. Also the usefulness of SSR and ISSR markers to establish the DNA-fingerprinting of each tree could be focused to select clonal lines of commercial interest.     

Intensity and timing of warming and drought differentially affect growth patterns of co-occurring Mediterranean tree species

Climate change involves warmer temperatures, altered precipitation patterns, increased climatic variability and, in Mediterranean regions, increased frequency and severity of droughts. Tree species may show different growth responses to these components of climatic change, which may trigger changes in forest composition and dominance. We assessed the influence of recent climatic changes on secondary growth of mature trees from four species co-occurring in a Mediterranean continental forest: Quercus ilex, Quercus faginea, Pinus nigra and Juniperus thurifera. We used dendrochronology to relate radial-growth variables [earlywood and latewood widths, basal area increment (BAI)] to annual and seasonal climatic variables for the period 1977–2007. Our results showed that Q. faginea BAI has declined, whereas J. thurifera BAI has increased over time while Q. ilex and P. nigra have maintained their growth rates. Growth was mainly favored by higher precipitations and tree size for all species. Reduced growth during extremely dry years was observed for all study species, but all of them except Q. faginea recovered their growth levels 2 years after drought. Our findings illustrate how the effects of climatic changes on growth should include analyses of seasonal climatic trends and extreme events such as severe droughts. We conclude that the seasonal timing of warming and precipitation alterations leading to drought events caused contrasting effects on growth of co-occurring Mediterranean tree species, compromising their future coexistence.