Key Tree Species Research Articles

Influence of Drought on Foliar Water Uptake Capacity of Temperate Tree Species

Foliar water uptake (FWU) has been investigated in an increasing number of species from a variety of areas but has remained largely understudied in deciduous, temperate tree species from non-foggy regions. As leaf wetting events frequently occur in temperate regions, FWU might be more important than previously thought and should be investigated. As climate change progresses, the number of drought events is expected to increase, basically resulting in a decreasing number of leaf wetting events, which might make FWU a seemingly less important mechanism. However, the impact of drought on FWU might not be that unidirectional because drought will also cause a more negative tree water potential, which is expected to result in more FWU. It yet remains unclear whether drought results in a general increase or decrease in the amount of water absorbed by leaves. The main objectives of this study are, therefore: (i) to assess FWU-capacity in nine widely distributed key tree species from temperate regions, and (ii) to investigate the effect of drought on FWU in these species. Based on measurements of leaf and soil water potential and FWU-capacity, the effect of drought on FWU in temperate tree species was assessed. Eight out of nine temperate tree species were able to absorb water via their leaves. The amount of water absorbed by leaves and the response of this plant trait to drought were species-dependent, with a general increase in the amount of water absorbed as leaf water potential decreased. This relationship was less pronounced when using soil water potential as an independent variable. We were able to classify species according to their response in FWU to drought at the leaf level, but this classification changed when using drought at the soil level, and was driven by iso- and anisohydric behavior. FWU hence occurred in several key tree species from temperate regions, be it with some variability, which potentially allows these species to partly reduce the effects of drought stress. We recommend including this mechanism in future research regarding plant–water relations and to investigate the impact of different pathways used for FWU.

In Mediterranean drylands microclimate affects more tree seedlings than adult trees

Abstract Topography creates contrasting microclimates, especially between northern and southern slopes in drylands, which result in clear differences of tree cover patterns in the landscape. These local-scale differences in tree cover patterns may result from limitations occurring at different plant development stages, such as seed germination, seedling establishment, tree growth rate and survival, all crucial for the maintenance and expansion of plant populations through natural regeneration. Holm oak (Quercus rotundifolia Lam.) is a key tree species in Mediterranean drylands. We aim at measuring the impact of microclimatic conditions on holm oak trees regeneration success using traits as indicators of adult tree performance in an average climatic year and tree’s distribution pattern at the landscape level as an indicator of tree establishment success. We hypothesize that under contrasting microclimatic conditions, seedlings performance is limiting the regeneration potential of holm oak trees rather than adult trees physiological performance. To quantify the microclimatic conditions originated by topography, two indicators were used: i) Potential Solar Radiation, as the amount of potential solar energy reaching the site above tree canopy; and ii) functional lichen diversity, as ecological indicators of microclimatic conditions under the tree canopy. The performance of holm oak was assessed on 40 adult trees growing in contrasting microclimatic conditions (high and low Potential Solar Radiation sites). Several indicators based on leaf, tree and stand response traits, frequently used as ecological indicators to evaluate tree performance and susceptibility to drought stress, were selected: specific leaf area, leaf reflectance indices, tree size, tree growth rate, tree age and tree density. We found that leaf physiological performance was similar under contrasting microclimatic conditions. However, in areas with higher Potential Solar Radiation tree age and density were significantly reduced. These results suggest that microclimatic differences located in southern slopes with high Potential Solar Radiation are limiting for germination and sapling establishment. Thus, forest regeneration, restoration and nature conservation practices aiming at increasing forests resilience in Mediterranean dryland climates should account for the importance of microclimate in defining the niche of seedlings and of adult trees.

Demographic, seed and microsite limitations to seedling recruitment in semi-arid mine site restoration

Understanding limitations to plant recruitment is a key element in devising effective restoration of semi-arid ecosystems: only when these limitations are identified can management interventions be effectively targeted. This study investigated demographic, seed and microsite limitations to establishing native plant species in a semi-arid, post-mining restoration context. We assessed ex situ and in situ germination and in situ emergence for eight key tree, shrub and annual herb species. We sowed non-treated seeds and seeds that were pre-treated to overcome dormancy, at differing densities and across diverse microsites to assess the roles of dormancy, seed density and microsite type as limiting factors for seedling recruitment. We found that dormancy loss, in situ germination and in situ emergence limited one or more species, and we were able to improve emergence of one species by seed addition and targeted manipulation of microsites. The study has resulted in management implications including the importance of understanding methods to overcome dormancy to maximise germination; identifying key and species-specific demographic transitions; the importance of species-specific testing of seed sowing density; and the potential for increasing emergence by sowing seeds in furrows rather than broadcasting across rises and furrows, or on flat, unripped soil.

Competition of key tree species with selective cutting at different intensities in broadleaved-korean pine mixed forest in the Changbai Mountain, China.

Selective cutting changes tree species composition and stand structure, modifies tree competition intensity in the stand, with consequences on tree growth and population dynamics. Key tree species play a crucial role in maintaining community structure and ecosystem function. To clarify the competitive characteristics of three key species (Pinus koraiensis, Tilia amurensis, and Fraxinus mandshurica, which accounted for about 70% of growing stock) of typical forest types in broadleaved-Korean pine mixed forest, Hegyi competition index was used in four permanent 1-hm2 plots, i.e. virgin forest (VF), low-intensity cutting forest (LCF), moderate-intensity cutting forest (MCF) and high-intensity cutting forest (HCF). Compared with VF, the stand density and mean DBH of big trees (DBH≥20 cm) significantly decreased in MCF and HCF, but the stand density of young trees (2 cm≤DBH<10 cm) increased, but no significant changes of stand or DBH in LCF. In all the four forest types, individual competition index (CI) of the three species decreased with increasing DBH. There was a power function relation between CI and DBH. CI curve turned to be gentle at DBH reaching 20 cm, and this rule was not affected by selective cutting. In VF, LCF and HCF, most of competition pressure of young trees of all key species derived from other tree species in secondary canopy or understory, but the competition pressure of small trees (10 cm≤DBH<20 cm) and big trees of P. koraiensis originated mainly from intra-species and other species in secondary canopy or understory. The competition stress of F. mandshurica was mainly affected by P. koraiensis and other species in secondary canopy or understory. T. amurensis was mainly affected by intra-species and P. koraiensis. Betula platyphylla contributed most of the competition stress (over 50%) to all three key species in HCF. Our results suggested that removing the trees which are in secondary canopy or understory but suppress the three key trees species intensively would be beneficial to the regeneration and growth of key species before tree DBH exceeds 20 cm. We proposed to regulate the density of key tree species in overstory to cultivate large diameter timber according to the competition among the key trees species. Once tree DBH exceeds 20 cm, tree growth would not be affected by competition. This study had guiding significance for the cultivation of key tree species and rapid recovery of natural forests after selective cutting.

Effect of neighborhood competition on key tree species growth in broadleaved-Korean pine mixed forest in Changbai Mountain, China.

Competition is the main factor affecting the growth, morphology and death of trees in fore-sts. The analysis of individual competition can reflect the characteristics of interaction among individuals and their interaction ranges, which is important for reducing individual competition and promoting tree growth. To understand the effects of competition on tree growth in broad-leaved Korean pine forest, based on Hegyi single-tree competition index and neighborhood analysis method, we explored the neighborhood radius of competition for five key tree species, i.e. Pinus koraiensis, Tilia amurensis, Fraxinus mandshurica, Quercus mongolica and Ulmus japonica (80% of basal area at breast height in total), and analyzed the effects of competition on the growth and death of the key tree species. The results showed that the neighborhood radius of single-tree competition of four tree species, P. koraiensis, T. amurensis, F. mandshurica and Q. mongolica was 11 m, while that of U. pumila was 13 m. The single-tree competition intensity for all five key tree species was negatively correlated with the logarithm of its growth increment, and positively correlated with the size of individual trees. The relative importance of competition intensity on tree growth decreased with tree growth. Neighborhood competition significantly increased tree mortality. Our results revealed the effects of neighborhood competition on the growth and survival of the key tree species at different developmental stages in broad-leaved Korean pine forests in Changbai Mountain. The results are instructive to the adjustment of competitive environment and the improvement of productivity of key tree species in broad-leaved Korean pine forests.

Identifying cloud forest conservation areas in Mexico from the potential distribution of 19 representative species

Cloud forest is a sensitive and vulnerable ecosystem that is threatened by human activities as well as climate change. Previous studies have shown how transitional ecosystems such as cloud forests will be the most negatively impacted by the global increase in temperature. Therefore, the niche modeling framework was used in this study to geographically identify the areas with the climatic potential to host the largest number of key tree species in this ecosystem and to propose them as priority conservation areas. A total of 19 species were modeled using the MaxEnt algorithm; binary maps were generated for each species and combined to produce one potential suitability map and identify climatic priority areas. Thus, 7% of the national area of Mexico shows suitability for the cloud forest ecosystem, although it is currently distributed in less than 1% of the country. Finally, potential suitability areas were compared with natural protected areas, current land use and priority conservation areas. We found that of the current suitable area, only 5% coincides with some federal or state protection regime. Natural protected areas have proven to be a mechanism for forest conservation, so we must consider increasing the number and area of those protected areas that favor the conservation of these key cloud forest species.

Metabarcoding reveals that rhizospheric microbiota of Quercus pyrenaica is composed by a relatively small number of bacterial taxa highly abundant

Melojo oak (Quercus pyrenaica Willd.) is a key tree species of Mediterranean forests; however, these forests show an advanced stage of deterioration in the Iberian Peninsula. Plant-associated microorganisms play an essential role improving their host’s fitness, hence, a better understanding of oak rhizospheric microbiome, especially of those active members, could be the first step towards microbiome-based approaches for oak-forest improvement. Here we reported, for the first time, the diversity of total (DNA-based) and potentially active (RNA-based) bacterial communities of different melojo-oak forest formations through pyrosequencing of 16S rRNA gene amplicons. We found that potentially active bacterial communities were as rich and diverse as total bacterial communities, but different in terms of relative abundance patterns in some of the studied areas. Both core microbiomes were dominated by a relatively small percentage of OTUs, most of which showed positive correlation between both libraries. However, the uncoupling between abundance (rDNA) and potential activity (rRNA) for some taxa suggests that the most abundant taxa are not always the most active, and that low-abundance OTUs may have a strong influence on oak’s rhizospheric ecology. Thus, measurement of rRNA:rDNA ratio could be helpful in identifying major players for the development of bacterial bioinoculants.

The demography of a resource specialist in the tropics: Cecropia trees and the fitness of three-toed sloths.

Resource specialists persist in a narrow range of resources. Consequently, the abundance of key resources should drive vital rates, individual fitness, and population viability. While Neotropical forests feature both high levels of biodiversity and numbers of specialist species, no studies have directly evaluated how the variation of key resources affects the fitness of a tropical specialist. Here, we quantified the effect of key tree species density and forest cover on the fitness of three-toed sloths ( Bradypus variegatus), an arboreal folivore strongly associated with Cecropia trees in Costa Rica, using a multi-year demographic, genetic, and space-use dataset. We found that the density of Cecropia trees was strongly and positively related to both adult survival and reproductive output. A matrix model parametrized with Cecropia-demography relationships suggested positive growth of sloth populations, even at low densities of Cecropia (0.7 trees ha-1). Our study shows the first direct link between the density of a key resource to demographic consequences of a tropical specialist, underscoring the sensitivity of tropical specialists to the loss of a single key resource, but also point to targeted conservation measures to increase that resource. Finally, our study reveals that previously disturbed and regenerating environments can support viable populations of tropical specialists.

Remote sensing of β‐diversity: Evidence from plant communities in a semi‐natural system

AbstractQuestionDo remote sensing signals represent β‐diversity? Does β‐diversity agree with community types?LocationUNESCO Man and the Biosphere Reserve, La Palma, Canary Islands.MethodsWe recorded perennial, vascular plant species abundances in 69 plots (10 m × 10 m) in three pre‐defined community types along an elevational gradient of 2,400 m: succulent scrubland, Pinus canariensis forest and subalpine scrubland. The remote sensing data consists of structural variables from airborne Light Detection and Ranging (LiDAR) and multispectral variables from a time series of Sentinel‐2 (S2) images. Non‐metric Multidimensional Scaling was used to assess β‐diversity between plots. K‐means unsupervised clustering was applied to remote sensing variables to distinguish three community types. We subsequently quantified the explanatory power of S2 and LiDAR variables representing β‐diversity via the Mantel test, variation partitioning and multivariate analysis of variance. We also investigated the sensitivity of results to grain size of remote sensing data (20, 40, 60 m).ResultsThe β‐diversity between the succulent and pine community is high, whereas the β‐diversity between the pine and subalpine community is low. In the wet season, up to 85% of β‐diversity is reflected by remote sensing variables. The S2 variables account for more explanatory power than the LiDAR variables. The explanatory power of LiDAR variables increases with grain size, whereas the explanatory power of S2 variables decreases.ConclusionAt the lower ecotone, β‐diversity agrees with the pre‐defined community distinction, while at the upper ecotone the community types cannot be clearly separated by compositional dissimilarity alone. The high β‐diversity between the succulent scrub and pine forest results from positive feedback switches of P. canariensis, being a fire‐adapted, key tree species. In accordance with the spectral variation hypothesis, remote sensing signals can adequately represent β‐diversity for a large extent, in a short time and at low cost. However, in‐situ sampling is necessary to fully understand community composition. Nature conservation requires such interdisciplinary approaches.

Recent rising temperatures drive younger and southern Korean pine growth decline

The Earth has experienced an unequivocal warming, with the warmest period of the past 150 years occurring in the last three decades. Korean pine (Pinus koraiensis), a key tree species in northeast Asia, is predicted to be particularly vulnerable to climate change. Here, we use dendrochronological methods to test whether the observed growth decline of Korean pine in northeast China is related to climate warming and whether climate-growth responses varied with age. A total of 628 cores from 401 trees across 16 sites were sampled over the entire distribution area of Korean pine in China. Samples were divided into three age classes: younger (50–130 years), middle (131–210 years), and older trees (>210 years), and measured by the ring-width index and basal area increment (BAI). Results showed a significant decline in BAI in most sites coinciding with an increase of temperature in the growing season and a decrease in precipitation since the 1980s. Meanwhile, we found that temperature-induced growth decline was significantly related to tree age. The BAI of younger trees decreased significantly and sharply (0.44 cm2 year−1, P < 0.0001), while old trees either decreased slightly or stabilized (0.04 cm2 year−1, P = 0.33). Tree growth in the southernmost locations was more likely to decline, what was most likely a result of forest-stand age. The age-related growth decline induced by climate warming might be explained by tree species traits, differences in growth rates between age classes and their relation to stress, changes in root system, competition/stand structure or physiological mechanisms. Our results might also predict that early stand process-thinning is exacerbated by warming and drying. This research informs that the age effect of growth response to rising temperature should be considered in forest management under climate change, and particularly models of future carbon cycle patterns and forest dynamics.

Litterfall and Nutrient Returns in the Rainforest of Southwestern Cameroon: Some Implications for Tropical Forest Productivity

Understanding litterfall and macronutrients in the rainforest ecosystem gives baseline information on nutrient dynamics. Litterfall and macronutrients return were studied for 12 months from November 2011 to October 2012 in a 50 ha plot in the Takamanda National Park, South-western Cameroon. This study evaluates the pattern and quantity of litterfall, with implications for forest productivity. It thus assesses the macronutrient concentrations, nutrient inputs into the surface soil, nutrient retranslocation by some key tree species and some physicochemical properties of the soil in the study site. Litter traps where placed randomly in the study plot. Litter was collected every fortnight sorted and air-dried after which they were oven dried at 70°C to constant weight. Soils were sampled from three flanks at depths of 0-10cm, 10-20cm and 20-30cm. Percentage retranslocation or accumulation before leaf fall was calculated from freshly fallen litter and mature green leaf. Total annual litterfall was 5.46 t/ha/yr and this varied with the seasons. Leaf litter contributed 90.9% of total litterfall. The concentration of N and Ca was higher than other nutrient elements Mg, K, P in all litter fragments. Nitrogen had the highest total nutrient input with the following pattern N&amp;gt;Ca&amp;gt;K&amp;gt;Mg&amp;gt;P (85.36 kg/ha/yr&amp;gt; 56.71 kg/ha/yr&amp;gt; 23.1 kg/ha/yr&amp;gt; 17.32 kg/ha/yr&amp;gt; 4.27 kg/ha/yr) respectively.Pterocarpus soyauxii had the highest retranslocation percentages for all the macronutrients studied compared to Afziliabipidensis and Terminalia ivorensis. It was observed that Terminalia ivorensis could be a good nutrient recycler that could be used to improve on degraded soils. It was however observed that Ca and Mg tend to accumulate in leaf litter for all the three species.

Hypo-virulent Cryphonectria parasitica and distribution/infection factors in southern Appalachia.

Prior to its decline and functional extinction due to an invasive blight fungus (Cryphonectria parasitica) in the early 20th century, the American chestnut was a key dominant tree species in most eastern deciduous forests. The infection mechanism, and associated factors affecting rates of infection, must be understood if a hybrid chestnut species is to be reintroduced within native range tree stands. The focus of our work was on on the blight fungus itself. Our objectives were to: 1) determine the possibility of hypo-virulent (or less infectious) strains of the fungus being present at our research site, 2) identify factors correlated with infection rates at the site, and 3) examine possible connections between infection and chestnut mortality rates and factors like chestnut type, family, and site location. We sampled each of four types of chestnut (Pure American/Chinese and two hybrids [B3F2 and B3F3]) at the St. George research site where we characterized cankers and tree environment in addition to culturing canker samples under lab conditions. We did not find evidence of hypo-virulent strains of the chestnut blight at the research site, which could be attributed to hypo-virulent fungus having relatively low success rates due to inhibited sporulation. There was no significant relationship between chestnut species/lineage and infection/mortality rates. This research could inform the development and success of hybrids used in the reintroduction of American chestnut in the future.

Total and Active Core Microbiomes of Melojo Oak Are Composed by a Minority of Bacterial Taxa Highly Abundant

Melojo oak (Quercus pyrenaica Willd.) is a key tree species of Mediterranean forests with high landscape value in the Iberian Peninsula. However, these forests exhibit an advanced stage of deterioration and their distribution area has been seriously reduced over the last decades. Plant-associated microorganisms play an essential role improving their host’s fitness, hence, a better understanding of oak rhizospheric microbiome, especially of those active members, could be the first step towards microbiome-based approaches for the improvement of the survival and growth of oak trees. Here we reported, for the first time, the diversity of total (DNA-based) and potentially active (RNA-based) bacterial communities of three types of Quercus pyrenaica Willd. forest formations through 454 pyrosequencing of 16S rDNA amplicons, and defined the rhizospheric core microbiome of Q. pyrenaica at Sierra Nevada National and Natural Park during spring season. In addition rRNA:rDNA ratio was calculated as a proxy of the contribution of each core taxon to the rhizosphere environment. We found that potentially active bacterial communities were as rich and diverse as DNA-based populations, but different in terms of relative abundance patterns in some of the studied areas. Both microbiomes were dominated by a relatively small percentage of OTUs, most of which showed positive correlation between both libraries. However, the uncoupling between abundance (rDNA) and potential activity (rRNA) for some taxa suggests that the most abundant taxa are not always the most active, and that low-abundance OTUs may have a strong influence on oak’s rhizospheric ecology. Thus, measurement of rRNA:rDNA ratio could be helpful in characterizing rhizospheric bacterial communities, their potential involvement in the functioning of the soil ecosystem and, therefore, in identifying major bacterial players for the development of microbiome-based strategies for future afforestation tasks.

Rapid 21st century climate change projected to shift composition and growth of Canada’s Acadian Forest Region

Abstract The impact of climate change on forests is expected to vary globally and regionally. Canada’s Acadian Forest Region lies in the transition between the North American boreal and temperate forest biomes and may be particularly sensitive to changes in climate because many of its component species are currently at their southern or northern climatic range limits. Although some species may be lost, others may exhibit major productivity boosts—affecting the goods and services we derive from them. In this study, we use a well-established forest ecosystem simulation model, PICUS, to provide the first exploration of the impact of climate change on the composition and growth of the Acadian Forest Region for the period 2011 to 2100 under two radiative forcing scenarios, RCP 2.6 and RCP 8.5. In the short term (2011–2040), little to no changes in forest composition or growth were projected under either forcing scenario compared with current forest conditions (simulated for 1981–2010 baseline climate); however, by mid-century, PICUS projected increasing departures from the baseline simulations in both composition and growth, with the greatest changes occurring under RCP 8.5 during the late 21st century (2071–2100). Our study indicates that under rapid 21st century warming, Canada’s Acadian Forest Region will begin to lose its boreal character (i.e., “deborealize”) as key tree species fail to regenerate and survive. Furthermore, increased growth and establishment by warm-adapted, temperate tree species may be unable to keep pace with the rapid loss of boreal species. This potential “lag effect” may lead to a temporary decrease in forest growth and wood supply during the late 21st century.

Use of space in two neighboring groups of the howler monkey Alouatta palliata mexicana (Primates: Atelidae): overlap and home range size

The interaction between primate groups and the dynamics involved in the use of space are important factors affecting both competition for resources and intergroup dominance. In the present study we analyzed the differences in home range overlap and intergroup size, as well as the diversity of tree species within the home range, the Value Index for the key tree species, and the daily activity pattern of two neighboring groups of the howler monkey Alouatta palliata. From March 2002 to June 2003, the behavior and location of two groups of monkeys (G1, two adult males, four adult females and four infants; G2, six adult males, five adult females, one juvenile and three infants) were recorded in the same forest patch at Los Tuxtlas Biosphere Reserve, Veracruz, Mexico. Using the Minimum Convex Polygon (100 %), grid (100 m), and Kernel (adapted and fixed) methods, as well as transect sampling, significant differences (F1, 20 = 14.45, P = 0.001) were found in the home range size of the groups, being greater in G2. The habitat in the G2 home range had greater richness and diversity of tree species, as well as a higher Importance Value Index for the key tree species (Ficus spp.) included in the howler monkey diet. On the other hand, significant differences between groups (Mann-Whitney U = 38, P < 0.05) were found only as regards locomotion behavior, likely due to a behavioral adaptation to optimize food resource use or search. The two groups displayed a similar use of food resources; however, there was a slight overlap in the home range between both groups with no direct aggression, likely because their habitat included sufficient space and food. Our data suggest that the reduced overlap may vary between neighboring groups because of factors such as group size. However, groups could weigh various factors to avoid home-range overlap.

The shifting phenological landscape: Within- and between-species variation in leaf emergence in a mixed-deciduous woodland.

Many organisms rely on synchronizing the timing of their life‐history events with those of other trophic levels—known as phenological matching—for survival or successful reproduction. In temperate deciduous forests, the extent of matching with the budburst date of key tree species is of particular relevance for many herbivorous insects and, in turn, insectivorous birds. In order to understand the ecological and evolutionary forces operating in these systems, we require knowledge of the factors influencing leaf emergence of tree communities. However, little is known about how phenology at the level of individual trees varies across landscapes, or how consistent this spatial variation is between different tree species. Here, we use field observations, collected over 2 years, to characterize within‐ and between‐species differences in spring phenology for 825 trees of six species (Quercus robur, Fraxinus excelsior, Fagus sylvatica, Betula pendula, Corylus avellana, and Acer pseudoplatanus) in a 385‐ha woodland. We explore environmental predictors of individual variation in budburst date and bud development rate and establish how these phenological traits vary over space. Trees of all species showed markedly consistent individual differences in their budburst timing. Bud development rate also varied considerably between individuals and was repeatable in oak, beech, and sycamore. We identified multiple predictors of budburst date including altitude, local temperature, and soil type, but none were universal across species. Furthermore, we found no evidence for interspecific covariance of phenology over space within the woodland. These analyses suggest that phenological landscapes are highly complex, varying over small spatial scales both within and between species. Such spatial variation in vegetation phenology is likely to influence patterns of selection on phenology within populations of consumers. Knowledge of the factors shaping the phenological environments experienced by animals is therefore likely to be key in understanding how these evolutionary processes operate.

The frankincense tree Boswellia neglecta reveals high potential for restoration of woodlands in the Horn of Africa

Boswellia neglecta S. Moore is a frankincense-producing tree species dominantly found in the dry woodlands of southeastern Ethiopia. Currently, the population of this socio-economically and ecologically important species is threatened by complex anthropogenic and climate change related factors. Evaluation of tree age and its radial growth dynamics in relation to climate variables helps to understand the response of the species to climate change. It is also crucial for sustainable forest resource management and utilization. Dendrochronological and remote-sensing techniques were used to study periodicity of wood formation and leaf phenology and to assess the growth dynamics of B. neglecta. The results show that B. neglecta forms two growth rings per year in the study area. The growth ring structure is characterized by larger vessels at the beginning of each growing season and smaller vessels formed later in the growing season, suggesting adaptation to decreasing soil moisture deficits at the end of the growing season. Seasonality in cambial activity matches with a bimodal leaf phenological pattern. The mean annual radial growth rate of B. neglecta trees is 2.5mm. Tree age varied between 16 and 28years, with an average age of 22years. The young age of these trees indicates recent colonization of B. neglecta in the study region. The growth rate and seasonal canopy greenness (expressed by Normalized Difference Vegetation Index – NDVI) were positively correlated with rainfall, suggesting that rainfall is the main climatic factor controlling growth of B. neglecta. The observed temporal changes in leaf phenology and vessel size across the growth rings indicate that the species is drought tolerant. Therefore, it can be regarded as a key tree species for restoration of moisture-related limited areas across the Horn of Africa.

Exploring nest webs in more detail to improve forest management

The interactions between birds that use tree cavities for breeding, roosting and sheltering have been named ‘nest webs’. We applied for the first time in nest-web studies some tools developed in network theory, in order to develop conservation and management recommendations of forest biodiversity. We recorded 109 interactions between 15 bird and 11 cavity-bearing tree species, in a subtropical piedmont forest (PF) of northwestern Argentina. Bird species in this nest-web included four woodpecker species, whose cavities were scarcely (9%) used by non-excavator birds, such as parrots, owls, and woodcreepers. Based on the Importance and Strength indices the most important tree species were Calycophyllum multiflorum (Rubiaceae) and Anadenanthera colubrina (Fabaceae). The nest web contained three main interaction modules: one composed by woodpeckers interacting with both living and standing dead trees; another by non-excavator birds using decay-formed cavities in living trees; and a third small module that had a few birds using woodpecker-excavated cavities in living trees. Important tree species were different for woodpecker and non-excavator modules. Extinction simulation of the most important tree species tripled the negative impact on cavity-using bird assemblage compared with the random extinction of tree species. In logging operations special consideration should be taken to ensure the maintenance of key tree species for the conservation of all the nest-web components in PF.

First record of baobab (Adansonia digitata L.) in Uganda

The baobab (Adansonia digitata L.) is a remarkable key tree species with different uses in many African countries. International interest in the species has intensified in recent years. Despite the wide distribution of the baobab in many African regions, the tree has been reported to be absent in Uganda. In 2015 and 2016, research trips in the Central, Western, Eastern and Northern Regions of Uganda were conducted to screen the cultivated and natural flora for baobabs. As a result, four vigorous baobab trees aged 9 and 22 years were identified in two gardens in the Iganga and Soroti Districts in the Eastern Region of Uganda. The origins of the planting materials were Nyala in Sudan and Mombasa in Kenya. To our knowledge, these are the first scientific records of baobab in Uganda and some research questions and key propositions are formulated based on this discovery.

Genetic analysis across life stages of Metrodorea nigra (Rutaceae) in a population located in an urban landscape of Southeastern Brazil using a new set of microsatellite markers

Metrodorea nigra A. St.-Hil. (Rutaceae) is a submontane tropical tree species that develops preferably in the shade and innermost preserved regions of the semi-deciduous forests of Brazil; as a result, its presence can indicate good levels of conservation. Therefore, it is important to have a set of molecular markers to facilitate genetic studies on this species of tree. The goal of this study was to perform genetic analyses of three generations of one population of M. nigra located in an urban landscape (Ribeirao Preto, Sao Paulo state) using a new set of microsatellite molecular markers (i.e., SSR—simple sequence repeat). A genomic library was developed from M. nigra, and 11 putative molecular markers were isolated and characterized using samples from different life stages. Seven SSR markers amplified and showed polymorphism across 61 M. nigra samples. A total of 83 alleles were detected, with an average of 11.85 alleles per locus. The genetic diversity index (He) across M. nigra generations was high and ranged from a mean of 0.804 (saplings) to 0.827 (adults). These results show the resilience of M. nigra population located in Bosque Municipal de Ribeirao Preto-SP, Brazil, to adverse effects of fragmentation, and can serve as a base for conservation programs. Furthermore, more than 50 % of the primers were also amplified for the congeneric tree species Metrodorea stipularis. Overall, the new marker set developed here will be useful for studies of population genetics of M. nigra and other key tree species from the Atlantic Rainforest of Brazil.