Evergreen Woody Species Research Articles

A global analysis of elevational gradients in leaf herbivory and its underlying drivers: Effects of plant growth form, leaf habit and climatic correlates

Abstract Research on elevational gradients in species interactions holds that herbivore pressure increases towards warmer and more stable climates found at lower elevations. However, the generality of this expectation has been challenged by recent studies reporting no evidence of expected trends or even positive associations between elevation and herbivory, presumably due to uncontrolled biotic and abiotic factors influencing such relationships. Using a world‐wide dataset of insect leaf herbivory including 1,027 plant species and spanning an elevation gradient of 2,755 m, we tested if elevational gradients in herbivory were contingent on whether species were found at tropical vs. temperate latitudes, plant growth form (non‐woody vs. woody species), and leaf habit (deciduous vs. evergreen woody species). In addition, we tested the influence of climatic correlates of elevation presumably underlying such elevational gradients. Although there was no evidence of an overall relationship between elevation and damage, we found that elevational gradients in herbivory were contingent on species growth form whereby herbivory increased towards lower elevations for woody species, but no gradient was observed for non‐woody species. We further found that elevational gradients in herbivory were contingent on leaf habit as herbivory increased towards lower elevations for deciduous species, but no gradient was present for evergreen species. Elevational variation in damage was not contingent upon latitudinal region. Finally, analyses of climatic factors indicated that although a significant association between temperature and herbivory for woody species was detected, the elevational gradient in leaf herbivory remained largely unchanged after accounting for temperature and precipitation, suggesting that climate does not fully account for the gradient. Synthesis. This study delivers the first global assessment of elevational gradients in leaf herbivory and emphasizes the role of plant (e.g. life‐history or defensive) traits and climatic factors in shaping elevational gradients in herbivory.

Differences in ozone sensitivity among woody species are related to leaf morphology and antioxidant levels.

Ozone (O3) sensitivity varies greatly among plant species. Leaf traits such as stomatal conductance, antioxidant capacity and leaf morphology and anatomy may play important roles in controlling this variation, but the relative contributions of each trait remain elusive. In this study, we examined the differences in O3 sensitivity among 29 deciduous and evergreen woody species used for urban greening in China in an open-top chamber experiment. Elevated O3 caused visible injury and reductions in net photosynthesis, and these effects differed significantly among species. The deciduous species Sorbaria sorbifolia, Hibiscus syriacus and Fraxinus chinensis were the most sensitive, while evergreen species ranked among the most tolerant. O3 sensitivity was linked to both low leaf mass per area (LMA) and low leaf area-based antioxidant levels, but not to variation in leaf mass-based antioxidant levels or stomatal conductance. The well-known and easily measured leaf trait LMA thus represents a potentially useful metric for O3 risk assessment and for selecting appropriate species for urban greening in O3-polluted areas.

Leaf age dependent changes in within-canopy variation in leaf functional traits: a meta-analysis.

Within-canopy variation in leaf structural and photosynthetic characteristics is a major means by which whole canopy photosynthesis is maximized at given total canopy nitrogen. As key acclimatory modifications, leaf nitrogen content (N A) and photosynthetic capacity (A A) per unit area increase with increasing light availability in the canopy and these increases are associated with increases in leaf dry mass per unit area (M A) and/or nitrogen content per dry mass and/or allocation. However, leaf functional characteristics change with increasing leaf age during leaf development and aging, but the importance of these alterations for within-canopy trait gradients is unknown. I conducted a meta-analysis based on 71 canopies that were sampled at different time periods or, in evergreens, included measurements for different-aged leaves to understand how within-canopy variations in leaf traits (trait plasticity) depend on leaf age. The analysis demonstrated that in evergreen woody species, M A and N A plasticity decreased with increasing leaf age, but the change in A A plasticity was less suggesting a certain re-acclimation of A A to altered light. In deciduous woody species, M A and N A gradients in flush-type species increased during leaf development and were almost invariable through the rest of the season, while in continuously leaf-forming species, the trait gradients increased constantly with increasing leaf age. In forbs, N A plasticity increased, while in grasses, N A plasticity decreased with increasing leaf age, reflecting life form differences in age-dependent changes in light availability and in nitrogen resorption for growth of generative organs. Although more work is needed to improve the coverage of age-dependent plasticity changes in some plant life forms, I argue that the age-dependent variation in trait plasticity uncovered in this study is large enough to warrant incorporation in simulations of canopy photosynthesis through the growing period.

Phenological variation of leaf functional traits within species.

A basic assumption of the trait-based approach in plant ecology is that differences in functional trait values are greater between species than within species. We questioned this assumption by assessing (1) the relative extent of inter- and intraspecific leaf trait variation throughout a complete growing season (phenological variation) in a group of deciduous and evergreen woody species, and (2) whether species rankings based on leaf traits were maintained across the growing season. We analysed leaf mass per area (LMA) and leaf nutrient concentrations (C, N, P), including the C:N and N:P ratios. Intraspecific trait variation (ITV) due to phenology was significantly greater than interspecific variation for leaf N concentration on a mass basis (Nm; 68.90 %) and for the leaf C:N ratio (60.60 %), whereas interspecific variation was significantly higher than ITV for LMA (62.30 %) and for leaf C concentration on a mass (Cm) and area (Ca) basis (Cm 70.40 %; Ca 65.30 %). ITV was particularly low for LMA (<20 %). Species rankings were highly modified by phenology for a number of leaf traits (Pm, N:P ratio) but were relatively well conserved throughout the growing season for others (LMA, Nm). Patterns of ITV across the growing season differed significantly between deciduous and evergreen species for all traits except leaf P but did not vary between native and exotic species. Overall, our results show that intraspecific phenological variation in leaf traits may be similar to or greater than interspecific variation and that temporal patterns of ITV vary considerably among traits and species, especially for leaf nutrient concentrations, factors which can potentially affect quantitative interspecific relationships.

Strategies in nitrogen uptake and use by deciduous and evergreen woody species in a seasonally dry sandhill community

Dry seasonal ecosystems such as the Florida sandhill are defined by a pronounced and consistent dry season that results in both water and nutrient limitation. Deciduous and evergreen species have evolved different leaf phenologies, which change the temporal pattern of nutrient demands for leaf growth. To measure N uptake for deciduous and evergreen species during late dry season deciduous leaf-out, we labeled the shallow soil with 15N by spreading a mixture of native sand and 15N-KNO3 around each tree and measured foliar nitrogen isotopic composition. We also measured foliar N content and nitrogen resorption efficiency (NRE). Evergreen and deciduous species were not consistently different in foliar N content and NRE, but natural foliar δ15N values were consistently higher in deciduous species. Labeling experiments show that uptake rate of 15N- labeled NO3 − was lowest for the deciduous species. Inconsistent results in foliar N content and NRE do not explain the differences in leaf habit in nutrient-poor ecosystems. Low N uptake during leaf-out limits deciduous species to the most fertile regions of the Florida scrub as well as in several other ecosystems, so that they can take up sufficient N to meet the demands of leaf growth.

Hnojiva s pozvolným uvolňováním a možnosti jejich využití ve školkařství

Reserve, slow-release fertilizers (SRF) enable to simplify the whole system of plant nutrition and fertilisation. Tabletted fertilizers of the Silvamix series represent a prospective product of Czech provenience. At our university, these fertilizers have been tested and used since the year 1991. Ornamental woody species grown in containers were investigated in two stages. Experiments with ornamental plants were established using one-year-old cuttings and seedlings of the following deciduous and evergreen woody species:Cotoneaster dammeri Skogholm,Berberis thunbergii,Potentilla fruticosa Snowflake,Ligustrum vulgare AtrovirensandPicea omorika. After planting into containers, fertilizers in the dose of 1 tablet (i.e. 10 g) per litre of substrate were applied either to roots level or on the soil surface in the container. Silvamix in the dose of 5 g.l-1was used as the tested fertilizer in the second stage. It was applied during the planting in the form of tablets and/or a powder. Control plants were fertilized in the course of growing season using a common agricultural fertilizer Cererit Z. The annual plants increments were measured. These experiments demonstrated a long-term optimum effect of this product on woody species and an equal quality and efficiency of its tabletted and powdered forms.

Growth synchrony between leaves and stems during twig development differs among plant functional types of subtropical rainforest woody species.

During the development of woody twigs, the growth in leaf may or may not be proportional to the growth in stem. The presence or absence of a synchronicity between these two phenologies may reflect differences in life history adaptive strategies concerning carbon gain. We hypothesized that sun-adapted species are more likely to be less synchronous between growths in total leaf area (TLA) and stem length compared with shade-adapted species, with a bias in growth in stem length, and that shade-adapted species are more likely to be more synchronous between increases in individual leaf area (ILA) (leaf size) and leaf number (LN) during twig development compared with sun-adapted species, giving priority to growth of leaf size. We tested these two hypotheses by recording the phenologies of leaf emergence, leaf expansion and stem elongation during twig development for 19 evergreen woody species (including five shade-adapted understory species, six sun-adapted understory species and eight sun-adapted canopy species) in a subtropical evergreen broad-leaved forest in eastern China. We constructed indices to characterize the synchronicity between TLA and stem length (αLS) and between leaf size and leaf number (αSN) and we derived the α values from logistic functions taking the general form of A = A(max)/[1 + exp(β - αB)] (where A is the TLA or average ILA, B is the corresponding stem length or LN at a specific time, and A(max) is the maximum TLA or the maximum ILA of a twig; the higher the numerical value of α, the less synchronous the corresponding phenologies). Consistent with our hypotheses, sun-adapted species were higher both in α(LS) and α(SN), showing less synchronous patterns in the growths of TLA vs stem length and leaf size vs LN during twig development. Moreover, α(LS) and α(SN) were significantly positively correlated with relative growth rates of LN and leaf size across species, as indicated by both analyses of ordinary regression and phylogenetic generalized least squares. The across-species synchronies during twig development show that the temporal dynamics of the leaf size-twig size spectrum is of adaptive significance in plants. We suggest that temporal dynamics of plant functional traits should be extensively studied to characterize plant life history.

A DECIDUIDADE FOLIAR INDICA A VULNERABILIDADE DE ESPÉCIES LENHOSAS AO FOGO

Pesquisas indicaram que a ocorrência de queimadas pode ocasionar comportamentos fenológicos divergentes aos padrões comumente descritos. Este estudo teve como objetivo avaliar se a deciduidade foliar pode indicar a vulnerabilidade de espécies lenhosas ao fogo. Os índices de atividade e intensidade de diferentes fenofases foram comparados entre indivíduos queimados e não queimados de espécies lenhosas com diferentes graus de deciduidade foliar (decídua, semidecídua e sempre-verde). Para a espécie decídua, as fenofases vegetativas foram similares entre indivíduos queimados e não queimados. Indivíduos queimados de uma espécie semidecídua apresentaram maior intensidade e atividade das fenofases vegetativas. Para as espécies sempre-verdes, foi registrado o estímulo à produção de novas folhas, retardamento de folhas expandidas e senescentes para indvíduos queimados. Quanto à fenologia reprodutiva, em indivíduos queimados, foram registradas menor intensidade e atividade de frutos verdes e maduros para espécies decídua e semidecídua, bem como o estímulo da floração e da frutificação para as espécies sempre-verdes. A periodicidade das fenofases pode ser modulada pela ocorrência do fogo mesmo após um intervalo de dois anos. O efeito do fogo foi gradualmente mais pronunciado de espécies decíduas às sempre-verdes, o que indica maior vulnerabilidade de espécies lenhosas sempre-verdes a esse distúrbio.

Faecal nitrogen of browser and mixed feeder game species during different seasons

A practical measure of assessing periods of potential nutritional stress of game species is needed in the management of these species in the Acacia karroo Riparian Thicket of the central Free State. The objectives of the study were to determine Nf concentration of four game species (browsers and mixed feeders) during different seasons, compare Nf with leaf phenology patterns, and assess whether Nf reaches levels at which body condition loss can be expected. A seasonal pattern was observed with the lowest Nf concentrations recorded during late winter, which correlated with the seasonal phenology pattern (leaf carriage) of the winter-deciduous tree species. The Nf concentrations (g N kg−1 dung DM) of giraffe ranged from 18.3 (late winter) to 36.7 (summer) and that of kudu from 13.6 to 33.2. Likewise, the Nf of impala ranged from 16.9 to 28.0 and that of eland from 16.3 to 34.9. Access to evergreen woody species during the late-winter period proved to be essential in avoiding condition loss that corresponds with Nf levels below published critical levels (<16). In the absence of evergreen species, supplementary feeding is essential. Faecal nitrogen proved to be a useful indicator of seasonal trends in the nutritional status of browsing game species.

Foliar photochemical processes and carbon metabolism under favourable and adverse winter conditions in a Mediterranean mixed forest, Catalonia (Spain)

Abstract. Evergreen trees in the Mediterranean region must cope with a wide range of environmental stresses from summer drought to winter cold. The mildness of Mediterranean winters can periodically lead to favourable environmental conditions above the threshold for a positive carbon balance, benefitting evergreen woody species more than deciduous ones. The comparatively lower solar energy input in winter decreases the foliar light saturation point. This leads to a higher susceptibility to photoinhibitory stress especially when chilly (&lt; 12 °C) or freezing temperatures (&lt; 0 °C) coincide with clear skies and relatively high solar irradiances. Nonetheless, the advantage of evergreen species that are able to photosynthesize all year round where a significant fraction can be attributed to winter months, compensates for the lower carbon uptake during spring and summer in comparison to deciduous species. We investigated the ecophysiological behaviour of three co-occurring mature evergreen tree species (Quercus ilex L., Pinus halepensis Mill., and Arbutus unedo L.). Therefore, we collected twigs from the field during a period of mild winter conditions and after a sudden cold period. After both periods, the state of the photosynthetic machinery was tested in the laboratory by estimating the foliar photosynthetic potential with CO2 response curves in parallel with chlorophyll fluorescence measurements. The studied evergreen tree species benefited strongly from mild winter conditions by exhibiting extraordinarily high photosynthetic potentials. A sudden period of frost, however, negatively affected the photosynthetic apparatus, leading to significant decreases in key physiological parameters such as the maximum carboxylation velocity (Vc, max), the maximum photosynthetic electron transport rate (Jmax), and the optimal fluorometric quantum yield of photosystem II (Fv/Fm). The responses of Vc, max and Jmax were highly species specific, with Q. ilex exhibiting the highest and P. halepensis the lowest reductions. In contrast, the optimal fluorometric quantum yield of photosystem II (Fv/Fm) was significantly lower in A. unedo after the cold period. The leaf position played an important role in Q. ilex showing a stronger winter effect on sunlit leaves in comparison to shaded leaves. Our results generally agreed with the previous classifications of photoinhibition-tolerant (P. halepensis) and photoinhibition-avoiding (Q. ilex) species on the basis of their susceptibility to dynamic photoinhibition, whereas A. unedo was the least tolerant to photoinhibition, which was chronic in this species. Q. ilex and P. halepensis seem to follow contrasting photoprotective strategies. However, they seemed equally successful under the prevailing conditions exhibiting an adaptive advantage over A. unedo. These results show that our understanding of the dynamics of interspecific competition in Mediterranean ecosystems requires consideration of the physiological behaviour during winter which may have important implications for long-term carbon budgets and growth trends.

Coordination of leaf N, anatomy, photosynthetic capacity, and hydraulics enhances evergreen expansive potential

Key message Reduced leaf longevity, N-fixation, and enhanced hydraulic capacity combined support greater shifts in seasonal photosynthetic capacity of an expansive understory evergreen woody species relative to co-occurring less expansive evergreen species.

Seasonal water use by deciduous and evergreen woody species in a scrub community is based on water availability and root distribution

AbstractIn a seasonally dry plant community of central Florida, USA, that experiences water limitation in the dry season and high water availability in the wet season, we first tested whether evergreen woody species shift from shallow water in the wet season to deep water in the dry season. Second, we tested whether deciduous woody species restrict water uptake to the shallow soil during the wet season and cease water uptake during the dry season. To address these questions, we measured water source use of two deciduous and three evergreen species over 13 months using stable isotopes. As hypothesized in previous studies, we showed that leaflessness in deciduous plants is an important source of stem water isotopic fractionation. Therefore, we compared stable isotope ratios of stem water only when deciduous species had leaves and found that all species, except the evergreen Lyonia ferruginea, used proportionally the same water sources. Early dry season water use was based on water availability for all species except L. ferruginea, and deep soil (50–150 cm) was the most important water source. During the late dry and wet seasons, water uptake from each soil layer was based on its respective proportion of fine roots. Nevertheless, deep water remained an important water source throughout the year. This study clearly demonstrates the limitations of using stable isotopes of stem water when comparing deciduous versus evergreen species. Further, this study is the first to directly quantify depth of water uptake via isotope analysis and couple these findings with root distribution. Copyright © 2014 John Wiley &amp; Sons, Ltd.

First and second sets of shoots in five evergreen woody species from Tiantong National Forest Park of Zhejiang, China

Aims Some woody species of subtropical evergreen broad-leaved forests in Eastern China form a second set of shoots in late summer or autumn after a first set in spring. Our objective is to elucidate features of this second set of shoots, including their adaptive significance. Methods We investigated differences between the first and second sets of shoots for five evergreen woody species (Symplocos lancifolia, Loropetalum chinense, Eurya rubiginosa var. attenuata, Myrica rubra, and Castanopsis fargesii) from an evergreen broad-leaved forest in Tiantong National Forest Park of Zhejiang, China. Herbivore damage of leaves was estimated, leaf emergence rate, leaf expansion rate and duration were calculated, and twig investment (leaf number and individual leaf area within twigs, twig stem length and diameter) was measured for both sets of shoots. Important findings Leaves of M. rubra and C. fargesii suffered greater herbivore damage to the second shoots compared with the first, and no significant difference was found in damage between the two sets of shoots for S. lancifolia, L. chinense and E. rubiginosa var. attenuata. The first and second sets of shoots shared the same leaf emergence pattern. Symplocos lancifolia, L. chinense, E. rubiginosa var. attenuata, and M. rubra showed a succeeding type of leaf emergence, and C. fargesii showed a flushing type of leaf emergence. However, duration of leaf emergence was much shorter in the second set of shoots for S. lancifolia, E. rubiginosa var. attenuata and M. rubra than in the first but not for the other two species. Leaf expansion rate was significantly higher for the second set of shoots for S. lancifolia, L. chinense and E. rubiginosa var. attenuata and was indistinguishable for M. rubra, C. fargesii leafed out late in the first set of shoots. Moreover, leaf number (except for L. chinense), individual leaf area, twig stem length (except for L. chinense) and diameter were significantly smaller in the second than in the first set of shoots for four species, indicating lower twig investment in the second shoots for all the sampled species. In general, leaf herbivory damage, rates of leaf emergence and expansion were not smaller (sometimes significantly greater), but the total investment on twigs was significantly lower in the second shoots compared to the first. We speculate that these differences might result from the selective force of heavy herbivory pressure and adverse climate conditions of coming winter for the leaves produced during the second set of shoots.

Elevated ozone negatively affects photosynthesis of current-year leaves but not previous-year leaves in evergreen Cyclobalanopsis glauca seedlings

To assess the effects of leaf age/layer on the response of photosynthesis to chronic ozone (O3), Cyclobalanopsis glauca seedlings, a dominant evergreen broadleaf tree species in sub-tropical regions, were exposed to either ambient air (AA) or elevated O3 (AA + 60 ppb O3, E-O3) for two growing seasons in open-top chambers. Chlorophyll content, gas exchange and chlorophyll a fluorescence were investigated three times throughout the 2nd year of O3 exposure. Results indicated that E-O3 decreased photosynthetic parameters, particularly light-saturated photosynthesis rate, stomatal conductance and effective quantum yield of PSII photochemistry of current-year leaves but not previous-year leaves. Stomatal conductance of plants grown under ambient conditions partially contributed to the different response to E-O3 between leaf layers. Light radiation or other physiological and biochemical processes closely related to photosynthesis might play important roles. All suggested that leaf ages or layers should be considered when assessing O3 risk on evergreen woody species.

The importance of leaf cuticle for carbon economy and mechanical strength

Cuticle thickness of leaves varies >100 times across species, yet its dry mass cost and ecological benefits are poorly understood. It has been repeatedly demonstrated that thicker cuticle is not superior as a water barrier, implying that other functions must be important. Here, we measured the mechanical properties, dry mass and density of isolated cuticle from 13 evergreen woody species of Australian forests. Summed adaxial and abaxial cuticle membrane mass per unit leaf area (CMA) varied from 2.95 to 27.4g m(-2) across species, and accounted for 6.7-24% of lamina dry mass. Density of cuticle varied only from 1.04 to 1.24gcm(-3) ; thus variation in CMA was mostly due to variation in cuticle thickness. Thicker cuticle was more resistant to tearing. Tensile strength and modulus of elasticity of cuticle were much higher than those of leaf laminas, with significant differences between adaxial and abaxial cuticles. While cuticle membranes were thin, they could account for a significant fraction of leaf dry mass due to their high density. The substantial cost of thicker cuticle is probably offset by increased mechanical resistance which might confer longer leaf lifespans among evergreen species.

Regeneration of Different Plant Functional Types in a Masson Pine Forest Following Pine Wilt Disease

Pine wilt disease is a severe threat to the native pine forests in East Asia. Understanding the natural regeneration of the forests disturbed by pine wilt disease is thus critical for the conservation of biodiversity in this realm. We studied the dynamics of composition and structure within different plant functional types (PFTs) in Masson pine forests affected by pine wilt disease (PWD). Based on plant traits, all species were assigned to four PFTs: evergreen woody species (PFT1), deciduous woody species (PFT2), herbs (PFT3), and ferns (PFT4). We analyzed the changes in these PFTs during the initial disturbance period and during post-disturbance regeneration. The species richness, abundance and basal area, as well as life-stage structure of the PFTs changed differently after pine wilt disease. The direction of plant community regeneration depended on the differential response of the PFTs. PFT1, which has a higher tolerance to disturbances, became dominant during the post-disturbance regeneration, and a young evergreen-broad-leaved forest developed quickly after PWD. Results also indicated that the impacts of PWD were dampened by the feedbacks between PFTs and the microclimate, in which PFT4 played an important ecological role. In conclusion, we propose management at the functional type level instead of at the population level as a promising approach in ecological restoration and biodiversity conservation.

Functional relationships of leafing intensity to plant height, growth form and leaf habit

Leafing intensity, i.e. the number of leaves per unit of stem volume or mass, is a common developmental correlate of leaf size. However, the ecological significance and the functional implications of variation in leafing intensity, other than its relation to leaf size, are unknown. Here, we explore its relationships with plant height, growth form, leaf size, and leaf habit to test a series of corollaries derived from the leafing intensity premium hypothesis. Volume-based leafing intensities and plant heights were recorded for 109 woody species from the subtropical evergreen broadleaf forests of eastern China. In addition, we compiled leafing intensity data from published literature, and combined it with our data to form a 398 species dataset, to test for differences of leafing intensity between plant growth forms (i.e. herbaceous and woody) and leaf habits (i.e. deciduous and evergreens). Leafing intensity was negatively correlated with plant height and individual leaf mass. Volume-based leafing intensities were significantly higher in herbaceous species than in woody species, and also higher in deciduous than in evergreen woody species. In conclusion, leafing intensity relates strongly to plant height, growth form, leaf size, and leaf habit in directions generally in accordance to the leafing intensity premium hypothesis. These results can be interpreted in terms of the evolution of adaptive strategies involving response to herbivory, competitive ability for light and reproductive economy.

Manipulation of VOC emissions with methyl jasmonate and carrageenan in the evergreen conifer Pinus sylvestris and evergreen broadleaf Quercus ilex

Plant defence can be induced by exposing plants to the plant hormone jasmonic acid (JA) or its volatile ester, methyl jasmonate (MeJA). Carrageenans (Carr) - sulphated D-galactans extracted from red algae - can also induce plant defences. In this study, the effects of exogenous MeJA and Carr application (concentration 300 and 12.7 μmol, respectively) on volatile emissions from two widespread evergreen woody species, Pinus sylvestris (nine Turkish and one Finnish provenance) and Quercus ilex (Italian provenance) were investigated. We collected headspace samples from seedlings and analysed the quality and quantity of volatile compounds emitted by treated and control plants. In total, 19 monoterpenes, 10 sesquiterpenes, 10 green leaf volatiles (GLVs) and two aromatic compounds were emitted by P. sylvestris from all the provenances studied. Foliar MeJA application clearly affected the volatile profiles of trees from all the provenances. Effects of Carr were genotype specific. In Q. ilex, emissions of sesquiterpenes, GLVs and the homoterpene (E)-DMNT were all induced by MeJA application. However, emissions of most constitutively emitted monoterpenes were significantly reduced. Carr application also led to a significant reduction in monoterpene emissions, but without corresponding increases in other emissions. Our results indicate that exogenously applied MeJA and Carr can both significantly modify the volatile profiles of P. sylvestris and Q. ilex, but also that there are important provenance- and species-specific differences in the overall degree of elicitation and compositions of elicited compounds.

The effect of land use on the recruitment and population structure of the important food and fodder plant, Dobera glabra (Forssk.) Poir., in northern Afar, Ethiopia

Dobera glabra (Forssk.) Poir. is a drought-tolerant evergreen woody species that is important for food security of pastoral Afar people in north-eastern Ethiopia. We examined population structure and abundance of D. glabra in the Afar rangelands, which have been subjected to considerable land-use changes. Factors determining the abundance of seedlings, shrubs and trees were analyzed using generalized linear models with land-use type, landform, aspect, elevation and soils as explanatory variables. The relative abundances of seedlings, shrubs and trees were 11%, 71% and 18%, respectively, which indicates poor recruitment. Land-use changes are a major reason for the low recruitment of seedlings, due to the clearance of land for cultivation, or increases in browsing pressure caused by pastoral sedentarization. Although the overall abundance of D. glabra was low, the ‘little disturbed’ areas had a relatively high abundance of shrubs compared to ‘moderately disturbed’, ‘disturbed’, and ‘highly disturbed’ areas. Some soil parameters were related to abundance, but there was no clear evidence that environmental variables contributed to the decline of D. glabra. In order to preserve this important species, we propose management strategies that focus on protection of certain areas in combination with planting in the home gardens of settled Afar pastoralists.

Within-species correlations in leaf traits of three boreal plant species along a latitudinal gradient

Evergreen boreal plant species express high variability in their leaf traits. It remains controversial whether this within-species variability is constrained to the same leaf trait relationships as has been observed across species. We sampled leaves of three boreal evergreen woody species along a latitudinal gradient (from 57o56′N to 69o55′N). Leaf longevity (LL) of Pinus sylvestris L. and Vaccinium vitis-idaea L. correlated negatively with mean annual air temperature (MAT), whereas the LL of Ledum palustre L. was not affected by MAT. V. vitis-idaea and L. palustre had a negative relationship between leaf mass per area (LMA) and MAT. In P. sylvestris, the LMA–MAT relationship was positive. A negative correlation between LL and LMA was significant only for P. sylvestris. Leaf nitrogen concentration was positively related to leaf phosphorus concentration in all three species. Leaf potassium concentration was related to nitrogen concentration only in L. palustre, and to phosphorus concentration in P. sylvestris and L. palustre. Our results demonstrate that although within the studied species the variation in some of the leaf traits may have the same degree as interspecific variation, there is no such intercorrelation of leaf traits within the studied species as has been observed across species.