Food resource partition in the beech leaf-feeding guild

Abstract. 1. The position and zonation of mines and galls along beech leaves were recorded and analysed by means of an R X C test of independence using the G-test; in a few cases analysis of variance was applied.
2. Ten arthropod species, of which a few were congeneric, were studied. All species were recorded from all leaf sections; however, in all species except one, significant preferences for certain zones were demonstrated. High frequencies of leaf mines and galls were recorded from the middle and basal leaf sections. Apparently, the leaf apex is an unimportant microhabitat for stationary beech phyllophages, except the eriophyid Aceric stenaspis stenaspis and final leaf mining stages of the beech weevil Rhynchaenus fagi; intra-leaf differences are discussed in relation to leaf grazing by mobile, chewing phyllophagous insects.
3. The position of some abundant phyllophages in space and time is discussed. In old beech stands feeding activity is largely concentrated in the low canopy. Presumably, differences in feeding technique and position of feeding tracks of beech phyllophages on the leaf contribute to food resource partition in this canopy layer. In three congeneric eriophyid species niche diversification occurred. Further, in two cecidomyiid species phenologjcal differentiation may contribute to subdivision of food resources.     

Semiochemical attractants for the beech leaf‐mining weevil,Orchestes fagi

The beech leaf‐mining weevil, Orchestes fagi L. (Curculionidae: Curculioninae: Rhamphini), a pest of European beech, Fagus sylvatica L. (Fagaceae), was recently discovered infesting American beech, Fagus grandifolia Ehrh., in Nova Scotia, Canada. Adult O. fagi feed on both young and mature leaves of beech as well as on other species (e.g., raspberry, Rubus spp.), but oviposition and larval feeding are restricted to beech. Females oviposit in young developing beech leaves at the time of bud burst. We characterized volatiles emitted from buds, leaves, and sapwood of American beech and examined their potential as attractants alone or when combined with other weevil pheromones for O. fagi. We predicted that adults would be attracted to volatiles emitted from beech leaves, especially those emitted from bursting beech buds. Gas chromatography/mass spectrometry (GC/MS) analyses of volatiles collected from buds at pre‐ and post‐budburst identified two diterpene hydrocarbons, 9‐geranyl‐p‐cymene ( 1 ) and 9‐geranyl‐α‐terpinene ( 2a ), that were emitted in large amounts at the time of bud burst. Compound 1 significantly increased mean catch of males and total O. fagi (but not females) on sticky traps compared with unbaited controls. Y‐tube bioassays confirmed attraction of male O. fagi to bursting beech buds and compound 1 . Attraction of male O. fagi to 1 , emitted in large quantities from American beech, is likely adaptive because both oviposition and mating of O. fagi coincide with budburst. Our data suggest that traps baited with 1 may be useful for monitoring the spread of O. fagi in North America.     

Leaf mines: their effect on leaf longevity

Summary The effects of a number of factors, notably leaf mining insects, on the longevity of beech and holm oak leaves have been studied. The regular monitoring of individually labelled leaves was complemented by analysis of leaf fall data. Both methods confirm that these mining insects have only a slight impact on their host trees. The presence of first generation Phyllonorycter maestingella mines on beech leaves and winter generation P. messaniella mines on holm oak leaves accelerates leaf loss. Beech leaves mined by second generation P. maestingella and Rhynchaenus fagi did not show this accelerated loss. Their patterns of leaf fall can be explained by within-tree variation in both mine distribution and the timing of leaf fall. It is argued that this premature leaf fall is a damage response, and is not an attempt by the tree to regulate miner numbers.     

Variability of stomatal conductance, leaf anatomy, and seasonal leaf wettability of young and adult European beech leaves along a vertical canopy gradient

This study assessed the variation of leaf anatomy, chlorophyll content index (CCI), maximal stomatal conductance (g _s ^max ) and leaf wettability within the canopy of an adult European beech tree (Fagus sylvatica L.) and for beech saplings placed along the vertical gradient in the canopy. At the top canopy level (CL_28m) of the adult beech, CCI and leaf anatomy reflected higher light stress, while g _s ^max increased with height, reflecting the importance of gas exchange in the upper canopy layer. Leaf wettability, measured as drop contact angle, decreased from 85.5°?±?1.6° (summer) to 57.5°?±?2.8° (autumn) at CL_28m of the adult tree. At CL_22m, adult beech leaves seemed to be better optimized for photosynthesis than the CL_28m leaves because of a large leaf thickness with less protective and impregnated substances, and a higher CCI. The beech saplings, in contrast, did not adapt their stomatal characteristics and leaf anatomy according to the same strategy as the adult beech leaves. Consequently, care is needed when scaling up experimental results from seedlings to adult trees.     

Systematic within-tree variation in mountain birch leaf quality for a geometrid, Epirrita autumnata

Abstract.

• 1 We studied within-tree variation in leaf quality of the mountain birch, Betula pubescens ssp. tortuosa, for larvae of the autumnal moth, Epirrita autumnata.
• 2 The purpose of the study was to determine the possible occurrence of systematic differences in larval growth on short shoot leaves (i.e. leaves of the same age): among leaves facing in different compass directions, between leaves of lower and upper branches, among leaves on different positions within a branch and among leaves of different sizes within a short shoot. We also measured larval growth between short shoot and long shoot leaves (i.e. between leaves of different age).
• 3 The larvae grew best on leaves on the north side of trees and most poorly on south side leaves, the east and west sides being intermediate. Leaves from the upper branches supported larval growth better than leaves from the lower ones. The larvae grew better on the smallest leaf of each short shoot and were able to utilize it more efficiently than the two larger leaves. Short shoot leaves from the basal and middle parts of the upper branches of the trees were of better quality for the larvae than short shoot leaves from the tip part of the branches. The larval growth rate did not differ between short shoot and long shoot leaves. In general, within-tree variation in the larval growth rate was lower than variation among different trees.
• 4 Damage to leaves can decrease leaf quality for herbivores in the same year (rapidly inducible responses) or the following year(s) (delayed inducible responses). Our results show that systematic within-tree variation in larval growth can be as great as the effects of rapidly inducible responses and that variation among individual trees can be as great as the mean effects of delayed inducible responses.

     

Modelling canopy CO2 fluxes: are ‘big‐leaf’ simplifications justified?

• 1 The ‘big‐leaf’ approach to calculating the carbon balance of plant canopies is evaluated for inclusion in the ETEMA model framework. This approach assumes that canopy carbon fluxes have the same relative responses to the environment as any single leaf, and that the scaling from leaf to canopy is therefore linear.
• 2 A series of model simulations was performed with two models of leaf photosynthesis, three distributions of canopy nitrogen, and two levels of canopy radiation detail. Leaf‐ and canopy‐level responses to light and nitrogen, both as instantaneous rates and daily integrals, are presented.
• 3 Observed leaf nitrogen contents of unshaded leaves are over 40% lower than the big‐leaf approach requires. Scaling from these leaves to the canopy using the big‐leaf approach may underestimate canopy photosynthesis by ~20%. A leaf photosynthesis model that treats within‐leaf light extinction displays characteristics that contradict the big‐leaf theory. Observed distributions of canopy nitrogen are closer to those required to optimize this model than the homogeneous model used in the big‐leaf approach.
• 4 It is theoretically consistent to use the big‐leaf approach with the homogeneous photosynthesis model to estimate canopy carbon fluxes if canopy nitrogen and leaf area are known and if the distribution of nitrogen is assumed optimal. However, real nitrogen profiles are not optimal for this photosynthesis model, and caution is necessary in using the big‐leaf approach to scale satellite estimates of leaf physiology to canopies. Accurate prediction of canopy carbon fluxes requires canopy nitrogen, leaf area, declining nitrogen with canopy depth, the heterogeneous model of leaf photosynthesis and the separation of sunlit and shaded leaves. The exact nitrogen profile is not critical, but realistic distributions can be predicted using a simple model of canopy nitrogen allocation.

     

Effects of drought on mesophyll conductance and photosynthetic limitations at different tree canopy layers

In recent years, many studies have focused on the limiting role of mesophyll conductance (g_m) to photosynthesis (A_n) under water stress, but no studies have examined the effect of drought on g_m through the forest canopy. We investigated limitations to A_n on leaves at different heights in a mixed adult stand of sessile oak (Quercus petraea) and beech (Fagus sylvatica) trees during a moderately dry summer. Moderate drought decreased A_n of top and lowest beech canopy leaves much more than in leaves located in the mid canopy; whereas in oak, A_n of the lower canopy was decreased more than in sunlit leaves. The decrease of A_n was probably not due to leaf‐level biochemistry given that V_Cmax was generally unaffected by drought. The reduction in A_n was instead associated with reduction in stomatal and mesophyll conductances. Drought‐induced increases in stomatal limitations were largest in leaves from the top canopy, whereas drought‐induced increases in mesophyll limitations were largest in leaves from the lowest canopy. Sensitivity analysis highlighted the need to decompose the canopy into different leaf layers and to incorporate the limitation imposed by g_m when assessing the impact of drought on the gas exchange of tree canopies.     

The distribution of a typhlocybine leafhopper, Ribautiana ulmi (Homoptera: Cicadellidae) on a specimen wych elm tree

ABSTRACT.

• 1 Higher numbers of feeding and resting Ribautiana ulmi (L.) were found on the more highly illuminated areas of the canopy of a wych elm tree, Ulmus glabra Huds. cv. Camperdownii.
• 2 Higher numbers were also found on the basal leaves of each branch when compared with the distal leaves, and on exposed areas of individual leaves when compared with the shaded areas which they overlapped.
• 3 Leaf thickness, tannin concentrations and leaf toughness were greater, and water content lower, in leaves from exposed areas of the canopy than from shaded ones.
• 4 R.ulmi feeds selectively on the contents of the palisade mesophyll cells, and therefore was assumed to ingest the highest available levels of tannins.

     

A new life table of leaves ofPhaseolus vulgris L. in relation to their position within the canopy and plant density

In order to demonstrate in detail the relationship between the longevity and productivity of leaves within a canopy, a new life table approach, the ‘bioeconomic life table’, was applied to the leaves of kidney bean plants (Phaseolus vulgaris L.) in relation to planting density and their position within the canopy. The net photosynthetic rate for upper leaves under full daylight tended to decline gradually due to leaf senescence from about 20 days after leaf emergence, and for the lower leaves the decrease was very rapid due to both shading and senescence about 10 days after emergence. Analysis of the survivorship curves and daily surplus production of leaves suggested that the lower and middle leaves, especially the latter, survived without surplus production of dry matter after they had reached mean longevity, and while the upper leaves at high density had a much shorter mean longevity, they had very large values of daily surplus production throughout the survival period. For the total foliage, the summed value of accumulated surplus production during the survival period was about five times as large as the summed value of the dry weight of the dead leaves, regardless of planting density. The daily rate of canopy leaf respiration was almost proportional to that of canopy gross photosynthesis for the various leaf area indices of the canopy, so that there was no optimum leaf area index that maximized canopy daily surplus production.     

Influence of leaf traits on the spatial distribution of arboreal arthropods within an overstorey rainforest tree

Abstract.

• 1 Several attributes of foliage were measured from the Australian rainforest tree Argyrodendron actinophyllum Edlin (Sterculiaceae). These were related to estimates of abundance per leaf area of the most common arthropod guilds and families sampled with restricted canopy fogging.
• 2 When all these arthropod groups were considered, much of the overall variance in arthropod spatial distribution could be attributed to leaf age characteristics, arthropod aggregation patterns, arthropod activity and distance to tree trunk.
• 3 The fraction of variance which could be specifically explained by foliage attributes such as nitrogen-, water- and fibre-content, specific leaf weight, and epiphyll load was small for most arthropod groups (usually <30%). However, an index of food quality explained a higher proportion of variance (50%) in the abundance of phloem-feeders. Leaf size and foliage compactness did not influence significantly the abundance of any arthropod group.
• 4 Most herbivores were more abundant on young foliage than on mature leaves. With the exception of Corylophidae and Chrysomelidae, which were more abundant in the lower and upper canopy respectively, arthropod stratification was not conspicuous within the inner core of tree crowns.
• 5 The results firstly emphasize the distribution of young foliage as a key factor affecting the abundance of many herbivores and, secondly, the importance of the local illumination regime for host leaf production and its indirect effects on the spatial distribution of arboreal arthropods.

     

Evidence for a substantial host‐use bottleneck following the invasion of an exotic,polyphagous weevil

1. The successful establishment of novel plant–insect interactions may depend on the availability of suitable hosts, which itself is influenced by the inherent flexibility of the herbivore for the native plants in its new range. The polyphagous beech leaf mining weevil, Orchestes fagi L., is a recent invader to eastern Canada, and while beech is a primary host, it remains unclear the extent to which it might also utilise co‐occurring secondary hosts, as has been observed in its native European range. 2. A combination of field and laboratory feeding trials were used to quantify weevil secondary host use. Based on its expansive native host range in Europe, it was predicted that American beech (Fagus grandifolia Ehrh.), as well as several additional plant species, would be susceptible to weevil damage. 3. Contrary to this prediction, weevil feeding was almost entirely exclusive to beech in both the field and laboratory feeding trials. This result is further supported by field observations that revealed an absence of weevils and eggs on species other than beech. In general, the lack of pre‐diapause feeding on any alternate host species represented an extreme departure from feeding habits observed within the native range. 4. Overall, this host‐use bottleneck suggests that the adoption of a novel primary host by O. fagi, in this case American beech, may remove the normal requirement for secondary hosts and suggests a significant departure from native feeding habits with possible consequences for related life‐history parameters such as overwintering survival and fecundity.     

TEMPORAL AND SPATIAL PATTERNS OF SPECIFIC LEAF WEIGHT IN SUCCESSIONAL NORTHERN HARDWOOD TREE SPECIES

Temporal and spatial patterns of specific leaf weight (SLW, g/m²) were determined for deciduous hardwood tree species in natural habitats in northern lower Michigan to evaluate the utility of SLW as an index of leaf photosynthetic capacity. No significant diurnal changes in SLW were found. Specific leaf weight decreased and then increased during leaf expansion in the spring. Most species, especially those located in the understory, then had relatively constant SLW for most of the growing season, followed by a decline in SLW during autumn. Specific leaf weight decreased exponentially down through the canopy with increasing cumulative leaf area index. Red oak (Quercus rubra), paper birch (Betula papyrifera), bigtooth aspen (Populus grandidentata), red maple (Acer rubrum), sugar maple (A. saccharum), and beech (Fagus grandifolia) generally had successively lower SLW, for leaves at any one level in the canopy. On a given site, comparisons between years and comparisons of leaves growing within 35 cm of each other showed that differences in SLW among species were not due solely to microenvironmental effects on SLW. Bigtooth aspen, red oak, and red maple on lower-fertility sites had lower SLW than the same species on higher-fertility sites. Maximum CO₂ exchange rate, measured at light-saturation in ambient CO₂ and leaf temperatures of 20 to 25 C, increased with SLW. Photosynthetic capacities of species ranked by SLW in a shaded habitat suggest that red oak, red maple, sugar maple, and beech are successively better adapted to shady conditions.     

Abundance and stratification of foliage arthropods in a lowland rain forest of Cameroon

Abstract.

• 1 Arthropod densities and apparent leaf damage were compared within the canopy ecotone and the shrub layer of a lowland rain forest in Cameroon, using a branch clipping method.
• 2 Most of the individuals collected consisted of ants (average 44%) and various herbivores (31%). Overall arthropod densities amounted to 17 individuals per sample, which, on average, consisted of 0.85 m² of foliage area. Arthropod densities were lower than on temperate foliage.
• 3 Arthropod densities were about 3 times higher in the canopy than within the shrub layer. In particular, ants and herbivores were significantly more abundant in the canopy than within the shrub layer. Usually, layer effects rather than site effects appeared to cause greater variance in arthropod abundance.
• 4 Arthropod species-richness, as estimated by the number of operational taxonomic units sorted, was higher in canopy samples than in samples obtained from the shrub layer. However, apparent leaf damage was higher within the shrub layer (10.9%) than on the canopy (5.2%).
• 5 Possible factors responsible for the high densities of ants and herbivores on the canopy and for the high leaf damage within the shrub layer are discussed.

     

冠层高度对毛竹叶片光合生理特性的影响

借助LI-6400便携式光合作用系统,研究了冠层高度对不同林龄毛竹(Phyllostachys pubescens)叶片光合生理特性和水分利用效率(WUE)的季节性影响,为促进毛竹林碳汇能力和生产力提升的林分结构调整等可持续栽培技术提供理论依据。结果表明:(1)出笋期,不同竹龄毛竹叶片净光合速率(Pn)和蒸腾速率(Tr)的日均值呈现出冠层上部小于冠层下部的梯度变化趋势,且2a生毛竹不同冠层Pn日均值大于3a生毛竹;孕笋行鞭期,不同林龄毛竹各时间点Pn值和日均值、以及2年生毛竹各时间点的Tr值均为冠层上部大于冠层下部。各生长季节,不同林龄毛竹个体叶片的气孔导度(Gs)均与Tr的变化趋势一致。(2)2年生毛竹各季节仅冠层上部叶片会出现"光合午休",而3年生毛竹仅于出笋期时各冠层叶片出现"光合午休"现象。(3)出笋期毛竹叶片WUE日均值随着冠层高度增加而增加,这种变化趋势不受竹龄影响;而孕笋行鞭期,仅2年生毛竹叶片WUE日均值随着冠层高度增加而下降。不同冠层高度的孕笋行鞭期毛竹叶片WUE日均值都显著高于出笋期;冠层高度对毛竹叶片气体交换特性和WUE的影响受生长发育关键期的季节因素影响,且毛竹叶片WUE与Gs之间存在负相关关系,其不受毛竹个体年龄和叶片冠层高度影响。(4)不同生长季节各冠层叶绿素a/b值均随着冠层高度下降而降低,不同林龄毛竹叶片叶绿素含量基本随着冠层自上而下呈逐渐增加的趋势。各生长季节,不同林龄个体叶片氮素含量、比叶重随冠层高度垂直变化趋势与叶片Pn日均值的垂直变化趋势一致。研究认为,毛竹不同冠层部位叶片通过改变形态、氮素含量来适应不同生长季节生长环境的变化,以便充分利用光能提高光合能力。     

Beech forest management does not affect the infestation rate of the beech scale Cryptococcus fagisuga across three regions in Germany

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Do the capacity and kinetics for modification of xanthophyll cycle pool size depend on growth irradiance in temperate trees?

The present study investigated the interaction of growth irradiance (Q_int) with leaf capacity for and kinetics of adjustment of the pool size of xanthophyll cycle carotenoids (sum of violaxanthin, antheraxanthin and zeaxanthin; VAZ) and photosynthetic electron transport rate (J_max) after changes in leaf light environment. Individual leaves of lower‐canopy/lower photosynthetic capacity species Tilia cordata Mill. and upper canopy/higher photosynthetic capacity species Populus tremula L. were either illuminated by additional light of 500–800 µmol m^?2 s^?1 for 12 h photoperiod or enclosed in shade bags. The extra irradiance increased the total amount of light intercepted by two‐fold for the upper and 10–15‐fold for the lower canopy leaves, whereas the shade bags transmitted 45% of incident irradiance. In control leaves, VAZ/area, VAZ/Chl and J_max were positively associated with leaf growth irradiance (Q_int). After 11 d extra illumination, VAZ/Chl increased in all cases due to a strong reduction in foliar chlorophyll, but VAZ/area increased in the upper canopy leaves of both species, and remained constant or decreased in the lower canopy leaves of T. cordata. The slope for VAZ/area changes with cumulative extra irradiance was positively associated with Q_int only in T. cordata, but not in P. tremula. Nevertheless, all leaves of P. tremula increased VAZ/area more than the most responsive leaves of T. cordata. Shading reduced VAZ content only in P. tremula, but not in T. cordata, again demonstrating that P. tremula is a more responsive species. Compatible with the hypothesis of the role of VAZ in photoprotection, the rates of photosynthetic electron transport declined less in P. tremula than in T. cordata after the extra irradiance treatment. However, foliar chlorophyll contents of the exposed leaves declined significantly more in the upper canopy of P. tremula, which is not consistent with the suggestion that the leaves with the highest VAZ content are more resistant to photoinhibition. This study demonstrates that previous leaf light environment may significantly affect the adaptation capacity of foliage to altered light environment, and also that species differences in photosynthetic capacity and acclimation potentials importantly alter this interaction.     

The effect of flutter on the temperature of poplar leaves and its implications for carbon gain

The leaf temperatures of two poplar species (Populus tremuloides Michx. and P. fremontii Wats.) were characterized by attaching thermocouples to leaves that were either constrained to a fixed position or allowed to flutter naturally. There were no observed temperature differences between fluttering and constrained leaves in the lower canopy, but fluttering leaves at the top of the canopy were as much as 2–4°C cooler than constrained leaves. An increase in heat transfer, a decrease in light interception or both could account for these observed differences in the temperature of fluttering versus constrained leaves. Fluttering can increase the boundary-layer conductance to convective heat exchange by as much as 50 and 20% for laminar and turbulent flow, respectively. The benefit that these leaf temperature differences may provide to the carbon economy of a poplar canopy was dependent on the ambient temperature. Populus fremontii, which is frequently exposed to daytime temperatures exceeding 35°C during summer months in the central valley of California, USA, could show an increase in carbon gain as a result of lower upper canopy leaf temperatures. For aspen, the benefit would be much smaller and often negative because of much lower air temperatures. Lower leaf temperatures may also increase the water use efficiency of poplars. However, the maintenance of lower leaf temperatures may not be the primary adaptive significance of leaf flutter.     

Differential leaf traits of a neotropical tree Cariniana legalis (Mart.) Kuntze (Lecythidaceae): comparing saplings and emergent trees

Cariniana legalis is an emergent tree that reaches the upper canopy in Brazilian Semideciduous Forest. Spatial contrasts in microclimatic conditions between the upper canopy and understorey in a forest may affect morpho-physiological leaf traits. In order to test the hypothesis that the upper canopy is more stressful to leaves than a gap environment we compared emergent trees of C. legalis, 28–29 m in height to gap saplings, 6–9 m in height, for the following parameters: leaf area, leaf mass area (LMA the dry weight:leaf area ratio), leaf thickness, leaf anatomical parameters, stomata conductance, and chlorophyll a fluorescence. Leaves from emergent trees had smaller leaf areas but greater LMA compared to saplings. Leaf thickness, palisade layer thickness, and stomatal density were higher for emergent trees than for saplings. The opposite pattern was observed for spongy layer thickness and spongy/palisade ratio. Stomatal conductance was also higher for emergent tree leaves than for sapling leaves, but the magnitude of depression on stomatal conductance near midday was more pronounced in emergent trees. The potential quantum yield of photosystem II, as determined by the F _v/F _m ratio was lower for leaves from saplings. The lower values of stomatal conductance, indicating restriction in CO₂ diffusion into the mesophyll can be related to higher photoinhibition observed in the saplings. Leaves from emergent trees and saplings exhibited similar values for apparent electron transport rates and non-photochemical quenching. Our results suggest that changes in leaf traits could be associated to dry conditions at the upper canopy as well as to the ontogenetic transition between sapling/emergent tree life stages.     

Does the invasive horse-chestnut leaf mining moth, <Emphasis Type="Italic">Cameraria ohridella</Emphasis>, affect the native beech leaf mining weevil, <Emphasis Type="Italic">Orchestes fagi</Emphasis>, through apparent competition?

Apparent competition, through the action of shared natural enemies, is frequently suggested as a possible mechanism underlying the impact of invasive alien species on native species, but examples are rare, particularly in insects. A previous study showed that the beech leaf mining weevil, Orchestes fagi, was significantly less abundant close to horse-chestnut trees infested by the invasive horse-chestnut leaf mining moth, Cameraria ohridella, compared to control sites. Apparent competition through the sharing of natural enemies was proposed as a potential mechanism underlying this effect. To test the occurrence of apparent competition between the two leaf miner species, three observational studies and one experimental manipulation were carried out in Switzerland during 3 years. The total mortality, parasitism, predation and parasitoid diversity of larvae and pupae of O. fagi were compared between sites with and without horse-chestnut trees severely attacked by C. ohridella. Total mortality and predation rates of O. fagi were not significantly different between sites with and sites without C. ohridella. Despite a large overlap between the parasitoid complexes of the two leaf miners, parasitism of O. fagi was found to be positively influenced by the presence of horse-chestnuts infested by C. ohridella in only one of the four studies and only for 1 year. Similarly, parasitoid diversity was not higher near infested horse-chestnut trees compared to control sites. Thus, little evidence for apparent competition was found. Possible reasons, including possible insufficiencies in the experimental circumstances and design, are discussed.     

Field study of beech (t Fagus sylvatica L.) and melojo oak (t Quercus pyrenaica Willd) leaf litter decomposition in the centre of the Iberian Peninsula

The effect of the canopy on leaf decomposition of beech (t Fagus sylvatica) and melojo oak (t Quercus pyrenaica) was studied during a period of 660 days in a mountain forest of central Spain; response of leaves to leaching was also studied to determine the effects of rainfall after leaf fall. Beech leaves lost 5.8% of their weight by leaching, whereas melojo oak leaves lost 13%. Under both types of canopy, beech leaves showed almost no difference in their decomposition patterns, with decay constants of 0.31 and 0.32 respectively. Melojo oak leaves showed quite a different behaviour under both canopies; decay constant was 0.47 under t Quercus pyrenaica and 0.77 under beech canopy. Total immobilization of nitrogen was less in the melojo oak forest. Effects of summer dryness were sharper in the melojo oak forest, where decomposition stopped during the summer. This delay in the decomposition might have been due to the lower canopy density in the melojo oak forest. The decomposition patterns of the leaves of both species, under the canopy of the other species, suggests what might happen in mixed stands. Thus, the presence of melojo oaks in beech forest would increase decay and decrease nitrogen immobilization. The presence of beech trees in melojo oak forests would improve microclimatic conditions and increase decay, whereas beech litter on the soil would immobilizate more nitrogen.