Within-tree and among-tree variation in growth of Epirrita autumnata on mountain birch leaves

Abstract.

• 1 We studied among-tree and within-tree variation in the growth of larvae of a geometrid, Epirrita autumnata, on mountain birch (Betula pubescens ssp. tortuosa) leaves at different hierarchical levels: among trees (genets), among ramets within trees, among branches within ramets, among shoots within branches and among leaves within shoots. We used only short shoot leaves, which burst simultaneously in spring.
• 2 Trees accounted for most of the variation in larval growth rate, but there was substantial variation also among ramets within trees, among branches within ramets, and among short shoots within branches. Variation among leaves within short shoots was negligible. When the probabilities from different experiments were combined, the differences were statistically significant at the tree, ramet and branch levels, and approached significance at the shoot level.
• 3 In different experiments, larval growth was from 9% to 54% lower on the worst tree than on the best tree of the experiment. On average, larval growth rate was in different experiments from 11% to 32% lower on the worst ramet than on the best ramet within tree, from 8% to 18% lower on the worst than on the best branch within ramet, and from 12% to 30% lower on the worst than on the best shoot within branch.
• 4 The amount of among-and within-tree variation shown by our results may have ecological and evolutionary implications: among-tree variation should select for discrimination by ovipositing females and dispersing larvae, within-tree variation should select also for optimal foraging behaviour of larvae.

     

Carbon stock and cycling in a bambooPhyllostachys bambusoides stand

Gross production and carbon cycling in aPhyllostachys bambusoides stand in Kyoto Prefecture, central Japan, were determined, and then a compartment model showing the carbon stock and cycling within the ecosystem was developed. Aboveground carbon stock was 52.3 tC ha⁻¹, increasing at a rate of 3.6 tC ha⁻¹ year⁻¹. Belowground carbon stock was 20.8 tC ha⁻¹ in the root system and 92.0 tC ha⁻¹ in the soil. Aboveground net production was 11.2 tC ha⁻¹ year⁻¹. Belowground net production was crudely estimated at 4.5 tC ha⁻¹ year⁻¹. The gross production was estimated at 41.8 tC ha⁻¹ year⁻¹ by summing the amount of outflow to the environment and the increment in biomass. Leaves consumed 13.7 tC ha⁻¹ year⁻¹ by respiration; the rest (41.8−13.7=28.1 tC ha⁻¹ year⁻¹) was surplus production of the leaves and flowed into the other compartments. The amounts of construction and maintenance respiration of the aboveground compartments were 3.4 and 18.5 tC ha⁻¹ year⁻¹, respectively. The annual amount of soil respiration was 11.2 tC ha⁻¹ year⁻¹. Soil respiration levels of 4.3 and 3.1 tC ha⁻¹ year⁻¹ were estimated for the flow of root respiration and root detritus. The proportion of net to gross production was 37%, which fell within the range of young and mature forests. A shorter life span of culms, compared to tree trunks, resulted in smaller biomass accumulation ratio (biomass/net production) in the ecosystem, of 4.66.     

Treeline advances along the Urals mountain range – driven by improved winter conditions?

High‐altitude treelines are temperature‐limited vegetation boundaries, but little quantitative evidence exists about the impact of climate change on treelines in untouched areas of Russia. Here, we estimated how forest‐tundra ecotones have changed during the last century along the Ural mountains. In the South, North, Sub‐Polar, and Polar Urals, we compared 450 historical and recent photographs and determined the ages of 11 100 trees along 16 altitudinal gradients. In these four regions, boundaries of open and closed forests (crown covers above 20% and 40%) expanded upwards by 4 to 8 m in altitude per decade. Results strongly suggest that snow was an important driver for these forest advances: (i) Winter precipitation has increased substantially throughout the Urals (~7 mm decade^?1), which corresponds to almost a doubling in the Polar Urals, while summer temperatures have only changed slightly (~0.05 °C decade^?1). (ii) There was a positive correlation between canopy cover, snow height and soil temperatures, suggesting that an increasing canopy cover promotes snow accumulation and, hence, a more favorable microclimate. (iii) Tree age analysis showed that forest expansion mainly began around the year 1900 on concave wind‐sheltered slopes with thick snow covers, while it started in the 1950s and 1970s on slopes with shallower snow covers. (iv) During the 20th century, dominant growth forms of trees have changed from multistemmed trees, resulting from harsh winter conditions, to single‐stemmed trees. While 87%, 31%, and 93% of stems appearing before 1950 were from multistemmed trees in the South, North and Polar Urals, more than 95% of the younger trees had a single stem. Currently, there is a high density of seedlings and saplings in the forest‐tundra ecotone, indicating that forest expansion is ongoing and that alpine tundra vegetation will disappear from most mountains of the South and North Urals where treeline is already close to the highest peaks.     

Root system architecture of Quercus pubescens trees growing on different sloping conditions

BACKGROUND AND AIMS: Plant roots' growth direction has important implications for plant development and survival; moreover it plays an effective and vital role in stabilizing weathered soil on a steep slope. The aim of this work was to assess the influence of slope on the architecture of woody root systems. METHODS: Five mature, single-stemmed Quercus pubescens trees growing on a steep slope and five on a shallow slope were excavated to a root diameter of 1 cm. A very precise numeric representation of the geometry and topology of structural root architecture was gained using a low-magnetic-field digitizing device (Fastrak, Polhemus). Several characteristics of root architecture were extracted by macros, including root volume, diameter, length, number, spatial position and branching order. KEY RESULTS: The diameter at breast height (dbh) was the best predictor of the root volume but had no correlation with length and number of roots. The slope affected the root volume for each branching order, and the basal cross-sectional area (CSA), number and length of the first-order roots. Number and length of the second- and third-order laterals were closely related in both conditions, although this relationship was closer in the shallow trees, suggesting the influence of a genetic control. Sloping trees showed a clustering tendency of the first- and second-order lateral roots in the up-slope direction, suggesting that the laterals rather than the taproots provide much of the anchorage. In a steep-slope condition, the taproot tapering was positively correlated with the asymmetry magnitude of first-order roots, indicating compensation between taproot and main lateral roots' clustering tendency. CONCLUSIONS: These results suggest that on a slope, on clayey soils, root asymmetry appears to be a consequence of several environmental factors such as inclination, shallow-slides and soil compactness. In addition, this adaptive growth seems to counteract the turning moment induced by the self-loading forces acting in slope conditions, and as a consequence improves the tree stability.     

Do competition and herbivory alter the internal nitrogen dynamics of birch saplings?

Deciduous trees recycle nitrogen within their tissues. The aim of this study was to test the hypothesis that reductions in plant growth, caused by competition and herbivory, reduce the sink strength for N during autumn nutrient withdrawal, and reduce the storage capacity and hence the amount of N remobilized in the following spring. We used (15)N-labelled fertilizer to quantify N uptake, leaf N withdrawal and remobilization. Betula pubescens saplings were grown with either Molinia caerulea or Calluna vulgaris, and subjected to simulated browsing damage. Competition reduced B. pubescens leaf N withdrawal and remobilization, with C. vulgaris having a greater effect than M. caerulea. However, simulated browsing had no significant effect on sapling N dynamics. The patterns of leaf N withdrawal and remobilization closely followed sapling dry mass. We conclude that the effect of competition on sapling mass reduces their N-storage capacity. This reduces sink strength for leaf N withdrawal and the source strength for remobilized N. The ability of saplings to compensate for browsing damage removed any potential effect of browsing on N dynamics.     

A Comparison of ITS Nuclear rDNA Sequence Data and AFLP Markers for Phylogenetic Studies in Phyllostachys (Bambusoideae, Poaceae)

Phyllostachys , a large, economically important genus of woody bamboos. DNA sequences of the internal transcribed spacer (ITS) region of nuclear ribosomal DNA (nrDNA) were used in a parsimony analysis. Phyllostachys was well supported as monophyletic with Chimonobambusa as its closest allied genus. The 5S spacer region of nrDNA was investigated but found unsuitable for this purpose. The AFLP analysis showed much higher discriminating power between species and was more useful for phylogenetic reconstruction at this taxonomic level. The combined data were used to review the previous infra-generic classifications. Section Heteroclada Wang & Ye is strongly supported and can be further divided into sub-groups. A group within section Phyllostachys is strongly supported, but a further group of taxa previously included in this section is difficult to place. The ability of the methods to help separate species such as P. sulphurea and investigate genetic diversity at the infra-specific level was also assessed. It is argued that AFLPs could often be the method of choice for phylogenetic studies of closely related taxa for which DNA sequence data provide insufficient resolution. Received 18 April 2000/ Accepted in revised form 10 June 2000     

Ultrastructural Study of Secondary Wall Formation in the Stem Fiber of Phyllostachys pubescens

Ultrastructural changes in secondary wall formation of Phyllostachys pubescens Mazel fiber were investigated with transmission electron microscopy. Fiber developed initially with the elongation of cells containing ribosomes, mitochondria and Golgi bodies in the dense cytoplasm. During the wall thickening, the number of rough endoplasmic reticulum and Golgi bodies increased apparently. There were two kinds of Golgi vesicles, together with the ones from endoplasmic reticulum formed transport vesicles. Many microtubules were arranged parallel to the long axis of the cell adjacent to the plasmalemma. Along with the further development of fiber, polylamellate structure of the secondary wall appeared, with concurrent agglutination of chromatin in the nucleus, swelling and disintegration of organelles, while cortical microtubules were still arranged neatly against the inner side of plasmalemma. Lomasomes could be observed between the wall and plasmalemma. The results indicated that the organelles, such as Golgi bodies together with small vesicles, rough endoplasmic reticulum and lomasomes, played the key role in the thickening and lignification of the secondary wall of bamboo fiber, though cortical microtubules were correlative with the process as well.     

不同管理措施对毛竹林节肢动物群落结构和组成的影响

通过对不同管理措施下毛竹林Phyllostachys heterocycla cv. pubescens节肢动物群落的系统调查,研究了垦复施肥、垦复、劈草、化学除草和撂荒5种典型管理措施对群落结构和组成的影响。结果表明,与撂荒林相比,其他各管理措施均降低了群落竹冠层和林下层类群的丰富度,在林下层主要表现为蜘蛛目、膜翅目、半翅目和鞘翅目物种的减少,在竹冠层主要表现为膜翅目和鞘翅目物种的减少,这些减少的物种主要是偶见种（相对丰盛度小于0.01）。垦复施肥、垦复和劈草增加了林下层中性功能群和减少了捕食性功能群的个体数量,垦复施肥、垦复、劈草和化学除草增加了竹冠层捕食性功能群和减少了植食性功能群的个体数量。总体上各种管理措施均降低了林下层和提高了竹冠层类群的多样性和均匀度,但化学除草对林下层的影响较小,垦复对竹冠层的影响较小。长期撂荒和垦复林毛竹叶部害螨的优势度较高,长期撂荒、劈草和化学除草林蠕须盾蚧Kuwanaspis vermiformis的优势度较高,长期垦复施肥、垦复和劈草林刚竹毒蛾Pantana phyllostachysae的优势度较高,说明长期的单一管理措施可能导致特定种类害虫的暴发。因此提出在毛竹林的管理中,应避免长期采用单一方式,注重不同年份多种管理措施的轮换。     

Tree invasion in managed tropical forests facilitates endemic species

Aim To determine whether different abundances of introduced species of Cinchona (Rubiaceae) affect species composition and facilitate species richness in managed tropical forests, to test whether any facilitative effects on understorey species depend on forest type, and to investigate whether facilitative effects can be attributed to the ‘substitutive facilitation model’. Location Makawao Forest Reserve on Maui, Hawai’i, USA. Methods Cinchona species (Cinchona pubescens and Cinchona calisaya) were mapped within various forest types. In three forest types (ageing Eucalyptus and Pinus plantations, and near‐natural Acacia koa forests), we analysed environmental parameters (e.g. canopy cover, litter cover, pH value and soil depth) and the species composition of Cinchona‐invaded and non‐invaded plots; data were compared based on Cinchona cover and forest types. Habitat modelling for several endemic species and tree ferns was carried out to test whether Cinchona cover is an important variable for the probability of occurrence of these endemics. Results Cinchona species have naturalized mainly in Eucalyptus and Pinus plantations and Acacia koa forests and here add an additional shrub layer. In contrast to other studies, we revealed facilitative effects of Cinchona on native species within all forest types. Species richness is about 20% higher in invaded plots than in non‐invaded plots, and these show a nearly 50% higher proportion of endemic species, including tree ferns. The proportion of endemics even increases with increasing Cinchona cover. For several endemics, Cinchona is found to be an important variable for the probability of occurrence, and the removal of Cinchona cover as an explanatory variable lowers the model fit. In addition to Cinchona, variables delineating vegetation structure and light availability have a strong effect on the model fit. Main conclusions In the structurally simplified Hawaiian forests studied, Cinchona facilitated endemic species in accordance with the ‘substitutive facilitation model’. This contrasts with the results of an earlier study in the naturally treeless Galápagos highlands, which revealed a sharp decrease in the abundance of endemics under Cinchona canopy. These results illustrate that, through the same structural change (addition of a vegetation layer), an invasive species may exert divergent effects across different ecosystem types. The facilitation of endemic understorey species by invasive tree species in managed forests leads to a dilemma in conservation but also to new perspectives for ecosystem restoration.