1. High elevation treelines 1.1 The task 1.2 Previous works 2. Definitions and conventions 2.1 The life form 'tree' 2.2 Lines and transitions 2.3 Limitation, stress and disturbance 2.4 Altitude-related and other environmental drivers 2.5 Treeline nomenclature 3. Treeline patterns 3.1 Treeline taxa 3.2 The summit syndrome and other treeline depressions 3.3 Mass elevation effect 3.4 Treeline elevation 3.5 Time matters 3.6 Forest structure near treeline 4. Treeline climate 4.1 Specific aspects of treeline climatology 4.2 Criteria to define temperature regimes at treeline 4.3 Treeline temperatures in different bioclimatic regions 4.4 Seedbed and branch temperatures 4.5 Whole forest temperatures 5. Global mountain statistics based on treeline elevation 5.1 Mountain geostatistics 5.2 Elevational belts 5.3 Global treeline ecotones 6. Structure and stature of treeline trees 6.1 Foliage properties 6.2 Wood properties 6.3 Bark properties 6.4 Root traits 6.5 Tree stature 6.6 Dry matter allocation in treeline trees 7. Growth and development 7.1 Tree growth near treeline 7.2 Xylogenesis at treeline 7.3 Apical growth dynamics 7.4 Root growth 7.5 Phenology at treeline 8. Evolutionary adjustments to life at treeline 8.1 Phylogenetic selection 8.2 Genotypic responses of growth and development 8.3 Genotypic responses of physiological traits 9. Reproduction, early life stages and tree demography 9.1 Amount and quality of seeds at high elevation 9.2 Germination, seedling and sapling stage 9.3 Tree demography at treeline 10. Freezing and other forms of stress 10.1 Stress at treeline in a fitness context 10.2 Mechanisms and principles of freezing resistance 10.3 Freezing resistance in treeline trees 10.4 Other forms of stress at treeline 11. Water, nutrient and carbon relations 11.1 Tree water relations during the growing season 11.2 Nutrient relations 11.3 Carbon relations 12. Treeline formation - currently, in the past and in the future 12.1 Causes of current treelines 12.2 Treelines in the recent past 12.3. Treelines in the distant past (Holocene) 12.4 Future treelines References Taxonomic index Subject index

Alpine treelines : functional ecology of the global high elevation tree limits

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Physiological Plant Ecology Ecophysiology And Stress Physiology Of Functional Groups

Phylogenetic relationships among 76 species of Oleaceae, representing all 25 recognized genera of the family, were assessed by a cladistic analysis of DNA sequences from two noncoding chloroplast loci, the rps16 intron and the trnL-F region. Consensus trees from separate and combined analyses are congruent and agree well with nonmolecular data (chromosome numbers, fruit and wood anatomy, leaf glycosides, and iridoids). The two debated genera Dimetra and Nyctanthes, previously suggested to belong to Verbenaceae (sensu lato) or Nyctanthaceae, are shown to belong to Oleaceae, sister to the hitherto genus incertae sedis Myxopyrum. This clade is also supported by anatomical and chemical data. The subfamily Jasminoideae is paraphyletic, and a new classification is presented. The subfamily level is abandoned, and the former Jasminoideae is split into four tribes: Myxopyreae (Myxopyrum, Nyctanthes, and Dimetra), Fontanesieae (Fontanesia), Forsythieae (Abeliophyllum and Forsythia), and Jasmineae (Jasminum and Menodora). The tribe Oleeae (previous subfamily Oleoideae) is clearly monophyletic, comprising the subtribes Ligustrinae (Syringa and Ligustrum), Schreberinae status novus (Schrebera and Comoranthus), Fraxininae status novus (Fraxinus), and Oleinae (12 drupaceous genera). An rps16 sequence obtained from Hesperelaea, known only from the type specimen collected in 1875, confirmed the placement of this extinct taxon in the subtribe Oleinae.

Phylogeny and classification of Oleaceae based on rps16 and trnL-F sequence data

Birch (Betula) trees and forests are found across much of the temperate and boreal zones of the Northern Hemisphere. Yet, despite being an ecologically significant genus, it is not well studied compared to other genera like Pinus, Picea, Larix, Juniperus, Quercus, or Fagus. In the Himalayas, Himalayan birch (Betula utilis) is a widespread broadleaf timberline species that survives in mountain rain shadows via access to water from snowmelt. Because precipitation in the Nepalese Himalayas decreases with increasing elevation, we hypothesized that the growth of birch at the upper timberlines between 3900 and 4150 m above sea level is primarily limited by moisture availability rather than by low temperature. To examine this assumption, a total of 292 increment cores from 211 birch trees at nine timberline sites were taken for dendroecological analysis. The synchronous occurrence of narrow rings and the high interseries correlations within and among sites evidenced a reliable cross-dating and a common climatic ...

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Is the growth of birch at the upper timberline in the Himalayas limited by moisture or by temperature

Phylogenetic reconstruction is fundamental to study evolutionary biology and historical biogeography. However, there was not a molecular phylogeny of gymnosperms represented by extensive sampling at the genus level, and most published phylogenies of this group were constructed based on cytoplasmic DNA markers and/or the multi-copy nuclear ribosomal DNA. In this study, we use LFY and NLY, two single-copy nuclear genes that originated from an ancient gene duplication in the ancestor of seed plants, to reconstruct the phylogeny and estimate divergence times of gymnosperms based on a complete sampling of extant genera. The results indicate that the combined LFY and NLY coding sequences can resolve interfamilial relationships of gymnosperms and intergeneric relationships of most families. Moreover, the addition of intron sequences can improve the resolution in Podocarpaceae but not in cycads, although divergence times of the cycad genera are similar to or longer than those of the Podocarpaceae genera. Our study strongly supports cycads as the basal-most lineage of gymnosperms rather than sister to Ginkgoaceae, and a sister relationship between Podocarpaceae and Araucariaceae and between Cephalotaxaceae-Taxaceae and Cupressaceae. In addition, intergeneric relationships of some families that were controversial, and the relationships between Taxaceae and Cephalotaxaceae and between conifers and Gnetales are discussed based on the nuclear gene evidence. The molecular dating analysis suggests that drastic extinctions occurred in the early evolution of gymnosperms, and extant coniferous genera in the Northern Hemisphere are older than those in the Southern Hemisphere on average. This study provides an evolutionary framework for future studies on gymnosperms.

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Phylogeny and Divergence Times of Gymnosperms Inferred from Single-Copy Nuclear Genes

Distribution and community structure of treeline birch (Betula utilis D. Don) forest in a trans-Himalayan dry valley was studied in Manang (central Nepal) with the major focus on regeneration. Along 5 vertical transects, a total of 41 square quadrats (10 m x 10 m) were sampled to determine the importance value index (IVI) of tree species, distribution pattern of seedlings and saplings, and soil attributes. Regeneration was assessed by a density–diameter curve. Moisture plays an important role in spatial (horizontal) distribution of Betula utilis. Pure Betula forest forming the treeline was mature, with high basal area (2.3%), but mixed Betula forest at lower elevations was young. This might have developed after large-scale clear cutting of Abies spectabilis. If not severely disturbed, mixed Betula forest may be replaced by Abies spectabilis. In general, Betula utilis was regenerating, as evident from a reverse J-shaped density–diameter curve for both forests. However, the distribution of seedling...

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Regeneration of Treeline Birch (Betula utilis D. Don) Forest in a Trans-Himalayan Dry Valley in Central Nepal

In this study, the allelopathic properties of Medicago sativa on different weeds were investigated under in vitro conditions. The compounds involved in the autotoxicity of M. sativa were analyzed using high-performance liquid chromatography. The extracts of all concentrations inhibited the growth of the calluses of Digitaria ciliaris, Chenopodium album, Amaranthus lividus, Portulaca oleracea, and Commelina communis. Six allelopathic compounds in alfalfa were identified and quantified, and the most predominant phenolic compounds were salicylic acid and p-hydroxybenzoic acid. Various concentrations (10−2, 10−3, and 10−5 M) of all the tested phenolic compounds exerted inhibitory effects on callus fresh weight. Rutin, salicylic acid, scopoletin, and quercetin significantly inhibited alfalfa seed germination. Of the seven identified saponins, medicagenic acid saponins exhibited the highest autotoxic effect and significantly lowered seed germination rate. Principal component analysis showed that the phenolic compounds and saponin composition significantly contributed to the different variables. The highly phytotoxic properties of the alfalfa-derived phenolic compounds and saponins indicate that these phytochemicals can be a potential source of bioherbicides.

https://www.mdpi.com/2223-7747/8/7/233/pdf

Allelopathic and Autotoxic Effects of Medicago sativa-Derived Allelochemicals.

We studied the elevational pattern of forest composition and regeneration of the subalpine conifer tree species Pinus wallichiana in Manang, a trans-Himalayan dry valley in north-central Nepal. Thirty-five quadrats (10 m × 10 m) were laid between 3300 and 4000 masl on both north- and south-facing slopes. We measured diameter at breast height (DBH) of each mature individual of all tree species (DBH ≥10 cm), and recorded the number of seedlings (DBH 30 cm). We also measured soil moisture and soil pH, estimated canopy cover, and recorded slope and altitude in each quadrat. For all species together and for several species individually, tree density, seedling density, sapling density and tree basal area were found to decrease with elevation on both north and south aspects. This trend is largely explained by the progressively harsher environment at higher elevations. The north-facing slopes in our study area have denser forests than the south-facing slopes, the density of all size classes (seedling, sapling and mature plants) and basal area being greater on the northern aspects. These aspect-wide differences are attributable to the stark difference in soil moisture between northern and southern aspects, which is in turn due to the difference in insolation. Irrespective of elevation and aspect, all the forests studied are regenerating, as indicated by inverse J-shaped density-diameter curves. The elevational pattern of seedling and sapling abundance is explained only by elevation. Whereas other variables (e.g., canopy) are considered to have an important influence on seed germination and seedling establishment, they turn out not to be significant predictors of density of seedlings and saplings. This failure to identify a relationship is probably due to our use of non-parametric test (tree regression analysis) that we used to establish the relationship between density and its potential explanatory variables or due to our selection of 1 standard error rule yielding sub-optimal models for regression trees. Key words: density-diameter curve; regeneration; seedling; sapling; altitude; canopy; Manang Valley DOI: http://dx.doi.org/10.3126/hjs.v6i8.1798 Himalayan Journal of Sciences Vol.6 Issue 8 2010 pp.19-26

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Regeneration of Pinus wallichiana AB Jackson in a trans-Himalayan dry valley of north-central Nepal

The comparative study on leaf anatomy and stomata structures of six genera of Taxaceae s. l. was conducted. Leaf anatomical structures were very comparable to each other in tissue shape and their arrangements. Taxus, Austrotaxus, and Pseudotaxus have no foliar resin canal, whereas Amentotaxus, Cephalotaxus, and Torreya have a single resin canal located below the vascular bundle. Among them, Torreya was unique with thick-walled, almost round sclerenchymatous epidermal cells. In addition, Amentotaxus and Torreya were comprised of some fiber cells around the vascular bundle. Also, Amentotaxus resembled Cephalotaxus harringtonia and its var. nana because they have discontinuous fibrous hypodermis. However, C. fortunei lacked the same kind of cells. Stomata were arranged in two stomatal bands separated by a mid-vein. The most unique stomatal structure was of Taxus with papillose accessory cells forming stomatal apparatus and of Torreya with deeply seated stomata covered with a special filament structure. Some morphological and molecular studies have already been discussed for the alternative classification of taxad genera into different minor families. The present study is also similar to these hypotheses because each genus has their own individuality in anatomical structure and stomata morphology. In conclusion, these differences in leaf and stomata morphology neither strongly support the two tribes in Taxaceae nor fairly recognize the monogeneric family, Cephalotaxaceae. Rather, it might support an alternative classification of taxad genera in different minor families or a single family Taxaceae including Cephalotaxus. In this study, we would prefer the latter one because there is no clear reason to separate Cephalotaxus from the rest genera of Taxaceae. Therefore, Taxaceae should be redefined with broad circumscriptions including Cephalotaxus.

Leaf anatomy and its implications for phylogenetic relationships in Taxaceae s . l .

Taxaceae s. l. is a wider concept of classification treating five genera of Taxaceae s. str. and Cephalotaxus together. Cephalotaxus is morphologically very similar to the five genera of Taxaceae s. str. Various models of classification for six genera have already been published. However, the phylogenetic position and genuine relationships of these genera and species are still confusing. A cladistic analysis of Taxaceae s. l. has been carried out to resolve the problem existing in their phylogeny and to provide a new approach regarding the relationships of these six genera. Parsimony analyses were based on 28 characters and eight genera including two outgroups Agathis and Sciadopitys. The most parsimonious tree retained with branch length 38 and 194 rearrangement trials. Consistency index was 0.68 and retention index was 0.66. Principally, two main clades were found: one represented by Austrotaxus forming the base of the tree and another by the remaining five genera. Taxus + Pseudotaxus clade split after Austrotaxus, and Cephalotaxus was sister to Torreya + Amentotaxus clade. Taxus + Pseudotaxus clade was supported by the highest bootstrap value. Finally, cladistic analysis does not support existence of Cephalotaxaceae. Therefore, it would be better to classify Cephalotaxus within Taxaceae s. l. with the other five genera.

Balkrishna Ghimire

Papers

Regeneration of Treeline Birch (Betula utilis D. Don) Forest in a Trans-Himalayan Dry Valley in Central Nepal

Allelopathic and Autotoxic Effects of Medicago sativa-Derived Allelochemicals.

Regeneration of Pinus wallichiana AB Jackson in a trans-Himalayan dry valley of north-central Nepal

Leaf anatomy and its implications for phylogenetic relationships in Taxaceae s . l .

Cladistic analysis of Taxaceae s. l.