| 1. |
- Hellström, Lars, 1974-, et al.
(författare)
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Branch Thinning and the Large-Scale, Self-Similar Structure of Trees
- 2018
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Ingår i: American Naturalist. - : UNIV CHICAGO PRESS. - 0003-0147 .- 1537-5323. ; 192:1, s. E37-E47
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Tidskriftsartikel (refereegranskat)abstract
- Branch formation in trees has an inherent tendency toward exponential growth, but exponential growth in the number of branches cannot continue indefinitely. It has been suggested that trees balance this tendency toward expansion by also losing branches grown in previous growth cycles. Here, we present a model for branch formation and branch loss during ontogeny that builds on the phenomenological assumption of a branch carrying capacity. The model allows us to derive approximate analytical expressions for the number of tips on a branch, the distribution of growth modules within a branch, and the rate and size distribution of tree wood litter produced. Although limited availability of data makes empirical corroboration challenging, we show that our model can fit field observations of red maple (Acer rubrum) and note that the age distribution of discarded branches predicted by our model is qualitatively similar to an empirically observed distribution of dead and abscised branches of balsam poplar (Populus balsamifera). By showing how a simple phenomenological assumptionthat the number of branches a tree can maintain is limitedleads directly to predictions on branching structure and the rate and size distribution of branch loss, these results potentially enable more explicit modeling of woody tissues in ecosystems worldwide, with implications for the buildup of flammable fuel, nutrient cycling, and understanding of plant growth.
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| 2. |
- Lindh, Magnus, et al.
(författare)
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Latitudinal effects on crown shape evolution
- 2018
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Ingår i: Ecology and Evolution. - : John Wiley & Sons. - 2045-7758. ; 8:16, s. 8149-8158
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Tidskriftsartikel (refereegranskat)abstract
- Large variations in crown shape are observed across the globe, from plants with wide and deep crowns to those with leaves clustered at the top. While there have been advances in the large-scale monitoring of forests, little is known about factors driving variations in crown shape with environmental conditions. Previous theoretical research suggests a gradient in crown shape with latitude, due to the effects of sun angle. Yet, it remains unclear whether such changes are also predicted under competition. Using a size-structured forest-growth model that incorporates self-shading from plants and competitive shading from their neighbors, we investigate how changes in site productivity and sun angle shape crown evolution. We consider evolution in two traits describing the top-heaviness and width-to-height ratio of crowns, shaped by trade-offs reflecting the costs and benefits of alternative architectures. In top-heavy trees, most of the leaves are at the top half of the trunk. We show that, contrary to common belief, the angle of sun beams per se has only a weak influence on crown shapes, except at low site productivity. By contrast, reduced site productivity has a strong effect, with trees growing in less productive sites keeping their leaves closer to the ground. The crown width-to-height ratio is generally higher at a lower site productivity, but this trait is not strongly influenced by any environmental factor. This theoretical analysis brings into question established beliefs about the effects of latitude on crown shapes. By introducing geometry-related growth constraints caused by shading from both the surrounding forest and the tree on itself, and costs for constructing and maintaining a three-dimensional crown, our analysis suggests crown shapes may vary with latitude, mostly via effects on overall site productivity, and less because of the angle of the sun.
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| 3. |
- Rani, Raffaele, et al.
(författare)
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Effects of bud-flushing strategies on tree growth
- 2018
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 38:9, s. 1384-1393
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Tidskriftsartikel (refereegranskat)abstract
- Allocation of carbohydrates between competing organs is fundamental to plant development, growth and productivity. Carbohydrates are synthesized in mature leaves and distributed via the phloem vasculature to developing buds where they are consumed to produce new biomass. The distribution and mass-allocation processes within the plant remain poorly understood and may involve complex feedbacks between different plant functions, with implications for the emergent structure of the plant. Here, we investigate how the order in which dormant buds are flushed affects the development of tree size and reproductive output during the first 20 years of growth in full light and shaded canopy environments. We report the following findings: (i) Bud-flushing strategies strongly affect the temporal dynamics of height, mass and the size of reproduction pool, as well as the resulting architectures. (ii) Bud-flushing strategies affect tree growth by altering the rate of growth and final size of trees. (iii) No single bud-flushing strategy performs best when both the size and allocation for reproduction of the resulting trees are compared. However, we observe that the strategy that optimizes the net carbon gain for the entire tree architecture always results in a high reproduction output. (iv) Branch turnover and meristem regeneration enhance the performance of certain strategies with respect to the measured quantities. These results highlight the importance of employing generic models of architecture (i.e., non-species-specific) to identify general mechanisms of carbon allocation and the spatial distribution of newly formed biomass in growing trees.
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| 4. |
- Wenk, Elizabeth Hedi, et al.
(författare)
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Investment in reproduction for 14 iteroparous perennials is large and associated with other life-history and functional traits
- 2018
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Ingår i: Journal of Ecology. - : John Wiley & Sons. - 0022-0477 .- 1365-2745. ; 106:4, s. 1338-1348
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Tidskriftsartikel (refereegranskat)abstract
- 1. While theoretical models predict reproductive allocation (RA) should approach 100% of available energy as a plant ages, available empirical data suggest much lower RA values in perennial plants. In this study, we have two aims. First, we assess whether the discrepancy between theory and data arises from methodological differences in how growth and RA are calculated. Specifically, we hypothesize RA in older plants is large when compared to growth in leaf area, that is, after excluding turnover of stem and leaf tissues. Second, we hypothesize that species with cheap tissues or those that are shorter reach RA = 0.5 at a younger age.2. We measured investment in leaf, stem and reproduction on individuals from 14 co-occurring woody perennial iteroparous species. A fire chronosequence allowed us to use a space-for-time substitution to estimate RA schedules for each species, simultaneously measuring reproductive and vegetative production on individuals differing in age.3. For most (11 of 14) species, we found RA eventually reached 100% of available energy, with another two species reaching at least 80%. Increases in RA were associated with a decline in growth of leaf area. Comparing species, we found that species with cheap leaves reached RA = 0.5 sooner (they could be called fast-living), whereas delayed maturation and slower increases in RA were associated with greater maximum height.4. Synthesis. Explicitly accounting for the cost of leaf replacement leads to the high estimates of reproductive allocation in perennial plants predicted by theoretical models, limiting or even halting leaf area expansion. For some species, so much energy is allocated to reproduction that leaf area declines year-upon-year for multiple growing seasons preceding death. Connecting lifetime reproductive allocation schedules with leaf area expansion, leaf life span, and plant maximum height demonstrates how reproductive allocation schedules synthesize a plant's life-history strategy, making them a valuable tool for connecting plant traits and demography.
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