An analysis of structure: biomass structure relationships for characteristic species of the western <scp>K</scp>alahari, <scp>B</scp>otswana

Meyer, Thoralf; D’Odorico, Paolo; Okin, Gregory S.; Shugart, Herman H.; Caylor, K. K.; O'Donnell, F. C.; Bhattachan, Abi; Dintwe, K.

doi:10.1111/aje.12086

Cited by 20 publications

(24 citation statements)

References 17 publications

(16 reference statements)

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“…) and also does not account for inter‐ and intraspecific differences in canopy height and size, we believe that it offers a simple, low‐cost tool to compare differences in canopy density, if comparisons are done within the same morphological category of trees and shrubs (see Meyer et al. ).…”

Section: Resultsmentioning

confidence: 99%

“…To our knowledge, our approach to calculate a dendrometric proxy for canopy shading effect is one of the first to quantify species-specific differences in canopy shade. Although our proxy could be biased by species-specific differences in the proportion of stem biomass (Hasen-Yusuf et al 2013) and also does not account for inter-and intraspecific differences in canopy height and size, we believe that it offers a simple, low-cost tool to compare differences in canopy density, if comparisons are done within the same morphological category of trees and shrubs (see Meyer et al 2014).…”

Section: Resultsmentioning

confidence: 99%

“…We restricted this analysis to legume tree species previously known as Acacia ( Vachellia and Senegalia ), as these have distinct morphological and thus dendrometric characteristics (Meyer et al. ).…”

Section: Methodsmentioning

confidence: 99%

“…We used Pearson's correlation coefficient r to check if species' perceived encroachment status (CSI values) was correlated to their canopy shading index, treating both indices as continuous. We restricted this analysis to legume tree species previously known as Acacia (Vachellia and Senegalia), as these have distinct morphological and thus dendrometric characteristics (Meyer et al 2014).…”

Section: Canopy Densitymentioning

confidence: 99%

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Are trees of intermediate density more facilitative? Canopy effects of four East African legume trees

Linstädter

Bora

Tolera

et al. 2015

Applied Vegetation Science

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Questions Do East African legume trees differ in their canopy effects? Have species with intermediate canopy density more pronounced facilitative effects on understorey primary production, community composition and diversity? How are canopy effects related to species' encroachment status, and modulated by a local aridity gradient? Location Upland and lowland environments of the Borana rangelands, an arid thornbush savanna in southern Ethiopia. Methods We harnessed pastoralists' local ecological knowledge to rank the encroachment status of six legume tree species previously known as Acacia, and correlated this rank to a dendrometric proxy of canopy density. Vegetation relevés (1 m²) were placed in sub‐canopy and adjacent inter‐canopy habitats of four legume tree species that differed in canopy density and encroachment status (Vachellia bussei, V. drepanolobium, V. seyal, V. tortilis). Using mixed‐effects ANOVA, we evaluated effects of tree species and habitat (sub‐canopy or inter‐canopy) on total, forb and grass biomass, and on species diversity, comparing results for lowland and upland sites. Effects on floristic composition were assessed via PERMANOVA and NMDS. Results Species' encroachment status and canopy density were negatively correlated. Most pronounced facilitative effects (more frequent and larger differences between sub‐canopy and inter‐canopy habitats) were found for a species with intermediate canopy density (V. bussei). Diversity in its understorey vegetation increased up to 32% (total biomass: 29%, forb biomass: 40%). In contrast, the species with the most open canopy (V. drepanolobium; also the most encroaching species) never exerted significant facilitative effects. In contrast to expectations, canopy effects were more frequent in (climatically less arid) upland environments, probably due to a redistribution of water within the landscape. Large differences in facilitative effects across tree individuals indicate that a high intraspecific variability of canopy traits and/or small‐scale differences in abiotic site conditions have partly overridden species‐specific differences in canopy architecture. Conclusion Our study provides new insights on why encroaching legume tree species may decrease herbaceous production: they tend to have more open canopies, with small facilitative effects on sub‐canopy herbaceous production. We thus recommend promoting an open savanna with the tree layer dominated by species with a high facilitative potential to maintain forage provision and species diversity.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Canopy Densitymentioning

confidence: 99%

See 2 more Smart Citations

Are trees of intermediate density more facilitative? Canopy effects of four East African legume trees

Linstädter

Bora

Tolera

et al. 2015

Applied Vegetation Science

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“… W p is determined based on the field data from Meyer et al . (), who found that woody plant biomass at the landscape scale is W l = 2.5 kg m −2 at plant fractional cover ( f c ) = 70%. …”

Section: Methodsmentioning

confidence: 99%

Hydraulic lift as a determinant of tree–grass coexistence on savannas

D’Odorico

2015

New Phytologist

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SummaryThe coexistence of woody plants and grasses in savannas is determined by a complex set of interacting factors that determine access to resources and demographic dynamics, under the control of external drivers and vegetation feedbacks with the physical environment. Existing theories explain coexistence mainly as an effect of competitive relations and/or disturbances. However, theoretical studies on the way facilitative interactions resulting from hydraulic lift affect tree-grass coexistence and the range of environmental conditions in which savannas are stable are still lacking.We investigated the role of hydraulic lift in the stability of tree-grass coexistence in savannas. To that end, we developed a new mechanistic model that accounts for both competition for soil water in the shallow soil and fire-induced disturbance.We found that hydraulic lift favors grasses, which scavenge the water lifted by woody plants. Thus, hydraulic lift expands (at the expenses of woodlands) the range of environmental conditions in which savannas are stable.These results indicate that hydraulic lift can be an important mechanism responsible for the coexistence of woody plants and grasses in savannas. Grass facilitation by trees through the process of hydraulic lift could allow savannas to persist stably in mesic regions that would otherwise exhibit a forest cover.

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Conductive sapwood area prediction from stem and canopy areas—allometric equations of Kalahari trees, Botswana

2017

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Conductive sapwood (xylem) area (Ax) of all trees in a given forested area is the main factor contributing to spatial tree transpiration. One hundred ninety‐five trees of 9 species in the Kalahari region of Botswana were felled, stained, cut into discs, and measured to develop allometric equations predicting Ax from estimates of stem (As) and canopy (Ac) areas. Stem discs were also subjected to laboratory‐based computed tomography, which well detected wood density contrasts but was not diagnostic with regard to delineation of Ax. The staining experiment, along with the help of visual and computed tomography analysis, allowed the definition of 4, tree‐species categories of Ax, C1–C4. In C1 (Acacia erioloba, Terminalia sericea, and Burke Africana), the staining and visual delineation of Ax matched the natural color difference between sapwood and heartwood; in C2 (Dichrostachys cinerea and Ochna pulchra), sapwood was divided into external conductive and internal nonconductive annuli; in C3 (Acacia fleckii and Acacia luederitzii), sapwood had sharp staining boundary between external highly conductive and internal low‐conductive annuli; and in C4 (Lonchocarpus nelsii and Boscia albitrunca), stems had no heartwood. Per‐species 0‐intercept linear regression models, Ax = slope.As (slope = 0.392 ÷ 0.794; R2 = 96.7 ÷ 99.8%) and Ax = slope.Ac (slope = 1.477 ÷ 17.044; R2 = 82.1 ÷ 92.2%) yielded excellent to good predictive allometric equations. The first equation is suitable for Ax scaling of small‐size Kalahari areas, where the As of all trees can be estimated on the ground, whereas the second, as contribution to automated tree transpiration mapping of large‐size Kalahari areas, where the Ac of trees can be derived through remote sensing interpretation of high‐resolution images.

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An analysis of structure: biomass structure relationships for characteristic species of the western Kalahari, Botswana

Cited by 20 publications

References 17 publications

Are trees of intermediate density more facilitative? Canopy effects of four East African legume trees

Are trees of intermediate density more facilitative? Canopy effects of four East African legume trees

Hydraulic lift as a determinant of tree–grass coexistence on savannas

Conductive sapwood area prediction from stem and canopy areas—allometric equations of Kalahari trees, Botswana

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