Transpiration dynamics support resource partitioning in African savanna trees and grasses

Holdø, Ricardo M.; Nippert, Jesse B.

doi:10.1890/14-1986.1

Cited by 30 publications

(43 citation statements)

References 31 publications

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“…This hypothesis claims that the coexistence of trees and grasses in these water-limited ecosystems can be explained by a vertical niche partitioning in water source utilization, with grasses using shallow soil water and trees exploiting deeper water sources. To date, evidence for this spatial partitioning of soil water exists for savanna ecosystems mainly (Ward, Wiegand, & Getzin, 2013, Holdo & Nippert, 2015, Priyadarshini et al, 2015 and we are aware of only one study in an agroforestry system (Smith et al, 1997). The occurrence of such spatial complementarity in water use between trees and crops in dryland agroforestry systems is highly relevant, as it may enhance their productivity (Ong & Leakey, 1999).…”

Section: Figurementioning

confidence: 99%

Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa

et al. 2017

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Agroforestry parklands, in which annual crops are grown under scattered mature trees, constitute the most prevalent farming system in semiarid West Africa, covering vast areas of land. The most dominant tree species in these systems is Vitellaria paradoxa, an indigenous tree to West Africa. Despite the importance of this tree in the region, no study to our knowledge has examined its sources and patterns of water uptake. In this study, we used oxygen stable isotopes at natural abundance levels to investigate water sources used by V. paradoxa both in the dry and wet season in an agroforestry parkland in Burkina Faso. We found that during the wet season soil moisture was highest near the soil surface (<10 cm depth), yet during this time V. paradoxa preferentially accessed water from slightly deeper soil depths, obtaining ca. 90% of its water from 10 to 50 cm depth. In contrast, soil moisture in the upper soil layers was significantly lower during the dry season and as a result V. paradoxa shifted to deeper water sources, obtaining ca. 30% of its water from groundwater and ca. 50% from 30 to 600 cm depth. We also found a negative relationship between tree size and the contribution of groundwater during the dry season, whereas during the wet season V. paradoxa predominantly used water near the soil surface regardless of tree size. Knowledge about the sources and patterns of tree water uptake provides crucial information to better understand how trees influence the local water balance.

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Section: Figurementioning

confidence: 99%

Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa

et al. 2017

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“…This is supportive of the hypothesis that increased precipitation results in increased deep water infiltration and availability and thus favors woody species (Walker & Noy‐Meir, ). However, in some cases, this is not observed due to an increased transpiration from the grass species resulting in a decrease in deep water availability (February et al, ; Holdo & Nippert, ), highlighting the complex nature of interactions between different species' response strategies to stochastic forcing.…”

Section: Introductionmentioning

confidence: 99%

Assessing the Roles of Fire Frequency and Precipitation in Determining Woody Plant Expansion in Central U.S. Grasslands

et al. 2017

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Woody plant expansion into grasslands and savannas is occurring and accelerating worldwide and often impacts ecosystem processes. Understanding and predicting the environmental and ecological impacts of encroachment has led to a variety of methodologies for assessing its onset, transition, and stability, generally relying on dynamical systems approaches. Here we continue this general line of investigation to facilitate the understanding of the roles of precipitation frequency and intensity and fire frequency on the conversion of grasslands to woody‐dominated systems focusing on the central United States. A low‐dimensional model with stochastic precipitation and fire disturbance is introduced to examine the complex interactions between precipitation and fire as mechanisms that may suppress or facilitate increases in woody cover. By using Lyapunov exponents, we are able to ascertain the relative control exerted on woody encroachment through these mechanisms. Our results indicate that precipitation frequency is a more important control on woody encroachment than the intensity of individual precipitation events. Fire, however, exerts a much more dominant impact on the limitation of encroachment over the range of precipitation variability considered here. These results indicate that fire management may be an effective strategy to slow the onset of woody species into grasslands. While climate change might predict a reduced potential for woody encroachment in the near future, these results indicate a reduction in woody fraction may be unlikely when considering anthropogenic fire suppression.

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“…This produces regularized models that include only strong predictors, while shrinking weak predictor variables toward zero (Friedman, Hastie, & Tibshirani, ; Guisan & Zimmermann, ). Elastic net models have been successfully used in a variety of ecological studies when dealing with a large number of potential predictors, especially when those predictors have low predictive power (Holdo & Nippert, ; Lemoine et al., ; Prospere, McLaren, & Wilson, ). This regularization shrinks coefficients to 0 unless they substantially improve model fit and predictive performance in cross‐validation.…”

Section: Methodsmentioning

confidence: 99%

Leap frog in slow motion: Divergent responses of tree species and life stages to climatic warming in Great Basin subalpine forests

Smithers

North

Millar

et al. 2017

Global Change Biology

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In response to climate warming, subalpine treelines are expected to move up in elevation since treelines are generally controlled by growing season temperature.Where treeline is advancing, dispersal differences and early life stage environmental tolerances are likely to affect how species expand their ranges. Species with an establishment advantage will colonize newly available habitat first, potentially excluding species that have slower establishment rates. Using a network of plots across five mountain ranges, we described patterns of upslope elevational range shift for the two dominant Great Basin subalpine species, limber pine and Great Basin bristlecone pine. We found that the Great Basin treeline for these species is expanding upslope with a mean vertical elevation shift of 19.1 m since 1950, whichis lower than what we might expect based on temperature increases alone. The largest advances were on limber pine-dominated granitic soils, on west aspects, and at lower latitudes. Bristlecone pine juveniles establishing above treeline share some environmental associations with bristlecone adults. Limber pine above-treeline juveniles, in contrast, are prevalent across environmental conditions and share few environmental associations with limber pine adults. Strikingly, limber pine is establishing above treeline throughout the region without regard to site characteristic such as soil type, slope, aspect, or soil texture. Although limber pine is often rare at treeline where it coexists with bristlecone pine, limber pine juveniles dominate above treeline even on calcareous soils that are core bristlecone pine habitat. Limber pine is successfully "leap-frogging" over bristlecone pine, probably because of its strong dispersal advantage and broader tolerances for establishment. This early-stage dominance indicates the potential for the species composition of treeline to change in response to climate change. More broadly, it shows how species differences in dispersal and establishment may result in future communities with very different specific composition.

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Transpiration dynamics support resource partitioning in African savanna trees and grasses

Cited by 30 publications

References 31 publications

Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa

Strategies trees use to overcome seasonal water limitation in an agroforestry system in semiarid West Africa

Assessing the Roles of Fire Frequency and Precipitation in Determining Woody Plant Expansion in Central U.S. Grasslands

Leap frog in slow motion: Divergent responses of tree species and life stages to climatic warming in Great Basin subalpine forests

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