Effects of sheep grazing and temporal variability on population dynamics of the clonal herb Geranium sylvaticum in an alpine habitat

Evju, Marianne; Halvorsen, Rune; Rydgren, Knut; Austrheim, Gunnar; Mysterud, Atle

doi:10.1007/s11258-011-9906-2

Cited by 13 publications

(19 citation statements)

References 55 publications

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“…The contrast between no sheep and low or high densities of sheep is greater than the variation in growth seen within the range of summer temperature over the past 50 years, whilst the contrast between low and high sheep densities becomes important at higher altitudes and lower temperatures. The greater importance of herbivore density over climate in determining tree radial growth contrasts with the dominant role of climate over herbivore density in determining the population dynamics of herb species (Evju et al. 2010, in press).…”

Section: Discussionmentioning

confidence: 99%

Browsing interacts with climate to determine tree-ring increment

et al. 2011

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Summary 1.A warming climate has been linked to shifts in plant distribution and growth. The relationship between climate and growth is used to infer past climate conditions within dendrochronological studies. However, browsing may interact with climate to determine growth, yet the impact of large herbivores on tree-ring growth series is largely unknown. 2. Here, we disentangle the interactions between climate and herbivory in determining plant growth at the upper distribution limit of mountain birch (Betula pubescens ssp. czerepanovii). 3. Stem discs of 206 birch were sampled within an altitudinal tree line ecotone in southern Norway, after 9 years of experimental browsing at three sheep densities (unbrowsed, low and high with 0, 25 and 80 sheep km )2 ). Annual radial growth was measured using digital microscopy and related to summer temperatures, altitude and sheep density. 4. Radial growth was negatively related to altitude and related to summer temperature in a nonlinear fashion, increasing from low temperatures and saturating and decreasing at high temperatures. However, the variation between browsing treatments overrode the influence of interannual temperature in determining growth. Increasing sheep densities limited radial growth and interacted with both temperature and altitude. The temperature of peak radial growth increased at higher densities of sheep, and growth was less limited by altitude at low sheep density. 5. This demonstrates that browsing interacts with temperature to determine the growth of mountain birch at the upper distribution limit and that the variation in growth linked to sheep density was greater than that linked to the 50-year range of interannual temperatures. The ability of browsing to affect radial growth has important implications for the use of dendrochronology to infer past climatic conditions, where samples are taken from regions that have undergone past land-use change.

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Section: Discussionmentioning

confidence: 99%

Browsing interacts with climate to determine tree-ring increment

et al. 2011

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“…This area is in the sub‐continental alpine climatic zone (Førland ). It has an annual precipitation of ∼ 1000 mm (Evju et al ) and a mean annual temperature of −0.7°C. During the study period, the mean summer (June–August) temperature was 8.9°C (Speed et al ).…”

Section: Methodsmentioning

confidence: 99%

“…Th is area is in the sub-continental alpine climatic zone (F ø rland 1993). It has an annual precipitation of ∼ 1000 mm (Evju et al 2011) and a mean annual temperature of Ϫ 0.7 ° C. During the study period, the mean summer (June -August) temperature was 8.9 ° C (Speed et al 2012). Th e dominant bedrock is metaarkose, which is arkose that has been welded or recrystallized by metamorphosis to resemble granite (Sigmond 1998), and the soil is relatively dry, productive and moderately base-rich .…”

Section: Study Areamentioning

confidence: 99%

Temporal scales of density‐dependent habitat selection in a large grazing herbivore

Blix

Mysterud

Loe

et al. 2014

Oikos

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Habitat selection is a density‐dependent process, but little is known regarding how this relationship may vary across different temporal scales. Over long time scales, grazing shapes the structure, diversity and functioning of terrestrial ecosystems, and grazing‐induced changes in forage production over time are likely to affect the level of density dependence in habitat selection. In this fully‐replicated, landscape‐scale experiment, we investigated how density‐dependent habitat selection by a large grazing herbivore, sheep Ovis aries, develops over the time scale of a decade. We also address an often‐neglected challenge in habitat selection studies; namely, whether there is variation in use within a particular habitat or vegetation type and why. We found clear evidence of density dependence in habitat selection, with a wider use of habitats at high density. Despite a change in the standing biomass of high‐productivity vegetation at high herbivore density over the years, with herb biomass declining and graminoid biomass increasing, there was no clear evidence that these grazing‐induced changes in habitat over the years were strong enough to affect the level of density‐dependent habitat selection. The difference in selection for high versus low‐productivity habitats remained similar, despite annual fluctuations in the strength of selection. We found strong variation in selection within each vegetation type, even when vegetation types were mapped at a fine‐resolution scale. Our study shows that despite the interactive effects of herbivores and habitats, they are not always sufficiently strong enough to affect the level of density‐dependent habitat selection.

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“…Grazing and the increased isolation of stands have the potential to influence genotypic diversity directly through decreased population size, and indirectly through reduction in interpopulation gene flow or alteration of reproductive tactics. This influence will be greatest if, as demonstrated in other terrestrial systems, grazing promotes asexual reproduction (albeit through vegetative spread rather than apomictic parthenogenesis) (Evju et al, 2011) and/or disrupts plant-pollinator interactions (Yoshihara et al, 2008;Kimoto et al, 2012). Nevertheless, it is also possible that, prior to European settlement in Australia, many arid-zone species already exhibited low levels of connectedness, reflecting the spatially patchy distribution of suitable habitat (Hopper, 1979;Coates, 2000;Byrne & Hopper, 2008;O'Brien, Denham & Ayre, 2014) and also the presence of poorly understood landscape features that may act as barriers to dispersal or demarcate strongly contrasting but cryptic environmental conditions, such as those created by Australia's complex system of inland rivers.…”

Section: Introductionmentioning

confidence: 99%

“…Such taxa may therefore be less resilient to disturbance than obligately sexual congeners that occur in more mesic or temperate areas in Australia. This influence will be greatest if, as demonstrated in other terrestrial systems, grazing promotes asexual reproduction (albeit through vegetative spread rather than apomictic parthenogenesis) (Evju et al, 2011) and/or disrupts plant-pollinator interactions (Yoshihara et al, 2008;Kimoto et al, 2012). E-mail: dave.roberts@uwa.edu.au The links between resilience and reproductive mode and contemporary and historical processes are poorly understood for most of Australia's arid and semi-arid plant species.…”

Section: Introductionmentioning

confidence: 99%

Varying levels of clonality and ploidy create barriers to gene flow and challenges for conservation of an Australian arid-zone ecosystem engineer,Acacia loderi

Roberts

Forrest

Denham

et al. 2015

Biol. J. Linn. Soc.

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Acacia loderi, the ecosystem engineer of the endangered Acacia loderi Shrublands in arid eastern Australia, spans a persistent (> 15 000 year) but poorly studied landscape feature, the Darling River. We investigated the genetic structure of 19 stands of eight to > 1000 plants separated by < 300 km to test for variation in life histories between semi-arid and arid stands to the east and west of the Darling River, respectively. Eight of nine stands east of the Darling were exclusively sexual, whereas most of those to the west were clonal. Three western stands were monoclonal, two were polyploid, and one was a diverse mix of diploid and triploid phenotypes. Bayesian analysis revealed a complex genetic structure within the western stands, whereas the eastern stands formed only two genetic clusters. Conservation of small stands may require augmentation of genotypic diversity. However, most genotypic diversity resides within the eastern stands. Although arid zone stands of A. loderi are not always clonal, clonality and polyploidy are more common in the arid west. Clear demarcation of life histories either side of the Darling River may reflect ancient or contemporary effects of physical disturbance associated with the river channel, or cryptic environmental differences, with sexual and asexual reproduction, respectively, at a selective premium in the semi-arid east and arid west. The restricted distribution of clones and variation in clonality and polyploidy suggests that smaller stands may be vulnerable and warrant individual management.

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Effects of sheep grazing and temporal variability on population dynamics of the clonal herb Geranium sylvaticum in an alpine habitat

Cited by 13 publications

References 55 publications

Browsing interacts with climate to determine tree-ring increment

Browsing interacts with climate to determine tree-ring increment

Temporal scales of density‐dependent habitat selection in a large grazing herbivore

Varying levels of clonality and ploidy create barriers to gene flow and challenges for conservation of an Australian arid-zone ecosystem engineer,Acacia loderi

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