Effects of Warming on Shrub Abundance and Chemistry Drive Ecosystem-Level Changes in a Forest–Tundra Ecotone

Kaarlejärvi, Elina; Baxter, Robert C.; Hofgaard, Annika; Hytteborn, Håkan; Khitun, Olga KhitunO.; Molau, Ulf; Sjögersten, Sofie; Wookey, Philip A.; Olofsson, Johan

doi:10.1007/s10021-012-9580-9

Cited by 50 publications

(61 citation statements)

References 56 publications

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“…; Kaarlejärvi et al . ; Kaarlejärvi, Hoset & Olofsson ). Similar increases of E. nigrum above the tree line were found in a long‐term monitoring study in northern Sweden (Wilson & Nilsson ).…”

Section: Discussionmentioning

confidence: 99%

Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range

et al. 2017

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Summary One of the most palpable effects of warming in Arctic ecosystems is shrub expansion above the tree line. However, previous studies have found that reindeer can influence plant community responses to warming and inhibit shrubification of the tundra.We revisited grazed (ambient) and ungrazed study plots (exclosures), at the southern as well as the northern limits of the Swedish alpine region, to study long‐term grazing effects and vegetation changes in response to increasing temperatures between 1995 and 2011, in two vegetation types (shrub heath and mountain birch forest).In the field layer at the shrub heath sites, evergreen dwarf shrubs had increased in cover from 26% to 49% but were unaffected by grazing. Deciduous dwarf and tall shrubs also showed significant, though smaller, increases over time. At the birch forest sites, the increase was similar for evergreen dwarf shrubs (20–48%) but deciduous tall shrubs did not show the same consistent increase over time as in the shrub heath.The cover and height of the shrub layer were significantly greater in exclosures at the shrub heath sites, but no significant treatment effects were found on species richness or diversity.July soil temperatures and growing season thawing degree days (TDD) were higher in exclosures at all but one site, and there was a significant negative correlation between mean shrub layer height and soil TDD at the shrub heath sites. Synthesis. This study shows that shrub expansion is occurring rapidly in the Scandes mountain range, both above and below the tree line. Tall, deciduous shrubs had benefitted significantly from grazing exclosure, both in terms of cover and height, which in turn lowered summer soil temperatures. However, the overriding vegetation shift across our sites was the striking increase in evergreen dwarf shrubs, which were not influenced by grazing. As the effects of an increase in evergreen dwarf shrubs and more recalcitrant plant litter may to some degree counteract some of the effects of an increase in deciduous tall shrubs, herbivore influence on shrub interactions is potentially of great importance for shaping arctic shrub expansion and its associated ecosystem effects.

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Section: Discussionmentioning

confidence: 99%

Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range

et al. 2017

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“…The dynamics observed during the past 15 years suggests that warmer temperatures increase the capacity of rstb.royalsocietypublishing.org Phil Trans R Soc B 368: 20120486 plants to regrow following herbivore outbreaks. Increased temperatures can also decrease nutrient levels and influence the levels of defence substances in dwarf-shrub species [85]. The devastating browning of E. hermaphroditum seems to have been a result of climatic conditions not only favouring both the moth and the pathogen, but also contributing to a dramatic alteration of the nutrient source -sink dynamic in the host plant.…”

Section: Discussionmentioning

confidence: 99%

Complex biotic interactions drive long-term vegetation dynamics in a subarctic ecosystem

Olofsson

Beest

Ericson

2013

Phil. Trans. R. Soc. B

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Predicting impacts of global warming requires understanding of the extent to which plant biomass and production are controlled by bottom-up and top-down drivers. By annually monitoring community composition in grazed control plots and herbivore-free exclosures at an Arctic location for 15 years, we detected multiple biotic interactions. Regular rodent cycles acted as pulses driving synchronous fluctuations in the biomass of field-layer vegetation; reindeer influenced the biomass of taller shrubs, and the abundance of plant pathogenic fungi increased when densities of their host plants increased in exclosures. Two outbreaks of geometrid moths occurred during the study period, with contrasting effects on the field layer: one in 2004 had marginal effects, while one in 2012 severely reduced biomass in the control plots and eliminated biomass that had accumulated over 15 years in the exclosures. The latter was followed by a dramatic decline of the dominant understory dwarf-shrub Empetrum hermaphroditum , driven by an interaction between moth herbivory on top buds and leaves, and increased disease severity of a pathogenic fungus. We show that the climate has important direct and indirect effects on all these biotic interactions. We conclude that long time series are essential to identify key biotic interactions in ecosystems, since their importance will be influenced by climatic conditions, and that manipulative treatments are needed in order to obtain the mechanistic understanding needed for robust predictions of future ecosystem changes and their feedback effects.

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“…They attributed the decline in response long-term to a shift in the competitive balance of species [22]. It is also possible that initial warming increases nutrient availability and in turn plant productivity, but over time plants grow and store these nutrients in their biomass, making the nutrients less available in the soil [23, 24]. As the nutrients become less available for plant uptake, plant growth will decline [23, 24].…”

Section: Introductionmentioning

confidence: 99%

“…It is also possible that initial warming increases nutrient availability and in turn plant productivity, but over time plants grow and store these nutrients in their biomass, making the nutrients less available in the soil [23, 24]. As the nutrients become less available for plant uptake, plant growth will decline [23, 24]. These nutrients will eventually return to the soil through litter decomposition, but the time-scale of nutrient cycling may be much longer depending on shifts in community composition (i.e, shifting from a graminoid-dominated community to a shrub-dominated community, [8]).…”

Section: Introductionmentioning

confidence: 99%

Diminished Response of Arctic Plants to Warming over Time

2015

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The goal of this study is to determine if the response of arctic plants to warming is consistent across species, locations and time. This study examined the impact of experimental warming and natural temperature variation on plants at Barrow and Atqasuk, Alaska beginning in 1994. We considered observations of plant performance collected from 1994–2000 “short-term” and those from 2007–2012 “long-term”. The plant traits reported are the number of inflorescences, inflorescence height, leaf length, and day of flower emergence. These traits can inform us about larger scale processes such as plant reproductive effort, plant growth, and plant phenology, and therefore provide valuable insight into community dynamics, carbon uptake, and trophic interactions. We categorized traits of all species monitored at each site into temperature response types. We then compared response types across traits, plant growth forms, sites, and over time to analyze the consistency of plant response to warming. Graminoids were the most responsive to warming and showed a positive response to temperature, while shrubs were generally the least responsive. Almost half (49%) of response types (across all traits, species, and sites combined) changed from short-term to long-term. The percent of plants responsive to warming decreased from 57% (short-term) to 46% (long-term). These results indicate that the response of plants to warming varies over time and has diminished overall in recent years.

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Effects of Warming on Shrub Abundance and Chemistry Drive Ecosystem-Level Changes in a Forest–Tundra Ecotone

Cited by 50 publications

References 56 publications

Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range

Expansion of deciduous tall shrubs but not evergreen dwarf shrubs inhibited by reindeer in Scandes mountain range

Complex biotic interactions drive long-term vegetation dynamics in a subarctic ecosystem

Diminished Response of Arctic Plants to Warming over Time

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