Recent advance of forest–grassland ecotones in southwestern Yukon

Conway, Alexandra J.; Danby, Ryan K.

doi:10.1139/cjfr-2013-0429

Cited by 18 publications

(17 citation statements)

References 45 publications

(56 reference statements)

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“…This reflects a correlation between white spruce recruitment and warm summer temperatures at all time lags represented by our life stages (e.g., 10-100 years), and stands in contrast to the weakly negative relationship between establishment and temperature reported from sites in southwestern Yukon (Conway & Danby, 2014). This reflects a correlation between white spruce recruitment and warm summer temperatures at all time lags represented by our life stages (e.g., 10-100 years), and stands in contrast to the weakly negative relationship between establishment and temperature reported from sites in southwestern Yukon (Conway & Danby, 2014).…”

Section: Discussionmentioning

confidence: 59%

“…In our study, all life stages responded positively to July maximum temperature. This reflects a correlation between white spruce recruitment and warm summer temperatures at all time lags represented by our life stages (e.g., 10-100 years), and stands in contrast to the weakly negative relationship between establishment and temperature reported from sites in southwestern Yukon (Conway & Danby, 2014). A recent study of temperate forest species in the eastern U.S. found higher temperature and precipitation optima for juveniles than for mature individuals in most species analyzed, consistent with a scenario of greater species turnover in warmer areas of the range, rather than a migration of species to cooler areas (Zhu, Woodall, Ghosh, Gelfand, & Clark, 2014).…”

Section: Discussionmentioning

confidence: 59%

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Warming drives a front of white spruce establishment near western treeline, Alaska

Miller

Wilson

Sherriff

et al. 2017

Global Change Biology

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Regional warming has led to increased productivity near the boreal forest margin in Alaska. To date, the effects of warming on seedling recruitment have received little attention, in spite of forecasted forest expansion. Here, we used stand structure and environmental data from 95 white spruce (Picea glauca) plots sampled across a longitudinal gradient in southwest Alaska to explore factors influencing spruce establishment and recruitment near western treeline. We used total counts of live seedlings, saplings, and trees, representing five life stages, to evaluate whether geospatial, climate, and measured plot covariates predicted abundance, using current abundance distributions as a surrogate for climate conditions in the past. We used generalized linear models to test the null hypothesis that conditions favorable for recruitment were similar along the environmental gradient represented by longitude, by exploring relationships between per-plot counts of each life stage and the covariates hypothesized to affect abundance. We also examined the relationship between growing degree days (GDD) and seedling establishment over a period of three decades using tree-ring chronologies obtained from cores taken at a subset of our sites (n = 30). Our results indicated that seedling, sapling, and tree abundance were positively correlated with temperature across the study area. The response to longitude was mixed, with earlier life stages (seedlings, saplings) most abundant at the western end of the gradient, and later life stages (trees) most abundant to the east. The differential relationship between longitude and life-stage abundance suggests a moving front of white spruce establishment through time, driven by changes in environmental conditions near the species' western range limit. Likewise, we found a positive relationship between periods of seedling establishment and GDD, suggesting that longer summers and/or greater heat accumulation might enhance establishment, consistent with the positive relationship we found between life-stage abundance and temperature.

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Section: Discussionmentioning

confidence: 59%

Section: Discussionmentioning

confidence: 59%

Warming drives a front of white spruce establishment near western treeline, Alaska

Miller

Wilson

Sherriff

et al. 2017

Global Change Biology

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“…The climate in all regions is continental, and as a consequence tree growth and forest succession are slow. The effects of climate change in these regions in the last 50 years are significant but not large (Conway and Danby 2014). From 1980-2014 the change of July summer temperature at the Haines Junction weather station has been 0.021 °C increase per year, a slight but significant change (p = 0.04).…”

Section: The Study Areasmentioning

confidence: 95%

Predicting white spruce cone crops in the boreal forests of southern and central Yukon

et al. 2017

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18White spruce cone crops were measured at five regional centers in the southern and central 19Yukon for 30 years at one site from 1986 to 2015 and at four other sites from 9-11 years to select 20 the best climatic model that use cues from growing season temperature and rainfall to predict the 21 size of cone crops. We evaluated six climate models that use summer temperature and rainfall of 22 years t-1, and t-2 to predict cone crops in year t. July temperatures provided the best predictors of 23 white spruce cone crops and no rainfall variable was related to the size of cone crops. We 24 explored three variants of July temperatures: mean temperature, degree-days > 5°C, and 25 maximum temperatures. For each of these we used the ∆T model that uses the difference in the 26July temperature measures of year t-1 and t-2. We compared the resulting 6 models with AIC c to 27 Cone crops of white spruce (Picea glauca (Moench) Voss) in the boreal forest region 37 vary dramatically from year to year. A combination of climatic events are usually put forward to 38 explain these variations in plant production (Juday et al. 2003; Messaoud et al. 2007; Allen et al. 39 2014, Pearse et al. 2016. In 2012 we produced a quantitative model for the prediction of white 40 spruce cone crops in the Yukon from climatic factors one and two years prior to the crop (Krebs 41 et al. 2012). After our analysis, a new model, the ∆T model, for cone crops was proposed by 42 Kelly et al. (2013). This model is based solely on temperature in the growing season of the 43 previous 2 years, and is thus a conceptually simple model suggesting the cues for the response of 44 masting trees to temperature variations. 45The new ∆T model is particularly attractive as an alternative model because of its 46 simplicity, involving only summer temperatures, and because as Kelly et al. (2013) show the ∆T 47 model fits a variety of masting records from many plant species and thus achieves a level of 48 generality often lacking in climatic models of biological events. Climatic models are particularly 49 difficult to construct because of the plethora of variables possible, so that development of models 50 can too often turn into a fishing expedition. 51We began measuring white spruce cone production in the Kluane region in 1986 because 52 of the ecological implications of highly variable seed crops for seed-eating mammals and birds. 53We have added data here from the Yukon Community Ecological Monitoring Program (CEMP) 54 for sites at Faro (2007Faro ( -2015, Mayo, Whitehorse, and Watson Lake (all 2005-2015). The utility 55 of a model of masting is that natural resource managers and government seed collection agencies 56 can use it to anticipate years of high and low seed production, particularly if the model 57 predictions can be generalized over large spatial areas. This paper reports on the statistical associations between climatic measurements and 59 white spruce cone production for all these CEMP regions in the southern and central Yukon. 60In a broa...

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“…However, xeric Beringian grasslands may be as vulnerable to climate change as other Arctic ecosystems. Conway and Danby [47] found a reduction in the extent of grassland due to forest encroachment, particularly on flat terrain and south-facing slopes near Kluane Lake, Yukon. Although more restricted than other arctic ecosystems, these grasslands host a unique species assemblage.…”

Section: Discussionmentioning

confidence: 99%

Phylogeography of higher Diptera in glacial and postglacial grasslands in western North America

et al. 2019

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BackgroundPleistocene glaciations have had an important impact on the species distribution and community composition of the North American biota. Species survived these glacial cycles south of the ice sheets and/or in other refugia, such as Beringia. In this study, we assessed, using mitochondrial DNA from three Diptera species, whether flies currently found in Beringian grasslands (1) survived glaciation as disjunct populations in Beringia and in the southern refugium; (2) dispersed northward postglacially from the southern refugium; or (3) arose by a combination of the two. Samples were collected in grasslands in western Canada: Prairies in Alberta and Manitoba; the Peace River region (Alberta); and the southern Yukon Territory. We sequenced two gene regions (658 bp of cytochrome c oxidase subunit I, 510 bp of cytochrome b) from three species of higher Diptera: one with a continuous distribution across grassland regions, and two with disjunct populations between the regions. We used a Bayesian approach to determine population groupings without a priori assumptions and performed analysis of molecular variance (AMOVA) and exact tests of population differentiation (ETPD) to examine their validity. Molecular dating was used to establish divergence times.ResultsTwo geographically structured populations were found for all species: a southern Prairie and Peace River population, and a Yukon population. Although AMOVA did not show significant differentiation between populations, ETPD did. Divergence time between Yukon and southern populations predated the Holocene for two species; the species with an ambiguous divergence time had high haplotype diversity, which could suggest survival in a Beringian refugium.ConclusionsPopulations of Diptera in Yukon grasslands could have persisted in steppe habitats in Beringia through Pleistocene glaciations. Current populations in the region appear to be a mix of Beringian relict populations and, to a lesser extent, postglacial dispersal northward from southern prairie grasslands.

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Recent advance of forest–grassland ecotones in southwestern Yukon

Cited by 18 publications

References 45 publications

Warming drives a front of white spruce establishment near western treeline, Alaska

Warming drives a front of white spruce establishment near western treeline, Alaska

Predicting white spruce cone crops in the boreal forests of southern and central Yukon

Phylogeography of higher Diptera in glacial and postglacial grasslands in western North America

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