Canopy gaps facilitate upslope shifts in montane conifers but not in temperate deciduous trees in the Northeastern United States

Tourville, Jordon; Wason, Jay W.; Dovčiak, Martin

doi:10.1111/1365-2745.13993

Cited by 16 publications

(20 citation statements)

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“…(Greenwood et al, 2014; Lu et al, 2021; Sittaro et al, 2017; Zhu et al, 2012). Given that tree encroachment may also be limited by seed dispersal, and the time needed for seedlings to mature and recruit into larger size classes, we emphasize that care should be taken when using treeline positions as a direct bellwether for ecosystem response to climate change (Sittaro et al, 2017; Tourville et al, 2022).…”

Section: Discussionmentioning

confidence: 99%

“…A large body of research has been devoted to detecting shifts in tree species ranges, possible proximal causes of such shifts, and their ecosystem level consequences (Iverson et al, 2019; O'Sullivan et al, 2021; Prasad et al, 2020; Wason & Dovciak, 2017). Elevational vegetation gradients along mountain slopes covary with temperature (in addition to variation in precipitation and soils) and thus mountains can be used as natural study regions to detect early changes in forest communities caused by changing climate (Beckage et al, 2008; Brown & Vellend, 2014; Harsch et al, 2009; Jump et al, 2009; O'Sullivan et al, 2021; Tourville et al, 2022). This is also true of mountains in the northeastern United States, which are expected to experience increased temperatures (particularly during winter months) and fluctuating precipitation regimes over the next several decades (Burakowski et al, 2022; Janowiak et al, 2018; Wason, Bevilacqua, & Dovciak, 2017).…”

Section: Introductionmentioning

confidence: 99%

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Forests on the move: Tracking climate‐related treeline changes in mountains of the northeastern United States

Tourville,

Publicover,

Dovciak

2023

Journal of Biogeography

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AimAlpine treeline ecotones are influenced by environmental drivers and are anticipated to shift their locations in response to changing climate. Our goal was to determine the extent of recent climate‐induced treeline advance in the northeastern United States, and we hypothesized that treelines have advanced upslope in complex ways depending on treeline structure and environmental conditions.LocationWhite Mountain National Forest (New Hampshire) and Baxter State Park (Maine), USA.TaxonHigh‐elevation tree species—Abies balsamea, Picea mariana and Betula cordata.MethodsWe compared current and historical high‐resolution aerial imagery to quantify the advance of treelines over the last four decades, and link treeline changes to treeline form (demography) and environmental drivers. Spatial analyses of the aerial images were coupled with ground surveys of forest vegetation and topographical features to ground‐truth treeline classification and provide information on treeline demography and additional potential drivers of treeline locations. We used multiple linear regression models to examine the importance of both topographic and climatic variables on treeline advance.ResultsRegional treelines have significantly shifted upslope over the past several decades (on average by 3 m/decade). Gradual diffuse treelines (characterized by declining tree density) showed significantly greater upslope shifts (5 m/decade) compared to other treeline forms, suggesting that both climate warming and treeline demography are important correlates of treeline shifts. Topographical features (slope, aspect) as well as climate (accumulated growing degree days, AGDD) explained significant variation in the magnitude of treeline advance (R2 = 0.32).Main ConclusionsThe observed advance of treelines is consistent with the hypothesis that climate warming induces upslope treeline shifts. Overall, our findings suggest that gradual diffuse treelines at high elevations may be indicative of climate warming more than other alpine treeline ecotones and thus they can inform us about past and ongoing climatic changes.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Forests on the move: Tracking climate‐related treeline changes in mountains of the northeastern United States

Tourville,

Publicover,

Dovciak

2023

Journal of Biogeography

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“…Daily values were extracted for the entire year which the observation was recorded allowing us to calculate daily, monthly, seasonal, and annual mean values for each climate variable. Accumulated growing degree days (AGDD) were also derived from DAYMET temperature data using Equation 1 (Gavin et al, 2008;Wason and Dovciak, 2017;Tourville et al, 2022):…”

Section: Data Preparationmentioning

confidence: 99%

Distinct latitudinal patterns of shifting spring phenology across the Appalachian Trail Corridor

Tourville,

Murray,

Nelson

2023

Preprint

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Warming associated with climate change will likely continue to advance the onset of spring phenology for many forest plants across the eastern United States. Understory forbs and spring ephemerals which fix a disproportionate amount of carbon during spring may be negatively affected by earlier canopy closure (i.e., phenological windows), however, information on the spatial patterns of phenological change for these communities is still lacking. To assess the potential for changes in spring phenological windows we synthesized observations from the Appalachian Mountain Club’s (AMC) Mountain Watch (MW) project, the National Phenology Network (NPN), and AMC’s iNaturalist projects between 2004 and 2022 (n = 118,250) across the length of the Appalachian Trail (AT) Corridor (34°N-46°N latitude). We used hierarchical Bayesian modeling to examine the sensitivity of day of year of flowering and leaf-out for 11 understory species and 14 canopy tree species to mean spring temperature (April-June). We conducted analyses across the AT Corridor, partitioned by regions of 4° latitude (South, Mid-Atlantic, and North). Spring phenologies for both understory plants and canopy trees advanced with warming (∼6 days/°C and ∼3 days/°C, respectively). However, sensitivity of each group varied by latitude, with phenology of trees and understory plants advancing to a greater degree in the mid-Atlantic region (∼10 days/°C) than the southern or northern regions (∼5 days/°C). While we find evidence that phenological windows remain stable in southern and mid-Atlantic portions of the AT, we observed an expansion of the spring phenological window in the north where there was greater understory temperature sensitivity compared to trees (∼1.6 days/°C). Our analyses indicate differential sensitivity of forest plant phenology to potential warming across a large latitudinal gradient in the eastern United States. Further, evidence for a temperature-driven expansion of the spring phenological window suggests a potential beneficial effect for understory plants, although phenological mismatch with potential pollinators is possible. Using various extensive citizen-science derived datasets allows us to synthesize regional- and continental-scale data to explore spatial and temporal trends in spring phenology related to warming. Such data can help to standardize approaches in phenological research and its application to forest climate resiliency.

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“…The formation of canopy gaps are generally considered to have positive effect on seedlings' growth, due to the alleviated limitation of light availability (Alvarez-Clare and Avalos, 2007;Westerband and Horvitz, 2015). However, what species of tree are recruited and be more stimulated by increased light, becomes a critical determinant for the forest recovery and subsequent trajectory of natural regeneration after disturbance, in the understory of tropical forest (Matsuo et al, 2021;Tourville et al, 2022;Wang et al, 2022).…”

Section: Introductionmentioning

confidence: 99%

Light effects on seedling growth in simulated forest canopy gaps vary across species from different successional stages

Zhou¹,

Thakur²,

Jia³

et al. 2023

Front. For. Glob. Change

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Tropical forests continue to suffer from various kinds of disturbances in the Anthropocene. An immediate impact of disturbances on forest ecosystems is the creation of numerous large and small canopy gaps, which dramatically affect forest structure and function. Yet, we know little about the effect of canopy gaps on forest successional trajectory. More specifically, the responses of seedlings from different successional stages to increased light intensity under large and small canopy gaps in understory remain unclear. In this study, dominant tree seedlings from early-, mid-, and late-successional stages were selected, respectively from a tropical montane forest in Hainan Island, China to study their growth rate, biomass and traits. Our results showed that the light condition under small canopy gaps (SG, 10–15% of full sunlight) and large canopy gaps (LG, 40–50% of full sunlight) induced greater increment of relative growth rates for seedlings from early- and mid-successional stages relative to that in late-successional stage. Both SG and LG also significantly increased photosynthesis rate, leaf area (LA), light saturation point (LSP), root mass ratio (RMR) and root: shoot ratio, but decreased specific leaf area (SLA) of seedlings across successional stages. Tree seedlings from the early-successional stage displayed the greatest decrease in leaf mass ratio, increase in LA, LSP, and RMR, in comparison to those from mid- and late- successional stages. Light condition and SLA were the most important factors for seedlings’ relative growth rate across successional stages. SLA connected the interaction between the light condition and successional stage on seedlings’ growth, thereby jointly explaining the 93% variation of seedlings’ growth, combining with area-based light saturated rate of CO2 assimilation. Our study highlights the distinct effect of disturbance-induced canopy gaps on seedling regeneration in the understory in tropical forest due to the variation of light intensity. We suspect that the seedlings from late-successional stage will recover relatively slow after disturbances causing canopy losses, which can have detrimental impacts on structure feature and successional trajectory in tropical forest, as well as forest-based ecosystem services.

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Canopy gaps facilitate upslope shifts in montane conifers but not in temperate deciduous trees in the Northeastern United States

Cited by 16 publications

References 100 publications

Forests on the move: Tracking climate‐related treeline changes in mountains of the northeastern United States

Forests on the move: Tracking climate‐related treeline changes in mountains of the northeastern United States

Distinct latitudinal patterns of shifting spring phenology across the Appalachian Trail Corridor

Light effects on seedling growth in simulated forest canopy gaps vary across species from different successional stages

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