Browsing by Author "Montgomery, Rebecca A"
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Item Biomass growth response to spatial pattern of variable-retention harvesting in a northern Minnesota pine ecosystem(2014) Palik, Brian J; Montgomery, Rebecca A; Reich, Peter B; Boyden, Suzanne BVariable-retention harvesting (VRH) is an approach for sustaining complex structure in managed forests. A criticism of VRH is that ecological benefits may come at a cost of reduced growth of regeneration, due to competition with residual trees. However, the spatial pattern of retention, i.e., dispersed or aggregated, in VRH systems can be manipulated to minimize suppression of regeneration, and resource limitation to regeneration might be mitigated by reduction of woody shrubs. Continued growth of the residual cohort will compensate for growth reduction of regeneration, although this may differ with retention pattern. We examined aboveground whole-stand biomass growth of trees in a VRH experiment in Pinus resinosa forest in Minnesota, USA. Treatments included dispersed retention, aggregated retention, and an uncut control, as well as a shrub treatment (reduced density or ambient). We addressed the following hypotheses: (1) biomass growth of a cohort of planted pine seedlings will be highest with aggregated rather than dispersed retention, (2) biomass growth of the planted seedlings will increase with shrub reduction, and (3) biomass growth of the residual overstory will be higher with dispersed rather than aggregated retention. Aboveground biomass growth of the planted pines ranged from 0.4 kg·ha−1·yr−1 in the overstory-control–ambient-shrub treatment to 23 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. The difference between the control and the retention treatments was significant (P < 0.0001), but not between dispersed and aggregated retention (P = 0.97). Thus, our first hypothesis was not supported. In all treatments, biomass growth was significantly higher (>100% increase) with shrub reduction (P = 0.001), supporting our second hypothesis. Biomass growth of residual trees ranged from 2404 kg·ha−1·yr−1 in the uncut-control–ambient-shrub treatment to 1043 kg·ha−1·yr−1 in the aggregated-retention–shrub-reduction treatment. Differences were significant between the control and retention treatments (P = 0.003), and marginally higher with dispersed vs. aggregated retention (P = 0.09), lending support to our third hypothesis. Our results suggest that managers have flexibility in application of VRH and can expect similar stand-level biomass growth of planted regeneration regardless of retention pattern, but somewhat higher stand-level biomass growth of retained trees with dispersed retention.Item Boreal and temperate trees show strong acclimation of respiration to warming(Nature Publishing Group, 2016) Reich, Peter B; Sendall, Kerrie M; Stefanski, Artur; Wei, Xiaorong; Rich, Roy L; Montgomery, Rebecca APlant respiration results in an annual flux of carbon dioxide (CO2) to the atmosphere that is six times as large as that due to the emissions from fossil fuel burning, so changes in either will impact future climate. As plant respiration responds positively to temperature, a warming world may result in additional respiratory CO2 release, and hence further atmospheric warming1, 2. Plant respiration can acclimate to altered temperatures, however, weakening the positive feedback of plant respiration to rising global air temperature3, 4, 5, 6, 7, but a lack of evidence on long-term (weeks to years) acclimation to climate warming in field settings currently hinders realistic predictions of respiratory release of CO2 under future climatic conditions. Here we demonstrate strong acclimation of leaf respiration to both experimental warming and seasonal temperature variation for juveniles of ten North American tree species growing for several years in forest conditions. Plants grown and measured at 3.4 °C above ambient temperature increased leaf respiration by an average of 5% compared to plants grown and measured at ambient temperature; without acclimation, these increases would have been 23%. Thus, acclimation eliminated 80% of the expected increase in leaf respiration of non-acclimated plants. Acclimation of leaf respiration per degree temperature change was similar for experimental warming and seasonal temperature variation. Moreover, the observed increase in leaf respiration per degree increase in temperature was less than half as large as the average reported for previous studies4, 7, which were conducted largely over shorter time scales in laboratory settings. If such dampening effects of leaf thermal acclimation occur generally, the increase in respiration rates of terrestrial plants in response to climate warming may be less than predicted, and thus may not raise atmospheric CO2 concentrations as much as anticipated.Item Forests and Biodiversity cleaned biomass survey data 2013-2018(2021-02-12) Kothari, Shan; Montgomery, Rebecca A; Cavender-Bares, Jeannine; kotha020@umn.edu; Kothari, Shan; University of Minnesota Cavender-Bares Lab; University of Minnesota Montgomery Lab; Cedar Creek Ecosystem Science ReserveThis dataset includes annual growth survey measurements from the Forests and Biodiversity 1 (e271) experiment at Cedar Creek Ecosystem Science Reserve in East Bethel, MN. The dataset also includes a script that allows users to reproduce the figures and statistics reported in the cited paper. This version of the dataset is specifically meant to support the inferences in that paper, rather than serving as the version of record. Please consult the Cedar Creek Data Catalog (https://www.cedarcreek.umn.edu/research/data) to find the authoritative version to be used for general purposes.Item Geographic range predicts photosynthetic and growth response to warming in co-occurring tree species(Nature Publishing Group, 2015) Reich, Peter B; Sendall, Kerrie M; Rice, Karen; Rich, Roy L; Stefanski, Artur; Hobbie, Sarah E; Montgomery, Rebecca APopulations near the warm edge of species ranges may be particularly sensitive to climate change, but lack of empirical data on responses to warming represents a key gap in understanding future range dynamics. Herein we document the impacts of experimental warming on the performance of 11 boreal and temperate forest species that co-occur at the ecotone between these biomes in North America. We measured in situ net photosynthetic carbon gain and growth of >4,100 juvenile trees from local seed sources exposed to a chamberless warming experiment that used infrared heat lamps and soil heating cables to elevate temperatures by +3.4 °C above- and belowground for three growing seasons across 48 plots at two sites. In these ecologically realistic field settings, species growing nearest their warm range limit exhibited reductions in net photosynthesis and growth, whereas species near their cold range limit responded positively to warming. Differences among species in their three-year growth responses to warming parallel their photosynthetic responses to warming, suggesting that leaf-level responses may scale to whole-plant performance. These responses are consistent with the hypothesis, from observational data and models, that warming will reduce the competitive ability of currently dominant southern boreal species compared with locally rarer co-occurring species that dominate warmer neighbouring regions. © 2015 Macmillan Publishers Limited. All rights reserved.Item Is it getting hot in here? Adjustment of hydraulic parameters in six boreal and temperate tree species after 5 years of warming(Wiley, 2016) Mculloh, Katherine A; Petitmermet, Joshua; Stefanski, Artur; Rice, Karen E; Rich, Roy L.; Montgomery, Rebecca A; Reich, Peter BGlobal temperatures (T) are rising, and for many plant species, their physiological response to this change has not been well characterized. In particular, how hydraulic parameters may change has only been examined experimentally for a few species. To address this, we measured characteristics of the hydraulic architecture of six species growing in ambient T and ambient +3.4 °C T plots in two experimentally warmed forest sites in Minnesota. These sites are at the temperate–boreal ecotone, and we measured three species from each forest type. We hypothesized that relative to boreal species, temperate species near their northern range border would increase xylem conduit diameters when grown under elevated T. We also predicted a continuum of responses among wood types, with conduit diameter increases correlating with increases in the complexity of wood structure. Finally, we predicted that increases in conduit diameter and specific hydraulic conductivity would positively affect photosynthetic rates and growth. Our results generally supported our hypotheses, and conduit diameter increased under elevated T across all species, although this pattern was driven predominantly by three species. Two of these species were temperate angiosperms, but one was a boreal conifer, contrary to predictions. We observed positive relationships between the change in specific hydraulic conductivity and both photosynthetic rate (P = 0.080) and growth (P = 0.012). Our results indicate that species differ in their ability to adjust hydraulically to increases in T. Specifically, species with more complex xylem anatomy, particularly those individuals growing near the cooler edge of their range, appeared to be better able to increase conduit diameters and specific hydraulic conductivity, which permitted increases in photosynthesis and growth. Our data support results that indicate individual's ability to physiologically adjust is related to their location within their species range, and highlight that some wood types may adjust more easily than others.Item Phenological data (2009-2013) for ten tree species grown under experimental warming in northern Minnesota, USA(2020-03-27) Montgomery, Rebecca A; Stefanski, Artur; Reich, Peter B; Rice, Karen E; rebeccam@umn.edu; Montgomery, Rebecca A; University of Minnesota Forest Ecology GroupThis dataset contains five years of data on time of budburst, growing degree days at the time of budburst, time of senescence and phenological growing season length phenology data for ten tree species native to Minnesota, USA. Data were collected in a long-term open-air warming experiment located a the Cloquet Forestry Center, Cloquet, MN, USA and the Hubachek Wilderness Research Center, Ely, MN, USA. The design was a 2 (site) X 2 (habitat) x 3 (warming treatment) factorial, with 6 replicates (2 per block) for a total of 72 7.1 m2 circular plots. Species include: Quercus rubra, Quercus macrocarpa, Pinus banksiana, Pinus strobus, Populus tremuloides, Betula papyrifera, Abies balsamea, Picea glauca, Acer rubrum, Acer saccharum. These data are released in conjunction with a publication.Item Responses of two understory herbs, Maianthemum canadense and Eurybia macrophylla, to experimental forest warming: early emergence is the key to enhanced reproductive output(Botanical Society of America, 2015) Jacques, Marie-Hélène; Lapointe, Line; Rice, Karen; Montgomery, Rebecca A; Stefanski, Artur; Reich, Peter BUnderstory herbs might be the most sensitive plant form to global warming in deciduous forests, yet they have been little studied in the context of climate change. A field experiment set up in Minnesota, United States simulated global warming in a forest setting and provided the opportunity to study the responses of Maianthemum canadense and Eurybia macrophylla in their natural environment in interaction with other components of the ecosystem. Effects of +1.7° and +3.4°C treatments on growth, reproduction, phenology, and gas exchange were evaluated along with treatment effects on light, water, and nutrient availability, potential drivers of herb responses. Overall, growth and gas exchanges of these two species were modestly affected by warming. They emerged up to 16 (E. macrophylla) to 17 d (M. canadense) earlier in the heated plots than in control plots, supporting early-season carbon gain under high light conditions before canopy closure. This additional carbon gain in spring likely supported reproduction. Eurybia macrophylla only flowered in the heated plots, and both species had some aspect of reproduction that was highest in the +1.7°C treatment. The reduced reproductive effort in the +3.4°C plots was likely due to reduced soil water availability, counteracting positive effects of warming. Global warming might improve fitness of herbaceous species in deciduous forests, mainly by advancing their spring emergence. However, other impacts of global warming such as drier soils in the summer might partly reduce the carbon gain associated with early emergence.Item Untangling positive and negative biotic interactions: Views from above and below ground in a forest ecosystem(Ecological Society of America, 2010) Montgomery, Rebecca A; Reich, Peter B; Palik, Brian JIn ecological communities, the outcome of plant–plant interactions represents the net effect of positive and negative interactions occurring above and below ground. Untangling these complex relationships can provide a better understanding of mechanisms that underlie plant–plant interactions and enhance our ability to predict population, community, and ecosystem effects of biotic interactions. In forested ecosystems, tree seedlings interact with established vegetation, but the mechanisms and outcomes of these interactions are not well understood. To explore such mechanisms, we manipulated above- and belowground interactions among tree seedlings, shrubs, and trees and monitored seedling survival and growth of six species (Pinus banksiana, Betula papyrifera, P. resinosa, Quercus rubra, P. strobus, and Acer rubrum) in mature pine-dominated forest in northern Minnesota, USA. The forest had a moderately open canopy and sandy soils. Understory manipulations were implemented in the forest interior and in large gaps and included removal of shrubs (no interactions), tieback of shrubs (belowground), removal of shrubs with addition of shade (aboveground), and unmanipulated shrubs (both below- and aboveground). We found that shrubs either suppressed or facilitated seedling survival and growth depending on the seedling species, source of interaction (e.g., above- or belowground), and ecological context (e.g., gap or forest interior). In general, shrubs strongly influenced survival and growth in gaps, with more modest effects in the forest interior. In gaps, the presence of shrub roots markedly decreased seedling growth and survival, supporting the idea that belowground competition may be more important in dry, nutrient-poor sites. Shrub shade effects were neutral for three species and facilitative for the other three. Facilitation was more likely for shade-tolerant species. In the forest interior, shrub shade negatively affected seedling survival for the most shade-intolerant species. For several species the net effect of shrubs masked the existence of both positive and negative interactions above and below ground. Our results highlight the complexity of plant–plant interactions, demonstrate that outcomes of these interactions vary with the nature of resource limitation and the ecophysiology of the species involved, and suggest that ecological theory that rests on particular notions of plant–plant interactions (e.g., competition) should consider simultaneous positive and negative interactions occurring above and below ground.