Effects of past land use on spatial heterogeneity of soil nutrients in sourthern Appalachian forests

We examined patterns of nutrient heterogeneity in the mineral soil (0–15 cm depth) of 13 southern Appalachian forest stands in western North Carolina \u3e60 yr after abandonment from pasture or timber harvest to investigate the long-term effects of land use on the spatial distribution and supply of soil resources. We measured soil carbon (C), nitrogen (N), acid-extractable phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and pools, and potential net N mineralization and nitrification rates to evaluate differences in mean values, variance at multiple scales, and fine-scale spatial structure. While comparisons of averaged values rarely indicated that historical land use had an enduring effect on mineral soil or N cycling, differences in variance and spatial structure suggested that former activities continue to influence nutrient distributions by altering their spatial heterogeneity. Patterns differed by element, but generally variance of soil C, N, and Ca decreased and variance of soil P, K, and Mg increased with intensive past land use. Changes in variance were most conspicuous and consistent locally (\u3c28 m), but C, Ca, P, and Mg also exhibited appreciable differences in variance at coarser scales (\u3e150 m). High variability in soil compaction resulted in some changes in scale-dependent patterns of nutrient pool variance compared with nutrient concentration variance. It also affected the variance of N cycling rates, such that mass-based rates varied less and area-based rates varied more in intensively used areas than in reference stands. Geostatistical analysis suggested that past land use homogenized the spatial structure of soil C, K, and P in former pastures. In contrast, logged stands had highly variable spatial patterning for Ca. These results suggest that land use has persistent, multi-decadal effects on the spatial heterogeneity of soil resources, which may not be detectable when values are averaged across sites. By interacting with patterns of variability in the plant and heterotrophic biota, differences in nutrient distribution and supply could alter the composition and diversity of forest ecosystems. Scale-dependent changes in nutrient heterogeneity could also complicate efforts to determine biogeochemical budgets and cycling rates

SoDaH: the SOils DAta Harmonization database, an open-source synthesis of soil data from research networks, version 1.0

Data collected from research networks present opportunities to test theories and develop models about factors responsible for the long-term persistence and vulnerability of soil organic matter (SOM). Synthesizing datasets collected by different research networks presents opportunities to expand the ecological gradients and scientific breadth of information available for inquiry. Synthesizing these data is challenging, especially considering the legacy of soil data that have already been collected and an expansion of new network science initiatives. To facilitate this effort, here we present the SOils DAta Harmonization database (SoDaH; https://lter.github.io/som-website, last access: 22 December 2020), a flexible database designed to harmonize diverse SOM datasets from multiple research networks. SoDaH is built on several network science efforts in the United States, but the tools built for SoDaH aim to provide an open-access resource to facilitate synthesis of soil carbon data. Moreover, SoDaH allows for individual locations to contribute results from experimental manipulations, repeated measurements from long-term studies, and local- to regional-scale gradients across ecosystems or landscapes. Finally, we also provide data visualization and analysis tools that can be used to query and analyze the aggregated database. The SoDaH v1.0 dataset is archived and available at https://doi.org/10.6073/pasta/9733f6b6d2ffd12bf126dc36a763e0b4 (Wieder et al., 2020)

A framework to assess biogeochemical response to ecosystem disturbance using nutrient partitioning ratios

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Ecosystems 19 (2016): 387-395, doi:10.1007/s10021-015-9934-1.Disturbances affect almost all terrestrial ecosystems, but it has been difficult to identify general principles regarding these influences. To improve our understanding of the long-term consequences of disturbance on terrestrial ecosystems, we present a conceptual framework that analyzes disturbances by their biogeochemical impacts. We posit that the ratio of soil and plant nutrient stocks in mature ecosystems represents a characteristic site property. Focusing on nitrogen (N), we hypothesize that this partitioning ratio (soil N: plant N) will undergo a predictable trajectory after disturbance. We investigate the nature of this partitioning ratio with three approaches: (1) nutrient stock data from forested ecosystems in North America, (2) a process-based ecosystem model, and (3) conceptual shifts in site nutrient availability with altered disturbance frequency. Partitioning ratios could be applied to a variety of ecosystems and successional states, allowing for improved temporal scaling of disturbance events. The generally short-term empirical evidence for recovery trajectories of nutrient stocks and partitioning ratios suggests two areas for future research. First, we need to recognize and quantify how disturbance effects can be accreting or depleting, depending on whether their net effect is to increase or decrease ecosystem nutrient stocks. Second, we need to test how altered disturbance frequencies from the present state may be constructive or destructive in their effects on biogeochemical cycling and nutrient availability. Long-term studies, with repeated sampling of soils and vegetation, will be essential in further developing this framework of biogeochemical response to disturbance.This material is based upon work supported by the National Science Foundation under Grant No. DEB-1145815 and 0949420.2016-11-1

Data from: Fire increases drought vulnerability of Quercus alba juveniles by altering forest microclimate and nitrogen availability

1. Shifts in rainfall patterns due to climate change are expected to increase drought stress and mortality in forests. Natural and anthropogenic fire regimes are also changing, highlighting the need to understand the interactive effects of fire and drought on tree ecophysiological response and growth. 2. Using rainout shelters, we imposed summer drought on natural and planted populations of Quercus alba juveniles located in periodically burned and unburned sites in Shawnee National Forest, IL, USA. A subset of planted juveniles was clipped to simulate topkill. We measured predawn leaf water potential (Ψpd), leaf gas exchange (Amax, gmax), and relative growth rate (RGR) across treatments to test two hypotheses: (H1) fire reduces juvenile drought stress by improving water relations through increased root to shoot ratios after topkill, or (H2) fire exacerbates juvenile drought stress by promoting a warmer, drier microclimate or amplifying drought-induced nitrogen (N) limitation. 3. Burned stands had higher vapor pressure deficits and 13% lower soil inorganic N availability than unburned stands. Rainout shelters reduced soil moisture (0 – 45 cm) by 10 – 24% relative to ambient conditions. Consistent with H2, small, natural resprouts in burned stands experienced greater drought stress than unburned juveniles, with a 7% decrease in leaf nitrogen content (LNC), a 21-29% reduction in Amax and gmax, and a 41% reduction in RGR under drought. Drought effects on unburned juveniles, in contrast, were limited to a 5% reduction in LNC and a neutral to positive effect on leaf gas exchange and RGR. Large natural juveniles were largely unaffected by drought. Recent resprouts (i.e., clipped, planted juveniles) experienced less drought stress than unclipped juveniles, providing partial support for H1. 4. Collectively, these results suggest that resprouting after fire can temporarily improve leaf water relations until root to shoot ratios re-equilibrate. In contrast, fire can exacerbate drought-driven declines in the growth of small juveniles by both promoting a warmer, drier microclimate and intensifying N limitation. Our results suggest that despite the high drought tolerance of Quercus spp., fire-driven changes to local microclimate and resource conditions could limit tree recruitment under future scenarios of rainfall variability

Refsland and Fraterrigo Drought-fire effects on microclimate, nitrogen and juvenile Quercus alba

This database includes raw data on the forest microclimate, soil nitrogen availability and juvenile white oak (Quercus alba) physiological and growth responses to drought and fire treatments

Local-scale biotic interactions embedded in macroscale climate drivers suggest Eltonian noise hypothesis distribution patterns for an invasive grass

Abstract A hierarchical view of niche relations reconciles the scale-dependent effects of abiotic and biotic processes on species distribution patterns and underlies most current approaches to distribution modeling. A key prediction of this framework is that the effects of biotic interactions will be averaged out at macroscales -an idea termed the Eltonian noise hypothesis (ENH). We test this prediction by quantifying regional variation in local abiotic and biotic niche relations and assess the role of macroclimate in structuring biotic interactions, using a non-native invasive grass, Microstegium vimineum, in its introduced range. Consistent with hierarchical niche relations and the ENH, macroclimate structures local biotic interactions, while local abiotic relations are regionally conserved. Biotic interactions suppress M. vimineum in drier climates but have little effect in wetter climates. A similar approach could be used to identify the macroclimatic conditions under which biotic interactions affect the accuracy of local predictions of species distributions

Species traits as generalized predictors of forest community response to human disturbance

During the past decade, substantial effort has been aimed at identifying a group of easily measured, widely applicable plant traits that could serve as a metric to predict temporal change in plant communities. Traits that transcend regional differences in species composition and ecological conditions through their consistent response to disturbance would give managers a simple tool for tracking ongoing and future forest change in response to human disturbance. Although a wide range of plant traits has been associated with human disturbance, consistent traits have not emerged in the literature. However, this may due to differences in methodology among studies. Previously collected data from two eastern deciduous forest floras of North America (Iowa and Massachusetts) allowed us to evaluate whether such traits emerged, while controlling for methodological differences. We created a plot × traits matrix for each site and ordinated them used using principal components analysis (PCA) to identify disturbance gradients. We then assessed how well the traits most strongly associated with the disturbance gradients corresponded. The data sets shared only 4 of the 12 traits associated with disturbance and 6 of 12 traits associated with undisturbed sites. We did not find a consistent association between dispersal limitation and undisturbed sites or high dispersal capacity associated with disturbed sites. However, in both data sets degree of habitat specialization was an important variable on both ends of the disturbance gradient. Habitat generalists were associated with disturbance and habitat specialists were associated with more pristine sites in both data sets. These results agree with the findings of a wide range of site-specific studies, and we therefore propose that this variable is a promising candidate trait to provide a signal of forest community response to human disturbance. Our results are should be particularly encouraging for managers because in many regions morphological trait data are not readily available, and compiling such data is a very time-intensive task and unlikely to be feasible for most managers to undertake. With a list of species and a published flora, upwards of several hundred species can quickly be coded for degree of habitat specialization and used to track the impact of current disturbance, to predict future impacts, and to target specific species for reintroduction or restoration.This is a manuscript of an article published as Mabry, Catherine M., and Jennifer M. Fraterrigo. "Species traits as generalized predictors of forest community response to human disturbance." Forest Ecology and Management 257, no. 2 (2009): 723-730. doi:10.1016/j.foreco.2008.10.002. Posted with permission. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 License