Net primary production (NPP) is a critical ecosystem property that researchers and land managers attempt to quantify across ecosystems globally. Although the belowground NPP (BNPP) component of total ...NPP often contributes 50% or more to total NPP, it is infrequently measured due to the amount of labor involved. Here, I present a rapid method to estimate BNPP or fine root production in rangelands using sequential or root ingrowth cores and modifications to existing root-washing methods. The details provided should allow anyone to estimate BNPP in rangelands worldwide with minimal investment in materials and labor.
Climatic changes are altering Earth's hydrological cycle, resulting in altered precipitation amounts, increased interannual variability of precipitation, and more frequent extreme precipitation ...events. These trends will likely continue into the future, having substantial impacts on net primary productivity (NPP) and associated ecosystem services such as food production and carbon sequestration. Frequently, experimental manipulations of precipitation have linked altered precipitation regimes to changes in NPP. Yet, findings have been diverse and substantial uncertainty still surrounds generalities describing patterns of ecosystem sensitivity to altered precipitation. Additionally, we do not know whether previously observed correlations between NPP and precipitation remain accurate when precipitation changes become extreme. We synthesized results from 83 case studies of experimental precipitation manipulations in grasslands worldwide. We used meta‐analytical techniques to search for generalities and asymmetries of aboveground NPP (ANPP) and belowground NPP (BNPP) responses to both the direction and magnitude of precipitation change. Sensitivity (i.e., productivity response standardized by the amount of precipitation change) of BNPP was similar under precipitation additions and reductions, but ANPP was more sensitive to precipitation additions than reductions; this was especially evident in drier ecosystems. Additionally, overall relationships between the magnitude of productivity responses and the magnitude of precipitation change were saturating in form. The saturating form of this relationship was likely driven by ANPP responses to very extreme precipitation increases, although there were limited studies imposing extreme precipitation change, and there was considerable variation among experiments. This highlights the importance of incorporating gradients of manipulations, ranging from extreme drought to extreme precipitation increases into future climate change experiments. Additionally, policy and land management decisions related to global change scenarios should consider how ANPP and BNPP responses may differ, and that ecosystem responses to extreme events might not be predicted from relationships found under moderate environmental changes.
Future changes in precipitation will strongly impact ecosystem functioning and services through changes in plant growth. Here, we synthesize 83 precipitation experiments to look at responses of above and belowground plant growth (ANPP and BNPP) across climatic gradients and levels of precipitation change extremity. Overall, we found that (1) ANPP was more responsive to precipitation increases than decreases, and this was especially evident in dry ecosystems; (2) BNPP responses were similar under precipitation increases vs. decreases; (3) under extreme wet conditions, NPP responses leveled off, creating a saturating function of NPP response vs. the magnitude of precipitation change. Based on these findings, we suggest that future research focus on BNPP and plant responses to extreme precipitation change.
Question: Anthropogenic climate change is altering temperature and precipitation in grasslands worldwide. As grasslands are primarily water-limited, these changes in climate will likely have dramatic ...impacts on ecosystem function and community structure, yet the magnitude of change and the types of species favoured may differ among ecosystems or even among local communities within ecosystems. How much might plant community responses to altered precipitation vary at two sites within one grassland region? Location: Semi-arid and sub-humid natural grasslands in the US Great Plains. Methods: At two sites we used rainfall shelters and irrigation to create irrigation, drought and control treatments. We measured changes in species composition, richness, Shannon's diversity, evenness and cover by plant functional groups across 4 yr (2008-2011). Results: The semi-arid grassland community was relatively insensitive to precipitation manipulations, and in the few cases where there was a significant relationship between treatment precipitation and the response variable, the slope of the relationship was weak. In contrast, the sub-humid grassland community was very sensitive to changes in treatment precipitation throughout the experiment, and responded more strongly, and negatively, to drought compared to irrigation. Conclusions: The differing sensitivity of the dominant species to altered precipitation amount appears to largely determine the overall differences in community response at these sites. The variable responses we observed within a single grassland region highlight the challenge of forecasting community impacts of climate change.
In grassland ecosystems, where soil water most frequently controls ecosystem processes, expected changes in precipitation and temperature may have dramatic effects on ecosystem dynamics. Previous ...observational studies have reported that aboveground net primary production (ANPP) in grasslands is very sensitive to changes in precipitation. Yet, we lack experimentally based evidence to support these observations. Further, most of the studies have focused solely on ANPP, neglecting belowground production (BNPP). This is an important gap in our knowledge, as BNPP represents 50% or more of total net primary production (NPP) in grasslands. Here, we present results from a 3-year water manipulation experiment (2008-2010) at two sites in the central grassland region of North America, USA. We were successful in changing the soil water content in our treatments, but these changes resulted in different, but significant responses in ANPP and BNPP at our two sites. At the shortgrass steppe, we found that neither NPP nor ANPP were sensitive to treatment precipitation, and although we found BNPP was sensitive to changes in treatment precipitation, the direction of the response varied between years. In contrast, ANPP was very sensitive to treatment precipitation on the mixed-grass prairie, whereas BNPP was insensitive. Based on our finding that two grassland ecosystems showed dramatically different above and belowground production responses to soil water manipulations, we cannot assume that predicted changes in climate will cause similar above- and belowground production responses. Second, our results demonstrated that sites within the same region may differ markedly in the sensitivity of ANPP to changes in growing season precipitation.
1. Models predict that the duration and intensity of drought will increase under future climate regimes. Although semi‐arid grasslands are adapted to moisture limitation, the sensitivity of semi‐arid ...grassland vegetation to extreme and sustained dry periods that may occur in the future has not been tested. 2. In this study, we analysed vegetation cover data from an 11‐year drought manipulation in the semi‐arid shortgrass steppe in Colorado, USA. We examined changes in total vegetation cover, dominant plant (Bouteloua gracilis) cover and ruderal cover in plots receiving 25% and 50% of ambient precipitation during the growing season. 3. We found that 11 years of drought resulted in large reductions in total cover and cover of the dominant species, but significant differences did not emerge until the 4th and 7th year of drought. Drought severity significantly influenced the degree to which ruderal cover increased in the later period of the drought, but reductions in B. gracilis cover under drought were not significantly different under different drought severities. Bouteloua gracilis reduction did correspond strongly with increases in ruderal cover and species richness, suggesting that the dominant species plays a strong role in maintaining the structure of communities in the shortgrass steppe. 4. Synthesis. Our results suggest that the shortgrass steppe, and most notably the dominant species B. gracilis, can be significantly perturbed by long‐term droughts that may be more common in future decades. By quantifying the resistance‐limit of a drought‐tolerant system, our results can inform theories of stability and management decisions for grassland systems under new climate regimes and provide a new temporal context for previous and future manipulation studies.
Understanding drivers of aboveground net primary production (ANPP) has long been a goal of ecology. Decades of investigation have shown total annual precipitation to be an important determinant of ...ANPP within and across ecosystems. Recently a few studies at individual sites have shown precipitation during specific seasons of the year can more effectively predict ANPP. Here we determined whether seasonal or total precipitation better predicted ANPP across a range of terrestrial ecosystems, from deserts to forests, using long-term data from 36 plant communities. We also determined whether ANPP responses were dependent on ecosystem type or plant functional group. We found that seasonal precipitation generally explained ANPP better than total precipitation. Precipitation in multiple parts of the growing season often correlated with ANPP, but rarely interacted with each other. Surprisingly, the amount of variation explained by seasonal precipitation was not correlated with ecosystem type or plant functional group. Overall, examining seasonal precipitation can significantly improve ANPP predictions across a broad range of ecosystems and plant types, with implications for understanding current and future ANPP variation. Further work examining precipitation timing relative to species phenology may further improve our ability to predict ANPP, especially in response to climate change.
ObjectivesTo evaluate digital, multimedia information (MMI) for its effects on trial recruitment, retention, decisions about participation and acceptability by patients, compared with printed ...information.DesignStudy Within A Trial using random cluster allocation within the Forearm Fracture Recovery in Children Evaluation (FORCE) study.SettingEmergency departments in 23 UK hospitals.Participants1409 children aged 4–16 years attending with a torus (buckle) fracture, and their parents/guardian. Children’s mean age was 9.2 years, 41.0% were female, 77.4% were ethnically White and 90.0% spoke English as a first language.InterventionsParticipants and their parents/guardian received trial information either via multimedia, including animated videos, talking head videos and text (revised for readability and age appropriateness when needed) on tablet computer (MMI group; n=681), or printed participant information sheet (PIS group; n=728).Outcome measuresPrimary outcome was recruitment rate to FORCE. Secondary outcomes were Decision-Making Questionnaire (nine Likert items, analysed summatively and individually), three ‘free text’ questions (deriving subjective evaluations) and trial retention.ResultsMMI produced a small, not statistically significant increase in recruitment: 475 (69.8%) participants were recruited from the MMI group; 484 (66.5%) from the PIS group (OR=1.35; 95% CI 0.76 to 2.40, p=0.31). A total of 324 (23.0%) questionnaires were returned and analysed. There was no difference in total Decision-Making Questionnaire scores: adjusted mean difference 0.05 (95% CI −1.23 to 1.32, p=0.94). The MMI group was more likely to report the information ‘very easy’ to understand (89; 57.8% vs 67; 39.4%; Z=2.60, p=0.01) and identify information that was explained well (96; 62.3% vs 71; 41.8%). Almost all FORCE recruits were retained at the 6 weeks’ timepoint and there was no difference in retention rate between the information groups: MMI (473; 99.6%); PIS (481; 99.4%).ConclusionsMMI did not increase recruitment or retention in the FORCE trial, but participants rated multimedia as easier to understand and were more likely to evaluate it positively.Trial registration numberISRCTN73136092 and ISRCTN13955395.
A frequently advocated approach for forecasting the population‐level impacts of climate change is to project models based on historical, observational relationships between climate and demographic ...rates. Despite the potential pitfalls of this approach, few historically based population models have been experimentally validated. We conducted a precipitation manipulation experiment to test population models fit to observational data collected from the 1930s to the 1970s for six prairie forb species. We used the historical population models to predict experimental responses to the precipitation manipulations, and compared these predictions to ones generated by a statistical model fit directly to the experimental data. For three species, a sensitivity analysis of the effects of precipitation and grass cover on forb population growth showed consistent results for the historical population models and the contemporary statistical models. Furthermore, the historical population models predicted population growth rates in the experimental plots as well or better than the statistical models, ignoring variation explained by spatial random effects and local density‐dependence. However, for the remaining three species, the sensitivity analyses showed that the historical and statistical models predicted opposite effects of precipitation on population growth, and the historical models were very poor predictors of experimental responses. For these species, historical observations were not well replicated in space, and for two of them the historical precipitation‐demography correlations were weak. Our results highlight the strengths and weaknesses of observational and experimental approaches, and increase our confidence in extrapolating historical relationships to predict population responses to climate change, at least when the historical correlations are strong and based on well‐replicated observations.
Soil seed banks are critical biodiversity repositories for dryland plant communities. Understanding how environmental factors alter seed bank composition provides valuable information on ecological ...processes within a community and can be useful for creating land management strategies. We assessed seed bank response to drought and microsite within an Artemisia arbuscula dominated community and a directly adjacent (∼60m apart) A. cana dominated community, and characterized the similarity between these two seed banks and the corresponding aboveground vegetation. We found that drought increased exotic grass seed density and decreased seed species diversity and evenness within the A. arbuscula community, whereas shrub microsites enhanced seed species diversity and native forb seed density. In contrast, there were only minor drought effects within the A. cana community. Within both plant communities, there was low similarity between the seed bank and existing vegetation (<28%), and both seed banks were comprised of over 50% exotic annual grass seeds. Our study suggests that seed banks of drylands similar to A. arbuscula dominated plant communities (with heterogenous landscapes and low soil moisture availability) may experience more drought induced impacts than adjacent sagebrush communities, and highlights the role of shrub canopies as beneficial microsites for seeds in some drylands.
•Environmental factors contrastingly affected seed banks of two sagebrush communities.•Drought increased Ventenata seeds in a low sagebrush dominated community.•Shrubs promoted native forb seed density and diversity in a low sagebrush community.•Above- and belowground had dissimilar plant functional group and species composition.
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