Summary Trait‐based models of ecological communities typically assume intraspecific variation in functional traits is not important, although such variation can change species trait rankings along gradients in resources and environmental conditions, and thus influence community structure and function. We examined the degree of intraspecific relative to interspecific variation, and reaction norms of 11 functional traits for 57 forest understorey plant species, including: intrinsic water‐use efficiency (iWUE), Δ15N, five leaf traits, two stem traits and two root traits along gradients in light, nitrogen, moisture and understorey cover. Our results indicate that interspecific trait variation exceeded intraspecific variation by at least 50% for most, but not all traits. Intraspecific variation in Δ15N, iWUE, leaf nitrogen content (LNC) and root traits was high (47–70%) compared with most leaf traits and stem traits (13–38%). Δ15N varied primarily along gradients in abiotic conditions, while light and understorey cover were relatively less important. Intrinsic water‐use efficiency was related primarily to light transmission, reflecting increases in photosynthesis relative to stomatal conductance. Leaf traits varied mainly as a function of light availability, with some reaction norms depending on understorey cover. Plant height increased with understorey cover, while stem‐specific density was related primarily to light. Resources, environmental conditions and understorey cover did not contribute strongly to the observed variation in root traits. Gradients in resources, environmental conditions and competition all appear to control intraspecific variability in most traits to some extent. However, our results suggest that species cross‐over (i.e. trait rank reversals) along the gradients measured here are generally not a concern. Intraspecific variability in understorey plant species traits can be considerable. However, trait data collected under a narrow range of environmental conditions appears sufficient to establish species rankings and scale between community and ecosystem levels using trait‐based models. Investigators may therefore focus on obtaining a sufficient sample size within a single set of conditions rather than characterizing trait variation across entire gradients to optimize sampling efforts. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12898/suppinfo is available for this article.

Cover crops are suites of non-marketable plants grown to improve soil tilth and reduce erosion. Despite these agronomic benefits, the use of cover crops is often limited because they do not provide a direct source of revenue for producers. Integrating livestock to graze cover crops could provide both an expeditious method for cover crop termination and an alternative source of revenue. However, there has been little research on the agronomic impacts of grazing for cover crop termination, especially in horticultural market-gardens. We conducted a 3-year study comparing the effects of sheep grazing to terminate a four species cover crop (buckwheat, sweetclover, peas and beets) with those of mowing on soil quality indicators, cover crop termination efficacy, and subsequent cash-crop yields. In addition, we tested the nutritional quality of the cover crop as forage. Compared with mowing, sheep grazing did not affect soil chemistry, temperature or moisture. Our study demonstrates that sheep grazing removed more cover crop biomass than mowing at termination. The assessment of nutritional indices suggests that the four-species cover crop mixture could provide high-quality forage with a potential value of US$144.00-481.80 ha −1 of direct revenue as a grazing lease. Cash-crop yields did not differ between previously grazed and previously mowed plots in the subsequent growing season. We conclude that integrating sheep grazing into market vegetable garden operations could make cover crops more economically viable without having adverse effects on subsequent cash crops.

No abstract

1.Overbrowsing by ungulates is a major cause of poor aspen stand regeneration across North America and Eurasia. In general, factors driving ungulate browser preferences include concentrations of plant secondary compounds and the nutritional composition (non-structural carbohydrates, protein and minerals) of foliage. While each of these phytochemical factors has been shown to independently influence ungulate preference, the relative impact of each factor is unknown, as no study to date has examined them simultaneously. 2. Plant fitness depends not only on the capacity of plants to resist browsing, but also on their capacity to tolerate browsing once it has occurred. Little is known of aspen tolerance to browsing, which inflicts a different form of damage than insect herbivory. 3. We employed multiple aspen genotypes, replicate trees of which were subjected to different soil nutrient treatments, to investigate: (i) the effects of aspen genotype, nutrient treatment and genotype 9 nutrient interactions on susceptibility to browsing by white-tailed deer, (ii) the phytochemical basis for the patterns observed in (i), and (iii) the effects of genotype, soil nutrients and their interaction on short-term tolerance to deer browsing. 4. Aspen genotypes varied markedly in their vernal susceptibility to deer browsing. Genetic variation in early season levels of non-structural carbohydrates (sugars), protein and multiple macro-and trace minerals had the strongest influence on tree susceptibility to browsing. In contrast, levels of phytochemical defences had minimal effects, although the range of levels expressed in this study was small. Soil nutrient availability did not significantly influence deer preference. 5. The extent of browsing affected post-browse tolerance across genotypes. Soil nutrient treatment had little differential effect on tolerance, and, for the most part, genotypes did not display differential tolerance to browsing, regardless of which soil nutrient treatment they experienced. 6. Synthesis. Genetic variation for susceptibility to browsing indicates that ungulate browsers have the potential to be agents of selection in aspen populations. In contrast with previous studies in aspen highlighting the importance of phytochemical defences in shaping preferences of browsing mammals, our results indicate that the nutritional composition of foliage (sugars, protein and mineral concentrations) can have sizable effects on preference. The observed lack of influence of soil nutrient availability on tree browsing tolerance contrasts with predictions of the limiting resource model, the prevailing model for plant tolerance.

Multiple herbicide-resistant (MHR) weed populations pose significant agronomic and economic threats and demand the development and implementation of ecologically based tactics for sustainable management. We investigated the influence of nitrogen fertiliser rate (56, 112, 168, or 224 kg N ha À1 ) and spring wheat seeding density (67.3 kg ha À1 or 101 kg ha À1 ) on the demography of one herbicide susceptible and two MHR Avena fatua populations under two cropping systems (continuous cropping and crop-fallow rotation). To represent a wide range of environmental conditions, data were obtained in field conditions over 3 years (2013)(2014)(2015). A stochastic density-dependent population dynamics model was constructed using the demographic data to project A. fatua populations. Elasticity analysis was used to identify demographic processes with negative impacts on population growth. In both cropping systems, MHR seedbank densities were negatively impacted by increasing nitrogen fertilisation rate and wheat density. Overall, MHR seedbank densities were larger in the wheat-fallow compared with the continuous wheat cropping system and seedbank densities stabilised near zero in the high nitrogen and high spring wheat seeding rate treatment. In both cropping systems, density-dependent seed production was the most influential parameter impacting population growth rate. This study demonstrated that while the short-term impact of weed management tactics can be investigated by field experiments, evaluation of long-term consequences requires the use of population dynamics models. Demographic models, such as the one constructed here, will aid in selecting ecologically based weed management tactics, such as appropriate resource availability and modification to crop competitive ability to reduce the impact of MHR.