Forage stoichiometry predicts the home range size of a small terrestrial herbivore

Consumers make space use decisions based on resource quality. Most studies that investigate the influence of resource quality on the spatial ecology of consumers use diverse proxies for quality including measures based on habitat classification, forage species diversity and abundance, and nutritional indicators, e.g., protein. Ecological stoichiometry measures resource quality in terms of elemental ratios, e.g., carbon (C):nitrogen (N) ratio, but rarely have these currencies been used to study consumer space use decisions. Yet, elemental ratios provide a uniquely quantitative way to assess resource quality. Consequently, ecological stoichiometry allows for investigation of how consumers respond to spatial heterogeneity in resource quality by changing their space use, e.g. their home range size, and how this may influence ecosystem dynamics and trophic interactions. Here, we test whether the home range size of a keystone boreal herbivore, the snowshoe hare (Lepus americanus), varies with differences in the C:N, C:phosphorus (P), and N:P ratios of two preferred forage species, lowland blueberry (Vaccinium angustifolium) and red maple (Acer rubrum). We consider forage resources with higher C content relative to N and P to be lower quality than resources with lower relative C content. We use a novel approach, combining elemental distribution models with herbivore home range size estimates to test our hypothesis that hare home range size will be smaller in areas with access to high, homogeneous resource quality compared to areas with access to low, heterogeneous resource quality during summer months. Our results support our prediction for lowland blueberry, but not for red maple. Herbivore home range size decreased with increasing blueberry foliage quality, but also with decreasing spatial heterogeneity in blueberry foliage quality, i.e. N or P content. Herbivores in the boreal forest face strong nutritional constraints due to the paucity of N and P. Access to areas of high, homogeneous resource quality is paramount to meeting their dietary requirements with low effort. In turn, this may influence community (e.g., trophic interactions) and ecosystem (e.g., nutrient cycling) processes. Paradoxically, our study shows that taking a reductionist approach of viewing resources through a biochemical lens can lead to holistic insights of consumer spatial ecology.

Growth, Flowering, and Cold Hardiness of Rockrose in Western Oregon

Ninety-three species, cultivars, and hybrid selections of rockrose (Cistus spp., Halimium spp., and ×Halimiocistus spp.) were evaluated for growth, flowering, and cold hardiness in a landscape trial in Aurora, OR, from 2004 to 2009. Plants were irrigated to aid establishment when planted in summer 2004, but thereafter were not watered, fertilized, or pruned throughout the trial. Cold damage was recorded following freezing events in Feb. 2006 and Dec. 2008 in which low temperatures were 20 and 17 °F, respectively. Those plants that consistently suffered the most cold damage were Halimium atriplicifolium, Cistus creticus ssp. creticus ‘Tania Compton’, Cistus ×pauranthus, and Cistus albidus forma albus. Other plants showed cold damage related to poor vigor. The length of the flowering period and foliage quality varied widely among plants in the evaluation. The plants with the longest flowering period were Halimium ×pauanum, Cistus inflatus, Cistus ×pulverulentus ‘Sunset’, and ×Halimiocistus ‘Ingwersenii’, all of which flowered for more than 55 days. Plant form and foliage quality declined drastically for some plants during the evaluation. Those that retained the best foliage quality included Cistus ×obtusifolius, Cistus ×laxus, Cistus salviifolius ‘Gold Star’, Cistus ‘Gordon Cooper’, Halimium lasianthum ‘Sandling’, Halimium ‘Susan’, and ×Halimiocistus sahucii. Based on ratings of foliage and bloom time, as well as hardiness, several Cistus are recommended as drought-tolerant groundcovers, including Cistus ×gardianus and C. ×obtusifolius. Cistus ×laxus, C. inflatus, Cistus ‘Gordon Cooper’, Cistus ‘Ruby Cluster’, and Cistus ‘Snow Fire’ are suggested as tall groundcovers or landscape specimens. Several Halimium are recommended for landscape use, including H. lasianthum ‘Sandling’, Halimium ‘Susan’, H. ×pauanum, and ×Halimiocistus ‘Ingwersenii’.

Greenhouse Rose Yield and Ion Accumulation Responses to Salt Stress as Modulated by Rootstock Selection

Greenhouse rose (Rosa × spp. L.) production is facing the use of poor-quality irrigation waters and regulatory pressures to recycle runoff and drainage effluents. Two experiments (were conducted to evaluate the yield and quality and ion accumulation responses of roses grafted on various rootstocks to increasing salinity stress. In Expt. 1, the scion ‘Bridal White’ grafted on ‘Manetti’, R. odorata (Andr.), ‘Natal Briar’, and ‘Dr. Huey’ were irrigated over four flowering cycles with complete nutrient solutions supplemented with NaCl at 0, 5, and 30 mm. In Expt. 2, plants of ‘Red France’ on ‘Manetti’ and ‘Natal Briar’ were irrigated over six flowering cycles with complete nutrient solutions supplemented with NaCl + CaCl2 (2:1 m ratio) at 0, 1.5, 3, 6, 12, and 24 mm. Salt concentration increases significantly and negatively affected the biomass, cut flower production, and foliage quality of the roses in both experiments, but the responses were modulated by rootstock selection. ‘Manetti’ plants in general sustained better absolute and relative biomass and flower yields, accumulated less Na+ and Cl− in its tissues, and showed less toxicity symptoms with increasing salinity than the others. ‘Natal Briar’ also had similar absolute productivity responses as ‘Manetti’ but were afflicted by a significantly different mineral nutrient profile, including higher accumulations and toxicities with Na+ and Cl− that led to lower foliage visual ratings. Conversely, the relative yields of plants on ‘Dr. Huey’ and R. odorata were similarly reduced by increasing salinity, but the former had lower Na+ and Cl− concentrations in its tissues and better visual scores than the latter, which fared as the worst. A combined analysis of the results suggests that on a productivity basis (biomass and flower yields), greenhouse roses could withstand overall maximum electrical conductivities (i.e., osmotic effects) of applied fertigation solutions of 3.0 ± 0.5 dS·m−1. On the other hand, and considering the aesthetic responses (visual scores) of on-plant and harvested foliage (cut flower shoots), greenhouse rose tolerance to applied Na+ and Cl− concentrations (ion-specific effects) could range up to 10 ± 2 mm.