Dormant Season Research Articles

Strategic Supplementation to Manage Fine Fuels in a Cheatgrass (Bromus tectorum)−Invaded System

Management of areas invaded by cheatgrass (Bromus tectorum) continues to be one of the greatest challenges for US Great Basin ecosystems. Targeted cattle grazing in the fall and winter has shown positive results as a management tool to reduce dormant fine fuel biomass within cheatgrass-invaded areas, but management of targeted grazing within large pastures can be challenging. We evaluated the use of strategically placed liquid protein supplement stations over a 4-wk period in the fall to focus cattle grazing along a linear transect stretching away from water to reduce residual cheatgrass biomass on a production-scale, working ranch from 2014 to 2017. Liquid protein supplement stations were moved approximately 1 km farther from water during each week of the study, eventually reaching 4 km from a single water source. Global Positioning System−tracked cattle visited supplement stations 52% ± 4% of the days during the study period and were within 100 m of the supplement station transect line 17.7% ± 2.6% of the time: more than 3 × greater (P = 0.07) than random locations (5.1% ± 2.6%). Week of the study and the subsequent supplement distance from water did not influence the number of visits cattle made to supplement. The duration that cattle remained at supplement was greater in wk 4, when supplement was placed 4 km from water, compared with wk 1 and 2, when the supplement was 1 and 2 km from water, respectively. At the conclusion of grazing, utilization along the supplement station transect averaged 66.0% ± 5.7% and did not differ between supplement stations at 1 km, 3 km, or 4 km from water. Strategic supplementation provides a valuable tool to target cattle grazing at specific locations within cheatgrass-invaded systems to reduce fine fuel buildup during the dormant season.

Interspecific morphological variation in Juglandoideae resting bud organization: a winter's tale?

Dormant resting buds are frequently regarded as static units, with protective cataphylls on the outside and embryonic foliage leaves on the inside. How the presence of cataphylls influences the dynamic, cyclical, annually repeating sequence of leaf forms that a resting bud gives rise to has rarely been interrogated. To examine the connection between dormant structure and growing-season development, we compare the complete seasonal heteroblastic sequence of leaf forms of six species of temperate Juglandaceae with distinctly different vegetative resting bud structures. These include buds with cataphylls; buds without cataphylls; and buds with caducous cataphylls that are lost before the onset of winter. In a common garden setting over a 7-month growing season, the dimensions of 2249 individual vegetative metamers were tracked from first exposure to abscission along the shoots of saplings and mature trees. The timing of metamer initiation within terminal buds was investigated using micro-CT scanning. Character state transitions of resting bud types were estimated using a phylogenetic tree of Juglandaceae. The presence of cataphylls within a heteroblastic sequence is associated with a single cohort of foliage leaves that flush and abscise synchronously. This growing pattern is highly determinate, with next year's terminal-bud cataphylls already initiated before spring leaf out. In contrast, in sequences without cataphylls, shorter-lived foliage leaves appear and abscise in a staggered fashion. Despite these differences in leaf demography, all examined heteroblastic sequences produce a series of small, caducous leaf forms that precede terminal bud set. The ubiquity of caducous leaf forms in Juglandoideae may point to the importance of shoot tip protection far beyond the dormant season. In addition, the presence or absence of cataphylls in resting buds is indicative of distinct shoot ontogenetic patterns, and functional strategies, in summer.

Grazing management on commercial cattle ranches: Incorporating foraging ecology and biodiversity conservation principles

• Sustainable ranch management must consider not only impacts of grazing management on range condition (ecological sustainability) but also on cattle production relative to overhead costs (economic sustainability) and on biodiversity (biological sustainability). • Rates of growth and reproduction in herbivore populations are determined by access to sufficient high-quality forage and concomitant optimal nutrition during the growing season. By contrast, maintenance of body condition and survival over the dormant season is determined by access to a reserve of adequate-quality forage. • Rotational grazing systems rely on resting paddocks after grazing for sustaining rangeland productivity and desired species composition, yet a dilemma for managers is forage loses digestibility and nutrient concentration as it matures during rest periods. • Grazing cattle in large, dense herds, frequently rotated through small paddocks may also compromise nutrition by increasing competition for forage and minimizing adaptive foraging movements. The economic viability of ranches is further compromised by the installation and maintenance costs of fencing numerous small paddocks across a ranch. • We use foraging ecology principles to highlight how intensive multipaddock grazing systems can compromise cattle production while their infrastructure requirements increase overhead costs of management, thereby minimizing profits. We provide working examples of how these problems can be practically overcome while maintaining ecological sustainability.

Weather explains differences in sagebrush-obligate songbird nest success under various grazing regimes

Livestock grazing occurs worldwide, spanning over 25% of land globally, and effective conservation of biodiversity relies upon understanding the interactions of agricultural management practices and increasingly variable weather associated with climate change. We evaluated precipitation and temperature and the daily nest survival rates of two species of sagebrush-obligate songbirds, Brewer’s sparrow ( Spizella breweri ) and sagebrush sparrow ( Artemisiospiza nevadensis ) under dormant season grazing, rotational grazing and a non-grazed control. Precipitation and temperature were quantified as daily time-varying and averages across the breeding season. Both sparrow species in our study were influenced by within-year weather variation, and experienced declines in daily nest survival beyond precipitation thresholds. For sagebrush sparrows, an interaction of precipitation and temperature indicated nest survival was lowest during 5-day time frames with minimal precipitation and high temperatures. While we found moderate grazing lowered perennial grass cover, there was no support for vegetation differences associated with moderate grazing explaining daily nest survival. Our results indicate that variable weather presented a much greater threat to these birds than reductions in herbaceous cover caused by moderate grazing under the studied conditions. Management should focus on conserving extensive tracts of suitable habitat to increase songbird populations and resiliency to increasingly variable and extreme weather conditions. • Sagebrush Sparrow daily nest survival decreased in hotter and drier weather. • Brewer’s Sparrow nest survival was resilient to most weather. • Vegetation was influenced by grazing but did not decrease nest survival. • Weather influenced sparrow nest survival more than grazing regime.

Working toward a fire-scar network for the Cumberland Plateau—Fire history results from Bridgestone Nature Reserve at Chestnut Mountain, Tennessee1

We reconstructed historical fire regime characteristics at the Bridgestone Nature Reserve at Chestnut Mountain using tree-ring dated fire scars on live and dead shortleaf pine (Pinus echinata Mill.) trees. Fire-scar records described the historical fire frequency and seasonality from the mid-18th century to present. Overall, we found historical fires occurred relatively frequently, predominantly in the dormant season, and were likely low-severity events. Mean fire intervals (MFIs) were slightly longer in the pre-Euro-American period (1744–1834; MFI = 9.6 yrs) versus the post-Euro-American period (1834–1935; MFI = 5.6 yrs). No fires were recorded after 1940, which in combination with past logging and land uses, is likely a major contributor to the ongoing decline of shortleaf pine and pyrophytic oak species observed here. Surprisingly, the majority of fire event years after 1834 were also recorded at Savage Gulf State Natural Area (52 km to the south), raising questions about potential historical fire sizes, patterns, and driving factors across the Cumberland Plateau landscape. In a landscape where fire-scarred remnants are present but relatively scarce and rapidly disappearing, these data are important for evidencing historical fire regimes and developing a more comprehensive regional network of fire history sites that could reveal valuable historical ecological information for the Cumberland Plateau.

Non-target effects of agrichemicals applied in the fall or during the dormant season on subsequent development of Exobasidium leaf and fruit spot of blueberry

The basidiomycete Exobasidium maculosum causes Exobasidium leaf and fruit spot, an early-season disease of blueberry in the southern United States. Previous research suggested that the pathogen oversummers and overwinters epiphytically on the surface of blueberry bark and buds, most likely in its yeast stage. This is supported by the finding that a single dormant application of lime sulfur provides substantial control of the disease the following spring. As a surface resident for much of the year, E. maculosum is thus exposed to various horticultural and pest management practices which may affect its epiphytic population dynamics and impact subsequent disease development. The magnitude and consistency of such non-target effects was evaluated in multi-year field trials on susceptible ‘Premier’ and ‘Tifblue’ rabbiteye blueberry in southern Georgia. One fall application of stylet oil (timed to mimic sprays for blueberry bud mite control) or two fall applications of captan (timed to coincide with the management window for fungal foliar diseases) did not suppress Exobasidium leaf and fruit spot the following spring, whereas two fall applications of lime sulfur reduced the disease significantly (by 74.3% on average), albeit not to the same level as the late dormant lime sulfur standard (close to 90% average reduction across leaf and fruit spot intensity). A single late dormant spray of the growth regulator hydrogen cyanamide (a caustic compound with antimicrobial activity) suppressed disease intensity in most trials, but disease reduction was only partial (averaging 56.2% for leaf lesion density and 39.3% for fruit spot incidence). In contrast, a late dormant application of dormant oil consistently increased both leaf lesion density (by 80.7% on average) and fruit disease incidence (by 78.6%). The pronounced non-target effects associated with these off-season applications could explain variations in Exobasidium leaf and fruit spot risk among blueberry sites and years.

Bumblebee: A Path Towards Fully Autonomous Robotic Vine Pruning

Dormant season grapevine pruning requires skilled seasonal workers, but they are becoming less available. As workers hasten to prune more vines in less time due to the short-term seasonal hiring culture and low wages, vines are often pruned inconsistently, leading to imbalanced grapevines. In addition, grapevines cannot be pruned selectively using currently existing mechanical methods, thus manual follow-up operations are often required, further increasing production cost. In this paper, we present the design and field evaluation of a rugged and fully autonomous robot for end-to-end pruning of dormant season grapevines. The proposed design incorporates novel camera systems, a kinematically redundant manipulator, a ground robot, and novel algorithms in the perception system. The presented research prototype robot system was able to spur-prune a row of vines from both sides completely in 213 s/vine with a total pruning accuracy of 87%. Initial field tests of the autonomous system in a commercial vineyard have shown significant variability reduction in dormant season pruning when compared to mechanical prepruning trials. The design approach, system components, lessons learned, future enhancements, as well as a brief economic analysis are described in the manuscript.

Low-disturbance farming regenerates healthy deep soil toward sustainable agriculture - Evidence from long-term no-tillage with stover mulching in Mollisols

Currently, global agricultural development is in a critical period, as it contends with a growing population, degraded farmland, and serious environmental issues. Although low-disturbance practices are recommended to improve soil health, it is unclear whether such practices benefit critical deep soil functioning. Here, we compared the soil bacterial communities and physicochemical parameters across 3-m deep soil profiles in a Mollisol of Northeast China at the end of the dormant season after 10 years of farming under conventional tillage without stover mulching (CT), no-tillage without stover mulching (NTNS), and no-tillage with stover mulching (NTSM). We found that low-disturbance practices (NTNS and NTSM), compared with CT, evidently promoted soil bacterial species richness and diversity and enriched potential metabolic diversity. When compared to the bacterial communities in CT, the vertical dissimilarity of bacterial communities in NTNS decreased, while that in NTSM increased, indicating that no-tillage alone homogenized the composition of the bacterial community through soil depth profiles, but straw mulching enhanced the uniqueness of community composition at each layer. In comparison to CT, no-tillage with stover mulching significantly increased the soil water content and root-associated organic carbon (SEOC), and decreased soil pH. Mineral nitrogen declined with depth to 60 cm and then increased to its maximum at 250–300 cm under CT and at 120–150 cm under NTNS and NTSM. More mineral nitrogen at 0–150 cm under low-disturbance practices would provide more available nitrogen for crops in the coming growing season, while the accumulated nitrogen at 150–300 cm under CT may leach into the groundwater. Taken together, our results show that low-disturbance practices can regenerate whole-soil bacterial diversity and potential function, and promote water retention and nitrogen holding capacity within the root zone, thus reducing the dose of nitrogen fertilizer and mitigating nitrogen contamination to deep groundwater, ultimately contributing to agricultural sustainability in Mollisol regions.

Changes in the quality of marcescent and shed senescent leaves during the dormant season

Changes in the quality of marcescent and shed senescent leaves during the dormant season

Seasonal hydrological traits in Salix psammophila and its responses to soil moisture and meteorological factors in desert areas

Drought is a key factor limiting vegetation water use and growth. More frequent and extreme drought events are increasing around the world, which may affect plant physiological reactions and vegetation restoration activities. The present study explored the seasonal trends of sap flow in Salix psammiphlia (Sf) by continuously collecting data on abiotic factors (net radiation [Rn], atmospheric relative humidity [Rh], atmospheric temperature [T], saturated vapor pressure difference [VPD], wind speed at 2 m height [U2], soil water storage [SWS], soil temperature [ST]) and transpiration rate (Ts) in the Mu Us Desert. According to the results, Sf exhibited considerable seasonal trends accompanied by a unimodal pattern during the growing season, and with a bimodal pattern during the dormant season. Notably, the ratio of nocturnal sap flow to whole daily sap flow could increase by up to 100% (from October to December and March to May). Multivariate stepwise regression and structural equation modeling results suggested that different factors drive the seasonal trends. During the growing season, Rn, VPD, and U2 controlled Ts directly (R2 = 0.80). While Ts was directly controlled by Rh, T, U2, SWS2 (20–100 cm) and ST_50 during the dormant season (R2 = 0.43). Topsoil freezing in winter may led to water stress in S. psammiphlia, and then appeared the bimodal pattern. The plants survived freezing drought water stress by using the soil moisture stored in the deep soil layer (50–100 cm) and reducing Ts, or even temporarily stopping transpiration. According to this data, the threshold of S. psammophila in the region was estimated to be 480–540 clusters/ha2. These findings could guide ecosystem restoration activities and facilitate sustainable development in dry and degraded regions.

Relationship of Supplement Intake Behavior to Performance and Grazing Behavior of Cattle Grazing Mixed-Grass Rangelands

This study evaluated the relationships between supplement intake behavior, beef cattle performance, and grazing behavior on dormant northern mixed-grass rangelands. In each of two years, a commercial herd of bred cows grazed a rangeland pasture from November to January. All cattle were managed as one contemporary group. Calf birth date, birth weight, and adjusted 205-day weaning weight were collected for each cow following the grazing season each year as cow performance metrics. During the grazing season, all cattle were provided free-choice access to a self-fed supplement. Supplement intake behavior was measured for each individual. Grazing behavior was monitored for 30 randomly selected individuals. The relationship of individual average daily supplement intake (R = 0.65; ρ = 0.65), supplement consumption rate (R = 0.58; ρ = 0.54), the coefficient of variation of supplement intake (R = 0.51; ρ = 0.50), and the amount of time spent at the feeder (R = 0.47; ρ = 0.49) were positively correlated and ranked across years (P < 0.01), suggesting individual animal supplement intake behavior is repeatable for cattle grazing dormant season rangelands. Additionally, there were multiple significant associations between supplement intake behavior, cattle performance, and grazing behavior (P ≤ 0.05); however, the majority were weak associations that accounted for minimal variation in cattle performance and grazing behavior (R ≤ 0.27; r2 ≤ 0.07). Although supplement intake behavioral traits were repeatable across years, its use as a metric to predict animal performance and grazing behavior may be limited.

Mapping time-to-trafficability for California agricultural soils after dormant season deep wetting

Soil compaction is a threat to agricultural soil function due to constriction of macro- and meso-pores necessary for air and water movement and crop root elongation. Soils are most vulnerable to compaction when moist. Agricultural soils saturated from winter precipitation or from intentional flooding for groundwater recharge may limit growers’ operational access to fields. The objective of this research was to develop guidance for rain-free “time-to-trafficability” (including shallow workability—when a soil is conducive to both tillage and traffic) after deep wetting, using soil survey data, pedotransfer functions, and a hydroclimatological modeling approach. Trafficability is defined as a threshold of field capacity (θfc) at the soil surface (0–10 cm), ranging from 85% of θfc (clays and silty clays) to 95% of θfc (sands and loamy sands). The θfc threshold is guided by the soil texture plasticity index, an indicator of compaction risk. 2911 soil profiles from soil survey databases were subjected to a wetting simulation, followed by drainage and evaporation using HYDRUS-1D across 11 locations representing mean annual potential evapotranspiration (PET) quantiles from 5% to 95%, four months (January-April), and three different years, assuming no precipitation. Rain-free time-to-trafficability was greatest in fine and loamy soils during cold months (January and February). However, seasonal effects on time-to-trafficability were more pronounced in loamy soils. Non-linear predictive functions were developed for each 0–10 cm textural class to enable mapping the typical time-to-trafficability across PET gradients, revealing clear regional and temporal patterns. Model derived estimates can inform agricultural managed aquifer recharge timing decisions and subsequent risk of soil compaction. Additional research is needed for validation and to better constrain time-to-trafficability estimates for loamy and fine textured soils, which show a greater degree of uncertainty amid greater risk of compaction indicated by plasticity indices.

A trade‐off between growth and hydraulic resilience against freezing leads to divergent adaptations among temperate tree species

Abstract In humid temperate forests, the occurrence of frequent freeze–thaw cycles (FTC) is a main factor limiting tree growth, as xylem embolism induced by FTC poses a serious threat to the hydraulic integrity of trees. A high resilience to hydraulic dysfunction involves the enhancement of embolism resistance and/or extra non‐structural carbohydrate (NSC) inputs for restoration of an impaired hydraulic system. However, potentially negative implications of such NSC allocation on tree growth have not yet been explored. At a temperate forest site of northeast China, we studied xylem hydraulics and NSC contents in relation to winter embolism resilience in 15 sympatric broadleaf tree species belonging to three genera with relatively high species richness, but having distinct strategies in maintaining hydraulic integrity over the winter, that is, Acer species that generate positive stem and root pressures contributing to winter embolism refilling, Betula species that only generate root pressure and Populus species that do not generate positive pressure. Acer and Betula species had higher soluble sugar contents in the dormant season and indeed had higher hydraulic resilience to FTC‐induced embolism but slower stem growth. Populus species had higher NSC contents during the growing season and their faster stem growth was also consistent with higher hydraulic efficiency and leaf photosynthetic rate. The positive correlation between tree trunk radial growth rate and hydraulic conductivity suggests that xylem water transport efficiency can be a fundamental basis for tree productivity due to a significant hydraulic‐photosynthetic coordination. The negative correlation between soluble sugar concentration in the dormant season and stem growth rate indicates that metabolic carbon costs for enhancing hydraulic resilience may compromise tree growth during the growing season. Comparisons among Acer, Betula and Populus and the correlation analyses based on phylogenetic independent contrasts strongly support the existence of a trade‐off between hydraulic resilience against FTC‐induced embolism and growth rate among sympatric tree species under humid temperate climate conditions. This trade‐off has likely contributed to the sorting of temperate tree species and genera to different niches along environmental gradients with respect to freezing stress and interspecific competition. A free Plain Language Summary can be found within the Supporting Information of this article.

Movement, activity, and landscape use patterns of heritage and commercial beef cows grazing Chihuahuan Desert rangeland

The objective of this study was to compare foraging behavior of mature Raramuri Criollo (RC, heritage breed) and Angus Hereford crossbred (AH, commercial breed) cows grazing Chihuahuan Desert rangeland during summer and winter in three consecutive years. Movement, activity, and spatial distribution variables were calculated from 10-min interval GPS positions of 5–11 randomly selected cows of each breed. Thirteen pasture pixel attributes were used to analyze grazing utilization and selection patterns of both breeds. Statistical mixed models were used to determine the effects of breed and season on all foraging response variables. Spatial regression analysis was used to examine resource utilization. Compared to AH, RC cows traveled farther at higher velocity rates, spent less time resting, more time grazing and traveling, explored larger areas as individuals, and exhibited lower herd cohesion. The RC herd explored more grazing patches (30-m pixel) overall and exhibited lower patch residence times in winter, a foraging strategy linked with lighter environmental footprint. During summer, similar pixel variables explained re-visitation rates of cows of both breeds. Both breeds avoided areas far from water, but RC cows showed higher avoidance of pixels farther out from a drinker during the dormant season. RC cows appeared to exhibit a keener ability to select patches with differing surface temperature, and greenness compared to AH counterparts. RC cows showed higher preference for pixels with high shrub density than AH counterparts in summer. During the dormant season, AH cows exhibited a strong preference for black grama patches, a species with high ecological value, and higher avoidance of patches with high density of other grasses. Differences in foraging behavior documented in this study support the hypothesis that RC cattle could impose a lighter footprint on desert rangeland relative to commonly raised commercial beef cattle.

Development of a Nocturnal Temperature Inversion in a Small Basin Associated with Leaf Area Ratio Changes on the Mountain Slopes in Central Japan

Nocturnal temperature inversion (NTI) is an important factor characterizing the local climate in mountainous areas. In central Japan, most of the mountain slopes are covered by forests, but the effects of their leaf expansion/fall on the NTI variations in basins have not been clarified. According to a three-year leaf area index (LAI) observation in the mixed forest of the Sugadaira Highland (1320 m a.s.l.), Nagano Prefecture, Japan, we identified weakening of the NTI associated with leaf expansion and strengthening after leaf fall in a small basin. Using digital elevation and land-cover data, we defined the distribution of the deciduous and mixed forests in the catchment area of nocturnal cold air drainage. The estimated timings of leaf expansion/fall at the catchment scale based on the effective cumulative temperature almost coincided with the NTI changes. Micrometeorology observations showed that NTI at the forest floor and downslope winds at the adjacent grassland strengthened during the dormant (leafless) season in the nighttime when the radiative cooling is strong. Calm and clear nights were chosen during the spring dormant season and the summer growing season for 22 and 30 nights, respectively. The heat loss during the cold-air pool development was estimated, and converted to storage heat flux in the forest areas. The storage heat flux was 3.8 W m−2 more on average in the growing season than the dormant season, and it was less than that of forests estimated in previous studies (several 10 W m−2), indicating that an increase in storage heat flux of the forests with leaf expansion could cancel nocturnal radiative cooling and weaken gravity currents at the forest floor.

Quantification of Urban Forest and Grassland Carbon Fluxes Using Field Measurements and a Satellite‐Based Model in Washington DC/Baltimore Area

AbstractCities are taking the lead on climate change mitigation with ambitious goals to reduce carbon dioxide (CO2) emissions. The implementation of effective mitigation policies will require accurate measurements to guide policy decisions and monitor their efficacy. Here, we present a comprehensive CO2inventory of an urban temperate forest and unmanaged grassland using field observations. We estimate the annual storage of CO2by vegetation and soils and place our biogenic flux estimates in the context of local fossil fuel (FF) emissions to determine when, where, and by how much biogenic fluxes alter net CO2flux dynamics. We compare our hourly estimates of biogenic fluxes in the forest site to modeled estimates using a modified version of Urban‐Vegetation Photosynthesis and Respiration Model (Urban‐VPRM) in Washington DC/Baltimore area presenting the first urban evaluation of this model. We estimate that vegetation results in a net biogenic uptake of −2.62 ± 1.9 Mg C ha−1 yr−1in the forest site. FF emissions, however, drive patterns in the net flux resulting in the region being a net source of CO2on daily and annual timescales. In the summer afternoons, however, the net flux is dominated by the uptake of CO2by vegetation. The Urban‐VPRM closely approximates hourly forest inventory based estimates of gross ecosystem exchange but overestimates ecosystem respiration in the dormant season by 40%. Our study highlights the importance of including seasonal dynamics in biogenic CO2fluxes when planning and testing the efficacy of CO2emission reduction polices and development of monitoring programs.

Automated Vigor Estimation on Vineyards

Estimating the balance or vigor in vines, as the yield to pruning weight relation, is a useful parameter that growers use to better prepare for the harvest season and to establish precision agriculture management of the vineyard, achieving specific site planification like pruning, debriefing or budding. Traditionally growers obtain this parameter by first manually weighting the pruned canes during the vineyard dormant season (no leaves); second during the harvest collect the weight of the fruit for the vines evaluated in the first step and then correlate the two measures. Since this is a very manual and time-consuming task, growers usually obtain this number by just taking a couple of samples and extrapolating this value to the entire vineyard, losing all the variability present in theirs fields, which imply loss in information that can lead to specific site management and consequently grape quality and quantity improvement. In this paper we develop a computer vision-based algorithm that is robust to differences in trellis system, varieties and light conditions; to automatically estimate the pruning weight and consequently the variability of vigor inside the lot. The results will be used to improve the way local growers plan the annual winter pruning, advancing in the transformation to precision agriculture. Our proposed solution doesn\textsc{\char13}t require to weight the shoots (also called canes), creating prescription maps (detail instructions for pruning, harvest and other management decisions specific for the location) based in the estimated vigor automatically. Our solution uses Deep Learning (DL) techniques to get the segmentation of the vine trees directly from the image captured on the field during dormant season

Rhizosphere effects on soil extracellular enzymatic activity and microbial abundance during the low-temperature dormant season in a northern hardwood forest

Plant roots alter nutrient cycling, including nitrogen (N) and phosphorus (P) cycling, within the soil surrounding them (rhizosphere) by affecting microbes and enzyme activities. Recent studies have focused on nutrient uptake by plants in low-temperature seasons. This study aimed to reveal the nutrient dynamics in the rhizosphere during low-temperature seasons in a northern hardwood forest in Japan. For this purpose, the potential extracellular enzymatic activity, bacterial, fungal, and archaeal abundances, and soil chemical properties in the rhizosphere of canopy trees and understory vegetation and non-rhizosphere bulk soil were measured at the beginning of the dormant season (November), end of the dormant season (April and May), and middle of the growing season (August) in a northern hardwood forest in Japan. The abundance of fungi was 1.1–1.7 times higher in the rhizosphere than in non-rhizosphere bulk soil regardless of the season. The activity of enzymes involved in N- and P- cycles in the rhizospheres was also 1.4 to 4.0 and 1.3 to 1.9 times higher than that in bulk soil, respectively. The concentration of extractable organic N was 1.5–2.0 times higher in the rhizosphere than in the non-rhizosphere bulk soil at the beginning and end of the dormant season, respectively, but this trend was not observed in the middle of the growing season for organic N. Since the concentration of nutrients in the rhizosphere is determined by the balance between nutrient uptake by fine roots and root-induced acceleration of decomposition, our results suggest that plant roots would accelerate N and P cycles during the dormant season, even though the amount of nutrient uptake by plants was lower during the season.

Fire Seasonality, Seasonal Temperature Cues, Dormancy Cycling, and Moisture Availability Mediate Post-fire Germination of Species With Physiological Dormancy.

Fire seasonality (the time of year of fire occurrence) has important implications for a wide range of demographic processes in plants, including seedling recruitment. However, the underlying mechanisms of fire-driven recruitment of species with physiological seed dormancy remain poorly understood, limiting effective fire and conservation management, with insights hampered by common methodological practices and complex dormancy and germination requirements. We sought to identify the mechanisms that regulate germination of physiologically dormant species in nature and assess their sensitivity to changes in fire seasonality. We employed a combination of laboratory-based germination trials and burial-retrieval trials in natural populations of seven species of Boronia (Rutaceae) to characterize seasonal patterns in dormancy and fire-stimulated germination over a 2-year period and synthesized the observed patterns into a conceptual model of fire seasonality effects on germination. The timing and magnitude of seedling emergence was mediated by seasonal dormancy cycling and seasonal temperature cues, and their interactions with fire seasonality, the degree of soil heating expected during a fire, and the duration of imbibition. Primary dormancy was overcome within 4–10 months’ burial and cycled seasonally. Fire-associated heat and smoke stimulated germination once dormancy was alleviated, with both cues required in combination by some species. For some species, germination was restricted to summer temperatures (a strict seasonal requirement), while others germinated over a broader seasonal range of temperatures but exhibited seasonal preferences through greater responses at warmer or cooler temperatures. The impacts of fires in different seasons on germination can vary in strength and direction, even between sympatric congeners, and are strongly influenced by moisture availability (both the timing of post-fire rainfall and the duration soils stay moist enough for germination). Thus, fire seasonality and fire severity (via its effect on soil heating) are expected to significantly influence post-fire emergence patterns in these species and others with physiological dormancy, often leading to “germination interval squeeze.” Integration of these concepts into current fire management frameworks is urgently required to ensure best-practice conservation. This is especially pertinent given major, ongoing shifts in fire seasonality and rainfall patterns across the globe due to climate change and increasing anthropogenic ignitions.

Evaluation of Pruning Wound Protection Products for the Management of Almond Canker Diseases in California.

Almond trunk and branch canker diseases constitute a major cause of tree mortality in California. Numerous fungal pathogens have been associated with these canker diseases and pruning wounds act as major infection courts. Before this study, there were no products registered in California for the management of these diseases. In this study, fungicidal products including synthetic chemistries, biocontrols, paint, and a sealant were evaluated for preventing fungal pathogen infection via pruning wounds. In four field trials conducted over two dormant seasons, 16 pruning wound treatments were tested using handheld spray applications against five almond canker pathogens, namely Botryosphaeria dothidea, Neofusicoccum parvum, Cytospora sorbicola, Ceratocystis destructans, and Eutypa lata. The fungicide thiophanate-methyl (Topsin M; United Phosphorus, Bandra West, Mumbai, India) provided 82% overall disease prevention against four fungal pathogens. The biological control agent, Trichoderma atroviride SC1 (Vintec; Bi-PA, Londerzeel, Belgium), tested at three application rates, resulted in 90 to 93% protection of pruning wounds in field trials, and for individual pathogens ranged from 81 to 100% protection for the three rates. At the time of this publication, Vintec is being considered for registration as a biological control product for the prevention of almond canker diseases, while Topsin M is recommended to growers for the prevention of almond canker diseases. This research indicates that effective protection of pruning wounds from infection by almond canker pathogens can be achieved with a one-time spray application of thiophanate-methyl or the biocontrol T. atroviride SC1 (recommended 2 g/liter) after pruning.