Fine Fuels Research Articles

Preceding Fall Drought Conditions and Overwinter Precipitation Effects on Spring Wildland Fire Activity in Canada

Spring fire activity has increased in parts of Canada, particularly in the west, prompting fire managers to seek indicators of potential activity before the fire season starts. The overwintering adjustment of the Canadian Fire Weather Index System’s Drought Code (DC) is a method to adjust and carry-over the previous season’s drought conditions into the spring and potentially point to what lies ahead. The occurrence of spring fires is most strongly influenced by moisture in fine fuels. We used a zero-inflated Poisson regression model to examine the impact of the previous end of season Drought Code (DCf) and overwinter precipitation (Pow) while accounting for the day-to-day variation in fine fuel moisture that drives ignition potential. Impacts of DCf and Pow on area burned and fire suppression effectiveness were also explored using linear and logistic regression frameworks. Eight fire management regions across the boreal forests were analyzed using data from 1979 to 2018. For the majority of regions, drier fall conditions resulted in more human-caused spring fires, but not in greater area burned or reduced suppression effectiveness. The influence of Pow was much more variable pointing to the conclusion that Pow alone is not a good indicator of spring drought conditions.

Falkland Island peatland development processes and the pervasive presence of fire

Palaeoecological analyses of Falkland Island peat profiles have largely been confined to pollen analyses. In order to improve understanding of long-term Falkland Island peat development processes, the plant macrofossil and stable isotope stratigraphy of an 11,550 year Falkland Island Cortaderia pilosa (‘whitegrass’) peat profile was investigated. The peatland developed into an acid, whitegrass peatland via a poor fen stage. Macrofossil charcoal indicate that local fires have frequently occurred throughout the development of the peatland. Raman spectroscopy analyses indicate changes in the intensity of burning which are likely to be related to changes in fuel types, abundance of fine fuels due to reduced evapotranspiration/higher rainfall (under weaker Southern Westerly Winds), peat moisture and human disturbance. Stable isotope and thermogravimetric analyses were used to identify a period of enhanced decomposition of the peat matrices dating from ∼7020 cal yr BP, which possibly reflects increasing strength of the Southern Westerly winds. The application of Raman spectroscopy and thermogravimetric analyses to the Falkland Island peat profile identified changes in fire intensity and decomposition which were not detectable using the techniques of macrofossil charcoal and plant macrofossil analyses.

Hydrogenation of Lignin-Derived Phenolic Compound Eugenol over Ruthenium-Containing Nickel Hydrotalcite-Type Materials

Sustainable production of fine chemicals and fuels from renewable energy resources are important process-es in the current scenario of the energy crisis. In this study, we have reported complete hy...

The Canadian versus the National Forest Fire Danger Rating Systems tested in Mediterranean forests fire Crete, Greece

The Canadian Forest Fire Danger Rating System (CFFDRS) and the National Forest Fire Danger Rating System (NFFDRS) were exercised under the Mediterranean forest type conditions of Crete Island, Greece in 2008–2009. The CFFDRS shows a high association between the assessed values of the duff moisture content on one hand and the Fine Fuel Moisture Code and the Duff Moisture Code on the other hand. During the designated fire seasons, there was an insignificant association between the Fire Weather Index and the wild forest fires which are contrary associated with wildfire occurrences. Meanwhile, the NFFDRS showed monitoring capabilities but with the insufficient prediction of the daily fire danger in the Mediterranean forests. During the tested forest fire seasons, there was an unstable association between the burnt area and the fire occurrences. Consequently, there was no significant correlation between the CFFDRS and the litter soil content. Although, CFFDRS has a higher prediction accuracy of moisture content of some shallow roots annual plants within the studied area. The findings of the current research emphasized that there is no single system that is adequate enough for both soil moisture content and the annuals moisture content simultaneously.

A Multi-Scale Approach to Predict the Fractional Cover of Medusahead (Taeniatherum Caput-Medusae)

Medusahead is an aggressive, winter annual that is of dire concern for the health and sustainability of western rangelands in the United States. Medusahead reduces plant diversity, alters ecosystem function, and reduces carrying capacities for both livestock and wildlife. The species has competitive advantages over cheatgrass and native grasses that causes an increased amount of fine fuels deposited on western rangelands. The Channeled Scablands of eastern Washington in the United States represent a typical example of a region being challenged by the expansion of this weed. The costs of the invasion are high and financial constraints can limit successful management. Managers need the ability to identify medusahead across entire landscapes, so they can work towards effective and efficient management approaches. Remote sensing offers the ability to measure vegetation cover at large spatial scales, which can lead to a better understanding of the invasive characteristics of problematic species like medusahead. For instance, research has been successful in creating large-scale distribution maps of cheatgrass over western rangelands. Many applications rely on the phenological characteristics of a target plant which can present problems in separating two species with similar phenologies (i.e. cheatgrass & medusahead). A medusahead-specific map gives managers the flexibility to prioritize and direct management needs when attempting to control the spread of medusahead into non-invaded areas. This study integrated GPS acquired field locations from three study sites (Sites S, C, & N) and imagery from two remote sensing platforms (1-m aerial imagery & 30-m Landsat), to model and predict fractional cover of medusahead over 37,000+ ha of rangelands in the Channeled Scabland region of eastern Washington. Using a multi-scaled approach, this research showed that regression tree algorithms can model the complex spectral response of senesced medusahead using late summer Landsat scenes. The predictive performances resulted in a R2 of 0.80 near the model's training site (Site S) and an average R2 of 0.68 away from the training site (Sites C & N). This research provides a non-phenological approach to produce accurate large-scale, distribution maps of medusahead which can aid land managers who are challenged by its invasion.

Experimental study on flaming ignition of pine needles by simulated lightning discharge

Lightning is one of the main natural causes for wildfires, and lightning-caused wildfires are responsible for substantial losses of ecology, property, and lives worldwide. There is very limited research on the ignition process and mechanism by lightning, and significant knowledge gaps still exist. In this work, the flaming ignition process of fine natural fuels (pine needles) by simulated lightning discharge with a long-continuing current was studied experimentally. The 50% ignition probability was predicted by a logistic regression method. It was found that, under the current experimental conditions, the energy of simulated discharge needed for igniting pine needles increases with increasing fuel moisture content. The flaming duration is highly dependent on the fuel moisture content, and the moisture content dominates the risk of lightning-caused ignition when it is high enough. It was visually observed that the ignition underwent a very special process including three stages: discharge heating stage, thermal feedback stage, and self-sustaining flame stage, different from ignitions by firebrands or flame radiation. Discharge energy and fuel moisture content can affect the flaming ignition by dominating the first two stages and the last stage, respectively.

Prescribed fire effects on Pinus palustris woodland development after catastrophic wind disturbance and salvage logging

Scientifically informed strategies to manage naturally disturbed forests are critical to support the sustained provisioning of ecosystem goods and services. In fire-adapted ecosystems, catastrophic canopy removal can disrupt surface fuel continuity and challenge the continued use of low-intensity prescribed fire. Although salvage logging is used globally after natural disturbance events, little information is available on how salvage logging interacts with subsequent use of prescribed fire. This study investigated the impacts of operational-scale prescribed fire on Pinus palustris (longleaf pine) stand development in areas differentially impacted by an April 2011 EF3 tornado and a subsequent salvage logging operation. Twenty 0.04-ha nested plots were systematically established in mature, wind-disturbed, and salvage-logged sites (n = 60) to measure seedlings, saplings, woody fuels, organic litter, and mineral soil before and after prescribed fire. Prescribed fire-induced fine fuel consumption, mineral soil exposure, and substantial sapling density reductions were observed throughout the treatment area. Prescribed fire effects were not apparently impacted by salvage logging, which did not alter the amount of fine fuels available for prescribed fire consumption. Despite overall sapling density reductions, fire-resistant P. palustris saplings exhibited increased densities on wind-disturbed and salvage-logged sites. Pinus palustris seedlings, however, exhibited marked post-fire reductions, which contrasted with a strong resprouting response observed among top-killed hardwood species. Concerning woody plant recovery, this study indicated that salvage logging was not detrimental to P. palustris stand development and that prescribed fire effectively enhanced recovery in unlogged and logged wind-disturbed sites.

Radical-based photoinactivation of fatty acid photodecarboxylases

Fatty acid photodecarboxylases (FAP) are a recently discovered family of FAD-containing, light-activated enzymes, which convert fatty acids to n-alkanes/alkenes with potential applications in the manufacture of fine and speciality chemicals and fuels. Poor catalytic stability of FAPs is however a major limitation. Here, we describe a methodology to purify catalytically stable and homogeneous samples of recombinant Chlorella variabilis NC64A FAP (CvFAP) from Escherichia coli. We demonstrate however that blue light-exposure, which is required for photodecarboxylase activity, also leads to irreversible inactivation of the enzyme, especially in the absence of palmitate substrate. Photoinactivation is attributed to formation of protein based organic radicals, which were observed by EPR spectroscopy. To suppress photoinactivation, we prepared stable and catalytically active FAP in the dark. The steady-state kinetic parameters of CvFAP (kcat: 0.31 ± 0.06 s−1 and KM: 98.8 ± 53.3 μM) for conversion of palmitic acid to pentadecane were determined using gas chromatography. Methods described here should now enable studies of the catalytic mechanism and exploitation of FAPs in biotechnology.

Catalytic transfer hydrogenolysis of lignin α-O-4 model compound 4-(benzyloxy)phenol and lignin over Pt/HNbWO6/CNTs catalyst

Cleavage of C–O bonds in aryl ether through the catalytic transfer hydrogenolysis (CTH) is an encouraging method for the valorization of lignin into fine chemicals and liquid fuels. In this contribution, the CTH of typical lignin α-O-4 model compound 4-(benzyloxy)phenol (BOP) and lignin extracted from ash wood have been explored over 0.45 wt% Pt/HNbWO6/CNTs catalyst. The effect of solvents was elaborated and the highest catalytic activity was achieved in the CTH of BOP using isopropanol as the solvent (98.1%). This was because isopropanol can provide more hydrogen atoms to promote CTH reaction due to the weakest interaction between isopropanol and BOP among all H-donor solvents. The favorable results obtained in the model compound study inspired us to afford Pt/HNbWO6/CNTs catalyst in the CTH of lignin. The relative oxygen content of lignin was sharply decreased after the CTH process, and the higher heating value (HHV) significantly increased from 21.4 MJ/kg to 30.8 MJ/kg. GPC, FT-IR, GC-MS, and 2D-NMR results revealed that lignin was successfully depolymerized into small molecule compounds over Pt/HNbWO6/CNTs catalyst through the CTH process. Thereinto, phenolic compounds were the major components in the liquid products in which most of them were monophenols. The results obtained in this work shed light on that Pt/HNbWO6/CNTs was a favorable catalyst in the depolymerization of lignin into valuable phenolic compounds via the CTH method.

Photoredox dual reaction for selective alcohol oxidation and hydrogen evolution over nickel surface-modified ZnIn2S4

The photocatalytic coupling reaction can be conducted in one pot to realize the simultaneous utilization of electrons and holes, thereby obtaining value-added fine chemicals and fuels. Herein, we report a binary nickel modified ZnIn2S4 (Ni:ZIS) for highly efficient photocatalytic selective oxidation of benzyl alcohol (BA) to benzaldehyde (BAD) integrated with hydrogen (H2) evolution, in which Ni can promote photogenerated charge transfer for enhancing photoactivity. Particularly, the products of converting BA to aromatic compounds over blank ZnIn2S4 (ZIS) and Ni:ZIS show a marked difference under the same reaction conditions. Hydrobenzoin (HB) is the primary product over blank ZIS. After the introduction of Ni, the formation of HB is dramatically suppressed, resulting in higher selectivity of BAD, because the introduction of Ni facilitates the α-H abstraction. In addition, an analogous phenomenon has been observed on Ni-based compounds modified ZIS, such as NixP and NiS. It is hoped that this work would provide a feasible paradigm for modifying the surface of photocatalysts to tune the selectivity of product-oriented alcohols oxidation coupled with H2 evolution in water.

Contemporary Fire Regimes Provide a Critical Perspective on Restoration Needs in the Mexico-United States Borderlands

The relationship between people and wildfire has always been paradoxical: fire is an essential ecological process and management tool, but can also be detrimental to life and property. Consequently, fire regimes have been modified throughout history through both intentional burning to promote benefits and active suppression to reduce risks. Reintroducing fire and its benefits back into the Sky Island mountains of the United States-Mexico borderlands has the potential to reduce adverse effects of altered fire regimes and build resilient ecosystems and human communities. To help guide regional fire restoration, we describe the frequency and severity of recent fires over a 32-year period (1985-2017) across a vast binational region in the United States-Mexico borderlands and assess variation in fire frequency and severity across climate gradients and in relation to vegetation and land tenure classes. We synthesize relevant literature on historical fire regimes within 9 major vegetation types and assess how observed contemporary fire characteristics vary from expectations based on historical patterns. Less than 28% of the study area burned during the observation period, excluding vegetation types in warmer climates that are not adapted to fire (eg, Desertscrub and Thornscrub). Average severity of recent fires was low despite some extreme outliers in cooler, wetter environments. Midway along regional temperature and precipitation gradients, approximately 64% of Pine-Oak Forests burned at least once, with fire frequencies that mainly corresponded to historical expectations on private lands in Mexico but less so on communal lands, suggesting the influence of land management. Fire frequency was higher than historical expectations in extremely cool and wet environments that support forest types such as Spruce-Fir, indicating threats to these systems possibly attributable to drought and other factors. In contrast, fires were absent or infrequent across large areas of Woodlands (~73% unburned) and Grasslands (~88% unburned) due possibly to overgrazing, which reduces abundance and continuity of fine fuels needed to carry fire. Our findings provide a new depiction of fire regimes in the Sky Islands that can help inform fire management, restoration, and regional conservation planning, fostered by local and traditional knowledge and collaboration among landowners and managers.

Climatic and edaphic gradients predict variation in wildland fuel hazard in south‐eastern Australia

Understanding spatial variation in wildland fuel is central to predicting wildfire behaviour as well as current and future fire regimes. Vegetation (plant material) – both live (biomass) and dead (necromass) – constitutes most aspects of wildland fuel (hereafter ‘fuel’). It therefore is likely that factors influencing vegetation structure and composition – climate, soils, disturbance – also will influence fuel structure and associated hazard. Nonetheless, these relationships are poorly understood in temperate environments. In this study, we used an extensive database of fuel hazard assessments to determine the extent to which environmental variables (climatic conditions and soil type) and disturbance (fire) can predict fuel hazard in native vegetation across south‐eastern Australia. Fuel hazard ratings are based on the horizontal and vertical continuity of fine fuels (dead plant material < 6 mm thick, and live plant material < 3 mm thick) that burn in the flaming front of a fire. These scores are used widely by fire managers in Australia. We used environmental and disturbance variables to develop models to predict spatial patterns of hazard for each fuel stratum (surface, near‐surface, elevated and bark) and the height of two fuel strata (near‐surface, elevated). Soil, climate and time since fire were strong predictors of fuel hazard for at least one stratum, and soil predictors were the strongest predictors of fuel hazard across all strata. We used models to predict fuel hazard by stratum at a fixed time since fire in two regions with contrasting environments in south‐eastern Australia to better understand the spatial arrangement of fuel hazard. Fuel hazard varied within and between regions, emphasising the complexity and heterogeneity of fuel patterns that affect fuel hazard from local to landscape extents. The models improve the basis for analysing fuel hazard patterns and therefore increase the capacity to predict fire regimes under future climates.

Scaling-up individual-level allometric equations to predict stand-level fuel loading in Mediterranean shrublands

Allometric biomass equations developed for individual shrubs can be applied to estimate shrubland fuels from measurements of cover and average height by species. Shrubs are a major component of surface fuels in many fire-prone ecosystems. Shrub fuel loading is often estimated by “double sampling”, where data from a destructive vegetation survey is used to model vegetation-fuel relationships (development phase), and these relationships are then applied to vegetation data from a second survey (application phase). Vegetation-fuel relationships can be modeled at different levels of vegetation detail, from individual plants to stands, but the increased effort of detailed measurements may compromise large-scale applications. To facilitate fuel loading assessments in Mediterranean shrublands, we present and test a novel method to estimate stand-level shrub loading that consists in applying individual-level allometric equations to vegetation plot data collected by measuring the percent cover and mean height of each shrub species. We used individual-level data (i.e., plant dimensions and dry weights) to develop allometric equations for total and fine (leaves and branches < 6 mm) biomass of 26 Mediterranean shrub species. We then evaluated the accuracy and precision of the proposed method in comparison to an approach assuming constant bulk density, using data from 131 vegetation plots and taking as benchmark stand-level loading estimates derived by aggregation of individual biomass allometric estimates. A second set of 13 plots was used to quantify the additional error derived from visual estimation of species mean height and cover. The performance of species-specific models was acceptable in estimating total and fine biomass at the individual level. When based on species mean height and cover data, stand-level fuel loading estimates calculated using the proposed method had a better precision and accuracy than those obtained using bulk density values (− 4 vs. + 39% in relative bias; 10 vs. 40% in relative MAE). Visual estimation of species mean height and percent cover led to 10 and 16% increase in MAE for species loading estimates of total and fine fuels, respectively, with respect to estimates obtained without this source of error. Our approach to estimate shrub loading allows combining fast species-level vegetation sampling with the flexibility of individual-level allometries to model to size-related variations of bulk density.

Damage‐Free Solar Dewatering of Micro‐Algal Concentrates via Multifunctional Hierarchical Porous Graphene

AbstractA damage‐free dewatering method, without centrifugation, mechanical squeezing, and solar irradiation, is important for separating solids from pure water and can be used for the production of biomass‐derived renewable fine chemicals, fertilizers, and fuels in biotechnological applications. Herein a damage‐free steam generator constructed by a single sheet of nitrogen‐doped nanoporous graphene and nitrogen‐doped porous graphene foam as hierarchical structures is reported. The multifunctional hierarchical graphene steam generator has a high water evaporation rate (1.54 kg m−2 h−1) accompanied by a high energy conversion efficiency (82.2%). Furthermore, it exhibits excellent persistence in dewatering performance over multiple uses, unlike the graphene foam that shows marked reduction in performance after several reuses. Therefore, the multifunctional hierarchical graphene steam generator is a cost‐effective material for accelerating both the harvesting of biomass concentrates and the production of pure water.

Assessment of resource-use strategy of some common woody plant species grown under semiarid climatic condition of Quetta Balochistan-Pakistan

The aim of this study was to evaluate the resource use strategy of some woody plants in semi-arid climatic condition of Quetta, Balochistan Pakistan. The plant sample were collected from eleven selected different woody plant species namely; Fraxinus xanthoxyloides, Robinia pseudoacacia, Ficus carica, Morus alba, Morus nigra, Ailanthus altissima, Melia azedarach, Pinus halepensis. Malus domestica, Prunus armeniaca and Tamarix sp. during three seasons spring, summer and autumn, in 2017-18. The resources-use strategy of the selected plant species was determined by commonly used indicators such as Leaf Relative Water Content (LRWC), Leaf Dry Matter Content (LDMC) and Live Fine Fuel Moisture Content (LFFMC). Data regarding annual average RWC, LDMC and LFFMC in all the investigated plant was found in ranged between 25.12-73.89 %, 0.21-0.40 mg/g and 58.0-221.0 mg/g, respectively. The maximum annual average RWC, LDMC and LFFMC was reported in Ficus carica, Pinus halepensis and Melia azedarach, while the minimum was found in Alianthus altissima, Fraxinus xanthoxyloides and Alianthus altissima, respectively. Among seasons; the highest RWC was found during spring which followed by summer and minimum was originated in autumn season. The higher LDMC was recorded in autumn season as compared to summer and spring, suggesting a more efficient conservation of nutrients and the maximum LFFM contents were found in autumn followed by summer and lowest was in spring. Keywords: Balochistan; Plant species; Relative water content; Live fine fuel moisture content; Dry matter content http://dx.doi.org/10.19045/bspab.2019.80127

CFD Design of Hydrogenation Reactor for Transformation of Levulinic Acid to γ-Valerolactone (GVL) by using High Boiling Point Organic Fluids

Levulinic acid (LA) has been ranked as one of the “Top 10” building blocks for future bio-refineries as proposed by the US Department of Energy. It is considered one of the most important platform molecules for the production of fine chemicals and fuels based on its compatibility with existing processes, market economics, and industrial ability to serve as a platform for the synthesis of important derivatives. Hydrogenation of LA to produce γ-valerolactone (GVL) is an active area of research due to the potential of GVL to be used as a biofuel in its own right and for its subsequent transformation into hydrocarbon fuels. This paper contains a new design for a simple, cost effective, and safe hydrogenation reactor for the transformation of levulinic acid to γ-valerolactone (GVL) by utilizing high boiling point organic fluid. The hydrogenation reactor is composed of a heating source—organic fluid (called “DOWTHERM A” or “thermex”) and the catalytic reactor. The advantages of high boiling temperature fluids, along with advances in hydrocracking and reforming technologies driven by the oil and gas industries, make the organic concept more suitable and safer (water coming in contact with liquid metal is well understood in the metallurgical industry to be a steam explosion hazard) for heating the hydrogenation reactor. COMSOL multi-physics software version 4.3b was applied in this work and simultaneously solves the continuity, Navier-Stokes (fluid flow), energy (heat transfer), and diffusion with chemical reaction kinetics equations. It was shown that the heat flux supplied by the DOWTHERM A organic fluid could provide the necessary heat flux required for maintaining the hydrogenation process. It was found that the mass fractions of hydrogen and levulinic acid decreased along the reactor axis. The GVL mass fraction increased along the reactor axis.

Post-spruce beetle timber salvage drives short-term surface fuel increases and understory vegetation shifts

Recent, widespread spruce beetle (Dendroctonus rufipennis) outbreaks have driven extensive tree mortality across western North America. Post-disturbance forest management often includes salvage logging to capture economic value of dead timber, reduce fire hazard, and meet other social or ecological objectives. Little is known about effects of salvage logging on surface fuel loads or plant understory communities in Engelmann spruce (Picea engelmannii)-dominated forests. We sampled fine and coarse woody debris, ground cover, and plant species composition along transects in spruce-beetle impacted stands in southwestern Colorado, USA. Twenty stands had been subject to clearcut 1–2 years prior to sampling; 32 stands were unlogged controls.Salvage logged stands exhibited altered surface fuels, ground cover, plant species cover, and community composition. Salvage increased 1-, 10-, and 100-hr fuels, and cover by bare ground and woody debris; cover by litter and cryptogams was reduced. Understory plant cover was reduced in salvaged stands, primarily due to losses of shrub cover. We found no difference in species diversity or richness between treated stands and controls. Salvage logging also drove shifts in plant community composition. Mean cover by non-native species was low, and not different, between control and salvage stands.Our study characterizes short-term effects that will undoubtedly change substantially over longer periods, in particular due to anticipated tree seedling growth and movement of standing dead wood from the canopy to the surface. In the near term, abundant fine woody surface fuels at salvage sites could influence the likelihood and rate of spread of surface fires, though over time we expect surface fuels in untreated stands to increase to comparable or greater levels than in salvaged stands. Differences in vascular plant cover and composition imparted by salvage harvests is also expected to change over time, though whether treated and untreated communities diverge or converge is not known. As such, we recommend that salvage harvest effects be monitored over extended time frames in order to detect longer-term trends.

Influence of Fine Fuel Particles on Ash Deposition in Industrial-Scale Biomass Combustion: Experiments and Computational Fluid Dynamics Modeling

This work focuses on the contribution of fuel particles with diameters smaller than 1 mm on the ash deposition behavior of different kinds of biomass feedstock. Special emphasis lies on their impac...

Evaluation of Gridded Precipitation Data and Interpolation Methods for Forest Fire Danger Rating in Alberta, Canada

AbstractThe Canadian Forest Fire Weather Index System is the primary measurement of wildfire danger in Canada. Interpolating daily precipitation, one of the inputs for the Fire Weather Index System is a key challenge in areas without sufficient weather stations. This work evaluates the performance of gridded precipitation from the Canadian Precipitation Analysis (CaPA) System and six interpolation methods to achieve the best fire danger rating in Alberta, Canada. Results show that the CaPA System has only average performance due to limited radar coverage (10%) in the forested region; however, using the CaPA System as a covariate with regression kriging generates significantly better precipitation estimates. Ordinary kriging, regression kriging with elevation as a covariate, and the thin‐plate smoothed spline are methods with similar performance. Fuel moisture codes of the Fire Weather Index System respond differently to precipitation amounts due to differences in their time constants for drying. Fine fuels with a short drying time (Fine Fuel Moisture Code) are best estimated by the CaPA System because of its enhanced skill in estimating small precipitation events. Compacted organic fuels with longer drying times (Duff Moisture Code and Drought Code) are best estimated by regression kriging with CaPA because it better predicts significant precipitation events. The dense fire weather station network in our study area (~3.0 stations/10,000 km2) allows us to perform a sensitivity analysis, and we find that a threshold of &gt;0.5 stations/10,000 km2 is needed for regression kriging with CaPA to become appreciably better than the CaPA System.

Native lagomorphs suppress grass establishment in a shrub-encroached, semiarid grassland.

Shrub encroachment into arid grasslands has been associated with reduced grass abundance, increased soil erosion, and local declines in biodiversity. Livestock overgrazing and the associated reduction of fine fuels has been a primary driver of shrub encroachment in the southwestern United States, but shrublands continue to persist despite livestock removal and grassland restoration efforts. We hypothesized that an herbivory feedback from native mammals may contribute to continued suppression of grasses after the removal of livestock. Our herbivore exclusion experiment in southeastern Arizona included five treatment levels and allowed access to native mammals based on their relative body size, separating the effects of rodents, lagomorphs, and mule deer. We included two control treatments and replicated each treatment 10 times (n = 50). We introduced uniform divisions of lawn sod (Cynodon dactylon) into each exclosure for 24‐hr periods prior to (n = 2) and following (n = 2) the monsoon rains and used motion‐activated cameras to document herbivore visitations. In the pre‐monsoon trials, treatments that allowed lagomorph access had less sod biomass relative to other treatments (p < 0.001), averaging 44% (SD 36%) and 29% (SD 45%) remaining biomass after the 24‐hr trial periods. Following the onset of monsoons, differences in remaining biomass among treatments disappeared. Desert cottontails (Sylvilagus audubonii) were detected more frequently than any of the other 11 herbivore species present at the site, accounting for 83% of detections during the pre‐monsoon trials. Significantly more (p < 0.001) desert cottontails were detected during the pre‐monsoon trials (2,077) compared to the post‐monsoon trials (174), which coincided with biomass removal from lagomorph accessible treatments. We conclude that desert cottontails are significant consumers of herbaceous vegetation in shrub‐encroached arid grasslands and they, along with other native herbivores, may act as a biotic feedback contributing to the competitive advantage and persistence of shrubs.