Defoliation Frequency Research Articles

Harvest Management Effects on Canopy Height and Light Interception of ‘Performer’ Switchgrass and its Relationship with Weed Infestation

Defoliation management can determine the presence or absence of desirable forage species. Canopy characteristics and light interception are two critical determinants of productivity and can influence weed pressure. The objectives of this study were to determine the effect of the factorial combination of four defoliation heights (clipped to 10, 20, 30, and 40 cm; DH) and four defoliation frequencies (clipped every 3, 6, 9, and 12 wk; DF) on light interception, canopy height, and weed canopy cover and frequency for ‘Performer’ (Panicum virgatum L.) switchgrass and to relate the abovementioned responses to previously reported productivity measurements. The experiment was conducted for 2 yr (2016 and 2017) at the Central Crops Research Station, Clayton, NC. The 16 treatments were allocated in a randomized complete block design replicated four times. Across years, light interception before harvest ranged from ∼45 to 88%, canopy height ranged from 35 to 97 cm, and weed cover and frequency ranged from 0 to 75 and 0 to 95%, respectively. Greater canopy height was associated with greater light interception and lower weed infestation. Weed infestation occurred mainly for treatments harvested every 3 and 6 wk and defoliated to lower stubble heights; however, there was no impact of DH for DF treatments harvested every 9 and 12 wk. Canopy light interception values of at least 70% obtained in our study were associated with defoliation thresholds previously reported in the literature for sustained yields of ‘Performer’ switchgrass. Switchgrass canopy light interception values of at least 70% were achieved with canopy heights before harvest of ∼60 cm tall.

Tissue flow and biomass production of piatã grass in function of defoliation frequency and nitrogen fertilization

Tissue flow and biomass production of piatã grass in function of defoliation frequency and nitrogen fertilization

Herbage accumulation dynamics in digit grass subjected to defoliation frequencies

This study was undertaken to examine the herbage accumulation dynamics and structural characteristics of digit grass subjected to different defoliation frequencies in the period of January 2015 to February 2016. Four defoliation frequencies [very high (25 cm), high (35 cm), medium (45 cm), and low (55 cm)] were evaluated in two periods of the year [greater insolation (September to March) and lesser insolation (April to August)]. The experiment was set up as a randomized-block design with four replicates. Overall, the decreasing defoliation frequencies increased the cutting interval; leaf area index; total-herbage, stem, and dead-herbage accumulation rates; and percentages of stems and dead herbage. This reduction in defoliation frequency also resulted in a lower leaf accumulation rate and percentage of leaves. In overall terms, digit grass showed higher total-herbage, leaf, and stem accumulation rates; percentages of stems and dead herbage; stem volume density; and tiller density in the period of greater insolation. In the period of lesser insolation, however, digit grass exhibited a lower dead-herbage accumulation rate and a lower percentage of dead herbage. Less frequent defoliations increase the herbage accumulation rates of digit grass, but result in a less desirable morphological composition.

Strategic grazing management and nitrous oxide fluxes from pasture soils in tropical dairy systems

Greenhouse gases emissions are considered one of the most important environmental issues of dairy farming systems. Nitrous oxide (N2O) has particular importance owing to its global warming potential and stratospheric ozone depletion. The objective of this study was to investigate the influence of two rotational grazing strategies characterized by two pre-grazing targets (95% and maximum canopy light interception; LI95% and LIMax, respectively) on milk production efficiency and N2O fluxes from soil in a tropical dairy farming system based on elephant grass (Pennisetum purpureum Schum. cv. Cameroon). Results indicated that LI95% pre-grazing target provided more frequent defoliations than LIMax. Water-filled pore space, soil and chamber temperatures were affected by sampling periods (P1 and P2). There was a significant pre-grazing target treatment × sampling period interaction effect on soil NH4+ concentration, which was most likely associated with urinary-N discharge. During P1, there was a greater urinary-N discharge for LI95% than LIMax (26.3 vs. 20.9 kg of urinary-N/paddock) caused by higher stocking rate, which resulted in greater N2O fluxes for LI95%. Inversely, during P2, the soil NH4+ and N2O fluxes were greater for LIMax than LI95%. During this period, the greater urinary-N discharge (46.8 vs. 44.8 kg of urinary-N/paddock) was likely associated with longer stocking period for LIMax relative to LI95%, since both treatments had similar stocking rate. Converting hourly N2O fluxes to daily basis and relating to milk production efficiency, LI95% was 40% more efficient than LIMax (0.34 vs. 0.57 g N˗N2O/kg milk·ha). In addition, LI95% pre-grazing target decreased urea-N loading per milk production by 34%. Strategic grazing management represented by the LI95% pre-grazing target allows for intensification of tropical pasture-based dairy systems, enhanced milk production efficiency and decreased N-N2O emission intensity.

Tissue flow and biomass production of piatã grass in function of defoliation frequency and nitrogen fertilization

Due to the multifactorial interplay of the morphogenic, morphologic and agronomic characteristics of forage species, it is necessary to find management options that increase the production and utilization of the forage mass of grasses when submitted to different defoliation frequencies and nitrogen application levels The objective of this study was to assess the effects of two defoliation frequencies and two nitrogen levels applied in a single dose on the morphogenic and structural characteristics and forage production of Piata grass (Brachiaria brizantha cv. Piata) grown in the rainy season. The experiment was carried out in the agrostological field of the School of Veterinary Medicine and Zootechnics of Mato Grosso do Sul Federal University (UFMS), in Campo Grande, Mato Grosso do Sul, Brazil. The experimental area was composed of 12 plots measuring 18 m² each, planted with Brachiaria brizantha cv. Piata (Syn. Urochloa brizantha cv. Piata). The experimental design was completely randomized and the treatments consisted of two defoliation frequencies (with cutting intervals of 28 and 35 days) and two nitrogen levels (100 and 200 kg ha-1 of N, in the form of urea, in a single application ), with three repetitions per treatment. The results showed that for Piata grass swards established in soil having good fertility, the recommended management strategy is to set the minimum cutting or grazing height at 20 cm, with an interval of 28 days when the grass reaches an approximate height of 30 cm. In swards established in the rainy season, to reduce the fractioning of the N dose, it should be applied in a single dose of up to 100 kg of N ha-1 immediately after the first cutting.

Tissue flow and biomass production of piatã grass in function of defoliation frequency and nitrogen fertilization

Tissue flow and biomass production of piatã grass in function of defoliation frequency and nitrogen fertilization

Anatomical characterization of elephant grass under different defoliation frequencies and levels of insertion on the tiller

ABSTRACT The objective evaluates the anatomy of elephant grass under different defoliation frequencies and levels of insertion on the tiller. The experiment was set up as a completely randomized design with a 3 × 5 factorial arrangement consisting of leaf sheath insertion levels (IL) on the tiller and defoliation frequencies (30, 45, 60, 75, and 90 days). Leaf area and number of vascular bundles present in the leaf blade and leaf sheath were influenced by IL and defoliation frequencies (P < 0.05). The abaxial epidermis was thicker at the basal IL for both leaf blade and sheath. Regarding the proportion of leaf blade anatomical tissues, for the xylem area, whose highest percentages (9.21 and 10.10%) were observed at the apical IL at the highest defoliation frequencies (30 and 45 days, respectively). The area occupied by the sclerenchyma increased as the level of maturity advanced, in both the leaf and the leaf sheath.

Long‐term effects of mulching, traditional cutting and no management on plant species composition of improved upland grassland in the Czech Republic

AbstractA shortage of available livestock for utilizing grassland biomass in Central Europe is challenging for the management of both semi‐natural grasslands and previously intensified (limed, fertilized and reseeded) upland grasslands. An alternative method of grassland management is mulching, in which aboveground biomass is cut, crushed and subsequently spread on the surface. This paper reports on an experiment to compare three different mulching frequencies (one, two and three times per year) with an unmanaged treatment and traditional management of two cuts per year (control) on a previously improved upland meadow. Plant species composition was monitored over 13 years. Traditional management of two cuts with biomass removal was the most suitable method for maintaining plant species richness and diversity, and both were reduced significantly in the once‐mulched and especially in the unmanaged treatment. Tall dicotyledonous weeds such as Urtica dioica, Cirsium arvense and Aegopodium podagraria were promoted by the unmanaged treatment and by mulching once a year. Higher frequency of defoliation had positive effects on the spread of short forbs such as Taraxacum spp., Plantago lanceolata and Trifolium repens. After eight years, there were changes in sward structure in the unmanaged and mulched‐once‐a‐year treatments, with increase in the tall/short species ratio. In conclusion, repeated mulching cannot substitute fully for traditional two‐cut management in improved upland meadows without decreasing plant species richness and diversity, and changing the sward structure. Although mulching once a year may prevent invasion by shrubs and trees, it also supports the spread of weedy species similar to no management.

Grass Yields Under Clipping and Watering Explain Varied Efficacy of Management Intensive Grazing on Rangelands

Management intensive grazing (MIG) may not maximize plant productivity on rangelands because of morphophysiological traits of grassland vegetation. We examined defoliation and moisture effects on the biomass yield of rhizomatous and caespitose grass pairs that were either phylogenetically similar or of similar agroclimatic adaptation, including two agronomic grasses. From relatively low to high moisture regime adaptation, species pairs included western wheatgrass (Pascopyrum smithii [Rydb.] A. Love) and needle-and-thread (Hesperostipa comata [Trin. & Rupr.] Barkw.), northern wheatgrass (Elymus lanceolatus [Scribn. & J.G. Sm.]) and western porcupine grass (H. curtiseta [Hitchc.] Barkw.), plains and foothills rough fescue (Festuca hallii [Vasey] and F. campestris Rydb.), and smooth and meadow brome (Bromus inermis Leyss. and B. riparius Rehm). Response variables were shoot yield, root-shoot ratio, and water-use efficiency. We hypothesized that caespitose grasses, regardless of their origin or adaptation to agroclimate regime, would respond more determinately in biomass accumulation. Defoliation effects on shoot biomass were more pronounced under high moisture. Low intensity−high frequency defoliation yielded similarly to deferred controls in all grasses, and the same was true for high-intensity−low-frequency (HILF) defoliation in 1 rhizomatous grass. Three of the 4 rhizomatous grasses and 1 caespitose grass yielded greater under HILF defoliation compared with high-intensity−high-frequency defoliation. Caespitose grasses allocated more biomass to roots under low moisture conditions. Water-use efficiency decreased under high moisture conditions and more intense and/or frequent defoliation and peaked in agronomic grasses. Overall, our results suggested that growth patterns corresponded more with phylogenetic similarity as opposed to growth form. A conceptual model from these results showed that across all species, only the introduced bromes generated greater biomass under HILF defoliation, and this may explain why past research consistently concludes that MIG does not enhance plant productivity on rangelands.

Morphogenetic and structure characteristics of marandu grass subjected to grazing management strategies

ABSTRACT The objective of this study was to evaluate the morphogenetic and structural characteristics of Brachiaria brizantha cv. marandu subjected to grazing management strategies. The treatments corresponded to four grazing management strategies (25-10; 25-15; 35-15; and 45-15 pre and post grazing swards heights, respectively). Grazing management strategies were allocated to the experimental units (100 m2 paddocks) in a completely randomized blocks design with four repetitions. There was no effect of the grazing management on leaf elongation rate and leaf senescence rate, with average values of 11.22 mm/day and 2.17 mm/day, respectively. There were significant differences (p < 0.05) of leaf appearance rate, leaf elongation rate and stem elongation rate among months, where higher values were seen in months with greater rainfall. The evaluated management strategies showed a small effect on the morphogenetic and structural characteristics and can consequently be utilized for the management of marandu grass. In addition, during rainy periods, farmers can use management with higher defoliation frequencies (25-15), while the opposite (45-15) may be used during months with low rainfall in order not to exhaust the organic reserves of the plant.

Tillering dynamics of digit grass subjected to different defoliation frequencies

Abstract: The objective of this work was to evaluate the tillering dynamics of 'Suvernola' digit grass (Digitaria eriantha) when subjected to different defoliation frequencies. Four defoliation frequencies (interval among harvests) were evaluated - very high, when the grass reached 25 cm in height; high, 35 cm; medium, 45 cm; and low, 55 cm - in two seasons of the year, with higher and lower insolation, from January 2015 to January 2016. A randomized complete block design with four replicates was used. The increase in defoliation frequency increased the number of generations and the appearance, mortality, and density rates of tillers, besides decreasing their survival rate, without changing population stability. At the time of lower insolation, tiller appearance and mortality rates were higher, while tiller survival rate, balance, and density were lower. The evaluated defoliation frequencies and seasons of the year do not change the persistence of digit grass when irrigated. Higher defoliation frequencies result in a greater renewal of digit grass tillers.

Yield of Native Warm‐Season Grasses in Response to Nitrogen and Harvest Frequency

Core Ideas Within year, harvest frequency has the greatest effect on DM production of native warm‐season grasses. Nitrogen has little effect on native warm‐season grass DM yield. Eastern gamagrass can tolerate consecutive years of frequent defoliations and maintain yield. Five native warm‐season grass species and mixtures were grown in east‐central Mississippi on a coarse‐loamy, siliceous, semiactive, thermic Glossic Fragiudult, to determine their potential as forage grasses in response to harvest frequency and N application. Established stands were harvested at 30, 40, 60, and 120 d intervals, and were fertilized with N rates of 0, 56, 112, 168, and 224 kg N ha−1 for two consecutive years (2016 and 2017). Dry matter (DM) yield and agronomic nitrogen use efficiency (aNUE) were analyzed. Year, treated as a repeated measure, was the main source of variation affecting DM yields. Within year, harvest frequency had the greatest effect on cumulative yields in 2016, accounting for 44% of the variation observed. This effect was not observed in 2017. Frequent defoliations led to overall lower yields in 2017. Nitrogen was significant, but moderately, accounting for 2 and 4% of variation for 2016 and 2017, respectively. Species was also significant for both years. Agronomic N use efficiency varied between year, species, N rate, and harvest frequency. Eastern gamagrass [Tripsacum dactyloides (L.) L.] was the only species in which cumulative DM yield remained consistent across both years of the study, regardless of harvest frequency or N application. Results suggest that rest periods should be based on species present, and that less frequent harvests are required for sustained DM yields.

Long‐term effects of grazing intensity on strategies and spatial components of functional diversity in subtropical grassland

AbstractQuestionHow does grazing intensity affect plant community functional traits and the spatial components of functional diversity in subtropical grasslands?LocationLong‐term cattle grazing management experiment in subtropical Campos grassland, southern Brazil.MethodsFourteen experimental units (paddocks) maintained under seven grazing intensity treatments for 26 years. In each paddock, we recorded plant species cover and species functional traits in nine systematically located plots of 1 m2. Nineteen functional traits were used in the ordination of species to identify main axes of trait variation. Functional diversity measured by Rao entropy was partitioned into alpha, beta and gamma components. We tested, by linear models, for the effects of grazing intensity on community‐weighted mean traits and functional diversity components, using as traits the species scores on the PCA axes.ResultsThe two main axes of trait variation suggest a separation in species by their functional strategies (acquisition–conservation and tolerance–avoidance trade‐offs). Acquisitive and tolerant species increased while conservative and avoidant species decreased with grazing intensity. Rao quadratic entropy, considering the three spatial components, decreased with grazing intensity, but this trend was more accentuated with beta‐diversity.ConclusionsThe long‐term, strictly‐managed grazing experiment allowed us to reveal the effect of not only grazing disturbance per se, but also of different grazing intensities. Under high grazing intensity, frequent and severe defoliation allows only the persistence of species similarly adapted to regrowth. Under low grazing intensity, the lack of frequent defoliation enables the development of species with high investment in strong and long‐lived leaves. The partitioning of functional diversity revealed that the increase in functional diversity in areas with low grazing intensity is mostly due to an increase in heterogeneity among patches (beta‐component). The double stratum vegetation structure: tussocks, which escape grazing control, and short‐grazed patches often overgrazed, is maintained by grazer selectivity.

Resilience in the functional responses of Axonopus affinis Chase (Poaceae) to diurnal light variation in an overgrazed grassland

Overgrazed grasslands of Southern Brazil are responsible in part for the degradation, low productivity and loss of biodiversity of the grassland ecosystems submitted to such management. Axonopus affinis Chase, the carpet grass, is a dominant creeping grass species in overgrazed grasslands. The species readily spreads, is highly tolerant of frequent defoliation and to trampling. In any natural environment, different light intensity regimes vary considerably along the day. Such phenomenon requires a high level of plasticity, resistance, and resilience from plants. Within this context, the aim of this study was to describe the mechanisms of photochemical activity in Axonopus affinis (Poaceae) in response to natural variations in daylight. Here we report hysteresis related functional behavior in overgrazed grasslands. This study was conducted in grassland vegetation within an experimental overgrazed area from the Embrapa Pecuária Sul, Bagé/Rio Grande do Sul, Brazil (austral spring 2014). By means of preferential sampling, homogeneous areas with a 90% dominance of Axonopus affinis Chase were selected. In the present study 60 sample units were analyzed (young leaves, non-damaged and fully expanded). Photochemical variables and OJIP curves were sampled in two distinct conditions along one day, under light intensities labeled as: 1 – high photosynthetic photon flux density (HI), when under full sunlight; and 2 - low photosynthetic photon flux density (LI), when under cloudy days. It was possible to quantify and identify the alternative stable states of A. affinis in response to light resource availability, expanding the interpretation of the multivariate analysis (triangular trajectory) and therefore, contributing to univariate metrics (bimodal trajectory). In this study, HI produced hysteretic behavior while LI of dynamic photoinhibition in A. affinis. The ΔF/Fm′ variable was the most important mechanism to explain the plasticity of A. affinis in HI and LI (R2 > 0.98 in function of the PCoA coordinates). However, the non-photochemical quenching activity was responsible for the stability in the OJIP curve. Therefore, A. affinis presented photochemical mechanisms that contribute to the occupation and dominance of overgrazed grasslands with different light regimes.

Morfogênese de capim-canarana com duas frequências e duas intensidades de desfolhação

Objetivou-se avaliar o fluxo de biomassa do capim-canarana erecta lisa (Echinochloa pyramidalis LAM.) pastejado por novilhas leiteiras num delineamento em blocos casualizados com cinco repetições (piquetes) e arranjo fatorial 2 x 2 (frequência e intensidade). As frequências de desfolhação (FD) corresponderam à intercepção de 85 e 95% da radiação fotossinteticamente ativa e as intensidades de desfolhação (ID) corresponderam aos índices de área foliar residual 1,0 e 2,0. Foram avaliadas as seguintes variáveis: a taxas de alongamento foliar (TAlF) e das hastes (TAlH), a razão entre a taxa de alongamento da folha 1 e da folha 2 (TAlF1/TAlF2), taxa de senescência total (TST), o número de folhas vivas (NFV), o número de folhas totais (NFT); o tempo de vida da folha (TVF); a taxa de aparecimento da folha (TApF) e a taxa de acúmulo da cultura (TAC). A TAlF1/TAlF2, TAlF, TAlH e TST não foram influenciada pelas FD e ID, mas aumentaram com os ciclos. A TApF foi maior na FD de 85% em relação a FD de 95%. O capim-canarana pastejado por novilhas deve ser manejado com frequência de desfolhação de 95% de interceptação da radiação fotossinteticamente ativa associada a um índice de área foliar residual de 2,0.

Defoliation Management Affects Productivity, Leaf/Stem Ratio, and Tiller Counts of ‘Performer’ Switchgrass

Core Ideas Defoliation management resulted in a wide range of plant responses that varied by year, with deleterious responses more evident in the second year. Greater leaf/stem ratios occurred with more frequent defoliation treatments. Frequent defoliations such as every 3 wk should maintain a stubble height of at least 40 cm, defoliation frequencies ≥6 wk to 20‐cm stubble height, and ≥9 wk to 10 cm stubble height are warranted to ensure stand persistence. ‘Performer’ switchgrass (Panicum virgatum L.) was released in 2006 by the USDA‐NCSU forage program because of its greater digestibility compared to standard cultivars grown in the southeastern United States. Forages with greater digestibility have potential to positively impact animal responses, however, defoliation management can influence its productivity and persistence. The objectives were to determine the effect of the factorial combination of four defoliation heights (DH) (clipped to 10, 20, 30, and 40‐cm) and four defoliation frequencies (DF) (clipped every 3, 6, 9, and 12 wk) on productivity, leaf/stem ratio, and tiller counts. The experiment was conducted in 2016 and 2017 at the Central Crops Research Station, Clayton, NC. The 16 treatments were allocated in a complete randomized block design replicated four times. In 2016, total dry matter (DM) yield ranged from 4.2 to 13.1 Mg ha−1 being greatest for the 9‐ and 12‐wk DF at 10‐ and 20‐cm DH and lowest for all DH at 3‐wk defoliation frequency. In 2017, the DM yield range was wider ranging from 0.5 to 14.0 Mg ha−1 with lower tiller counts for the 10‐ and 20‐cm DH, 3‐wk DF treatments. Leaf/stem ratio was greater for the more frequently defoliated treatments in both years. ‘Performer’ switchgrass is a productive forage and on the basis of total DM harvested, leaf/stem ratio, and tiller counts, frequent defoliations such as every 3 wk to 40‐cm stubble height, ≥6 wk to 20‐cm stubble height, and ≥ 9 wk to 10 cm stubble height, are warranted to ensure stand persistence.

Forage yield, chemical composition and morphogenesis of Megathyrsus maximus cv. Tanzânia-1 under defoliation frequencies

The effects of defoliation frequencies (14, 21, 28, 35 and 42 days) on green dry matter (GDM) yield, chemical composition and morphogenetic and structural characteristics of Megathyrsus maximus cv. Tanzânia-1 were evaluated under natural field conditions. The increase of defoliation frequency resulted in higher GDM yields, however implied significant decreases in the levels of nitrogen, phosphorus, calcium, magnesium and potassium. The leaf appearance rate and populational tiller density are inversely proportional to defoliation, occurring the inverse for foliar senescence rate. Maximum GDM yields, number of leaves tiller-1, average leaf length, leaf expansion rate and leaf area index were obtained with defoliation frequencies of 38.5; 32.3; 40.2; 24.1 and 34.7 days, respectively. These data suggest that grass grazing at 35 to 40 days of rest period were optimal for obtain maximum yields and regrowth of rich forage.

Quantitative anatomy and in situ ruminal degradation parameters of elephant grass under different defoliation frequencies

SUMMARY This study aimed to determine the area occupied by different tissues present in the leaf blade and the in situ degradability of leaf and stem of elephant grass (Pennisetum purpureum Schum.) under different defoliation frequencies (30, 45, 60, 75 and 90 days). Plants were classified into three levels of insertion in the tiller (apical, medial and basal). The results were presented as a proportion of the area of each tissue in relation to the total area of the leaf blade, namely, parenchyma tissue (PT), lignified vascular tissue (LVT) and non-lignified vascular tissue (NLVT). The proportion of tissue in the leaf blade is altered in accordance with the insertion in the tiller and increase in cutting age of the plant. PT has greater proportion at lower cutting ages, LVT increases with frequency and NLVT is higher at 60 days. The parameters of DM degradation in the two fractions evaluated decreased significantly with increasing maturity of the plant. The effective degradability of CP in leaf and stem decreased with the increase in the rate of passage (2, 5, and 8% h-1). The highest rate (c) of CP degradation for the leaf fraction was obtained with a frequency of 60 days, for the stem, with 45 days. The advance in plant maturity increases the proportion of lignified vascular tissue, thus influencing the ruminal degradation parameters of elephant grass. The defoliation frequency of 60 days offers an optimal point regarding the proportion of anatomical tissues correlated with the degradation of elephant grass.

Contribution of basal and aerial tillers to sward growth in intermittently stocked elephant grass

AbstractElephant grass (Pennisetum purpureum Schumach. cv. Napier) is characterized by high dry matter production and a high contribution of aerial tillers to the tiller population. However, grazing management strategies that favor an increase in aerial tillers, such as long regrowth periods, particularly when associated with severe grazing, can result in a decrease in sward growth, as they are subject to a high level of intraclonal competition. We evaluated the contribution of basal and aerial tillers to sward growth in Napier elephant grass to comprehend how strategies of intermittent stocking management interfere with the relative contribution of each tiller class. Treatments corresponded to combinations of two post‐grazing heights (35 and 45 cm) and two pre‐grazing conditions (95% and maximum canopy light interception during regrowth—LI95% and LIMax, respectively) and were allocated to experimental units (850 m2 paddocks) according to a 2 × 2 factorial arrangement in a randomized complete block design with four replicates from January 2011 to April 2012. Basal tillers were the main contributors to sward growth in elephant grass. In this way, although the production of aerial tillers is an important adaptive response of this forage grass species, grazing management strategies that maximize aerial tillering do not result in greater leaf growth or minimize stem growth rates. The frequency of defoliation was the main modulator of plant responses related to light competition, and the higher leaf growth associated with lower stem growth rates were obtained with the LI95% pre‐grazing target. Severe grazing (35 cm) associated with LI95% is the grazing management strategy recommended to maximize leaf and sward growth rates in Napier elephant grass subjected to rotational stocking.

Ecoregional Patterns of Spruce Budworm—Wildfire Interactions in Central Canada’s Forests

Wildfires and outbreaks of the spruce budworm, Choristoneura fumiferana (Clem.), are the two dominant natural disturbances in Canada’s boreal forest. While both disturbances have specific impacts on forest ecosystems, it is increasingly recognized that their interactions also have the potential for non-linear behavior and long-lasting legacies on forest ecosystems’ structures and functions. Previously, we showed that, in central Canada, fires occurred with a disproportionately higher frequency during a ‘window of opportunity’ following spruce budworm defoliation. In this study, we use Ontario’s spatial databases for large fires and spruce budworm defoliation to locate where these two disturbances likely interacted. Classification tree and Random Forest procedures were then applied to find how spruce budworm defoliation history, climate, and forest conditions best predict the location of such budworm–fire interactions. Results indicate that such interactions likely occurred in areas geographically bound by hardwood content in the south, the prevalence of the three major spruce budworm host species (balsam fir, white spruce and black spruce) in the north, and climate moisture in the west. The occurrence of a spruce budworm–fire interaction inside these boundaries is related to the frequency of spruce budworm defoliation. These patterns provide a means of distinguishing regions where spruce budworm attacks are likely to increase fire risk.