Canopy Area and Aboveground Mass of Individual Redberry Juniper (Juniperus pinchotii) Trees

There is increasing interest in using canopy area to quantify biomass of invasive woody plants on large land areas of rangelands for a variety of reasons. For those woody species that emphasize lateral canopy growth over vertical growth it may be possible to relate canopy area to aboveground mass (AGM). Our objective was to determine the utility of external canopy measurements (area, volume, and height) for predicting AGM and the percentage of AGM that is wood (PW; i.e., stems > 3 cm diameter) in individual redberry juniper (Juniperus pinchotii Sudw.) plants in west Texas. The canopy area to height relationship was curvilinear and indicated that at heights > 3 m, there was more lateral (canopy area) than vertical canopy growth. We found a strong linear relationship between canopy area and AGM (r² = 0.94; AGM range 9 kg to 688 kg) and it appeared that AGM could be predicted in individual trees from canopy area. Moreover, the canopy area/AGM relationship developed from smaller trees was able to adequately predict AGM of larger trees. Height was a less effective predictor of AGM (r² = 0.66), and incorporation of height with canopy area to determine canopy volume did little to improve accuracy of estimating AGM over canopy area alone. The canopy area/PW relationship was curvilinear (the rate of increase in PW declined in larger trees) and PW reached 60–70% in the largest trees.     

TOXICITY OF LEUCAENA LEUCOCEPHALA

SUMMARY Steers fed a sole diet of Leucaena leucocephala cv. Peru (leucaena), rapidly developed a hypothyroid condition. Total serum thyroxine (T⁴) levels declined from c 120 n mol litre^-1 to 13 n mol litre^-1 within six weeks of full leucaena feeding. Associated with the hypothyroidism was a decline in feed intake, poor weight gain, hair loss, excessive salivation and the development of lesions on the oesophagus of some animals. Light steers (119 kg) were more severely affected than heavy steers (220 kg) and two light steers died. During the eight week period of full leucaena feeding animals gained only 0.18 kg head^-1 day^-1 compared with 0.73 kg head^-1day^-1 for steers fed cowpea (Vigna sinensis) hay. Supplementation with minerals (Fe, Cu, Zn) significantly increased mean daily intake (85.4 v 68.9 g/kg^0.75), daily liveweight gain, (334 v 14 g), and serum T₃ resin uptake (42.5 v 39.6%); decreased hair loss and skin lesions but did not alleviate the low serum T₄ levels. lodine supplementation did not affect intake, bodyweight gain, serum T₄ levels, serum T₃ uptake or toxicity scores compared with unsupplemented leucaena fed steers. When the leucaena fed animals were subsequently fed cowpea hay, appetite improved and the serum T₄ levels returned to normal within two weeks. For the heavy steers over this period, weight gain was similar to the controls; however, the light steers continued to gain poorly.     

A comparative study on mimosine, 3,4-dihydroxy pyridone (3,4-DHP) and 2,3-dihydroxy pyridone (2,3-DHP), purine derivatives (PD) excretion in the urine,thyroid hormone and blood metabolites profiles of Thai swamp buffalo (Bubalus bubalis) and Murrah buffalo (Bubalus bubalis)

Four Thai swamp buffaloes (SB) and four Murrah buffaloes (MB) fed a based diet of fresh ruzi grass (Bachiaria ruziziensis) with an increased proportion of fresh leucaena leaves. Intake of nutrients in animals increased when ruzi grass was mixed with leucaena. Digestibility of nutrients were the highest in SB and MB fed diets containing 25% and 50% of leucaena, respectively, and nitrogen (N) balances in both animal breeds were varied among diets. The regression equation coefficient of mimosine + DHP in the urine was twice as high in SB than in MB. Urinary purine derivatives excretion rate in SB was higher than that in MB. Plasma triiodothyronine and thyroxine declined in both animal breeds fed a diet containing >1 g mimosine intake/kg BW^0.75/day. Plasma urea–N was the lowest in SB, but the highest in MB when fed a diet containing 84% of leucaena. Plasma β-HBA in SB have declined when diets contained >50% of leucaena but that in MB was not affected by any diet. In conclusion, the effect of leucaena in diet upon buffalo breeds depends on the proportion of leucaena in the diet, mimosine contents and condensed tannins components.     

Nondestructive Age Estimation of Mountain Big Sagebrush (Artemisia tridentata ssp. vaseyana) Using Morphological Characteristics

Current methods for determining plant age of shrub species require destructive sampling and annual growth ring analysis on the primary stem. Although individual plant ages can frequently be determined in this manner, the method is time consuming and of limited value for plants that have lost stem wood from stem splitting and rot. Nondestructive methods for estimating big sagebrush (Artemisia tridentata Nutt.) plant age would be useful in assessing stand age structure and population dynamics at variable spatial scales. The purpose of this study was to test a suite of traits for potential use in estimating mountain big sagebrush (Artemisia tridentata ssp. vaseyana [Rydb.] Beetle) age. We evaluated traits including plant height, crown area, subcanopy litter depth, percent crown mortality, bark furrow depth, bark fiber length, circumference and diameter of plant basal stem, and circumference of secondary and tertiary branches. We measured and harvested basal cross-sections from 163 plants of varying sizes from five locations in central and south-central Utah. Plant age was determined from annual growth rings. Linear regression analyses revealed that stem diameter (r² = 0.507 P < 0.0001) was the most highly correlated variable with plant age across all sites, followed by stem circumference (r² = 0.474 P < 0.0001), secondary branch circumference (r² = 0.360, P < 0.0001), tertiary branch circumference (r² = 0.405, P < 0.0001), and bark fiber length (r² = 0.373, P < 0.0001). Results support previous findings that stem girth has value for estimating mountain big sagebrush plant age and that this trait is a better indicator of age than any other tested traits. Although the relationship between stem diameter and plant age was significant, substantial stem size variability associated with plants of the same approximate age indicates that the method is most appropriate when precise age estimates are not required. This technique was developed specifically for mountain big sagebrush, but it is expected that it can be adapted for other sagebrush taxa.     

The use of tropical protein-rich leaves as supplements to Thai swamp buffalo receiving a basal diet of rice straw and treated leucaena (<Emphasis Type="Italic">Leucaena leucocephala</Emphasis>)

Two experiments were conducted to determine (i) the effects of protein-rich trees (PRTs) and (ii) the effects of leucaena treated with NaOH solution and leucaena plus polyethylene glycol (PEG) on nutrient digestibility, nitrogen (N) balance, urinary purine derivatives excretion and blood metabolites in Thai swamp buffaloes. In Experiment 1, animals were fed with rice straw as a basal diet and one of the four PRT supplements: (i) oven-dried rain tree pods (RTPP, control); (ii) sun-dried leucaena leaves; (iii) sun-dried cassia leaves and (iv) sun-dried mulberry leaves. Fibre digestibility and N balance were lower (P < 0.05), but microbial N in the rumen was higher (P < 0.05) in animals supplemented with RTPP than in those fed with the other supplements. In Experiment 2, animals were fed with rice straw as a basal diet and leucaena were treated in one of three ways: (i) untreated (control), (ii) leucaena treated with NaOH solution and (iii) leucaena + PEG. Fibre digestibility and N balance in the rumen improved (P < 0.05) in animals supplemented with leucaena + PEG, but microbial N was not increased. The study demonstrated a way of using local PRTs for a suitable and worthwhile method to improve the quality of buffalo feeding systems in the tropics.     

Effect of cutting height and frequency on Leucaena leucocephala forage and wood production

Abstract

Leucaena leucocephala is a fast‐growing tree that can provide both high quality forage and firewood. The objective of this trial was to determine the optimum height and frequency of cutting for both wood and forage production. Cutting heights at 0.3 m, 0.6 m and 1.0 m were superimposed on 3‐month and 6‐month cutting frequencies on mature rows of L. leucocephala for three years. Effects of year or its interaction with the other factors were not significant (P≥0.10). There was an increase (P=0.07) in wood production but not forage production (P≥0.10) with the longer interval. Cutting height had an effect on forage (P<0.001) production, with 5.47 t ha^?1 a^?1 for the 0.3‐m height, 7.62 t ha^?1 a^?1 for the 0.7‐m height, and 8.71 t ha^?1 a^?1 for the 1.0‐m height. Cutting height also had an effect on wood production (P<0.001), with 7.22 t hd^?1 a^?1 for the 0.3‐m height, 9.33 t ha^?1 a^?1 for the 0.7‐mheight, and 11.55 t hd^?1 a^?1 for the 1.0‐m height. In this experiment, the six‐month interval produced more wood than the three‐month interval, but there were no differences in quantity of forage dry matter in L. leucocephala; there were advantages in both wood and forage production with the taller trunk base.     

Characteristics of night‐time sleeping places selected by golden monkeys (Rhinopithecus bieti) in the Samage Forest,Baima Snow Mountain Nature Reserve,China

We examined the criteria for sleeping place selection in a social band of Rhinopithecus bieti (black‐and‐white snub‐nosed or golden monkeys) living in the mountainous Samage Forest, Baima Snow Mountain Nature Reserve, Yunnan, China. We performed principal component analysis and found that slope aspect, tree height and trunk diameter were likely key variables influencing selection of sleeping places. Sleeping sites were preferentially located in mixed deciduous/conifer forest. The monkeys slept exclusively in evergreen trees, of which 82% were conifers (mostly Picea likiangensis and Tsuga dumosa) and 18% evergreen oaks (Cyclobalanopsis oxyodon and Quercus spp.). Sleeping trees were tall (mean 30.5 m), had high boles (mean 18.4 m), large diameters (mean 62.6 cm) and large crown areas (mean 57.9 m²). A comparative analysis of phytological and architectural features between trees in “sleeping site plots” (n= 18) and trees in “non‐sleeping‐site plots” (n= 66) revealed that diameter, crown surface area and tree height were significantly (P < 0.01) larger in the former compared with the latter. All investigated roosting sites were situated on steep mountain slopes. Valleys and mountain ridges were avoided. We also detected re‐use of roosting sites on several occasions, but not on consecutive nights. It is most likely that a mix of factors (stability of trees, access to food, unit cohesion, monitoring potential) explains the pattern of sleeping site preference, but predation at night seems to be only slightly important. Climate appears to have a profound influence on patterns of sleeping site selection in the monkeys' harsh temperate habitat. This is demonstrated by the monkeys' preference for mixed forest at medium elevations over montane fir forest at high elevations and slopes instead of ridges, with reduced exposure to wind and precipitation inherent in the former. We also emphasize the possibly substantial role that non‐environmental factors (the nature of social organization and socio‐behavioral strategies) play in determining sleeping site use in R. bieti and other primates.     

Prescribed Fire Effects on Deciduous Oak Woodland Stand Structure,Northern Diablo Range,California

Despite the increasing use of fire in managing oak woodlands, little information exists on quantitative changes to stand structure from prescribed burning. Fire damage and recovery in a mixed deciduous oak woodland were recorded after a prescribed fire on the northern Diablo Range, Santa Clara County, California. Blue oak (Quercus douglasii Hook. & Arn.), valley oak (Q. lobata Nee), and black oak (Q. kelloggii Newb.) trees were monitored for 4 yr to determine the effects of a late spring burn on stand structural characteristics. Fire-caused mortality was low; 4 yr after the low intensity ground fire only four oaks died (1.9%). There were significant differences in mean percent tree crown scorch and mean trunk char height between plots that burned under different fire intensities, but not between tree size classes. Although overall tree damage was low, crown resprouts developed on 80% of the trees and were found as shortly as 2 wk after the fire. Recovery was vigorous; both valley oaks and blue oaks produced crown resprouts on trees with 100% crown scorch. Classification tree analysis identified aspect (mostly southern exposures) and tree size related to the presence of crown resprouting. Crown damage was also an important factor; trees with greater than 40% of their crown scorched resprouted. Fire-induced trunk scars occurred on a small number of trees (9.1%) but was disproportionately higher for black oak compared to blue and valley oak. Stand structural characteristics (species composition, tree density, basal area, and crown closure) were not substantially altered by the event but rather maintained. Prescribed fire might be a viable tool in reducing fuels and maintaining oak woodlands; however, further investigations that include relationships of regeneration with repeated fire are needed.     

Performance of Nellore heifers, forage mass, and structural and nutritional characteristics of Brachiaria brizantha grass in integrated production systems

Our objective was to evaluate production, nutritive value and carrying capacity of piatã grass (Brachiaria brizantha cv. BRS Piatã), and performance of Nellore heifers in agrosilvopastoral systems (ASPS) with three eucalyptus (Eucalyptus urograndis) tree densities, during winter, spring, summer, and fall. Three integrated systems were evaluated: ASPS-1 (357 trees ha^?1), ASPS-2 (227 trees ha^?1), and CON (5 trees ha^?1). In each system, two sward heights were evaluated: short and tall. A total of 80 11-month-old Nellore heifers were randomly allocated in a randomized split-plot block, 3?×?2 factorial. Greater dry matter availability was observed on CON pastures during the fall season. Greater percentage of leaf lamina was detected on ASPS-1 with short sward height and greater during summer, compared with other seasons. A greater forage production was observed between tree rows and for tall sward height. Spring was the season with less forage nutritive value. Average daily gain was greater during summer and fall. Gain per hectare and stocking rate were greater on CON system and on ASPS-2. Pastures with short sward height had greater gain per hectare and stocking rate. Agrosilvopastoral systems with intermediate tree density seem to be a good choice for producers willing to diversify their revenue sources without decreasing animal production.     

Characteristics of roost cavities used by Lilian's Lovebird Agapornis lilianae in Liwonde National Park,Malawi

Lilian's Lovebird Agapornis lilianae is a non-excavating cavity user of mopane Colophospermum mopane woodlands. We investigated roost characteristics of Lilian's Lovebirds in Liwonde National Park, Malawi. We quantified tree and roost site variables for roost and non-roost trees. Sixty-six roosts were found. Roosts were in large tall mopane trees with a mean diameter at breast height (dbh) of 57.4 ± 1.64?cm, a mean height of 16.5 ± 0.42?m, and with a mean cavity entrance height of 10.0 ± 0.05?m. Non-roost areas had significantly smaller trees (mean dbh = 39.4 ± 1.72?cm). Human disturbance was low in both areas, but browsing of African elephant Loxodonta africana was evident by large areas of stunted mopane woodland recorded in non-roost areas. We recommend that the current Liwonde National Park vegetation map be updated to highlight areas of stunted mopane woodland unsuitable for Lilian's Lovebird roosts. The impact of elephant browsing on large mopane trees should be assessed to understand its impact on the availability of suitable cavities for lovebirds and other tree cavity reliant vertebrate species.     

Hydrologic Vulnerability of Sagebrush Steppe Following Pinyon and Juniper Encroachment

Woodland encroachment on United States rangelands has altered the structure and function of shrub steppe ecosystems. The potential community structure is one where trees dominate, shrub and herbaceous species decline, and rock cover and bare soil area increase and become more interconnected. Research from the Desert Southwest United States has demonstrated areas under tree canopies effectively store water and soil resources, whereas areas between canopies (intercanopy) generate significantly more runoff and erosion. We investigated these relationships and the impacts of tree encroachment on runoff and erosion processes at two woodland sites in the Intermountain West, USA. Rainfall simulation and concentrated flow methodologies were employed to measure infiltration, runoff, and erosion from intercanopy and canopy areas at small-plot (0.5 m²) and large-plot (13 m²) scales. Soil water repellency and vegetative and ground cover factors that influence runoff and erosion were quantified. Runoff and erosion from rainsplash, sheet flow, and concentrated flow processes were significantly greater from intercanopy than canopy areas across small- and large-plot scales, and site-specific erodibility differences were observed. Runoff and erosion were primarily dictated by the type and quantity of ground cover. Litter offered protection from rainsplash effects, provided rainfall storage, mitigated soil water repellency impacts on infiltration, and contributed to aggregate stability. Runoff and erosion increased exponentially (r² = 0.75 and 0.64) where bare soil and rock cover exceeded 50%. Sediment yield was strongly correlated (r² = 0.87) with runoff and increased linearly where runoff exceeded 20 mm·h^?1. Measured runoff and erosion rates suggest tree canopies represent areas of hydrologic stability, whereas intercanopy areas are vulnerable to runoff and erosion. Results indicate the overall hydrologic vulnerability of sagebrush steppe following woodland encroachment depends on the potential influence of tree dominance on bare intercanopy expanse and connectivity and the potential erodibility of intercanopy areas.     

Breeding for persistency of milk yield

Initial yield and persistency of 10400 Friesian heifers were measured by a linear regression model. The “theoretical” initial yield (a) was 17.7 kg with a standard deviation of 3.4 kg, the persistency as regression (b) was ?31 g/day. Phenotypic and genetic correlations between initial yield and regression were r_P = ?0.65 and r_G = ?0.43. Heritabilities were h² = 0.26 and 0.18, respectively, for initial yield and regression. In cases when marginal profit during the first half of lactation was half as much as in the second (case A) or when marginal profit during the first half was zero (case B), there resulted selection indices which corresponded closely to a selection on the basis of 305-days-records. If part lactations are used, persistency should be considered in addition to initial yield.     

Rainfall Interception by Singleleaf Piñon and Utah Juniper: Implications for Stand-Level Effective Precipitation

The expansion of piñon and juniper trees into sagebrush steppe and the infilling of historic woodlands has caused a reduction in the cover and density of the understory vegetation. Water is the limiting factor in these systems; therefore, quantifying redistribution of water resources by tree species is critical to understanding the dynamics of these formerly sagebrush-dominated rangelands. Tree canopy interception may have a significant role in reducing the amount of rainfall that reaches the ground beneath the tree, thereby reducing the amount of available soil moisture. We measured canopy interception of rainfall by singleleaf piñon (Pinus monophylla Torr. & Frém.) and Utah juniper (Juniperus osteosperma [Torr.] Little) across a gradient of storm sizes. Simulated rainfall was used to quantify interception and effective precipitation during 130 rainfall events ranging in size from 2.2 to 25.9 mm hr^? 1 on 19 trees of each species. Effective precipitation was defined as the sum of throughfall and stemflow beneath tree canopies. Canopy interception averaged 44.6% (± 27.0%) with no significant difference between the two species. Tree allometrics including height, diameter at breast height, stump diameter, canopy area, live crown height, and width were measured and used as predictor variables. The best fit predictive model of effective precipitation under canopy was described by stump diameter and gross precipitation (R² = 0.744, P < 0.0001). An alternative management model based on canopy area and gross precipitation predicted effective precipitation with similar accuracy (R² = 0.741, P < 0.0001). Canopy area can be derived from various remote sensing techniques, allowing these results to be extrapolated to larger spatial scales to quantify the effect of increasing tree canopy cover on rainfall interception loss and potential implications for the water budget.     

Growth of Chickasaw Plum in Oklahoma

Management of rangelands for wildlife and livestock entails understanding growth of clonal shrubs such as Chickasaw plum (Prunus angustifolia Marsh.). We studied growth of this species in one county in north-central (Payne) and two counties in northwestern Oklahoma (Ellis, Harper) during 2006 and 2007. We estimated age of stems and roots by growth rings and area of stands with the use of a handheld GPS unit. Based on zero-intercept regression models, stands grew at similar rates (overlapping 95% confidence intervals [CIs]) among counties with a pooled estimate of 31.0 m² · yr⁻¹ (95% CI = 26.5–35.6 m² · yr⁻¹; n = 95). This rate showed considerable variability within and among study sites (r = 0.52). Stem diameter increased (zero-intercept models) more rapidly in north-central Oklahoma (5.27 mm · yr⁻¹; 95% CI = 5.01–5.53 mm · yr⁻¹; r = 0.90; n = 53) than in northwestern Oklahoma (3.68 mm · yr⁻¹; 95% CI = 3.55–3.81 mm · yr⁻¹; r = 0.91; n = 102); data were pooled because of similar rates in Ellis and Harper counties. Stem height was a power function of stem age (y = 0.97x^0.28; r = 0.56), indicating rate of growth in height (m · yr⁻¹) declined with age according to dy/dx = 0.27x^−0.72. Knowledge of the area expansion rate of Chickasaw plum clones aids in management planning to increase or decrease canopy coverage by this shrub.     

Use of test-day records to predict first lactation 305-day milk yield using artificial neural network in Kenyan Holstein–Friesian dairy cows

The study is focused on the capability of artificial neural networks (ANNs) to predict next month and first lactation 305-day milk yields (FLMY305) of Kenyan Holstein–Friesian (KHF) dairy cows based on a few available test days (TD) records in early lactation. The developed model was compared with multiple linear regressions (MLR). A total of 39,034 first parity TD records of KHF dairy cows collected over 102 herds were analyzed. Different ANNs were modeled and the best performing number of hidden layers and neurons and training algorithms retained. The best ANN model had one hidden layer of logistic transfer function for all models, but hidden nodes varied from 2 to 7. The R ² value for ANNs for training, validation, and test data were consistently high showing that the models captured the features accurately. The R ², r, and root mean square were consistently superior for ANN than MLR but significantly different (p > 0.05). The prediction equation with four variables, i.e., first, second, third, and fourth TD milk yield, gave adequate accuracy (79.0%) in estimating the FLMY305 from TD yield. It emerges from this study that the ANN model can be an alternative for prediction of FLMY305 and monthly TD in KHF.     

Estimation of beef marbling in the Longissimus muscle with computer image analysis of ultrasonic pictures of the Iliocostalis muscle area

This study investigated an objective method for estimating beef marbling using ultrasonic images of the Iliocostalis muscle and the Lomgissimus muscle area sections. Thirty‐one Japanese Black cattle steers were used in this study. The end of the left side shoulder blade bone was scanned using an ultrasonic device. Ultrasonic images were captured of the Longissimus muscle area and that around the Iliocostalis muscle area. Twenty items were measured in the two images using computer image analysis software. The level of beef marbling was measured according to the Beef Marbling Standard (BMS) for carcass grading, and the percentage of ether‐extractable fat content in the Longissimus muscle (EE). The difference in the gray level between the Iliocostalis muscle and intermuscular fat (X10) was used to estimate the BMS and the EE, which were highly correlated (r² = 67.72% and 61.30%). An equation was developed using four parameters from the two ultrasonic images, which could estimate the BMS (r² = 85.88%). This equation could also estimate the EE (r² = 68.98%). The equations used to estimate beef marbling were based on one to four parameters that included X10. Thus, ultrasonic images of the Iliocostalis muscle area section are important for estimating beef marbling.     

Effect of plant height at cutting,source and level of fertiliser on yield and nutritional quality of Napier grass (Pennisetum purpureum (L.) Schumach.)

Napier grass (Pennisetum purpureum (L.) Schumach.) was studied using a 5 x 3 factorial experiment arranged in a randomised complete block design with three replications. The treatments were five fertiliser applications (0kg ha^-1 N, 46kg ha^-1 N and 92kg ha^-1 N, 1t ha^-1 and 2t ha^-1 cattle manure) and three plant heights at cutting (0.5m, 1m and 1.5m). The mean dry matter (DM) yield was 8.21t ha^-1 per cut but increased when the plant height at cutting increased and when the level of N fertilisation increased (P<0.05). Neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), cellulose, calcium, in vitro dry matter digestibility (IVDMD) and metabolisable energy were significantly (P<0.05) affected by plant height at cutting while total ash, crude protein (CP), ADF-ash, hemicelluose and phosphorus were affected by both plant height at cutting and fertiliser level. As plant height at cutting increased from 0.5m to 1.5m, IVDMD declined from 71.74% to 61.03% (P<0.05). Correlations between IVDMD versus CP, NDF, ADF, ADL, cellulose and hemicellulose were high with r = 0.92, -0.94, -0.96, -0.98, -0.83 and 0.74, respectively. CP yield per hectare per day of growth was highest for the 0.5m height at cutting, whereas the digestible DM yield was highest at both the 0.5m and 1.0m cutting height. The results of the present study suggest that Napier grass could be categorised under medium to high quality forage if cut at 0.5m or 1.0m height.     

Landscape Factors Influencing the Abundance and Dominance of the Invasive Plant Potentilla Recta

Little is known about the relative importance of environmental, biotic, historical, and spatial factors that influence invasive plant abundance, dominance, and distribution across landscapes. We identified factors that influence the abundance and dominance of Potentilla recta L. (sulfur cinquefoil) in bunchgrass grasslands of northeastern Oregon to better understand the conditions under which it becomes a major component of plant communities. We estimated P. recta stem density and dominance from field measurements across the landscape and used classification and regression tree analyses to assess the importance of environmental, biotic, spatial, and historical factors in explaining P. recta presence, stem density, and dominance. Plots were sampled within a systematic grid with 250-m spacing within our 6.5-km² study landscape. At each sample point we recorded P. recta presence, stem density, and dominance as well as 11 biological, environmental, spatial, and historical variables. P. recta was widely distributed, with stem densities in occupied plots averaging 5.8 stems • m^-2 and dominance values ranging from 1% to 52%. Percent cover of bare ground was the most important variable to predict the presence of P. recta, though the model fit was poor, likely because the entire study area is suitable for P. recta establishment. A strong relationship between P. recta dominance and habitat type (r² = 67.5%) was found, with dominance greatest in old fields on relatively flat slopes (mean dominance of 34.1%). Dominance estimates were ≤ 1% in plots located in forest, shrub, and grassland habitats. Factors that make old fields susceptible to dominance remain unknown, though microsite conditions that increase P. recta seedling survival rates and limited native propagule availability due to previous cultivation may be involved. Since old fields are found throughout the region, are highly susceptible to P. recta invasion, and represent a source of seeds, containment and restoration activities should focus on these areas.     

Lesser Prairie-Chicken Avoidance of Trees in a Grassland Landscape

Grasslands are among the most imperiled ecosystems in North America. Reasons that grasslands are threatened include conversion to row-crop agriculture, fragmentation, and changes in fire regimes. The reduction of fire processes in remaining prairies has resulted in tree encroachment and establishment in grasslands, further reducing grassland quantity and quality. Grassland birds have been experiencing precipitous population declines in recent decades, commensurate with landscape changes to grasslands. The lesser prairie-chicken (Tympanuchus pallidicinctus Ridgway) is a declining species of prairie grouse of conservation concern. We used second- and third-order habitat selection metrics to test if female lesser prairie-chickens avoid grasslands where trees were present. Our results indicated that female lesser prairie-chickens selected habitats avoiding the nearest trees by 283 m on average, nearly twice as far as would be expected at random. Lesser prairie-chickens were 40 times more likely to use habitats with tree densities of 0 trees ? ha^? 1 than habitats with 5 trees ? ha^? 1. Probability of use indicated that lesser prairie-chickens were 19 times more likely to use habitats 1000 m from the nearest tree when compared with using habitats 0 m from the nearest tree. Nest survival was not affected at densities < 2 trees ? ha^? 1; however, we could not test if nest survival was affected at greater tree densities as no nests were detected at densities > 2 trees ? ha^? 1. Avoidance of trees could be due to perceived increased predation risk, reduced habitat quality, or a combination of these potentially confounding factors. Preventing further establishment and expansion of trees in landscapes occupied by lesser prairie-chickens could contribute to the continued persistence of the species. Additionally, restoring grasslands through tree removal may facilitate conservation efforts for grassland species such as the lesser prairie-chicken by improving habitat quality and promoting expansion of occupied range.     

Kouebeskadiging van houtagtige plante in die Suuragtige‐Gemengde Bosveld

Cold damage to woody plants in the Sourish Mixed Bushveld. An incident of damage to woody plants by cold in the Sourish Mixed Bushveld was investigated. Woody plants in eight paddocks which were subjected to long‐term grazing treatments and which gave rise to different tree densities, were examined. The most common form of damage was top kill, and these plants subsequently coppiced from the base. Four woody species, namely Dichrostachys cinerea (the dominant woody species in the area), Acacia nilotica, A. gerrardii and A. robusta were severely damaged by the cold. The greatest effect was on trees in a certain height range; 1,0–3,0 m in the case of D. cinerea and 0,5–2,0 m in the case of the Acacia species. There was a negative curvilinear relationship between the number of trees larger than 2,0 m per hectare and the percentage damage. In paddocks where the tree density was relatively low the number of tree equivalents (equivalents of a tree 1,5 m high) was reduced by as much as 30%.