HERMAPHRODITIC FLOWERING IN GAMBEL OAK

Gambel oak (Quercus gambelii Nutt.) is normally monoecious, flowering once a year in spring. In Utah, August 1978, several individuals were observed producing hermaphroditic flowers in riparian habitats. This unusual event was preceded by a general freeze of male catkins in May which resulted in low acorn production. In 1979 the same individuals flowered normally, with no evidence of freeze damage or hermaphroditic flowers being observed. Acorns were produced on these individuals in both years. It is suggested that hermaphroditic flowering in the Fagaceae is an ancestral condition, still present in the genome, but normally suppressed, which may be evoked by unusual environmental conditions.     

Influence of physiographic and climatic factors on spatial patterns of acorn production in Maryland and Virginia,USA

Aim The aims of this study were to identify the effects physiographic differences have on the spatial synchrony of acorn production within red (Quercus rubra) and white (Quercus alba) oak subgenus groups, to identify climatic factors associated with acorn production patterns, and to assess if and how these relationships vary across a distinct physiographic boundary. Location Maryland and Virginia in the eastern United States. Methods Using data from 36 survey sites in Virginia (1973–2000) and Maryland (1977–2000), we described the spatial synchrony of annual acorn production based on Mantel tests and modified correlograms at three spatial scales: (1) the entire study area, (2) within two ecological regions (mountain and Piedmont), and (3) between these ecoregions. Using climate data obtained from the National Climate Data Centre, we described the relationship between climate and acorn production within each ecological region using linear regression. Results Spatial synchrony in the white oak group acorn production was strong among sites closest together, and declined with distance. The average April temperature during the year of acorn drop was positively related to acorn crop size within the mountain and Piedmont ecoregions. Spatial synchrony in the red oak group was strong among sites closest together and declined with distance in the mountain region. Synchrony was weaker in the Piedmont than in the mountain ecoregion and declined slightly with increasing distance. Between the mountain and Piedmont ecoregions, synchrony was not detected among the closest sites, but was detected with increasing strength as the distance between site pairs increased. In the Piedmont ecoregion, the number of April freeze events and total July precipitation, both 2 years prior to acorn drop, were negatively related to red oak acorn production. In the mountains, average July temperature 2 years prior to acorn drop was positively related to acorn production. Main conclusions Physiographic differences affected the spatial acorn production synchrony in the red oak but not in the white oak subgenus group. Climatic factors related to annual acorn production variability differed between subgenus groups and physiographic regions. The physiographic differences between the mountain and Piedmont ecoregions may define spatial patterns of acorn production synchrony in some oak species and mediate climatic influences on acorn production.     

Associations Among Breeding Birds and Gambel Oak in Southwestern Ponderosa Pine Forests

Abstract: Ponderosa pine (Pinus ponderosa) forests with Gambel oak (Quercus gambelii) are associated with higher bird abundance and diversity than are ponderosa pine forests lacking Gambel oak. Little is known, however, about specific structural characteristics of Gambel oak trees, clumps, and stands that may be important to birds in ponderosa pine-Gambel oak (hereafter pine-oak) forests. We examined associations among breeding birds and structural characteristics of Gambel oak at a scale similar in size to individual bird territories in pine-oak forests in northern Arizona and western New Mexico, USA. Avian species richness and occurrence of some bird species were associated with specific growth forms of Gambel oak. Estimated probability of Virginia's warblers (Vermivora virginiae), black-headed grosbeaks (Pheucticus melanocephalus), and red-faced warblers (Cardellina rubrifrons) occurring at points increased with increasing density of pole-sized Gambel oak 7–15 cm in diameter at breast height. We also found evidence that large Gambel oak trees (≥23 cm dbh) were associated with increased occurrence of yellow-rumped warblers (Dendroica coronata) at points. Some avian associations with oak were influenced by characteristics of ponderosa pines. For example, bird species richness was positively associated with the abundance of large Gambel oak when density of large pine trees ≥23 cm in diameter at breast height was low. Because large oak trees are rare and their numbers are thought to be declining, efforts should be made to retain and promote growth of additional oaks in this size class. Forest management practices that maintain forest openings, such as prescribed burning, could promote growth of pole-sized Gambel oak, which appears important to some bird species in pine-oak forests.     

Acorn production prediction models for five common oak species of the eastern United States

Acorn production varies considerably among oak (Quercus) species, individual trees, years, and locations, which directly affects oak regeneration and populations of wildlife species that depend on acorns for food. Hard mast indices provide a relative ranking and basis for comparison of within- and between-year acorn crop size at a broad scale, but do not provide an estimate of actual acorn yield—the number of acorns that can potentially be produced on a given land area unit based on the species, number, and diameter at breast height (dbh) of oak trees present. We used 10 years of acorn production data from 475 oak trees to develop predictive models of potential average annual hard mast production by five common eastern oak species, based on tree diameter and estimated crown area. We found a weak (R² = 0.08–0.28) relationship between tree dbh and acorn production per unit crown area for most species. The relationship between tree dbh and acorn production per tree was stronger (R² = 0.33–0.57). However, this is because larger-dbh trees generally have larger crowns, not because they have a greater capacity to produce more acorns per unit crown area. Acorn production is highly variable among individual trees. We estimated that dbh of at least 60 dominant or codominant oak trees per species should be randomly sampled to obtain an adequate representation of the range of dbhs (≥12.7 cm dbh) in a given forest area, and achieve precise estimates when using these equations to predict potential acorn production. Our predictive models provide a tool for estimating potential acorn production that land managers and forest planners can apply to oak inventory data to tailor estimates of potential average annual acorn production to different forest management scenarios and multiple spatial scales. © 2011 The Wildlife Society.     

Changes in Oregon white oak (Quercus garryana Dougl. ex Hook.) following release from overtopping conifers

Oregon white oak or Garry oak (Quercus garryana Dougl. ex Hook.) is a shade-intolerant, deciduous species that has been overtopped by conifers during the past century in parts of its range due to an altered disturbance regime. We examined the response of suppressed Oregon white oak trees in western Washington, USA, to three levels of release from overtopping Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco). We treated individual oak trees with either full release from competition, partial (“half”) release from competition, or a stand-level thinning of Douglas-fir not directed toward release (control). Five years after treatment, oak trees had suffered no mortality or windthrow. Stem diameter growth was 194% greater in the full-release treatment relative to the control. Acorn production varied widely by year, but in years of higher production, acorn production was significantly greater in both release treatments than in the control. Frequency of epicormic branch formation was significantly increased for years 1 and 2 by the full release; the greatest response occurred between 2 and 6 m above ground level. The greatest number of epicormic branches formed on trees on which the majority of original limbs had died back prior to treatment. Trees with relatively less crown dieback at the time of treatment generally had greater stem growth and acorn production responses to release treatments. Our findings indicate that these released Oregon white oak trees are beginning to recover after an extended period of suppression.     

Relation of ramet size to acorn production in five oak species of xeric upland habitats in south-central Florida

This study examined variation in two components of acorn production. Percentage of bearing ramets (stems) and number of acorns per bearing ramet were examined in five clonal oaks in three xeric habitats of south-central peninsular Florida in relation to ramet size within and between species and vegetative associations. Counts of acorns on two white oaks (Quercus chapmanii and Q. geminata) and three red oaks (Q. inopina, Q. laevis, and Q. myrtifolia) were conducted annually from 1969 to 1996 (except in 1991) on permanent grids in southern ridge sandhill, sand pine scrub, and scrubby flatwoods associations at the Archbold Biological Station, Florida, USA. Percentage of bearing individuals and mean number of acorns per bearing individual increased with increasing ramet size for all species across all vegetation associations. However, in Q. geminata and Q. myrtifolia, acorn production declined in the largest size class (>3.2 m), implying that larger individuals of these clonal species may become senescent. All oak species in sand pine scrub, which had a nearly closed overstory, had lower frequencies of bearing oaks and mean numbers of acorns compared with similar-sized individuals of the same species in the more open-canopied southern ridge sandhill and scrubby flatwoods associations, suggesting light limitation. The annual production of acorns by a given oak species was correlated across vegetative associations and annual acorn production of oak species was correlated for species within the same section. Intermediate-size class oaks contributed the most acorns per unit area, suggesting that stands managed with short fire-return times will provide fewer acorns to wildlife than stands managed to produce more variable distributions of oak size classes. However, our study suggests that long-unburned stands, such as those studied here, will maintain relatively constant levels of acorn production as a consequence of ramet replacement within the clones of these shrubby oaks to create a variable distribution of size classes. Of the oak species studied, Q. myrtifolia had the highest acorn production and the smallest acorns, while Q. laevis had the lowest acorn production and the largest acorns, suggesting an allocation trade-off between acorn numbers and size.     

Understorey plant community structure in lower montane and subalpine forests, Grand Canyon National Park, USA

Aim Our objectives were to compare understorey plant community structure among forest types, and to test hypotheses relating understorey community structure within lower montane and subalpine forests to fire history, forest structure, fuel loads and topography. Location Forests on the North Rim of Grand Canyon National Park, Arizona, USA. Methods We measured understorey (< 1.4 m) plant community structure in 0.1‐ha plots. We examined differences in univariate response variables among forest types, used permutational manova to assess compositional differences between forest types, and used indicator species analysis to identify species driving the differences between forest types. We then compiled sets of proposed models for predicting plant community structure, and used Akaike's information criterion (AIC_C) to determine the support for each model. Model averaging was used to make multi‐model inferences if no single model was supported. Results Within the lower montane zone, pine–oak forests had greater understorey plant cover, richness and diversity than pure stands of ponderosa pine (Pinus ponderosa P. & C. Lawson var. scopulorum Engelm.). Plant cover was negatively related to time since fire and to ponderosa pine basal area, and was highest on northern slopes and where Gambel oak (Quercus gambelii Nutt.) was present. Species richness was negatively related to time since fire and to ponderosa pine basal area, and was highest on southern slopes and where Gambel oak was present. Annual forb species richness was negatively related to time since fire. Community composition was related to time since fire, pine and oak basal area, and topography. Within subalpine forests, plant cover was negatively related to subalpine fir basal area and amounts of coarse woody debris (CWD), and positively related to Engelmann spruce basal area. Species richness was negatively related to subalpine fir basal area and amounts of CWD, was positively related to Engelmann spruce basal area, and was highest on southern slopes. Community composition was related to spruce, fir and aspen basal areas, amounts of CWD, and topography. Main conclusions In montane forests, low‐intensity surface fire is an important ecological process that maintains understorey communities within the range of natural variability and appears to promote landscape heterogeneity. The presence of Gambel oak was positively associated with high floristic diversity. Therefore management that encourages lightning‐initiated wildfires and Gambel oak production may promote floristic diversity. In subalpine forests, warm southern slopes and areas with low amounts of subalpine fir and CWD were positively associated with high floristic diversity. Therefore the reduction of CWD and forest densities through managed wildfire may promote floristic diversity, although fire use in subalpine forests is inherently more difficult due to intense fire behaviour in dense spruce–fir forests.     

Cues versus proximate drivers: testing the mechanism behind masting behavior

Masting, the intermittent and synchronized production of seeds, is a common and important phenomenon throughout the plant kingdom. Surprisingly, the proximate mechanisms by which populations of masting plants synchronize their seed sets have been relatively unexplored. We examined how temperature influences the acorn crop of the valley oak Quercus lobata, a masting species common in California, USA, over 33 years in order to assess whether temperature acts directly on acorn crop as a cue or whether it acts instead through intermediate steps indicative of a direct mechanistic connection to acorn production. Compared to several alternatives, the difference in temperature during the spring flowering period over the prior two years (Δt) was a good predictor of annual acorn crop in valley oak, as proposed recently by Kelly et al. Significantly, Δt correlates positively with temperatures the previous April, a likely driver of pollination success in valley oak, and negatively with the previous year's acorn crop, which is in turn negatively correlated with the current year's acorn crop, presumably due to resource limitation. Thus, the success of Δt is not as a cue but rather explained by its close relationship to the proximate drivers that have a direct, mechanistic relationship with acorn crop size.     

Holocene altitudinal shifts in vegetation belts and environmental changes in the Sierra Madre Occidental, Northwestern Mexico, based on modern and fossil pollen data

A modern pollen rain study was performed in a 300 km-long altitudinal transect (~ 28° N latitude) from 300 to 2300 m elevation. The higher elevation modern communities: epithermal oak–pines, pine–oak forest, pine forest, and mixed conifer forest were easy to distinguish from their pollen content. In contrast, lower elevation subtropical communities: thornscrub and tropical deciduous forest were difficult to separate, because they share many pollen taxa. Nevertheless we identify high frequencies of Bursera laxiflora as an important component of the tropical deciduous forest.Additionally, fossil pollen was analyzed at three sites located between 1700 and 1950 m altitude at ~ 28° latitude north in the Sierra Madre Occidental of northwestern Mexico. The sites were in pine–oak (Pinus–Quercus), pine, and mixed-conifer forests respectively. Shifts in the altitudinal distribution of vegetation belts were recorded for the last 12,849 cal yr BP, and climate changes were inferred. The lowest site (pine–oak forest) was surrounded by pine forest between 12,849 and 11,900 cal yr BP, suggesting a cold and relatively dry Younger Dryas period. The early Holocene was also cold but wetter, with mixed conifer forest with Abies (fir) growing at the same site, at 1700 m elevation, 300 m lower than today. After 9200 cal yr BP, a change to warmer/drier conditions caused fir migration to higher elevations and the expansion of Quercus at 1700 m. At 5600 cal yr BP Abies was growing above 1800 m and Picea (spruce) that is absent today, was recorded at 1950 m elevation. Fir and spruce disappeared from the 1950 m site and reached their present distribution (scattered, above 2000 m) after 1000 cal yr BP; we infer an episodic Holocene migration rate to higher elevations for Abies of 23.8 m/1000 cal yr and for Picea of 39.2 m/1000 cal yr. The late Holocene reflects frequent climate oscillations, with variations in the representation of forest trees. A tendency towards an openness of the forest is recorded for the last 2000 yrs, possibly reflecting human activities along with short-term climate change.     

Trade-offs between vegetative growth and acorn production in Quercus lobata during a mast year: the relevance of crop size and hierarchical level within the canopy

The concept of trade-offs between reproduction and other fitness traits is a fundamental principle of life history theory. For many plant species, the cost of sexual reproduction affects vegetative growth in years of high seed production through the allocation of resources to reproduction at different hierarchical levels of canopy organization. We have examined these tradeoffs at the shoot and branch level in an endemic California oak, Quercus lobata, during a mast year. To determine whether acorn production caused a reduction in vegetative growth, we studied trees that were high and low acorn producers, respectively. We observed that in both low and high acorn producers, shoots without acorns located adjacent to reproductive shoots showed reduced vegetative growth but that reduced branch-level growth on acorn-bearing branches occurred only in low acorn producers. The availability of local resources, measured as previous year growth, was the main factor determining acorn biomass. These findings show that the costs of reproduction varied among hierarchical levels, suggesting some degree of physiological autonomy of shoots in terms of acorn production. Costs also differed among trees with different acorn crops, suggesting that trees with large acorn crops had more available resources to allocate for growth and acorn production and to compensate for immediate local costs of seed production. These findings provide new insight into the proximate mechanisms for mast-seeding as a reproductive strategy.     

Do seed predation and dispersal limit downslope movement of a semi-desert grassland/oak woodland transition?

Abstract. Semi-desert grasslands and dryland forests are typically arranged along elevation gradients, with low elevation grasslands and savannas separated from higher-elevation woodlands by a diffuse boundary. Recent (< 200 yr) woody plant encroachment into adjacent semi-desert grasslands appears to be a cosmopolitan phenomenon, and has been attributed to disturbance by humans (e.g., livestock grazing, fire suppression); however, little is known about rates, patterns and mechanisms. Are observations of increased woody plant abundance in semi-arid grasslands indicative of a downslope shift in the boundary zone? Experimental plots were established in adjacent oak woodlands and semi-desert grasslands in southeastern Arizona, to determine if mechanisms of acorn predation and dispersal would facilitate or limit downslope movement of oak woodlands. We recovered acorns that had been dispersed 50 m into adjacent grasslands, which suggests that they were cached by acorn predators. Acorns in grassland plots were more than twice as likely to escape predation than acorns that remained in woodland or cleared woodland plots. Contrary to previously published research, simulated perturbations (gap formation, understory and below-ground vegetation removal) did not affect seed predation, suggesting that generalizations from mesic, deciduous oak forests may not be accurately extrapolated to xeric, evergreen oak forests. Recently published studies indicate that xeric conditions limit survival of oak seedlings across the boundary zone, suggesting that observed patterns of acorn dispersal and predation provide the potential for colonization of adjacent grassland only during infrequent years with cool, moist conditions during late summer months.     

Moth outbreaks in relation to oak masting and population levels of small mammals: an alternative explanation to the mammal-predation hypothesis

The relationship between population outbreaks of the gypsy moth (Lymantria dispar) and oak masting in North America has been interpreted as an effect of reduced predation on moth pupae from small mammals after years of acorn failure. However, moth defoliation could be a consequence of high acorn production rather than of acorn failure, as all moth outbreaks in two time series presented by Liebhold et al. [Popul Ecol (2000) 42:257–266] were reported shortly after mast years. A similar pattern has been found for the green oak leaf roller moth (Tortrix viridana) in southern Norway. Because predation from small mammals should be less important for the latter species, I argue that the acorn-moth relationships are most likely caused by mast-induced changes in the chemical composition of oak leaves. Given the high number of eggs laid by each moth female, there is a huge potential for population growth in or shortly after a mast year if larval survival is no longer limited by low food quality.     

A Rapid Hard-Mast Index From Acorn Presence-Absence Tallies

Abstract: We used 21 years of acorn data from visual surveys of oak (Quercus spp.) trees (n = 20,113) conducted in western North Carolina, USA, to develop predictive equations for hard-mast indices (HMIs) based on the proportion of trees bearing acorns (PBA). We calculated PBA using visual estimates of the percentage of oak crown with acorns (PCA), assigning acorn presence if PCA ≥ 33.5%.The proportion of trees bearing acorns and average PCA were highly correlated, and PBA alone was a successful predictor of HMIs. Precise estimates of PBA (therefore HMIs) at a 95% confidence level required 139-385 sample trees for each oak subgroup or spatial scale of interest, and the sample size required varied with the true PBA. Substituting this faster, simpler visual survey method for others involving labor-intensive counts of twigs and acorns means that more trees can be sampled (if needed) with less time and effort for improved PBA (therefore HMI) precision. We offer a reliable method for predicting HMIs that are comparable to past HMI estimates for states using the Whitehead (1969) method, thus providing continuity in tracking long-term acorn production patterns. We also developed categories for subjectively ranking acorn crop sizes based on the range of PBA observed during 21 years. We recommend that PBA be adopted by resource management agencies as a standard, stand-alone index of acorn production to ensure comparable data among years and across the eastern United States. A standardized protocol for assigning acorn presence or absence must be used for consistent, comparable regional use of PBA in predicting HMIs or by itself as an index of acorn production.     

Dietary circumvention of acorn tannins by blue jays

Blue jays consume large quantities of acorns to fuel energy-demanding caching flights in the fall. Yet blue jays possess no known physiological adaptation to counter the negative effects of a high tannin diet on protein digestion. Dietary experiments were conducted to determine if blue jays could subsist on an acorn-only diet, and if they could not, to determine whether supplements of acorn weevil larvae (Curculio), present inside acorns, enabled them to maintain their mass. Comparative tannin assays also were conducted on Lepidobalanus (low tannin; white oak) and Erythrobalanus (high tannin; pin oak) acorns using radial diffusion assay. Captive jays consumed considerable acorn material, yet were unable to maintain mass on ad lib. acorn-only diets or on an acorn +1.5 g larvae/day supplement. There were no significant differences in mass loss between high and low tannin diets. In contrast, blue jays were able to stabilize mass on a diet of acorns +5.0 g larvae supplement/day. These results suggest that acorn weevil larvae, or perhaps other insects, counteract the effects of acorn tannins in the jay diet allowing jays to subsist largely on acorns during the fall caching season. Oak demographic processes may be partly regulated by a tri-trophic relationship among plant, insect and bird. Acorn weevil larvae, considered damaging to oak populations, may actually facilitate oak recruitment and population vagility in the long-term.     

Variation of stand structure and regeneration of Mediterranean holm oak along a grazing intensity gradient

Mediterranean ecosystems are traditionally influenced by human disturbance. In the mountain chains of south-eastern Spain, holm oak forests representing the potential natural vegetation are currently highly fragmented and subjected to extensive grazing by goats and sheep. This grazing activity by large herbivores has important impacts on community structure and dynamics of the remaining remnants because several processes associated with reproduction are affected. The present research analyses the variation of stand structure and regeneration of six forests dominated by Quercus ilex along a gradient of increasing grazing intensity. Stands of higher grazing intensity are characterized by a lower trunk number. Particularly, trees > 1.3 m height and diameter classes < 20 cm are clearly less represented. In addition, more intensively grazed forests show a highly aggregated dispersion of trees, which might be explained by an increase of clonally produced ramets by silvipastoral use. On the other hand, no Quercus ilex seedlings were found in any of the stands examined, although acorn production was high and did not correlate with grazing intensity. However, grazing clearly influences the quality of acorn harvest. We found a significant negative correlation between acorn length, acorn mass and grazing intensity and a positive correlation between the percentage of aborted acorns, acorn predation and herbivore activity. Thus, management of grazing in holm oak forests must take the high influence that livestock exerts on the regeneration of Quercus ilex into account, and maximum sustainable grazing intensity should be significantly lower than 0.8 animals per ha.     

Oaks, acorns, and the geographical ecology of acorn woodpeckers

We investigated the geographical ecology of acorn woodpeckers (Melanerpes formicivorus) using 30 years of Audubon Christmas Bird Counts and data on the diversity and abundance of oaks. Spatial autocorrelation in acorn woodpecker population densities is not significantly greater than zero both in either the southwestern United States, where populations are often locally isolated, or along the Pacific Coast, where they are more evenly distributed. In both regions, the effective distributional limit of acorn woodpeckers is set not by the limits of oaks but by sites where oak diversity drops to a single species. This result is consistent with acorn production patterns in central coastal California demonstrating that variability in overall acorn production and the probability of acorn crop failure decline with increasing oak species number but drop most markedly when two, compared to one, species of oaks are present together. Along the Pacific Coast, acorn woodpecker densities increase and population variability decreases with increasing abundance and diversity of oaks; however, analyses indicate that overall population size in this region is primarily determined by resource abundance while population stability is determined by resource diversity. Comparable patterns are not obvious in the Southwest, where acorn woodpecker densities are much lower than along the Pacific Coast. This may be due to a combination of greater competition for resources and oak communities that differ both qualitatively and quantitatively in their productivity compared to those along the Pacific Coast.     

Ecological effects of changes in fire regimes in Pinus ponderosa ecosystems in the Colorado Front Range

Question: What is the relative importance of low‐ and high‐severity fires in shaping forest structure across the range of Pinus ponderosa in northern Colorado? Location: Colorado Front Range, USA. Methods: To assess severities of historic fires, 24 sites were sampled across an elevation range of 1800 to 2800 m for fire scars, tree establishment dates, tree mortality, and changes in tree‐ring growth. Results: Below 1950 m, the high number of fire scars, scarcity of large post‐fire cohorts, and lack of synchronous tree mortality or growth releases, indicate that historic fires were of low severity. In contrast, above 2200 m, fire severity was greater but frequency of widespread fires was substantially less. At 18 sites above 1950 m, 34 to 80% of the live trees date from establishment associated with the last moderate‐ to high‐severity fire. In these 18 sites, only 2 to 52% of the living trees pre‐date these fires suggesting that fire severities prior to any effects of fire suppression were sufficient to kill many trees. Conclusions: These findings for the P. ponderosa zone above ca. 2200 m (i.e. most of the zone) contradict the widespread perception that fire exclusion, at least at the stand scale of tens to hundreds of hectares, has resulted in unnaturally high stand densities or in an atypical abundance of shade‐tolerant species. At relatively mesic sites (e.g. higher elevation, north‐facing), the historic fire regime consisted of a variable‐severity regime, but forest structure was shaped primarily by severe fires rather than by surface fires.     

Relationships of overstory to understory cover variables in a Ponderosa pine/Gambel oak ecosystem

Many studies have indicated relationships between individual species, but none have related combinations of overstory variables to understory herbaceous vegetation in a Ponderosa pine/Gambel oak ecosystem. Our objective was to determine not only the general relationships between the two sets of variables, but also identify the hyghest contributing variables. We used canonical correlation analysis to relate overstory variables (canopy cover, basal cover and density) to herbaceous vegetation cover variables. Canopy, basal, and ground cover were measured by the line intercept method using a 12.2 m tape as a sample unit. Tree density was measured by the Point-Center-Quarter method. The analysis was made with selected overstory variables and 5 understory herbaceous cover variables. This analysis revealed a significant canonical correlation between the two canonical variables (r=0.69). The analysis showed that among herbaceous cover variables, Oregon grape, Kentucky bluegrass, sedge, and foxtail barley; and among overstory variables, the density and the basal cover of Ponderosa pine indicated the highest positive contribution to the correlation of the two linear combinations while the density and canopy of Gambel oak negatively affected the canonical correlation.     

Pollen-limited reproduction in blue oak: implications for wind pollination in fragmented populations

Human activities are fragmenting forests and woodlands worldwide, but the impact of reduced tree population densities on pollen transfer in wind-pollinated trees is poorly understood. In a 4-year study, we evaluated relationships among stand density, pollen availability, and seed production in a thinned and fragmented population of blue oak (Quercus douglasii). Geographic coordinates were established and flowering interval determined for 100 contiguous trees. The number of neighboring trees within 60 m that released pollen during each tree's flowering period was calculated and relationships with acorn production explored using multiple regression. We evaluated the effects of female flower production, average temperature, and relative humidity during the pollination period, and number of pollen-producing neighbors on individual trees' acorn production. All factors except temperature were significant in at least one of the years of our study, but the combination of factors influencing acorn production varied among years. In 1996, a year of large acorn crop size, acorn production was significantly positively associated with number of neighboring pollen producers and density of female flowers. In 1997, 1998, and 1999, many trees produced few or no acorns, and significant associations between number of pollen-producing neighbors and acorn production were only apparent among moderately to highly reproductive trees. Acorn production by these reproductive trees in 1997 was significantly positively associated with number of neighboring pollen producers and significantly negatively associated with average relative humidity during the pollination period. In 1998, no analysis was possible, because too few trees produced a moderate to large acorn crop. Only density of female flowers was significantly associated with acorn production of moderately to highly reproductive trees in 1999. The effect of spatial scale was also investigated by conducting analyses with pollen producers counted in radii ranging from 30 m to 80 m. The association between number of pollen-producing neighbors and acorn production was strongest when neighborhood sizes of 60 m or larger were considered. Our results suggest that fragmentation and thinning of blue oak woodlands may reduce pollen availability and limit reproduction in this wind-pollinated species.     

Removal of water turbidity by natural coagulants obtained from chestnut and acorn

The ability of seed extracts of several species of chestnut and acorn to act as natural coagulants was tested using a synthetic turbid water. Active components were extracted from ground seeds of Horse chestnut and acorns of some species of family Fagaceae: Common oak, Turkey oak, Northern red oak and European chestnut. All investigated extracts had coagulation capabilities and their amounts depended on pH values and initial turbidities. The seed extracts from European chestnut and Common oak acorn were the most efficient expressing the highest coagulation activities, about 80% and 70%, respectively, in both low and medium investigated water turbidities at the lowest coagulant dose 0.5 ml/L.