Tree Preference and Temporal Activity Patterns for a Native Ant Community in an Urbanized California Woodland

Anthropogenic disturbances, including land use change and exotic species, can alter the diversity and dynamics of ant communities. To examine foraging behavior in an urbanized habitat in northern California, we surveyed the presence of 9 ant species on 876 trees across 4 seasons during both day and night in a 9.5-hectare urbanized oak-exotic woodland. Ants were more likely to be observed on native, evergreen trees, suggesting that native evergreen species may help maintain ant diversity. Species showed clear patterns of temporal partitioning of foraging activity. Ant species varied in their use of native evergreen Quercus agrifolia trees across season and day/night axes. Of the 3 ant species most frequently observed, Camponotus semitestaceus was most active during spring and summer nights, Formica moki was most active during spring and summer days, and Prenolepis imparis was most active during both day and night during fall and winter. Liometopum occidentale was the second most active species during summer day and night, and winter day. Our findings demonstrate that an oak-exotic urban woodland in Northern California was able to maintain a native ant community, and strong temporal partitioning within that community.

Incidence of Galls on Sympatric California Oaks: Ecological and Physiological Perspectives

Galls are abnormal outgrowths on the external tissues of plants caused by a restricted group of organisms. In this study, we surveyed the incidence and diversity of galling structures in sympatric oak species of a biological preserve (Jasper Ridge Biological Preserve, NC, USA). We also measured different physiological parameters (SLA-specific leaf area, chlorophyll, nitrogen, flavonol, anthocyanin, and water content) in galled and ungalled leaves on the same individuals of the most abundant oak species (Quercus agrifolia, Q. lobata, and Q. douglasii). Overall, Q. lobata showed the highest gall incidence, with 64.5% of the sampled leaves affected by galls, followed by Q. douglasii, Q. agrifolia, Q. durata, and Q. kelloggii. The proportion of stems with galls was considerably lower than for leaves in all oak species, ranging from 0% incidence in Q. kelloggii to 27.4% in Q. lobata. The highly schlerophyllous Q. agrifolia supported the most diverse galling community at Jasper Ridge, with ten species, mostly belonging to the Cynipidae family. Our results show that leaf galling had no significant impact on the studied ecophysiological variables. The lack of differences between galled and ungalled leaves under controlled conditions (same tree and position in the tree) suggests that the ecophysiological variables measured are not significantly affected by galling agents or that our data collected for fully-developed galls (end of summer) are not sensitive enough to detect differences. However, there were some trends in plant responses to galling. Changes in galled vs. ungalled leaves were greater in flavonols, followed by chlorophyll, nitrogen, anthocyanin, SLA, and water content, indicating a nutrient deficiency in the plant nutrients. Our findings underscore the complexity of the gall-plant interaction and suggest some promising lines of future research.

Reproduction and Control of the Invasive Polyphagous Shot Hole Borer, Euwallacea nr. fornicatus (Coleoptera: Curculionidae: Scolytinae), in Three Species of Hardwoods: Effective Sanitation Through Felling and Chipping

The invasive ambrosia beetle polyphagous shot hole borer is one member of the cryptic species, Euwallacea nr. fornicatus (Eichhoff), and poses a great ecological and environmental threat to ornamental and native hardwood trees and agriculturally important tree crops in southern California, United States. We monitored the emergence of polyphagous shot hole borer adults from chipped and unchipped cut logs of infested boxelder, Acer negundo L. (Sapindales: Sapindaceae), California sycamore, Platanus racemosa Nutt. (Proteales: Platanaceae), coast live oak, Quercus agrifolia Née (Fagales: Fagaceae), and red willow, Salix laevigata Bebb (Malpighiales: Salicaceae), every week for 4 to 5 mo. No polyphagous shot hole borer adults emerged from chipped or unchipped coast live oak logs, suggesting this species is not a preferred reproductive host. However, following chipping, a small number of polyphagous shot hole borer adults emerged from boxelder (up to 7 wk) and from California sycamore and red willow (both up to 9 wk). A significantly greater number of polyphagous shot hole borer adults emerged from unchipped logs of boxelder (up to 14 wk) and California sycamore and red willow (both up to 5 mo). Chipping of boxelder, California sycamore, and red willow by using common commercially available chippers reduced polyphagous shot hole borer emergence by over 97%. Emerged polyphagous shot hole borer adults were strongly female-biased, regardless of host. Chipping treatments were highly effective, but for the complete elimination of polyphagous shot hole borer from woody material, other sanitation measures such as solarization in conjunction with chipping are recommended. Environmental and ecological impact of polyphagous shot hole borer is reviewed and discussed.

Spatial and temporal partitioning and tree preference in California woodland ants

Spatial and temporal partitioning of habitat may facilitate diversity and have important impacts on ant communities. To investigate niche overlap in an ant community in a northern California oak woodland, we observed ant foraging on trees in 4 seasonal surveys, each lasting 2 weeks, in a 9.5-hectare plot over the course of a year. Foraging activity in all 5 observed ant species differed by season, time of day, and/or the genera of trees used. Of the 3 ant species most frequently observed, Camponotus semitestaceus was most active during spring and summer nights, Formica moki was most active during spring and summer days, and Prenolepis imparis was most active during both day and night of fall and winter. All ant species preferred native trees to exotic trees and preferred evergreen trees to deciduous trees. Our results suggest that native evergreen oaks such as Quercus agrifolia, currently threatened by sudden oak death (Phytophthora ramorum), may be important for supporting ant biodiversity.

Measurements of NO and NO₂ exchange between the atmosphere and <i>Quercus agrifolia</i>

NO2 foliar deposition through the stomata of leaves has been identified as a significant sink of NOx within a forest canopy. In this study, we investigated NO2 and NO exchange between the atmosphere and the leaves of the native California oak tree Quercus agrifolia using a branch enclosure system. NO2 detection was performed with laser-induced fluorescence (LIF), which excludes biases from other reactive nitrogen compounds and has a low detection limit of 5–50 ppt. We performed both light and dark experiments with concentrations between 0.5 and 10 ppb NO2 and NO under constant ambient conditions. Deposition velocities for NO2 during light and dark experiments were 0.123±0.009 and 0.015±0.001 cm s−1, respectively. Much slower deposition was seen for NO, with deposition velocities of 0.012±0.002 and 0.005±0.002 cm s−1 measured during light and dark experiments, respectively. This corresponded to a summed resistance of the stomata and mesophyll of 6.9±0.9 s cm−1 for NO2 and 140±40 s cm−1 for NO. No significant compensation point was detected for NO2 uptake, but compensation points ranging from 0.74 to 3.8 ppb were observed for NO. NO2 and NO deposition velocities reported here are comparable both with previous leaf-level chamber studies and inferences from canopy-level field measurements. In parallel with these laboratory experiments, we have constructed a detailed 1-D atmospheric model to assess the contribution of leaf-level NOx deposition to the total NOx loss and NOx canopy fluxes. Using the leaf uptake rates measured in the laboratory, these modeling studies suggest that loss of NOx to deposition in a California oak woodland competes with the pathways of HNO3 and RONO2 formation, with deposition making up 3 %–22 % of the total NOx loss. Additionally, foliar uptake of NOx at these rates could account for ∼15 %–30 % canopy reduction of soil NOx emissions.

Measurements of NO and NO₂ exchange between the atmosphere and <i>Quercus agrifolia</i>

NO2 foliar deposition through the stomata of leaves has been identified as a significant sink of NOx within a forest canopy. In this study, we investigated NO2 and NO exchange between the atmosphere and the leaves of the native California oak tree Quercus agrifolia using a branch enclosure system. NO2 detection was performed with laser-induced fluorescence (LIF), which excludes biases from other reactive nitrogen compounds and has a low detection limit of 5–50 ppt. We performed both light and dark experiments with concentrations between 0.5–10 ppb NO2 and NO under constant ambient conditions. Deposition velocities for NO2 during light and dark experiments were 0.123 ± 0.007 cm s−1 and 0.015 ± 0.001 cm s−1, respectively. Much slower deposition was seen for NO, with deposition velocities of 0.012 ± 0.002 cm s−1 and 0.005 ± 0.002 cm s−1 measured during light and dark experiments, respectively. This corresponded to a summed resistance of the stomata and mesophyll of 6.9 ± 0.9 cm s−1 for NO2 and 140 ± 40 cm s−1 for NO. No significant compensation point was detected for NO2 uptake, but compensation points ranging from 0.74–3.8 ppb were observed for NO. NO2 and NO deposition velocities reported here are comparable both with previous leaf-level chamber studies and inferences from canopy-level field measurements. In parallel with these laboratory experiments, we have constructed a detailed 1-D atmospheric model to assess the contribution of leaf-level NOx deposition to the total NOx loss and NOx canopy fluxes. Using the leaf uptake rates measured in the laboratory, these modeling studies suggest loss of NOx to deposition in a California oak woodland competes with the pathways of HNO3 and RONO2 formation, with deposition making up 3–22 % of the total NOx loss. Additionally, foliar uptake of NOx at these rates could account for ~15–30 % canopy reduction of soil NOx emissions.

Constitutive phenolic biomarkers identify naïve Quercus agrifolia resistant to Phytophthora ramorum, the causal agent of sudden oak death

Sudden oak death, caused by the invasive pathogen Phytophthora ramorum Werres, de Cock & Man in't Veld, can be deadly for Quercus agrifolia Neé (coast live oak, CLO). However, resistant trees have been observed in natural populations. The objective of this study was to examine if pre-attack (constitutive) levels of phenolic compounds can be used as biomarkers to identify trees likely to be resistant. Naïve trees were selected from a natural population and phloem was sampled for analysis of constitutive phenolics. Following P. ramorum inoculation, trees were phenotyped to determine disease susceptibility and constitutive phenolic biomarkers of resistance were identified. Seasonal variation in phloem phenolics was also assessed in a subset of non-inoculated trees. Four biomarkers, including myricitrin and three incompletely characterized flavonoids, together correctly classified 80% of trees. Biomarker levels were then used to predict survival of inoculated CLO and the proportion of resistant trees within a subset of non-inoculated trees from the same population. Levels of five phenolics were significantly affected by season, but with no pronounced variation in average levels among seasons. These results suggest that pre-infection levels of specific phenolic compounds (i.e., biomarkers) can identify trees naturally resistant to this invasive forest pathogen. Knowledge of resistant trees within natural populations may be useful for conserving and breeding resistant trees and for disease management.