Sites In Coastal British Columbia Research Articles

Northward migration, molting locations, and winter residency of California breeding pigeon guillemots Cepphus columba

Pigeon guillemots Cepphus columba are ubiquitous along the coasts of the eastern North Pacific, yet little is known about their winter migration patterns, habitat needs, and potential threats faced during the non-breeding period. We used 3 seasons of year-long light level data from tagged individuals to estimate the migration timing and winter residency of pigeon guillemots breeding on Southeast Farallon Island in California (USA). Light level data were combined with a movement model to estimate positions of tagged animals, revealing that individuals from this population undertook a coordinated coastal migration north in the fall, stopping at sites near Haida Gwaii in British Columbia (Canada), presumably during a flightless prebasic molt, before continuing north to stationary overwintering sites in coastal British Columbia and Southeast Alaska. Birds then made an uninterrupted migration south in the spring, returning to waters around Southeast Farallon in late March and early April. Wet/dry data indicated nocturnal resting on land during the breeding season and likely on the water throughout the non-breeding months. This is the first study to confirm the migratory patterns of pigeon guillemots from California, and highlights the importance of the waters of British Columbia and Southeast Alaska for the studied population and possibly other major populations of this species.

Modeling realized gains in Douglas-fir (Pseudotsuga menziesii) using laser scanning data from unmanned aircraft systems (UAS)

Tree breeding programs form an integral part of sustainable forest management by providing genetically improved stock for reforestation. These programs rely on accurate phenotyping of forest trials, which become increasingly difficult to assess as trees grow larger and canopy closure occurs. Airborne laser scanning (ALS) provides three-dimensional point cloud information on forest structure which can be used to characterize phenotypes of forest trees. We analyzed 22-year-old realized gain trials of coastal Douglas-fir (Pseudotsuga menziesii [Mirb.] Franco var. menziesii) at three sites in coastal British Columbia, Canada, using dense point clouds produced from ALS acquired by unmanned aircraft system (UAS). We assessed the accuracy of ALS data against ground estimates of stand maximum height (r2 = 0.90, p < 0.001) and leaf area (r2 = 0.82, p < 0.001). We characterized phenotypes in blocks of differing levels of predicted genetic gain by generating a suite of quantitative point cloud metrics to describe four categories of stand attributes: Height, Density, Heterogeneity, and Volume. By normalizing all metrics to percent change from the means of unimproved control blocks, we analyzed point cloud metrics in terms of realized gains comparable across sites. Variable importance scores derived from conditional Random Forests indicated that descriptors of canopy height were the most important predictors of genetic gain for volume-per-ha. We selected a simple bivariate regression model using gains in mean canopy height and effective leaf area index to predict realized genetic gain for total stand volume (R2 = 0.82 – 0.94, p < 0.01, RMSE = 9.12 – 10.8%). Based on the consistent performance of this model across sites, we suggest that characterizing genetic trials in terms of increases in tree height and leaf area is a robust approach to predicting volume gains in this system. Additionally, we discuss the application of ALS as part of a phenotyping platform to inform operational decision making and forestry policy in British Columbia.

Comparison of Remotely-Sensed Sea Surface Temperature and Salinity Products With in Situ Measurements From British Columbia, Canada

Sea surface temperature (SST) and salinity (SSS) are essential variables at the ocean and atmosphere interface when considering risk factors for disease in farmed and wild fish stocks. Ecological research has witnessed a recent trend in use of digital and satellite technologies, including remote-sensing tools. We explored spatial coverage of remotely-sensed SST and SSS data and compared them with in situ measurements of water temperatures and salinity, which led to suggested adjustments to the remotely-sensed data for its use in aquaculture research. The in situ data were from farms and wild surveillance sites in coastal British Columbia, Canada, from 2003 to 2016. Concurrent SST and SSS values were extracted from remotely-sensed products and compared with 20,513 and 20,038 in situ records for water temperature and salinity, respectively, from 232 different sites. Among nine SST products evaluated, the UKMO OSTIA SST (UK Meteorological Office) had the highest retrieval, and highest concordance correlation coefficient (0.86), highest index of agreement (0.93), fewest missing values, and smallest mean and SD values for bias, when compared to in situ measurements. A mixed linear regression model with UKMO OSTIA SST as the predictor for in situ measurements estimated an adjustment coefficient of 0.89 °C for UKMO OSTIA SST. None of the three SSS products evaluated provided appropriate corresponding values for in situ sites, suggesting that spatial coverage for the study area is currently lacking. This study demonstrates that, among SST products, UKMO OSTIA SST is currently best suited for aquaculture studies in coastal BC. The near real-time availability of these data with the estimated adjustment would allow their use in forecast models, surveillance of pathogens, and the creation of risk maps.

Short-Term Effects of Variable-Retention Logging Practices on Terrestrial Gastropods in Coastal Forests of British Columbia

Abstract Variable-retention (VR) logging practices provide an alternative to clearcutting, but much uncertainty exists on their effectiveness in maintaining biodiversity. We compared patterns of abundance of terrestrial gastropods in areas subjected to either clearcutting or VR treatments, in relation to an uncut control at six experimental sites in coastal British Columbia before and 2–4 years after logging. Gastropods sensitive to the logging treatments in most comparisons included Haplotrema vancouverense, Pristiloma stearnsii and P. lansingi (as a group), and Striatura pugetensis. Several generalist species showed no response to the treatments, and the abundance of two species (Punctum randolphii and Vespericola columbianus) increased in some logged treatments relative to the control. At sites where trees were retained in small groups (0.2–0.5 ha), the abundance of four species was depressed when compared to the control and pre-logging values. No differences among retention levels of 10%, 20%, and 30%...

Growth, Mortality, and Damage in Fast Growing Douglas-fir Stands in Coastal British Columbia Twenty Years After Heavy Juvenile Thinning and Moderate Pruning at Age Nine

Abstract The purpose of this research was to examine the effects of pruning and thinning on the growth and mortality of young Douglas-fir (Pseudotsuga menziesii [Mirb] Franco) stands on high-productivity sites in coastal British Columbia. To accomplish this, a two-way randomized incomplete block design with two blocks was established on a coastal site with three levels of thinning (no thinning, thin to 500 stems per ha, and thin to 250 stems per ha) and three levels of pruning (no pruning, prune 250 stems per ha, and prune all trees). The response variables of interest were diameter at breast height (dbh), height, basal area, total and merchantable volume, mortality, damage, and deformities. Dbh and height were examined both for all trees and for only the largest 250 sph by dbh trees (the crop trees). The dynamics in partially pruned stands were also examined. We found that only dbh, basal area, total and merchantable volume, and mortality were affected by thinning. Pruning did not have any effect on the ...

Genetic analysis and clonal stability of two yellow cypress clonal populations in British Columbia

Abstract Genetic analysis of height and form at age 12 years of 697 yellow cypress (Callitropsis nootkatensis [D. Don] Oerst.) clones tested across seven sites in coastal British Columbia (BC) were explored in populations: Population 1 - No Pedigree and Population 2 - Reconstructed Pedigree. Genetic variances were statistically significant but generally higher σ̂g 2 was observed for Population 2. Height and form were under low to moderate genetic control as indicated by clonal repeatability and estimates were relatively similar between populations. For example, average Ĥ2 in Population 2 was 0.31 for height (range: 0.18-0.45) and 0.22 for form (range: 0.06-0.32). While average Ĥ2 in Population 1 was 0.25 for height (range: 0.19-0.35) and 0.18 for form (range: 0.09-0.27). The reconstructed pedigree in Population 2 allowed partitioning the genetic variance (σ̂g 2) into component parts of additive (σ̂a 2), specific combining ability (σ̂s 2 ), and clone (σ̂c 2 ); however, general lack of structure within the population resulted in variance components to be estimated with little precision for additive and specific combining ability. The majority of genetic variation was associated with clone for both traits. For example, σ̂c 2 accounted for 57.6% and 62.5% of the total genetic variance for height and form, respectively. Growth and form responses of clones across test environments were relatively stable and overall type-B genetic correlations were in excess of 0.8 for both traits implying clones selected for production populations should respond favorably across the seed planning zone for yellow cypress in coastal BC.

Predictive Models for Differentiating Habitat Use of Coastal Cutthroat Trout and Steelhead at the Reach and Landscape Scale

AbstractSteelhead Oncorhynchus mykiss and Coastal Cutthroat Trout Oncorhynchus clarkii clarkii are closely related species that are difficult to differentiate as juveniles and are commonly sympatric at the watershed scale. If Cutthroat Trout spawning and early rearing occur in small streams, it is often difficult to assess which parts of a stream network are dominated by each species. In this study I used catch data from 649 sites in coastal British Columbia to develop quantitative models of species presence and relative dominance as a function of stream size. An independent data set of 561 streams from the USA was used for the cross validation of models developed with data from British Columbia. The relative dominance of Cutthroat Trout or steelhead was predicted using logistic regression with stream and channel width, stream order, watershed area, unit runoff, ecoregion placement, and long‐term mean annual discharge (LT mad) as predictor variables. The LT mad was the best predictor of Cutthroat Trout and steelhead dominance, with a correct classification rate of 98% for the entire species range. Costal Cutthroat Trout dominated in reaches or streams where LT mad was ≤630 L/s, and steelhead dominated in reaches where LT mad was &gt;1,000 L/s. The models have practical application for predicting stream‐bearing length and area used primarily by each species at the landscape scale of productive capacity relative to habitat threats.Received June 18, 2012; accepted July 17, 2013

Invertebrate uptake of lipids in the vicinity of Atlantic salmon (Salmo salar) aquaculture sites in British Columbia

Samples of invertebrates, primary producers, seawater and cores were taken surrounding several aquaculture sites in coastal British Columbia, Canada. Analysis of dissolved organic carbon (DOC) showed a significant decrease (P = 0.027) over 1 km and an overall average of 290 ± 40 μM at 1 m depth. At 10 m, the decrease was not significant and DOC averaged 81 ± 3 μM. The essential fatty acid 22:6ω3 (docosahexaenoic acid, DHA) was significantly lower nearer to the farm sites for all mollusc taxa as well as for mussels alone (P < 0.01). However, mussel wet weight as well as the zooplankton fatty acid marker (ZFA; Σ 20:1ω9, 22:1ω11, 22:1ω9) and 20:1ω9 individually, decreased significantly with distance from the farms (P < 0.03). Principal components analysis showed a similar trend with DHA being higher in molluscs further from the farm. Mussels had significantly higher amounts of DHA compared with other molluscs indicating their potential in multi-trophic, co-culturing systems. Bacterial fatty acid markers increased in molluscs with distance from the farms; however, 18:1ω7, which is representative of methane-oxidizing bacteria, remained higher closer to the farm. In addition, DHA proportions in mussels showed a significant breakpoint at 339 m from the farm suggesting co-cultured mussels would benefit from placement further than 339 m from farms where DHA would be optimized.

Geographic and Temporal Variation in Diet of Wintering White-winged Scoters

Quantifying variation in diet over time and space is important for understanding patterns of habitat use in marine birds. Diet composition of adult male White-winged Scoters (Melanitta fusca) was quantified at five study sites in coastal British Columbia and Washington during mid-winter (December) and late winter (February-— March). At four sites where White-winged Scoters fed in nearshore areas, diet varied little between winter periods and birds fed almost exclusively on large infaunal bivalves (≥85% of mean ash-free dry mass of esophagus contents for each season × site combination). The main prey of White-winged Scoters in intertidal foraging areas (N = 3 of 5 study sites) were Varnish clams (Nuttalia obscurata), which were introduced to the region within the last 25 years. At an offshore site, diet consisted mainly of bivalves except during one period when White-winged Scoters had consumed mainly fish, crustaceans, polychaetes and echinoderms. Greater temporal variation in diet at the offshore site may have been an effect of reduced time available to locate preferred prey items and lower predictability of prey distributions owing to this site's greater exposure to wind and waves. However, neither exposure nor water depth received appreciable support in models of the dietary fraction of bivalves across sites and periods. Our results underscore the importance of marine areas with high densities of infaunal bivalves to White-winged Scoters, but also show that White-winged Scoters exhibit flexibility to adjust diet in response to differences in prey composition across habitats.

Neural network prediction of bending strength and stiffness in western hemlock (Tsuga heterophylla Raf.)

Abstract The stiffness and strength, modulus of elasticity (MOE) and modulus of rupture (MOR), as well as density, moisture content, microfibril angle and diffraction pattern coefficient of variation of azimuthal intensity profile (ICV) was determined for 259 small clear specimens. These samples represent 38 old- and second-growth western hemlock (Tsuga heterophylla) trees harvested from several sites in coastal British Columbia, Canada. The data were analyzed by classic statistical regression techniques to reveal interrelations among the mechanical properties and the inherent wood properties. Simultaneously, the predictive power of artificial neural networks was evaluated with the same data set by employing several optimization techniques. Regression analysis of wood density and the flexural strength properties resulted in R2 of 0.172 and 0.332 for MOE and MOR, respectively. The most efficient network model proved to be far superior demonstrating correlation coefficients with models for MOE ranging between 0.693 and 0.750, and the corresponding MOR models ranging between 0.438 and 0.561 in all testing phases. It is apparent that neural networks have the potential and capacity to self-train and become powerful adaptive systems that can predict the strength and stiffness of wood samples. The neural network analysis also revealed the importance level of each independent variable on both MOE and MOR properties.

Habitat factors affecting the abundance and distribution of juvenile cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch)

The distribution, abundance, and habitat associations of juvenile anadromous coastal cutthroat trout (Oncorhynchus clarki) and coho salmon (Oncorhynchus kisutch) were evaluated using survey data from 119 sites in coastal British Columbia. Both cutthroat and coho occurred at their highest densities in very small streams (&lt;5 m channel width), and bankfull channel width was the single best predictor of cutthroat presence (p = 0.0001) and density (R2 = 0.55). Within a channel, densities of coho and larger (yearling and older) cutthroat parr were highest in pools, while densities of young-of-the-year cutthroat were significantly lower in pools and highest in shallower habitats. Abundance of larger cutthroat parr and pool habitat were positively correlated with large woody debris (LWD) within a subset of intermediate-gradient gravel-cobble streams, where pools appear to be limiting to larger cutthroat parr abundance. More than 50% of pools were formed by scour associated with LWD in streams ranging from 1.2 to 11 m channel width, and pools formed by LWD scour were on average 10% deeper than pools formed by other mechanisms. Disproportionate use of small streams by cutthroat indicates that protection of small stream habitat is important for long-term conservation of sea-run populations.

Organic nitrogen use by salal ericoid mycorrhizal fungi from northern Vancouver Island and impacts on growth in vitro of Gaultheria shallon

Salal (Gaultheria shallon) recovers quickly from rhizomes after clear-cut timber harvesting and dominates clearcuts of Tsuga heterophylla and Thuja plicata forests. Thus it contributes to considerable problems in regeneration of these sites in coastal British Columbia, Canada. Based on what is known about other ericaceous plants, we speculated that mycorrhizal fungi of salal play a vital role in the growth and dominance of salal by providing access to organic nitrogen. In this study, the ability of four species of fungi isolated from salal to use different forms of organic nitrogen was tested in pure culture and in association with salal. The organic forms of nitrogen applied were glutamine (an amino acid), glutathione (a peptide), and bovine serum albumin (BSA, a protein). The fungi tested were Oidiodendron maius, Acremonium strictum, and two nonsporulating fungi. Inoculated plants always grew better than noninoculated plants regardless of nitrogen source. Glutamine was used as readily as ammonium nitrogen by all four fungi and the mycorrhizal plants of salal colonized by those fungi. There was considerable variation between fungus species or the plants inoculated with those fungi in using glutathione and BSA. Salal inoculated with O. maius grew better on glutathione than BSA, while A. strictum and unknown 1 produced significantly greater yields of salal on BSA. Colonization rates of salal by all four fungi was higher on glutathione or BSA than on ammonium or glutamine.

Alnus rubra nodulation capacity of soil under five species from harvested forest sites in coastal British Columbia

Nodulation of Alnus rubra seedlings after inoculation with soil from under A. rubra, Betula papyrifera. Rubus lacianutus, R. spectabilis, and R.ursinus on 2 recently harvested sites was compared. Nodulation capacity was low compared to other published reports, ranging from 0 to 18.9 infective units cm-3 of soil and was significantly affected by the site and plant species. Nodulation capacity of soil under alder was significantly higher than under all other species except R. spectabilis, regardless of site. The lowest nodulation capacity was found in soil under B. papyrifera.

An ecological study about assemblages of endophytic fungi in Acer macrophyllum in British Columbia: in search of candidate mycoherbicides

Healthy 2- to 3-year-old twig pieces with adherent foliage were collected from 3- to 10-year-old Acer macrophyllum at seven sites in coastal British Columbia and examined for the presence of endophytic fungi. Eighty-three percent of the leaves and 52% of the twigs were colonized by endophytic fungi. Fungal assemblages of leaves were dominated by Phomopsis spp., whereas Diplodina acerina was most frequently isolated from twigs. Cryptosporiopsis abietina, Glomerella cingulata (with Colletotrichum gloeosporioides anamorph), and Phomopsis spp. also occurred quite frequently in twigs at some sites. No correlations between weather conditions and any of the endophyte species were detected. Diplodina acerina and G. cingulata were the only two species with a certain potential to be employed as mycoherbicides: D. acerina is distributed over most of its hosts' range, and frequency and density of colonization are high among and within trees and some degree of virulence is present; some formae speciales of G. cingulata are already used as mycoherbicides. Key words: endophytic fungi, mycoherbicides, Diplodina acerina, Colletotrichum, fungal ecology.

Factors limiting early growth of western redcedar, western hemlock and Sitka spruce seedlings on ericaceous-dominated clearcut sites in coastal British Columbia

A 3 year field and pot study was conducted to determine the effects of several biotic and abiotic factors on the early growth of western hemlock ( Tsuga heterophylla (Raf.) Sarg.), western redcedar ( Thuja plicata, Donn) and Sitka spruce ( Picea sitchensis, Bong. Carr.) seedlings established on 2- and 8-year-old clearcut sites previously occupied by old-growth western hemlock and western redcedar forests (referred to as younger and older CH, respectively), and on adjacent 2-year-old clearcut sites previously occupied by second-growth western hemlock and amabilis fir ( Amabilis amabilis (Dougl.) Forbes) forests (referred to as younger HA) in coastal British Columbia. The objective of the study was to determine which factors are associated with the poor growth characteristic of the salal ( Gaultheria shallon, Pursh) dominated CH clearcut sites. No soil moisture deficits were measured on any of the three types of clearcut sites at any time of year. The best seeding growth was on the younger HA sites followed by the younger CH sites and then the older CH sites. The better growth on the younger HA sites was associated with a higher availability of N and P in the first 20 cm depth of the forest floor. No differences in matric soil water potential and pH, and only small differences in soil temperature were measured between the three types of clearcut sites. Complete removal of the competing vegetation on the younger and older CH sites resulted in an increase in conifer seedling growth and in the availability of N (22–40%) and P (15–32%); however, it did not affect cellulose decomposition and matric soil water potential, and increased soil temperature only slightly. Both western hemlock and Sitka spruce seedlings were very responsive to differences in nutrient availability measured between types of clearcut sites and planting treatments. In contrast, western redcedar was not responsive. All three conifer species had very high mycorrhizal colonization on the younger CH sites, and this was not altered by the removal of the competing vegetation (mainly salal). These results suggest that the nutritional stress and poor growth of conifers on salal-dominated CH clearcut sites in coastal British Columbia can be explained by:(1) inherently low forest floor nutrient availability; (2) competition between salal and conifer seedlings for scarce nutrients and nutrient immobilization in salal; (3) declining nutrient availability a few years after clearcutting and slashburning.

Growth of western red cedar seedlings in relation to microtopography, forest floor nutrient status, and fireweed and salal on clear-cut sites in coastal British Columbia

The growth of western red cedar (Thujaplicata Donn) seedlings was studied in relation to microtopography, to forest floor nutrient status, and to fireweed (Epilobiumangustifolium L.) and salal (Gaultheriashallon Pursh) abundance on 4-year-old logged and burned sites dominated by salal on northern Vancouver Island, British Columbia. These relationships were sought to determine some possible factors at the microsite level that influence the growth of western red cedar on recently clear-cut sites. Western red cedar growth and fireweed abundance and height were significantly greater in depressions than on flats and mounds, but these differences were not related to any major differences in forest floor pH, cellulose decomposition, total N and P, and available NH4+, NO3−, and phosphate P as measured using resin bags. The ecological significance of and possible reasons for the lack of correlation found between (i) western red cedar and fireweed growth and (ii) many measures of forest floor nutrient status are discussed.

Forest floor characteristics and soil nitrogen availability on slash-burned sites in coastal British Columbia

Organic forest floor materials were surveyed on spring and fall slash-burned sites in the Sproat Lake region of Vancouver Island 2 years after burning. Dominant organic matter types, distinguished according to morphological criteria, were sampled and incubated in the laboratory for 26 weeks with periodic leaching and measurement of mineral N. Mineralization data closely fit a first-order kinetic model. Field mineralization, estimated using mass of each organic matter type in the field and first-order model parameters corrected for local temperature, ranged from 2 to 6 g N•m−2•year−1, depending on burn severity, suggesting that slash burning did not reduce N availability below levels required to support early plantation growth, except in situations of severe burns on coarse-textured soils. Differential consumption of forest floor organic matter types increased spatial variability in N mineralization and resulted, at the most severely burned site, in 50% of mineralizable N being derived from materials covering only 5% of the site. Significant correlation between N mineralization and codes and indices of the Canadian Forest Fire Weather Index System indicated that predictions of slash-burn impacts on site fertility may be made from weather conditions prior to and during burning.

Nitrogen mineralization characteristics of forest floor organic matter on slash-burned sites in coastal British Columbia

Nitrogen mineralization characteristics of the dominant types of organic matter in the forest floor of slash-burned sites were measured using a 26-week aerobic incubation. Six classes of forest floor material were distinguished on the basis of morphology and N mineralization characteristics. Fermentation layer materials, matted together with fungal hyphae, had a high content of total and potentially mineralizable N (N0) (7804 and 2816 μg/g, respectively) and mineralized the most N during incubation (1605 μg/g). Decayed wood had the lowest level of total N (1816 μg/g) and N0 (195 μg/g) and mineralized the least N (266 μg/g) despite a high inherent mineralization rate (k) (0.16). Humified materials (Hd and Hr) occupied a midrange, with the exception of those from thin residual horizons, which had high N0 values (2246–6009 μg/g) and low k-values (0.005–0.012). The significant differences in N mineralization among organic materials that are morphologically or ecologically distinct in the field suggest that it may be possible to assess site N fertility using intensive forest floor and soil survey data and information on the N characteristics of dominant horizon types.

Spatial variation in black cottonwood (Populustrichocarpa) foliar nutrient concentrations at seven alluvial sites in coastal British Columbia

Spatial variability of 13 foliar nutrients was assessed within and between individual black cottonwood (Populustrichocarpa Torr. &amp; Gray ex Hook.) trees at seven alluvial sites in coastal British Columbia to help in the development of foliar sampling protocol for the determination of black cottonwood nutrient status. Foliar nutrients were divided into two groups based on concentration differences in foliage samples from within black cottonwood canopies: group 1 included N, P, K, S, SO4-S, Cu, and possibly Mg and B, mostly macronutrients that are mobile in the phloem; group 2 included mostly immobile micronutrients (Mn, Zn, Ca, and possibly Fe and active Fe, although these last two might best be included in a third group). Group 1 nutrient concentrations were significantly higher in the upper canopy, while group 2 nutrient concentrations were higher in the lower canopy at the two sites studied. Numbers of samples required for several combinations of accuracy (including both α and β significance) and precision were calculated based on mean coefficient of variation estimates from the seven stands. Fifteen foliar samples collected from the most recently matured late leaves on lateral branches in the top one-third of the canopy of dominant or codominant black cottonwood trees will estimate the mean with an allowable error of 10% at an α significance level of 0.95 for most macronutrients (N, P, K, S, Mg, and Ca). Including a β significance level of 0.95 at this level of precision and α significance would increase the number of required samples to at least 20 for these nutrients. Between 21 and 56 samples would be required to estimate the mean concentrations of SO4-S, Cu, Zn, Mn, B, active Fe, and Fe at the same levels of accuracy and precision.

Observations on Nectar Secretion in Fireweed,Epilobium AngustifoliumL. (Onagraceae)

SummaryCapillary tubes were used to extract nectar accumulating in protected flowers of fireweed at various sites in coastal British Columbia. Mean sugar yields collected from individual flowers ranged from 0·66 mg/flower/day to 4·11 mg/flower day. Sixty four percent of the variation in daily yield was shared by different sites, suggesting that weather factors were of primary importance to nectar secretion patterns. Sunshine and mean temperature demonstrated the best correlations with nectar yield, explaining 62% and 63% of the variation, respectively. Flowers on plants defoliated 90% secreted an average of 68% of the sugar secreted by control flowers over a 3 day period, suggesting that stored phatosynthate was mobilized for secretion as nectar. Measurements of nectar secretion in a controlled environment under conditions of saturated photosynthesis revealed that variations in temperature alone could influence yield significantly. Mean yields of sugar collected under conditions of constant temperature ra...