International Tundra Experiment, Barrow, Alaska

On cover: "Subcontract with Ohio State University NSF Grant OPP 9214897."During the growing season 1994 an ITEX site was established and monitored at Barrow, Alaska. The site is situated just outside the village on an old beach ridge within Barrow Environmental Observatory. 24 open-top chambers (OTC) and 24 control plots were placed randomly in a population of the circumpolar vascular plant species Cassiope tetragona (L.) D. Don and the amphiberingian willow species Salix rotundifolia Trautv. Temperature and humidity data loggers were placed as pairs in 5 OTCs and 5 controls. Temperature and humidity were recorded every 1.2 hour during the entire summer. 13 additional temperature data loggers were installed in 7 OTCs and 6 control plots in the beginning of August. The phenological monitoring was carried out mostly on a daily basis in a period of 69 days from mid June to the end of August. Selected ramets of Cassiope tetragona were used whereas the monitoring unit of Salix rotundifolia was plants delimited within a 100 cm2 (10 cm x 10 cm) area. All other vascular plant species, totalling 23, emerging in the plots were monitored according to phenological parameters most relevant for each species. Temperature data from the data loggers that have been operating during the entire summer show that the temperature difference between OTCs and the controls was on an average 1.75° C. The temperature difference between OTC's and controls was 1.23°C of the data loggers operating only in August The average temperature in the controls was exactly 2°C above the temperature recorded at a high of 2 meters at the close by NOAA observatory. The maximum temperature in the control plots was 0.6°C above the maximum temperature measured by NOAA. The maximum temperature in the OTCs was 33.3°C; app. 9°C higher than in the control plots. The average minimum temperature was the same in the experimental plots and in the controls. The experimental manipulations of Cassiope tetragona had a significant impact on all phenological parameters. The early phenological stages started c. 3 days earlier in experimental plots compared to the controls, whereas the differences between the later phenological stages were c. 8 days. The length of the period of developing mature seeds was increased by at least a few days in the manipulated plots. The total length of the period when the flowers were open and exposed to pollinators was only prolonged by c. 1 day in the chambers although the flowering started c. 8 days earlier in the experimental plots. There was no significant difference in annual growth increment between experimental and control plants. There was a significant difference between the early phenological stages of Salix rotundifolia comparing experimental plots with controls. The emerging of leaves and stigmas started c. 5 days earlier in the experimental plots. Onset of seed dispersal started c. 6 days earlier in the experimental plots; a highly significant difference. As the emerging of new leaves in the beginning of the growing season was on an average 5.2 days earlier in the OTCs and as there was no significant difference of the time of onset of yellowing of leaves, the total length of the growing season was prolonged by c. 5 days in the manipulated plots. The average difference of 2.0 mm of the length of the longest leaf of female plants between manipulated and control plots was highly significant. There was a significant difference in the weight of largest leaf between the treated and untreated plants; leaves weighing on an average 1.1 mg more in the experimental plots. The ratio between number of mature catkins and number of young, just flowering catkins was significantly larger in the experimental plots, indicating that the temperature enhancement has a positive effect on the survivability of the young catkins. The onset of dispersal of pollen and the time of all pollen released were significantly earlier in the OTCs; on an average 5.5 days and 3.0 days earlier, respectively. The period of pollen release was 34% longer in the experimental plots. There was a highly significant difference in the length of the longest leaf of male plants in the OTCs compared to the controls. There was no difference between the two types of plots, when comparing the weight of the largest leaf of male plants. There was a variation in how the non-ITEX species were responding to the experimental manipulations. None of the species were responding to the manipulation by on selling aU phenological stages significantly earlier in the experimental plots. There was a highly significant response of the length of the pedicel in all three species where this growth measurement was carried out. Suggestions to changes of the ITEX manual is proposed and the plans for the continuation of the research project is outlined.National Science Foundation Grant OPP 9214897