Rise in temperature has been reported as the principal cause of variation in flowering phenology in several tree species around the globe. In this study, we hypothesized that not only temperature but also rainfall periodicity, soil moisture and the related changes of twig water potential (ψ) in winter and early spring are important drivers of bud expansion and flowering in Rhododendron arboreum in central Himalayas. To this purpose, phenological and physiological variables (flowering time, flower bud size and twig water potential) were monitored over two years in a wild population of R. arboreum (Uttarakhand, India) and related with environmental variables (rainfall, soil moisture and temperature). Results showed that a rise in twig ψ to -0.7MPa, one week after moderate winter precipitation resulted in flower bud enlargement. In both years flowering was triggered after twig ψ reached the threshold of -0.5 Mpa, though the starting date differed between years. Floral bud size was correlated positively with twig ψ (r = 0.43, df =162, p < 0.001) and soil moisture (r = 0.61, df = 71, p < 0.001), while temperature did not influence flower bud size, soil moisture and twig ψ. Flower bud size increment was related with increase in twig ψ and soil moisture. Based on our results, we concluded that water availability plays an important role in inducing flowering in R. arboreum.
Phenology is one of the simplest and most effective study to understanding the role of climate change in recent scenario. A number of biotic and abiotic drivers controlled the timing and duration of various phenophases in same or different species. Temperature, rainfall and photoperiod are key drivers which adversely affect the phenology of woody plant. The study sites were conductedat 413 and 2345m elevation in Nainital forest division of Kumaun Himalaya. The phenological study were carried out onShores robusta, Mallotus philippinensis, Pinus roxburghii, Myrica esculenta,Quercus leucotrichophora and Rhododendron arboreum. The phenological observations were made at 15 days interval for low activity period and weekly in the periods of high activity. Phenological records were made for four phenophases, viz., leafing, leaf drop, flowering and seed fall.The leaf fall in S. robusta started from March 2nd week and was complete by the end of April. In M. philippinensis the fruiting commenced from the beginning of December and seed fall was complete by the 3rd week of April. In M. esculenta male flowers appear from August end and flowering was complete by October end.In R. arboreum seed dispersal started from February end and all the capsules had opened by mid-March. It is apparent from the present study that the phenological events of species controlled/shifted due to climatic irregularities and temperaturerise and these phenomena showed worldwide. Microclimatic condition alsoresponsible for controlling/shifting the phenological patterns of same or different species.
The present study investigated the timing and duration of phenological events of A. indica in different elevational range Kumaun Himalayan forest. A total of four sites at elevation ranging between 1,900m and 2,200m were selected and at each site 10 s were marked for observations. The phenological events, i.e. leaf bud formation, leaf bud busting, leafing, flowering bud formation, flowering bud busting, flowering, fruit/seed formation, seed fall and leaf fall were monitored. Phenological duration and asynchrony of these phenophases were determined at 10 day intervals and every 2-3 day intervals during the period of peak activities. The minimum length displayed leaf bud formation (44 days) and maximum by leaf fall (86 days) across the elevation. The environmental conditions, particularly temperature, affected the phenological patterns of A. indica. The leaf bud busting activity of A. indica was 51 days. Flowering activity started on May 1st and was extended over 76 days until July 15th. Seed fall activity was extended over 66 day across elevations. ANOVA showed the longevity of phenophases were varied significantly respective to elevations (p<0.05). Our observation showed that all the phenological events of A. indica appear early at lower (1900 m) and are delayed with increasing elevation. All corresponding phenological events were earlier at lower elevations because the optimum (9.0 to 19.5°C) is met earlier in these conditions.
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