Phenological response patterns of forest communities to annual weather variability at long-term ecological monitoring sites in Western Himalaya

Abstract

This paper presents the periodicity of phenophases in 28 tree species (142 individuals), 58 shrub, and 72 herb species' populations for 23 months (during 2018–2020) vis-a-vis weather variability in four semi-deciduous and evergreen forests along an altitudinal transect (680–1860 m asl) in long-term ecological monitoring (LTEM) sites in Western Himalaya. Across these forests, atmospheric temperature, relative humidity, and annual rainfall declined significantly with increasing elevation. The autumn to winter period (October-February) of 2019 was characterized by higher temperature (0.49 °C), rainfall (48.5 mm), and relative humidity (9%) in comparison to 2018. Vegetative bud-break, leafing and leaf drop occurred predominantly in the spring season (March-April) followed by flowering and fruiting through summer until the onset of the rainy season. All the phenophases occurred in 3–4 episodes of varying magnitudes year-round, except for a few months during the rainy season. The year 2019 was characterized by earliness in bud-break and leafing by over 2 weeks as compared to 2018. This may be attributed to the greater elevation-dependant warming as reflected by the shallow mean annual temperature lapse rate (−0.36 ± 0.2 °C/100 m) observed for the study area than the commonly used value (−0.65 °C/100 m). In the warmer winter of 2019–20 owing to greater temperature and rainfall, the leaf senescence delayed resulting in a lower magnitude of leaf drop by ∼25% than that recorded in winter 2018–19. This shift may have certain structural and functional implications in these forests which need to be investigated for a longer period establishing LTEM sites to understand the impact of climate change.