The influence of altitude and urbanisation on trends and mean dates in phenology (1980–2009)

Abstract

Long-term studies on urban phenology using network data are commonly limited by the small number of observation sites within city centres. Moreover, cities are often located on major rivers and consequently at lower altitudes than their rural surroundings. For these reasons, it is important (1) to go beyond a plain urban-rural comparison by taking the degree of urbanisation into account, and (2) to evaluate urbanisation and altitudinal effects simultaneously. Temporal phenological trends (1980-2009) for nine phenological spring events centred on the German cities of Frankfurt, Cologne and Munich were analysed. Trends of phenological onset dates were negative (i.e. earlier onset in phenology) for 96% of the 808 time series and significantly negative for 56% of the total number. Mean trends for the nine phenological events ranged between -0.23 days year(-1) for beech and -0.50 days year(-1) for hazel. The dependence of these trends and of mean dates on altitude and on the degree of urbanisation was explored. For mean dates, we demonstrated an earlier phenological onset at lower altitude and with a higher degree of urbanisation: altitude effects were highly significant and ranged between 1.34 days (100 m)(-1) (beech) and 4.27 days (100 m)(-1) (hazel). Coefficients for the log-transformed urban index were statistically significant for five events and varied greatly between events (coefficients from -1.74 for spruce to -5.08 for hazel). For trends in phenology, altitude was only significant for Norway maple, and no urban effects were significant. Hence, trends in phenology did not change significantly with higher altitudes or urbanised areas.

Intra-Urban Microclimate Effects on Phenology

“…However, their weather stations were positioned uniformly (open to the south and west), so they did not capture microclimate variations within the landscape. Jochner et al [17] studied phenological differences within three German cities using in-situ phenological sites. They attempted to address landscape variations by using a two-km buffer around each phenological station to establish an urban index (extent of built up land use).…”

Investigation of Urbanization Effects on Land Surface Phenology in Northeast China during 2001–2015

“…We further generate 3 buffers extending 0-2 km, 2-5 km, and 20-25 km from the edge of the union and define the 20-25 km buffer as rural area according to [4]. In this way, this study focused on 4 stationary areas in and around the urban area (OUAs, urbanized areas, 0-2 km buffer and 2-5 km buffer) and one stationary area in a rural area (20)(21)(22)(23)(24)(25) We used the phenology differences between OUAs or urbanized areas or buffers (0-2 km buffer, 2-5 km buffer) and rural areas (20-25 km buffer) to represent the UELSP as follows [4]:…”

Impacts of Urbanization on Vegetation Phenology over the Past Three Decades in Shanghai, China

“…Manipulative experiments and ground observations have documented earlier starts of growing seasons (SOS) and later ends of growing seasons (EOS) in the urban center than the surrounding rural areas [16,17]. While those studies provide important evidences of effects of urbanization on vegetation phenology, site-based observations cannot provide an assemble understanding of spatially-explicit phenological changes in urban areas due to the lack of standard data collection protocols and consistent data analysis methods [18].…”