Data from: The ameliorating influence of neighbouring plants on aboveground microclimate depends on their number, size, and proximity

Plants can have a facilitative effect on co-occurring neighbours by
moderating microclimate conditions. In forested areas, vegetation can
ameliorate macroclimate extremes relative to open areas, yet the
neighbourhood characteristics that contribute to this buffering effect,
particularly during early stand development, remain unclear. Here, we
examined how the local neighbourhood affects aboveground temperature and
relative humidity in the canopy layer of 76 mapped neighbourhood plots in
an 8-year-old experimental forest in Tasmania, Australia. We assessed
which aspects of the neighbourhood – species identity, density, summed
basal area and spatial arrangement – best described the microclimatic
conditions over a year-long period, and examined how seasonal and extreme
climatic conditions influenced the strength of neighbourhood effects on
microclimate. Microclimate conditions varied substantially across
neighbourhoods, with a significant proportion explained by neighbourhood
metrics (NMs). Daytime temperature and relative humidity (RH) were
strongly associated with the community neighbourhood index (NI), which
reflects the number, size and proximity of neighbouring trees rather than
their species identity. Higher NI values – indicating more, larger or
closer neighbours – led to cooler, moister microclimates, with the
strongest effects observed in summer, where NI explained 57 % of the
variation in temperature and 33% in RH. Although nighttime microclimate
relationships with NMs were generally weaker, they were positively
associated with the number and size of neighbours (summed basal area). The
buffering effect of high NI and basal area neighbourhoods was most evident
under extreme climatic conditions, with temperatures 3.5 °C cooler on the
hottest recorded day and 1.2 °C warmer during the coldest. The
amelioration in microclimatic conditions due to neighbouring plants has
important implications for tree performance and forest regeneration,
particularly in projected hotter and drier conditions.