MICROCLIMATIC DIFFERENCES BETWEEN AND WITHIN CANOPY GAPS IN A TEMPERATE RAIN-FOREST

The microclimate in the understorey and in two canopy gaps of different size (249 m(2) and 12.6 m(2)) within a temperate rainforest in northern New Zealand were characterised using net all-wave radiation (Q*), vapour pressure deficit (VPD), vertical air temperature gradient (VTG), and maximum and minimum air temperatures. Hemispherical fisheye photographs were used to define the exposure to the sky at each microclimate recording site both within and between gaps, and in the un derstorey. Under condiions of clear skies during the summer, with the sun close to its maximum altitude, the large gap centre had a mean daytime (0700-1700 hours) Q* of 452 W/m(2). This value was similar to that estimated for an open field nearby, but three times greater than Q* at the centre of the small gap, and six times greater than in the understorey. The east and west sides of both gaps had higher values of Q* than the north and south sides. Both Q* and mean daily maximum temperature were strongly correlated with the amount of sky expo sure. VPD and VTG were higher in gaps than in the understorey, with maximum values for both variables occurring at the centre of the large gap.