drought

Ascarina lucida Hook.f. (Chloranthaceae) is a small tree species endemic to New Zealand. The distribution of A. lucida suggests an inability to survive severe frosts or droughts. Therefore, peaks in the abundance of A. lucida in pollen records have usually been interpreted as indicating periods of mild, moist climates. The environmental tolerance of A. lucida seedlings to climatic extremes was experimentally tested by exposing seedlings to frost, drought, and waterlogged soil conditions. This research confirms the sensitivity of A. lucida to climatic extremes.

The exotic sand-binder Ammophila arenaria (marram grass) has displaced the native sedge Desmoschoenus spiralis (pingao or pikao) from many of New Zealand’s coastal dunes. This study explores the possible role of drought as a mechanism promoting marram invasion and pingao displacement. The response of the two sandbinders to conditions of increasing soil water deficit was compared in a four-week pot trial. Water potential, relative water content and stomatal conductance were measured every 3–4 days on randomly selected individuals from a control and two drought treatments.

In the 1950s, increased erosion, flooding and sedimentation was widely observed in New Zealand. The ruling opinion then was that the forests prevented erosion and floods, and browsing mammals were primarily responsible for the increased erosion of mountain lands. It followed that effective control of browsing mammal populations was necessary to prevent erosion and alleviate lowland flooding and alluviation. In the 19608 evidence was found for much severe erosion on the Ruahines in the 1840s -long before browsing mammals were there.

During the last 1800 years there have been eight periods of increased erosion and alluvial sedimentation in New Zealand, which have generally decreased in magnitude towards the present. Throughout New Zealand, alluvium of all erosion periods contains abundant remains of plants as evidence of widespread destruction of vegetation during erosion periods. Indices of the relative magnitude of alluviation, and estimates of the damage to vegetation in the current Waipawa Period (since 1950), are applied to estimate the impact of earlier erosion periods.

Meteorological data from stations around and within the Kaimai Ranges and data from temporary sites are used to characterise the climate of the ranges. Lowland climate is warm temperate with ample rainfall but the upland region is cooler, wetter and frequently enveloped in fog. Frequent fog plays an important part in the climate of upland regions. By modifying light, moisture and temperature regimes fog may be a significant determinant of plant associations and may severely restrict growth.