Why we monitor forest fragmentation
This indicator measures indigenous forest fragmentation in the Waikato region and how this has changed over time (from 1840 to 2012). It reports on the change in the number, size, edge to interior ratio, and isolation of indigenous forest fragments in the Waikato region.
Indigenous forest is defined as being:
- tall - with a canopy generally taller than three metres
- closed - with greater than 80 per cent cover
- dominated by indigenous tree species.
Interior forest is defined as being areas of a forest patch that are more than 60 m from the indigenous forest edge, irrespective of whether that forest patch is in pasture, plantation forest, or a type of non-forest indigenous vegetation.
Our indigenous forests are important reservoirs of indigenous biodiversity. Fragmentation of indigenous forest threatens indigenous biodiversity at the genetic, species, community and ecosystem levels. However, in some parts of the Waikato region, small forest fragments are the only areas of indigenous forest left.
Small forest fragments often have a high proportion of vegetation exposed to edge effects. Conditions in the forest 'edge' are quite different to those in the forest interior, and often favour introduced weeds. It's important we manage small forest fragments to reduce edge effects and increase the amount of 'interior' forest.
Small forest fragments rely on interaction with neighbouring fragments of sufficient size to maintain their biodiversity. As more forests are cleared, they are split into smaller, more isolated 'habitat islands' separated by pasture, plantations, orchards, roads or urban settlements. The cleared land between forest fragments can be a barrier to the movement of indigenous animals and plants, making it difficult for them to find enough food, a mate or to disperse their seeds to suitable sites.
It's important that we monitor changes in forest fragmentation to provide information about:
- pressures on forest fragments, for example, from land use and development
- the areas where forest patches are being lost
- where we may need to consider planting to restore or reconnect fragments.
This information helps us identify policy responses to avoid or reverse negative effects on our forest communities (part of the region’s indigenous biodiversity).
In 1840 (around the time of European settlement) about half of the Waikato region was covered in indigenous (native) forest. The forest was in about 100 huge areas, 13,200ha each on average, separated by scrub, tussock grasslands, wetlands, lakes, or rivers.
Over time, large areas of forest were cleared, leaving behind smaller patches, or 'forest fragments'. This process is called forest fragmentation.
Forest fragments can be:
- the patchy remains of larger indigenous forests, left over when the land around them has been cleared, or
- new areas of forest which have grown back on cleared land.
In 2012 we had 8183 indigenous forest areas larger than 0.4ha, totalling 472,908ha (20 per cent of our region).
Most of our region's indigenous forest is found in a few large fragments. The 10 largest fragments are each bigger than 10,000ha, and contain over 62 per cent of the indigenous forest in the region. However, 92 per cent of the individual forest patches remaining in the Waikato region are small fragments (less than 25ha).
Although their combined area makes up just 6 percent of our region's total indigenous forest, small fragments are important because in some parts of our region they are all that remain. This is particularly so in Hamilton city where 79 per cent, and Waipa District where 30 per cent, of all remaining indigenous forest is found in small fragments.
Contact at Waikato Regional Council
Terrestrial Ecologist - Science and Strategy Directorate