When we introduce plants to our covenants we want to know they will grow into well-formed specimens that complement existing vegetation, provide food and shelter for native wildlife, and regenerate over time, just as nature intends. Sadly, this may not always be the case. We might be disappointed to find years on that some are struggling to survive, not reproducing, not contributing to the biodiversity of the covenant – no seeds, no flowers, no insects for the birds. Buying plants for covenant enhancement projects can be an expensive exercise so you want to be sure of success. QEII regional representatives and botanists, Miles Giller and Alice Shanks, provide tips for choosing plants that will give you the best possible results for your covenant.
Every remnant of native vegetation is unique, a chronicle of your local original flora and fauna. The species and genetics present in your covenant reflect evolutionary development in your district. Covenants are forever so don’t feel pressured to rush your planting project. Take time to consider what your covenant needs, talk to your rep or local restoration experts, and plan plantings that will truly enhance your covenant and safeguard the integrity of the plant life protected in it.
Sometimes simply controlling rank exotic grasses, weeds, and browsers will allow native seedlings to establish through natural processes. Or moving a few of your forest’s own seedlings or some forest duff around might be all you need to do to assist your covenant towards greater health.
If your covenanted area was once grazed or logged, some species from its original makeup might now be missing. Re-establishment of missing species can add to your covenant’s health and sustainability. Consult experts or specialist websites (like www.natureservices.landcareresearch.co.nz/app/) to see if there are any important gaps you can fill with your planting plan. If you can’t get the species you need immediately, order for the following year. In some cases you may need to contract a nursery to grow the plants you need.
Planting species known to occur in your district helps with ecosystem health. Non-local species generally detract from covenant integrity. Some can even become troublesome weeds. For example, when North Island species like Hoheria populnea (lacebark/ribbonwood) are established in the South Island they sometimes spread prolifically, not only as pure-breds but also by crossing with South Island species. Seeds or seedlings should be sourced from local wild populations so that we avoid introducing non-local species and genetics. Better still, try and get plants and seeds from several local sources to maintain a range of local genetic diversity. Unless you are sure of plant sources, avoid collecting seed from restoration plantings as they may not necessarily have followed ecosourcing best practice guidelines at the time they were done.
Many birds and insects need trees for food, and many trees need birds and insects for pollination. Many plants also require birds for seed dispersal, and insects for the breakdown of leaf litter back to soil. The relationships between local plants and local fauna can be quite specific, so planting local strains of species known to occur in your district can increase the chance of providing suitable habitat for your local fauna. For example, plants produce various chemicals that act as either attractants or deterrents for local insects. Insects can be fussy about the chemical signatures of non-local trees, and those insects may be important pollinators or a food source for local birds.
Some plants can self-pollinate but this is not necessarily the best way to reproduce. If a lone specimen self-pollinates, its offspring may be less viable and may grow more slowly. Examples of this are kowhai and Olearia. Try to collect seed from large healthy groups of a species, where cross-pollination is likely to occur. This can maximise the genetic diversity, biological fitness, and the survival and growth rates of any seedlings. When these seedlings mature, cross pollinate, and produce their own seedlings, they are more likely to be vigorous.
Think twice about using cutting-grown plants and where possible opt for seed-grown stock. Plants grown from cuttings taken from a single parent plant exhibit no genetic variation; they are clones of their parent. When planted en masse, resulting plants will lack the opportunity to cross with genetically different plants of their species, and are unlikely to produce much seed. Seedlings will often be of poor vigour. Cutting-grown plants often fail to grow with typical form. With some tree species this leads to the lack of a normally dominant leading trunk, adopting instead a more shrub-like habit.
Most native plants live in close association with plant-specific soil fungi known as mycorrhizae, each benefiting from the relationship. Perhaps you are experiencing continuing failure with some plantings? This could be because the soil in your covenant lacks the associated fungi required by the plant (native beeches, kānuka, mānuka, and tōtara seem to be particularly sensitive to the loss of associated fungi). It is recommended that you choose seedlings that have been inoculated with the appropriate (not imported) fungi to enhance plant establishment and growth rates. If your plants have not been inoculated by the nursery try adding soil and duff (decaying organic matter on the forest floor) to the planting hole, taken from below naturally occurring plants of the same species.
Many New Zealand tree species are dioecious (have separate male and female reproductive features on separate trees). To get viable seeds we generally need both sexes present. If your plants are grown from cuttings collected from a single dioecious tree then all plants will have the same sex feature as the parent tree. For example, if a nursery takes cuttings from a single male broadleaf tree the progeny will be male and therefore won’t have seeds to feed birds and support regeneration. However, if your plants are grown from seed then we are likely to have a balance of males and females and better chances of good seed production for birds and for the next generation of trees.
Many plants in the garden nursery industry have been selected for their appearance. They might be eye-catching, but may be unsuited to your district. Some may simply fail to survive, others may dominate the site. Others may fail to produce fruit, contributing nothing to habitat health.
A poor quality sapling is unlikely to do as well as a good one. Select stocky plants with representative form, a strong root-collar diameter (the diameter of the lower stem is a good indicator of a plant’s reserves and resilience), and a well-developed and balanced root system.
Nature is far from random! All species have particular sites (niches) where they are more likely to flourish. Some species have wide tolerances, others can be very specific. Look at where each species grows in naturally occurring vegetation and mimic those conditions as best you can when you plant your trees and shrubs. Remember, vegetation often changes naturally through successional processes. Planting of some of the more tender species may need to be deferred until sufficient cover is first established.
The principle of eco-sourcing has been around for a long time. The following extract (abridged) comes from Department of Lands and Survey guidelines dated April 1976.
The aim should be to ensure the proper kinds of plants are grown. The planted species should be:
Article published in Open Space magazine, issue 90, March 2016.