THE FOREST FOR THE TREES On a site dominated by weeds, this fitting together of complementary strategies is compromised, often resulting in the domination of a few species. This may lead to fewer species and lower biomass for a given area and an impaired habitat for native animals. Replacing the weed–infested site with a natural plant community, based on careful study of a healthy ecosystem, can contribute not only to the resilience of local native plant populations in the area, but also ensure more nutrients and carbon are sequestered as a result of both greater productivity and biomass. Disturbed areas where weeds have established are likely to remain dominated by weeds without some intervention. Lack of nearby seed sources and the vectors for dispersal may account for this, or our native forest species may be well adapted to succeed native colonising species, but may not have developed strategies to out–compete introduced ones. An important precursor to restoration planting is the suppression of those weeds dominating the site, long enough to establish a native plant community. In areas where a rich forest is the natural order, the plan is always to establish a tall, dense plant community, better equipped to resist further weed incursions. Just as the native species dominant on the site will change as the project progresses, so will the weeds present. Quick–establishing weeds like inkweed (Phytolacca octandra) and wild turnip (Brassica rapa sub sp.sylvestris) can be a real problem soon after planting, but as the new native seedlings establish, these will be shaded out and more shade tolerant., taller or climbing weed species now become the biggest threats. The aptly–named bindweed (Calystegia spp.) is intermediate in this regard. This species can be a real problem for young plantings. Although it may not be apparent at the time of preparation or planting, bindweed can move in quickly from either spreading stems
or seed to become the most prevalent species on a site. Without control, bindweed (Calystegia spp.) will bind the emerging top leaves of cabbage trees/ti kouka (Cordyline australis), causing the growing tip to rot. Young shrubs and trees can be bent over and deprived of energy–bringing sunlight. But eventually, these young trees and shrubs will grow too tall and dense for the new spring growth of this deciduous climber to emerge over the canopy, and it will cease to be a threat. There is no altruism in native plants and although successive species modify the environment, facilitating ecological succession — the process by which the structure of a biological community evolves over time — they can, on occasion, also interrupt this process. Pohuehue (Muehlenbeckia australis), for instance is a vigorous climber, creating such a dense canopy that few native plants will thrive in its shade and some control may be necessary to establish a more complex plant community. Pohuehue is, however, an important part of a plant community, sustaining both butterflies and birds, so although its control may be necessary, its elimination is not. It would be nice to think we could easily eliminate all weeds before we start a project, but in reality, we have to prioritise on most projects, assessing the potential of each weed species to compromise the planting. This will not only vary from species to species, but also from site to site. To use our previous example, wandering Jew (Tradescantia fluminensis) will be a serious threat on damp, shady, frost free sites, but on dry sites, very shady sites or where frost will always be a factor, or a combination of these, it may not grow with sufficient density to be a problem. Weediness will only be one factor in the equation. Species that are not yet common, but have the potential to spread, will be a high priority. Royal fern (Osmunda regalis) is well established in some Waikato wetlands and beginning to establish in others. 20