Why are wilding conifers worse than other weeds?
Wilding conifers differ from other weeds in a variety of ways:
Wilding conifer seeds are able to spread over large distances in high wind events due to the seed having a 'wing' attached which helps it to fly. This means that seeds are scattered over the landscapes considerable distances from the parent tree.
Wilding conifers have the ability to completely displace native ecosystems in Central Otago. They grow taller than any natives vegetation that occurs naturally in Central Otago and consequently shades out the natives. The pine needles also acidify the soil and alter the soil biota to make it harder for natives to establish.
Wilding conifers use a huge amount of water and have the ability to alter groundwater and base water flows in addition to competing with native plants for water. Catchments covered in wilding conifers have been estimated to have a reduced water yield of between 40 - 80% when compared to tussock covered catchments.
What species are considered 'wilding conifers'?
Wilding conifers are any conifers or pines that are established through self-seeding. Currently the species we know wild in New Zealand are Corsican Pine (Pinus Nigra), Lodgepole Pine (Pinus Contorta), Radiata Pine (Pinus radiata), Scots Pines (Pinus sylvestris), Ponderosa Pines (Pinus Ponderosa), Douglas Fir (Pseudotsuga menziesii), and European larch (Larix decidua).
Why don't we use Wilding forests for wood harvest?
Due to the dry climate and short growing season experienced in Central Otago, pines are slow growing. Wilding conifers are also generally un-tendered, often grow in a stunted and twisted form making the timber of poor quality, are of mixed age and often establish in inaccessible sites making harvesting expensive. Added to these factors is the fact that Central Otago is relatively far from a port making transport costs high. All these factors together makes the harvesting of wilding forests in Central Otago commercially non-viable.
What about carbon storage?
Wilding forests cannot be registered in the Emission Trading Scheme and so can't be used to offset carbon emissions. Even if it was possible to claim carbon credits from wildings, Central Otago would not be a particularly desirable location for this purpose because of the slow growth rates compared to other parts of the country. The costs to water yield, biodiversity and landscape integrity from the uncontrolled spread of wilding conifers in Central Otago outweigh the value gains from carbon sequestered.
Where do the trees come from?
Wilding conifers originally spread from conifers planted in our landscape as an alternative landuse (forestry), for shelterbelts, for homestead plantings or for erosion control. Today our seed sources are still largely the same, coming from forests, shelterbelts and town amenity plantings.
What are the major challenges to controlling wilding conifers?
Identifying and understanding patterns of spread:
Killing a conifer tree is the easy part. The more difficult aspect is to ensure that another tree doesn't grow in its place. This involves identifying where the seed for that tree came from, using its species, prevailing wind directions and knowledge of the landscape to determine the source of the seed rain for that infestation.
Working with communities in our cultural landscapes to come up with a solution to the complex issue of conifer trees around towns, shelterbelts and historic settlements. These are often beautiful trees, sometimes with historic, cultural or amenity significance, however they also pose an ongoing issue of spreading thousands of conifer seeds over our landscape.
I want to plant some shelter/trees, what should I plant?
Firstly, consider if natives fit your purpose. Natives have lots of ecosystem services such as providing food and shelter for native birds and insects.
Alternatively, look for a hardy, non spreading species of conifer such as redwoods or cedar. For fast growing, tall shelter, the non-spreading hybrid pine of Pinus attenuata x radiata may be the best option.