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Planting Native Trees for Biodiversity

What is a native tree?
 
These are tree species which have colonised the landscape of Wales by natural processes since the last ice age, approximately 50, 000 years ago. Historically, trees that were well adapted to the soil and climatic conditions succeeded and thrived; whereas those ill-adapted failed. Over many generations, the successful species have adapted to local conditions resulting in the genetic make-up of woodland that we say is of local provenance.
 
Species widely accepted as being truly native are mainly broadleaved, deciduous species, including birch, oak, ash, willow, as well as evergreens such as holly, yew, scots pine and juniper.

The main advantages of native trees and shrubs over non-native species (such as exotic conifers) are now widely appreciated:
1005590.jpg 
 
Cardinal Beetle
  • Maintaining local landscape heritage and conservation value.
  • Supporting a wider range of plants and animals than introduced species (eg Oak, Willow and Birch all support over 200 native insect species, compared to 19 present on Larch).
  • Native species are more likely to thrive than most introduced species, particularly in more challenging conditions.
  • Producing more sustainable economic benefits, whether from quality hardwood timber or as a multitude of coppice wood and non-timber forest products.
Human Activity

Humans have been adding to the native woodland gene pool for centuries, both unintentionally and deliberately, through planting. Many non-native species (eg sycamore, exotic conifers) as well as non-native varieties of native species (eg exotic birches, oaks, pines) have been introduced. Some of these introductions have succeeded in become naturalised (sweet chestnut, beech) and are often now regarded as being native.
 
Even many of the truly native trees that have been planted in Wales over the years have been grown from imported seed, particularly from central and eastern Europe where large areas of woodland still exist and where the labour costs involved in collection are much lower. These trees are not necessarily well adapted to the very different environmental conditions found in Wales, and may not be a desirable source of seeds.
 
Cross-fertilisation between 'local provenance' native plants and imported species, has produced a range of genotypes reflecting local and alien gene adaptations. Consequently, local provenance trees now make up a quite small proportion of the total woodland gene pool.
 
To reduce the risk of further diluting this gene-pool, it is therefore advisable to collect tree seed from sites which are reliably identified as of longstanding local origin, such as from designated ancient semi-natural woodland.
 
What does provenance mean today?
The provenance of a tree describes the seed it grew from and where the seed was collected. As a guide the Forestry Commission has divided the UK into broad seed zones based on regional, environmental zones.
 
How local is local
Local provenance is not simply a matter of collecting seeds from the most geographically local parent trees; of far greater importance is the ecological appropriateness of the seed source to the tree planting site. Particular consideration needs to be taken to match altitude, frost-hardiness, soil type and drainage.
  
Why Plant Local Provenance Native Trees and Shrubs?

  • The genetic makeup of local provenance native trees and shrubs ensures that they are better adapted to local conditions found in Wales.
  • Planting better adapted trees ensures better survival rates, avoiding the costs of replanting.
  • Trees grown from imported seed may differ significantly in important genetic characteristics, such as the time they come into leaf, flower and fruit, upsetting the fine balance between native trees and the wildlife they support.
  • Sourcing trees and seeds locally reduces transport costs, reduces pollution and helps to safeguard local employment.
  • Most agencies involved in tree planting, including Coed Cymru, Forestry Commission, C.C.W., Woodland Trust, Flora Locale, Highways Directorate of W.A.G. and Unitary Authorities now recommend using local provenance trees.
Planting or natural regeneration
 
Remember that tree planting and habitat creation are not always acceptable substitutes for protecting existing sites of high wildlife value. Consider the potential for natural regeneration of woodland in situ before planting, even with local provenance native trees.
 
Conserving biodiversity

Thousands of years of adaptation have resulted in local provenance, native trees becoming well adapted to local conditions. These genetic characteristics could be lost forever through cross-pollination with imported material. Reducing biodiversity and diluting the gene pool reduces an ecosystems’ long-term ability to adapt and thrive. For that reason it is important to ensure local provenance seed is collected from a range of genetically distinct local sources.
 
Rural development and seed source diversity

Developing small-scale, local tree nurseries in Wales is a priority, both for supporting local economies and to diversify tree seed sources:
 
In Wales a majority of native woodlands are in private ownership and are widely dispersed across rural Wales. In the past, a number of existing nurseries and specialist seed merchants have collected native tree seed of welsh provenance, but it has simply been uneconomic for larger nurseries, often based outside Wales, to collect from anything but a small sample of these potential sites. These collections have been from a small number of well-known sources, with associated limitations on the local provenance seed collected:
  • A small number of sites restricts both the quantity of seed available and, more importantly, its genetic diversity.
  • Quality of timber production has, in the past, been the only criterium for selecting seed from this small number of registered seed stands. This is not necessarily the best approach for maintaining biodiversity.
  • Equally, there is a danger that, by focusing wholly on local provenance tree-planting for conservation, the importance of timber quality for seed provenance is discarded completely.
There is a need to consider seed collecting and tree planting in the context of long-term sustainability of woodlands, not purely in ecological terms, but also in terms of the management and employment they support, as this has very often been the main reason why native woodlands have survived, particularly in private ownership.
 
Climate Change and native trees
Predictions have matched welsh climates in 2050 to be similar to that currently experienced in south-west England/north-west France (low/high climate change impact scenarios). More specifically, “most recent predictions from the UK Climate Impacts Programme suggest an increase in temperature, changes in rainfall, windspeed, cloud cover and vapour pressure,”1 all of which have a range of implications for the survival and growth of trees, including:
  • Due to increased temperatures and CO2 levels there is potential for a general increase in tree growth rates.
  • Equally there is significant potential for increases in losses due to drought, storm damage and incidence of pests and diseases.
  • With the worst impact of drought and raised temperatures predicted for south-east and south-west England, the most productive areas of some native tree species are predicted to move broadly north-westwards across the UK.
  • For Wales, the overall effects of climate change is likely to be neutral, although a more favourable environment could result in a change in the composition of species considered to be native, for example permitting better survival and growth rates for sweet chestnut, beech and increased displacement of sessile oak by pedunculate and hybrid varieties.
 
Climate Change and local provenance
Historically, reducing biodiversity reduces an ecosystems’ long-term ability to adapt to change and thrive, making them more prone to degrade and collapse.
 
Therefore, avoiding future degradation in native woodland and wider environmental impact, hinges on conserving genetic diversity, for example by
  • increasing the range of local provenance seed sources.
  • the increased availability and use of local provenance, native trees.
 
Recently, there have been suggestions made for planting non-native provenances in anticipation of predicted future climates in the UK, but:
  • This is not to be confused as a justification for abandoning the use of native provenances in favour of imported provenance.
  • Nor is it a justification for previous and continuing practice of sourcing inappropriate, imported seed simply because it is more abundant, lower cost or meets timber quality criteria.
  • There may be some justification for some limited planting of non-native provenances from areas currently experiencing climates similar to predicted UK climates.
  • However, the balance of advantages and disadvantages of climate change to forestry is as inconclusive as the case for employing non-native provenances.
 
The priority has to be to conserve the existing native biodiversity and permit this to respond naturally to climate change through prioritising natural regeneration over tree planting.
 
 
 
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