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Policy Statement on Tree Planting

Adopted September 1991; Revised September 1993 (PDF Version)

Preamble

The California Native Plant Society (CNPS) is dedicated to the preservation of native flora, and to the restoration of that flora where it has been damaged or destroyed. Thus CNPS will encourage the planting of trees where appropriate. Tree planting projects have been frequently damaging to local ecosystems, due primarily to poor planning. The intent of this policy statement is to encourage appropriate tree planting programs and discourage those which are inappropriate. The cumulative impact of development in California has removed so much native vegetation that appropriate native species should be planted wherever possible, even in the context of the urban garden. CNPS encourages persons planning a tree planting program to evaluate their program relative to this policy.

Why should native trees be used in urban settings?

• Many California native trees are attractive in urban settings by conventional landscape criteria. Enjoyment of these trees by urban residents can broaden public awareness of what is truly beautiful in natural environments.
• The planting of native trees in urban settings may enhance gene flow between native stands separated by urban development and habitat fragmentation.
• The planting of native trees in urban settings can result in increased numbers of native birds in the area; many birds and other fauna are adapted to using native trees and prefer to feed and rest in these plants.
• The presence of native trees in an urban environment provides an educational benefit. They serve as a living illustration for discussions about the biology, identification, and uses of native species.
• Many native trees (in particular, many oaks) are adapted to low summer water demands; indeed, mature trees of these species need no summer water, and are particularly appropriate for areas with low water availability.

When should native trees be planted in natural settings?

1) The tree species exists, or existed, in the area chosen for planting.
   Tree planting is not appropriate where trees have not been a historic component of the plant community. Planting should enhance an altered or destroyed part of a plant community.
   Tree planting is encouraged by CNPS when the planting contributes to the attributes of the local ecosystem. Species selection should be of species found, or once found, naturally in the area considered for planting.
   Since a CNPS goal is to enhance natural, native plant communities, a planting should be representative of that plant community. The definition of natural and native should be rigorous and highly localized. This, however, is a very common misunderstanding in tree planting, where 'any' California native tree has been considered appropriate. Tree planters should consider and evaluate variations in slope aspect, soil type, degree of soil saturation, amount of shading, and several other factors when selecting particular species to be planted.

2) The seeds or planting stock were gathered from local sources, or can be shown to be genetically identical to local sources.
   Genetic contamination may result from the importation of seed or cutting stock from a different area. For example, different foreign stocks are currently contaminating local stands of Monterey Pine in the Monterey area. It should be recognized that local populations may have subtle genetic adaptation to the area that may not be present in other populations.
   In some cases plantings have used species that are closely related to the endemic species. These might result in unforeseen effects to dependent ecosystems, and possible undesirable genetic contamination, but may in some cases be harmless and would restore such things as a vertical layered structure or animal habitat that could not otherwise be attained.

3) The planted species should represent a full range of species that are found naturally in the area.
   The plantings should represent an appropriate range of species, in order to recreate as natural an ecosystem as possible, and to avoid the replacement of a heterogeneous, multispecies community with a monotonous single species community.
   Tree replanting after fire or harvest has frequently been from a single species, usually with the goal of enhancing some commercially exploitable species. This leads to a loss of diversity, and the possible risk of extinction of non-target species. It is therefore CNPS policy that the natural state of tree species diversity be a primary goal of any tree planting, and that the species selection represent all successional stages in the development of the ecosystem, especially where the establishment of such communities is vital to species preservation.

4) The planted species should be appropriate to the stage of plant community development at the site.
   It is important for tree planters to understand the level of development in the plant community. Certain trees occur early in the development of the community, to be replaced by different species as the community changes with time. The stage of plant community development into which a planting would be placed should be understood, so that planting be appropriate to the stage that is desired. In addition, there could be poor survivability of a species not suited to the stage currently represented at the site. Plantings should not be designed to eliminate successional communities that are vital parts of the regional ecosystem, and plantings should be appropriate to the successional community at the planting site.

5) The planting will not have an adverse effect on rare, threatened, or endangered animal or plant species.
   The likely impact on surrounding rare, endangered, or threatened species of plants and animals should be strongly considered. Evaluate what changes in shading, water distribution, litter buildup, habitat provision, secondary support for competitive species, etc., would be induced by the planting. This may invalidate the selection of otherwise appropriate species in the area occupied by rare, endangered, or threatened species. CNPS realizes that, due to loss of community diversity and the loss of availability of sites for plant reintroduction, it is necessary to inhibit the natural community progression and development in order to protect certain species. Thus tree planting should be considered relative to these goals.

6) If the first five conditions cannot be met, but a significant advantage can be claimed through the planting of a non-native species, then only non-invasive species should be used.
   Invasive non-native taxa have excluded native species from millions of acres in California. Examples include highly invasive trees such as Tree of Heaven (Ailanthus altissima).
   Exceptions to policy may be made where range extension or community alteration is being attempted in order to preserve a rare and endangered species that cannot be protected by other means