After noticing two large tree planting camps along Highway 20 during my last trip out west it got me thinking about my time as the silviculture audit forester. With all the forest fires and the unprecedented warm weather I have some sympathy for the planting crews as well as the seedlings trying to survive in a year like this.
It has been three-plus decades since my silviculture work so I wanted the latest information on the practices for successful tree establishment.
My first source was a provincial publication “Best Management Practices for Improving Survival for Planted Douglas-fir in The Cariboo Natural Resource Region” by Colin Hegan and Tanja Armstrong Whitworth. The authors point out that Douglas-fir is extremely difficult to establish and trends of increased exposure will make this more challenging.
Once Douglas-fir is established it becomes increasingly resistant to these events so it is desirable to maintain Douglas-fir forests where they currently exist to improve the chances of seedling survival. The best practices for harvesting in Douglas-fir forests are through silvicultural systems such as uniform shelterwoods, single tree or group selection.
Because of the extensive catastrophic fires and a recent history of clearcut harvesting in the region much of the planting must occur where there is little protection. The authors go on to outline the various things that must be considered to accomplish successful establishment including proper planning along with planting prescriptions and sowing requests. Choosing good planting sites that consider frost and drought and in some cases mechanical site preparation may be necessary.
With the potential for a warming climate it has been proposed that planting in the fall may be a more viable option.
Wesley Brookes describes a project in the Cariboo Chilcotin where in the fall of 2019, 155 000 seedlings were planted on different microsites and were monitored for health and vigour along with specific microsite data including soil temperature and moisture, air temperature, and vapour pressure deficit (VPD) for one year.
The results are described in the Zanzibar Holdings site entitled “Fall planting in the Cariboo- Chilcotin a response to a warming climate.”
The data analysis showed what environmental factors proved most significant to the survival of the seedlings. These factors introduced some unique management considerations relative to spring planting that silviculturists must take into account when planting seedlings in the fall.
As would be expected the fall planting reduced the impact of drought conditions but increased the concern about frost pockets. When developing planting prescriptions, silviculturists need to take into consideration such factors as cold air drainage. While large surface features such as logs can provide seedlings with shade during the hot summer months, thereby lowering surface temperatures and increasing access to soil moisture, they can also obstruct cold air drainage.
This leads to the pooling of cold air and greater occurrences of frost, which can cause seedling damage and mortality. Therefore, the orientation of large surface features relative to slope must be considered when assessing suitable microsites.
During the fall, plants and other vegetation are hardening off for the winter which makes the supple and sweet foliage of newly planted seedlings particularly appetizing and more susceptible to herbivores. While good preparation and planting practices are important a little help from mother nature like the recent rain also help.