Does Douglas fir have significantly higher wood reserves than spruce under our conditions?
Introduced forest tree species have been utilized in the forestry of the Czech lands for a long time, as well as in other European countries. In our conditions, these species were intended to address several challenges. For certain tree species, the primary goal was to afforest extreme habitats. For instance, the black locust, which is now recognized as an invasive species, and the black pine have been used since the 19th century.
Photo: Massive Douglas firs along a forest path, Central Bohemia, author Jan Řezáč
Some introduced species, such as red oak and grand fir, were intended to partially replace native species that were impacted by catastrophic extinctions. A specific issue in the Czech Republic was the growth of replacement tree species, particularly due to the extensive use of Norway spruce. Other species, like black walnut and especially Douglas fir, were introduced mainly for production purposes.
It is important to consider the impact of established non-native tree species on the environment, especially in light of European documentation. We should approach the introduction of new species with the utmost caution and limit the use of those that have already been proven to be invasive. So, preliminary caution is essential.
Photo: Massive natural regeneration of Douglas fir, Central Bohemia, author Jan Řezáč
Douglas fir is classified as a naturalized tree species. In addition to its high-quality wood production, it serves as a potential partial replacement for domestic spruce, which has become extinct in unsuitable natural conditions. Due to its ability to regenerate naturally in various types of forests, including semi-natural ones, Douglas fir displays some characteristics of an invasive species.
The production function (wood production) of Douglas fir was compared to that of Norway spruce in research conducted by Ing. Karel Matějka, CSc. (IDS, https://www.infodatasys.cz), and Ing. Jan Mondek, Ph.D. (Forest Management Institute, Brandýs nad Labem, České Budějovice branch). Their findings were published in the paper Comparison of Douglas-fir and Norway spruce growth according to data from forest management plans and outlines (Porovnání růstu douglasky tisolisté a smrku ztepilého podle dat lesních hospodářských plánů a osnov) which appeared in the journal Reports of Forestry Research, Issue 1/2024.
The aim of this study is to compare the production characteristics of two tree species using data from forest management plans (FMP – LHP) and forest management outlines (FMO – LHO). While we acknowledge the challenges associated with this data, we seek to develop a growth model for both species based on the information obtained from the FMPs and FMOs.
Photo: Douglas fir is doing well there, in the Czech Republic, Central Bohemia, author Jan Řezáč
Douglas fir is native to the western United States and has been cultivated in Europe for a long time. There are ongoing efforts to introduce it more extensively into forests across Europe, including the Czech Republic. However, in recent years, these initiatives have faced challenges due to increasingly evident climate changes, which have caused significant physiological stress to vital commercial tree species, particularly Norway spruce. This stress has made Norway spruce more susceptible to attacks from the spruce bark beetle. As a result, foresters are exploring the possibility of replacing spruce with other tree species.
Douglas fir has been categorized as an amelioration and stabilization tree species. It contributes to mechanical stability, including wood strength and root system shape, and positively affects soil conditions, serving a stabilizing and enriching function. However, there are challenges associated with the silviculture of Douglas fir.
- It increases nitrogen activity in the ecosystem, which amplifies the negative effects of its increased deposition from human sources.
- The composition of herbaceous vegetation under Douglas fir stands differs from that under native tree species, with new communities showing signs of ruderalization.
- It regenerates spontaneously in nearly all habitats, sometimes occurring in large numbers. In subsequent generations, it can displace native tree species, fulfilling some characteristics of invasive species.
Photo: A high-quality stand of Norway spruce with scattered European beech in Central Bohemia, author: Jan Řezáč
Older research studies demonstrate that Douglas fir has a high production capacity. Various studies indicate that introducing Douglas fir into a stand mixture significantly increases overall stand production. For instance, at the age of 100 years, it is expected that the volume of a single Douglas fir tree can reach up to 6 cubic meters. This high production of quality wood is a primary reason for incorporating Douglas fir into mixed stands.
Additionally, there is a pressing need to replace Norway spruce, which has become increasingly unsuitable for its habitat. The development and silviculture of Norway spruce have been problematic in recent decades due to the effects of warming and drought.
Scientists have analysed the annual ring growth of Norway spruce and Douglas fir in southern Bohemia and found that these two tree species respond differently to various climatic factors. This suggests that their growth dynamics may vary under different environmental conditions, a comparison that has not been previously conducted in the Czech Republic.
Additionally, by processing FMP/FMO (LHP/LHO) data from the Czech Republic, the authors developed growth models for Douglas fir and Norway spruce grown in the same locations. The growth model for Douglas fir can serve as a substitute for the absent growth tables for this tree species.
Photo: A high-quality stand of Norway spruce with scattered Silver fir in Central Bohemia, author: Jan Řezáč
Scientists have found that Douglas fir has an average of 4.2% higher stock than Norway spruce at the age of 140 years, but the potential volume of material extracted during pruning and thinning is significantly higher, namely by 32%. The total stock at the compared age of 140 years is an average of 599 m3/ha for Douglas fir and 575 m3/ha for spruce. The ratio of Douglas fir to spruce stock varies with altitude, with Douglas fir stock being 7.5% higher in the 3rd LVS, and only 1.5% higher in the 6th LVS. A higher growth rate of Douglas fir is evident up to approximately 100 years of age, with final stocks being similar, although Douglas fir has more stands with very high stocks.
Both tree species exhibit the highest production potential during the fifth stage of forest vegetation, particularly in nutrient-rich habitats. However, the greatest volume growth rate is observed in acidic habitats.
It remains uncertain whether the high reserves reported in some studies result from selecting particularly favourable habitats for Douglas fir or from cultivation practices that significantly enhance its production. In these studies, the reported reserves often exceed those predicted by the model developed by Ing. Matějka and Ing. Mondek.
Photo: A high-quality stand of Norway spruce with scattered European beech in Central Bohemia, Author: Jan Řezáč
Their model is based on the average condition of forest stands in the Czech Republic and is influenced by the method of data collection used to create the Forest Management Plan (FMP) or Large-scale Forest Plan (LHP). This method may not accurately reflect the actual situation, particularly for Douglas fir, which lacks comprehensive taxonomic and growth tables in the Czech Republic.
This discrepancy likely explains why the calculated difference in stocks between Douglas fir and Norway spruce is not as significant as it could be when comparing selected research areas that are optimally situated for Douglas fir growth.
Douglas fir has a high production potential in the forests of the Czech Republic. However, this tree species can negatively impact local plant communities and possibly other organisms. It has a strong ability for spontaneous regeneration, which increases the risk of its unintentional spread both within and beyond its original ecosystem. Additionally, Douglas fir affects nutrient dynamics, particularly nitrogen levels.
Given these factors, caution is essential when introducing Douglas fir into forest stands. When replacing unsuitable Norway spruce, it is advisable to primarily use tree species that are native to the region and compatible with the local habitat.
Additional information regarding this tree species can be found on the website for Introduced Tree Species in the Forests of the Czech Republic /Introdukované dřeviny v lesích ČR/ (https://www.infodatasys.cz/proj009/default.htm).
The paper Comparison of Douglas-fir and Norway spruce growth according to data from forest management plans and outlines (Porovnání růstu douglasky tisolisté a smrku ztepilého podle dat lesních hospodářských plánů a osnov) can be downloaded here.
Authors of original paper: Ing. Karel Matějka, CSc., IDS; Ing. Jan Mondek, Ph.D., Forest Management Institute (Ústav pro hospodářskou úpravu lesů Brandýs nad Labem), branch (pobočka) České Budějovice, e-mail: matejka@infodatasys.cz
Prepared in accordance with the original by Jan Řezáč, FGMRI (VÚLHM, v. v. i.), e-mail: rezac@vulhm.cz