Experimental plantations of future tree species

Between 2020 and 2022 a network of experimental plantations of tree species adapted to future climate is established throughout Switzerland as a joined effort of the Federal Institute for Forest, Snow and Landscape Research (WSL), the Federal Office for the Environment (FOEN), cantonal forest services, forest managers, professional organizations and forest owners. The experimental plantations, consisting of 55.000 plants, will be monitored for several decades and will allow insights in the suitability of tree species across broad environmental gradients in a changing climate. This network offers a unique infrastructure for practitioners as well as researchers.

Current status:

The last 9 sites will be established in spring 2023. They complete our network of 57 sites. In the summers of 2021 and 2022, the already established sites were visited and mortality was recorded. Most seedlings grew well. Tree provenances that grew poorly at a site are replanted up to two years after the original planting. This work is limited in parts by the availability of the plants. The media has shown great interest in the project and the experimental plantations have been the subject of numerous reports in newspapers, on the radio and on television.

Background:

A warmer climate with drier summers will affect the climatic suitability of tree species in their current habitat and, subsequently, future ecosystem services. On many forest sites other tree species than those in place will grow better towards the end of the 21^st century. While some tree species already grow on sites where the future climate is supposed to suit them, others are currently still absent.

In this context foresters are exposed to the following question:

Which of the tree species supposedly adapted to the climate expected on a given site towards the end of the 21^st century can already establish and grow there today?

To find answers to this question the project ‘experimental plantations of tree species adapted to future climates’ was started. Within its scope a network of 50-60 experimental plantations will be established throughout Switzerland and monitored over 30-50 years to find answers to pressing issues in climate change adaptation. The project will allow verification of results of the research program ‘Forests and climate change’. Its results will help the validation of site-specific tree species recommendations for forest practitioners, and it will create a long-term infrastructure for applied research. The scientific question behind the project is: which factors determine mortality, health and growth of tree species and provenances along large environmental gradients?

The great advantage of this project is the coordinated approach. While a single plantation provides only answers for the specific site, the network allows comprehensive and robust statements on the performance of tree species along large environmental gradients. Thus, this long-term trial will improve our understanding of effects of climate and climatic extremes on the trees species and provenances under investigation. The project is a follow-up activity of the research program "Forest and Climate Change", which FOEN and WSL conducted from 2009 to 2018.

Design

All test plantations are consistent in their design which allows reliable statistical analyses. The experimental design includes both the distribution of tree species over the experimental plantations and the arrangement of plants within each site. The design has been worked out in collaboration with researchers and revised by external statisticians. The 57 experimental plantations are distributed over all biogeographic regions and altitudinal belts occurring in Switzerland. Every experimental plantation is split in three blocks. The blocks are split in as many plots as there are tree species assigned to a specific site. All tree species will be planted once in every block and assigned randomly to a plot within the block. The number of tree species tested per site and therefore the number of plots and the size of the plantation is variable. Each plot is split in four subplots to which four provenances per tree species are assigned randomly. Finally, every subplot contains nine individual trees.

The area needed for a test plantation is given by the number of tree species assigned to this site and by the height of the neighboring stands, which determines the width of the buffer zone needed. The spacing between plants is 2 m, between plots 4 m. The area needed for a test plantation with 4 tree species is approximately 0.75 ha. A plantation with 10 tree species requires approximately 1.3 ha.

To record the local climate, an automated climate station is operated on each experimental site. It measures among other things soil moisture .

Detailed information about the experimental design can be found in the report ‘Versuchsdesign für Testpflanzungen’ (available in German and French only).

Plantation sites

In mid-March 2018 the cantons have been invited to propose experimental sites meeting the requirements described in the report ‘Site selection for experimental plantations’ (only available in German and French). From November 2018 to July 2019, the WSL project team visited 125 of the 172 sites proposed by the cantonal forest services. In July 2019, 57 sites were selected and the tree species to be tested on each site were assigned (report `Site selection for experimental plantations’ (only available in German and French). Later, minor changes were made to the selection of sites and tree species allocation, and two sites were added in the canton of Baselland, while two sites were cancelled in the canton of Bern.

All experimental plantation sites are contractually secured for the long term.

The 57 experimental plantations are distributed over all biogeographic regions and altitudinal belts occurring in Switzerland. Depending on site size, four to 18 tree species are tested in an experimental plantation. On six sites (‘supersites’), all 18 tree species are tested.

Table of all experimental plantations sorted by number.

Number TS = Number of tree species tested on site

Planting period = Planting period in which the site is established

1 means fall 20 to spring 21, 2 means fall 21 to spring 22, 3 means fall 22 to spring 23.

No.	Canton	Municipality	Locality	Number TS	PP	Month	Year
1	AI	Schwende	Berneregg	6	1	May	21
4	GR	Safiental	Gampel	5	2	Sept	21
9	ZH	Oberrieden	Neuforst	6	1	Mar	21
10	LU	Emmen	Oberschiltwald	6	3	Nov	22
11	LU	Pfaffnau	Birchwald	6	3	Mar	23
15	LU	Escholzmatt-Marbach	Buhhütte	10	1	May	21
16	GR	Val Müstair	Cuoir	10	2	May	22
17	GR	Bregaglia	Dre Mota	7	1	Oct	20
18	GR	Valsot	Vadrain	6	3	Oct	22
22	GR	Samedan	Sur Plaun God	8	2	May	22
25	FR	Bulle	La Joretta	8	1	Oct	20
26	FR	Belmont-Broye	Forêt du Grand Belmont	8	1	Nov	20
28	SZ	Schwyz	Galleren	8	2	May	22
36	SZ	Feusisberg	Friesisschwand	8	2	Apr	22
37	GR	Albula/Alvra	Tgavrouls	6	3
38	GR	Bergün Filisur	Spena	8	1	Sep	20
42	AG	Villigen	Güllenholz	8	3	Nov	22
43	AG	Murgenthal	Fätzholz	6	3	Mar	23
45	SO	Seewen	Holzenberg	6	3	Nov	22
47	SO	Luterbach	Dorn-Ischlag	8	1	Nov	20
48	SO	Himmelried	Steffenschmiede	8	2	Nov	21
50	GE	Presinge	Le Bois des Eaux	8	1	Nov	20
51	SH	Schaffhausen	Rändli	18	3	Oct	22
54	ZH	Aesch (ZH)	Seegaden	4	2	Nov	21
66	BL	Arisdorf	Eileten	18	2	Nov	21
68	SG	Gaiserwald	Hoferst	8	2	Mar	22
72	SG	Quarten	Oberer Nüchen	6	1	May	21
74	SG	Amden	Vorem Platt	6	3	Sep	22
80	SG	Uznach	Chrüzweg	8	1	Nov	20
82	VD	Froideville	Jorat d'Echallens	10	1	Nov	20
85	VD	Apples	Bois de Saint Pierre	18	2	Mar	22
87	VD	Vallorbe	Crêt Cantin	8	3	Mar	23
91	VD	Château-d'Oex	Les Jeurs	10	2	Sept	21
93	VS	Riederalp	Riederwald	6	2	Sept	21
96	VS	Riddes	Forêt des Conches	8	1	Dec	21
97	VS	Champéry	La Forêt Derrière	8	3	Oct	22
99	VS	Leuk	Baronsächer	6	3	Oct	22
100	VS	Bagnes	Forêt du Marais	6	2	Sept	21
101	TG	Ermatingen	Hauptmeshööli	10	2	Mar	22
105	TI	Serravalle	Caslóu	7	2	Mar	22
108	TI	Losone	Piano di Arbigo	6	2	Nov	21
109	TI	Ronco sopra Ascona	Casone	12	3	Oct	22
118	TI	Stabio	Baragge	4	2	Nov	21
119	TI	Novaggio	Ur Pián Pülpit	10	1	Mar	21
124	UR	Unterschächen	Alt Rüti	8	3	May	23
129	BE	Neuenegg	Ruessemattbode	18	1	Oct	20
131	BE	Rüschegg	Hirschböde	6	1	May	21
132	BE	Innertkirchen	Militalwald	na	na	na	na
154	BE	Petit-Val	Droit des Ecorcheresses	na	na	na	na
156	BE	Grandval	La Haute Joux	18	2	Apr	22
162	BE	Boltigen	Bäderegg	5	2	May	22
166	BL	Muttenz	Oberi Hard	6	1	Nov	20
167	JU	Haute-Ajoie	Foirgeret	8	2	Nov	21
168	GR	Maienfeld	Fuchsenwinkel	18	2	Oct	21
170	ZG	Unterägeri	Hinterwidenwald	8	2	Oct	21
172	ZH	Zürich	Waldlabor	8	1	Mar	21
173	TI	Locarno	Cappelletta	10	3	Mar	23
174	BL	Buus	Schöönenberg	12	1	Jan	21
175	BL	Pfeffingen	Bielgrabe	8	2	Mar	22

Tree species

The tree species to be tested in the fixed design were chosen taking into account the considerations of cantonal stakeholders and experts in a multistage procedure. While nine tree species belong to the core set and will be planted in approximately 35 sites, another nine tree species belong to the extension set and will be planted in only approximately 15 sites. The process of tree species selection is reported in ‘Tree species selection for experimental plantations’ (only available in German and French).

The 18 tree species under investigation comprise many of the species which are probably suitable in future climates. For tree species of the core set reliable results will be generated to analyze and compare their performance over a broad environmental gradient, while for tree species of the extension set the explanatory power will be smaller.

Core set (9 tree species)	Ergänzungsset (9 Arten)
Abies alba (silver fir) Acer pseudoplatanus (Sycamore maple) Fagus sylvatica (European beech) Larix decidua (European larch) Picea abies (Norway spruce) Pinus sylvestris (Scots Pine) Pseudotsuga menziesii (Douglas fir) Quercus petraea (Sessile oak) Tilia cordata (Small-leaved Lime)	Acer opalus (Italian maple) Acer platanoides (Norway maple) Cedrus atlantica (Atlas ceda) Corylus colurna (Turkish hazel) Juglans regia (Persian walnut) Prunus avium (Wild cherry) Quercus cerris (Turkey oak) Quercus robur (Pedunculate oak) Sorbus torminalis (Wild service tree)

Provenances

For each tree species seven provenances will be tested. In order to keep the size of the experimental plantations manageable only four out of the seven provenances are assigned to each test plantation. While six provenances will be tested in half of the experimental plantations only, one provenance will be tested as reference in all experimental plantations a species is assigned to. This allows for better coverage of the genetic variability within the tree species, while it keeps site sizes manageable.

The provenances were selected in an elaborate process (report ‘Provenance selection and seedling provisioning’). The plant material was procured in cooperation with several Swiss nurseries and foreign partners. Most of the plants are grown at the Emme AG nursery, a few tree species are also grown at the nursery of the Canton of Ticino (Morbio Superiore) and at the WSL experimental nursery.

Funding

The establishment and maintenance of the experimental plantations is partly financed by subsidies from the Federal Office for the Environment. In addition, the cantons contribute significantly to the financing of their own experimental plantation sites.

Outlook

The plan is to establish all plantations by spring 2023. Replanting will take place as needed over a two-year period in case of major failures. The forest managers are responsible for planting their sites, the WSL team accompanies the plantings and distributes the plants to the marked planting spots. Maintenance is also the responsibility of the forest managers, which adhere to the specifications of the ‘Guidelines for vegetation management’. In summer of 2021, the condition of the planted trees (on the sites already planted) was recorded for the first time. These inventories are to be carried out annually during the first few years, and later at intervals of several years.