C2-C3-D1 : Testing forest management procedures adapted to global change

The adaptation of forests to climate change is currently a hot topic for research all around the world. However, the scientific results at a global change need to be tested at a local scale. For this reason, FORECCAsT supports the implementation of more than 20 silvicultural tests all around the Haut-Languedoc Regional Nature Park territory.

These tests concern both forest renewal projects and existing forest stands. Concerning forest renewal projects, we will test new tree species for the territory and mixed forest modalities. Concerning existing forest stands, we will test management procedures to save water and to help resilient or resistant trees.


Arboretums

In order to know better the tree species that could be introduced in Haut-Languedoc, we planted three arboretums. The main objective of these trials is to test in situ some genetic units (origin x species) a priori adapted to the local effects of climate change, especially concerning the lack of water and summer droughts.

Planting Taussac-la-Billière arboretum (Juliane Casquet - Pnr HL)

Planting Taussac-la-Billière arboretum (Juliane Casquet - Pnr HL)

We chose the localisation of these arboretums according to a climatic gradient. The three trials were implanted respectively in Lacaune plateau (Senaux, 81), in Montagne Noire (Mazamet, 81) and in the mediterranean area (Taussac-la-Bilière, 34). We tested the same genetic units in the three trials (with one or two exceptions), which will allow the estimation, at the Haut-Languedoc scale, of the climatic limits of each species.

To chose which species to test, we benefited from the lessons from previous research projects ( NOMADES, REINFFORCE,…). We chose the species according to their potential for adaptation to the Haut-Languedoc climate.

The genetic units we chose are the following:

Scientific name Vernacular name Scientific name Vernacular name
Abies alba Silver fir Pinus pinaster Maritime pine
Abies bornmuelleriana Turkish fir Pinus pinea Stone pine
Abies cephalonica Greek fir Pseudotsuga menziesii Douglas fir Luzette origin
Abies nordmanniana Nordmann fir Pseudotsuga menziesii Douglas fir California origin
Castanea sativa Sweet chestnut Quercus canariensis Algerian oak
Cedrus atlantica Atlas cedar Quercus cerris Turkey oak
Cedrus libani Lebanon cedar Quercus faginea Portuguese oak
Celtis australis European nettle tree Quercus petraea Sessile oak
Fagus orientalis Oriental beech Quercus pubescens Downy oak
Fagus sylvatica European beech Quercus suber Cork oak
Pinus laricio corsicana Corsican pine Robinia pseudoacacia Black locust
Pinus nigra salzmanii Pyreneean pince Sorbus domestica Service tree

List of the genetic units tested in our arboeretums

During at least 10 years, the Occitania CRPF will monitor the growth and mortality of these plants. This will allow the study of the potential for adaptation of these species to the Haut-Languedoc climate.


Mixed forest stands

Recent scientific researches tend to demonstrate that mixing species in forest stands could be favourable at many levels. Some mixed forest stands have a water consumption that differs in quantity or seasonality when compared to monospecific forest stands. The biodiversity increases with the number of tree species in the forest stands. Mixed forest stands also tends to be less sensitive to sanitary issues, which is partly due to the fact that it is harder for a pathogen to find its host in this type of forests. For some mixing pattern, the global productivity of the stand can also increase.

However, interactions between species are complex and should also be studied at a local scale. For this reason, we are planting nine mixed forest stands in the Haut-Languedoc territority, in areas belonging to volunteer forest owners. In these trials, we will also plant some control forest stands with just one species, to compare the growth and productivity between monospecific and mixed forest stands.

Just like for arboretums, the Occitania CRPF will monitor the growth and mortality to study the dynamics and the productivity of each stand.

Planting a mixed forest stand in Cassagnoles (Constance Proutière - Pnr HL)

Planting a mixed forest stand in Cassagnoles (Constance Proutière - Pnr HL)


Silviculture for existing forest stands

The last part of these actions is about adapting existing forest stands to climate change. We will test some new management procedures in ten forest stands that varies in age and species compositions.

Our objectives are to:

  • Decrease the water consumption of these stands to reduce their sensitivity to acute climate events
  • Mitigate climate risks by favouring healthy or resilient individuals, diversifying the stand structure or introducing complementary species
  • Favour the natural regeneration and the gene flow to benefit from the possible genetic adaptations of the species
  • Preserve the natural habitat and the biodiversity

Saving water (young forest stands)

To decrease the water consumption in young forest stands, we will observe the effect of a thinning (with or without pruning) stronger than the usual one in the Haut-Languedoc territory. We will test this on species such as firs, cedars or larches. Reducing the number of trees per hectare reduces the water consumption of the forest for the same surface. These tests will also include the comparison between a thinning and a trimming around crop trees (crop tree management).

Mitigating risks and favouring the natural regeneration (mature forest stands)

When the forest stands are older, it is risky to perform a strong thinning that could be detrimental to existing trees. In this case, we will gradually transform them into uneven-aged stands instead, by favouring the natural regeneration with gap-harvesting or by planting enrichment species. In species such as the douglas fir, the silver fir or the chestnut tree, thinning according to the health status of trees will enable a natural regeneration based on healthy or resilient seed bearing trees.

Preserving natural habitats

In order to help the conservation and regeneration of the "Atlantic acidophilous beech forests with Ilex and sometimes also Taxus in the shrublayer" habitat (HIC 9120), we selected three sites to test some interventions. To make these habitats durable (through the balance between the vegetation layers), we will do some thinning with the aim of improving the health status of the beech or its natural regeneration (gaps and sometimes a removal of some of the holly if it is too dense and prevents the regeneration from happening).


Monitoring trials

Given how slowly trees grow, we will not know the results of our trials right away. Therefore, we had to set up a long-term monitoring of our trial stands, so that we could follow the impact of our tests on stands vitality, fire risk, carbone sequestration and biodiversity.

Stands vitality

We will follow the vitality of each trial stand, which means following, depending on the test:

  • the growth and survival of plants;
  • the success of the natural regeneration ;
  • the health status of trees.

Thanks to the agreement we signed with forest owners, this monitoring will be done by the Occitania CRPF, at first every year and then every five years.

Fire risk

In some of our trials, the conversion towards uneven-aged stands will change the stratification of the forest, which could potentially increase the risk for fire propagation. Conversely, we will plant both broad-leaved and conifer trees in our mixed forest stands, which could decrease the fire risk compared to the one in monospecific conifer stands. For these reasons, in each of our trial stands, we will monitor the fire risks in the long-term to follow how our tests impact on this issue.

Carbon sequestration

We will also evaluate if our tests modify the quantity of carbon sequestrated by forest stands. We plan to use the CNPF Climafor tool, which allows an estimation of the evolution of the quantity of carbon sequestrated over time from the data gathered for the stands vitality monitoring.

Biodiversity

Finally, we will monitor the impact of our tests on biodiversity by following in the long run the presence, abundance and diversity of several groups of organisms:

Monitoring birds with the LPO H2rault in a HIC 9120 forest stand (Juliane Casquet - Pnr HL)

Monitoring birds with the LPO Hérault in a HIC 9120 forest stand (Juliane Casquet - Pnr HL)

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