Vulnerabilities forests

Climate change can harm many species by disrupting existing interactions or by favouring new ones. Climatic warming will, for instance, intensify the interaction between the pine processionary caterpillar, a Mediterranean pest that causes severe defoliation, and the relict Andalusian Scots pine. The homogeneous structure of the afforested pine woodlands favours the outbreak capacity of the newcomer, promoting this new interaction between a Mediterranean caterpillar pest and a boreal tree at its southern distribution limit (1).

Plagues and diseases can play a fundamental role in the fragmentation of forest areal. There is an increased risk that much of the forest ecosystems during the second half of this century turn into a net loss of carbon. Most vulnerable forests are high parts of mountains (2).

The decrease in water reserves in soils will be a major stress factor that will result in a trend towards decreasing forest density, and in extreme cases, towards its substitution by shrubs (3). Severe droughts in the 1990s and 2000s may have caused forest decline of pine plantations in southeastern Spain; future persistence of Scots pine stands is unlikely under the predicted warmer and drier conditions (15).

Among all European regions, the Mediterranean appears most vulnerable to global change. Multiple potential impacts are related primarily to increased temperatures and reduced precipitation. The impacts included water shortages, increased risk of forest fires, northward shifts in the distribution of typical tree species, and losses of agricultural potential. Mountain regions also seemed vulnerable because of a rise in the elevation of snow cover and altered river runoff regimes (4).

In the Iberian Peninsula, forests in eastern Spain and central Portugal in particular are very vulnerable to droughts (27). 

Vulnerabilities - Overview

The increased vulnerability of forests (and people) with respect to climate change refers to several impacts (7,13):

• Forest cover: conversion of forests to non-woody energy plantations; accelerated deforestation and forest degradation; increased use of wood for domestic energy.
• Biodiversity: alteration of plant and animal distributions; loss of biodiversity; habitat invasions by non-native species; alteration of pollination systems; changes in plant dispersal and regeneration.
• Productivity: changes in forest growth and ecosystem biomass; changes in species/site relations; changes in ecosystem nitrogen dynamics.
• Health: increased mortality due to climate stresses; decreased health and vitality of forest ecosystems due to the cumulative impacts of multiple stressors; deteriorating health of forest-dependent peoples.
• Soils and water: changes in the seasonality and intensity of precipitation, altering the flow regimes of streams; changes in the salinity of coastal forest ecosystems; increased probability of severe droughts; increased terrain instability and soil erosion due to increased precipitation and melting of permafrost; more/earlier snow melt resulting in changes in the timing of peak flow and volume in streams. The capacity of the forest ecosystem to purify water is an important service, obviating the cost of expensive filtration plants.
• Carbon cycles: alteration of forest sinks and increased CO2 emissions from forested ecosystems due to changes in forest growth and productivity.
• Tangible benefits of forests for people: changes in tree cover; changes in socio-economic resilience; changes in availability of specific forest products (timber, non-timber wood products and fuel wood, wild foods, medicines, and other non-wood forest products).
• Intangible services provided by forests: changes in the incidence of conflicts between humans and wildlife; changes in the livelihoods of forest-dependent peoples (also a tangible benefit); changes in socio-economic resilience; changes in the cultural, religious and spiritual values associated with particular forests.

Productivity

Increasing CO2 concentration can affect tree growth through increased photosynthetic rates and through improved water-use efficiency. There will be complex interactions, however: forest growth rates may well be increased in some cases by rising levels of atmospheric CO2, but rising temperatures, higher evaporation rates and lower rainfall may lower growth rates in other cases (5).

Non-timber products

Increasingly there are concerns about the productivity of non-timber products such as medicines and foods. Relatively little information is available in the scientific literature about the sustainable management of such products, and even less is known about their vulnerability to climate change (7).

Vulnerabilities peatlands

Europe’s southernmost blanket bogs, peatlands where a continuous mantle of peat covers entire landscapes, occur in in the Cantabrian Mountains of northern Spain (21). Known Spanish peatlands represent only 0.07% of the total land surface of the country (22). Peatlands in northern Spain suffer from a range of anthropogenic pressures, including livestock (23), vegetation burning (24), commercial peat extraction (25) and wind farm infrastructure (26).

Vulnerabilities – Subtropical dry forests in Europe

Subtropical dry forests occur in parts of Europe with at least eight months of over 10°C: parts of Spain, Italy, Greece, and Turkey. These regions have hot dry summers and humid mild winters, with annual rainfall in the 400–900 mm range (5).

Subtropical species are partly already well adapted to warm and dry climates. However, many subtropical species now exist in highly fragmented environments as islands of natural forest amongst oceans of agricultural land. Species at a particular location may not have access to new sites where they would be better adapted to the new climatic conditions. Less tolerant species may then decrease in abundance and hereby create for other, more tolerant resident species opportunities to become more abundant because of reduced competition (5).

Benefits

Globally, based on both satellite and ground-based data, climatic changes seemed to have a generally positive impact on forest productivity since the middle of the 20th century, when water was not limiting (14).

Timber production in Europe

Climate change will probably increase timber production and reduce prices for wood products in Europe. For 2000–2050 a change of timber production in Europe is expected of -4 to +5%. For 2050–2100 an increase is expected of +2 to +13% (6).

Mushroom productivity in Mediterranean forests

Wild edible mushrooms represent an important food source and may be regarded as a key non-wood forest product in the Mediterranean region. The economic value of mushroom-based ecosystem services of forests can be much higher than the economic profit traditionally obtained from timber-oriented forestry (17). Forest fungi also play a critical role in forest ecosystem functioning through their contribution to nutrient and carbon cycles (18). The provision of these ecosystem services may be affected by climate change, especially as a result of changes in precipitation and soil moisture. Previous research has raised concerns about the potentially negative effect of climate change on future mushroom productivity, with strong implications on the provision of mushroom-based ecosystem services related to the socioeconomic activities surrounding mushroom picking and trade. Mushroom productivity in Mediterranean ecosystems might experience a sharp drought-induced decrease. Future hotter and drier conditions for the Mediterranean region would reduce soil water availability and negatively affect mushroom productivity (19).

For the northeast of Spain these changes were studied based on the combination of long-term monitoring of (edible and marketed) mushrooms on forest plots and climate projections towards 2100. For the latter, both a moderate (RCP 4.5) and a high-end scenario (RCP 8.5) of climate change was used, and two regional climate models. Unexpectedly, the results of this study revealed a positive effect of climate change on long-term mushroom productivity for the period 2016 - 2100. Projected mushroom yield increased under both climate change scenarios. Apparently, autumn precipitation and soil moisture are expected to remain more or less stable (or even increase slightly) during the fruiting season along the 2016 - 2100 period while the fruiting season lasts longer. Temperatures are expected to increase in the end of the season (November-December), when precipitation and water availability in the soil are sufficient for mushroom fruiting. In the current climate, low temperatures limit mushroom production in these months (20). 

Adaptation strategies - Forest management measures in general

Measures such as the establishment of migration corridors, connecting nature reserves, may assist the predicted poleward migration of tree species. Also, forest management should focus on reducing stress from external sources, such as extreme events and disturbances. Some additional management options reported for promoting adaptation are: high-quality genetic selection or selection of trees from specific varieties/origins; promotion of mixed-species forests; decrease of the area of monocultures; reducing the threats of pests and diseases; afforestation; fire prevention (11).

Adaptive management

The terms adaptation and adaptive management are often incorrectly used interchangeably. The former involves making adjustments in response to or in anticipation of climate change whereas the latter describes a management system that may be considered, in itself, to be an adaptation tactic (8). Adaptive management is a systematic process for continually improving management policies and practices by learning from the outcomes of operational programmes (9). It involves recognizing uncertainty and establishing methodologies to test hypotheses concerning those uncertainties; it uses management as a tool not only to change the system but to learn about the system (10).

Both the climate and forest ecosystems are constantly changing, and managers will need to adapt their strategies as the climate evolves over the long term. An option that might be appropriate today given expected changes over the next 20 years may no longer be appropriate in 20 years’ time. This will require a continuous programme of actions, monitoring and evaluation – the adaptive management approach described above (7).

There is a widespread assumption that the forest currently at a site is adapted to the current conditions, but this ignores the extent to which the climate has changed over the past 200–300 years, and the lag effects that occur in forests. As a result, replacement of a forest by one of the same composition may no longer be a suitable strategy (7).

Adaptation to climate change has started to be incorporated into all levels of governance, from forest management to international forest policy. Often these policies are not adopted solely in response to climate, and may occur in the absence of knowledge about longer-term climate change. They often serve more than one purpose, including food and fuel provision, shelter and minimizing erosion, as well as adapting to changing climatic conditions (11).

Socio-economic and political conditions have significant influences on vulnerability and adaptive capacity. Climate change projections are perceived by many forest managers as too uncertain to support long-term and potentially costly decisions that may be difficult to reverse. Similarly, uncertainty over future policy developments may also constrain action. Finance is a further barrier to implementing adaptation actions in the forest sector (12).

References

The references below are cited in full in a separate map 'References'. Please click here if you are looking for the full references for Spain.

1. Hodar and Zamorra (2004)
2. Government of Spain. Quinta Comunicación Nacional de España
3. Oficina Española de Cambio Climático (2008)
4. Schröter et al. (2005)
5. Fischlin (ed.) (2009)
6. Karjalainen et al. (2003); Nabuurs et al. (2002); Perez-Garcia et al. (2002); Sohngen et al. (2001), in: Osman-Elasha and Parrotta (2009)
7. Innes (ed.) (2009)
8. Ogden and Innes (2007), in: Innes (ed.) (2009)
9. BCMOF (2006a), in: Innes (ed.) (2009)
10. Holling (1978); Lee (1993, 2001), all in: Innes (ed.) (2009)
11. Roberts (ed.) (2009)
12. Keskitalo (2008), in: Roberts (ed.) (2009)
13. Kirilenko and Sedjo (2007)
14. Boisvenue et al. (2006)
15. Sánchez-Salguero et al. (2012)
16. Karavani et al. (2018)
17. Palahí et al. (2009); Martínez de Aragón et al. (2011), both in: Karavani et al. (2018)
18. Mohan et al. (2014); Stokland et al. (2012), both in: Karavani et al. (2018)
19. Ágreda et al. (2015); Büntgen et al. (2015), both in: Karavani et al. (2018)
20. Hernández-Rodríguez et al. (2015), in: Karavani et al. (2018)
21. Chico et al. (2020)
22. Tanneberger et al. (2017), in: Chico et al. (2020)
23. Chico et al. (2019b), in: Chico et al. (2020)
24. Heras (2002), in: Chico et al. (2020)
25. Guerrero (1987); Heras et al. (2017), both in: Chico et al. (2020)
26. Heras and Infante (2008); Chico et al. (2019a), both in: Chico et al. (2020)
27. Bento et al. (2023)