Scientists consider it key to understand why droughts kill so many trees and the influence of local forest histories on tree mortality. They also warn that we know very little about the joined effects of different disturbances on each ecosystem, and highlight the necessity to plan research projects covering more time and space.
A multidisciplinary team of 28 researchers (of which 15 were from CREAF) has evaluated scientific progress of the last 16 years in the study of global change in terrestrial Mediterranean ecosystems, and has identified which should be immediate research priorities to make our ecosystems more resistant to the negative effects of this phenomenon.
In the article published in the journal Global Ecology and Biogeography, the authors arrive to the conclusion that science is faced with thirteen challenges and three fundamental considerations which need to be taken into account.
First, they assert that it is no longer sufficient to study different modifications which we provoke in ecosystems (climate change, changes in forest fire regimes, biodiversity loss, etc.) as if there were closed boxes. It is instead necessary invest effort in "understanding how each of these boxes interacts with other boxes," says Enrique Doblas, CREAF researcher. He poses an example: "drought can provoke soil erosion, but the erosion which we are finding cannot be explained if we don't add to this drought all the changes in land use of the last 50 or 60 years."
Second, data gathered on a small scale often generate too much error when we try to use them to predict the effects of global change on a large scale. To deal with this problem, the authors of the article propose improving data exchange networks between researchers, and planning of long-term experiments at the regional or even global scale.
Thirdly, the article insists on the importance of local history of the ecosystem on how it is capable of responding to global change, and especially the ever-increasing effect of droughts. "In the same was that you don't recover from an infection the same way the first or second time that you have it, two ecosystems can seem identical but really not be so in any way due to their personal histories," says Doblas.
The following table shows the list of the 13 scientific challenges organized into umbrella categories of five predominant questions:
1 Understand how the typical mosaic form of the Mediterranean landscape affects forest fire propagation
2 Understand the combined effects of different phenomena comprising global change on biological invasions and the expansion of plagues
3 Understand the interaction between the phenomena comprising global change and most recent forest management practices
4 Obtain more realistic information (at larger spatial and temporal scales) of the impacts of global change on services provided by the ecosystem
5 Improve the assessment of tree mortality associated with climate extremes, with particular interest on drought phenomena.
6 Identify and manage the areas most vulnerable to global change
7 Use ecosystem functioning and history to study its capacity to return to an initial state following a perturbation (resilience)
8 Open research to other fields to study the importance that genetics could have on this resilience capacity
9 Study how forest management can improve ecosystems' capacities to store carbon and water in the long term and large scale
10 Analyse how biodiversity changes when the landscape changes
11 Increase the precision of models of prediction of global change by including the influence of socio-economic context
12 Carry out manipulative and interdisciplinary experiments at different scales to understand the interaction between forests and the atmosphere
13 Improve understanding of how water availability at the landscape scale affects plants' hydraulic systems
13 new challenges which substitute 25 challenges proposed by Sandra Lavorel in 1998
In order to identify these 13 challenges the researchers did not begin from zero; instead, they analysed the degree of satisfaction of challenges posed 16 years ago in a similar article, published in the same journal by the scientist Sandra Lavorel. Of the 25 challenges posed in 1998, nine have been successfully achieved, and only two remain unanswered. The remaining 14 (the majority) have only been answered in part (see following table):
1 Predict wildfires based on soil use: Partial
2 Predict wildfires based on climate: Yes
3 Predict wildfires based on the influence of atmospheric composition: No
4 Measure impacts of wildfires on the landscape: Yes
5 Measure impacts of wildfires on vegetation: Partial
6 Measure impacts of wildfires in the context of climate chnage: Yes
7 Measure the impacts of wildfires on ecosystem function: Partial
8 Control wildfires using prevention: Yes
9 Control the effects of wildfires using restoration: Partial
10 Understand how soil use interacts with climate: Partial
11 Understand how physiology of living beings interacts with atmospheric CO2 and the planet's temperature: Partial
12 Understand the interaction between gasses emitted by living beings and the planet's temperature: Partial
13 Understand the interaction between gases emitted by wildfires and the atmosphere: Yes
14 Create models which work with all of the above data: Partial
15 At the small parcel or patch scale, understand how physiology such as leaf surface affects water circulation in plants: Yes
16 At the small parcel or patch scale, understand the hydrologic equilibrium: Partial
17 At the small parcel or patch scale, study how the quantity and quality of water changes with time: Partial
18 At the small parcel or patch scale, create simulation models which work with the above data: No
19 At the landscape scale, make water availability maps: Yes
20 At the landscape scale, check to see if patterns and effects are similar to the small scale: Yes
21 At the landscape scale, study the effects of landscape change on water availability: Yes
22 At the landscape scale, create simulation models which work with the above data: Partial
23 Understand changes in genetic diversity: Partial
24 Understand changes in species diversity: Partial
25 Understand changes in landscape diversity: Partial
The authors wrote the article in the context of the project MONTES-Consolider (CSD2008-00040), financed by the Spanish Ministry of Economy and Competitively. Participating writers were from CREAF, the Autonomous University of Barcelona, the University of Granada, the Centre Tecnològic i Forestal de Catalunya (CTFC), the Museum of Natural Sciences of the Spanish Council for Scientific Research (CSIC), The University of Castilla-La Mancha, the Center for Mediterranean Environmental Studies (CEAM), the University Rey Juan Carlos I, the University of Macquarie (Australia), the Institut de Diagnosi Ambiental i Estudis de l'Aigua (CSIC), and the University Carlos III de Madrid.
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