Theme 5: Drought--Oral Sessions

Description

Marginal grasslands provide the basis for livestock rearing and rural livelihoods globally, but are subject to permanent degradation from mismanagement and climate change. Global biogeochemical models are so far not able to represent degradation tipping points in marginal grasslands because plant growth is dependent only on bio-climatic conditions and nutrient availability. Due to their central role for sustaining livelihoods, this lack of representation in such models needs to be addressed. We present an idea on processes and interactions to be considered and on the actual implementation of necessary changes. The model for which we exemplarily develop implementation strategies, LPJmL, accounts already for grassland dynamics globally in a fully coupled framework including soil dynamics and the hydrological cycle. Recent developments include the implementation of grassland harvesting schemes, the nitrogen cycle, fire management practices and representation of a variety of grass and legume species. Existing knowledge on the role of annual and perennial grass species for drought resistance will have to be utilized in order to advance model development. Different strategies for forming below-ground plant organs (roots and storage) have to be better understood from experimental studies before this can be implemented in models. Here, assumptions on functional relationships can be implemented and the resulting grass productivity can be analysed in comparison to field observations. Additionally, the formation of closed swards or tussocks plays a big role for the vulnerability to degradation by avoiding bare soil patches. This spatial phenomenon is usually neglected in models and can only be included by assumptions or in the form of aggregated effects. The long-term development of seed banks of key species determine the capability of regrowth after major drought periods so that seed bank formation and persistence is another component of necessary model development. All these components together with current developments of species competition and niche separation would build a framework that allows scenario assessments on tipping points depending on climatic conditions and management.

Share

COinS
 

Strategies for Assessing Grassland Degradation with Biogeochemical Models

Marginal grasslands provide the basis for livestock rearing and rural livelihoods globally, but are subject to permanent degradation from mismanagement and climate change. Global biogeochemical models are so far not able to represent degradation tipping points in marginal grasslands because plant growth is dependent only on bio-climatic conditions and nutrient availability. Due to their central role for sustaining livelihoods, this lack of representation in such models needs to be addressed. We present an idea on processes and interactions to be considered and on the actual implementation of necessary changes. The model for which we exemplarily develop implementation strategies, LPJmL, accounts already for grassland dynamics globally in a fully coupled framework including soil dynamics and the hydrological cycle. Recent developments include the implementation of grassland harvesting schemes, the nitrogen cycle, fire management practices and representation of a variety of grass and legume species. Existing knowledge on the role of annual and perennial grass species for drought resistance will have to be utilized in order to advance model development. Different strategies for forming below-ground plant organs (roots and storage) have to be better understood from experimental studies before this can be implemented in models. Here, assumptions on functional relationships can be implemented and the resulting grass productivity can be analysed in comparison to field observations. Additionally, the formation of closed swards or tussocks plays a big role for the vulnerability to degradation by avoiding bare soil patches. This spatial phenomenon is usually neglected in models and can only be included by assumptions or in the form of aggregated effects. The long-term development of seed banks of key species determine the capability of regrowth after major drought periods so that seed bank formation and persistence is another component of necessary model development. All these components together with current developments of species competition and niche separation would build a framework that allows scenario assessments on tipping points depending on climatic conditions and management.