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Mediterranean basin supports characteristic Mediterranean forests, woodlands, and scrub vegetation, highly adapted to the mild, rainy winters and hot, dry summers that characterize the Mediterranean climate. Never less the Mediterranean region has been identified as one of the hot spots of climate change. This study aims to understand what are the conditions of coexistence, thus biodiversity, of Mediterranean tree species in humid areas under future scenarios of altered hydrological regimes. The core of the work is a quantitative, dynamic model exploring the coexistence of different mediterranean tree species, typical of the arid or semi-arid wetland where ecological overlaps exist between mesic communities and those dominated by wetland specialists. The original idea of the paper is to address this topic from a deterministic approach using a dynamical model which is validated by existing data on species abundance. The dynamic of the population is broadly-defined according to the distinct adaptive strategies of trees for water stress of summer drought and winter flooding while climate change are explored as external forcing by means of a bifurcation analysis and compared with the major regional climate scenarios. I argue that at intermediate levels of water supply, which do not benefit either of the two species, the dual role of water (resource and stress) results in the coexistence of two kind of species, namely Hygrophilous and Non-hygrophilous. In order to support the validity of the ideas contained in the present study I applied the model to a Mediterranean coastal forested wetlands of Central Italy located into Castelporziano Estate and Circeo National Park. The results obtained show that there are distinct rainfall thresholds on the ability of Mediterranean wetlands to maintain species coexistence and hence to sustain biodiversity, calling for an urgent adaptation and mitigation response to prevent human pressure on water resources in proximity of wetland forested areas. Come è noto, il bacino del mediterraneo ospita una vegetazione fortemente adattata alle particolari condizioni climatiche che ne caratterizzano l’area. Inoltre la regione mediterranea è ricca di zone umide naturali ad elevata valenza ecologica. L’equilibrio di questi complessi sistemi naturali corre il rischio di essere alterato a causa dei cambiamenti climatici globali che, secondo i maggiori scenari climatici, mostrano un hot spot proprio nella regione mediterranea. Alla luce di questi fatti, la presente tesi mira ad individuare le condizioni climatiche per le quali la coesistenza, intesa quale sinonimo di biodiversità, di diverse specie arboree delle zone umide del mediterraneo è preservata. A tal fine è stato sviluppato un modello dinamico di competizione idrica per descrivere la coesistenza di due distinti gruppi di specie arboree (i.e. specie denominate igrofile e non-igrofile) che mostrano diverse strategie adattative allo stress idrico che caratterizza le zone umide del mediterraneo: drought estivo e flooding invernale. Al fine di verificarne la validità, il modello è stato validato sulle foreste umide planinziali della costa tirrenica integrando le informazioni rinvenute per i siti del Parco Nazionale del Circeo e della Tenuta Presidenziale di Castelporziano. I risultati ottenuti mostrano che per un regime idrico intermedio, rappresentato da quello attuale, in cui nessuna delle due specie è avvantaggiata, il duplice ruolo dell’acqua, risorsa-stress, garantisce la coesistenza delle due specie. Tuttavia, il trend con cui la precipitazione sta diminuendo è destinato a destabilizzare tale l’equilibrio nell’arco di qualche decennio, spostando il regime di vegetazione attuale da uno stato di coesistenza ad uno dominato dalle sole specie sclerofille. In generale, il modello è in grado di descrivere la dinamica delle popolazioni delle zone umide delle regioni aride o semi-aride in cui è facile rilevare sovrapposizioni ecologiche tra popolazioni relativamente più xeriche e quelle tipicamente più igrofile. Dottorato di ricerca in Ecologia forestale

This is the pre-print version of the chapter"Climate change sustainable agriculture and food systems_The world after the Paris agreement"published as final paper inAchieving the Sustainable Development Goals Through Sustainable Food Systems,10 October 2019, Pages 1-262https://doi.org/10.1007/978-3-030-23969-5 lntroduction 1.1 Climate Change and Agriculture According to the fifth assessment report of the IPCC (2014), the concentrations of greenhouse gases (GHG) in the atmosphere are at the highest they have been in the past 800 thousand years. Current levels of CO2 have increased by 30% from 280 ppm in pre-industrial times to 407 ppm today (2019), and they continue to rise. Present CH4 concentrations of 2000 ppb are nearly triple their pre-industrial value of 700 ppm. N2O levels reached 328 ppb in 2019 compared with the 280 ppb of pre-industrial time. Only in the past 50 years we have doubled human population (from 4 to 7 billion), increased GHG emissions by 2.5 times, doubled freshwater withdrawal, halved the agricultural land per capita (from 1. 4 to 0.7 ha) by agricul­ture intensification. This is an unprecedented velocity of transformation that our Planet and human society had never experienced. Today, the agro-food sector alone accounts for some 80% of the world freshwa­ter use, 30% of world energy demand, and more than 12% of man-made greenhouse gas emissions worldwide, including indirect emissions such as those of deforesta­tion (Foley et al. 2011). Moreover, according to the Food and Agriculture Organization (FAO) of the United Nations, croplands and pastures occupy about 38% of Earth's terrestrial surface, the largest use of land on the planet (Foley et al. 2011). With global food production expected to increase 70% by 2050, and consid­ering the meat dietary changes, the sector is facing unprecedented resource pres­sures and strong perturbations to the climate systems. By 2050 more than nine billion of people will be in search of food and most of them (68%) will be living in mega-cities (UN DESA 2018). Under these circumstances, a substantial redefinition of the actual food supply chain is essential. Meanwhile, many rural-communities, which strongly depends on domestic-subsistence agriculture, will be exposed to food scarcity and accessibility. lndeed, in some regions of the world (i.e. tropics and part of temperate regions) increasing of climate extremes will produce adverse effects on agriculture, forestry and fisheries sectors with yield reduction of 35% in African countries and 2% globally per decade, despite the increasing food demand (Barros et al. 2014). It is time to reflect on the global agro-food systems, its para­ doxes, inequalities and capacities to support future generations. On the other side global warming can also expand the land suitability for some crops, like wheat at high latitudes (Di Paola et al. 2018). Humanity needs to act urgently and fast, push­ ing the high-level governmental agenda (SDGs, Climate Paris agreement) as well as industry sector and citizens in the most difficult and challenging transformation of our society to feed the new two billion of people expected by 2050 and, at same time, stabilize climate below 2.0° (possibly 1.5°) and reducing the pressures on natural resources. 1.2The Paris Agreement: Implications for the Agriculture Sector The significant role that agriculture can play in climate change was relatively under­ represented in the previous discussions and decisions under the frame of the United Nations Framework Convention on Climate Change (UNFCCC), before the Paris Agreement (PA) was adopted by the 21st Conference of the Parties (COP21) of the UNFCCC on the 12th of December 2015. Food security and food production are explicitly mentioned in the PA: in its pre­ amble the Parties recognize "the fundamental priority of safeguarding food security and ending hunger, and the particular vulnerabilities of food production systems to the adverse impacts of climate change", and the Artide 2 highlights the importance of "increasing the ability to adapt to the adverse impacts of climate change and foster climate resilience and low greenhouse gas emissions development, in a man­ ner that does not threaten food production". Moreover, the role of agriculture in the PA is also linked to the capacity to be a possible sink and reservoir of GHG in soils and vegetation biomass: in the Artide 5 Parties are invited to "take action to con­ serve and enhance, as appropriate, sinks and reservoirs of greenhouse gases". This opened to agriculture as a key sector, not only impacted by climate change but also with a great potential for mitigation. In fact, more in generai, the PA has the ambition to keep "the increase in the global average temperature to well below 2 °C above pre-industrial levels and to pursue efforts to limit the temperature increase to 1.5 °C above pre-industrial levels, recognizing that this would significantly reduce the risks and impacts of climate change". In order to achieve this long-term temperature goal, parties are therefore committed to achieve a balance between anthropogenic emissions by sources and removals by sinks in the second half of this century. Different options are feasible and the agriculture sector can play an active role, in particular by contributing to the net emissions reduction, while guaranteeing food security. Besides, under the UNFCCC processa specific programme on agriculture was launched (the "Koronivia Joint Work on Agriculture", see Box below) that provides space and opportunities for Parties to fully engage on climate related discussions in the agriculture sector in order to foster actions related to adaptation and mitigation taking into consideration the sectors vulnerabilities. In pathways limiting global warrning to 1.5 °C with limited or no overshoot, Agriculture, Forestry and Other Land-Use (AFOLU) related carbon dioxide removal measures are projected to remove 0-5, 1-11, and 1-5 GtCO2 year- 1 in 2030, 2050, and 2100 respectively (IPCC 2018). Due to this key potential role plaid by the agri­ culture, the 80% of the Nationally Determined Contributions (NDCs) submitted by countries committed to actions on agricultural mitigation, and 90% ofNDCs selected agriculture as a priority sector for action on adaptation (CCAFS 2016; FAO 2016). Despite the inclusion of agriculture and the land sector in general in most NDC, this is still not enough to achieve the 2 °C goal and additional reduction targets are needed (Fujimori et al. 2016). According to the Fujimori et al. (2016) modelling exercise, large-scale negative CO2 emissions and land-based CO2 emissions­ reduction measures are required and the bioenergy crops need to be an important component in addition to agriculture, with an area of cropland used for bioenergy to be 24-36% of the total cropland. Indeed, the deployment of such a large-scale land­ related measures, like afforestation and bioenergy supply, can compete with food production raising not only food security concerns (IPCC 2018) but also increasing the environmental footprint, due to the increased use of natural resource (e.g. water and nitrogen for bioenergy crops) and environmental impacts (e.g. loss of biodiver­sity and increasing pollution from fertilizers). Furthermore, climate-related risks on food security are projected to increase under global warming, with projected net reductions in maize, rice, wheat and, potentially, other cereal yields in many regions of the world (IPCC 2018). Studies based on multi-model inter-comparisons (Schleussner et al. 2016) fore­ see a general crop yield reduction, particularly in tropics, for maize and wheat under increasing temperature scenarios, with more significant reductions projected at 2 °C than 1.5 °C. On the other side, local rice and soy yields are projected to increase in the tropics, as the positive effect of CO2 fertilization counterbalances the detrimen­tal impacts of climate change in the model projections (Schleussner et al. 2016). However, additional gains for warming above 1.5 °C resulted not significant, and yield reductions are expected for all the four widespread global crops. In the light of these evidences, trade-offs between mitigation and adaptation, as well as economie and environmental benefits, need to be addressed when balancing the need of land for bioenergy crops, reforestation or afforestation, versus the land needed for agricultural adaptation under a changing climate, not undermining food security, livelihoods, ecosystem functions and services and other aspects of sustain­able development.