bioRxiv2024
1As the effects of climate change are becoming more evident, different countries around the world are adopting new policies to intervene on the regulation of greenhouse gasses emission. Recent frameworks acknowledge the potential contribution that forest ecosystems can give to carbon sequestration. These are indicating reforestation programmes as effective climate change mitigation options. Yet, there are possibilities that reforestation may have counteractive effects on biodiversity. However the long term consequences of reforestation for biodiversity are poorly understood. Reforestation policies have already been widely implemented around the world. For instance, in northern Italy and central Europe plantations of spruce trees (Picea abies) have been highly promoted during the last century. The objective of our research is to address the long term consequences of reforestation by answering the following questions. What is the spruce plantations impact on plant diversity? Does the spruce plantation impact environmental factors like luminosity and ground surface temperature and do these environmental factors affect plant diversity? We hypothesize that the spruce plantation causes a reduction of plant diversity. Indeed, we expect that the spruce plantation affects different environmental factors that have an important role in determining plant composition and abundance. To answer our research questions, we have conducted a study in two different sites of the Como Prealps. The potential vegetation of the selected area is represented by mixed forests of deciduous trees dominated by beech trees (Fagus sylvatica). Historically, the land has also been used for grazing and mowing. However, some stands of the potential vegetation are here replaced by spruce plantations, the presence of which is linked to national forestry policies of the twentieth century. For our research we have conducted a total of 100 vegetation surveys to collect data on plant diversity and environmental factors, namely luminosity and ground surface temperature. We then compared plant diversity among land-use treatments (i.e., habitat types): the spruce plantation, the natural mixed forest and the semi-natural grassland-pasture. For our analysis we have used linear regression models to test the impact of the different habitat types on plant diversity. We have also measured covariance and correlation to analyse the relationship between the environmental factors and plant diversity. The analysis on plant diversity reveals the long-lasting impact of spruce monoculture plantation on plant diversity. The number of plant species decreases by 57percent from the grassland-pasture to the spruce plantation and by 41percent compared to the natural mixed forest. Likewise, the diversity of plant functional forms decreases in the spruce plantation as compared to mixed forests and grassland-pasture. At last, although luminosity and ground surface temperature do not vary from the mixed forest to the spruce plantation, we have measured a positive relationship between the number of plant species and the two environmental parameters. Our research provides novel evidence that the spruce plantation negatively impacts plant diversity still one hundred years after. As biodiversity loss and climate change are two interwoven processes, they must not be treated separately. For what concerns future reforestation programmes, we recommend that they include biodiversity-friendly measures and address win-win solutions, for their effectiveness in climate change mitigation would otherwise be compromised.