Species Composition and Changes in Land Use

Changes in land use are currently the main factor in terrestrial biodiversity transformation and loss¹. These changes impact the composition and diversity of ecosystems as well as their ecological processes and services. Identifying changes in species composition over gradients of natural and anthropic land covers allows for measuring the current transformation impact on natural ecosystems and making forecasts for certain socioeconomic and climate change scenarios. Such predictions are decisive in a country such as Colombia, which is the second most diverse in the world in its ecosystems but it is also highly vulnerable^2,3

Within the case studies evaluated by the PREDICTS3 initiative, which aims to measure and predict the impact of changes in land use on biodiversity, Colombia resulted to be a priority case. Based on the four climate change scenarios (Representative Concentration Pathways) proposed by the Intergovernmental Panel on Climate Change (IPCC), models were made for the trends of biodiversity in the face of climate change for the years from 1500 to 2100 according to the availability of historic information⁴. Using secondary data and variables associated to the four scenarios, the list of species in areas with varying amount of human intervention (late and new secondary vegetation vegetation, crops, grasslands, and urban areas) was compared to the list of species in primary native vegetation³ . Then, these differences in diversity between habitats were linked to projections in changes of land use under the four scenarios of climate change⁵ in order to forecast changes in biodiversity under distinct socio-economic scenarios.

It was therefore evidenced that primary vegetation has been replaced by homogeneous vegetation covers such as crops and grasslands. This transition has caused a 18 % change in species composition over the whole country (due to decreasing species numbers or replacement by invasive species, particularly in areas where anthropic presence is more extensive, such as the Andean region.

Between different forms of land use, the presence of crops and grasslands has a greater impact on biodiversity. In other words, crops and grasslands hold the smallest proportion of species in comparison to areas without transformation. The decrease in diversity caused by grasslands is resulting in a “biotic homogenization”⁶ process due to the large expansion of these areas. Such biotic process is characterized by dominating generalist species and homogeneous areas that put the diversity of ecosystem functions at risk.

Given the similarity of existing habitats, species composition does not vary much between primary and late secondary vegetation. This suggests that there is a dependant relation between spatial distribution of the landscape and the natural regeneration of the forest, which in turn would ensure the availability and conservation of ecosystem services that could lessen impacts caused by human disturbances. Those patches closest to primary forests would have a bigger regeneration capacity caused by the presence of species and proximity in terms of dispersal. In relation to climate change scenarios, the scenario “without socio-economic changes” presents the greatest local reduction in species complexity and thus causes the largest impact on biodiversity. Under this scenario, species composition would reduce on an average of 79 % to 2090, chiefly owed to the expansion of agricultural and cattle raising areas that respond to an increasing population demand.

Taking into account the rate of change in land use in Colombia, and specially considering those areas that are vulnerable, databases of samples that follow protocols and are comparable^7,8,9 must be generated and combined in order to understand patterns of change in biodiversity at different spatial and temporal scales. Similarly, information gaps in models must be strengthened by field research, notably in areas of low rates of scientific publications such as the Amazon, Orinoquía, and Chocó.