Linking land-use and land-cover transitions to their ecological impact in the Amazon

Abstract

Human activities pose a major threat to tropical forest biodiversity and ecosystem services. Although the impacts of deforestation are well studied, multiple land-use and land-cover transitions (LULCTs) occur in tropical landscapes, and we do not know how LULCTs differ in their rates or impacts on key ecosystem components. Here, we quantified the impacts of 18 LULCTs on three ecosystem components (biodiversity, carbon, and soil), based on 18 variables collected from 310 sites in the Brazilian Amazon. Across all LULCTs, biodiversity was the most affected ecosystem component, followed by carbon stocks, but the magnitude of change differed widely among LULCTs and individual variables. Forest clearance for pasture was the most prevalent and high-impact transition, but we also identified other LULCTs with high impact but lower prevalence (e.g., forest to agriculture). Our study demonstrates the importance of considering multiple ecosystem components and LULCTs to understand the consequences of human activities in tropical landscapes.

Keywords: biodiversity; carbon; deforestation; degradation; logging.

Fig. 1.

LULCT rates in the Brazilian Amazon. Mean annual LULCT rates were calculated and estimated (*) based on land-use change maps [2006 to 2019 (15)] and on forest degradation maps [2006 to 2014 (29)]. Primary forests have never been clear-cut, and secondary forests are regenerating forests. Young secondary forests are <20 y old and old secondary forests are ≥20 y old. Agriculture includes perennial and temporary crops. The width of the arrows is proportional to the mean annual rate of the transition.

Fig. 2.

Impacts of 18 LULCTs on (A) biodiversity, (B) carbon pools, and (C) soil properties in the Brazilian Amazon. Biodiversity is given as species richness, carbon pools are given as Mg⋅ha⁻¹ of carbon, the unit for Al (aluminum) is mmolc⋅dm⁻³, and N (nitrogen) is given in % soil mass. Arrows indicate the transitions and their effect, where gray indicates no effect, green is a significant increase, and blue is a significant decrease. The size of symbols represents averages based on 21 undisturbed primary forests (UF), 68 logged primary forests (LF), 65 logged-and-burned primary forests (LBF), 72 pastures (PA), 26 mechanized agriculture fields (MA), 33 young secondary forests (SFy, <20 y old), and 25 old secondary forests (SFo, ≥20 y old) distributed in two regions of the eastern Brazilian Amazon.

Fig. 3.

Standardized effect sizes of LULCTs on the ecosystem in the Brazilian Amazon. (A) Standardized effect sizes (ES) of 15 LULCTs (three of which are bidirectional and are shown only once: PA–MA, PA–SFy, and MA–SFy) on seven biodiversity groups, four carbon pools, and seven soil properties. (B) Boxplots of the absolute values of effect sizes (dots) for the impact of 15 LULCTs on biodiversity, carbon pools, and soil properties in the Brazilian Amazon. The numbers in B, Right are the median standardized effect sizes, converted to absolute values. The standardized effect sizes were derived from mixed-effects models analyzing the impact of LULCTs on individual variables within an ecosystem component. Note that in B the transitions are ordered from largest to smallest impact based on their median effect sizes and therefore differ among ecosystem components. The transitions MA–SFy, PA–SFy, and PA–MA are bidirectional.

Fig. 4.

Relationship between LULCT rates and their impacts on ecosystem components in the Brazilian Amazon. Within each ecosystem component (biodiversity, carbon, or soil), the dotted lines represent medians separating four classes of transitions: high impact, low rate (Top Left), high impact, high rate (Top Right), low impact, high rate (Bottom Right), and low impact, low rate (Bottom Left). Mean annual rates (km²⋅y⁻¹) are log-transformed, and the impacts are represented by the median standardized effect sizes (converted to absolute values) obtained from models assessing the effects of 18 LULCTs on seven biodiversity groups, four carbon pools, and seven soil properties.