Acacia invasion is facilitated by landscape permeability: The role of habitat degradation and road networks

Abstract

Context: The sandy-savanna ecosystem "Mussununga", a natural ecosystem that occurs as patches throughout the Atlantic Forest domain, is threatened by anthropogenic factors and biological invasions of Australian Acacia species. Habitat degradation in the Atlantic Forest domain and extensive road networks could facilitate Acacia invasion into Mussununga. Objectives: We investigated whether: (a) landscape permeability (measured by effective conductance) facilitates Acacia invasion; (b) forest fragments are barriers, and roads and highways are corridors for invasive spread of Acacia; and (c) size and shape of Mussununga patches play a role in biological invasion. Methods: Acacia invasion was investigated in 32 Mussununga sites within the Atlantic Forest domain. We tested the effect of a set of landscape permeability scenarios based on circuit analysis and nine other metrics of landscape structure on Acacia occurrence using three buffer-zone sizes (0.5, 1, and 2 km). Results: The likelihood of Acacia invasion significantly increased with landscape permeability. The best-fitting landscape permeability scenario designated road networks as corridors, intact forests and water surfaces as barriers, and degraded habitats as non-barriers. We also found that Mussununga areas within a 0.5 km buffer negatively affected the biological invasion by Acacia. Conclusions: Extensive habitat degradation by deforestation and dense road networks facilitate Acacia invasion into sandy-savanna Mussununga ecosystems. Landscape permeability may be used as a risk-assessment tool for biological invasion by Acacia species. Mussununga patches can be protected from Acacia invasion | 599 Applied Vegetation Science HERINGER Et al.

Functional Changes and Threats to Hyperseasonal Neotropical Savannas After Australian Acacia Invasion

“…C3 plants Among C3 plants, there were no differences between non-invaded (Marcetia centered plots) and invaded (Acacia centered plots) Mussunungas. The explained d 13 C increases as d 15 N increases and as leaf C% decreases, with d 15 N explaining more than 60% of the global model (Figure 1 A, B and C and 2 A, B and C). Among C3 monocots the d 15 N is high, especially in Actinocephalus ramosus and Lagenocarpus rigidus, the same monocots that predominate near termite mounds (Tables 2-4 and S1-S3, see Figure S2).…”

“…The monocots Lagenocarpus rigidus and Actinocephalus ramosus as well as Blechnum serrulatum, a pteridophyte species, are 15 N-enriched with low N-nutritional status and with high d 13 C (Tables 2-4 and S1-S3, see Figure S2). Syngonanthus nitens and Panicum trinii are also C3 monocots that have high d 15 N, high d 13 C and low C/N (Tables 2-4 and S1-S3).…”

“…Generalized Linear Models (GLMs ) were used to explain the variation of leaf elements concentrations, such as C/N, δ 13 C, δ 15 N and δ 18 O and the relationship between these variables. The most suitable data distribution based on family error and link function was evaluated for all GLM tested using the lme4 package with the 'lmer' function (Bates et al 2014) using the multi-model inference approach with the dredge function of the MuMIn package (Bartón 2018) all possible xed variables included in the models were tested.…”

“…For C3 plants, the Acacia invasion did not induce changes in the Mussununga functioning. In noninvaded and invaded plots, the d 13 C increases as d 15 There is a difference between C3 and C4, especially in invaded plots. In C3 plants, the higher d 13 C, the higher d 15 N and the lower Leaf C%.…”

“…In noninvaded and invaded plots, the d 13 C increases as d 15 There is a difference between C3 and C4, especially in invaded plots. In C3 plants, the higher d 13 C, the higher d 15 N and the lower Leaf C%. Also, the greater the need of C3 plants in N, the greater will be the d 15 N. Therefore, on the one hand the C3 plants that have low N-nutritional status depend on 15 N-enriched sources of N to succeed in sites with strong N-limitation because of high WUE and high d 13 C, especially small monocots like Lagenocarpus rigidus and Actinocephalus ramosus.…”