A plea for scale, and why it matters for invasive species management, biodiversity and conservation

Abstract

Invasive species are suspected to be major contributors to biodiversity declines worldwide. Counterintuitively, however, invasive species effects are likely scale dependent and are hypothesized to be positively related to biodiversity at large spatial scales. Past studies investigating the effect of invasion on biodiversity have been mostly conducted at small scales (<100 m2) that cannot represent large dynamic landscapes by design. Therefore, replicated experimental evidence supporting a negative effect of invasive plants on biodiversity is lacking across many landscape types, including large grasslands. We collected data across eight large (333–809 ha) grassland landscapes managed with pyric herbivory—that is the recoupling of fire and grazing—to test how an invasive legume Lespedeza cuneata affected plant and bird communities at spatial grains ranging from 0.1 m2 to >3,000,000 m2. Lespedeza cuneata invasion effects on grassland plant diversity and composition changed with scale, being negative at small spatial grains (0.1 m2) and neutral or positive at large spatial grains (>3,000,000 m2). Lespedeza cuneata abundance did not significantly affect bird diversity at any spatial grain measured. Lespedeza cuneata may negatively affect biodiversity if abundances are greater than those observed in this study. However, previous research suggests that Lespedeza cuneata may not be capable of exceeding 20% canopy cover across large landscapes (>400 ha). Control and eradication strategies can be costly and are fraught with risk. If data do not clearly support a negative Lespedeza cuneata abundance–biodiversity relationship, and if invasion is spatially limited across large landscapes, ongoing control and eradication efforts may be unwarranted and ineffective. Synthesis and applications: Invasive species effects gleaned from small‐scale studies may not reliably predict their effects at larger scales. Although we recognize the importance of small‐scale studies in potentially isolating individual mechanisms, management strategies based solely on results from small‐scale studies of invasion are unlikely to increase or conserve biodiversity across large landscapes. Rather, processes that generate landscape heterogeneity—like pyric herbivory—are probably more important for promoting biodiversity across all scales. Scale is a central problem in ecology, and defining scale in management objectives is essential for effective biodiversity conservation.

A nature-positive future with biological invasions: theory, decision support and research needs

“…While we identify the landscape scale as the focal unit for understanding and management, and communities and metacommunities as the concomitant level of organization, scale considerations remain central to both research and management for NPF-BI ( table 2 ). There is pervasive evidence for the scale-dependence of pattern and process in ecology broadly, but also in invasion ecology specifically [ 35 ]. Scale dependence is evident when detecting the effects of environmental filtering, competitive interactions [ 36 ], phylogenetic relatedness [ 37 ], and the relationship between species richness of native communities and invasion success [ 22 ].…”

“…The invasion process is also by definition a temporal one, including ongoing propagule pressure from the regional species pool. Time since invasion and community successional stages are therefore key considerations in decisions about invasion management ([ 35 ]; table 2 ).…”

Growing Season Fires and Herbicide May not Be the Silver Bullet to Lespedeza cuneata Management

“…For example, to calculate the average patch-scale L. cuneata abundance, we summed the L. cuneata abundance across all the plots in each patch and divided that value by the total number of plots sampled per patch (i.e., 168 plots patch −1 yr −2 ). Although scaling up our data from plot-level observations to larger spatial scales likely reduced our statistical power, significant observations at those scales are unlikely to be biologically meaningful and potentially more influenced by sheer sample size alone ( McMillan et al 2023 ). Our approach was to experimentally examine how our management approaches affected L. cuneata abundances at scales that are relevant to rangeland managers and producers in the tallgrass prairie.…”

“…S1). A study of treatment effects at small scales (i.e., < 100 m 2 plots) where L. cuneata is homogenously distributed with high canopy cover does not, and cannot, represent the typical variability in L. cuneata cover across large landscapes ( McMillan et al 2023 ). While large-scale experiments with replicated landscapes such as our study often have substantially less statistical power compared with those at smaller scales, they are more relevant to boots-on-the-ground rangeland managers and producers.…”

Spatial Patterns and Associations of Tree Species in a Temperate Forest of National Forest Park, Huadian City, Jilin Province, Northeast China

“…Previous studies have examined the spatial distribution of species on a large scale and their relationship to biodiversity conservation [15,[17][18][19][20]. These studies generally found a significant correlation between the diameter at breast height (DBH) and the age of individuals of the same species in the same living environment [21,22].…”