Rangelands in a fragmented grass-dominated landscape are vulnerable to tree invasion from roadsides

Roadsides can be vectors for tree invasion within rangelands by bisecting landscapes and facilitating propagule spread to interior habitat. Current invasive tree management in North America’s Great Plains focuses on reducing on-site (i.e., interior habitat) vulnerability through on-site prevention and eradication, but invasive tree management of surrounding areas known to serve as invasion vectors, such as roadsides and public rights-of-ways, is sporadic. We surveyed roadsides for invasive tree propagule sources in a central Great Plains grassland landscape to determine how much of the surrounding landscape is potentially vulnerable to roadside invasion, and by which species, and thereby provide insights into the locations and forms of future landcover change. Invasive tree species were widespread in roadsides. Given modest seed dispersal distances of 100–200 m, our results show that roadsides have potential to serve as major sources of rangeland exposure to tree invasion, compromising up to 44% of rangelands in the study area. Under these dispersal distances, funds spent removing trees on rangeland properties may have little impact on the landscape’s overall vulnerability, due to exposure driven by roadside propagule sources. A key implication from this study is that roadsides, while often neglected from management, represent an important component of integrated management strategies for reducing rangeland vulnerability to tree invasion.

The Effect of the Distance from a Path on Abiotic Conditions and Vascular Plant Species in the Undergrowth of Urban Forests and Parks

Urban forests and parks are essential for the maintenance of biodiversity as well as human health and well-being. Residents and tourists commonly use urban forests and parks for recreational and sport purposes, contributing to changes in vegetation. This study aimed to assess the effect of distance from formal paths on the abiotic conditions, vegetation cover, as well as ecological diversity of vascular plant species in the undergrowth of urban forests and parks. The investigations were carried out in 2021 in 10 urban forests and 10 urban parks located in Kraków (southern Poland), using a total of 400 plots (1 × 1 m) situated in close (CL) and further (FU) vicinity of formal paths. We found a positive effect of the distance from the path on the depth of the compact soil layer, vegetation cover and height of the tallest shoot in the undergrowth of urban forests and parks. On the other hand, the distance from the path had a negative effect on the number of vascular plant species in the undergrowth in both forests and parks. Forests and parks differed significantly from each other in light intensity, the content of P in soil, depth of compact soil layer, number of species, as well as in cover-abundance of species representing different life forms, dispersal types, habitat affiliations and origins. Trampling leads to low plant cover and height of the undergrowth, as well as contributing to shallow localization of the compact soil layer near paths. Human movement on paths (walking, running, biking) with accompanying pets contributes to the successful dispersal of plants, resulting in high species richness. High light intensity in urban parks enhances the total number of species, cover-abundance of meadow and grassland plants, as well as cover-abundance of hemicryptophytes. The number of alien species was higher in parks than in forests, but the cover-abundance of alien plants was higher in forests than in parks. Urban forests are more suitable for the growth and biomass production of some alien herbs than urban parks, as mowing commonly used in parks appears to be an important factor in reducing their cover abundance. Regular fertilization and irrigation contribute to the high content of phosphorus in the soil, as well as to the high cover-abundance of meadow and grassland plants in urban parks. Urban forests enhance cover abundance of plants with dispersal mechanisms of the Bidens and Lycopodium types, whereas urban parks promote cover abundance of plants with the dispersal of the Allium type. Further study is needed to confirm the role of urban forests and parks in the preservation of ancient forest species, as well as to develop an appropriate design of paths that will allow the protection of vegetation and soil in urban forests and parks.

The impacts of trail infrastructure on vegetation and soils: Current literature and future directions

Reflecting the popularity of nature-based activities such as hiking and mountain biking, there are thousands of kilometres of recreational trails worldwide traversing a range of natural areas. These trails have environmental impacts on soils and vegetation, but where has there been research, what impacts have been found and how were they measured? Using a systematic quantitative literature review methodology, we assessed the impacts of trails on vegetation and soils, highlighting what is known, but also key knowledge gaps. Of the 59 original research papers identified on this topic that have been published in English language peer-reviewed academic journals, most were for research conducted in protected areas (71%), with few from developing countries (17%) or threatened ecosystems (14%). The research is concentrated in a few habitats and biodiversity hotspots, mainly temperate woodland, alpine grassland and Mediterranean habitats, often in the USA (32%) or Australia (20%). Most examined formal trails, with just 15% examining informal trails and 11% assessing both types. Nearly all papers report the results of observational surveys (90%), collecting quantitative data (66%) with 24% using geographic information systems. There was an emphasis on assessing trail impacts at a local scale, either on the trail itself and/or over short gradients away from the trail edge. Many assessed changes in composition and to some degree, structure, of vegetation and soils with the most common impacts documented including reduced vegetation cover, changes in plant species composition, trail widening, soil loss and soil compaction. There were 14 papers assessing how these local impacts can accumulate at the landscape scale. Few papers assessed differences in impacts among trails (7 papers), changes in impacts over time (4), species-specific responses (3) and only one assessed effects on plant community functioning. This review provides evidence that there are key research gaps including assessing informal trails, comparing trail types, landscape and temporal scale impacts, functional responses and impacts on threatened ecosystems/species. A more diverse geographic spread of research is also required including in regions experiencing rapid growth in tourism and recreation.

Recreational trails as a source of negative impacts on the persistence of keystone species and facilitation

Hiking trails, which are among the most common forms of infrastructure created for nature-based tourism, can alter key ecological processes. Trails can damage plants that facilitate the establishment and growth of other species leading to changes in community and functional composition. This can be a particular concern in harsh alpine ecosystems where plant communities are often dominated by one or two keystone species that provide shelter to a suite of beneficiary species. We analysed how a hiking trail affects interspecific facilitation by a dominant trampling-sensitive nurse shrub in the highest National Park in Australia. First we assessed the effects of the trail on the abundance, size and density of the nurse shrub at different distances from the trail. We then compared species richness and composition between areas in, and out, of the nurse shrub's canopy at different distances from the trail. To better understand why some species may benefit from facilitation and any effects of the trail on the quality of facilitation we compared functional composition between quadrats using community trait weighted means calculated by combining plant composition with species functional traits (canopy height, leaf area, % dry weight of leaves and specific leaf area). The abundance, size and density of nurse shrubs was lower on the trail edges than further away, particularly on the leeward edge, where there was more bare ground and less shrub cover. There were differences in species richness, cover, composition and functional composition in and outside the nurse shrub canopy. The shrubs appeared to facilitate species with more competitive, but less stress tolerant traits (e.g. taller plants with leaves that were larger, had high specific leaf area and low dry matter content). However, despite reductions in nurse shrubs near the trail, where they do exist, they appear to provide the same 'quality' of facilitation as nurse shrubs further away. However, longer-term effects may be occurring as the loss of nurse shrubs alters the wind profile of the ridgeline and therefore succession. The use of a steel mesh walkway along the trail may facilitate the regeneration of nurse shrubs and other plants that require protection from wind. Our results highlight the importance of diversifying recreation ecology research to assess how trails affect important ecological processes.

Differences in the impacts of formal and informal recreational trails on urban forest loss and tree structure

Recreational trails are one of the most common types of infrastructure used for nature-based activities such as hiking and mountain biking worldwide. Depending on their design, location, construction, maintenance and use, these trails differ in their environmental impacts. There are few studies, however, comparing the impacts of different trail types including between formal management-created trails and informal visitor-created trails. Although both types of trails can be found in remote natural areas, dense networks of them often occur in forests close to cities where they experience intense visitor use. To assess the relative impacts of different recreational trails in urban forests, we compared the condition of the trail surface, loss of forest strata and changes in tree structure caused by seven types of trails (total network 46.1 km) traversing 17 remnants of an endangered urban forest in Australia. After mapping and classifying all trails, we assessed their impact on the forest condition at 125 sites (15 sites per trail type, plus 15 control sites within undisturbed forest). On the trail sites, the condition of the trail surface, distance from the trail edge to four forest strata (litter, understory, midstorey and tree cover) and structure of the tree-line were assessed. Informal trails generally had poorer surface conditions and were poorly-designed and located. Per site, formal and informal trails resulted in similar loss of forest strata, with wider trails resulting in greater loss of forest. Because there were more informal trails, however, they accounted for the greatest cumulative forest loss. Structural impacts varied, with the widest informal trails and all formal hardened trails resulting in similar reductions in canopy cover and tree density but an increase in saplings. These structural impacts are likely a function of the unregulated and intense use of large informal trails, and disturbance from the construction and maintenance of formal trails. The results demonstrate that different types of recreational trails vary in the type and range of impacts they cause to forests. They highlight the importance of careful consideration towards management options when dealing with trail networks especially in areas of high conservation value.