Past Management Spurs Differential Plant Communities within a Giant Single-Clone Aspen Forest

Abstract

Sustainable aspen ecosystems hold great promise for global biodiversity conservation. These forests harbor relatively high species diversity, yet are threatened by fire suppression, land development, timber-focused management, extended droughts, and chronic herbivory. “Pando” is a high-profile quaking aspen (Populus tremuloides) forest in Utah, USA which is putatively the ‘largest living organism on earth.’ Pando comprises an estimated 47,000 genetically identical stems, but is threatened by human impacts. Our interest in the present study is whether changes to the giant organism were affecting understorey vegetation and whether discrete zones are displaying divergent community compositions. For instance, recent research has demonstrated strong herbivory impacts that are affecting portions of Pando differentially. This study consists of 20 randomly distributed vegetation survey plots within three de facto management regimes (hereafter, management group or type) along an herbivory protection gradient: No Fence, 2013 Fence (total protection), and 2014 Fence (imperfect protection). The plant survey was supplemented by previously-established forest and herbivore measurements to test for community assemblage explanatory agents. Sixty-eight species were found across the entire study. Analyses indicated strong links between management group orientation, species assemblages, and tree density/canopy openings. We found distinct evidence that within management group species composition was more similar than across groups for two of the three pairings. However, the other pairing, the most successfully protected area and the completely unprotected area, was not statistically distinct; likely a result a deteriorating overstorey in these two areas, whereas the third management type (2014 Fence) exhibited higher canopy cover. Indicator species analysis found that a small group of plant species had statistical allegiances to specific management groups, suggesting resource preference selection within Pando. Ordination analysis searching for causal factors reached two broad conclusions: (1) aspen regeneration, and therefore long-term resilience, is being negatively affected by chronic animal browsing and (2) current understorey species diversity is highest where forest canopy gaps are abundant. Future research at the massive Pando clone will continue informing linkages between understorey communities and overstorey-driven ecological pathways.

Comparison of Forest Species- Diversity and Composition Inside and Outside of the Holedná Game Reserve (The City of Brno, Czech Republic)

“…In our study, after only 35 years this management favouring high fallow deer and mouflons led to a significant decrease of shrub and herb layers cover and specific plant species composition. Rogers & Šebesta (2019) also support our findings and argue that ungulates are making preferential food choices regarding plant consumption which are affecting current understorey communities.…”

“…The long-term pressure of high levels of game in the herb layer leads to significant changes, which are primarily reflected in the structure and species composition, as well as in its dynamics and functions. Besides, higher presence of deer generally reduce tree recruitment (Rogers & Šebesta, 2019). They also secondarily affect other follow-up groups of organisms, change the nutrients cycle, soil conditions, and microclimatic conditions in the forest ecosystem.…”

“…Also, herb species that prefer disturbation exhibited affiliation to the interior of the game reserve -Poa annua, Stellaria media, Cerastium holosteoides. This affiliation could be explained by the direct and indirect effect of animals (Rogers & Šebesta, 2019). Fallow deer and mouflons take the nutrients to forest environment and they disturb soil surface by trampling and raking.…”

Pando’s Pulse: Vital Signs Signal Course Correction at World-Renowned Aspen Forest

“…The present assessment at Pando indicates protection regimes (treatments) are driving this genetically uniform forest toward divergent ecological pathways based on an array of tree and herbivore measures (Table 3). This divergence was supported by previous work at Pando where dissimilar vegetation assemblages track the same protection regimes [17]. Evidently past management-limiting or allowing herbivores differentially-is driving observed understorey and overstorey departures from a relatively consistent forest overstorey.…”

“…Pando's increasing notoriety via international media [15,16] has paralleled the steady decline of the clone (e.g., Nature 2018; Dykes 2022). Fences have been erected to mitigate herbivory at Pando (Figure 1), but such visual and ecological intrusions potentially bring additional problems, such as creating aesthetic impairments and novel oristic pathways [17] at this natural wonder.…”