Global biodiversity is in decline. This is of concern for aesthetic and ethical reasons, but possibly also for practical reasons, as suggested by experimental studies, mostly with plants, showing that biodiversity reductions in small study plots can lead to compromised ecosystem function. However, inferring that ecosystem functions will decline due to biodiversity loss in the real world rests on the untested assumption that such loss is actually occurring at these small scales in nature. Using a global database of 168 published studies and >16,000 nonexperimental, local-scale vegetation plots, we show that mean temporal change in species diversity over periods of 5–261 y is not different from zero, with increases at least as likely as declines over time. Sites influenced primarily by plant species’ invasions showed a tendency for declines in species richness, whereas sites undergoing postdisturbance succession showed increases in richness over time. Other distinctions among studies had little influence on temporal richness trends. Although maximizing diversity is likely important for maintaining ecosystem function in intensely managed systems such as restored grasslands or tree plantations, the clear lack of any general tendency for plant biodiversity to decline at small scales in nature directly contradicts the key assumption linking experimental results to ecosystem function as a motivation for biodiversity conservation in nature. How often real world changes in the diversity and composition of plant communities at the local scale cause ecosystem function to deteriorate, or actually to improve, remains unknown and is in critical need of further study.

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Global meta-analysis reveals no net change in local-scale plant biodiversity over time

Computational Methods of Multivariate Analysis in Physical Geography

https://www.fs.fed.us/nrs/pubs/jrnl/2018/nrs_2018_webster_001.pdf

Promoting and maintaining diversity in contemporary hardwood forests: Confronting contemporary drivers of change and the loss of ecological memory

Throughout much of its range, Tsuga canadensis (L.) Carr. (eastern hemlock) is severely threatened by the hemlock woolly adelgid (HWA; Adelges tsugae Annand), an exotic, invasive insect introduced from Japan. HWA causes defoliation and mortality, which presents a serious threat to the survival of T. canadensis in forests of eastern North America. Although HWA has been extensively studied in the forests of New England and the Mid-Atlantic, its spread into forested ecosystems throughout the southern Appalachian Mountains is relatively recent, and few studies have addressed the early impacts of this biological invasion. This study utilized forest inventory data collected in 2003, and again in 2008–2009 to quantify T. canadensis mortality and consequential shifts in species composition resulting from infestations of HWA throughout Great Smoky Mountains National Park. We observed significant decreases in the density of overstory and understory T. canadensis. The majority of the surviving overstory T. ...

https://www.jstor.org/stable/pdfplus/41262021.pdf

Early impacts of hemlock woolly adelgid in Tsuga canadensis forest communities of the southern Appalachian Mountains1

Herbaceous layer response to 17 years of controlled deer hunting in forested natural areas

Large ungulates are an important driver of plant community composition and structure. In eastern North America, white-tailed deer (Odocoileus virginianus) thrive in agricultural mosaics and fragmented forested landscapes, at times reaching unprecedented densities. Nevertheless, few long-term data sets are available that allow an assessment of the long-term consequences of chronic herbivory. We quantified herbaceous-layer change over a 26 y period in Cades Cove, Great Smoky Mountains National Park, USA. Cades Cove has a long and well-documented history of deer overabundance, with densities reaching 43 deer km−2 during the late 1970s. Over the 26 y sampling interval, mean coverage of herbaceous species declined significantly (P < 0.001) in the forests bordering Cades Cove. Although most plots only lost 1–2 species during the interval, 46 herbaceous species recorded on plots during the 1970s were wholly absent in 2004 (63% of which were forest species). Additionally, the herbaceous layer has become ...

https://bioone.org/journals/The-American-Midland-Naturalist/volume-162/issue-1/0003-0031-162.1.148/Herbaceous-layer-impoverishment-in-a-post-agricultural-southern-Appalachian-landscape/10.1674/0003-0031-162.1.148.pdf

Jennifer A. Thiemann

Papers

Herbaceous-layer impoverishment in a post-agricultural southern Appalachian landscape