Herb-Layer Dynamics in an Old-Growth Forest: Vegetation–Environment Relationships and Response to Invasion-Related Perturbations

Temperate forests of eastern North America are subject to multiple invasions from non-native species that have the potential to drive long-term dynamics in biodiversity. Garlic mustard (Alliaria petiolata (M. Bieb.) Cavara and Grande) is an invasive plant in many deciduous forests, and management efforts often focus on removing this species to initiate native species restoration. Agrilus planipennis Fairmaire (emerald ash borer; Coleoptera: Buprestidae) is a non-native insect pest that has caused substantial loss of ash trees (Fraxinus spp. L.) in North America. Our goal was to understand how the herbaceous layer in an old-growth forest responded to the removal of a significant invasion of A. petiolata and the loss of Fraxinus spp. due to A. planipennis. Herbaceous diversity and environmental parameters were measured in 32 permanent plots (1 m2 each) from 2012 to 2020 in an old-growth forest remnant that had experienced A. petiolata invasion and subsequent removal as well as mortality of Fraxinus spp. due to A. planipennis. Near-total loss of Fraxinus spp. as a canopy tree was not associated with changes in the understory light environment, possibly due to rapid canopy closure by adjacent trees not susceptible to the insect. Alliaria petiolata removal was associated with changes in herbaceous species richness and possibly shifts in individual species importance. Vegetation–environment relationships remained stable throughout the sampling period, suggesting that resource-related factors that structure the herb layer prevailed throughout the changes associated with Fraxinus spp. mortality and A. petiolata management. From a natural area management perspective, our data offer support for the idea that A. petiolata removal influences herb-layer diversity and indicate that in stands with a diverse tree community, the loss of Fraxinus spp. may not directly influence understory biodiversity

Herb-Layer Dynamics in an Old-Growth Forest: Vegetation–Environment Relationships and Response to Invasion-Related Perturbations

Temperate forests of eastern North America are subject to multiple invasions from non-native species that have the potential to drive long-term dynamics in biodiversity. Garlic mustard (Alliaria petiolata (M. Bieb.) Cavara and Grande) is an invasive plant in many deciduous forests, and management efforts often focus on removing this species to initiate native species restoration. Agrilus planipennis Fairmaire (emerald ash borer; Coleoptera: Buprestidae) is a non-native insect pest that has caused substantial loss of ash trees (Fraxinus spp. L.) in North America. Our goal was to understand how the herbaceous layer in an old-growth forest responded to the removal of a significant invasion of A. petiolata and the loss of Fraxinus spp. due to A. planipennis. Herbaceous diversity and environmental parameters were measured in 32 permanent plots (1 m2 each) from 2012 to 2020 in an old-growth forest remnant that had experienced A. petiolata invasion and subsequent removal as well as mortality of Fraxinus spp. due to A. planipennis. Near-total loss of Fraxinus spp. as a canopy tree was not associated with changes in the understory light environment, possibly due to rapid canopy closure by adjacent trees not susceptible to the insect. Alliaria petiolata removal was associated with changes in herbaceous species richness and possibly shifts in individual species importance. Vegetation–environment relationships remained stable throughout the sampling period, suggesting that resource-related factors that structure the herb layer prevailed throughout the changes associated with Fraxinus spp. mortality and A. petiolata management. From a natural area management perspective, our data offer support for the idea that A. petiolata removal influences herb-layer diversity and indicate that in stands with a diverse tree community, the loss of Fraxinus spp. may not directly influence understory biodiversity

Herbaceous 2017

Herbaceous vegetation data collected in 2017 at Drew Woods State Nature Preserve in Darke County, OH. Data key is provided in a supplemental file.https://ecommons.udayton.edu/mcewanlab_4_data/1016/thumbnail.jp

Persistent Phytoplankton Bloom in Lake St. Lucia (iSimangaliso Wetland Park, South Africa) Caused by a Cyanobacterium Closely Associated with the Genus Cyanothece (Synechococcaceae, Chroococcales) ▿

Lake St. Lucia, iSimangaliso Wetland Park, South Africa, is the largest estuarine lake in Africa. Extensive use and manipulation of the rivers flowing into it have reduced freshwater inflow, and the lake has also been subject to a drought of 10 years. For much of this time, the estuary has been closed to the Indian Ocean, and salinities have progressively risen throughout the system, impacting the biotic components of the ecosystem, reducing zooplankton and macrobenthic biomass and diversity in particular. In June 2009, a bloom of a red/orange planktonic microorganism was noted throughout the upper reaches of Lake St. Lucia. The bloom persisted for at least 18 months, making it the longest such bloom on record. The causative organism was characterized by light and electron microscopy and by 16S rRNA sequencing and was shown to be a large, unicellular cyanobacterium most strongly associated with the genus Cyanothece. The extent and persistence of the bloom appears to be unique to Lake St. Lucia, and it is suggested that the organism's resistance to high temperatures, to intense insolation, and to hypersalinity as well as the absence of grazing pressure by salinity-sensitive zooplankton all contributed to its persistence as a bloom organism until a freshwater influx, due to exceptionally heavy summer rains in 2011, reduced the salinity for a sufficient length of time to produce a crash in the cyanobacterium population as a complex, low-salinity biota redeveloped