Sci-Comm: Holt Research Forest Understory Relevés (1m2 Plots, S1 Lines, and Subquadrats)

At Holt Research Forest, technicians conduct understory relevés across the study grid to create a comprehensive snapshot of forest vegetation. Relevés are a standardized vegetation sampling method used to document plant species composition and abundance, allowing researchers to detect changes in vegetation structure over time and in response to management or environmental change. Because understory vegetation responds quickly to disturbance, climate variability, and browsing pressure, these datasets provide an early indicator of shifts in forest dynamics.

Technicians identifying vegetation in 1m² plots at Holt Research Forest.

During each relevé, vegetation is identified and recorded by height class within distinct vertical strata of the forest. These strata represent the forest's layered structure, from understory plants to the overstory canopy. For example, the overstory canopy forms the uppermost layer of the forest and strongly influences light availability, regeneration, and habitat conditions below.

For each species observed within a stratum, technicians estimate abundance using standardized cover classes. In the upper strata (5–10 m and >10 m), abundance is recorded as percent cover rather than by counting individual trees. This approach reflects the ecological influence of canopy trees, which is better captured by the amount of area they occupy than by stem density alone.

Lady Slipper Orchids at Holt Research Forest.

Percent cover is defined as the proportion of the ground surface that would be covered by a species if its foliage were projected vertically onto a horizontal plane (Fig. 1). Overlapping leaves within a single plant are not counted multiple times. Using this method, species are assigned to one of several cover classes (<1%, 1–5%, 5–25%, 25–50%, 50–75%, or 75–100%),

Figure 1. Visualizing percent cover. 

Relevé surveys have been conducted within the 1m² plots, S1 lines, and the subquadrats. The Holt Research Forest Understory Relevé, 1m² Plots includes three datasets of vegetation from 1m² plots located in harvest gaps, tree gaps, ledge gaps, and control areas (under undisturbed canopy). The Holt Research Forest Understory Relevé, S1 Lines includes three datasets of vegetation from 1m² plots along the north and south S1 lines. The Holt Research Forest Understory Relevé, Subquadrats includes a relevé survey per subquadrat (25m x 25m) throughout the study area. A Holt Research Forest plant list with identification characteristics is available under the filename: PLANT-ID.LST in Basic Documentation. Visit the Holt Research Forest data archive to learn more about our Relevé datasets and metadata at https://www.uvm.edu/femc/CI4/holt#projects!