Landscapes Forest and Global Change - ESA - Escola Superior ...

K. L. Martin & P.C. Goebel 2010. Impact of hemlock decline on successional pathways and ecosystem function
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1. Virginia (Jefferson and George Washington National Forests), where HWA has been present
for 25-30 years and hemlocks in invaded stands are likely dead (based on the 4-15 year
mortality timeframe; McClure 1991);
2. West Virginia (New River and Gauley River National Recreation Areas, Monongahela
National Forest), where HWA has recently invaded (2-5 years) and trees are declining; and,
3. Ohio (Lake Katherine State Nature Preserve, Sheick Hollow State Nature Preserve, Hocking
State Forest) where HWA is not yet present.
In this paper, we focus on data collected in the Unglaciated Allegheny Plateau physiographic
province of southeastern Ohio (Brockman 1998). This province of deep cliffs and valleys cut
into the sandstone bedrock supports the majority of T. canadensis within Ohio (Black and Mack
1976). Three of our steam reaches were located at Lake Katharine, an 817-ha State Nature
Preserve, four were located within the 3,924-ha Hocking State Forest, and one at Sheick
Hollow, a 61-ha State Nature Preserve. The climate in the area is continental with cold, snowy
winters (mean = 0 o C) and warm, humid summers (mean = 21.6 o C) with an average rainfall of
102 cm distributed evenly throughout the year (Kerr 1985; Lemaster and Glimore 1989). All
areas were second-growth forest ravines with hemlock approximately 50% or more of the basal
area. Any areas with evidence of recent human disturbance (logging roads, stumps) were
excluded.
We sampled vegetation using a series of five 100-m 2 circular plots (5.64 m radius) centered 10,
30, and 50-m from small streams and 15 m apart. The species and d.b.h. (diameter at breast
height, 1.67 m) of all woody vegetation was recorded. Stems 2.5 - 10 cm d.b.h. were classified
as saplings. All stems > 10 were coded as dominant (full canopy in sun), co-dominant (portions
of canopy in sun), intermediate (top of canopy not overtopped), or sub-canopy (overtopped). For
analyses, the five subplots in each transect were added together for analyses for a 500-m 2 scale.
To understand community characteristics at different slope positions across the ravines, we also
analyzed functional diversity using species guilds developed for the Central Hardwood Forest of
the USA by Sutherland et al. (2000). As we are focused on T. canadensis as a foundation
species currently subjected to species-specific mortality, we separated it into its own functional
group for analyses.
Mean species and functional richness and diversity were compared by transect using one-way
analysis of variance (ANOVA) tests. In cases where means differed, the three transects were
subjected to Tukey’s mean separation test. All analyses were calculated using PASW statistics
18 software (SPSS Inc, Chicago, IL)
3. Results
Our results indicate that in ravines of the Unglaciated Allegheny Plateau of Ohio, T. canadensis
is highly dominant with few other species in the canopy, sub-canopy, or sapling layers (Table
1). Hemlock basal area did not vary by transect, and neither did overall basal area. Although
there was not a strong separation (Canopy species richness F = 2.57, P = 0.100, d.f. = 2), Betula
lenta L. and Liriodendron tulipifera L., as well as Fagus grandifolia Ehrh., were more common
adjacent to the stream. Sutherland et al. (2000) categorize B. lenta and L. tulipifera as a part of a
long-lived, shade intolerant functional group, indicating they are gap-dependent in hemlock
ravines. On the other hand, F. grandifolia is part of the same extremely shade tolerant, slowgrowing,
and long-lived functional group that includes T. canadensis (Sutherland et al. 2000).
Moving from the stream upslope, there was also a slight increase in canopy functional richness
(F= 3.95, P = 0.035, d.f. = 2). This was largely due to increases in Quercus and Carya species,
which Sutherland et al. (2000) group into the red oak- hickory (i.e. Quercus rubra L., Q.
coccinea Münchh. and Carya spp.) and the white oak (Q. alba L., Q. prinus L. ) groups due to
differing germination requirements. Along the 30-m transect, the shade-tolerant Acer-Ulmus
Forest Landscapes and Global Change-New Frontiers in Management, Conservation and Restoration. Proceedings of the IUFRO Landscape Ecology
Working Group International Conference, September 21-27, 2010, Bragança, Portugal. J.C. Azevedo, M. Feliciano, J. Castro & M.A. Pinto (eds.)
2010, Instituto Politécnico de Bragança, Bragança, Portugal.