uid=HFR,o=lter,dc=ecoinformatics,dc=org all public read doi:10.6073/pasta/e29f8868194e68cd2add3c823bfe756b David Orwig https://orcid.org/0000-0001-7822-3560 David Foster https://orcid.org/0000-0003-1171-3762 David Mausel Researcher 2023 English

The hemlock woolly adelgid (Adelges tsugae Annand; HWA), a small, aphid-like insect native to Japan, is currently migrating northward through eastern North America and threatens to eliminate eastern hemlock (Tsuga canadensis (L.) Carriere), one of the most abundant, long-lived shade tolerant species, across its range. In addition, a second invasive pest, the elongate hemlock scale (Fiorinia externa; EHS), often co-occurs with HWA on hemlock with unknown long-term consequences. The major objectives of this study were: (1) To characterize the pre-HWA distribution, composition, and structure of hemlock stands; (2) to characterize the spatial patterns of damage generated by HWA across southern New England since the time of its arrival in 1985; (3) to examine environmental and stand factors that are associated with declines in crown vigor and mortality of hemlock; (4) examine the dynamics of HWA and EHS in hemlock stands over time; and (5) assess whether there is a difference in the response of these insects to abiotic conditions (winter temperature, summer temperature, summer precipitation), and whether the distribution and abundance of each insect species is dependent on biotic interactions with the co-occurring insect species.

Aerial photographs, photographic overlays, and extensive field study were used to map and develop GIS overlays of almost 6000 hemlock stands in a 4900 km2 study region extending from Long Island Sound northward to the Massachusetts border and including the Connecticut River Valley in Connecticut, USA. Intensive sampling of a random selection of 114 hemlock stands across the study area was used to document patterns of hemlock infestation, vigor, and mortality in relation to stand and site characteristics. Mantel tests were utilized to assess the relative importance of environmental and stand variables in controlling the intensity of HWA infestation and damage. Most stands were located along ridge tops, steep hillsides, and narrow valleys. Hemlock importance values ranged from 22 to 96% and stand densities varied from 300 to 1450 stems ha-1. Adelgid presence and adelgid-induced hemlock mortality were found in 88% and 74% of the sampled forests, respectively. Approximately 25% of stands were logged recently, ranging in intensity from partial hemlock cutting to large clearcuts. A geographical trend in reduced HWA infestation intensity and tree mortality and enhanced crown vigor of overstory and understory hemlock occurs from south to north, coincident with the temporal colonization pattern of HWA. Mantel analyses indicated that patterns of HWA infestation, hemlock mortality, and crown vigor were most strongly correlated with latitude. Mortality was also weakly related to aspect and stand size. Average mortality was highest on western aspects but exceeded 20% on most slopes. Remaining trees averaged over 50% foliar loss, with no significant difference among aspects. Results suggest that as HWA becomes abundant, stands on xeric aspects succumb rapidly, but that stand and landscape variables such as overstory composition and structure, slope, and elevation, exert little control over susceptibility or eventual mortality. Ultimately, duration of infestation controls the intensity of hemlock decline and mortality. Over 4,290 ha of hemlock forest were eliminated by logging or HWA just within the southern part of our transect since the mid-1980s, and we predict continued HWA infestation will lead to unprecedented hemlock loss throughout the northeastern U.S., regardless of site conditions or location.

Using aerial photographs, we documented hemlock distribution throughout central Massachusetts and subsampled 123 stands to examine the spatial pattern of HWA and its impact on tree vigor and mortality since its arrival in 1989. In the study region, over 86,000 ha of hemlock forest were mapped in 5,127 stands. White pine (Pinus strobus), red oak (Quercus rubra), red maple (Acer rubrum), and black birch (Betula lenta) were common overstory associates. Hemlock abundance increased from south to north, commonly on western and northwestern slopes. Average stand size was 55 ha, overstory basal area ranged from 23 to 55m2 ha-1 and overstory stem densities averaged 993 ha-1. By 2004, 40% of sampled stands were infested, but most stands remained in good health overall; only 8 stands contained high HWA densities and only two had lost >50% overstory hemlock. Out of fifteen stand and landscape predictor variables examined, only latitude and winter climate variables were related to HWA density. Cold temperatures appear to be slowing the spread and impact of HWA at its northern extent as HWA infestation intensity and hemlock mortality and vigor were significantly correlated with average minimum winter temperature. Contrary to predictions, there was no regional increase in hemlock harvesting. The results suggest that regional HWA-hemlock dynamics are currently being shaped more by climate than by a combination of landscape and social factors. The persistence and migration of HWA continues to pose a significant threat regionally, especially in the northern portion of the study area, where hemlock dominates many forests.

We created a multivariate spatio-temporal model of the joint abundance of HWA and EHS, which share a host plant. Data on abundance of both insects were examined from the time the stand was initially sampled and again in 2005, 2007, 2009, and 2011. The model revealed differences in the way each species responded to weather extremes, and indicated a commensalism in which high abundance of HWA increased the probability of subsequent infestation by EHS– but not vice versa. This study provides evidence that incorporating biotic interactions into a species distribution model indicates whether a species’ distribution and abundance is dependent on other species in the community, and importantly, improves estimation of the abiotic niche for species whose abundance depends on interactions with other species in the community.

hemlock hemlock woolly adelgid landscape mortality timber harvest LTER controlled vocabulary disturbance LTER core area Harvard Forest HFR LTER USA HFR default

This dataset is released to the public under Creative Commons CC0 1.0 (No Rights Reserved). Please keep the dataset creators informed of any plans to use the dataset. Consultation with the original investigators is strongly encouraged. Publications and data products that make use of the dataset should include proper acknowledgement.

Creative Commons Zero v1.0 Universal https://spdx.org/licenses/CC0-1.0.html CC0-1.0 https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf081 Central Connecticut, Central Massachusetts. Coordinates based on WGS84 datum. -72.73 -72.25 +42.73 +41.28 1997 2011 genus Adelges species tsugae hemlock woolly adelgid genus Betula species lenta black birch genus Tsuga species canadensis eastern hemlock complete Information Manager Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 hf-im@lists.fas.harvard.edu Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu

Aerial photographs and extensive field study were used to map and develop GIS overlays of 6000+ hemlock stands in a 7500 km2 study region extending from Long Island Sound northward to the Massachusetts border and including the Connecticut River Valley. During the summers of 1997-1998 in Connecticut and 2002 – 2004 in Massachusetts, vegetation was sampled in one fixed-area (20 x 20 m) plot and 5 to 10 variable-radius plots located every 30 to 50 m along a transect oriented through the long dimension of the forest in each stand. In fixed-area plots, all trees (stems at least 8 cm diameter breast height (dbh)) were tallied by species and dbh, and assigned a canopy position based on a visual estimation of the amount of intercepted light received by the tree crown. Hemlocks that died within the previous 2 to 4 years, which were identified by extensive retention of fine twigs in the crown, were tallied to determine species composition prior to HWA infestation. Crown vigor classes were assigned to each hemlock tree based on the amount of retained foliage: 1 = 76 - 100%; 2 = 51 - 75%; 3 = 26 - 50%; 4 = 1 - 25%; 5 = dead. Presence and intensity of infestation by HWA, EHS, and hemlock borer were estimated from the number of egg sacs present on branches from several trees in each plot and categorized as: 0 = absent; 1 = low density (1-10 insects/m branch); 2 = moderate density (11-100 insects/m branch); or 3 = heavy density (>100 insects/m branch). All saplings (less than 8 cm dbh and over 1.4 m tall) were tallied by species. Overstory species composition, degree of hemlock mortality, and basal area were also assessed within variable radius cruise plots using the Bitterlich method with a 5 or 10 basal area factor gauge. Slope, aspect, elevation, and depth of the soil organic horizon to the nearest 0.5 cm were recorded at each sampling point. A relative importance value was calculated for each overstory species in every stand by summing the relative basal area derived from the variable radius sampling and the relative density derived from the fixed-area plots. Values for hemlock included both live and recently dead trees to represent "pre-HWA" importance.

A subset of the hemlock stands sampled in central Connecticut and Massachusetts (n = 142) were intensively sampled for insect densities over time and climatic variables were obtained for each forest. In the initial year of sampling (1997-98 in Connecticut and 2002-2004 in Massachusetts), each stand was given an ordinal score for each insect species (hemlock woolly adelgid and elongate hemlock scale) representing the average infestation level of the stand based on thorough examination of trees as follows: 0 = 0 insects per meter of branch; 1 = 1-10 insects per meter; 2 = 11 – 100 insects per meter; 3 = >100 insects per meter. In subsequent years (2005, 2007, 2009, 2011), 50 trees were haphazardly selected in each stand for observation, and the density of each insect species on each tree was assigned to one of the above categories. Individual trees could not be marked. Fewer than 50 trees were sampled per stand in some highly-damaged stands, and stands impacted by logging or development during the study period were not sampled post-disturbance. Daily temperature (maximum/minimum) and precipitation data were obtained for each stand from 1996 to 2011 from the online PRISM Gridded Climate database (PRISM Climate Group, Oregon State University, http://prism.oregonstate.edu, created 26 Mar 2015) by interpolating 4km2 resolution climate data at the centroid of each eastern hemlock stand using values from surrounding grid cell centers and inverse-distance squared weighting.

Harvard Forest

324 North Main Street Petersham MA 01366 USA

(978) 724-3302 (978) 724-3595 https://harvardforest.fas.harvard.edu https://ror.org/059cpzx98 pointOfContact The Harvard Forest Long-Term Ecological Research (LTER) program examines ecological dynamics in the New England region resulting from natural disturbances, environmental change, and human impacts. National Science Foundation LTER grants: DEB-8811764, DEB-9411975, DEB-0080592, DEB-0620443, DEB-1237491, DEB-1832210. hf081-01-ct.csv Connecticut data hf081-01-ct.csv 14676 698bae4198788efc497f028172fc6593 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p08/hf081/hf081-01-ct.csv stand 4-5 letter site abbreviation, arranged N to S site abbreviation, arranged N to S year year of sampling YYYY 1 year NA missing value aspect direction slope faces in degrees degree 1 whole NA missing value slope percent slope number 0.01 real NA missing value elevation elevation of plot in m a.s.l. estimated from topo. maps meter 1 whole NA missing value latitude latitude of stand derived from arcview degree 0.00001 real NA missing value longitude longitude of stand derived from arcview degree 0.00001 real NA missing value humus depth of soil organic matter from quantitative plot centimeter 0.01 real NA missing value hem.dbh average hemlock dbh from quantitative plot centimeter 0.01 real NA missing value hard.dbh average hardwood dbh from quantitative plot centimeter 0.01 real NA missing value qba stand basal area derived from quantitative plot meterSquaredPerHectare 0.01 real NA missing value cba average stand basal area derived from cruise plots meterSquaredPerHectare 0.01 real NA missing value hem.cc average hemlock crown class derived from quantitative plot 1 overtopped tree 2 intermediate canopy position 3 codominant canopy position 4 dominant canopy position hard.cc average hardwood crown class derived from quantitative plot 1 overtopped tree 2 intermediate canopy position 3 codominant canopy position 4 dominant canopy position hem.vigor average crown vigor of hemlock trees 1 healthy; no visible foliar loss 2 healthy; 1 – 25% foliar loss 3 declining; 26-50% foliar loss 4 declining; 51-75% foliar loss 5 declining; 76-99% foliar loss 6 dead hem.bad average amount of dead hemlock basal area from cruise plots meterSquaredPerHectare 0.01 real NA missing value hem.d.per percent of dead overstory hemlock in quantitative plots number 1 whole NA missing value hem.dead density of dead overstory hemlock stems in quantitative plots numberPerHectare 1 whole NA missing value live.hem density of live hemlock overstory stems in quantitative plots numberPerHectare 1 whole NA missing value hem.dens density of hemlock overstory stems in quantitative plots numberPerHectare 1 whole NA missing value stem.dens total overstory stem density in quantitative plots numberPerHectare 1 whole NA missing value hwa.dens average density of HWA observed on hemlock branches 0 absent 1 low density 2 moderate density 3 heavy density, or HWA egg sacs at the base of most to all needles or many scale insects on most to all needles scale.dens average density of hemlock scale insects observed on hemlock branches 0 absent 1 low density 2 moderate density 3 heavy density, or HWA egg sacs at the base of most to all needles or many scale insects on most to all needles hem.sapl total density of live hemlock saplings within quantitative plots numberPerHectare 1 whole NA missing value hem.sapd percent of dead hemlock saplings within quantitative plots number 0.01 real NA missing value hem.iv importance value derived by summing basal area from cruise plots and density from quantitative plots number 0.1 real NA missing value size stand size hectare 0.01 real NA missing value 114 hf081-02-ma.csv Massachusetts data hf081-02-ma.csv 22735 8a4566b2073cd52ed01e3266987e94bc 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p08/hf081/hf081-02-ma.csv stand town name from USGS topo maps stand name year year when stand was sampled (2002-2004) YYYY map.code map delineation of hemlock A at least 50% hemlock B 1- 50% hemlock aspect direction slope faces in degrees, derived from cruise and fixed-area, quantitative plots degree 0.01 real NA missing value slope percent slope averaged from cruise and quantitative plots number 0.01 real NA missing value long longitude of stand derived from Arcview degree 0.00001 real NA missing value lat latitude of stand derived from Arcview degree 0.00001 real NA missing value elevation elevation of plot in meters a.s.l. estimated from topo maps meter 0.01 real NA missing value area stand size hectare 0.01 real NA missing value humus depth of soil organic matter from quantitative plot centimeter 0.01 real NA missing value ba average stand basal area derived from cruise plots meterSquaredPerHectare 0.01 real NA missing value hem.ba average hemlock basal area from cruise plots meterSquaredPerHectare 0.01 real NA missing value hard.ba average hardwood basal area from cruise plots meterSquaredPerHectare 0.01 real NA missing value live.ba average live basal area from cruise plots meterSquaredPerHectare 0.01 real NA missing value dead.hem.ba average dead hemlock basal area from cruise plots meterSquaredPerHectare 0.01 real NA missing value hem.mort average hemlock mortality from cruise plots (%) number 0.01 real NA missing value hem.dbh average hemlock dbh from quantitative plot centimeter 0.01 real NA missing value hard.dbh average hardwood dbh from quantitative plot centimeter 0.01 real NA missing value qba stand basal area derived from quantitative plot meterSquaredPerHectare 0.01 real NA missing value hem.cc average hemlock crown class derived from quantitative plot 1 overtopped tree 2 intermediate canopy position 3 codominant canopy position 4 dominant canopy position hard.cc average hardwood crown class derived from quantitative plot 1 overtopped tree 2 intermediate canopy position 3 codominant canopy position 4 dominant canopy position hem.vigor average crown loss of hemlock trees 1 healthy; no visible foliar loss 2 healthy; 1-25% foliar loss 3 declining; 26-50% foliar loss 4 declining; 51-75% foliar loss 5 declining; 76-99% foliar loss 6 dead hem.iv importance value derived by summing relative basal area from cruise plots and relative density from quantitative plots number 0.01 real NA missing value hem.den total hemlock overstory density in quantitative plots numberPerHectare 1 whole NA missing value dead.hem.den dead hemlock density in quantitative plots numberPerHectare 1 whole NA missing value tree.den total overstory stem density in quantitative plots numberPerHectare 1 whole NA missing value sap.den total sapling stem density in quantitative plots numberPerHectare 1 whole NA missing value live.sap.den live sapling density in quantitative plots numberPerHectare 1 whole NA missing value live.hem.sap.den live hemlock sapling density in quantitative plots numberPerHectare 1 whole NA missing value dead.hem.sap.den dead hemlock sapling density in quantitative plots numberPerHectare 1 real NA missing value acer.sap sapling density of maple species numberPerHectare 1 whole NA missing value bele.sap sapling density of black birch numberPerHectare 1 whole NA missing value quru.sap sapling density of red oak numberPerHectare 1 whole NA missing value pist.sap sapling density of white pine numberPerHectare 1 whole NA missing value hwa.density average density of HWA observed on hemlock branches 0 absent 1 low density 2 moderate density 3 heavy density, HWA egg sacs at base of most to all needles, or many scale insects on most to all needles scale.density average density of elongate hemlock scale observed on hemlock branches 0 absent 1 low density 2 moderate density 3 heavy density, HWA egg sacs at base of most to all needles, or many scale insects on most to all needles borer.density average density of hemlock borer observed on hemlock branches 0 absent 1 low density 2 moderate density 3 heavy density, HWA egg sacs at base of most to all needles, or many scale insects on most to all needles logged presence of any past logging activity 0 no 1 yes hem.logged evidence of past hemlock logging 0 no 1 1-10 years ago 2 more than 10 years ago under.rich number of understory species tallied in quantitative plots (herb, shrub, and seedlings) number 1 whole NA missing value 123 hf081-03-stands.csv stand location hf081-03-stands.csv 4085 6a44ab30255bc17b3e43d30d56bcaf47 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p08/hf081/hf081-03-stands.csv state state location of hemlock stand CT Connecticut MA Massachusetts NA missing value stand eastern hemlock stand identification - 3 letter town abbreviation (CT) or town name (MA) and stand number eastern hemlock stand identification - 3 letter town abbreviation (CT) or town name (MA) and stand number NA missing value long longitude degree 0.0001 real NA missing value lat latitude degree 0.0001 real NA missing value 142 hf081-04-climate.csv climate hf081-04-climate.csv 35622 b857381429efd885b4ea2fe714b6a38f 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p08/hf081/hf081-04-climate.csv state state location of hemlock stand CT Connecticut MA Massachusetts NA missing value stand eastern hemlock stand identification - 3 letter town abbreviation (CT) or town name (MA) and stand number eastern hemlock stand identification - 3 letter town abbreviation (CT) or town name (MA) and stand number NA missing value year year of sampling YYYY 1 year NA missing value sample.size number of trees in the stand for which abundance was recorded in the year of sampling number 1 whole NA missing value mins.yr minimum winter temperature in the preceding winter celsius 0.1 real NA missing value winter.tmean.yr mean winter temperature Dec 1 through Mar 31 in the winter preceding sampling celsius 0.1 real NA missing value precip.yr precipitation sum April 1 – Sept 30 of the sampling year millimeter 0.01 real NA missing value max.yr maximum temperature April 1 through Sept 31 of the sampling year celsius 0.1 real NA missing value 852 hf081-05-hwa-ehs.csv abundance hf081-05-hwa-ehs.csv 562597 cec324499e4273efd2ceba326af4b191 1 \r\n column , https://harvardforest.fas.harvard.edu/data/p08/hf081/hf081-05-hwa-ehs.csv stand eastern hemlock stand identification - 3 letter town abbreviation (CT) or town name (MA) and stand number eastern hemlock stand identification - 3 letter town abbreviation (CT) or town name (MA) and stand number NA missing value year year of sampling YYYY 1 year NA missing value tree tree number (individual trees were not marked, so e.g. tree #3 is the third tree observed in a stand in a year, but tree #3 is not the same individual year after year) tree number (individual trees were not marked, so e.g. tree #3 is the third tree observed in a stand in a year, but tree #3 is not the same individual year after year) NA missing value hwa hemlock woolly adelgid density per meter of branch on an ordinal scale 0 0 insects per meter of branch 1 1-10 insects per meter 2 11 – 100 insects per meter 3 greater than 100 insects per meter NA missing value ehs elongate hemlock scale density per meter of branch on an ordinal scale 0 0 insects per meter of branch 1 1-10 insects per meter 2 11 – 100 insects per meter 3 greater than 100 insects per meter NA missing value 27050 conservation informatics invasive plot community regional long-term measurement https://harvardforest.fas.harvard.edu/exist/apps/datasets/showData.html?id=hf021