Late Holocene Stand-Scale Invasion by Hemlock (Tsuga canadensis) at Its Western Range Limit

Abstract

The movement of plant range limits in the past has been clearly documented as a response to changing climate, but the pattern and timing of local invasions that result from these plant migrations are not well understood. Sedimentary evidence from small forest hollows is used here to reconstruct the pattern of stand-scale invasion by eastern hemlock (Tsuga canadensis (L.) Carr.) at its current range limit in Wisconsin. Pollen records from lakes show a slowly increasing regional hemlock population over the past 2500 yr, as its range expanded from the east in response to cooler, wetter climate. In contrast, hemlock pollen in each of the forest hollows increased abruptly within the past 500 yr, demonstrating stand-scale dynamics at a time when regional changes were small. Moreover, this abrupt rise in hemlock is part of a two-phase sequence of local invasion. First, stands were initially colonized as much as 2000 yr ago, but the size of these local populations remained low for as long as 1800 yr. This pattern suggests that scattered, small populations grew beyond the continuous range limit of hemlock, which was tens of kilometers to the east. Second, these small hemlock populations expanded in size between 100 and 500 yr ago during a time of cooler, wetter climate, which was apparently limiting population growth. These results illustrate contrasting patterns of change between local and regional populations, and the importance of outlying colonies as sources of rapid population expansion when environmental conditions become favorable.

Role of Multidecadal Climate Variability in a Range Extension of Pinyon Pine

“…Studies of Holocene migration dynamics from throughout North America (e.g., Woods and Davis 1989, Jackson and Booth 2002, Parshall 2002, Lyford et al 2003 suggest how such climatic variability can influence the progression of migration events. First, climate modulates the frequency of dispersal events and the distances covered.…”

Realized climatic niches of deciduous trees: comparing western Eurasia and eastern North America

“…Although the post-glacial range dynamics of individual species have been much affected by the different topographies of the two continents (e.g. Parshall, 2002;Hewitt, 2004;Williams et al, 2004), most of the climatic limits under which deciduous trees occur at present in eastern North America and western Eurasia are relatively similar. The absence of drought-sensitive tree species in Europe as compared to North America, however, can hardly be explained only by differences in recent climatic conditions.…”

Natural disturbance regimes as templates for the response of bird species assemblages to contemporary forest management

“…In eastern boreal forests, a recent palaeoecological study reconstructing fire history in the Holocene (Cyr et al, 2009) indicated that, despite strong variability in fire intervals, the proportion of old forest in the landscape ranged between 30% and 80% throughout this time period. Likewise, palaeoecological studies suggest low fire frequencies in northern hardwood forests (Foster & Zebryk, 1993;Davis et al, 1998;Parshall, 2002;Parshall & Foster, 2002). Natural fire history reconstruction using dendroecological records has shown that burn rates over the last 300 years were generally higher in the boreal plains region of Alberta (Larsen, 1997) than in the eastern portion of the boreal shield (Bergeron et al, 2001, Figure 1 Location of the study regions where forest bird surveys were conducted in Canadian boreal and northern hardwood forests.…”