Local and regional variation in hemlock seedling establishment in forests of the upper Great Lakes region, USA
نویسندگان
چکیده
Successful tree regeneration requires both successful seedling establishment and subsequent survival and growth suf®cient to ensure recruitment. We examined patterns of initial seedling establishment in randomly selected stands of eastern hemlock (Tsuga canadensis) distributed across northern Wisconsin and eastern Upper Michigan. In 1990, we counted all hemlock seedlings (de®ned as 4±29 cm tall) and sampled substrate conditions in two 7 7 m quadrats of 142 hemlock and hemlock± hardwood stands. In 1996, we resampled 109 of these stands more intensively using six 7 7 m quadrats. In 1997, we also intensively surveyed which substrate-supported hemlock seedlings in three 50 m replicate areas from each of ®ve stands. In 1990, we found no hemlock seedlings at 64 of the 142 stands sampled, and 46% of the stands had more than 100 hemlock seedlings haÿ1 (mean density480 90 haÿ1). In contrast, only 14 (13%) of the 109 stands resampled in 1996 had no seedlings and 66% had over 100 seedlings haÿ1 (mean density840 200 haÿ1). These results suggest that seedling establishment is patchy, causing the estimated frequency of successful establishment to depend strongly on the area sampled. Seedling abundance within sites was correlated between years, suggesting that site history may in part account for the abundance of seedlings. Analysis of variance to mean ratios reveals that seedlings are indeed strongly clumped at the 7 7 m scale or smaller. Such clumping probably results from the tendency for hemlock seedlings to occur most frequently on particular substrates (i.e. decaying wood). Hemlock seedlings occur less frequently in stands with high basal area of sugar maple but do not decline in stands with greater hemlock basal area, suggesting that maple litter may restrict local opportunities for seedling establishment. Seedling densities do not vary among habitat-types, and no other stand or regional variable signi®cantly affected hemlock seedling density. These results suggest that ground surveys are needed to assess hemlock seedling abundance, and that such surveys should be based on quadrats of at least 100 m. Successful hemlock regeneration should capitalize on local patches of existing hemlock seedlings where interference by hardwoods is minimal. Even high initial seedling establishment, however, may not guarantee regeneration in areas where high deer densities preclude recruitment into larger size classes. # 1998 Elsevier Science B.V.
منابع مشابه
Current and Predicted Long-term Effects of Deer Browsing in Hemlock Forests in Michigan, USA
Remnants of virgin hemlock Tsuga canadensis (L.) Carr. forest in the Porcupine Mountains, Michigan, USA, have experienced inadequate hemlock regeneration lasting several decades. White-tailed deer Odocoileus virginianus Zimmermann browsing seems to be the major cause of the observed decline ojhemlock regeneration, rather than poor seedbed conditions or changing climate. In some areas, significa...
متن کاملReport Submitted for the Great Lakes Regional Assessment
The natural ecosystems of the region are characterized by three prominent environmental gradients. First, a southwest to northeast gradient from prairie to forest in Minnesota is largely a function of moisture availability. Second a south to north gradient from Eastern deciduous (oak-hickory) to Northern mixed hardwoods forests (beech, maple, hemlock) in Michigan and Wisconsin is a prominent la...
متن کاملFire disturbance, forest structure, and stand dynamics in montane forests of the southern Cascades, Thousand Lakes Wilderness, California, USA
We examined tree diameter, age structure, and successional trends in 100 montane forest plots to identify the effects of variation in the return interval, severity, and extent of fires on forest structure and dynamics in the southern Cascade Range, California. We classified 100 forest plots into 8 groups based on stand structural characteristics. Median point fire return intervals were shortest...
متن کاملPost-Disturbance Plant Community Dynamics following a Rare Natural-Origin Fire in a Tsuga canadensis Forest
Opportunities to directly study infrequent forest disturbance events often lead to valuable information about vegetation dynamics. In mesic temperate forests of North America, stand-replacing crown fire occurs infrequently, with a return interval of 2000-3000 years. Rare chance events, however, may have profound impacts on the developmental trajectories of forest ecosystems. For example, it has...
متن کاملSpatiotemporal Influences of Climate on Altitudinal Treeline in Northern Patagonia
Tree radial growth and seedling establishment of Nothofagus pumilio at alpine treeline near 408 S latitude in Chile and Argentina show timeand site-dependent relationships to interannual-and decadal-scale climate variation. Six treelines were sampled at two spatial scales corresponding to regional and local climates. A shift in climate from cool–wet to warm–dry conditions facilitated comparison...
متن کامل