Tree Regeneration Patterns Research Articles

Survival of and Herbivore Damage to a Cohort of Quercus rubra Planted Across a Forest—Old-field Edge

Abstract Forest edges are known to affect plant community composition and habitat use by animals. However, the direct influence of edges in determining patterns of tree regeneration is poorly understood. Survival of and herbivore damage to Quercus rubra seedlings were experimentally determined for seedlings planted across a forest—old-field edge gradient. Seedling survival was lowest inside the forest (1%), intermediate at the edge (25%) and highest within the old-field portion of the gradient (49%). Deer herbivory decreased with increasing distance into the old field. Seedling survival increased under Rosa multiflora and decreased in plots with mammalian herbivory. Seedling height was significantly affected by distance from the edge but was unaffected by mammalian herbivory. Based on our results, herbivore effects on Quercus rubra growth and survivorship appear secondary to influences of distance from the forest edge.

Modeling landscape patterns of understory tree regeneration in the Pacific Northwest, USA

Abstract. Vegetation maps serve as the basis for spatial analysis of forest ecosystems and provide initial information for simulations of forest landscape change. Because of the limitations of current remote sensing technology, it is not possible to directly measure forest understory attributes across large spatial extents. Instead we used a predictive vegetation mapping approach to model Tsuga heterophylla and Picea sitchensis seedling patterns in a 3900‐ha landscape in the Oregon Coast Range, USA, as a function of Landsat TM imagery, aerial photographs, digital elevation models, and stream maps. Because the models explained only moderate amounts of variability (R2 values of 0.24–0.56), we interpreted the predicted patterns as qualitative spatial trends rather than precise maps.P. sitchensis seedling patterns were tightly linked to the riparian network, with highest densities in coastal riparian areas. T. heterophylla seedlings exhibited complex patterns related to topography and overstory forest cover, and were also spatially clustered around patches of old‐growth forest. We hypothesize that the old growth served as refugia for this fire‐sensitive species following wildfires in the late 19th and early 20th centuries. Low levels of T. heterophylla regeneration in hardwood‐dominated forests suggest that these patches may succeed to shrublands rather than to conifer forest.Predictive models of seedling patterns could be developed for other landscapes where georeferenced inventory plots, remote sensing data, digital elevation models, and climate maps are available.

Nutritional Effects of Seed Fall during Mast Years in Boreal Forest

Several hypotheses have been advanced to explain why masting (i.e. episodic. synchronized seed production) occurs in coniferous trees, as well as aspects of its evolution and importance for reproductive success. However, the nutritional effects of the large number of seeds that simultaneously fall to the ground, die and decompose in the soil during mast years have not previously been considered. Norway spruce (Picea abies) has a typical masting behavior and may add 5-10 kg N ha -1 yr -1 through seed fall in mast years in the boreal zone of Northern Sweden. We performed a field experiment in a strongly nitrogen-limited forest in N Sweden where pre-killed Norway spruce seeds were added to plots at an amount comparable to 7 kg N ha -1 yr - '. Seeds were added to an understory vegetation dominated by ericaceous shrubs and two different bottom layer components, Pleurozium schreberi and Cladina spp. Seedlings of Scots pine (Pinus sylvestris) were then planted in the same plots to evaluate growth response to and availability of nutrients from the dead Norway spruce seeds that were added to the two plant communities. Seedlings of Scots pine grew larger and acquired more nitrogen when dead seeds were added in plots dominated by Cladina spp. However, in plots dominated by P. schreberi, uptake of nutrients from dead seeds by Scots pine was blocked by P. schreberi except in treatments where the P. schreberi moss carpet was experimentally disturbed. Analysis of nutrients in field- and bottom-layer vegetation showed that P. schreberi acquired a large proportion (80%) of N released from dead seeds while the ericaceous dwarf shrub Vaccinium vitis-idaea and the Cladina spp. macrolichens gained much less nitrogen. The rates of nutrient release and decomposition of dead Norway spruce seeds were compared with Norway spruce needle litter in a litter bag experiment. Dead Norway spruce seeds decomposed at much higher rates than needle litter, and 65-75% of the seed nitrogen content was lost during the first growing season. We hypothesize that, if germination conditions (type of bottom-layer vegetation) allow tree seedlings to emerge, their survival, growth and nutrition may be enhanced by the nutrient flush from dead seeds and germlings in seed mast years and that this may aid in establishment of a new seedling cohort. Nutrient pulses from dead seeds during mast years may help to explain the strongly pulsed natural tree regeneration patterns that have been found in mixed late successional coniferous forests.

Noise-induced Regularity of Spatial Wave Patterns in SubalpineAbiesForests

In subalpine forests dominated byAbiesspecies in Japan and northeastern United States, trees show traveling wave of regeneration with many striped zones of tree dieback, moving downwind at a constant rate. Previous theoretical studies have demonstrated that a very simple model can generate wave-like spatio-temporal patterns of tree regeneration in a lattice-structured habitat with each site occupied by a cohort of trees. A cohort taller than the average height of its windward neighbor experiences stand-level dieback in the next time step and the height becomes zero. Otherwise the cohort increases its height at a constant rate. Starting from a random initial pattern, this simple deterministic model can generate a saw-toothed pattern that moves downwind at a constant rate, but the distance between adjacent dieback zones has a large variance. In this paper, we study the effects of “noises” in tree dieback rules in two forms which help to generate more regular patterns: (1) additional random disturbances at a low rate, which change the size of “clusters” (defined as a group of cohorts between adjacent dieback zones) by splitting a large cluster into two or by merging a small one with a neighbor, and (2) the stochastic rule of tree dieback, represented by the probability of dieback in unit time being a sigmoidal function of the difference in the tree height between the site and the windward neighbors. These noises are effective both for one-dimensional and two-dimensional models, but spatial patterns are much more regular in the two-dimensional model than in the one-dimensional model.

FLOODING ALTERS APPARENT POSITION OF FLOODPLAIN SAPLINGS ON A LIGHT GRADIENT

It has been hypothesized that flooding, interacting with light availability, can determine spatial patterns of tree regeneration by causing differential germination or survival among seedlings in river floodplains. We conducted a canonical correspondence analysis (CCA, a form of direct gradient analysis) of sapling and environmental data collected from 1980 to 1990 to investigate this hypothesis. The CCA recovered two significant axes, and of the eight environmental variables included, only elevation and percentage sky explained significant portions of the variability in species location. Axis 1 was correlated with elevation, while Axis 2 was correlated with percentage sky. Comparison of first axis rankings with species flood tolerance rankings obtained from the literature showed substantial agreement, indicating that elevation was a surrogate for flood tolerance. Comparison of second axis rankings with species shade tolerance rankings obtained from the literature showed little correspondence between position on the light gradient and species shade tolerance rankings; several of the most shade-tolerant species were placed on the high-light end of the light gradient. These results suggest that sapling distributions are responding primarily to flooding and light. The failure of the species to assort along the light gradient in accordance with their shade tolerance suggests that flooding interacts with life history traits of individual species, especially shade tolerance, resulting in complex species-specific responses. When we attempt to tease apart the interaction between light and flooding, we find two components: flood tolerance may allow persistence of some species under lower light conditions than normal, and flood intolerance may limit some normally shade-tolerant species to high-light conditions, where growth is fast enough to allow escape from the flooding hazard.

Flooding Alters Apparent Position of Floodplain Saplings on a Light Gradient

It has been hypothesized that flooding, interacting with light availability, can determine spatial patterns of tree regeneration by causing differential germination or survival among seedlings in river floodplains. We conducted a canonical correspondence analysis (CCA, a form of direct gradient analysis) of sapling and environmental data collected from 1980 to 1990 to investigate this hypothesis. The CCA recovered two significant axes, and of the eight environmental variables included, only elevation and percentage sky explained significant portions of the variability in species location. Axis 1 was correlated with elevation, while Axis 2 was correlated with percentage sky. Comparison of first axis rankings with species flood tolerance rankings obtained from the literature showed substantial agreement, indicating that elevation was a surrogate for flood tolerance. Comparison of second axis rankings with species shade tolerance rankings obtained from the literature showed little correspondence between position on the light gradient and species shade tolerance rankings; several of the most shade-tolerant species were placed on the high-light end of the light gradient. These results suggest that sapling distributions are responding primarily to flooding and light. The failure of the species to assort along the light gradient in accordance with their shade tolerance suggests that flooding interacts with life history traits of individual species, especially shade tolerance, resulting in complex species-specific responses. When we attempt to tease apart the interaction between light and flooding, we find two components: flood tolerance may allow persistence of some species under lower light conditions than normal, and flood intolerance may limit some normally shade-tolerant species to high-light conditions, where growth is fast enough to allow escape from the flooding hazard.

Tree regeneration patterns on Mount Usu, northern Japan, since the 1977?78 eruptions

Although the summit of Mount Usu was deforested by the 1977–78 eruptions, vegetative regeneration on the caldera rim was rapid due to the erosion of thick volcanic deposits by snow and rain. To obtain the mechanisms underlying regeneration patterns after the eruptions, we monitored the growth of permanently-marked stems from 1983 to 1990. Regeneration was from resprouting-branches buried in the volcanic deposits on the caldera rim, while on the crater basin, where thick volcanic deposits accumulated, regeneration was from seedlings. The seedling regeneration lagged approximately 3 years behind vegetative regeneration. Stem densities averaged 14,000 ha-1 in the vegetatively-regenerated community on the caldera rim, and 28,000 ha-1 in the seedling regeneration on the crater basin. Populus maximowiczii accounted for ca. 75% of total stems on the caldera rim, while P. maximowiczii accounted for ca. 30% on the crater basin where Salix integra and Betula platyphylla var. japonica were also common. In both stands, immigration and mortality rates were very low. The growth of vegetatively regenerated stems expressed as stem height and diameter was significantly faster than that of stems grown from seedlings. Herbivory damage on the terminal shoots of tall stems was restricted on the caldera rim and was restricted for B. platyphylla var. japonica on the crater basin, perhaps due to fast growth supporting herbivore avoidance or low palatability. Height growth was restricted when neighbors established in close proximity, especially in the seedling-regenerated forest. The results suggest that vegetative regeneration is rapid due to three mechanisms: 1) faster plant growth; 2) herbivore avoidance; and 3) decreased interference by neighboring.

Windstorm damage and microsite colonization in two Minnesota forests

Scattered trees were uprooted, snapped, or bent during a 1983 windstorm in two northwestern Minnesota pine forests. I tested potential correlates (tree species, tree size, cause of damage) of damage type, and compared consequences of the uprooting, snapping, and bending of trees by assessing postdamage survival and by surveying formation and colonization of microsites (mounds, pits, stumps, and dead boles). Larger trees damaged directly by wind were usually snapped and killed in both study areas, regardless of tree species. Smaller trees damaged by falling neighbors were either (i) bent without sustaining mortality or forming microsites, a damage type prevalent among strong-wooded Acersaccharum and Ostryavirginiana in a Pinus–Acer study area, or (ii) uprooted, forming small mounds and pits, a damage type prevalent among weakwooded Abiesbalsamea and Picea spp. in a Pinus–Abies study area. Bent trees usually survived, at least for several years. However, uprooted and snapped trees were equally unlikely to survive their damage. Thus, uprooting and snapping were equally likely to result in dead bole formation. Windstorm-related microsites covered small proportions (6 and 18%) of the floor of the two forests, most as dead boles rather than as stumps, mounds, or pits. Microsites from uprooting, microsites from snapping, and background substrates did not differ in colonizing tree flora but did differ in density of colonists. The role of microsites varied with the autecology of tree species present. In the Pinus–Abies area, rotting wood of stumps and boles was the major establishment substrate for all regenerating tree species. In the Pinus–Acer area, Acersaccharum and A. rubrum were numerically dominant over other species on all substrates, with seedling densities highest away from microsites. Observed patterns of survival and tree regeneration indicate that uprooting and snapping of trees do not differ strongly in their consequences for either forest.

Fire Suppression's Effects on Forest Succession within a Central Idaho Wilderness

Abstract In south-central Idaho, fire-scar and tree regeneration patterns in the Salmon River Breaks portion of the Frank Church River of No Return Wilderness suggest that primarily surface fires occurred frequently in semiarid ponderosa pine (Pinus ponderosa var. ponderosa)/Douglas-fir (Pseudotsuga menziesii var. glauca) forests. Efficient fire suppression since about 1935 has markedly reduced area fire frequency and has altered fuel succession, contributing to recent crown fire behavior in north- and east-facing stands. Prescribed fires might now be difficult to contain in these communities, but burning would help return fuels to pre-1935 conditions. West. J. Appl. For. 3(3):76-80, July 1988.

Composition, Structure and Regeneration Characteristics of the Open Woodlands of the New Forest, Hampshire

The study was carried out to provide the basis for an evaluation of the impact of human activities on tree regeneration in the New Forest woodlands. Five woodland types are distinguished on the basis of ground flora, using cluster analysis techniques. The species composition and size distribution characteristics of the primary and secondary canopies of each type are examined. Finally, the regeneration patterns, both for the woodlands as a whole and for each type, are described and discussed in relation to the composition and structure of the woodlands. Regeneration rates are low throughout the woodlands but appear to match broadly with the principal variations in the light regime of the woodland floor. This is reflected in the spatial distributions of seedlings of the different species. Other influences are also apparent, in particular that of Ilex aquifolium understoreys. In some instances the understorey contributes to the shade pressure on seedlings, whilst in others it appears to act as a nursery for certain species, probably by protecting against browsing. Introduction The New Forest contains perhaps the most extensive area of lowland forest in Britain and appears, moreover, to represent a link in the chain extending back to the original forest cover of the region (Rose & James, 1974). Yet the New Forest woodlands have been moulded by human influence over many centuries and that influence is just as strong, perhaps even stronger, today. When we consider changes in woodland communities in areas such as the New Forest, the central question that must be considered is: to what extent is the regeneration of the tree species controlled by human activities? The results of studies carried out on the impacts of human activities on open woodland regeneration in the New Forest are reported in Morgan (1987). However, evaluation of these impacts required an understanding of the broad patterns of tree regeneration in the woodlands at present, with particular reference to the effect of woodland structure and composition on the form and extent of regeneration. Accordingly, a survey of all the main open woodlands was carried out and the results are reported in this paper. The findings are further discussed in Morgan (1987) where a model of the interaction of the regeneration system and human activities in the New Forest open woodlands is outlined. For the purposes of this study, regeneration is defined as reproduction by seed. This is appropriate for the main tree species in the New Forest. However holly (Ilex aquifolium), an important sub-canopy species, appears to reproduce largely by vegetative means within woodland areas. In practice it was not always possible to differentiate established seedlings from vegetative shoots, therefore regeneration counts for Ilex include both seedling and vegetative individuals.

The composition and structure of deciduous woods in County Down, Northern Ireland

The results of an ecological survey of deciduous woods in County Down, Ireland, are presented. Variation in the composition of the ground flora, canopy composition and structure, and patterns of tree regeneration was related to environmental gradients of soil mineral nutrient status, the intensity of grazing and the degree of soil water-logging. The effects of the dominant species of the tree canopy on the ground flora were shown to be secondary. Woodland clearance has occurred mainly at low elevation sites with changes in land use to either coniferous plantation or agricultural land. The woods are very different in character from native Irish Blechno-Quercetum and Corylo-Fraxinetum but are closely related to mixed deciduous woods which have previously been described in England and Scotland. The introduced trees, Fagus sylvatica and Acer pseudoplatanus, have naturalised and their regeneration patterns at different sites are related to edaphic factors. The regeneration status of the current canopy dominants and associated trees, however, suggests that other changes in canopy composition will take place if the woods are not managed further. Replacement of Pinus sylvestris and Fagus sylvatica by Fraxinus excelsior and Acer pseudoplatanus is predicted, particularly at higher elevation sites.