Agricultural legacies in forest environments: tree communities, soil properties, and light availability.

Temperate deciduous forests across much of Europe and eastern North America reflect legacies of past land use, particularly in the diversity and composition of plant communities. Intense disturbances, such as clearing forests for agriculture, may cause persistent environmental changes that continue to shape vegetation patterns as landscapes recover. We assessed the long-term consequences of agriculture for environmental conditions in central New York forests, including tree community structure and composition, soil physical and chemical properties, and light availability. To isolate the effects of agriculture, we compared 20 adjacent pairs of forests that were never cleared for agriculture (primary forests) and forests that established 85-100 years ago on plowed fields (secondary forests). Tree communities in primary and secondary forests had similar stem density, though secondary forests had 14% greater basal area. Species composition differed dramatically between the two forest types, with primary forests dominated by Acer saccharum and Fagus grandifolia and secondary forests by Acer rubrum and Pinus strobus. Primary and secondary forests showed no consistent differences in soil physical properties or in the principal gradient of soil fertility associated with soil pH. Within stands, however, soil water content and pH were more variable in primary forests. Secondary forest soils had 15% less organic matter, 16% less total carbon, and 29% less extractable phosphorus in the top 10 cm than adjacent primary stands, though the ranges of the forest types mostly overlapped. Understory light availability in primary and secondary forests was similar. These results suggest that, within 100 years, post-agricultural stands have recovered conditions comparable to less disturbed forests in many attributes, including tree size and number, soil physical properties, soil chemical properties associated with pH, and understory light availability. The principal legacies of agriculture that remain in these forests are the reduced levels of soil organic matter, carbon, and phosphorus; the spatial homogenization of soil properties; and the altered species composition of the vegetation.

Seed dispersal by white-tailed deer: implications for long-distance dispersal, invasion, and migration of plants in eastern North America.

For many plant species in eastern North America, short observed seed dispersal distances (ranging up to a few tens of meters) fail to explain rapid rates of invasion and migration. This discrepancy points to a substantial gap in our knowledge of the mechanisms by which seeds are dispersed long distances. We investigated the potential for white-tailed deer ( Odocoileus virginianus Zimm.), the dominant large herbivore in much of eastern North America, to disperse seeds via endozoochory. This is the first comprehensive study of seed dispersal by white-tailed deer, despite a vast body of research on other aspects of their ecology. More than 70 plant species germinated from deer feces collected over a 1-year period in central New York State, USA. Viable seeds included native and alien herbs, shrubs, and trees, including several invasive introduced species, from the full range of habitat types in the local flora. A mean of >30 seeds germinated per fecal pellet group, and seeds were dispersed during all months of the year. A wide variety of presumed dispersal modes were represented (endo- and exozoochory, wind, ballistic, ant, and unassisted). The majority were species with small-seeded fruits having no obvious adaptations for dispersal, underscoring the difficulty of inferring dispersal ability from diaspore morphology. Due to their broad diet, wide-ranging movements, and relatively long gut retention times, white-tailed deer have tremendous potential for effecting long-distance seed dispersal via ingestion and defecation. We conclude that white-tailed deer represent a significant and previously unappreciated vector of seed dispersal across the North American landscape, probably contributing an important long-distance component to the seed shadows of hundreds of plant species, and providing a mechanism to help explain rapid rates of plant migration.

Seed dispersal and seedling emergence in an old field community in central New York (USA).

Seed dispersal and seedling emergence of common taxa growing in a Solidago-dominated old field in central New York (USA) were monitored from May 1982 to June 1984. Over 3.5x104 seeds per m2 were captured on seed traps in each of the two years, with peaks occuring in July (due to Hieracium) and in November (due to Solidago). About 4.0x103 seedling/m2 emerged beneath the intact community in each of the two years. Although seedlings emerged predominantly in the early spring, a secondary peak occurred in September and October when many seedlings of introduced grasses appeared. Two additional aspects of the reproductive biology of the major taxa were related to the seasonal timing of seed dispersal: As the date of peak seed dispersal (among taxa) became progressively later in the season, (1) the duration of dispersal increased from about one week to about one-half year, and (2) the delay between the peak of seed dispersal and the peak of seedling emergence increased from a few days to about one-half year.

Five years of tree death in a Fagus-Magnolia forest, southeast Texas (USA).

Death of trees (>4.5 cm dbh) and saplings (1.4 m tall-4.5 cm dbh) was monitored over 5 years in a Southern Mixed Hardwood Forest to determine causes of death, death rates, and to assess the nature and direction of forest change. Most trees died standing (77%), presumably the result of pathogen attack or adverse physiological condition; knockdown by other trees (10%) and wind breakage (11%) were other common causes of death. Frequency of wind break and knockdown varied with size, but standing death did not. Most trees (64%) and some saplings (26%) died outright (complete death of the genetic individual); the others had sprouts or living residual parts. For some species, survival of residual parts was high, and so resprouting or persistence may be important in population recruitment. For others, low survival of residual parts means that sprouting does not effectively prolong the life of an individual. Most populations were stable or declining slightly. Shade-intolerant species showed higher death rates in small size classes than did the more tolerant species, so in the absence of disturbance one might expect some change in species composition toward the putative climax dominants.

Revegetation following Forest Cutting: Mechanisms for Return to Steady-State Nutrient Cycling.

Dense stands of a woody, successional species, Prunus pensylvanica L., develop rapidly, with early closure of canopy and rapid attainment of high values of net annual production and nutrient accumulation. Such rapid growth following disturbance tends to minimize losses of nutrients from the ecosystem, thus promoting a return to steady-state cycling characteristic of a mature forest.