Features appear in each issue of Pennsylvania Heritage showcasing a variety of subjects from various periods and geographic locations in Pennsylvania.

The territory now recognized as Pennsylvania was once part of a Swedish colony stretching from Delaware to New York. Swedish farmers settled in small villages along the Delaware River, in southern New Jersey, and in the Hudson Valley. Established by the New Sweden Company in March 1638, it was administered from Fort Christina (Wilmington) in what is now Delaware. In 1655, a band of Dutch soldiers under the leadership of Peter Stuyvesant laid siege to Fort Christina. The Swedes gave up leaving the entire territory in Dutch hands, but Swedish settlers were allowed to remain and keep their farms. New Netherlands, as the Dutch renamed it, lasted only eleven years. In 1664, England took the territory from the Dutch. The Duke of York was granted New York and New Jersey by the British crown shortly afterward. The Duke, in turn, transferred New Jersey to two friends, John Berkeley and George Carteret. Pennsylvania had been awarded to William Penn (1644–1718) by King Charles II (1630–1685) in 1681 in satisfaction of a debt to his late father. Quakers then purchased half of New Jersey from Carteret’s estate in 1682, turning the territory over to three Quaker trustees, one of whom was Penn. The populations of the New Jersey and Delaware parts of New Sweden became citizens of Pennsylvania.

The Swedes seem not to have been overly distraught by the loss of their colonial claim. The number of colonists never amounted to more than several hundred families, and because the economy of Sweden in the late seventeenth century was almost entirely agrarian, it did not consider an American colony as a potential market for manufactured or transshipped goods. Support of administration and defense drained Sweden’s treasury. By the mid-eighteenth century, however, the country had become a leader in the study of natural science. Carl Linnaeus (1707–1778) at the University of Uppsala had undertaken the Herculean task of describing and classifying the world’s known plants and animals. In the feverish exploration of nature that accompanied European colonization of the New World, Asia, and the Pacific islands, naturalists sent specimens of plants they did not recognize to Linnaeus. If he decided the species was novel, he might name it for the finder, the ultimate honor for a naturalist, they believed.

Founded in 1739, the Swedish Academy of Sciences called for the pursuit of studies to increase the country’s economic welfare. Swedish farmers, bedrock of the economy, could grow only a limited range of crops because of the country’s proximity to the Arctic Circle. Southern Sweden’s climate, tempered by the Gulf Stream along its western coast, was mild enough to permit cultivation of some crops usually associated with more southerly latitudes, but the short days of spring and fall were unsuited to the success of many others that required a long growing season.

The academy believed it would be useful to send a naturalist to explore remote countries that shared characteristics of Swedish climate, with instructions to collect seeds of herbs and trees hardy enough to withstand the long, frozen Swedish winters and brief, mild summers. In addition to food for people and fodder for cattle, academy leaders eagerly sought plants that could supply dyes for the growing textile industry and mulberry trees to raise silkworms for a silk industry. In 1747, after considering places such as Iceland and Siberia, the academy settled on North America. For this task, they chose a promising young naturalist and a protégé of Linnaeus, Peter (or Pehr) Kalm (1716 –1779).

At the age of nineteen, Kalm entered Finland’s Abo Academy as a graduate student intent on studying theology. His mentor, Bishop Johan Brovallius, a clergyman and a naturalist, recognized Kalm’s aptitude for the study of nature and encouraged him to pursue it. He introduced him to Baron Sten Carl Bjelke, a wealthy nobleman, who thought so highly of the young man that he financed collecting expeditions in Finland and Sweden. Kalm transferred to the University of Uppsala for additional study, attracting the attention of Linnaeus, who furthered his career by extending his travels and helping him publish an account of his findings. In 1744, Kalm accompanied Linnaeus on an expedition to Russia and the Ukraine, earning the mentor’s praise for a thesis based on their findings. Given his broad knowledge of botany and willingness to tackle realistic problems, he was the ideal candidate to accomplish the task laid out by the Academy of Sciences.

The academy directed Kalm and an assistant, Lars Jungstrom, to explore the French colony of Quebec in Canada. The academy asked French officials to accord him whatever assistance he might need, but Kalm, who had to raise much of the funding for the trip, booked passage through England. England carried on year-round trade with its colonies, but the French were limited to summer voyages on the St. Lawrence River. Sailing from Gothenburg, Sweden’s second largest city, in mid-December 1747, Kalm’s ship was stranded by a storm off the coast of Norway. He whiled away six weeks with botanical explorations until another ship arrived on February 8, 1748. Nine days later he arrived in London, only to learn a ship with available space would not sail to Philadelphia for six months. Kalm used this time wisely, studying English and cultivating the acquaintance of influential individuals who had forged associations with counterparts in Philadelphia, including Quaker merchant and plantsman Peter Collinson (1694–1768).

He obtained letters of introduction to prominent members of society, among them Isaac Norris (1707–1766), merchant and member of the Pennsylvania Assembly, and to the scientific elite, such as Benjamin Franklin (1706–1790) and John Bartram (1699– 1777). He clearly intended to spend time in Philadelphia, believing the flora of Penn’s colony might yield plants that would grow in Sweden. However, Pennsylvania winters could be as harsh as Swedish winters but they were much shorter, and summers were much longer, warmer, and more humid.

Kalm, evidently misinformed about Pennsylvania’s climate, arrived in Philadelphia on September 15, 1747. “Of all the natural advantages of the town,” he wrote in his diary the following day, “its temperate climate is the most considerable, the winter not being over severe, and its duration but short and the summer not too hot.” He reiterated his evaluation of the winter weather a week later, supported by a reference to “meteorological observations” — temperature measurements and notes of weather conditions he had made during his stay — but he retrospectively revised his comments about summer. “The heat in summer is excessive and without intermission . . . I have seen the thermometer rise to . . . 30 degrees C. above the freezing point once in two or three summers in Abo [Finland], the same thermometer in America, did not only for three months stand at the same degree, but even sometimes rose higher . . . two or three times to thirty-six degrees C. (97 degrees F.).” For the remainder of his stay in Pennsylvania and Canada, he bitterly complained about summer heat and humidity and the discomforts caused by perspiration, mosquitoes, gnats, and malaria.

After realizing the error of his assumption, Kalm was in no hurry to proceed to Canada where the latitude was closer to that of Sweden. Franklin arranged for him to enjoy free use of the Library Company of Philadelphia, a subscription library established in 1731 by Franklin and other prominent Philadelphians. The merchant Isaac Norris entertained him at Fairhill, his residence in the Northern Liberties section of Philadelphia County. In February 1750, he married Anna Margaretha Sjoman Sandin, widow of a friend from student days at Uppsala, the Reverend Johan Sandin, a Church of Sweden missionary to the congregation in Raccoon (now Swedesboro), New Jersey, who died a month before Kalm reached the community in November 1748.

Kalm spent much time exploring Philadelphia and its environs and neighboring Pennsylvania territory in Delaware and New Jersey. He consulted Bartram about species and ranges of plants he might expect to find in Pennsylvania. He visited families of the original Swedish settlers, taking notes on their use of medicinal plants, changes they perceived in rainfall, ground water, length and onset of winter, and prevalence of game animals, fowl, and fishes. He was fascinated by geological, climatic, and biological changes, both natural and as a result of civilization. Because Swedish settlement preceded his visit by more than a century, he believed a collective memory would yield an accurate assessment of the magnitude of changes.

Kalm kept a daily journal of his travels and observations. After returning to Sweden, he edited the text, culling recitation of the attributes of plants he had collected so he “may not tire the patience of my readers by a tedious enumeration.” Botanical descriptions and comments relating to animals, insects, and geology were reported in Memoirs of the Swedish Academy of Sciences. The remainder, woven together with retrospective commentary to create coherence, was published in three volumes entitled Travels in North America. He completed a fourth volume but it was never printed because the manuscript was lost in a fire at his residence in Abo.

So great was the European appetite for information about the New World that Kalm’s books were quickly translated into German and later into Dutch, French, and English. Although other travelers had described visits to America, Kalm’s bore the distinctive stamp of a scientist trained to observe and record detail. It was the most comprehensive report of the life, civilization, technology, agriculture, and natural history of the colonies in the mid-eighteenth century. He paid careful attention to the impact of urban and agricultural development on the ecology during the seventy years since Penn had established Philadelphia and invited English Quaker and German Anabaptist farmers to settle his province. Kalm wrote nothing of the purpose of his trip, except to mention that he sent “seeds of walnut, chestnut, squash and other useful plants” to Sweden.

Ever the pragmatist, he discussed mulberry trees in eight places in his narrative, an interest undoubtedly prompted by the fact that silkworms feed on mulberry leaves. Within two weeks of his arrival in Philadelphia, he noted red mulberry trees in woodlands surrounding the city. He consulted Bartram who informed him that both red and white species grew in Pennsylvania but that the red was more common. Kalm questioned the colonists why they had not capitalized on their good fortune by establishing silk mills. They responded that caring for silkworms was too expensive and grains were less labor-intensive and had a ready market in South America. The discussion then turned to a more general consideration of the ranges in which tree species grew.

Mark Catesby (1679–1749), an English naturalist who studied the flora and fauna of South Carolina, Georgia, and Florida, observed “trees and plants decreased in size as they were brought further north,” an observation Kalm seemed to have found dubious. Bartram countered by explaining that some species of trees grow best in southern climates, while others thrive in the north. As the southern species are transferred northward or the northern species southward by birds and winds, they grow less and less well until they cease to grow at all. Kalm accepted Bartram’s explanation. “Afterwards on my travels,” he wrote, “I had frequent proofs of this truth,” explaining that two common Pennsylvania trees, the sassafras and the tulip, reached robust height and girth in Penn’s woods, however, in northern New York they were short and spindly.

Kalm recorded the range of the mulberry tree on his journey to Canada, noting that it entirely disappeared by the time he had reached Saratoga, New York. He was elated to report that the governor of Montreal, Charles Le Moyne, Baron de Longueil, had coaxed a few of the trees to grow at his summer home on the Isle de Madeleine in the St. Lawrence River. Although the leaves were lush and green, the trees bore no fruit. Noting that not a single mulberry was to be found near Montreal, he was, however, convinced that he had found a hardy specimen. Assuming that lack of fruit (and therefore seeds) was an anomaly that year, he was determined to send seeds of “hardy mulberry” to Sweden. Upon returning to the Saratoga area, he was delighted to find that a barber-surgeon had gathered a few seeds from the weak trees Kalm had seen on his journey north. These he packed off to the Swedish Academy, but nothing came of them. Bartram had taught him a valuable lesson, but he had allowed his hopes to blind his observations.

Especially interested in American hardwoods, Kalm recorded observations on how the quality of wood for various purposes compared to European species. Oaks were the most prevalent trees in Pennsylvania forests and were widely used in shipbuilding and construction. Bartram advised him American oak was more prone to rot than European wood. For shipbuilding purposes, black oak, which was very hard, was used for parts of the boat normally under water and red cedar was employed for those parts that were alternately wet and dry and, therefore, prone to rot. Red cedar was “reckoned the hardiest wood in the country.”

Fences were likewise subject to rot and were constructed of chestnut wood, where it was available, white oak where it was not, and red cedar for longevity. Roof shingles were another interesting case. Pennsylvanians used white cedar, which grew in cedar swamps, to make shingles for roofs. The advantage of this wood was its light weight and therefore it did not require strong beams or thick walls to support a roof. The wood was easy to cut through and relatively fire resistant because it was spongy and soaked up water; its oils functioned as a fire retardant. The problem was that excessive logging had reduced the number of cedar trees and they were not being replanted. Kalm surmised correctly that roofs for future buildings would need to be shingled with heavier materials and require extensive reinforcement to withstand the added weight.

Kalm’s notes on availability of white cedar for manufacture of shingles were part of a pattern of observations on changes in ecology of the American landscape. From the outset of his travels, he was struck by the destruction of forests. Early in his visit to Philadelphia, he noted wood was used for construction of houses and fences, fuel, baking of bricks, and smelting of iron. “The woods with which Philadelphia is surrounded,” he wrote, “would lead one to conclude that fuel must be cheap there. . . . The country is likewise more cultivated than it used to be, and consequently large forests have been cut down for that purpose; and the farms built in those places also consume a quantity of wood.” Farmers who sold wood in the city markets traveled great distances, driving up the price of fuel. Seven months later, his misgivings extended to the more serious matter of climate change. “About sixty years ago, the greatest part of this country was covered with tall and large trees, and the swamps were full of water. But it has undergone so great a change, as few other places have undergone in so short a time. At present the forests are cut down in most places, the swamps drained by ditches, the country cultivated, and changed to grain fields, meadows, and pastures. Therefore, it seems very reasonable to suppose, that so sudden a change has likewise had some effect upon the climate.”

He resolved to query the Swedish settlers and others who had lived in the colony since its inception. Norris informed him that recent winters began later than previously. The Delaware River used to be covered with a solid sheet of ice by mid-November, but by 1749 it did not freeze until early December. Farmers mentioned there had been more snow in the past, and once the weather grew cold, it stayed cold until late February. Now, they contended, the weather was inconstant: “it is warm, even the very next day after a severe cold; and sometimes the weather changes several times a day,” an observation Kalm documented. They also thought the amount of rainfall had decreased over the period in question.

Kalm was cautious in accepting the accounts of his respondents. Many of them averred that spring, as judged by warming and greening of the fields, arrived later. At present, they responded, the weather remained cold until late March, whereas milder temperatures and the sprouting of grasses used to begin in late February. He acknowledged the perception of late springs, but thought the explanation was not that it stayed cold longer. He noted that cattle were far more numerous on farms than in the past and that the cows likely ate any grass and other green shoots that peeked out early in the spring, making it appear that nothing was growing.

One week after reporting on his inquiry into a link between forest destruction and climate change, he documented another devastating agricultural practice. In spring months, farmers habitually burned the leaves that had accumulated in their woods and fields the previous autumn “in order to give the grass an opportunity of growing up.” Kalm saw nothing but disaster in the practice. In fields that had been scorched repeatedly, “all the young shoots of several trees were burnt . . . which diminishes the wood and timber considerably . . . the old trees only were left, which being cut down, there remained nothing but a large field . . . without any wood . . . all sorts of trees and plants were consumed by the fire, or at least deprived of their power of budding. . . . The upper mould [of the soil] likewise burns away,” diminishing the quality and fertility of the earth. The government of the colony had issued an edict prohibiting such burning, “but everyone does as he pleases and this prohibition meets with a general censure.”

Indians, who lived in villages twelve to eighteen miles apart, tilled small plots of corn, beans, and pumpkins. While they, like the colonists, engaged in the practice of exhausting the soil and then breaking virgin ground for new fields, the land was never devastated because it was allowed to lie fallow, reforest, and regain fertility after it was abandoned. The rape of the land in the hands of European colonists was, in Kalm’s opinion, “the reason why agriculture and its science is so imperfect here that one can travel several days and learn almost nothing about land . . . except that from their gross mistakes and carelessness of the future, one finds opportunities every day of making all sorts of observations, and of growing wise by their mistakes. . . . We can hardly be more hostile toward our woods in Sweden and Finland than they are here: their eyes are fixed upon the present gain, and they are blind to the future.”

Kalm saw a missed opportunity to do something creative to solve the problem. He noted that “cattle grow poorer daily in quality and size because of hunger,” scrounging for grasses on spent, burned fields. Farmers lacked knowledge of natural science, which they considered “a mere trifle, and the pastime of fools.” They were unable to see that they could capitalize on native plants to turn spent fields “into the richest and most fertile meadow, where great flocks of cattle would find superfluous food, and grow fat.” All that would be required was to harvest seeds from these plants and sow them on the exhausted soil. Farmers who did not have access to them on their own land could obtain the seed from those who did. His advice went unheeded.

He spent the summer and early fall of 1749 exploring Canada, returning to the English colonies in late autumn. He stopped in the Albany, New York, area to collect seeds of trees and vegetable species he had seen on his way north and did not reach Philadelphia until winter had set in. Because sailing ships were unable to navigate the frozen Delaware River, he was forced to remain in America for another year. He embarked on an exploration of western Pennsylvania and New York the following spring, collecting indigenous plants to add to the bounty he had dispatched to Sweden. His account of this venture was contained in the manuscript lost to fire. He had intended to conclude the narrative of his travels in western Pennsylvania and New York with a description of Niagara Falls.

A pragmatic individual, Kalm was concerned about the potential usefulness of what he observed. He had little use for ornamental plants and rarely described either botanical specimens or landscapes as possessing aesthetic value. Ironically, Linnaeus honored his protégé by naming the genus of mountain laurels for him, Kalmia latifolia. Kalm encountered the shrub early in his explorations around Philadelphia, entering it into his journal in November 1748. He could not have seen them in bloom at that time, but his description includes notes on the flowers which he added when he collated his diary in Sweden. “The spoon tree, which never grows to great height, was seen today in several places. The Swedes here have named it thus, because the Indians used to make their spoons and trowels of its wood.”

What intrigued Kalm about his namesake was that its leaves were poisonous to sheep, horses, oxen, and cows, but provided winter forage for stags and game birds. He enumerated practical uses of the wood, not only for spoons, but for making pulleys, weavers’ shuttles, and objects that required fine-grained hard wood. Kalmia latifolia was the only ornamental plant to garner lengthy commentary in his account.

None of the plants Kalm collected yielded significant benefits to Swedish agriculture or economy; the climate to which Pennsylvania plants are adapted is too different from that of Sweden. However, three-quarters of the plants he found in Montreal province, where the climate is more like that of his homeland, were the same or similar to those of Sweden, and so not much that was novel could be sent home. Another less obvious reason is suggested by his emphasis on what he called Canadian ginseng, Panax cinquefolium, a plant common to rich woodland soils in many parts of the northern United States, including Pennsylvania. Kalm did not mention seeing or collecting it in the Keystone State but he became ecstatic about its possibilities when he saw great bales of ginseng root in warehouses in Montreal awaiting shipment to France. The French used it in the lucrative export trade with China. With his knowledge of plant propagation, Kalm probably thought this species could be cultivated in Sweden. But why had he ignored it in Pennsylvania?

A European, Kalm was conditioned to look for plants that were similar to those known to be of economic value in Europe, such as fruits, nuts, berries, grains, medicinals, and woody and fibrous species. Europeans were unfamiliar with ginseng and did not use it. Iroquois Indians shared medicinal applications with Kalm, but there was no great demand for the root in the English colonies and the British did not recognize its potential as a commodity. That Kalm ignored ginseng until he saw it in volume reveals a great deal about how he evaluated the potential of unfamiliar species for economic development. He depended on observations and agricultural developments of others to tell him what might be useful but by choosing plants adapted to climate and geology unlike that of his home base he thwarted his own efforts.


For Further Reading

Kalm, Peter. Travels in North America. New York: Dover Publications, 1987.

Rhoads, Ann Fowler, and Timothy A. Block. The Plants of Pennsylvania: A Complete Reference Guide. Philadelphia: University of Pennsylvania Press, 2005.

____. Trees of Pennsylvania: An Illustrated Manual. Philadelphia: University of Pennsylvania Press, 2000.


The editor thanks Seth P. Cassell, Chief, Communications and Interpretation Section, Bureau of Forestry, Pennsylvania Department of Conservation and Natural Resources, for graciously providing photographs to illustrate this feature.


Myra K. Jacobsohn is professor of biology emerita from Arcadia University in Glenside, Montgomery County. Her research publications include several on the physiological ecology of Digitalis purpurea, the common foxglove.