Conservation of an Endangered Botanic Garden

Cappelletti E.M., Caniglia G., Cassina G.

Orto Botanico, Dipartimento di Biologia, Università di Padova

Home | Contents | Abstract | Introduction | Emergency Interventions | Preventitive Measures | Phytopathological Survey | Mycorrhization Status Survey | Improvement of Soil Water Conditions | Projects | Political Interventions

Abstract

The Botanic Garden of Padua, recently (1997) recognized as being of "outstanding universal value" to all humankind and therefore included in the UNESCO World Heritage List, has suffered from marked water-table lowering as a consequence of digging just beyond the boundaries of the garden for the construction of an underground garage.

A number of trees with superficial root systems, among which a sample of Cedrus deodara (D. Don) G. Don fil. of historical interest (the first sample introduced into Italy), showed symptoms imputable to water stress.

Vulnerability of the garden living collections as a consequence of the precarious soil water balance, easily influenced by events occurring in the surrounding area, caused the inclusion of the Botanic Garden of Padua in the World Monument Watch's "List of 100 Most Endangered Sites 1998-1999".

The efforts to face the situation followed three different directions:

• emergency intensive care to the most damaged tree (Cedrus deodara), including procedures to stimulate production of new absorbing roots with "in situ" monitoring of the fine root development;
• preventive measures, consisting in a new irrigation system with continuous automatic soil moisture monitoring;
• political interventions, at first aimed at stopping the building construction and later on at purchasing the area beyond the boundaries of the garden, which would resolve one of the major long-range threats to the garden, in the meantime assuring landscape safeguard and the possibility of future garden development.

The valuable support given by BGCI to our efforts to safeguard the Botanic Garden of Padua is gratefully acknowledged.

Introduction

The Botanic Garden of Padua (the world’s oldest one) has been recognized as being of outstanding universal value to all humankind because of its cultural heritage, and inserted (December, 1997) in the List of the UNESCO World Heritage Sites.

Therefore, its protection today and for future generations is the responsibility of the international community as a whole.

Since its establishment by decree of the Venetian Republic in 1545 and until the beginning of the 20^th century, the Botanic Garden of Padua (formerly called "Horto Medicinale" or "Horto de i Semplici" being originally devoted to cultivation of native and exotic medicinal plants) was surrounded by gardens and orchards.

Later on, the landscape rapidly deteriorated owing to a rapid and rash urbanization. At present, it is almost completely surrounded by a girdle of buildings.

In the meantime, the small rivers lining the Garden on its East and South borders and acting like a buffer with respect to the soil water conditions, were canalized. In recent years (1959) a small artificial lake in a landscape garden at the SW border, was silten up.

At present, the future of the Garden might be at risk owing to the construction, just beyond its SE boundary, in an area formerly occupied by low sheds, of a large apartment building (19,000 cubic metres, about 13 m high) with an underground garage of 10,000 cubic metres.

It would be too long and after all useless, to illustrate the story of the building permission from the beginning (dating back to 1987).

It is enough to say that the present situation is the result of a short-sighted town-planning policy with very scarce consideration for landscape and future garden development, underestimation of the extraordinary importance of the Padua Garden’s cultural heritage, and errors of evaluation of the impact of excavations on the soil water conditions.

Most of the observed damage had been largely anticipated by the Paduan botanists, the pressure of which had induced the town authorities to place a number of piezometers along the SE border of the garden for soil water-table monitoring.

On spring 1996, digging for construction of the underground garage with use of Well-Point pumps caused a marked water-table lowering (about 50 cm) along the SE border of the garden.

Since May 1996, an imposing Cedar of Himalaya, Cedrus deodara (D. Don) G. Don fil. of historical interest being the first specimen introduced into Italy, showed widespread yellowing of the leaves followed by their fall and, consequentely, by the fast thinning of the crown.

The colleague plant pathologist prof. Mutto Accordi verified that the soil close to the tree was very compact and hardly permeable and that most of the roots do not grow below 60 cm of depth. Therefore, it was presumed that the above illustrated symptoms might be correlated to water stress due to the strong water-table lowering consequent to excavation works in the area just beyond the garden boundary.

The damage to the water-table caused by the adjacent construction lead to the inclusion of the Botanic Garden of Padua in the World Monuments Watch’s "List of 100 Most Endangered Sites 1998 - 1999". The list has been conceived by the World Monuments Fund as a means of publicising the plight of major cultural monuments and sites throughout the world, whose existence is seriously threatened but which can be saved by timely and concrete action on the part of the international private sector, including both private industry and cultural foundations. The Botanic Garden of Padua is one of many major sites that has benefited from this important endeavour with the result that sufficient funding has been secured to implement the measures necessary to guarantee its survival.

Emergency Interventions

A program of emergency intensive care to the Cedar of Himalaya was immediately carried on. Besides rescue irrigation, an attempt was done to improve the water absorbing capabilities of the tree by inducing fast growth of a new and efficient root system. In fact the tree showed few feeding rootlets and many healing wounds (due to rotting probably started a few years ago); however, no parasites were observed. For inducing new rootlet formation, the following operations were undertaken:

• supply of humic acids and phosphates: 200 g/sq m granular fertilizer (superphosphate 19%) and 200 ml/sq m liquid humus containing organic nitrogen 3.6%, organic carbon 11.4%, humic acids 6%, aminoacids 25% (Energizer Combi);

• - soil airing with: a) substitution of the original soil with a mixture of sand, expanded building clay and original soil (3:1:2); b) installation of drainage pipes (10 cm of diameter) at 30, 40, and 60 centimeters of depth.

Physical and chemical analyses of the soil were also performed and tensiometers were located at 35, 50, and 70 centimeters of depth.

The above described operations to stimulate production of new roots gave good results, and two months after a few new rootlets were abready detected.

For periodical monitoring of Cedar rootlet formation, a non-destructive method (the "Minirhizotron" system) was used. At the end of last years’s growing season, three plexiglass pipes were inserted tangentially to the root’s directions, at about 150 centimeters from the trunk and at about 60 degrees from one another, up to 100 centimeters of depth. Using a proper camera, a few portions of the root system can be filmed at different moments both in daylight and in ultraviolet light and conclusions on the rootlet turn-over can be drawn from the images obtained in a known interval of time.

After one year, abundant new rootlets were formed; rootlet emission is still occurring as revealed by the described non-destructive monitoring method.

The combined effects of the emergency cares (rescue irrigation and improvement of the absorbing apparatus by stimulating fast emission of new rootlets), peculiar climatic conditions (very rainy spring and summer 1996), and a fortuitous circumstance (water loss from a fountain in close proximity) succeded in preventing heavier damage to the Cedar tree.

Preventive Measures

Having realized the extreme vulnerability of the Garden’s soil moisture conditions, a number of preventive measures were taken. Prevention was developed according to the three lines below:

Water stress being known to reduce resistance and predispose to plant pathogens, since 1996 all the garden trees were constantly monitored by the staff of the Institute of Plant Pathology (Faculty of Agriculture).

A map of the distribution of microorganisms responsible for decay and root rot was made, pointing out the areas where carpophores of Armillaria sp. grow every year, and the plants showing both decays at the base of the trunk and root rot. Samples of the dead roots were also collected to identify the potential pathogens for the root systems.

The phytopathological control of tree crowns was carried out by graduated personnel making use of the "tree climbing" procedure in order to avoid further soil compacting. Pruning of dead branches and control and healing of old cut surfaces and trunk cavities were made. Regarding crown diseases, declining phases were observed on a number of trees (Pinus nigra Arnold, Quercus ilex L. and Cupressus sempervirens L. where Diplodia pinea (Desm.) Kickx, Phyllosticta ilicina Sacc. and Seiridium cardinale (Wagener) B. Sutton & Gibson respectively, were constantly detected). As to insects, strong infestations by thrips on a few evergreen species were observed; Hyphantria cunea Drury nests on a Liquidambar orientalis Mill. were imediately collected and destroyed.

Low mycorrhization of the root tips or the complete absence of this important kind of symbiosis were observed in a number of trees (Cedrus deodara (D.Don) G.Don fil. , Pinus nigra Arnold, Quercus ilex L. , Quercus robur L. , Juglans X intermedia Carr. var. pyriformis Carr.).

Now the relation betwen mycorrhization and phytopatological status must be cleared up. In fact, the presence of severe diseases could induce a mycorrhization regression, but it is also possible that the decrease of the mycorrhized apexes contributed to the disease’s expansion. These data, anyway, cannot be compared to other similar studies on trees of such dimensions growing in urban parks, and that’s why it is impossible to evaluate the real dangerousness of the apex decline or to determine the ranges above and below which a tree living outside its natural environment starts to suffer from excessive decrease of the tip amounts. Studies should be undertaken to examine the evolution of the measured parameters over time.

The marked vulnerabilithy of the garden’s soil water balance, easily influenced by events occuring in the surrounding areas, requires both continuous watch and setting up of preventive interventions.

The main hydrologic problems of the garden are:

• hydric stagnation following up heavy rains, especially in the central quarters;
• influence exerted on the hydrologic balance by massive building just close to the garden boundary;
• quite different hydrologic and microclimate situations in different areas of the garden;
• co-occurrence, in close proximity, of plant species from different geographical origin and with different microclimatic and pedological requirements. Therefore, interventions must be aimed essentially at keeping survival of plants in a climate so different from their original ones.

The following projects to control and improve soil water conditions of the garden have been planned and works will start in a few months thanks to the financial support of the E. L. Wiegand Foundation of Reno, U.S.A., and to Fondazione Cassa di Risparmio of Padova and Rovigo.

Projects

NOTE: The University of Padua should support the costs of projects D and F. A project for improvemet of the soil chemical, physical and biological features was also set up by Sergio Mutto Accordi, professor of Plant Pathology and co-workers.

Political Interventions

At first attempts were made to stop building construction along the garden border.

The echo of the water-table lowering exposing to a risk the trees of the world’s oldest Botanic Garden spread far and wide and the local, national and foreign press gave prominence to the news.

A valuable support was given by BGCI, with a warm appeal by the Secretary General, on behalf of the international botanic garden community. I sent this appeal, together with a letter by myself, to more than three hundred persons: relevant representatives of the Italian Government and parties, regional and local authorities, scientific institutions, national and foreign press. The BGCI appeal was of paramount importance in making the public opinion very concerned about probable future risk for the Padua Botanic Garden. I received letters expressing regret, disdain, support and good will, but no concrete result was obtained.

At this point, our efforts to safeguard the garden were addressed towards purchase the area where building was in progress, taking advantage of funds available for projects connected with the Jubilee celebrations in 2000.

To this purpose, I worked at conceiving a project aimed at restoring the soil water-table of the garden recovering the ancient landscape of the area by planting of collections of old fruit tree cultivars and establishing a cultural-religious way connecting St. Antony’s and St. Giustina’s basilics. During the Jubilee period, temporary exhibitions would have been set up highlighting the importance of religious community of monks in divulgating knowledge on medicinal plants, and contribution given by different botanic disciplines to a number of religious subjects (i.e. botanical identification of the plants of the Bible and Gospel, pollen analyses carried out on the remains of St. Antony and other Saints, etc.).

Again I gratefully aknowledge the BGCI for the strong support given to our project; unfortunately, it was not financed.

Being convinced that land purchase is essential to provide an important "buffer" area for the garden, to protect both landscape and environment, and to allow future garden development, namely to enhance its role in biodiversity conservation and education, the Rector of the Padua University, professor Giovanni Marchesini, promoted a joint meeting of national, regional and local authorities aimed at finding the absolutely necessary finantial support to purchase the area, which is getting more and more expensive as the building grows.

At present, four ministries: Ministry of Works, Ministry of Education, Ministry of Environment and Ministry of Cultural Heritage and the Regione Veneto seem to be available to support the financial efforts of the University. Unfortunately, local authorities are puzzled about the benefits deriving to the garden from acquisition of the area.

The students of the University of Padua are very concerned with the risk to which the garden might be exposed and promoted a public debate. Warm appeals came also from botanists (professor Lack of Berlin), members of Scientific Academies, Professors of town-planning in the Italian Universities, the National Committee for Historic Gardens of the Ministry of Cultural Heritage, cultural and environmental associations. Their valuable help is gratefully acknowledged.

A "buffer" area around the garden is essential to safeguard this extraordinary cultural heritage and to allow its future development; therefore, all our efforts must be addressed towards this goal.

Again I ask for the valuable support of the international botanic garden community to protect today and for future generation the "mother" of all Botanic Gardens of the world, a cultural heritage of outstanding universal value to all humankind.