The reserve covers an area of 328 hectares, of which about 300 are covered by woodlands, while the remaining ones are grazing lands. Forest areas include about 186 hectares of artificial pinewood - mainly Austrian Pines - and 114 hectares of coppice.
Conifer plantations cover areas which are potentially bound to house a mixed wood of Beech trees and Silver firs at high altitudes and at northern exposures, while at lower altitudes they cover areas potentially bound to house woods of Downy oak, Hop Hornbeam, and Flowering Ash.
The western side of the Reserve is covered by deciduous woods mainly consisting of Hop Hornbeam, Downy Oak, and Flowering Ash with an occasional presence of Beech tree, Field maple, and Sessile oak and by shrubs such as Hazelnut tree, Laburnum, Juniper, and Hawthorn....
An almost abandoned chestnut tree wood covers the south-western side of the Reserve.
Monte Alpe pine woods were the first to be interested by the extensive reforestation program which the State Corps of Foresters has carried out in the Oltrepò Pavese region since the 30s.
The main reasons leading to this reforestation activity were due to the fact that at the beginning of the century, the whole Apennine area was interested by serious problems of hydrogeological instability.
Entire mountain slopes - such as Costa d'Alpe - were completely lacking in forest vegetation. The main aim of the reforestation activity was to recover as soon as possible the forest covering and therefore to prevent hydrogeological instability phenomena.
Given its modest ecological needs, the most used species was the Austrian Pine, together with the Scotch pine, the Larch, and the Spruce fir.
The pine woods currently highlight an exaggerated density, in some cases near to the planted ones, and this demonstrates how the attention of the silviculturist was concentrated in obtaining a rapid covering of the soil.
The exceeding thickness of the populations and the resulting scant quantity of light reaching the soil slows down the already difficult decay process of the litter.
Each Austrian Pine population is a poor ecosystem characterized by a scarce undergrowth and consequently by a scarce fauna.
These features tend to become more evident in artificial populations.
The result is the formation of poor and extremely simple ecosystems, and therefore unstable.
The main clues revealing a generalized situation of ecological instability are periodical demographic explosions of insects usually accompanying the Austrian Pine, without going beyond the main capacity of the ecosystem (Thaumetopoea pityocampa, Ips sexdentatus, Tomicus minor).
Processionary Moths are Lepidoptera species usually living in pine woods. They do not particularly damage the wood, except already suffering plants are concerned.
The use of the Austrian pine in artificial plantations - even outside its distribution area - has caused the parallel spreading of the Pine Processionary Moth, which has always followed its guest.
The eggs usually hatch out by the end of August. The larvae start feeding on pine needles and weave a thin web wherein needles get entangled.
Larvae go on feeding all along the autumn and during part of the winter. Right before the winter comes, larvae weave a thicker web forming their characteristic winter nest.
In the spring, larvae start their usual activity. As soon as they get out of their nest, they move in single file, sometimes forming very long "processions".
When they reach branches with leaves, they scatter and devour large quantities of needles. In this phase they can cause the greatest damages. At a certain moment of their growth, the hair covering the larvae become stinging, and they can represent a danger also for men.
Larvae reach maturity between the end of April and the first decade of May when they leave their nest and move to the ground, still forming long processions. They cover themselves with earth at 10-15 m of depth, where they turn into chrysalides.
Adults - that is butterflies - come out of the ground between the second half of June and the first days of August. After they leave their underground shelters, butterflies - which have crepuscular habits - fly away, even at great distances. They mate and lay eggs forming swellings around two pine needles in the sunniest portions of the crown. They preferably choose isolated trees or plants rising at the edges of clearings. Females generally lay from 100 to 300 eggs which hatch about 30 days later.
In each cycle, a certain number of larvae remain underground to emerge from their cocoon only two or three - exceptionally four - years later.
Defoliation caused by processionary moths can reduce the growth of the wood, and one defoliation after the other might lead to the death of entire reforested lots.
Infested plants are weaker than others and therefore they are easily subject to the attacks by other parasites.
To defend woods from the attacks of this insect, pure pine populations should give way to mixed formations with broadleaved trees. Mixed woods are more natural formations and therefore much more resisting.
In the 1950s, some experiments were carried out by Prof. Pavan from the University of Pavia. They aimed at containing infestations by phytophagous insects in the pinewoods - in particular by the Pine Processionary Moth - by using biological techniques to fight them.
The problem of the Processionary Moth has been faced by transplanting the Formica lugubris in the area of Monte Alpe. Entire ant-hills were moved from the Prealpi lombarde (Provinces of Bergamo and Brescia).
The experiments, which began in the 50s, continued until the last transplantation in the early 80s.
Most of the population of the ant-hill is made up by females, the workers, whose tasks are to defend the ant-hill, gather food, and breed the offspring.
In mature ant-hills, there are several queens laying as many eggs as possible to ensure the survival of the colony.
Formica lugubris lives in the forests where it builds ant-hills by gathering large heaps of conifer needles and digging the soil underneath. Transplanted into pine woods, Formica lugubris has quickly learnt how to use Pine needles (bigger and heavier) instead of Fir or Larch needles (much lighter).
The aim of the open air portion of the ant-hill is to collect heat for the rapid development of the larvae.
Queens live underground almost all the year round, while the workers find here their shelter during the bad season.
The presence of the underground portion of the ant-hill ensures the survival of great part of the population, also in case the external part gets damaged by the animals or by a fire.
The nourishing of the Formica lugubris consists by 1/3 of numberless insect species, particularly Imenoptera and Lepidoptera defoliating plants, among which the processionary moth larvae.
The hunt made by Formica lugubris can limit the proliferation of the Pine Processionary Moth, and therefore limit the damages it can cause to the woodland.