Diagnóstico, dinâmica e manejo de Hovenia dulcis Thunb. em fragmentos antropizados de Floresta Ombrófila Mista

Abstract

Hovenia dulcis Thunb. commonly known in Brazil as Japanese raisin tree is considered exotic invasive of different phytogeographic units in Southern Brazil as the Araucaria Forest, semideciduous forest and steppes Grassy-Woody. As it threatens the natural balance of invaded ecosystems, mechanisms for controlling and monitoring this species must be sought to establish joint mitigation strategies. This research aimed to diagnose anthropized fragments of Mixed Ombrophilous Forest (FOM) invaded by H. dulcis, evaluate the dynamics and develop a management model for the invasive alien species (IAS), seeking to control its expansion by generating income for rural owners. Specifically, it also aimed to: develop a methodology for stratifying forest fragments by the degree of H. dulcis invasion; determine the Maximum Present Value Diameter Class (MPVC) for H. dulcis; and assess crop damage to the remaining trees. The study was carried out on 12 anthropized fragments of FOM in the municipality of Fernandes Pinheiros, in the Center-South region of Paraná. Each fragment was considered to be a rural property. Several data sources were used in this research, some were used for multiple purposes. The diagnosis and dynamics of forest fragments with the presence of the IAS were performed with data coming from: 100% forest inventory of H. dulcis (2012 and 2018); sampling inventory with permanent plots (2011 and 2017); growth data generated by stem analysis technique; mapping of fragments with satellite image and aerial survey with non-tripulated aerial vehicle (UAV). In the inventory by sampling, 21 permanent plots were measured, totaling 2.9 hectares, comparing the results between the measurement periods, maintaining the number of genera and botanical families, and a minimal reduction in the number of species, passing from 82 in 2011 to 80 in 2017. Data on the number of trees.ha-1 underwent the greatest change over the six-year interval between measurements, reducing 90 trees.ha-1 in 2017. In addition to mortality, this reduction is also related to the cut of 129 trees of 36 different species within the plots, between 2011 and 2017. All 10 species with the highest importance value indexes (IVI) in 2011 reduced their density in the 2017 measurement. The diameter distribution describes a decreasing characteristic in both years 2011 and 2017. Unlike the diameter distribution by volume stock class describes a unimodal distribution, but rather asymmetric. With regard to the 100% inventory of H.dulcis in the 12 fragments, 514 trees were registered in 2012 and, after six years (2018) in the same forest fragments, 1008 trees with DBH above 10 cm were measured. There was a high increase in all parameters of the H.dulcis population (Number of trees, basal area and volume per hectare) in practically all diameter classes, mainly in the smallest classes. In total, 138 H. dulcis trees were harvested by forest fragment owners between 2012 and 2018, a value that corresponds to a harvest rate of 2.28% per year. Ingrowth and mortality were assessed using data from permanent plots in the following periods: 2011-2014 and 2014-2017. The average annual ingrowth rate found for H. dulcis was 6.19%, while the average annual mortality rate for the species between the periods was very close to zero (0.51%). The diametric increment for H. dulcis was 0.74 cm.year-1, which was determined based on the 100% inventory data for the remaining trees from the first evaluation (2012) remeasured in 2018. The average class increment (ACI) and the passage time was determined for different diametric amplitudes (3, 5, 6 and 10 cm), with 905 pairs of data from 33 trees sampled by stem analysis technique. Regarding stratification by the H. dulcis degree of invasion, the same methodology was applied to two different databases: land survey and aerial survey with UAV. Stratification was performed using multivariate statistics, submitting the data matrix to Cluster Analysis by the hierarchical agglomerative method, with the dendrogram obtained by the Euclidean distance as a similarity measure, using the complete connection method of the most distant neighbor. Based on the dendrogram, three strata (same cut line) were defined for both databases, and all fragments received the same classification regarding the degree of invasion (medium, high and very high). The MPVC for H. dulcis was defined from the evaluation of the average of the present value of each class. The MPVC is the diameter range in which the trees of the species are at their maximum present value, having been defined based on the trees sampled by stem analysis technique. The 8th diametric class that represents the diameters from 31 to 34 cm presented the highest present value per tree with R$ 35.67 and commercial volume of 0.820 m3, being considered, therefore, the class of optimal cut diameter for the species. Of the 12 fragments with presence of H.dulcis, was selected only three fragments/properties for the management of the species, two of them classified as high degree of invasion and the other as very high. The management proposal of H. dulcis was conceived with two main objectives: the control of the species as a way of maintaining the balance of the native forest fragments and the generation of incomes for the rural owners. The cutting intensity, that is, the determination of the number of trees that would be harvested, was the main parameter for the control of the IAS, since it is from the balance between trees inputs and outputs that the expansion will stabilize. For this, the average annual ingrowth rate was 6.19%, the cut cycle defined as three years and the number of trees of the species existing in each fragment. The number of trees harvested varies between fragments, as it depends on the number of pre-existing trees, being the only variable that differs between fragments. As expected, management results varied between the three fragments, for the number of trees harvested the average was 28.66 with a range of 22 to 38 trees, for the commercial volume harvested the weighted average was 12.77 m3 with variation of 11.32 to 14.36 m3 between the fragments. Based on the movement ratios technique, projections of the diametric distribution of the IAS population were made for 2021 and 2024 for the fragment 4. It is observed as a result of the projection that from the 2nd and 3rd cutting cycle, the parameters of the population of the IAS are stabilized and the results of the volume and number of trees remain balanced, reaching the idealized stabilization for sustainable management. The damage caused by the IAS harvesting operation was assessed for the degree and type of damage for all trees with DBH ≥ 10 cm. For the three fragments, the weighted average of damage of any kind was equivalent to 2.3 trees.ha-1, less than 1% of the total number of trees. However, the average damage that caused the trees to die was even lower. The damage in the basal area represented on average less than 1% (0.094 m2.ha-1) of the total basal area of the fragments. The most common type of damage in 38% of the cases was the breaking of the canopy, followed by the breaking of the stem with 22% and trees cut with 20%, together adding up to 80% of the types of damage. From the results generated in the research it is concluded that: The analysis of the alteration in the floristic composition and in the horizontal structural between the measurement periods, showed fragile fragments, mainly due to the anthropic actions, a fact that favor the invasion and expansion by H. dulcis , making clear and evident the need for actions that seek to change the current framework of anthropization; The mortality rate of the species close to zero shows that the natural control of the species in the FOM is practically null; H. dulcis showed great efficiency in the competition for resources and high capacity for regeneration, with high values for the annual periodic increment and for the annual rate of ingrowth, when compared to the native species of the FOM; The invasion of FOM by H. dulcis is far from regressing or stabilizing; In general, H.dulcis is characterized by a tendency to decrease in diameter in the course of its development; The stratification of forest fragments as to the degree of H. dulcis invasion by using the cluster analysis technique, both data from land surveys and from aerial surveys with UAVs, proved to be an efficient method in determining homogeneous strata; The first analysis of the management carried out indicates that the main objectives proposed initially in this research, that is, the generation of incomes and the control of the exotic species (reduction of the parameters) were achieved and, certainly, can serve as a management model for H. dulcis . In order to control H. dulcis and at the same time keep it generating income, a balance must be struck between the number of trees harvested and the number of trees growing in the forest. The harvest of H. dulcis caused irrelevant damage to the remaining trees with DBH ≥ 10 cm, less than 1%, for the number of trees.ha-1 and for the basal area.