Further, the responses of species and ecosystems services to increasing intensification levels were discussed . We here present a conceptual model to understand the ecological and ecosystems consequences of different land-use dynamics associated to agriculture intensification.Upper diagram in Figure 2 shows nine landscapes composed of different proportions of natural habitat and farming area, as well as different degrees of agriculture intensification on the agriculture part. Landscapes can change in all directions according to changes in natural habitat proportions and agriculture intensification levels.Agroecological conversion changes landscapes in the downward direction, while agriculture intensification is the upward opposite trend .
From left to right, decrease in NH characterizes “natural habitat’ contraction, and the right to left change is the “natural habitat” expansion or Forest Transition. A is a landscape totally occupied by “natural habitat”, B consist of 80% of habitat cover proportion and agriculture intensification index of farming area is 0.2, B’ has 0.8 of habitat cover and agriculture intensification index is 0.5 and so on. Here we use the term “natural habitat” in the operational sense, ebb and flow table defining it as areas subjected to very low levels of human intervention, rather than in the philosophical sense which refers to it as untouched or untamed nature.Additionally, the available data of remote sensing about wood cover, as well as theoretical approaches to estimate populations sizes, uses this term, which will simplify our analyses, enabling to address regional issues, as will be further developed.Farming systems in which AI is equals to 1 are characterized by high input, low heterogeneity and high levels of human disturbance and low planned and associated diversity.
Traditional and poly culture,home gardens and low shade agroforestry are considered having agriculture intensification equals to 0.5. Finally, we assume that agroforestry and extractives systems locate at 0.2 on the intensification scale. On the other hand, theoretical and empirical studies show that fragmentation affects population inhabiting these patchy landscapes in a non-linear association. Particularly, population sizes falls steeply below 30% of habitat cover proportion, which represented by the dashed line in the upper diagram of Figure 2. Although we assumed a linear area-density relationship in the bottom right graphic, total population size in landscapes with less than 30% of habitat proportion is overestimated for not accounting for decrease in habitat population pool. Because species response to fragmentations depend on several factors such as timing since fragmentation, species specific time-lags in the response to habitat contraction,and differential functional response given to sensitive to human disturbs , making precise estimations rather uncertain.
To make our model simple and reliable, we did not incorporate this non-linear aspects assuming that density is fixed regardless of habitat area. Therefore, values in dashed boxes may be overestimated, which is of further conservation concern as will be further discussed.According to LSP proponents, moving upward in the diagram will reflect in changes in the left direction, inducing habitat expansion . Jevons Paradox, on the other hand, concern increasing yields inducing habitat reduction.As we show in the land-use and economic session, although forest transition fostered by yield increase occurs by some extent, the Jevons Paradox is much more frequent.As intensification increases farm area and decrease biodiversity in agriculture portion, as well as in the habitat portion , landscapes will change in D or E direction, tending to very low associated landscape biodiversity. Due to the fact that actual population sizes must be smaller than presented lower right graphic in Figure 2 as above mentioned, these landscapes with small habitat proportion, which are patchily distributed and embedded in intensive matrixes, may harbor very few species, specially sometime after fragmentation and intensification. Decrease on population sizes of once common species in the European farmlands show the extreme effects of agriculture intensification at long term.
Unfortunately, tropical landscapes undergoing to agriculture intensification may face similar problems in the future.Most of the tropical high bio diverse regions , such as the Brazilian Cerrado, Atlantic Forest, Meso-America, Western-Ghats and and Siri Lanka are around or below the 30% habitat cover and simultaneously undergoing agriculture intensification. This multiple effects reduce populations sizes in the matrix, as well as biological fluxes among habitat patches.This combination of increasing deforestation and matrix agriculture intensification is predicted to cause local and global extinctions at long term. On the other hand, if intermediate levels of agriculture are maintained as assumed by LSH hypothesis,and habitat loss is controlled, significant amount of biodiversity is maintained although at lower levels then the“original” non-managed landscape.