of the Pyrenees, at Montbrun–Bocage (Cunill et al. 2015) and Vall de Madriu et al.
(work in progress).
At present, minimum Abies values have been found in all the diagrams studied.
Human impact, as well as Holocene climatic changes leading to temporary moisture
deficits, may have had a significant impact on the Abies forests. The species is
considered to be less competitive on the sunny slope. Nevertheless, its rapid
quantitative decline can only be understood if the silver fir was growing in habitats
outside its current range. Millennia of land use could have eliminated Abies alba
from the warmest portions of its potential range. Matías et al. (2016) recently
suggested that the greater genetic diversity observed in the oldest populations of
Abies alba provides greater resistance to drought and therefore the decline in silver
fir could be a consequence of reduced genetic variation and the corresponding lack
of adaptability.
The current presence of most firs is at the lowest level in history in the study area
(Fig. 5.2). In an analysis of Holocene history between 4000 and 5000 years cal BP in
Burg and Bassa Nera sequences and between 6000 and 7500 years cal BP in
Estanilles peat bog, Abies alba would have had a much more important presence
before the high human impacts observed. This time-point could provide the ecological baseline to be taken into account for conservation management studies.
However, this abundance could be explained by their location on the sunny slope, as
the values from Burg Lake, for example, seem to indicate. Beginning in
4200 years cal BP, the decline coincides with a period of rapid climate change (Bond
Event 3) and with the beginning of the Bronze Age in the region (Pèlachs et al. 2011).
A period of recovery coincided with the influence of Roman period. After this
phase, firs would never regain their previous coverage. In several pollen diagrams
(Coma de Burg, Estanilles, and Bassa Nera), it seems that there was a selective
management of firs or an unfavorable climate for these forests during this period.
The Abies percentage curves behaved differently from the arboreal pollen curve (AP
%) (Fig. 5.2). Some of our data are in good agreement with data from the Alps and
descriptions of the Romanche Valley, which explain the selective exploitation of
firs in the Roman period (Nakagawa et al. 2000).
Was the recovery of firs in the Pyrenees after the human perturbations a consequence of management? The data show marked declines after the Late Roman
period that could be related to intensive, generalized exploitation across the last two
millennia. Therefore, the RNV should, in any case, precede this decline, although it
is hard to pinpoint because of the many human and climatic changes occurring
throughout the entire time period.
From a forest management perspective, the question is whether or not fir should
be harvested at present. There are two conflicting positions: one argues that
selective cutting will encourage regeneration and the other contends that the trees
should not be touched. The first is based on the notion that, if we have arrived at the
current situation of a certain forest quality, it is thanks to the forest management
efforts of the past century. The data, however, demonstrate that this is not the case.
The interventionist management of recent centuries is precisely the reason for the
Abies alba decline.
116
A. Pèlachs et al.
(work in progress).
At present, minimum Abies values have been found in all the diagrams studied.
Human impact, as well as Holocene climatic changes leading to temporary moisture
deficits, may have had a significant impact on the Abies forests. The species is
considered to be less competitive on the sunny slope. Nevertheless, its rapid
quantitative decline can only be understood if the silver fir was growing in habitats
outside its current range. Millennia of land use could have eliminated Abies alba
from the warmest portions of its potential range. Matías et al. (2016) recently
suggested that the greater genetic diversity observed in the oldest populations of
Abies alba provides greater resistance to drought and therefore the decline in silver
fir could be a consequence of reduced genetic variation and the corresponding lack
of adaptability.
The current presence of most firs is at the lowest level in history in the study area
(Fig. 5.2). In an analysis of Holocene history between 4000 and 5000 years cal BP in
Burg and Bassa Nera sequences and between 6000 and 7500 years cal BP in
Estanilles peat bog, Abies alba would have had a much more important presence
before the high human impacts observed. This time-point could provide the ecological baseline to be taken into account for conservation management studies.
However, this abundance could be explained by their location on the sunny slope, as
the values from Burg Lake, for example, seem to indicate. Beginning in
4200 years cal BP, the decline coincides with a period of rapid climate change (Bond
Event 3) and with the beginning of the Bronze Age in the region (Pèlachs et al. 2011).
A period of recovery coincided with the influence of Roman period. After this
phase, firs would never regain their previous coverage. In several pollen diagrams
(Coma de Burg, Estanilles, and Bassa Nera), it seems that there was a selective
management of firs or an unfavorable climate for these forests during this period.
The Abies percentage curves behaved differently from the arboreal pollen curve (AP
%) (Fig. 5.2). Some of our data are in good agreement with data from the Alps and
descriptions of the Romanche Valley, which explain the selective exploitation of
firs in the Roman period (Nakagawa et al. 2000).
Was the recovery of firs in the Pyrenees after the human perturbations a consequence of management? The data show marked declines after the Late Roman
period that could be related to intensive, generalized exploitation across the last two
millennia. Therefore, the RNV should, in any case, precede this decline, although it
is hard to pinpoint because of the many human and climatic changes occurring
throughout the entire time period.
From a forest management perspective, the question is whether or not fir should
be harvested at present. There are two conflicting positions: one argues that
selective cutting will encourage regeneration and the other contends that the trees
should not be touched. The first is based on the notion that, if we have arrived at the
current situation of a certain forest quality, it is thanks to the forest management
efforts of the past century. The data, however, demonstrate that this is not the case.
The interventionist management of recent centuries is precisely the reason for the
Abies alba decline.
116
A. Pèlachs et al.