3.3 | Primary seed dispersers
The distribution of four primary seed dispersers and their overlap ratio with different pine distribution areas are shown in Fig. 2 and table 4, respectively.
N. caryocatactes is a typical coniferous forest bird that is mainly distributed across Northeast China (Fig. 2a). The distribution areas of N. caryocatactes cover 84.56% of P. armandii’sdistribution area. Additionally, it overlaps with all the distribution areas of the other pine trees, including P. koraiensis, P. pumila, and P. sibirica . Among the other pines of undetermined seed dispersal trends by N. caryocatactes , part of the distribution area of P. dabeshanensis and P. fenzeliana is are in the active area of N. caryocatactes , where the distribution areas of P. gerardiana and P. bungeanaare completely within the range of N. caryocatacte . This bird is very likely to eat the seeds of these pines, which indicates its potential role as their seed disperser.
S. vulgaris is mainly distributed across Northeastern to North China and is also present in some mountain forests in Northwestern China (Fig. 2b). At present, S. vulgaris have been reported to disperse the seeds of P. koraiensis and P. armandii . The natural geographical distribution of these two pines are all within the activity range of S. vulgaris . In addition, the distribution areas ofS. vulgaris coincided with the geographical distribution area ofP. sibirica and north of that as well as 7.20% of the distribution area of P. armandii , which also overlaps with 11.51% of the distribution area of P. bungeana . Therefore,S. vulgaris is likely to feed on the seeds of P. sibirica, P. armandii , and P. bungeana and disperses their seeds.
S. davidianus is mainly found in North China to Southwest China and East China to Midwest China (Fig. 2c). This covers all the geographical distribution areas of P. dabeshanensis , P. bungeana , 75.71% of P. armandii , and 6.16% of P. koraiensis . P. armandii and P. koraiensis have related reports in terms of seed dispersal by S. davidianus , where 91.61% of the geographical distribution areas of P. bungeana ,P. dabeshanensis, and P. fenzeliana, with punctate distribution, overlap with that of S. davidianus , hence, S. davidianus is likely to feed on the seeds of the aforementioned pines and disperse their seeds through storage behavior.
T. sibiricus are mainly distributed in the northeast to the midwest of China (Fig. 2d). At present, there have been reports regarding the effect of T. sibiricus on the seed dispersal ofP. koraiensis and P. armandii, where its geographic distribution covers 94.19% of the area of P. koraiensis and 57.21% of P. armandii’s area. In addition, 49.58% of the geographical distribution areas of P. bungeana, part of P. fenzeliana , the total area of both P. pumila and P. sibirica coincided with that of T. sibiricus , in which it is likely to practice foraging and store behavior on the pine seeds, which would affect their seed dispersal.
Generally speaking, the distribution of the primary seed dispersers and the eight large-seeded pines showed a high degree of consistency, where central spreading of the Pinus plants was observed. The natural distribution areas of P. dabeshanensis , P. koraiensis ,P. armandii , and P. sibirica were all within the range of their main seed dispersers. For pines of undetermined seed dispersal trends, there were potential seed dispersers in some or all of their distribution areas. For each seed disperser species, its distribution range was wide with complete or partial overlaps with four or more species of the large-seeded pines. In addition to P. gerardiana , which is distributed at the highest altitude of 2700 m, there were three or more seed dispersers in the distribution area of the other seven pine species, but two of them were only a small population with a spotty pattern of distribution.