Twelve-year dynamics of alien and native understorey plants following variable retention harvesting in Nothofagus pumilio forests in Southern Patagonia

SOLER, ROSINA; RUMPF, SABINE B.; SCHINDLER, STEFAN; MARTÍNEZ PASTUR, GUILLERMO; BARRERA, MARCELO; CELLINI, JUAN MANUEL; FLORES, MAGALÍ PÉREZ; ESSL, FRANZ; RABITSCH, WOLFGANG; LENCINAS, MARÍA VANESSA

FOREST ECOLOGY AND MANAGEMENT

ELSEVIER SCIENCE BV

Año: 2019 vol. 449 p. 117447 - 117447

0378-1127

Disturbances have frequently been shown to increase the invasibility of plant communities. Harvesting, the mostcommon and severe type of anthropogenic disturbance in forests, creates pulses of enhanced resource availabilityfor alien plants and for native colonizers. However, it is unclear for how long initial changes in speciescomposition of the understorey persist after harvesting. Using annually surveyed permanent plots (n=72 plotsacross six stands), we analysed temporal changes of plant understorey composition of Patagonian Nothofaguspumilio forests during 12 years under three different conditions created by variable retention harvesting: retainedforest patches (aggregates) of 30m radius in a density of one patch ha−1 (AR), dispersed retention within theinfluence of the aggregate (DRI), retained dispersed single trees (DR); and primary unharvested forests as control(PF). Our results show that: (i) cover of native forest species in the understorey declined only very slowly in AR,but alien species cover increased strongly and became dominant nine years after harvesting (YAH); (ii) DR andDRI supported higher cover of alien species in the understorey than AR and PF, and alien species becamedominant two to three YAH. Yet, they started to decline following a peak at eight YAH; (iii the cover of nativeforest species in the understorey was high in the beginning but alien species became dominant in DR and DRIafter four and seven YAH, respectively. Tree regeneration significantly influenced understorey dynamics, i.e. (iv)in DR, a negative relationship with alien species cover, and a positive relationship with native colonizers fromother habitats; (v) in DR and in DRI, this relationship was negative with alien species richness; (vi) in DRI, it waspositive with native colonizers from associated environments (cover and richness). We conclude that alien plantsinvade Patagonian forests after harvesting, but decline with time when tree regeneration is established. Ourresults highlight the role of harvesting in facilitating plant invasions in forests, and how the spatio-temporaltrajectories of such invasions are influenced by different levels of disturbance created by harvesting according tothe position within the resultant matrix.