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It is well known that inherent characteristics of forest species constitute the main control of litter decomposition. In mixed forest, chemical interactions occurring through precipitation turn mechanisms of litter decomposition very uncertain and difficult to predict. Early-stage leaf litter decomposition of Quercus potosina and Pinus cembroides and their controls were examined based on Ostrofsky's decomposition mechanisms. From June 2007 to May 2008, litterbags with pure and mixed leaf-litter of Q. potosina and P. cembroides were incubated in situ in monospecific and mixed tree stands, respectively. Sampling was carried out 3, 6, 9, and 12 months after incubation. After 12 months, two phases of decomposition of pure and mixed litter were identified; an early phase with a greater rate of mass loss of the labile litter fraction (k L ; soluble compounds) and a later phase with a lower rate of mass loss of the recalcitrant litter fraction (k R ; lignin). The labile fraction lost was observed at three and 6 months of incubation, which coincided with the months of highest rainfall likely triggering a rapid release of soluble carbon compounds from leaf litter. Results also indicate that leaf-litter from Q. potosina had higher concentration of soluble compounds and lower lignin concentration than leaf litter from P. cembroides. Observed facilitative and inhibitory mechanisms for mass loss in Q. potosina and P. cembroides were controlled by interaction between physico-chemical litter characteristics and rainfall.

Changes in species composition and abundance driven by land use change may alter canopy and litter characteristics of forests, and thereby modify rainfall redistribution and hydrological processes. To elucidate the interacting effects between tree species traits, forest structure and annual rainfall patterns on hydrological processes, three types of forest assemblages were selected in a semiarid forest of pine–oak in central northwest Mexico. Forest assemblages included monospecific and mixed patches of Quercus potosina and Pinus cembroides. Total precipitation, throughfall, stemflow and runoff were measured from June 2006 to July 2009. Additionally, tree and litter characteristics were measured. Forest traits played an important role differentiating volumes of each fraction among the three forest patches. Throughfall was 15% greater in Q. potosina than in the other forest patches (P < 0.01) and only occurred with rainfall events larger than 1.4 mm for all patch types, whereas Q. potosina stemflow was >20% larger compared with the other two forest patch types (P < 0.01) and occurred following rain events of at least 4.6 mm. Runoff exhibited divergences among forest patches (P > 0.05) that were related to both the litter decomposition stage and the capacity of litter bed to store water. Thus, Q. potosina litter layer exhibited the largest water holding capacity (62%) and P. cembroides (46%) the least. Hence, surface runoff for Q. potosina was seven times lower than that in P. cembroides patches. This study revealed tree trait effects on water fluxes that might have consequences on the dynamics and productivity of semiarid forests. Copyright © 2013 John Wiley & Sons, Ltd.

a b s t r a c tReductions of nitrogen (N) export from agricultural lands because of changes in specific N stocks and fluxes by incorporation of small amounts of prairie vegetation strips (PVS) are poorly understood. The primary objective of this study was to evaluate the effect of the presence and topographical position of PVS on soil and plant carbon (C) and N stocks relative to annual crop and native prairie vegetation. The study was implemented within three small adjacent watersheds, treated with one of the following cover types:(1) 100% row-crop agriculture (CROP); (2) 20% prairie vegetation (PVS) distributed along the contour across three topographical positions: upslope, sideslope and footslope position; and (3) 100% 17-year old reconstructed native prairie (RNP) as the control condition. Total soil organic C (SOC), total soil N (TN), inorganic N availability as indexed by ion exchange resins, N stocks in plant biomass and litter, and the ratio of C 3 :C 4 plant species were measured during the 2010 growing season. Results showed that over five years of treatment, PVS footslope improved soil quality by increasing TN by almost 100% and SOC by 37%; while CROP footslope TN decreased by 31% and SOC decreased by 28%. Overall, N stocks in plant biomass and litter were higher in PVS compared with RNP, except in the footslope where the lower N plant stocks was associated with higher C 3 abundance in RNP. Nitrogen availability was higher in CROP (25.4 ± 1.4), followed by PVS (10.2 ± 1.3), and RNP (2.2 ± 1.4); with the highest values recorded in the upslope position for PVS and RNP, and the footslope for CROP. These findings are important for designing watersheds with PVS to reduce N accumulation in the footslope position and promote additional N retention in soil organic matter and plant biomass, thereby minimizing N losses to streams.

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La acumulación y distribución de biomasa hacia los componentes estructurales de los árboles es determinante en bosques manejados, tanto en términos de productividad maderable como en la reactivación de diversos procesos ecosistémicos. En el presente estudio se analizó el patrón de acumulación de biomasa aérea total (BAT) y su asignación hacia fuste, ramas, corteza y follaje en una cronosecuencia de un bosque de Pinus patula bajo aprovechamiento forestal en Zacualtipán, Hidalgo. Mediante el uso de ecuaciones alométricas se estimó la BAT y por componente estructural de los árboles en rodales con diferentes años después de la cosecha, en diferentes años de remedición (años 2005, 2008 y 2012). Se encontró que la BAT aumentó con el tiempo después de la cosecha, con diferencias estadísticas significativas (p < 0.0001) entre los rodales. El rodal de 30 años después de la cosecha presentó una biomasa aérea total (BAT) de 178.1 Mg ha-1, la cual resultó solo 20% menor a la observada en el rodal sin cosecha (AN), lo que indica que un bosque bajo aprovechamiento podría alcanzar niveles de biomasa aérea similares a la del AN, en un menor tiempo. La asignación de biomasa aérea (BA) presentó el siguiente orden: fuste> ramas> corteza> follaje. Esta asignación de BA fue favorecida hacia fuste como un producto maderable comercial, objetivo principal de estos bosques bajo producción. El patrón de asignación de BA entre los componentes estructurales de los árboles puede ser incorporado como base para el diseño de prácticas silvicuturales en los programas de manejo forestal y contribuir en la evaluación de la sustentabilidad de los bosques. Además, puede clarificar el papel de los bosques regenerados después de los aprovechamientos en la fijación y almacenamiento de bióxido de carbono atmosférico.

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Geographical distribution of forest species is closely regulated by environmental conditions, particularly temperature and precipitation. Climate change predicted by general circulation models is expected to modify the distribution of many species' distribution, especially those adapted to extreme environmental conditions, leading to large-scale migrations or local extinctions. The aim of this research was to determine the potential impact of climatic change on Pinus hartwegii geographic distribution and the niche breadth of its populations. Ecological niche models were used by generated with four different algorithms based on 19 bioclimatic variables in addition to altitude. Climatic niche breadth was delimited by the dispersion of species occurrence records within the intervals of the bioclimatic variables. We modelled future distribution based on three general circulation models, MIROC-ESM-CHEM, CCSM4 and HadGEM2-ES, using two representative concentration pathways (RCP) 2.6 and 8.5, for two-time horizons 2050 and 2070. Niche breadth analysis showed narrow ranges of suitability, indicating a strong relationship between the presence of P. hartwegii with the temperature of the warmest quarter and precipitation of the coldest quarter. In addition, the suitability area of P. hartwegii is predicted to be reduced up to 70% by 2070; the populations of the extreme northern and southern latitudes will be reduced in greater proportion than those of central Mexico. This suggest that environmental suitability area of P. hartwegii are reduced by the effect of the increase in environmental temperature. Therefore, it is necessary to monitor extreme populations of this species in the long term in order to establish efficient conservation strategies and well adaptive management facing climate change.